Quasi-continuous transition from a Fermi liquid to a spin liquid in κ-(ET)2Cu2(CN)3.

PubMed

Furukawa, Tetsuya; Kobashi, Kazuhiko; Kurosaki, Yosuke; Miyagawa, Kazuya; Kanoda, Kazushi

2018-01-22

The Mott metal-insulator transition-a manifestation of Coulomb interactions among electrons-is known as a discontinuous transition. Recent theoretical studies, however, suggest that the transition is continuous if the Mott insulator carries a spin liquid with a spinon Fermi surface. Here, we demonstrate the case of a quasi-continuous Mott transition from a Fermi liquid to a spin liquid in an organic triangular-lattice system κ-(ET) 2 Cu 2 (CN) 3 . Transport experiments performed under fine pressure tuning have found that as the Mott transition is approached, the Fermi liquid coherence temperature continuously falls to the scale of kelvins, with a divergent quasi-particle decay rate on the metal side, and the charge gap continuously closes on the insulator side. A Clausius-Clapeyron analysis provides thermodynamic evidence for the extremely weak first-order nature of the transition. These results provide additional support for the existence of a spinon Fermi surface, which becomes an electron Fermi surface when charges are delocalized.

Fractionalized Fermi liquids and exotic superconductivity in the Kitaev-Kondo lattice

NASA Astrophysics Data System (ADS)

Seifert, Urban F. P.; Meng, Tobias; Vojta, Matthias

2018-02-01

Fractionalized Fermi liquids (FL*) have been introduced as non-Fermi-liquid metallic phases, characterized by coexisting electron-like charge carriers and local moments which form a fractionalized spin liquid. Here we investigate a Kondo lattice model on the honeycomb lattice with Kitaev interactions among the local moments, a concrete model hosting FL* phases based on Kitaev's Z2 spin liquid. We characterize the FL* phases via perturbation theory, and we employ a Majorana-fermion mean-field theory to map out the full phase diagram. Most remarkably we find nematic triplet superconducting phases which mask the quantum phase transition between fractionalized and conventional Fermi liquid phases. Their pairing structure is inherited from the Kitaev spin liquid; i.e., superconductivity is driven by Majorana glue.

Non-Fermi-liquid magic angle effects in high magnetic fields

NASA Astrophysics Data System (ADS)

Lebed, A. G.

2016-07-01

We investigate a theoretical problem of electron-electron interactions in an inclined magnetic field in a quasi-one-dimensional (Q1D) conductor. We show that they result in strong non-Fermi-liquid corrections to a specific heat, provided that the direction of the magnetic field is far from the so-called Lebed's magic angles (LMAs). If magnetic field is directed close to one of the LMAs, the specific heat corrections become small and the Fermi-liquid picture restores. As a result, we predict Fermi-liquid-non-Fermi-liquid angular crossovers in the vicinities of the LMA directions of the field. We suggest to perform the corresponding experiment in the Q1D conductor (Per) 2Au (mnt) 2 under pressure in magnetic fields of the order of H ≃25 T .

Fermi surface in the absence of a Fermi liquid in the Kondo insulator SmB 6

DOE PAGES

Hartstein, M.; Toews, W. H.; Hsu, Y. -T.; ...

2017-10-23

The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator–metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. In this paper, we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB 6 positioned close to the insulator–metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including amore » sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Finally, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB 6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.« less

Optical Response of Sr2RuO4 Reveals Universal Fermi-Liquid Scaling and Quasiparticles Beyond Landau Theory

NASA Astrophysics Data System (ADS)

Stricker, D.; Mravlje, J.; Berthod, C.; Fittipaldi, R.; Vecchione, A.; Georges, A.; van der Marel, D.

2014-08-01

We report optical measurements demonstrating that the low-energy relaxation rate (1/τ) of the conduction electrons in Sr2RuO4 obeys scaling relations for its frequency (ω) and temperature (T) dependence in accordance with Fermi-liquid theory. In the thermal relaxation regime, 1/τ∝(ℏω)2+(pπkBT)2 with p=2, and ω/T scaling applies. Many-body electronic structure calculations using dynamical mean-field theory confirm the low-energy Fermi-liquid scaling and provide quantitative understanding of the deviations from Fermi-liquid behavior at higher energy and temperature. The excess optical spectral weight in this regime provides evidence for strongly dispersing "resilient" quasiparticle excitations above the Fermi energy.

Quasiparticles and Fermi liquid behaviour in an organic metal

PubMed Central

Kiss, T.; Chainani, A.; Yamamoto, H.M.; Miyazaki, T.; Akimoto, T.; Shimojima, T.; Ishizaka, K.; Watanabe, S.; Chen, C.-T.; Fukaya, A.; Kato, R.; Shin, S.

2012-01-01

Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results. PMID:23011143

Breakdown of Landau Fermi liquid theory: Restrictions on the degrees of freedom of quantum electrons

NASA Astrophysics Data System (ADS)

Su, Yue-Hua; Lu, Han-Tao

2018-04-01

One challenge in contemporary condensed matter physics is to understand unconventional electronic physics beyond the paradigm of Landau Fermi-liquid theory. Here, we present a perspective that posits that most such examples of unconventional electronic physics stem from restrictions on the degrees of freedom of quantum electrons in Landau Fermi liquids. Since the degrees of freedom are deeply connected to the system's symmetries and topology, these restrictions can thus be realized by external constraints or by interaction-driven processes via the following mechanisms: (i) symmetry breaking, (ii) new emergent symmetries, and (iii) nontrivial topology. Various examples of unconventional electronic physics beyond the reach of traditional Landau Fermi liquid theory are extensively investigated from this point of view. Our perspective yields basic pathways to study the breakdown of Landau Fermi liquids and also provides a guiding principle in the search for novel electronic systems and devices.

Noise of a Chargeless Fermi Liquid

NASA Astrophysics Data System (ADS)

Moca, Cǎtǎlin Paşcu; Mora, Christophe; Weymann, Ireneusz; Zaránd, Gergely

2018-01-01

We construct a Fermi liquid theory to describe transport in a superconductor-quantum dot-normal metal junction close to the singlet-doublet (parity changing) transition of the dot. Though quasiparticles do not have a definite charge in this chargeless Fermi liquid, in the case of particle-hole symmetry, a mapping to the Anderson model unveils a hidden U(1) symmetry and a corresponding pseudocharge. In contrast to other correlated Fermi liquids, the back scattering noise reveals an effective charge equal to the charge of Cooper pairs, e*=2 e . In addition, we find a strong suppression of noise when the linear conductance is unitary, even for its nonlinear part.

Beyond the Fermi liquid paradigm: Hidden Fermi liquids

PubMed Central

Jain, J. K.; Anderson, P. W.

2009-01-01

An intense investigation of possible non-Fermi liquid states of matter has been inspired by two of the most intriguing phenomena discovered in the past quarter century, namely, high-temperature superconductivity and the fractional quantum Hall effect. Despite enormous conceptual strides, these two fields have developed largely along separate paths. Two widely employed theories are the resonating valence bond theory for high-temperature superconductivity and the composite fermion theory for the fractional quantum Hall effect. The goal of this perspective article is to note that they subscribe to a common underlying paradigm: They both connect these exotic quantum liquids to certain ordinary Fermi liquids residing in unphysical Hilbert spaces. Such a relation yields numerous nontrivial experimental consequences, exposing these theories to rigorous and definitive tests. PMID:19506260

Optical spectroscopy shows that the normal state of URu2Si2 is an anomalous Fermi liquid.

PubMed

Nagel, Urmas; Uleksin, Taaniel; Rõõm, Toomas; Lobo, Ricardo P S M; Lejay, Pascal; Homes, Christopher C; Hall, Jesse S; Kinross, Alison W; Purdy, Sarah K; Munsie, Tim; Williams, Travis J; Luke, Graeme M; Timusk, Thomas

2012-11-20

Fermi showed that, as a result of their quantum nature, electrons form a gas of particles whose temperature and density follow the so-called Fermi distribution. As shown by Landau, in a metal the electrons continue to act like free quantum mechanical particles with enhanced masses, despite their strong Coulomb interaction with each other and the positive background ions. This state of matter, the Landau-Fermi liquid, is recognized experimentally by an electrical resistivity that is proportional to the square of the absolute temperature plus a term proportional to the square of the frequency of the applied field. Calculations show that, if electron-electron scattering dominates the resistivity in a Landau-Fermi liquid, the ratio of the two terms, b, has the universal value of b = 4. We find that in the normal state of the heavy Fermion metal URu(2)Si(2), instead of the Fermi liquid value of 4, the coefficient b = 1 ± 0.1. This unexpected result implies that the electrons in this material are experiencing a unique scattering process. This scattering is intrinsic and we suggest that the uranium f electrons do not hybridize to form a coherent Fermi liquid but instead act like a dense array of elastic impurities, interacting incoherently with the charge carriers. This behavior is not restricted to URu(2)Si(2). Fermi liquid-like states with b ≠ 4 have been observed in a number of disparate systems, but the significance of this result has not been recognized.

Optical spectroscopy shows that the normal state of URu2Si2 is an anomalous Fermi liquid

PubMed Central

Nagel, Urmas; Uleksin, Taaniel; Rõõm, Toomas; Lobo, Ricardo P. S. M.; Lejay, Pascal; Homes, Christopher C.; Hall, Jesse S.; Kinross, Alison W.; Purdy, Sarah K.; Munsie, Tim; Williams, Travis J.; Luke, Graeme M.; Timusk, Thomas

2012-01-01

Fermi showed that, as a result of their quantum nature, electrons form a gas of particles whose temperature and density follow the so-called Fermi distribution. As shown by Landau, in a metal the electrons continue to act like free quantum mechanical particles with enhanced masses, despite their strong Coulomb interaction with each other and the positive background ions. This state of matter, the Landau–Fermi liquid, is recognized experimentally by an electrical resistivity that is proportional to the square of the absolute temperature plus a term proportional to the square of the frequency of the applied field. Calculations show that, if electron-electron scattering dominates the resistivity in a Landau–Fermi liquid, the ratio of the two terms, b, has the universal value of b = 4. We find that in the normal state of the heavy Fermion metal URu2Si2, instead of the Fermi liquid value of 4, the coefficient b = 1 ± 0.1. This unexpected result implies that the electrons in this material are experiencing a unique scattering process. This scattering is intrinsic and we suggest that the uranium f electrons do not hybridize to form a coherent Fermi liquid but instead act like a dense array of elastic impurities, interacting incoherently with the charge carriers. This behavior is not restricted to URu2Si2. Fermi liquid-like states with b ≠ 4 have been observed in a number of disparate systems, but the significance of this result has not been recognized. PMID:23115333

Anomalous Quasiparticle Reflection from the Surface of a ^{3}He-^{4}He Dilute Solution.

PubMed

Ikegami, Hiroki; Kim, Kitak; Sato, Daisuke; Kono, Kimitoshi; Choi, Hyoungsoon; Monarkha, Yuriy P

2017-11-10

A free surface of a dilute ^{3}He-^{4}He liquid mixture is a unique system where two Fermi liquids with distinct dimensions coexist: a three-dimensional (3D) ^{3}He Fermi liquid in the bulk and a two-dimensional (2D) ^{3}He Fermi liquid at the surface. To investigate a novel effect generated by the interaction between the two Fermi liquids, the mobility of a Wigner crystal of electrons formed on the free surface of the mixture is studied. An anomalous enhancement of the mobility, compared with the case where the 3D and 2D systems do not interact with each other, is observed. The enhancement is explained by the nontrivial reflection of 3D quasiparticles from the surface covered with the 2D ^{3}He system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartstein, M.; Toews, W. H.; Hsu, Y. -T.

The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator–metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. In this paper, we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB 6 positioned close to the insulator–metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including amore » sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Finally, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB 6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.« less

Seebeck effect on a weak link between Fermi and non-Fermi liquids

NASA Astrophysics Data System (ADS)

Nguyen, T. K. T.; Kiselev, M. N.

2018-02-01

We propose a model describing Seebeck effect on a weak link between two quantum systems with fine-tunable ground states of Fermi and non-Fermi liquid origin. The experimental realization of the model can be achieved by utilizing the quantum devices operating in the integer quantum Hall regime [Z. Iftikhar et al., Nature (London) 526, 233 (2015), 10.1038/nature15384] designed for detection of macroscopic quantum charged states in multichannel Kondo systems. We present a theory of thermoelectric transport through hybrid quantum devices constructed from quantum-dot-quantum-point-contact building blocks. We discuss pronounced effects in the temperature and gate voltage dependence of thermoelectric power associated with a competition between Fermi and non-Fermi liquid behaviors. High controllability of the device allows to fine tune the system to different regimes described by multichannel and multi-impurity Kondo models.

Non Fermi Liquid Crossovers in a Quasi-One-Dimensional Conductor in an Inclined Magnetic Field

NASA Astrophysics Data System (ADS)

Lebed, Andrei

We consider a theoretical problem of electron-electron scattering time in a quasi-one-dimensional (Q1D) conductor in a magnetic field, perpendicular to its conducting axis. We show that inverse electron-electron scattering time becomes of the order of characteristic electron energy, 1 / τ ~ ɛ ~ T , in a high magnetic field, directed far from the main crystallographic axes, which indicates breakdown of the Fermi liquid theory. In a magnetic field, directed close to one of the main crystallographic axis, inverse electron-electron scattering time becomes much smaller than characteristic electron energy and, thus, applicability of Fermi liquid theory restores. We suggest that there exist crossovers between Fermi liquid and some non Fermi liquid states in a strong enough inclined magnetic field. Application of our results to the Q1D conductor (Per)2Au(mnt)2 shows that it has to be possible to observe the above mentioned phenomenon in feasibly high magnetic fields of the order of H >=H* ~= 25 T . It was partially supported by NFS grant DMR-1104512.

Interband quasiparticle scattering in superconducting LiFeAs reconciles photoemission and tunneling measurements.

PubMed

Hess, Christian; Sykora, Steffen; Hänke, Torben; Schlegel, Ronny; Baumann, Danny; Zabolotnyy, Volodymyr B; Harnagea, Luminita; Wurmehl, Sabine; van den Brink, Jeroen; Büchner, Bernd

2013-01-04

Several angle-resolved photoemission spectroscopy (ARPES) studies reveal a poorly nested Fermi surface of LiFeAs, far away from a spin density wave instability, and clear-cut superconducting gap anisotropies. On the other hand a very different, more nested Fermi surface and dissimilar gap anisotropies have been obtained from quasiparticle interference (QPI) data, which were interpreted as arising from intraband scattering within holelike bands. Here we show that this ARPES-QPI paradox is completely resolved by interband scattering between the holelike bands. The resolution follows from an excellent agreement between experimental quasiparticle scattering data and T-matrix QPI calculations (based on experimental band structure data), which allows disentangling interband and intraband scattering processes.

Dense Chern-Simons matter with fermions at large N

NASA Astrophysics Data System (ADS)

Geracie, Michael; Goykhman, Mikhail; Son, Dam T.

2016-04-01

In this paper we investigate properties of Chern-Simons theory coupled to massive fermions in the large N limit. We demonstrate that at low temperatures the system is in a Fermi liquid state whose features can be systematically compared to the standard phenomenological theory of Landau Fermi liquids. This includes matching microscopically derived Landau parameters with thermodynamic predictions of Landau Fermi liquid theory. We also calculate the exact conductivity and viscosity tensors at zero temperature and finite chemical potential. In particular we point out that the Hall conductivity of an interacting system is not entirely accounted for by the Berry flux through the Fermi sphere. Furthermore, investigation of the thermodynamics in the non-relativistic limit reveals novel phenomena at strong coupling. As the 't Hooft coupling λ approaches 1, the system exhibits an extended intermediate temperature regime in which the thermodynamics is described by neither the quantum Fermi liquid theory nor the classical ideal gas law. Instead, it can be interpreted as a weakly coupled quantum Bose gas.

Two-component Fermi-liquid theory - Equilibrium properties of liquid metallic hydrogen

NASA Technical Reports Server (NTRS)

Oliva, J.; Ashcroft, N. W.

1981-01-01

It is reported that the transition of condensed hydrogen from an insulating molecular crystal phase to a metallic liquid phase, at zero temperature and high pressure, appears possible. Liquid metallic hydrogen (LMH), comprising interpenetrating proton and electron fluids, would constitute a two-component Fermi liquid with both a very high component-mass ratio and long-range, species-dependent bare interactions. The low-temperature equilibrium properties of LMH are examined by means of a generalization to the case of two components of the phenomenological Landau Fermi-liquid theory, and the low-temperature specific heat, compressibility, thermal expansion coefficient and spin susceptibility are given. It is found that the specific heat and the thermal expansion coefficient are vastly greater in the liquid than in the corresponding solid, due to the presence of proton quasiparticle excitations in the liquid.

Hidden Fermi liquid; the moral: a good effective low-energy theory is worth all of Monte Carlo with Las Vegas thrown in

NASA Astrophysics Data System (ADS)

Anderson, Philip W.; Casey, Philip A.

2010-04-01

We present a formalism for dealing directly with the effects of the Gutzwiller projection implicit in the t-J model which is widely believed to underlie the phenomenology of the high-Tc cuprates. We suggest that a true Bardeen-Cooper-Schrieffer condensation from a Fermi liquid state takes place, but in the unphysical space prior to projection. At low doping, however, instead of a hidden Fermi liquid one gets a 'hidden' non-superconducting resonating valence bond state which develops hole pockets upon doping. The theory which results upon projection does not follow conventional rules of diagram theory and in fact in the normal state is a Z = 0 non-Fermi liquid. Anomalous properties of the 'strange metal' normal state are predicted and compared against experimental findings.

Non-Fermi liquids in oxide heterostructures

NASA Astrophysics Data System (ADS)

Stemmer, Susanne; Allen, S. James

2018-06-01

Understanding the anomalous transport properties of strongly correlated materials is one of the most formidable challenges in condensed matter physics. For example, one encounters metal-insulator transitions, deviations from Landau Fermi liquid behavior, longitudinal and Hall scattering rate separation, a pseudogap phase, and bad metal behavior. These properties have been studied extensively in bulk materials, such as the unconventional superconductors and heavy fermion systems. Oxide heterostructures have recently emerged as new platforms to probe, control, and understand strong correlation phenomena. This article focuses on unconventional transport phenomena in oxide thin film systems. We use specific systems as examples, namely charge carriers in SrTiO3 layers and interfaces with SrTiO3, and strained rare earth nickelate thin films. While doped SrTiO3 layers appear to be a well behaved, though complex, electron gas or Fermi liquid, the rare earth nickelates are a highly correlated electron system that may be classified as a non-Fermi liquid. We discuss insights into the underlying physics that can be gained from studying the emergence of non-Fermi liquid behavior as a function of the heterostructure parameters. We also discuss the role of lattice symmetry and disorder in phenomena such as metal-insulator transitions in strongly correlated heterostructures.

Resonant pair tunneling in double quantum dots.

PubMed

Sela, Eran; Affleck, Ian

2009-08-21

We present exact results on the nonequilibrium current fluctuations for 2 quantum dots in series throughout a crossover from non-Fermi liquid to Fermi liquid behavior described by the 2 impurity Kondo model. The result corresponds to resonant tunneling of carriers of charge 2e for a critical interimpurity coupling. At low energy scales, the result can be understood from a Fermi liquid approach that we develop and use to also study nonequilibrium transport in an alternative double dot realization of the 2 impurity Kondo model under current experimental study.

Carrier density independent scattering rate in SrTiO3-based electron liquids

PubMed Central

Mikheev, Evgeny; Raghavan, Santosh; Zhang, Jack Y.; Marshall, Patrick B.; Kajdos, Adam P.; Balents, Leon; Stemmer, Susanne

2016-01-01

We examine the carrier density dependence of the scattering rate in two- and three-dimensional electron liquids in SrTiO3 in the regime where it scales with Tn (T is the temperature and n ≤ 2) in the cases when it is varied by electrostatic control and chemical doping, respectively. It is shown that the scattering rate is independent of the carrier density. This is contrary to the expectations from Landau Fermi liquid theory, where the scattering rate scales inversely with the Fermi energy (EF). We discuss that the behavior is very similar to systems traditionally identified as non-Fermi liquids (n < 2). This includes the cuprates and other transition metal oxide perovskites, where strikingly similar density-independent scattering rates have been observed. The results indicate that the applicability of Fermi liquid theory should be questioned for a much broader range of correlated materials and point to the need for a unified theory. PMID:26861764

Tuning bad metal and non-Fermi liquid behavior in a Mott material: Rare-earth nickelate thin films

PubMed Central

Mikheev, Evgeny; Hauser, Adam J.; Himmetoglu, Burak; Moreno, Nelson E.; Janotti, Anderson; Van de Walle, Chris G.; Stemmer, Susanne

2015-01-01

Resistances that exceed the Mott-Ioffe-Regel limit (known as bad metal behavior) and non-Fermi liquid behavior are ubiquitous features of the normal state of many strongly correlated materials. We establish the conditions that lead to bad metal and non-Fermi liquid phases in NdNiO3, which exhibits a prototype bandwidth-controlled metal-insulator transition. We show that resistance saturation is determined by the magnitude of Ni eg orbital splitting, which can be tuned by strain in epitaxial films, causing the appearance of bad metal behavior under certain conditions. The results shed light on the nature of a crossover to a non-Fermi liquid metal phase and provide a predictive criterion for Anderson localization. They elucidate a seemingly complex phase behavior as a function of film strain and confinement and provide guidelines for orbital engineering and novel devices. PMID:26601140

Unusual single-ion non-fermi-liquid behavior in Ce(1-x)LaxNi9Ge4.

PubMed

Killer, U; Scheidt, E-W; Eickerling, G; Michor, H; Sereni, J; Pruschke, Th; Kehrein, S

2004-11-19

We report on specific heat, magnetic susceptibility, and resistivity measurements on the compound Ce(1-x)LaxNi9Ge4 for various concentrations ranging from the stoichiometric system with x = 0 to the dilute limit x = 0.95. Our data reveal single-ion scaling with the Ce concentration and the largest ever recorded value of the electronic specific heat Deltac/T approximately 5.5 J K-2 mol(-1) at T = 0.08 K for the stoichiometric compound x = 0 without any trace of magnetic order. While in the doped samples Deltac/T increases logarithmically below 3 K down to 50 mK, their magnetic susceptibility behaves Fermi-liquid-like below 1 K. These properties make the compound Ce(1-x)LaxNi9Ge4 a unique system on the borderline between Fermi-liquid and non-Fermi-liquid physics.

Dense Chern-Simons matter with fermions at large N

DOE PAGES

Geracie, Michael; Goykhman, Mikhail; Son, Dam T.

2016-04-18

In this paper we investigate properties of Chern-Simons theory coupled to massive fermions in the large N limit. We demonstrate that at low temperatures the system is in a Fermi liquid state whose features can be systematically compared to the standard phenomenological theory of Landau Fermi liquids. This includes matching microscopically derived Landau parameters with thermodynamic predictions of Landau Fermi liquid theory. We also calculate the exact conductivity and viscosity tensors at zero temperature and finite chemical potential. In particular we point out that the Hall conductivity of an interacting system is not entirely accounted for by the Berry fluxmore » through the Fermi sphere. Furthermore, investigation of the thermodynamics in the non-relativistic limit reveals novel phenomena at strong coupling. Furthermore, as the ’t Hooft coupling λ approaches 1, the system exhibits an extended intermediate temperature regime in which the thermodynamics is described by neither the quantum Fermi liquid theory nor the classical ideal gas law. Instead, it can be interpreted as a weakly coupled quantum Bose gas.« less

Observation of Spin Polarons in a Tunable Fermi Liquid of Ultracold Atoms

NASA Astrophysics Data System (ADS)

Zwierlein, Martin

2009-05-01

We have observed spin polarons, dressed spin down impurities in a spin up Fermi sea of ultracold atoms via tomographic RF spectroscopy. Feshbach resonances allow to freely tune the interactions between the two spin states involved. A single spin down atom immersed in a Fermi sea of spin up atoms can do one of two things: For strong attraction, it can form a molecule with exactly one spin up partner, but for weaker interaction it will spread its attraction and surround itself with a collection of majority atoms. This spin down atom dressed with a spin up cloud constitutes the spin- or Fermi polaron. We have observed a striking spectroscopic signature of this quasi-particle for various interaction strengths, a narrow peak in the spin down spectrum that emerges above a broad background. The spectra allow us to directly measure the polaron energy and the quasi-particle residue Z. The polarons are found to be only weakly interacting with each other, and can thus be identified with the quasi-particles of Landau's Fermi liquid theory. At a critical interaction strength, we observe a transition from spin one-half polarons to spin zero molecules. At this point the Fermi liquid undergoes a phase transition into a superfluid Bose liquid.

Electronic structure and the van Hove singularity scenario in high-T(sub c)H(g)Ba2CuO(4+delta) superconductors

NASA Technical Reports Server (NTRS)

Agrawal, Bal K.; Agrawal, Savitri

1995-01-01

The electronic structure and the hole concentrations in the high Tc superconductor HgBa2CuO(4+delta) (delta = O, 1) has been investigated by employing a first principles full potential self-consistent LMTO method with the local density functional theory. The scalar relativistic effects have been considered. The hole concentrations of the Cu-d and O-p(x,y) orbitals are seen to be larger for the HgBaCuO5 system than those of the HgBaCuO4 solid. However, the van Hove singularity (vHs) induced Cu-d and O-p peak which is seen to lie comparatively away and above the Fermi level in the delta = 1 system shifts towards the Fermi level in the delta = 0 system. Thus, the superconducting behavior appears to originate from the occurrence of the vHs peak at the Fermi level. The Fermi surface nesting area in the delta = 0 compound is seen to be larger than in the delta = 1 compound. The calculation reveals that the increase in pressure on the crystal enhances the hole concentrations but without showing any optimum value, On the other hand, the vHs peak approaches to-wards the Fermi level with pressure and crosses the Fermi surface near V/Vo approximately equals 0.625 (V and Vo are the crystal volumes at high and normal pressures, respectively). Our calculated value of the bulk modulus equal to 0.626 Mbar predicts the occurrence of this crossover at about 24 GPa which is in complete agreement with the experimental value. At this pressure the compound has maximum nesting area and self-doped behavior.

Entanglement Entropy of the ν=1/2 Composite Fermion Non-Fermi Liquid State.

PubMed

Shao, Junping; Kim, Eun-Ah; Haldane, F D M; Rezayi, Edward H

2015-05-22

The so-called "non-Fermi liquid" behavior is very common in strongly correlated systems. However, its operational definition in terms of "what it is not" is a major obstacle for the theoretical understanding of this fascinating correlated state. Recently there has been much interest in entanglement entropy as a theoretical tool to study non-Fermi liquids. So far explicit calculations have been limited to models without direct experimental realizations. Here we focus on a two-dimensional electron fluid under magnetic field and filling fraction ν=1/2, which is believed to be a non-Fermi liquid state. Using a composite fermion wave function which captures the ν=1/2 state very accurately, we compute the second Rényi entropy using the variational Monte Carlo technique. We find the entanglement entropy scales as LlogL with the length of the boundary L as it does for free fermions, but has a prefactor twice that of free fermions.

Generalized susceptibilities and Landau parameters for anisotropic Fermi liquids

NASA Astrophysics Data System (ADS)

Rodríguez-Ponte, P.; Cabra, D.; Grandi, N.

2015-05-01

We study Fermi liquids (FLs) with a Fermi surface that lacks continuous rotational invariance and in the presence of an arbitrary quartic interaction. We obtain the expressions of the generalized static susceptibilities that measure the linear response of a generic order parameter to a perturbation of the Hamiltonian. We apply our formulae to the spin and charge susceptibilities. Based on the resulting expressions, we make a proposal for the definition of the Landau parameters in nonisotropic FL.

Hydrodynamic flows of non-Fermi liquids: Magnetotransport and bilayer drag

NASA Astrophysics Data System (ADS)

Patel, Aavishkar A.; Davison, Richard A.; Levchenko, Alex

2017-11-01

We consider a hydrodynamic description of transport for generic two-dimensional electron systems that lack Galilean invariance and do not fall into the category of Fermi liquids. We study magnetoresistance and show that it is governed only by the electronic viscosity provided that the wavelength of the underlying disorder potential is large compared to the microscopic equilibration length. We also derive the Coulomb drag transresistance for double-layer non-Fermi-liquid systems in the hydrodynamic regime. As an example, we consider frictional drag between two quantum Hall states with half-filled lowest Landau levels, each described by a Fermi surface of composite fermions coupled to a U (1 ) gauge field. We contrast our results to prior calculations of drag of Chern-Simons composite particles and place our findings in the context of available experimental data.

String theory, quantum phase transitions, and the emergent Fermi liquid.

PubMed

Cubrović, Mihailo; Zaanen, Jan; Schalm, Koenraad

2009-07-24

A central problem in quantum condensed matter physics is the critical theory governing the zero-temperature quantum phase transition between strongly renormalized Fermi liquids as found in heavy fermion intermetallics and possibly in high-critical temperature superconductors. We found that the mathematics of string theory is capable of describing such fermionic quantum critical states. Using the anti-de Sitter/conformal field theory correspondence to relate fermionic quantum critical fields to a gravitational problem, we computed the spectral functions of fermions in the field theory. By increasing the fermion density away from the relativistic quantum critical point, a state emerges with all the features of the Fermi liquid.

Strange metal transport realized by gauge/gravity duality.

PubMed

Faulkner, Thomas; Iqbal, Nabil; Liu, Hong; McGreevy, John; Vegh, David

2010-08-27

Fermi liquid theory explains the thermodynamic and transport properties of most metals. The so-called non-Fermi liquids deviate from these expectations and include exotic systems such as the strange metal phase of cuprate superconductors and heavy fermion materials near a quantum phase transition. We used the anti-de-Sitter/conformal field theory correspondence to identify a class of non-Fermi liquids; their low-energy behavior is found to be governed by a nontrivial infrared fixed point, which exhibits nonanalytic scaling behavior only in the time direction. For some representatives of this class, the resistivity has a linear temperature dependence, as is the case for strange metals.

Constructing the AdS dual of a Fermi liquid: AdS black holes with Dirac hair

NASA Astrophysics Data System (ADS)

Čubrović, Mihailo; Zaanen, Jan; Schalm, Koenraad

2011-10-01

We provide evidence that the holographic dual to a strongly coupled charged Fermi liquid has a non-zero fermion density in the bulk. We show that the pole-strength of the stable quasiparticle characterizing the Fermi surface is encoded in the AdS probability density of a single normalizable fermion wavefunction in AdS. Recalling Migdal's theorem which relates the pole strength to the Fermi-Dirac characteristic discontinuity in the number density at ω F , we conclude that the AdS dual of a Fermi liquid is described by occupied on-shell fermionic modes in AdS. Encoding the occupied levels in the total spatially averaged probability density of the fermion field directly, we show that an AdS Reissner-Nordström black holein a theory with charged fermions has a critical temperature, at which the system undergoes a first-order transition to a black hole with a non-vanishing profile for the bulk fermion field. Thermodynamics and spectral analysis support that the solution with non-zero AdS fermion-profile is the preferred ground state at low temperatures.

Transient and Sharvin resistances of Luttinger liquids

NASA Astrophysics Data System (ADS)

Kloss, Thomas; Weston, Joseph; Waintal, Xavier

2018-04-01

Although the intrinsic conductance of an interacting one-dimensional system is renormalized by the electron-electron correlations, it has been known for some time that this renormalization is washed out by the presence of the (noninteracting) electrodes to which the wire is connected. Here, we study the transient conductance of such a wire: a finite voltage bias is suddenly applied across the wire and we measure the current before it has enough time to reach its stationary value. These calculations allow us to extract the Sharvin (contact) resistance of Luttinger and Fermi liquids. In particular, we find that a perfect junction between a Fermi liquid electrode and a Luttinger liquid electrode is characterized by a contact resistance that consists of half the quantum of conductance in series with half the intrinsic resistance of an infinite Luttinger liquid. These results were obtained using two different methods: a dynamical Hartree-Fock approach and a self-consistent Boltzmann approach. Although these methods are formally approximate, we find a perfect match with the exact results of Luttinger/Fermi liquid theory.

Unusual Evolution of the Conduction-Electron State in CexLa1-xB6 from Non-Fermi Liquid to Fermi Liquid

NASA Astrophysics Data System (ADS)

Nakamura, S.; Endo, M.; Yamamoto, H.; Isshiki, T.; Kimura, N.; Aoki, H.; Nojima, T.; Otani, S.; Kunii, S.

2006-12-01

We report unusual evolution of the conduction-electron state in the localized f electron system CexLa1-xB6 from normal electron state to heavy Fermi liquid (FL) state through local FL and non-FL states with increasing Ce concentration and/or with increasing magnetic field. The effective mass of quasiparticle or the coefficient A of T2 term of resistivity is found to increase divergently near the boundary between FL state and non-FL state. The features of the non-FL state are also different from those of the typical non-FL systems previously observed or theoretically predicted.

Fermi liquid, clustering, and structure factor in dilute warm nuclear matter

NASA Astrophysics Data System (ADS)

Röpke, G.; Voskresensky, D. N.; Kryukov, I. A.; Blaschke, D.

2018-02-01

Properties of nuclear systems at subsaturation densities can be obtained from different approaches. We demonstrate the use of the density autocorrelation function which is related to the isothermal compressibility and, after integration, to the equation of state. This way we connect the Landau Fermi liquid theory well elaborated in nuclear physics with the approaches to dilute nuclear matter describing cluster formation. A quantum statistical approach is presented, based on the cluster decomposition of the polarization function. The fundamental quantity to be calculated is the dynamic structure factor. Comparing with the Landau Fermi liquid theory which is reproduced in lowest approximation, the account of bound state formation and continuum correlations gives the correct low-density result as described by the second virial coefficient and by the mass action law (nuclear statistical equilibrium). Going to higher densities, the inclusion of medium effects is more involved compared with other quantum statistical approaches, but the relation to the Landau Fermi liquid theory gives a promising approach to describe not only thermodynamic but also collective excitations and non-equilibrium properties of nuclear systems in a wide region of the phase diagram.

Anomalous transport phenomena in Weyl metal beyond the Drude model for Landau's Fermi liquids.

PubMed

Kim, Ki-Seok; Kim, Heon-Jung; Sasaki, M; Wang, J-F; Li, L

2014-12-01

Landau's Fermi-liquid theory is the standard model for metals, characterized by the existence of electron quasiparticles near a Fermi surface as long as Landau's interaction parameters lie below critical values for instabilities. Recently this fundamental paradigm has been challenged by the physics of strong spin-orbit coupling, although the concept of electron quasiparticles remains valid near the Fermi surface, where Landau's Fermi-liquid theory fails to describe the electromagnetic properties of this novel metallic state, referred to as Weyl metal. A novel ingredient is that such a Fermi surface encloses a Weyl point with definite chirality, referred to as a chiral Fermi surface, which can arise from breaking of either time reversal or inversion symmetry in systems with strong spin-orbit coupling, responsible for both the Berry curvature and the chiral anomaly. As a result, electromagnetic properties of the Weyl metallic state are described not by conventional Maxwell equations but by axion electrodynamics, where Maxwell equations are modified with a topological-in-origin spatially modulated [Formula: see text] term. This novel metallic state was realized recently in Bi[Formula: see text]Sb x around [Formula: see text] under magnetic fields, where the Dirac spectrum appears around the critical point between the normal semiconducting ([Formula: see text]) and topological semiconducting phases ([Formula: see text]) and the time reversal symmetry breaking perturbation causes the Dirac point to split into a pair of Weyl points along the direction of the applied magnetic field for a very strong spin-orbit coupled system. In this review article, we discuss how the topological structure of both the Berry curvature and the chiral anomaly (axion electrodynamics) gives rise to anomalous transport phenomena in [Formula: see text]Sb x around [Formula: see text] under magnetic fields, thus modifying the Drude model of Landau's Fermi liquids.

Non-Fermi-liquid to Fermi-liquid transports in iron-pnictide Ba(Fe1-x Co x )2As2 and the electronic correlation strength in superconductors newly probed by the normal-state Hall angle

NASA Astrophysics Data System (ADS)

Wang, L. M.; Wang, Chih-Yi; Zen, Sha-Min; Chang, Jin-Yuan; Kuo, C. N.; Lue, C. S.; Chang, L. J.; Su, Y.; Wolf, Th; Adelmann, P.

2017-03-01

Electrical transports in iron-pnictide Ba(Fe1-x Co x )2As2 (BFCA) single crystals are heavily debated in terms of the hidden Fermi-liquid (HFL) and holographic theories. Both HFL and holographic theories provide consistent physic pictures and propose a universal expression of resistivity to describe the crossover of transports from the non-Fermi-liquid (FL) to FL behavior in these so-called ‘strange metal’ systems. The deduced spin exchange energy J and model-dependent energy scale W in BFCA are almost the same, or are of the same order of several hundred Kelvin for over-doped BFCA, which is in agreement with the HFL theory. Moreover, a drawn line of W/3.5 for BFCA in the higher-doping region up to the right demonstrates the crossover from non-FL-like behavior to FL-like behavior at high doping, and shows a new phase diagram of BFCA. The electronic correlation strength in superconductors has been newly probed by the normal-state Hall angle, which found that, for the first time, correlation strength can be characterized by the ratios of T c to the Fermi temperature T F, J/T F, and the transverse mass to longitudinal mass.

Carrier density independent scattering rate in SrTiO₃-based electron liquids

DOE PAGES

Mikheev, Evgeny; Raghavan, Santosh; Zhang, Jack Y.; ...

2016-02-10

We examine the carrier density dependence of the scattering rate in two- and three-dimensional electron liquids in SrTiO 3 in the regime where it scales with T n (T is the temperature and n ≤ 2) in the cases when it is varied by electrostatic control and chemical doping, respectively. It is shown that the scattering rate is independent of the carrier density. This is contrary to the expectations from Landau Fermi liquid theory, where the scattering rate scales inversely with the Fermi energy (E F). We discuss that the behavior is very similar to systems traditionally identified as non-Fermimore » liquids (n < 2). This includes the cuprates and other transition metal oxide perovskites, where strikingly similar density independent scattering rates have been observed. Ultimately, the results indicate that the applicability of Fermi liquid theory should be questioned for a much broader range of correlated materials and point to the need for a unified theory.« less

Stokes paradox in electronic Fermi liquids

NASA Astrophysics Data System (ADS)

Lucas, Andrew

2017-03-01

The Stokes paradox is the statement that in a viscous two-dimensional fluid, the "linear response" problem of fluid flow around an obstacle is ill posed. We present a simple consequence of this paradox in the hydrodynamic regime of a Fermi liquid of electrons in two-dimensional metals. Using hydrodynamics and kinetic theory, we estimate the contribution of a single cylindrical obstacle to the global electrical resistance of a material, within linear response. Momentum relaxation, present in any realistic electron liquid, resolves the classical paradox. Nonetheless, this paradox imprints itself in the resistance, which can be parametrically larger than predicted by Ohmic transport theory. We find a remarkably rich set of behaviors, depending on whether or not the quasiparticle dynamics in the Fermi liquid should be treated as diffusive, hydrodynamic, or ballistic on the length scale of the obstacle. We argue that all three types of behavior are observable in present day experiments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jing-Yuan, E-mail: chjy@uchicago.edu; Stanford Institute for Theoretical Physics, Stanford University, CA 94305; Son, Dam Thanh, E-mail: dtson@uchicago.edu

We develop an extension of the Landau Fermi liquid theory to systems of interacting fermions with non-trivial Berry curvature. We propose a kinetic equation and a constitutive relation for the electromagnetic current that together encode the linear response of such systems to external electromagnetic perturbations, to leading and next-to-leading orders in the expansion over the frequency and wave number of the perturbations. We analyze the Feynman diagrams in a large class of interacting quantum field theories and show that, after summing up all orders in perturbation theory, the current–current correlator exactly matches with the result obtained from the kinetic theory.more » - Highlights: • We extend Landau’s kinetic theory of Fermi liquid to incorporate Berry phase. • Berry phase effects in Fermi liquid take exactly the same form as in Fermi gas. • There is a new “emergent electric dipole” contribution to the anomalous Hall effect. • Our kinetic theory is matched to field theory to all orders in Feynman diagrams.« less

Spin-triplet superconductivity in a weak-coupling Hubbard model for the quasi-one-dimensional compound Li0.9Mo6O17

NASA Astrophysics Data System (ADS)

Cho, Weejee; Platt, Christian; McKenzie, Ross H.; Raghu, Srinivas

2015-10-01

The purple bronze Li0.9Mo6O17 is of interest due to its quasi-one-dimensional electronic structure and the possible Luttinger liquid behavior resulting from it. For sufficiently low temperatures, it is a superconductor with a pairing symmetry that is still to be determined. To shed light on this issue, we analyze a minimal Hubbard model for this material involving four molybdenum orbitals per unit cell near quarter filling, using asymptotically exact perturbative renormalization group methods. We find that spin-triplet odd-parity superconductivity is the dominant instability. Approximate nesting properties of the two quasi-one-dimensional Fermi surfaces enhance certain second-order processes, which play crucial roles in determining the structure of the pairing gap. Notably, we find that the gap has more sign changes than required by the point-group symmetry.

Spin triplet superconductivity in a weak-coupling Hubbard model for the quasi-one-dimensional compound Li0.9 Mo6 O17

NASA Astrophysics Data System (ADS)

Platt, Christian; Cho, Weejee; McKenzie, Ross H.; Raghu, Sri

The purple bronze Li0.9Mo6O17 is of interest due to its quasi-one-dimensional electronic structure and the possible Luttinger liquid behavior resulting from it. For sufficiently low temperatures, it is a superconductor with a pairing symmetry that is still to be determined. To shed light on this issue, we analyze a minimal Hubbard model for this material involving four Molybdenum orbitals per unit cell near quarter filling, using asymptotically exact perturbative renormalization group methods. We find that spin triplet odd-parity superconductivity is the dominant instability. Approximate nesting properties of the two quasi-one-dimensional Fermi surfaces enhance certain second-order processes, which play crucial roles in determining the structure of the pairing gap. Notably, we find that the gap has accidental nodes, i.e. it has more sign changes than required by the point-group symmetry.

Dirac points, spinons and spin liquid in twisted bilayer graphene

NASA Astrophysics Data System (ADS)

Irkhin, V. Yu.; Skryabin, Yu. N.

2018-05-01

Twisted bilayer graphene is an excellent example of highly correlated system demonstrating a nearly flat electron band, the Mott transition and probably a spin liquid state. Besides the one-electron picture, analysis of Dirac points is performed in terms of spinon Fermi surface in the limit of strong correlations. Application of gauge field theory to describe deconfined spin liquid phase is treated. Topological quantum transitions, including those from small to large Fermi surface in the presence of van Hove singularities, are discussed.

Fractionalized Fermi liquid in a Kondo-Heisenberg model

DOE PAGES

Tsvelik, A. M.

2016-10-10

The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes amore » phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.« less

Unconventional Fermi surface associated with novel quasiparticles in the Kondo insulator SmB6

NASA Astrophysics Data System (ADS)

Sebastian, Suchitra

The search for a Fermi surface in the absence of a Fermi liquid has endured for decades. We present evidence for the realisation of such a state in the Kondo Insulator SmB6, which is an extreme example of Fermi liquid breakdown. Experimental results are presented from complementary techniques including quantum oscillations, specific heat capacity, thermal conductivity, and oscillatory entropy down to low temperatures. An experimental comparison is made with alternative theoretical models that associate novel quasiparticles with the unconventional Fermi surface we uncover in SmB6. A new paradigm for the realisation of a Fermi surface in the absence of conventional quasiparticles is proposed in the vicinity of a Kondo insulator transition. This work was performed in collaboration with M. Hartstein, W. H. Toews, Y.-T. Hsu, B. Zeng, X. Chen, M. Ciomaga Hatnean, Q. R. Zhang, S. Nakamura, A. S. Padgett, G. Rodway-Gant, J. Berk, M. K. Kingston, G. H. Zhang, M. K. Chan, S. Yamashita, T. Sakakibara, Y. Takano, J. -H. Park, L. Balicas, N. Harrison, N. Shitsevalova, G. Balakrishnan, G. G. Lonzarich, R. W. Hill, and M. Sutherland.

Aspects of the RVB Luttinger Liquid Theory of the High Temperature Superconductivity

NASA Astrophysics Data System (ADS)

Ren, Yong

1992-01-01

This thesis describes work on a large-U Hubbard model theory for high temperature superconductors. After an introduction to the Hubbard model and the normal state properties of the high T_{rm c} superconductors, we briefly examine the definition of the Fermi liquid and its breakdown. Then we explain why the 1D Hubbard model is the best starting point to approach our problem. In one dimension, the exact Lieb-Wu solution is available. We discuss the Lieb-Wu solution, and calculate various asymptotic correlation functions in the ground state. This clarifies the nature of the ground state which has not been known before. Instead of simply getting the exponents of the correlation functions from the Bethe Ansatz integral equations, we establish the connection between phase shifts at different Fermi points and the asymptotic correlation functions. We believe that this connection contains the most important physics and it can be readily generalized into higher dimensions. We then discuss bosonization in two dimensions and define the 2D RVB-Luttinger liquid theory, proposing that the ground state of the 2D Hubbard model belongs to a different fixed point than the Landau Fermi liquid-Luttinger liquid. Finally we apply the understanding of the 1D result to explain the normal state properties of the high T_ {c} superconductors, putting emphasis on how the non-Fermi liquid correlation functions explain the "anomalous" experimental results. In the Appendix, several issues related to the 1D and 2D Hubbard model are discussed.

Statistical Mechanics and Applications in Condensed Matter

NASA Astrophysics Data System (ADS)

Di Castro, Carlo; Raimondi, Roberto

2015-08-01

Preface; 1. Thermodynamics: a brief overview; 2. Kinetics; 3. From Boltzmann to Gibbs; 4. More ensembles; 5. The thermodynamic limit and its thermodynamic stability; 6. Density matrix and quantum statistical mechanics; 7. The quantum gases; 8. Mean-field theories and critical phenomena; 9. Second quantization and Hartree-Fock approximation; 10. Linear response and fluctuation-dissipation theorem in quantum systems: equilibrium and small deviations; 11. Brownian motion and transport in disordered systems; 12. Fermi liquids; 13. The Landau theory of the second order phase transitions; 14. The Landau-Wilson model for critical phenomena; 15. Superfluidity and superconductivity; 16. The scaling theory; 17. The renormalization group approach; 18. Thermal Green functions; 19. The microscopic foundations of Fermi liquids; 20. The Luttinger liquid; 21. Quantum interference effects in disordered electron systems; Appendix A. The central limit theorem; Appendix B. Some useful properties of the Euler Gamma function; Appendix C. Proof of the second theorem of Yang and Lee; Appendix D. The most probable distribution for the quantum gases; Appendix E. Fermi-Dirac and Bose-Einstein integrals; Appendix F. The Fermi gas in a uniform magnetic field: Landau diamagnetism; Appendix G. Ising and gas-lattice models; Appendix H. Sum over discrete Matsubara frequencies; Appendix I. Hydrodynamics of the two-fluid model of superfluidity; Appendix J. The Cooper problem in the theory of superconductivity; Appendix K. Superconductive fluctuations phenomena; Appendix L. Diagrammatic aspects of the exact solution of the Tomonaga Luttinger model; Appendix M. Details on the theory of the disordered Fermi liquid; References; Author index; Index.

The 3-Dimensional Fermi Liquid Description for the Iron-Based Superconductors

NASA Astrophysics Data System (ADS)

Misawa, Setsuo

2018-01-01

The quasiparticles in the normal state of iron-based superconductors have been shown to behave universally as a 3-dimensional Fermi liquid. Because of interactions and the presence of sharp Fermi surfaces, the quasiparticle energy contains, as a function of the momentum \\varvec{p}, a term of the form ( p - p_0)^3 ln {( |p-p_0|/p_0)} , where p = | \\varvec{p} | and p_0 is the Fermi momentum. The electronic specific heat coefficient, magnetic susceptibility (Knight shift), electrical resistivity, Hall coefficient and thermoelectric power divided by temperature follow, as functions of temperature T, the logarithmic formula a-b T^2 ln {(T/T^*)}, a, b and T^* being constant; these formulae have been shown to explain the observed data for all iron-based superconductors. It is shown that the concept of non-Fermi liquids or anomalous metals which appears in the literature is not needed for descriptions of the present systems. When the superconducting transition temperature TC and the b / a value for the resistivity are plotted as functions of the doping content x, there appear various characteristic diagrams in which regions of positive correlation and those of negative correlation between TC and b / a are interconnected; from these diagrams, we may make speculations about the types of superconductivity and the crossover between them.

Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate

DOE PAGES

Shen, Yao; Li, Yao-Dong; Wo, Hongliang; ...

2016-12-05

A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed ‘spinons’). In this paper, we report neutron scattering measurements of the triangular-lattice antiferromagnet YbMgGaO 4 that reveal broad spin excitations coveringmore » a wide region of the Brillouin zone. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, consistent with the particle–hole excitation of a spinon Fermi surface. Finally, our results therefore point to the existence of a quantum spin liquid state with a spinon Fermi surface in YbMgGaO 4, which has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.« less

Ferromagnetic CaRuO3

PubMed Central

Tripathi, Shivendra; Rana, Rakesh; Kumar, Sanjay; Pandey, Parul; Singh, R. S.; Rana, D. S.

2014-01-01

The non-magnetic and non-Fermi-liquid CaRuO3 is the iso-structural analog of the ferromagnetic (FM) and Fermi-liquid SrRuO3. We show that an FM order in the orthorhombic CaRuO3 can be established by the means of tensile epitaxial strain. The structural and magnetic property correlations in the CaRuO3 films formed on SrTiO3 (100) substrate establish a scaling relation between the FM moment and the tensile strain. The strain dependent crossover from non-magnetic to FM CaRuO3 was observed to be associated with switching of non-Fermi liquid to Fermi-liquid behavior. The intrinsic nature of this strain-induced FM order manifests in the Hall resistivity too; the anomalous Hall component realizes in FM tensile-strained CaRuO3 films on SrTiO3 (100) whereas the non-magnetic compressive-strained films on LaAlO3 (100) exhibit only the ordinary Hall effect. These observations of an elusive FM order are consistent with the theoretical predictions of scaling of the tensile epitaxial strain and the magnetic order in tensile CaRuO3. We further establish that the tensile strain is more efficient than the chemical route to induce FM order in CaRuO3. PMID:24464302

Dramatic changes in the electronic structure upon transition to the collapsed tetragonal phase in CaFe 2As 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dhaka, R. S.; Jiang, Rui; Ran, S.

2014-01-31

We use angle-resolved photoemission spectroscopy and density functional theory calculations to study the electronic structure of CaFe 2As 2 in the collapsed tetragonal (CT) phase. This unusual phase of iron arsenic high-temperature superconductors was hard to measure as it exists only under pressure. By inducing internal strain, via the postgrowth thermal treatment of single crystals, we were able to stabilize the CT phase at ambient pressure. We find significant differences in the Fermi surface topology and band dispersion data from the more common orthorhombic-antiferromagnetic or tetragonal-paramagnetic phases, consistent with electronic structure calculations. The top of the hole bands sinks belowmore » the Fermi level, which destroys the nesting present in parent phases. The absence of nesting in this phase, along with an apparent loss of Fe magnetic moment, are now clearly experimentally correlated with the lack of superconductivity in this phase.« less

Heavy fermion behavior in the quasi-one-dimensional Kondo lattice CeCo 2Ga 8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Le; Fu, Zhaoming; Sun, Jianping

Dimensionality plays an essential role in determining the anomalous non-Fermi liquid properties in heavy fermion systems. So far most heavy fermion compounds are quasi-two-dimensional or three-dimensional. Here we report the synthesis and systematic investigations of the single crystals of the quasi-one-dimensional Kondo lattice CeCo 2Ga 8. Resistivity measurements at ambient pressure reveal the onset of coherence at T * ≈ 20 K and non-Fermi liquid behavior with linear temperature dependence over a decade in temperature from 2 to 0.1 K. The specific heat increases logarithmically with lowering temperature between 10 and 2 K and reaches 800 mJ/mol K 2 atmore » 1 K, suggesting that CeCo 2Ga 8 is a heavy fermion compound in the close vicinity of a quantum critical point. Resistivity measurements under pressure further confirm the non-Fermi liquid behavior in a large temperature–pressure range. The magnetic susceptibility is found to follow the typical behavior for a one-dimensional spin chain from 300 K down to T *, and first-principles calculations predict flat Fermi surfaces for the itinerant f-electron bands. These suggest that CeCo 2Ga 8 is a rare example of the quasi-one-dimensional Kondo lattice, but its non-Fermi liquid behaviors resemble those of the quasi-two-dimensional YbRh 2Si 2 family. The study of the quasi-one-dimensional CeCo 2Ga 8 family may therefore help us to understand the role of dimensionality on heavy fermion physics and quantum criticality.« less

Heavy fermion behavior in the quasi-one-dimensional Kondo lattice CeCo2Ga8

NASA Astrophysics Data System (ADS)

Wang, Le; Fu, Zhaoming; Sun, Jianping; Liu, Min; Yi, Wei; Yi, Changjiang; Luo, Yongkang; Dai, Yaomin; Liu, Guangtong; Matsushita, Yoshitaka; Yamaura, Kazunari; Lu, Li; Cheng, Jin-Guang; Yang, Yi-feng; Shi, Youguo; Luo, Jianlin

2017-07-01

Dimensionality plays an essential role in determining the anomalous non-Fermi liquid properties in heavy fermion systems. So far most heavy fermion compounds are quasi-two-dimensional or three-dimensional. Here we report the synthesis and systematic investigations of the single crystals of the quasi-one-dimensional Kondo lattice CeCo2Ga8. Resistivity measurements at ambient pressure reveal the onset of coherence at T * ≈ 20 K and non-Fermi liquid behavior with linear temperature dependence over a decade in temperature from 2 to 0.1 K. The specific heat increases logarithmically with lowering temperature between 10 and 2 K and reaches 800 mJ/mol K2 at 1 K, suggesting that CeCo2Ga8 is a heavy fermion compound in the close vicinity of a quantum critical point. Resistivity measurements under pressure further confirm the non-Fermi liquid behavior in a large temperature-pressure range. The magnetic susceptibility is found to follow the typical behavior for a one-dimensional spin chain from 300 K down to T *, and first-principles calculations predict flat Fermi surfaces for the itinerant f-electron bands. These suggest that CeCo2Ga8 is a rare example of the quasi-one-dimensional Kondo lattice, but its non-Fermi liquid behaviors resemble those of the quasi-two-dimensional YbRh2Si2 family. The study of the quasi-one-dimensional CeCo2Ga8 family may therefore help us to understand the role of dimensionality on heavy fermion physics and quantum criticality.

Heavy fermion behavior in the quasi-one-dimensional Kondo lattice CeCo 2Ga 8

DOE PAGES

Wang, Le; Fu, Zhaoming; Sun, Jianping; ...

2017-07-04

Dimensionality plays an essential role in determining the anomalous non-Fermi liquid properties in heavy fermion systems. So far most heavy fermion compounds are quasi-two-dimensional or three-dimensional. Here we report the synthesis and systematic investigations of the single crystals of the quasi-one-dimensional Kondo lattice CeCo 2Ga 8. Resistivity measurements at ambient pressure reveal the onset of coherence at T * ≈ 20 K and non-Fermi liquid behavior with linear temperature dependence over a decade in temperature from 2 to 0.1 K. The specific heat increases logarithmically with lowering temperature between 10 and 2 K and reaches 800 mJ/mol K 2 atmore » 1 K, suggesting that CeCo 2Ga 8 is a heavy fermion compound in the close vicinity of a quantum critical point. Resistivity measurements under pressure further confirm the non-Fermi liquid behavior in a large temperature–pressure range. The magnetic susceptibility is found to follow the typical behavior for a one-dimensional spin chain from 300 K down to T *, and first-principles calculations predict flat Fermi surfaces for the itinerant f-electron bands. These suggest that CeCo 2Ga 8 is a rare example of the quasi-one-dimensional Kondo lattice, but its non-Fermi liquid behaviors resemble those of the quasi-two-dimensional YbRh 2Si 2 family. The study of the quasi-one-dimensional CeCo 2Ga 8 family may therefore help us to understand the role of dimensionality on heavy fermion physics and quantum criticality.« less

Two-color Fermi-liquid theory for transport through a multilevel Kondo impurity

NASA Astrophysics Data System (ADS)

Karki, D. B.; Mora, Christophe; von Delft, Jan; Kiselev, Mikhail N.

2018-05-01

We consider a quantum dot with K ≥2 orbital levels occupied by two electrons connected to two electric terminals. The generic model is given by a multilevel Anderson Hamiltonian. The weak-coupling theory at the particle-hole symmetric point is governed by a two-channel S =1 Kondo model characterized by intrinsic channels asymmetry. Based on a conformal field theory approach we derived an effective Hamiltonian at a strong-coupling fixed point. The Hamiltonian capturing the low-energy physics of a two-stage Kondo screening represents the quantum impurity by a two-color local Fermi liquid. Using nonequilibrium (Keldysh) perturbation theory around the strong-coupling fixed point we analyze the transport properties of the model at finite temperature, Zeeman magnetic field, and source-drain voltage applied across the quantum dot. We compute the Fermi-liquid transport constants and discuss different universality classes associated with emergent symmetries.

Kondo destruction in a quantum paramagnet with magnetic frustration

NASA Astrophysics Data System (ADS)

Zhang, Jiahao; Zhao, Hengcan; Lv, Meng; Hu, Sile; Isikawa, Yosikazu; Yang, Yi-feng; Si, Qimiao; Steglich, Frank; Sun, Peijie

2018-06-01

We report results of isothermal magnetotransport and susceptibility measurements at elevated magnetic fields B down to very low temperatures T on single crystals of the frustrated Kondo-lattice system CePdAl. They reveal a B*(T ) line within the paramagnetic part of the phase diagram. This line denotes a thermally broadened "small"-to-"large" Fermi-surface crossover which substantially narrows upon cooling. At B0 *=B*(T =0 ) =(4.6 ±0.1 ) T , this B*(T ) line merges with two other crossover lines, viz. Tp(B ) below and TFL(B ) above B0 *. Tp characterizes a frustration-dominated spin-liquid state, while TFL is the Fermi-liquid temperature associated with the lattice Kondo effect. Non-Fermi-liquid phenomena which are commonly observed near a "Kondo-destruction" quantum-critical point cannot be resolved in CePdAl. Our observations reveal a rare case where Kondo coupling, frustration, and quantum criticality are closely intertwined.

Observation of Dirac-like band dispersion in LaAgSb 2

DOE PAGES

Shi, X.; Richard, P.; Wang, Kefeng; ...

2016-02-16

In this paper, we present a combined angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations study of the electronic structure of LaAgSb 2 in the entire first Brillouin zone. We observe a Dirac-cone-like structure in the vicinity of the Fermi level formed by the crossing of two linear energy bands, as well as the nested segments of a Fermi surface pocket emerging from the cone. In conclusion, our ARPES results show the close relationship of the Dirac cone to the charge-density-wave ordering, providing consistent explanations for exotic behaviors in this material.

Non-Fermi liquid and heavy fermion behavior in CexLa1-xB6 with quadrupolar moments

NASA Astrophysics Data System (ADS)

Nakamura, Shintaro; Yamamoto, Harufumi; Endo, Motoki; Aoki, Haruyoshi; Kimura, Noriaki; Nojima, Tsutomu; Kunii, Satoru

2006-05-01

The electrical resistivity of the cubic Kondo system CexLa1-xB6 ( x=0.1-0.65) has been measured. Non-Fermi liquid behavior is found in paramagnetic phase I over the wide Ce concentration range. Heavy fermion behavior is found in ordered phases of Ce0.65La0.35B6. The mass enhancement of quasiparticles in this compound is strongly dependent of the magnetic field.

Electronic structure Fermi liquid theory of high T(sub c) superconductors: Comparison with experiments

NASA Astrophysics Data System (ADS)

Freeman, A. J.; Yu, Jaejun

1990-04-01

For years, there has been controversy on whether the normal state of the Cu-oxide superconductors is a Fermi liquid or some other exotic ground state. However, some experimentalists are clarifying the nature of the normal state of the high T(sub c) superconductors by surmounting the experimental difficulties in producing clean, well characterized surfaces so as to obtain meaningful high resolved photoemission data, which agrees with earlier positron-annihilation experiments. The experimental work on high resolution angle resolved photoemission by Campuzano et al. and positron-annihilation studies by Smedskjaer et al. has verified the calculated Fermi surfaces in YBa2Cu3O7 superconductors and has provided evidence for the validity of the energy band approach. Similar good agreement was found for Bi2Sr2CaCu2O8 by Olson et al. As a Fermi liquid (metallic) nature of the normal state of the high T(sub c) superconductors becomes evident, these experimental observations have served to confirm the predictions of the local density functional calculations and hence the energy band approach as a valid natural starting point for further studies of their superconductivity.

Electronic structure Fermi liquid theory of high T(sub c) superconductors: Comparison with experiments

NASA Technical Reports Server (NTRS)

Freeman, A. J.; Yu, Jaejun

1990-01-01

For years, there has been controversy on whether the normal state of the Cu-oxide superconductors is a Fermi liquid or some other exotic ground state. However, some experimentalists are clarifying the nature of the normal state of the high T(sub c) superconductors by surmounting the experimental difficulties in producing clean, well characterized surfaces so as to obtain meaningful high resolved photoemission data, which agrees with earlier positron-annihilation experiments. The experimental work on high resolution angle resolved photoemission by Campuzano et al. and positron-annihilation studies by Smedskjaer et al. has verified the calculated Fermi surfaces in YBa2Cu3O7 superconductors and has provided evidence for the validity of the energy band approach. Similar good agreement was found for Bi2Sr2CaCu2O8 by Olson et al. As a Fermi liquid (metallic) nature of the normal state of the high T(sub c) superconductors becomes evident, these experimental observations have served to confirm the predictions of the local density functional calculations and hence the energy band approach as a valid natural starting point for further studies of their superconductivity.

Entanglement sum rules.

PubMed

Swingle, Brian

2013-09-06

We compute the entanglement entropy of a wide class of models that may be characterized as describing matter coupled to gauge fields. Our principle result is an entanglement sum rule that states that the entropy of the full system is the sum of the entropies of the two components. In the context of the models we consider, this result applies to the full entropy, but more generally it is a statement about the additivity of universal terms in the entropy. Our proof simultaneously extends and simplifies previous arguments, with extensions including new models at zero temperature as well as the ability to treat finite temperature crossovers. We emphasize that while the additivity is an exact statement, each term in the sum may still be difficult to compute. Our results apply to a wide variety of phases including Fermi liquids, spin liquids, and some non-Fermi liquid metals. For example, we prove that our model of an interacting Fermi liquid has exactly the log violation of the area law for entanglement entropy predicted by the Widom formula in agreement with earlier arguments.

Momentum-resolved spectroscopy of a Fermi liquid

PubMed Central

Doggen, Elmer V. H.; Kinnunen, Jami J.

2015-01-01

We consider a recent momentum-resolved radio-frequency spectroscopy experiment, in which Fermi liquid properties of a strongly interacting atomic Fermi gas were studied. Here we show that by extending the Brueckner-Goldstone model, we can formulate a theory that goes beyond basic mean-field theories and that can be used for studying spectroscopies of dilute atomic gases in the strongly interacting regime. The model hosts well-defined quasiparticles and works across a wide range of temperatures and interaction strengths. The theory provides excellent qualitative agreement with the experiment. Comparing the predictions of the present theory with the mean-field Bardeen-Cooper-Schrieffer theory yields insights into the role of pair correlations, Tan's contact, and the Hartree mean-field energy shift. PMID:25941948

Electrons at the monkey saddle: A multicritical Lifshitz point

NASA Astrophysics Data System (ADS)

Shtyk, A.; Goldstein, G.; Chamon, C.

2017-01-01

We consider two-dimensional interacting electrons at a monkey saddle with dispersion ∝px3-3 pxpy2 . Such a dispersion naturally arises at the multicritical Lifshitz point when three Van Hove saddles merge in an elliptical umbilic elementary catastrophe, which we show can be realized in biased bilayer graphene. A multicritical Lifshitz point of this kind can be identified by its signature Landau level behavior Em∝(Bm ) 3 /2 and related oscillations in thermodynamic and transport properties, such as de Haas-Van Alphen and Shubnikov-de Haas oscillations, whose period triples as the system crosses the singularity. We show, in the case of a single monkey saddle, that the noninteracting electron fixed point is unstable to interactions under the renormalization-group flow, developing either a superconducting instability or non-Fermi-liquid features. Biased bilayer graphene, where there are two non-nested monkey saddles at the K and K' points, exhibits an interplay of competing many-body instabilities, namely, s -wave superconductivity, ferromagnetism, and spin- and charge-density waves.

Backflow and dissipation during the quantum decay of a metastable Fermi liquid

NASA Astrophysics Data System (ADS)

Iida, Kei

1999-02-01

The particle current in a metastable Fermi liquid against a first-order phase transition is calculated at zero temperature. During fluctuations of a droplet of the stable phase, in accordance with the conservation law, not only does an unperturbed current arise from the continuity at the boundary, but a backflow is induced by the density response. Quasiparticles carrying these currents are scattered by the boundary, yielding a dissipative backflow around the droplet. An energy of the hydrodynamic mass flow of the liquid and a friction force exerted on the droplet by the quasiparticles have been obtained in terms of a potential of their interaction with the droplet.

Non-equilibrium dynamics of artificial quantum matter

NASA Astrophysics Data System (ADS)

Babadi, Mehrtash

The rapid progress of the field of ultracold atoms during the past two decades has set new milestones in our control over matter. By cooling dilute atomic gases and molecules to nano-Kelvin temperatures, novel quantum mechanical states of matter can be realized and studied on a table-top experimental setup while bulk matter can be tailored to faithfully simulate abstract theoretical models. Two of such models which have witnessed significant experimental and theoretical attention are (1) the two-component Fermi gas with resonant s-wave interactions, and (2) the single-component Fermi gas with dipole-dipole interactions. This thesis is devoted to studying the non-equilibrium collective dynamics of these systems using the general framework of quantum kinetic theory. We present a concise review of the utilized mathematical methods in the first two chapters, including the Schwinger-Keldysh formalism of non-equilibrium quantum fields, two-particle irreducible (2PI) effective actions and the framework of quantum kinetic theory. We study the collective dynamics of the dipolar Fermi gas in a quasi-two-dimensional optical trap in chapter 3 and provide a detailed account of its dynamical crossover from the collisionless to the hydrodynamical regime. Chapter 4 is devoted to studying the dynamics of the attractive Fermi gas in the normal phase. Starting from the self-consistent T-matrix (pairing fluctuation) approximation, we systematically derive a set of quantum kinetic equations and show that they provide a globally valid description of the dynamics of the attractive Fermi gas, ranging from the weak-coupling Fermi liquid phase to the intermediate non-Fermi liquid pairing pseudogap regime and finally the strong-coupling Bose liquid phase. The shortcomings of the self-consistent T-matrix approximation in two spatial dimensions are discussed along with a proposal to overcome its unphysical behaviors. The developed kinetic formalism is finally utilized to reproduce and interpret the findings of a recent experiment done on the collective dynamics of trapped two-dimensional ultracold gases.

Observation of non-Fermi liquid behavior in hole-doped Eu2Ir2O7

NASA Astrophysics Data System (ADS)

Banerjee, A.; Sannigrahi, J.; Giri, S.; Majumdar, S.

2017-12-01

The Weyl semimetallic compound Eu2Ir2O7 and its hole-doped derivatives (which are achieved by substituting trivalent Eu by divalent Sr) are investigated through transport, magnetic, and calorimetric studies. The metal-insulator transition (MIT) temperature is found to get substantially reduced with hole doping, and for 10% Sr doping the composition is metallic down to temperature as low as 5 K. These doped compositions are found to violate the Mott-Ioffe-Regel condition for minimum electrical conductivity and show a distinct signature of non-Fermi liquid behavior at low temperature. The MIT in the doped compounds does not correlate with the magnetic transition point, and Anderson-Mott-type disorder-induced localization may be attributed to the ground-state insulating phase. The observed non-Fermi liquid behavior can be understood on the basis of disorder-induced distribution of the spin-orbit-coupling parameter, which is markedly different in the case of Ir4 + and Ir5 + ions.

Correlation between non-Fermi-liquid behavior and superconductivity in (Ca, La)(Fe,Co)As2 iron arsenides: A high-pressure study

NASA Astrophysics Data System (ADS)

Zhou, W.; Ke, F.; Xu, Xiaofeng; Sankar, R.; Xing, X.; Xu, C. Q.; Jiang, X. F.; Qian, B.; Zhou, N.; Zhang, Y.; Xu, M.; Li, B.; Chen, B.; Shi, Z. X.

2017-11-01

Non-Fermi-liquid (NFL) phenomena associated with correlation effects have been widely observed in the phase diagrams of unconventional superconducting families. Exploration of the correlation between the normal state NFL, regardless of its microscopic origins, and the superconductivity has been argued as a key to unveiling the mystery of the high-Tc pairing mechanism. Here we systematically investigate the pressure-dependent in-plane resistivity (ρ ) and Hall coefficient (RH) of a high-quality 112-type Fe-based superconductor Ca1 -xLaxFe1 -yCoyAs2 (x =0.2 ,y =0.02 ). With increasing pressure, the normal-state resistivity of the studied sample exhibits a pronounced crossover from non-Fermi-liquid to Fermi-liquid behaviors. Accompanied with this crossover, Tc is gradually suppressed. In parallel, the extremum in the Hall coefficient RH(T ) curve, possibly due to anisotropic scattering induced by spin fluctuations, is also gradually suppressed. The symbiosis of NFL and superconductivity implies that these two phenomena are intimately related. Further study on the pressure-dependent upper critical field reveals that the two-band effects are also gradually weakened with increasing pressure and reduced to the one-band Werthamer-Helfand-Hohenberg limit in the low-Tc regime. Overall, our paper supports the picture that NFL, multigap, and extreme RH(T ) are all of the same magnetic origin, i.e., the spin fluctuations in the 112 iron arsenide superconductors.

Valley density-wave (VDW) and Superconductivity in Iron-Pnictides

NASA Astrophysics Data System (ADS)

Cvetkovic, Vladimir; Tesanovic, Zlatko

2009-03-01

One of the experimentally observed features of iron-pnictide superconductors is the structural transition and SDW ordering occurring at almost the same temperature. Starting from a tight-binding model [1], we construct an effective theory for iron-pnictides with the distinctive two hole and two electron Fermi surfaces. This theory is then mapped onto a negative-U Hubbard model with additional orbital and spin flavors [2]. We demonstrate that the superconducting instability of the attractive Hubbard model --- valley density-wave (VDW) --- corresponds to the observed structural and SDW orders. The deviations from perfect nesting between the hole and electron Fermi surfaces are mapped onto the Zeeman field which causes portions of Fermi surface to remain ungapped. The origin of pnictide superconductivity in this model, and its ties to the VDW are discussed. [1] V. Cvetkovic and Z. Tesanovic, http://arxiv.org/abs/0804.4678. [2] V. Cvetkovic and Z. Tesanovic, http://arxiv.org/abs/0808.3742.

Superconductivity in YTE2Ge2 compounds (TE = d-electron transition metal)

NASA Astrophysics Data System (ADS)

Chajewski, G.; Samsel-Czekała, M.; Hackemer, A.; Wiśniewski, P.; Pikul, A. P.; Kaczorowski, D.

2018-05-01

Polycrystalline samples of YTE2Ge2 with TE = Co, Ni, Ru, Rh, Pd and Pt were synthesized and characterized by means of X-ray powder diffraction and low-temperature electrical resistivity and specific heat measurements, supplemented by fully relativistic full-potential local-orbital band structure calculations. We confirm that most of the compounds studied crystallize in a body-centered tetragonal ThCr2S2 -type structure (space group I 4 / mmm) and have three-dimensional Fermi surfaces, while only one of them (YPt2Ge2) forms with a primitive tetragonal CaBe2Ge2 -type unit cell (space group P 4 / nmm) and possesses quasi-two-dimensional Fermi surface sheets with some nesting. Physical properties data show conventional superconductivity in the phases with TE = Co, Pd and Pt, i.e. independently of the structure type (and hence the dimensionality of the Fermi surface).

Holographic non-Fermi liquid in a background magnetic field

NASA Astrophysics Data System (ADS)

Basu, Pallab; He, Jianyang; Mukherjee, Anindya; Shieh, Hsien-Hang

2010-08-01

We study the effects of a nonzero magnetic field on a class of 2+1 dimensional non-Fermi liquids, recently found in [Hong Liu, John McGreevy, and David Vegh, arXiv:0903.2477.] by considering properties of a Fermionic probe in an extremal AdS4 black hole background. Introducing a similar fermionic probe in a dyonic AdS4 black hole geometry, we find that the effect of a magnetic field could be incorporated in a rescaling of the probe fermion’s charge. From this simple fact, we observe interesting effects like gradual disappearance of the Fermi surface and quasiparticle peaks at large magnetic fields and changes in other properties of the system. We also find Landau level like structures and oscillatory phenomena similar to the de-Haas-van Alphen effect.

Electronic structure Fermi liquid theory of high Tc superconductors: Comparison of predictions with experiments

NASA Technical Reports Server (NTRS)

Yu, Jaejun; Freeman, A. J.

1991-01-01

Predictions of local density functional (LDF) calculations of the electronic structure and transport properties of high T(sub c) superconductors are presented. As evidenced by the excellent agreement with both photoemission and positron annihilation experiments, a Fermi liquid nature of the 'normal' state of the high T(sub c) superconductors become clear for the metallic phase of these oxides. In addition, LDF predictions on the normal state transport properties are qualitatively in agreement with experiments on single crystals. It is emphasized that the signs of the Hall coefficients for the high T(sub c) superconductors are not consistent with the types of dopants (e.g., electron-doped or hole-doped) but are determined by the topology of the Fermi surfaces obtained from the LDF calculations.

Fractionalized Fermi liquid with bosonic chargons as a candidate for the pseudogap metal

NASA Astrophysics Data System (ADS)

Chatterjee, Shubhayu; Sachdev, Subir

2016-11-01

Doping a Mott-insulating Z2 spin liquid can lead to a fractionalized Fermi liquid (FL*). Such a phase has several favorable features that make it a candidate for the pseudogap metal for the underdoped cuprates. We focus on a particular, simple Z2-FL* state which can undergo a confinement transition to a spatially uniform superconductor which is smoothly connected to the "plain vanilla" BCS superconductor with d -wave pairing. Such a transition occurs by the condensation of bosonic particles carrying +e charge but no spin ("chargons"). We show that modifying the dispersion of the bosonic chargons can lead to confinement transitions with charge density waves and pair density waves at the same wave vector K , coexisting with d -wave superconductivity. We also compute the evolution of the Hall number in the normal state during the transition from the plain vanilla FL* state to a Fermi liquid, and argue, following Coleman, Marston, and Schofield [Phys. Rev. B 72, 245111 (2005), 10.1103/PhysRevB.72.245111], that it exhibits a discontinuous jump near optimal doping. We note the distinction between these results and those obtained from models of the pseudogap with fermionic chargons.

Suppression of the "Quasiclassical" proximity gap in correlated-metal--superconductor structures.

PubMed

Nikolić, Branislav K; Freericks, J K; Miller, P

2002-02-18

We study the energy and spatial dependence of the local density of states in a superconductor--correlated-metal--superconductor Josephson junction, where the correlated metal is a non-Fermi liquid (described by the Falicov-Kimball model). Many-body correlations are treated with dynamical mean-field theory, extended to inhomogeneous systems. While quasiclassical theories predict a minigap in the spectrum of a disordered Fermi liquid which is proximity-coupled within a mesoscopic junction, we find that increasing electron correlations destroy any minigap that might be opened in the absence of many-body correlations.

Hund's Induced Fermi-Liquid Instabilities and Enhanced Quasiparticle Interactions.

PubMed

De' Medici, Luca

2017-04-21

Hund's coupling is shown to generally favor, in a doped half-filled Mott insulator, an increase in the compressibility culminating in a Fermi-liquid instability towards phase separation. The largest effect is found near the frontier between an ordinary and an orbitally decoupled ("Hund's") metal. The increased compressibility implies an enhancement of quasiparticle scattering, thus favoring other possible symmetry breakings. This physics is shown to happen in simulations of the 122 Fe-based superconductors, possibly implying the relevance of this mechanism in the enhancement of the critical temperature for superconductivity.

Properties of quasiparticles in Luttinger liquid

NASA Astrophysics Data System (ADS)

Koutouza, Andrei Boris

In this dissertation we first explain why the Fermi liquid theory breaks down in one dimension and introduce the concept of Luttinger Liquid and the idea of bozonization. In the second part, we study the tunneling through an impurity in a quantum wire with arbitrary Luttinger interaction parameter. By combining the integrable approach, developed in the case of quantum Hall edge states, with the introduction of radiative boundary conditions to describe the adiabatic coupling to the reservoirs, we are able to obtain the exact equilibrium and non-equilibrium current. One of the most striking features observed is the appearance of negative differential conductances out of equilibrium in the strongly interacting regime g < 0.2. In spite of the various charging effects, a remarkable form of duality is still observed. In the third part, the tunneling between edge states in the Fractional Quantum Hall Effect is studied and the shot noise is computed to determine the charge of the carriers in the system. We show that the inclusion of irrelevant terms in the Hamiltonian, describing tunneling between edge states in the fractional quantum Hall effect affect crucially the determination of charge through shot noise measurements. We show, for instance, that certain combinations of relevant and irrelevant terms can lead to an effective measured charge e in the strong backscattering limit and an effective measured charge e in the weak backscattering limit, in sharp contrast with standard perturbative expectations. This provides a possible scenario to explain the experimental observations by Heiblum et al. [35], which are so far not understood. And finally, the scattering amplitudes at a point contact between a Fermi liquid and a Luttinger liquid will be considered, and calculated in the certain cases, using the form-factors technique. These include the reflection and transmission amplitudes at a point contact between a Fermi liquid and a g = 1/3 Luttinger liquid for the processes 2e → 2e, and e → e. These results are obtained in closed form, and give rise to rather simple expressions for the probabilities of the most basic processes of non-Fermi liquid physics at these special values of the couplings.

Orbital-dependent electron correlation effects in iron-based superconductors

NASA Astrophysics Data System (ADS)

Yi, Ming

The iron chalcogenide superconductors constitute arguably one of the most intriguing families of the iron-based high temperature superconductors given their ability to superconduct at comparable temperatures as the iron pnictides, despite the lack of similarities in their magnetic structures and Fermi surface topologies. In particular, the lack of hole Fermi pockets at the Brillouin zone center posts a challenge to the previous proposal of spin fluctuation mediated pairing via Fermi surface nesting. In this talk, using angle-resolved photoemission spectroscopy measurements, I will present evidence that show that instead of Fermi surface topology, strong electron correlation observed in electron bandwidth is an important ingredient for superconductivity in the iron chalcogenides. Specifically, I will show i) there exists universal strong orbital-selective renormalization effects and proximity to an orbital-selective Mott phase in Fe1+yTe1-xSex, AxFe2-ySe2, and monolayer FeSe film on SrTiO3, and ii) in RbxFe2(Se1-zSz)2 , where sulfur substitution for selenium continuously suppresses superconductivity down to zero, little change occurs in the Fermi surface topology while a substantial reduction of electron correlation is observed in an expansion of the overall bandwidth, implying that electron correlation is one of the key tuning parameters for superconductivity in these materials.

Trial wave functions for a composite Fermi liquid on a torus

NASA Astrophysics Data System (ADS)

Fremling, M.; Moran, N.; Slingerland, J. K.; Simon, S. H.

2018-01-01

We study the two-dimensional electron gas in a magnetic field at filling fraction ν =1/2 . At this filling the system is in a gapless state which can be interpreted as a Fermi liquid of composite fermions. We construct trial wave functions for the system on a torus, based on this idea, and numerically compare these to exact wave functions for small systems found by exact diagonalization. We find that the trial wave functions give an excellent description of the ground state of the system, as well as its charged excitations, in all momentum sectors. We analyze the dispersion of the composite fermions and the Berry phase associated with dragging a single fermion around the Fermi surface and comment on the implications of our results for the current debate on whether composite fermions are Dirac fermions.

Short-period oscillations in photoemission from thin films of Cr(100)

NASA Astrophysics Data System (ADS)

Vyalikh, Denis V.; Zahn, Peter; Richter, Manuel; Dedkov, Yu. S.; Molodtsov, S. L.

2005-07-01

Angle-resolved photoemission (PE) study of thin films of Cr grown on Fe(100) reveals thickness-dependent short-period oscillations of the PE intensity close to the Fermi energy at k‖˜0 . The oscillations are assigned to quantum-well states (QWS) caused by the nesting between the Fermi-surface sheets around the Γ and the X points in the Brillouin zone of antiferromagnetic Cr. The experimental data are confirmed by density-functional calculations applying a screened Korringa-Kohn-Rostoker Green’s function method. The period of the experimentally observed QWS oscillations amounts to about 2.6 monolayers and is larger than the fundamental 2-monolayer period of antiferromagnetic coupling in Cr.

Thermal and electrical transport across a magnetic quantum critical point.

PubMed

Pfau, Heike; Hartmann, Stefanie; Stockert, Ulrike; Sun, Peijie; Lausberg, Stefan; Brando, Manuel; Friedemann, Sven; Krellner, Cornelius; Geibel, Christoph; Wirth, Steffen; Kirchner, Stefan; Abrahams, Elihu; Si, Qimiao; Steglich, Frank

2012-04-25

A quantum critical point (QCP) arises when a continuous transition between competing phases occurs at zero temperature. Collective excitations at magnetic QCPs give rise to metallic properties that strongly deviate from the expectations of Landau's Fermi-liquid description, which is the standard theory of electron correlations in metals. Central to this theory is the notion of quasiparticles, electronic excitations that possess the quantum numbers of the non-interacting electrons. Here we report measurements of thermal and electrical transport across the field-induced magnetic QCP in the heavy-fermion compound YbRh(2)Si(2) (refs 2, 3). We show that the ratio of the thermal to electrical conductivities at the zero-temperature limit obeys the Wiedemann-Franz law for magnetic fields above the critical field at which the QCP is attained. This is also expected for magnetic fields below the critical field, where weak antiferromagnetic order and a Fermi-liquid phase form below 0.07 K (at zero field). At the critical field, however, the low-temperature electrical conductivity exceeds the thermal conductivity by about 10 per cent, suggestive of a non-Fermi-liquid ground state. This apparent violation of the Wiedemann-Franz law provides evidence for an unconventional type of QCP at which the fundamental concept of Landau quasiparticles no longer holds. These results imply that Landau quasiparticles break up, and that the origin of this disintegration is inelastic scattering associated with electronic quantum critical fluctuations--these insights could be relevant to understanding other deviations from Fermi-liquid behaviour frequently observed in various classes of correlated materials.

Quantum criticality and universal scaling of strongly attractive spin-imbalanced Fermi gases in a one-dimensional harmonic trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin Xiangguo; Chen Shu; Guan Xiwen

2011-07-15

We investigate quantum criticality and universal scaling of strongly attractive Fermi gases confined in a one-dimensional harmonic trap. We demonstrate from the power-law scaling of the thermodynamic properties that current experiments on this system are capable of measuring universal features at quantum criticality, such as universal scaling and Tomonaga-Luttinger liquid physics. The results also provide insights on recent measurements of key features of the phase diagram of a spin-imbalanced atomic Fermi gas [Y. Liao et al., Nature (London) 467, 567 (2010)] and point to further study of quantum critical phenomena in ultracold atomic Fermi gases.

Higher-Order Fermi-Liquid Corrections for an Anderson Impurity Away from Half Filling

NASA Astrophysics Data System (ADS)

Oguri, Akira; Hewson, A. C.

2018-03-01

We study the higher-order Fermi-liquid relations of Kondo systems for arbitrary impurity-electron fillings, extending the many-body quantum theoretical approach of Yamada and Yosida. It includes, partly, a microscopic clarification of the related achievements based on Nozières' phenomenological description: Filippone, Moca, von Delft, and Mora [Phys. Rev. B 95, 165404 (2017), 10.1103/PhysRevB.95.165404]. In our formulation, the Fermi-liquid parameters such as the quasiparticle energy, damping, and transport coefficients are related to each other through the total vertex Γσ σ';σ'σ(ω ,ω';ω',ω ), which may be regarded as a generalized Landau quasiparticle interaction. We obtain exactly this function up to linear order with respect to the frequencies ω and ω' using the antisymmetry and analytic properties. The coefficients acquire additional contributions of three-body fluctuations away from half filling through the nonlinear susceptibilities. We also apply the formulation to nonequilibrium transport through a quantum dot, and clarify how the zero-bias peak evolves in a magnetic field.

Nematic order on the surface of a three-dimensional topological insulator

NASA Astrophysics Data System (ADS)

Lundgren, Rex; Yerzhakov, Hennadii; Maciejko, Joseph

2017-12-01

We study the spontaneous breaking of rotational symmetry in the helical surface state of three-dimensional topological insulators due to strong electron-electron interactions, focusing on time-reversal invariant nematic order. Owing to the strongly spin-orbit coupled nature of the surface state, the nematic order parameter is linear in the electron momentum and necessarily involves the electron spin, in contrast with spin-degenerate nematic Fermi liquids. For a chemical potential at the Dirac point (zero doping), we find a first-order phase transition at zero temperature between isotropic and nematic Dirac semimetals. This extends to a thermal phase transition that changes from first to second order at a finite-temperature tricritical point. At finite doping, we find a transition between isotropic and nematic helical Fermi liquids that is second order even at zero temperature. Focusing on finite doping, we discuss various observable consequences of nematic order, such as anisotropies in transport and the spin susceptibility, the partial breakdown of spin-momentum locking, collective modes and induced spin fluctuations, and non-Fermi-liquid behavior at the quantum critical point and in the nematic phase.

Higher-Order Fermi-Liquid Corrections for an Anderson Impurity Away from Half Filling.

PubMed

Oguri, Akira; Hewson, A C

2018-03-23

We study the higher-order Fermi-liquid relations of Kondo systems for arbitrary impurity-electron fillings, extending the many-body quantum theoretical approach of Yamada and Yosida. It includes, partly, a microscopic clarification of the related achievements based on Nozières' phenomenological description: Filippone, Moca, von Delft, and Mora [Phys. Rev. B 95, 165404 (2017)PRBMDO2469-995010.1103/PhysRevB.95.165404]. In our formulation, the Fermi-liquid parameters such as the quasiparticle energy, damping, and transport coefficients are related to each other through the total vertex Γ_{σσ^{'};σ^{'}σ}(ω,ω^{'};ω^{'},ω), which may be regarded as a generalized Landau quasiparticle interaction. We obtain exactly this function up to linear order with respect to the frequencies ω and ω^{'} using the antisymmetry and analytic properties. The coefficients acquire additional contributions of three-body fluctuations away from half filling through the nonlinear susceptibilities. We also apply the formulation to nonequilibrium transport through a quantum dot, and clarify how the zero-bias peak evolves in a magnetic field.

Nearly ferromagnetic Fermi-liquid behaviour in YFe2Zn20 and high-temperature ferromagnetism of GdFe2Zn20

NASA Astrophysics Data System (ADS)

Jia, S.; Bud'Ko, S. L.; Samolyuk, G. D.; Canfield, P. C.

2007-05-01

One of the historic goals of alchemy was to turn base elements into precious ones. Although the practice of alchemy has been superseded by chemistry and solid-state physics, the desire to dramatically change or tune the properties of a compound, preferably through small changes in stoichiometry or composition, remains. This desire becomes even more compelling for compounds that can be tuned to extremes in behaviour. Here, we report that the RT2Zn20 (R=rare earth and T=transition metal) family of compounds manifests exactly this type of versatility, even though they are more than 85% Zn. By tuning T, we find that YFe2Zn20 is closer to ferromagnetism than elemental Pd, the classic example of a nearly ferromagnetic Fermi liquid. By submerging Gd in this highly polarizable Fermi liquid, we tune the system to a remarkably high-temperature ferromagnetic (TC=86K) state for a compound with less than 5% Gd. Although this is not quite turning lead into gold, it is essentially tuning Zn to become a variety of model compounds.

Spin fluctations and heavy fermions in the Kondo lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khaliullin, G.G.

1994-09-01

This paper studies the spectrum of the spin and electronic excitations of the Kondo lattice at low temperatures. To avoid unphysical states, the Mattis {open_quotes}drone{close_quotes}-fermion representation for localized spins is employed. First, the known Fermi liquid properties of a single impurity are examined. The behavior of the correlator between a localized spin and the electron spin density at large distances shows that the effective interaction between electrons on the Fermi level and low-energy localized spin fluctuations scales as {rho}{sup {minus}1}, where {rho} is the band-state density. This fact is developed into a renormalization of the band spectrum in a periodicmore » lattice. If the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins is much smaller than the Kondo fluctuation frequency {omega}{sub k}, the temperature of the crossover to the single-parameter Fermi liquid mode is determined by {omega}{sub k}. When the RKKY interaction becomes of order {omega}{sub k}, there is a new scale {omega}{sub sf}, the energy of the (antiferromagnetic) paramagnon mode, with {omega}{sub sf}{much_lt}{omega}{sub k}. Here the coherent Fermi liquid regime is realized only below a temperature T{sub coh} of order {omega}{sub sf}, while above T{sub coh} quasiparticle damping exhibits a linear temperature dependence. Finally, the nuclear-spin relaxation rate is calculated. 42 refs.« less

Non-Fermi Liquid Behavior in the Single-Impurity Mixed Valence Problem

NASA Astrophysics Data System (ADS)

Zhang, Guang-Ming; Su, Zhao-Bin; Yu, Lu

An effective Hamiltonian of the Anderson single-impurity model with finite-range Coulomb interactions is derived near a particular limit, which is analogous to the Toulouse limit of the ordinary Kondo problem, and the physical properties around the mixed valence quantum critical point are calculated. At this quantum critical point, the local moment is only partially quenched and X-ray edge singularities are exhibited. Around this point, a new type of non-Fermi liquid behavior is predicted with an extra specific heat Cimp ~ T1/4 + AT ln T and spin-susceptibility χimp ~T-3/4 + B ln T.

Novel quantum criticality in CeRu2Si2 near absolute zero observed by thermal expansion and magnetostriction.

PubMed

Yoshida, J; Abe, S; Takahashi, D; Segawa, Y; Komai, Y; Tsujii, H; Matsumoto, K; Suzuki, H; Onuki, Y

2008-12-19

We report linear thermal expansion and magnetostriction measurements for CeRu2Si2 in magnetic fields up to 52.6 mT and at temperatures down to 1 mK. At high temperatures, this compound showed Landau-Fermi-liquid behavior: The linear thermal expansion coefficient and the magnetostriction coefficient were proportional to the temperature and magnetic field, respectively. In contrast, a pronounced non-Fermi-liquid effect was found below 50 mK. The negative contribution of thermal expansion and magnetostriction suggests the existence of an additional quantum critical point.

Electronic structure and magnetic ordering in manganese hydride

NASA Astrophysics Data System (ADS)

Magnitskaya, M. V.; Kulikov, N. I.

1991-03-01

The self-consistent electron energy bands of antiferromagnetic (AFM) and non-magnetic manganese hydride are calculated using the linear muffintin orbital method (LMTO). The calculated values of equilibrium volume and of magnetic moment on the manganese site are in good agreement with experiment. The Fermi surface of paramagnetic MnH contains two nesting parts, and their superposition gives rise to AFM gap.

Non-Fermi-liquid superconductivity: Eliashberg approach versus the renormalization group

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Huajia; Raghu, Srinivas; Torroba, Gonzalo

Here, we address the problem of superconductivity for non-Fermi liquids using two commonly adopted, yet apparently distinct, methods: (1) the renormalization group (RG) and (2) Eliashberg theory. The extent to which both methods yield consistent solutions for the low-energy behavior of quantum metals has remained unclear. We show that the perturbative RG beta function for the 4-Fermi coupling can be explicitly derived from the linearized Eliashberg equations, under the assumption that quantum corrections are approximately local across energy scales. We apply our analysis to the test case of phonon-mediated superconductivity and show the consistency of both the Eliashberg and RGmore » treatments. We next study superconductivity near a class of quantum critical points and find a transition between superconductivity and a “naked” metallic quantum critical point with finite, critical BCS couplings. We speculate on the applications of our theory to the phenomenology of unconventional metals.« less

Non-Fermi-liquid superconductivity: Eliashberg approach versus the renormalization group

DOE PAGES

Wang, Huajia; Raghu, Srinivas; Torroba, Gonzalo

2017-04-15

Here, we address the problem of superconductivity for non-Fermi liquids using two commonly adopted, yet apparently distinct, methods: (1) the renormalization group (RG) and (2) Eliashberg theory. The extent to which both methods yield consistent solutions for the low-energy behavior of quantum metals has remained unclear. We show that the perturbative RG beta function for the 4-Fermi coupling can be explicitly derived from the linearized Eliashberg equations, under the assumption that quantum corrections are approximately local across energy scales. We apply our analysis to the test case of phonon-mediated superconductivity and show the consistency of both the Eliashberg and RGmore » treatments. We next study superconductivity near a class of quantum critical points and find a transition between superconductivity and a “naked” metallic quantum critical point with finite, critical BCS couplings. We speculate on the applications of our theory to the phenomenology of unconventional metals.« less

Non-Fermi-liquid nature and exotic thermoelectric power in the heavy-fermion superconductor UBe13

NASA Astrophysics Data System (ADS)

Shimizu, Yusei; Pourret, Alexandre; Knebel, Georg; Palacio-Morales, Alexandra; Aoki, Dai

2015-12-01

We report quite exotic thermoelectric power S in UBe13. At 0 T, the negative S /T continues to strongly enhance down to the superconducting transition temperature with no Fermi-liquid behavior. |S /T | is dramatically suppressed and becomes rather modest with increasing field. We have also obtained precise field dependencies of (i) an anomaly in S due to an exotic Kondo effect and (ii) a field-induced anomaly in S /T associated with the anomalous upward Hc 2(T ) . In contrast to the field-sensitive transport property, the normal-state specific heat is magnetically robust, indicating that the largeness of the 5 f density of states remains in high fields. This unusual behavior in UBe13 can be explained by a considerable change in the energy derivative of the conduction-electron lifetime τc(ɛ ) at the Fermi level under magnetic fields.

Electron nematic fluid in a strained S r3R u2O7 film

NASA Astrophysics Data System (ADS)

Marshall, Patrick B.; Ahadi, Kaveh; Kim, Honggyu; Stemmer, Susanne

2018-04-01

S r3R u2O7 belongs to the family of layered strontium ruthenates and exhibits a range of unusual emergent properties, such as electron nematic behavior and metamagnetism. Here, we show that epitaxial film strain significantly modifies these phenomena. In particular, we observe enhanced magnetic interactions and an electron nematic phase that extends to much higher temperatures and over a larger magnetic-field range than in bulk single crystals. Furthermore, the films show an unusual anisotropic non-Fermi-liquid behavior that is controlled by the direction of the applied magnetic field. At high magnetic fields, the metamagnetic transition to a ferromagnetic phase recovers isotropic Fermi-liquid behavior. The results support the interpretation that these phenomena are linked to the special features of the Fermi surface, which can be tuned by both film strain and an applied magnetic field.

The thermodynamic properties of normal liquid helium 3

NASA Astrophysics Data System (ADS)

Modarres, M.; Moshfegh, H. R.

2009-09-01

The thermodynamic properties of normal liquid helium 3 are calculated by using the lowest order constrained variational (LOCV) method. The Landau Fermi liquid model and Fermi-Dirac distribution function are considered as our statistical model for the uncorrelated quantum fluid picture and the Lennard-Jones and Aziz potentials are used in our truncated cluster expansion (LOCV) to calculate the correlated energy. The single particle energy is treated variationally through an effective mass. The free energy, pressure, entropy, chemical potential and liquid phase diagram as well as the helium 3 specific heat are evaluated, discussed and compared with the corresponding available experimental data. It is found that the critical temperature for the existence of the pure gas phase is about 4.90 K (4.45 K), which is higher than the experimental prediction of 3.3 K, and the helium 3 flashing temperature is around 0.61 K (0.50 K) for the Lennard-Jones (Aziz) potential.

Direct constraints on minimal supersymmetry from Fermi-LAT observations of the dwarf galaxy Segue 1

DOE PAGES

Scott, Pat; Conrad, Jan; Edsjö, Joakim; ...

2010-01-26

The dwarf galaxy Segue 1 is one of the most promising targets for the indirect detection of dark matter. We examine what constraints 9 months of Fermi-LAT gamma-ray observations of Segue 1 place upon the Constrained Minimal Supersymmetric Standard Model (CMSSM), with the lightest neutralino as the dark matter particle. We also use nested sampling to explore the CMSSM parameter space, simultaneously fitting other relevant constraints from accelerator bounds, the relic density, electroweak precision observables, the anomalous magnetic moment of the muon and B-physics. We include spectral and spatial fits to the Fermi observations, a full treatment of the instrumentalmore » response and its related uncertainty, and detailed background models. We also perform an extrapolation to 5 years of observations, assuming no signal is observed from Segue 1 in that time. Our results marginally disfavour models with low neutralino masses and high annihilation cross-sections. Virtually all of these models are however already disfavoured by existing experimental or relic density constraints.« less

Electrons at the monkey saddle: a multicritical Lifshitz point

NASA Astrophysics Data System (ADS)

Shtyk, Alex; Goldstein, Garry; Chamon, Claudio

We consider 2D interacting electrons at a monkey saddle with dispersion px3 - 3pxpy2 . Such a dispersion naturally arises at the multicritical Lifshitz point when three van Hove saddles merge in an elliptical umbilic elementary catastrophe, which we show can be realized in biased bilayer graphene. A multicritical Lifshitz point of this kind can be identified by its signature Landau level behavior Em (Bm) 3 / 2 and related oscillations in thermodynamic and transport properties, such as de Haas-van Alphen and Shubnikov-de Haas oscillations, whose period triples as the system crosses the singularity. We show, in the case of a single monkey saddle, that the non-interacting electron fixed point is unstable to interactions under the renormalization group flow, developing either a superconducting instability or non-Fermi liquid features. Biased bilayer graphene, where there are two non-nested monkey saddles at the K and K' points, exhibits an interplay of competing many-body instabilities, namely s-wave superconductivity, ferromagnetism, and spin- and charge-density wave. DOE DE-FG02-06ER46316.

Electrostatic interactions between ions near Thomas-Fermi substrates and the surface energy of ionic crystal at imperfect metals

PubMed Central

Kaiser, V.; Comtet, J.; Niguès, A.; Siria, A.; Coasne, B.; Bocquet, L.

2017-01-01

The electrostatic interaction between two charged particles is strongly modified in the vicinity of a metal. This situation is usually accounted for by the celebrated image charges approach, which was further extended to account for the electronic screening properties of the metal at the level of the Thomas-Fermi description. In this paper we build upon the approach by [Kornyshev et al. Zh. Eksp. Teor. Fiz., 78(3):1008–1019, 1980] and successive works to calculate the 1-body and 2-body electrostatic energy of ions near a metal in terms of the Thomas-Fermi screening length. We propose workable approximations suitable for molecular simulations of ionic systems close to metallic walls. Furthermore, we use this framework to calculate analytically the electrostatic contribution to the surface energy of a one dimensional crystal at a metallic wall and its dependence on the Thomas-Fermi screening length. These calculations provide a simple interpretation for the surface energy in terms of image charges, which allow for an estimate of interfacial properties in more complex situations of a disordered ionic liquid close to a metal surface. A counterintuitive outcome is that electronic screening, as characterized by a molecular Thomas-Fermi length ℓTF, profoundly affects the wetting of ionic systems close to a metal, in line with the recent experimental observation of capillary freezing of ionic liquids in metallic confinement. PMID:28436506

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radzihovsky, Leo

Motivated by a realization of imbalanced Feshbach-resonant atomic Fermi gases, we formulate a low-energy theory of the Fulde-Ferrell and the Larkin-Ovchinnikov (LO) states and use it to analyze fluctuations, stability, and phase transitions in these enigmatic finite momentum-paired superfluids. Focusing on the unidirectional LO pair-density-wave state, which spontaneously breaks the continuous rotational and translational symmetries, we show that it is characterized by two Goldstone modes, corresponding to a superfluid phase and a smectic phonon. Because of the liquid-crystalline ''softness'' of the latter, at finite temperature the three-dimensional state is characterized by a vanishing LO order parameter, quasi-Bragg peaks in themore » structure and momentum distribution functions, and a ''charge''-4, paired-Cooper-pairs, off-diagonal long-range order, with a superfluid-stiffness anisotropy that diverges near a transition into a nonsuperfluid state. In addition to conventional integer vortices and dislocations, the LO superfluid smectic exhibits composite half-integer vortex-dislocation defects. A proliferation of defects leads to a rich variety of descendant states, such as the charge-4 superfluid and Fermi-liquid nematics and topologically ordered nonsuperfluid states, that generically intervene between the LO state and the conventional superfluid and the polarized Fermi liquid at low and high imbalance, respectively. The fermionic sector of the LO gapless superconductor is also quite unique, exhibiting a Fermi surface of Bogoliubov quasiparticles associated with the Andreev band of states, localized on the array of the LO domain walls.« less

Emergent phases of fractonic matter

NASA Astrophysics Data System (ADS)

Prem, Abhinav; Pretko, Michael; Nandkishore, Rahul M.

2018-02-01

Fractons are emergent particles which are immobile in isolation, but which can move together in dipolar pairs or other small clusters. These exotic excitations naturally occur in certain quantum phases of matter described by tensor gauge theories. Previous research has focused on the properties of small numbers of fractons and their interactions, effectively mapping out the "standard model" of fractons. In the present work, however, we consider systems with a finite density of either fractons or their dipolar bound states, with a focus on the U (1 ) fracton models. We study some of the phases in which emergent fractonic matter can exist, thereby initiating the study of the "condensed matter" of fractons. We begin by considering a system with a finite density of fractons, which we show can exhibit microemulsion physics, in which fractons form small-scale clusters emulsed in a phase dominated by long-range repulsion. We then move on to study systems with a finite density of mobile dipoles, which have phases analogous to many conventional condensed matter phases. We focus on two major examples: Fermi liquids and quantum Hall phases. A finite density of fermionic dipoles will form a Fermi surface and enter a Fermi liquid phase. Interestingly, this dipolar Fermi liquid exhibits a finite-temperature phase transition, corresponding to an unbinding transition of fractons. Finally, we study chiral two-dimensional phases corresponding to dipoles in "quantum Hall" states of their emergent magnetic field. We study numerous aspects of these generalized quantum Hall systems, such as their edge theories and ground state degeneracies.

Report on Work Performed for Office of Naval Research.

DTIC Science & Technology

1979-10-31

3 Electron Transport in COW Statey ............................ 4 i.Many-Body Effects.F-rbhl ich.Mode, tDiscommensurations...apart from such considerations the non-linear I-V characteristics in the COW phase may be exploited for device applications. The strong dispersion of...exist flat portions of the Fermi surface (FS) which are sufficiently parallel12 ("nesting" criterion) to drive the COW instability. The superlattice

Superconductivity and non-Fermi liquid behavior near a nematic quantum critical point.

PubMed

Lederer, Samuel; Schattner, Yoni; Berg, Erez; Kivelson, Steven A

2017-05-09

Using determinantal quantum Monte Carlo, we compute the properties of a lattice model with spin [Formula: see text] itinerant electrons tuned through a quantum phase transition to an Ising nematic phase. The nematic fluctuations induce superconductivity with a broad dome in the superconducting [Formula: see text] enclosing the nematic quantum critical point. For temperatures above [Formula: see text], we see strikingly non-Fermi liquid behavior, including a "nodal-antinodal dichotomy" reminiscent of that seen in several transition metal oxides. In addition, the critical fluctuations have a strong effect on the low-frequency optical conductivity, resulting in behavior consistent with "bad metal" phenomenology.

Electrical resistivity across the tricriticality in itinerant ferromagnet

NASA Astrophysics Data System (ADS)

Opletal, P.; Prokleška, J.; Valenta, J.; Sechovský, V.

2018-05-01

We investigate the discontinuous ferromagnetic phase diagram near tricritical point in UCo1-xRuxAl compounds by electrical resistivity measurements. Separation of phases in UCo0.995Ru0.005Al at ambient pressure and in UCo0.990Ru0.010Al at pressure of 0.2 GPa and disappearance of ferromagnetism at 0.4 GPa is confirmed. The exponent of temperature dependence of electrical resistivity implies change from Fermi liquid-like behavior to non-Fermi liquid at 0.2 GPa and reaches minimum at 0.4 GPa. Our results are compared to results obtained on the pure UCoAl and explanation for different exponents is given.

Breakdown of the coherence effects and Fermi liquid behavior in YbAl3 nanoparticles

NASA Astrophysics Data System (ADS)

Echevarria-Bonet, C.; Rojas, D. P.; Espeso, J. I.; Rodríguez Fernández, J.; Rodríguez Fernández, L.; Bauer, E.; Burdin, S.; Magalhães, S. G.; Fernández Barquín, L.

2018-04-01

A change in the Kondo lattice behavior of bulk YbAl3 has been observed when the alloy is shaped into nanoparticles (≈12 nm). Measurements of the electrical resistivity show inhibited coherence effects and deviation from the standard Fermi liquid behavior (T 2-dependence). These results are interpreted as being due to the effect of the disruption of the periodicity of the array of Kondo ions provoked by the size reduction process. Additionally, the ensemble of randomly placed nanoparticles also triggers an extra source of electronic scattering at very low temperatures (≈15 K) due to quantum interference effects.

Terahertz spectroscopic evidence of non-Fermi-liquid-like behavior in structurally modulated PrNi O3 thin films

NASA Astrophysics Data System (ADS)

Phanindra, V. Eswara; Agarwal, Piyush; Rana, D. S.

2018-01-01

The intertwined and competing energy scales of various interactions in rare-earth nickelates R Ni O3 (R =La to Lu) hold potential for a wide range of exotic ground states realized upon structural modulation. Using terahertz (THz) spectroscopy, the low-energy dynamics of a novel non-Fermi liquid (NFL) metallic phase induced in compressive PrNi O3 thin film was studied by evaluating the quasiparticle scattering rate in the light of two distinct models over a wide temperature range. First, evaluating THz conductivity in the framework of extended Drude model, the frequency-dependent scattering rate is found to deviate from the Landau Fermi liquid (LFL) behavior, thus, suggesting NFL-like phase at THz frequencies. Second, fitting THz conductivity to the multiband Drude-Lorentz model reveals the band-dependent scattering rates and provides microscopic interpretation of the carriers contributing to the Drude modes. This is first evidence of NFL-like behavior in nickelates at THz frequencies consistent with dc conductivity, which also suggests that THz technology is indispensable in understanding emerging electronic phases and associated phenomena. We further demonstrate that the metal-insulator transition in nickelates has the potential to design efficient THz modulators.

Mixed valent metals

NASA Astrophysics Data System (ADS)

Riseborough, P. S.; Lawrence, J. M.

2016-08-01

We review the theory of mixed-valent metals and make comparison with experiments. A single-impurity description of the mixed-valent state is discussed alongside the description of the nearly-integer valent or Kondo limit. The degeneracy N of the f-shell plays an important role in the description of the low-temperature Fermi-liquid state. In particular, for large N, there is a rapid cross-over between the mixed-valent and the Kondo limit when the number of f electrons is changed. We discuss the limitations on the application of the single-impurity description to concentrated compounds such as those caused by the saturation of the Kondo effect and those due to the presence of magnetic interactions between the impurities. This discussion is followed by a description of a periodic lattice of mixed-valent ions, including the role of the degeneracy N. The article concludes with a comparison of theory and experiment. Topics covered include the single-impurity Anderson model, Luttinger’s theorem, the Friedel sum rule, the Schrieffer-Wolff transformation, the single-impurity Kondo model, Kondo screening, the Wilson ratio, local Fermi-liquids, Fermi-liquid sum rules, the Noziéres exhaustion principle, Doniach’s diagram, the Anderson lattice model, the Slave-Boson method, etc.

Mixed valent metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riseborough, P. S.; Lawrence, Jon M.

Here, we review the theory of mixed-valent metals and make comparison with experiments. A single-impurity description of the mixed-valent state is discussed alongside the description of the nearly-integer valent or Kondo limit. The degeneracy N of the f-shell plays an important role in the description of the low-temperature Fermi-liquid state. In particular, for large N, there is a rapid cross-over between the mixed-valent and the Kondo limit when the number of f electrons is changed. We discuss the limitations on the application of the single-impurity description to concentrated compounds such as those caused by the saturation of the Kondo effectmore » and those due to the presence of magnetic interactions between the impurities. This discussion is followed by a description of a periodic lattice of mixed-valent ions, including the role of the degeneracy N. The article concludes with a comparison of theory and experiment. Topics covered include the single-impurity Anderson model, Luttinger's theorem, the Friedel sum rule, the Schrieffer–Wolff transformation, the single-impurity Kondo model, Kondo screening, the Wilson ratio, local Fermi-liquids, Fermi-liquid sum rules, the Nozieres exhaustion principle, Doniach's diagram, the Anderson lattice model, the Slave-Boson method, etc.« less

Mixed valent metals

DOE PAGES

Riseborough, P. S.; Lawrence, Jon M.

2016-07-04

Here, we review the theory of mixed-valent metals and make comparison with experiments. A single-impurity description of the mixed-valent state is discussed alongside the description of the nearly-integer valent or Kondo limit. The degeneracy N of the f-shell plays an important role in the description of the low-temperature Fermi-liquid state. In particular, for large N, there is a rapid cross-over between the mixed-valent and the Kondo limit when the number of f electrons is changed. We discuss the limitations on the application of the single-impurity description to concentrated compounds such as those caused by the saturation of the Kondo effectmore » and those due to the presence of magnetic interactions between the impurities. This discussion is followed by a description of a periodic lattice of mixed-valent ions, including the role of the degeneracy N. The article concludes with a comparison of theory and experiment. Topics covered include the single-impurity Anderson model, Luttinger's theorem, the Friedel sum rule, the Schrieffer–Wolff transformation, the single-impurity Kondo model, Kondo screening, the Wilson ratio, local Fermi-liquids, Fermi-liquid sum rules, the Nozieres exhaustion principle, Doniach's diagram, the Anderson lattice model, the Slave-Boson method, etc.« less

Enhancement of the superconducting gap by nesting in CaKFe 4 As 4 : A new high temperature superconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mou, Daixiang; Kong, Tai; Meier, William R.

We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe 4As 4. In contrast to the related CaFe 2As 2 compounds, CaKFe 4As 4 has a high T c of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearlymore » isotropic (within the explored portions of the Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos( k x)cos( k y) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. Finally, these results provide strong support for the multiband character of superconductivity in CaKFe 4As 4, in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting.« less

Enhancement of the superconducting gap by nesting in CaKFe 4 As 4 : A new high temperature superconductor

DOE PAGES

Mou, Daixiang; Kong, Tai; Meier, William R.; ...

2016-12-28

We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe 4As 4. In contrast to the related CaFe 2As 2 compounds, CaKFe 4As 4 has a high T c of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearlymore » isotropic (within the explored portions of the Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos( k x)cos( k y) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. Finally, these results provide strong support for the multiband character of superconductivity in CaKFe 4As 4, in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting.« less

Non-Fermi glasses: fractionalizing electrons at finite energy density

NASA Astrophysics Data System (ADS)

Parameswaran, Siddharth; Gopalakrishnan, Sarang

Non-Fermi liquids are metals that cannot be adiabatically deformed into free fermion states. We argue for the existence of ``non-Fermi glasses,'' which are phases of interacting disordered fermions that are fully many-body localized, yet cannot be deformed into an Anderson insulator without an eigenstate phase transition. We explore the properties of such non-Fermi glasses, focusing on a specific solvable example. At high temperature, non-Fermi glasses have qualitatively similar spectral features to Anderson insulators. We identify a diagnostic, based on ratios of correlation functions, that sharply distinguishes between the two phases even at infinite temperature. We argue that our results and diagnostic should generically apply to the high-temperature behavior of the many-body localized descendants of fractionalized phases. S.A.P. is supported by NSF Grant DMR-1455366 and a UC President's Research Catalyst Award CA-15-327861, and S.G. by the Burke Institute at Caltech.

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

NASA Astrophysics Data System (ADS)

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

2018-04-01

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three-dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb2 Pt2 Pb , a metal where itinerant electrons coexist with localized moments of Yb ions which can be described in terms of effective S =1 /2 spins with a dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasilinear temperature dependence.

Thermodynamics of Thomas-Fermi screened Coulomb systems

NASA Technical Reports Server (NTRS)

Firey, B.; Ashcroft, N. W.

1977-01-01

We obtain in closed analytic form, estimates for the thermodynamic properties of classical fluids with pair potentials of Yukawa type, with special reference to dense fully ionized plasmas with Thomas-Fermi or Debye-Hueckel screening. We further generalize the hard-sphere perturbative approach used for similarly screened two-component mixtures, and demonstrate phase separation in this simple model of a liquid mixture of metallic helium and hydrogen.

Optical Lattice Simulations of Correlated Fermions

DTIC Science & Technology

2013-10-04

Zhang, Xiaopeng Li, W. Vincent Liu. Stripe , checkerboard, and liquid-crystal ordering from anisotropic p-orbital Fermi surfaces in optical lattices...Meeting "The Role of Interactions in Disorder Induced Damping of Dipole Oscillations of a Bose-Einstein Condensate", S. Pollack, APS March Meeting...Rev. A 85, 043603 (2012)], and also worked out the diffusive transport behavior of the polarized Fermi gas, including heat transport, spin Seebeck

Gross violation of the Wiedemann–Franz law in a quasi-one-dimensional conductor

PubMed Central

Wakeham, Nicholas; Bangura, Alimamy F.; Xu, Xiaofeng; Mercure, Jean-Francois; Greenblatt, Martha; Hussey, Nigel E.

2011-01-01

When charge carriers are spatially confined to one dimension, conventional Fermi-liquid theory breaks down. In such Tomonaga–Luttinger liquids, quasiparticles are replaced by distinct collective excitations of spin and charge that propagate independently with different velocities. Although evidence for spin–charge separation exists, no bulk low-energy probe has yet been able to distinguish successfully between Tomonaga–Luttinger and Fermi-liquid physics. Here we show experimentally that the ratio of the thermal and electrical Hall conductivities in the metallic phase of quasi-one-dimensional Li0.9Mo6O17 diverges with decreasing temperature, reaching a value five orders of magnitude larger than that found in conventional metals. Both the temperature dependence and magnitude of this ratio are consistent with Tomonaga–Luttinger liquid theory. Such a dramatic manifestation of spin–charge separation in a bulk three-dimensional solid offers a unique opportunity to explore how the fermionic quasiparticle picture recovers, and over what time scale, when coupling to a second or third dimension is restored. PMID:21772267

Electrostatic interactions between ions near Thomas-Fermi substrates and the surface energy of ionic crystals at imperfect metals.

PubMed

Kaiser, V; Comtet, J; Niguès, A; Siria, A; Coasne, B; Bocquet, L

2017-07-01

The electrostatic interaction between two charged particles is strongly modified in the vicinity of a metal. This situation is usually accounted for by the celebrated image charges approach, which was further extended to account for the electronic screening properties of the metal at the level of the Thomas-Fermi description. In this paper we build upon a previous approach [M. A. Vorotyntsev and A. A. Kornyshev, Zh. Eksp. Teor. Fiz., 1980, 78(3), 1008-1019] and successive works to calculate the 1-body and 2-body electrostatic energy of ions near a metal in terms of the Thomas-Fermi screening length. We propose workable approximations suitable for molecular simulations of ionic systems close to metallic walls. Furthermore, we use this framework to calculate analytically the electrostatic contribution to the surface energy of a one dimensional crystal at a metallic wall and its dependence on the Thomas-Fermi screening length. These calculations provide a simple interpretation for the surface energy in terms of image charges, which allows for an estimation of the interfacial properties in more complex situations of a disordered ionic liquid close to a metal surface. The counter-intuitive outcome is that electronic screening, as characterized by a molecular Thomas-Fermi length l TF , profoundly affects the wetting of ionic systems close to a metal, in line with the recent experimental observation of capillary freezing of ionic liquids in metallic confinement.

Tunable (δπ, δπ)-Type Antiferromagnetic Order in α-Fe(Te,Se) Superconductors

NASA Astrophysics Data System (ADS)

Bao, Wei; Qiu, Y.; Huang, Q.; Green, M. A.; Zajdel, P.; Fitzsimmons, M. R.; Zhernenkov, M.; Chang, S.; Fang, Minghu; Qian, B.; Vehstedt, E. K.; Yang, Jinhu; Pham, H. M.; Spinu, L.; Mao, Z. Q.

2009-06-01

The new α-Fe(Te,Se) superconductors share the common iron building block and ferminology with the LaFeAsO and BaFe2As2 families of superconductors. In contrast with the predicted commensurate spin-density-wave order at the nesting wave vector (π, 0), a completely different magnetic order with a composition tunable propagation vector (δπ, δπ) was determined for the parent compound Fe1+yTe in this powder and single-crystal neutron diffraction study. The new antiferromagnetic order survives as a short-range one even in the highest TC sample. An alternative to the prevailing nesting Fermi surface mechanism is required to understand the latest family of ferrous superconductors.

MAGNETIC FIELD OF THE VELA C MOLECULAR CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kusune, Takayoshi; Sugitani, Koji; Nakamura, Fumitaka

We have performed extensive near-infrared ( JHK {sub s}) imaging polarimetry toward the Vela C molecular cloud, which covers the five high-density sub-regions (North, Centre-Ridge, Centre-Nest, South-Ridge, and South-Nest) with distinct morphological characteristics. The obtained polarization vector map shows that three of these sub-regions have distinct plane-of-the-sky (POS) magnetic-field characteristics according to the morphological characteristics. (1) In the Centre-Ridge sub-region, a dominating ridge, the POS magnetic field is mostly perpendicular to the ridge. (2) In the Centre-Nest sub-region, a structure having a slightly extended nest of filaments, the POS magnetic field is nearly parallel to its global elongation. (3) Inmore » the South-Nest sub-region, which has a network of small filaments, the POS magnetic field appears to be chaotic. By applying the Chandrasekhar–Fermi method, we derived the POS magnetic field strength as ∼70–310 μ G in the Centre-Ridge, Centre-Nest, and South-Ridge sub-regions. In the South-Nest sub-region, the dispersion of polarization angles is too large to apply the C-F method. Because the velocity dispersion in this sub-region is not greater than those in the other sub-regions, we suggest that the magnetic field in this sub-region is weaker than those in other sub-regions. We also discuss the relationship between the POS magnetic field (configuration and strength) and the cloud structure of each sub-region.« less

Quantum Engineering of Strongly Correlated Matter with Ultracold Fermi Gases

DTIC Science & Technology

2013-05-01

aim at realizing model systems of strongly correlated, disordered electrons using ultracold fermionic atoms stored in an optical "crystal". The general...theme is to study high-temperature superfluids, Fermi liquids ("metals") and insulators in the presence of disordered impurities whose influence on...Presidential Early Career Award for Science and Education (PECASE). In this program, we aim at realizing model systems of strongly correlated, disordered

Entanglement entropy of critical spin liquids.

PubMed

Zhang, Yi; Grover, Tarun; Vishwanath, Ashvin

2011-08-05

Quantum spin liquids are phases of matter whose internal structure is not captured by a local order parameter. Particularly intriguing are critical spin liquids, where strongly interacting excitations control low energy properties. Here we calculate their bipartite entanglement entropy that characterizes their quantum structure. In particular we calculate the Renyi entropy S(2) on model wave functions obtained by Gutzwiller projection of a Fermi sea. Although the wave functions are not sign positive, S(2) can be calculated on relatively large systems (>324 spins) using the variational Monte Carlo technique. On the triangular lattice we find that entanglement entropy of the projected Fermi sea state violates the boundary law, with S(2) enhanced by a logarithmic factor. This is an unusual result for a bosonic wave function reflecting the presence of emergent fermions. These techniques can be extended to study a wide class of other phases.

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

DOE PAGES

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

2018-04-10

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb 2Pt 2Pb, a metal where itinerant electrons coexist with localized moments of Yb-ions which can be described in terms of effective S = 1/2 spins with dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the twomore » interacting subsystems. Lastly, we characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasi linear temperature dependence.« less

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb 2Pt 2Pb, a metal where itinerant electrons coexist with localized moments of Yb-ions which can be described in terms of effective S = 1/2 spins with dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the twomore » interacting subsystems. Lastly, we characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasi linear temperature dependence.« less

Electron Dispersion in Liquid Alkali and Their Alloys

NASA Astrophysics Data System (ADS)

Vora, Aditya M.

2010-07-01

Ashcroft's local empty core (EMC) model pseudopotential in the second-order perturbation theory is used to study the electron dispersion relation, the Fermi energy, and deviation in the Fermi energy from free electron value for the liquid alkali metals and their equiatomic binary alloys for the first time. In the present computation, the use of pseudo-alloy-atom model (PAA) is proposed and found successful. The influence of the six different forms of the local field correction functions proposed by Hartree (H), Vashishta-Singwi (VS), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F), and Sarkar et al. (S) on the aforesaid electronic properties is examined explicitly, which reflects the varying effects of screening. The depth of the negative hump in the electron dispersion of liquid alkalis decreases in the order Li → K, except for Rb and Cs, it increases. The results of alloys are in predictive nature.

Extremely correlated Fermi liquid theory of the t-J model in 2 dimensions: low energy properties

NASA Astrophysics Data System (ADS)

Shastry, B. Sriram; Mai, Peizhi

2018-01-01

Low energy properties of the metallic state of the two-dimensional t-J model are presented for second neighbor hopping with hole-doping (t\\prime ≤slant 0) and electron-doping (t\\prime > 0), with various superexchange energy J. We use a closed set of equations for the Greens functions obtained from the extremely correlated Fermi liquid theory. These equations reproduce the known low energies features of the large U Hubbard model in infinite dimensions. The density and temperature dependent quasiparticle weight, decay rate and the peak spectral heights over the Brillouin zone are calculated. We also calculate the resistivity, Hall conductivity, Hall number and cotangent Hall angle. The spectral features display high thermal sensitivity at modest T for density n≳ 0.8, implying a suppression of the effective Fermi-liquid temperature by two orders of magnitude relative to the bare bandwidth. The cotangent Hall angle exhibits a T 2 behavior at low T, followed by an interesting kink at higher T. The Hall number exhibits strong renormalization due to correlations. Flipping the sign of t\\prime changes the curvature of the resistivity versus T curves between convex and concave. Our results provide a natural route for understanding the observed difference in the temperature dependent resistivity of strongly correlated electron-doped and hole-doped matter.

Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings

NASA Astrophysics Data System (ADS)

Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg

2011-08-01

We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter rS is increased, we observe—at a fixed spin magnetic moment—the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing rS. We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical rSc at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing rS the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.

Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings.

PubMed

Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg

2011-08-24

We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r(S) is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r(S). We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r(S)(c) at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r(S) the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid. © 2011 IOP Publishing Ltd

Universality class of non-Fermi-liquid behavior in mixed-valence systems

NASA Astrophysics Data System (ADS)

Zhang, Guang-Ming; Su, Zhao-Bin; Yu, Lu

1996-01-01

A generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper oxides. Using the Abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong-coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed-valence quantum critical point separating two different Fermi-liquid phases, i.e., the Kondo phase and the empty orbital phase. In the mixed-valence quantum critical regime, the local moment is only partially quenched and x-ray edge singularities are generated. Around the quantum critical point, a type of non-Fermi-liquid behavior is predicted with an extra specific heat Cimp~T1/4 and a singular spin susceptibility χimp~T-3/4. At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in UPdxCu5-x (x=1,1.5) alloys, which show single-impurity critical behavior consistent with our predictions.

Conductance scaling of junctions of Luttinger-liquid wires out of equilibrium

NASA Astrophysics Data System (ADS)

Aristov, D. N.; Wölfle, P.

2018-05-01

We develop the renormalization group theory of the conductances of N -lead junctions of spinless Luttinger-liquid wires as functions of bias voltages applied to N independent Fermi-liquid reservoirs. Based on the perturbative results up to second order in the interaction we demonstrate that the conductances obey scaling. The corresponding renormalization group β functions are derived up to second order.

Pairing of one-dimensional Bose-Fermi mixtures with unequal masses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rizzi, Matteo; Max Planck Institut fuer QuantenOptik, Hans Kopfermann Strasse 1, D-85748 Garching; Imambekov, Adilet

We have considered one-dimensional Bose-Fermi mixture with equal densities and unequal masses using numerical density matrix renormalization group. For the mass ratio of K-Rb mixture and attraction between bosons and fermions, we determined the phase diagram. For weak boson-boson interactions, there is a direct transition between two-component Luttinger liquid and collapsed phases as the boson-fermion attraction is increased. For strong enough boson-boson interactions, we find an intermediate 'paired' phase, which is a single-component Luttinger liquid of composite particles. We investigated correlation functions of such a 'paired' phase, studied the stability of 'paired' phase to density imbalance, and discussed various experimentalmore » techniques which can be used to detect it.« less

Field-temperature phase diagram and entropy landscape of CeAuSb 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Lishan; Yelland, Edward A.; Bruin, Jan A. N.

2016-05-12

Here, we report a field-temperature phase diagram and an entropy map for the heavy-fermion compound CeAuSb 2. CeAuSb 2 orders antiferromagnetically below T N = 6.6 K and has two metamagnetic transitions, at 2.8 and 5.6 T. The locations of the critical end points of the metamagnetic transitions, which may play a strong role in the putative quantum criticality of CeAuSb 2 and related compounds, are identified. The entropy map reveals an apparent entropy balance with Fermi-liquid behavior, implying that above the Neel transition the Ce moments are incorporated into the Fermi liquid. High-field data showing that the magnetic behaviormore » is remarkably anisotropic are also reported.« less

On the Crossover from Classical to Fermi Liquid Behavior in Dense Plasmas

NASA Astrophysics Data System (ADS)

Daligault, Jerome

2017-10-01

We explore the crossover from classical plasma to quantum Fermi liquid behavior of electrons in dense plasmas. To this end, we analyze the evolution with density and temperature of the momentum lifetime of a test electron introduced in a dense electron gas. This allows us 1) to determine the boundaries of the crossover region in the temperature-density plane and to shed light on the evolution of scattering properties across it, 2) to quantify the role of the fermionic nature of electrons on electronic collisions across the crossover region, and 3) to explain how the concept of Coulomb logarithm emerges at high enough temperature but disappears at low enough temperature. Work supported by LDRD Grant No. 20170490ER.

Gutzwiller charge phase diagram of cuprates, including electron–phonon coupling effects

DOE PAGES

Markiewicz, R. S.; Seibold, G.; Lorenzana, J.; ...

2015-02-01

Besides significant electronic correlations, high-temperature superconductors also show a strong coupling of electrons to a number of lattice modes. Combined with the experimental detection of electronic inhomogeneities and ordering phenomena in many high-T c compounds, these features raise the question as to what extent phonons are involved in the associated instabilities. Here we address this problem based on the Hubbard model including a coupling to phonons in order to capture several salient features of the phase diagram of hole-doped cuprates. Charge degrees of freedom, which are suppressed by the large Hubbard U near half-filling, are found to become active atmore » a fairly low doping level. We find that possible charge order is mainly driven by Fermi surface nesting, with competition between a near-(π, π) order at low doping and antinodal nesting at higher doping, very similar to the momentum structure of magnetic fluctuations. The resulting nesting vectors are generally consistent with photoemission and tunneling observations, evidence for charge density wave order in YBa₂Cu₃O 7-δ including Kohn anomalies, and suggestions of competition between one- and two-q-vector nesting.« less

Van Hove singularities in the paramagnetic phase of the Hubbard model: DMFT study

NASA Astrophysics Data System (ADS)

Žitko, Rok; Bonča, Janez; Pruschke, Thomas

2009-12-01

Using the dynamical mean-field theory (DMFT) with the numerical renormalization-group impurity solver we study the paramagnetic phase of the Hubbard model with the density of states (DOS) corresponding to the three-dimensional (3D) cubic lattice and the two-dimensional (2D) square lattice, as well as a DOS with inverse square-root singularity. We show that the electron correlations rapidly smooth out the square-root van Hove singularities (kinks) in the spectral function for the 3D lattice and that the Mott metal-insulator transition (MIT) as well as the magnetic-field-induced MIT differ only little from the well-known results for the Bethe lattice. The consequences of the logarithmic singularity in the DOS for the 2D lattice are more dramatic. At half filling, the divergence pinned at the Fermi level is not washed out, only its integrated weight decreases as the interaction is increased. While the Mott transition is still of the usual kind, the magnetic-field-induced MIT falls into a different universality class as there is no field-induced localization of quasiparticles. In the case of a power-law singularity in the DOS at the Fermi level, the power-law singularity persists in the presence of interaction, albeit with a different exponent, and the effective impurity model in the DMFT turns out to be a pseudogap Anderson impurity model with a hybridization function which vanishes at the Fermi level. The system is then a generalized Fermi liquid. At finite doping, regular Fermi-liquid behavior is recovered.

Fermionic spin liquid analysis of the paramagnetic state in volborthite

NASA Astrophysics Data System (ADS)

Chern, Li Ern; Schaffer, Robert; Sorn, Sopheak; Kim, Yong Baek

2017-10-01

Recently, thermal Hall effect has been observed in the paramagnetic state of volborthite, which consists of distorted kagome layers with S =1 /2 local moments. Despite the appearance of magnetic order below 1 K , the response to external magnetic field and unusual properties of the paramagnetic state above 1 K suggest possible realization of exotic quantum phases. Motivated by these discoveries, we investigate possible spin liquid phases with fermionic spinon excitations in a nonsymmorphic version of the kagome lattice, which belongs to the two-dimensional crystallographic group p 2 g g . This nonsymmorphic structure is consistent with the spin model obtained in the density functional theory calculation. Using projective symmetry group analysis and fermionic parton mean field theory, we identify twelve distinct Z2 spin liquid states, four of which are found to have correspondence in the eight Schwinger boson spin liquid states we classified earlier. We focus on the four fermionic states with bosonic counterpart and find that the spectrum of their corresponding root U (1 ) states features spinon Fermi surface. The existence of spinon Fermi surface in candidate spin liquid states may offer a possible explanation of the finite thermal Hall conductivity observed in volborthite.

Superconductivity versus quantum criticality: Effects of thermal fluctuations

NASA Astrophysics Data System (ADS)

Wang, Huajia; Wang, Yuxuan; Torroba, Gonzalo

2018-02-01

We study the interplay between superconductivity and non-Fermi liquid behavior of a Fermi surface coupled to a massless SU(N ) matrix boson near the quantum critical point. The presence of thermal infrared singularities in both the fermionic self-energy and the gap equation invalidates the Eliashberg approximation, and makes the quantum-critical pairing problem qualitatively different from that at zero temperature. Taking the large N limit, we solve the gap equation beyond the Eliashberg approximation, and obtain the superconducting temperature Tc as a function of N . Our results show an anomalous scaling between the zero-temperature gap and Tc. For N greater than a critical value, we find that Tc vanishes with a Berezinskii-Kosterlitz-Thouless scaling behavior, and the system retains non-Fermi liquid behavior down to zero temperature. This confirms and extends previous renormalization-group analyses done at T =0 , and provides a controlled example of a naked quantum critical point. We discuss the crucial role of thermal fluctuations in relating our results with earlier work where superconductivity always develops due to the special role of the first Matsubara frequency.

Theory of thermal conductivity in the disordered electron liquid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwiete, G., E-mail: schwiete@uni-mainz.de; Finkel’stein, A. M.

2016-03-15

We study thermal conductivity in the disordered two-dimensional electron liquid in the presence of long-range Coulomb interactions. We describe a microscopic analysis of the problem using the partition function defined on the Keldysh contour as a starting point. We extend the renormalization group (RG) analysis developed for thermal transport in the disordered Fermi liquid and include scattering processes induced by the long-range Coulomb interaction in the sub-temperature energy range. For the thermal conductivity, unlike for the electrical conductivity, these scattering processes yield a logarithmic correction that may compete with the RG corrections. The interest in this correction arises from themore » fact that it violates the Wiedemann–Franz law. We checked that the sub-temperature correction to the thermal conductivity is not modified either by the inclusion of Fermi liquid interaction amplitudes or as a result of the RG flow. We therefore expect that the answer obtained for this correction is final. We use the theory to describe thermal transport on the metallic side of the metal–insulator transition in Si MOSFETs.« less

Anisotropic Fermi surface and quantum limit transport in high mobility three-dimensional Dirac semimetal Cd 3As 2

DOE PAGES

Zhao, Yanfei; Liu, Haiwen; Zhang, Chenglong; ...

2015-09-16

Three-dimensional (3D) topological Dirac semimetals have a linear dispersion in the 3D momentum space and are viewed as the 3D analogues of graphene. Here, we report angle dependent magnetotransport on the newly revealed Cd 3As 2 single crystals and clearly show how the Fermi surface evolves with crystallographic orientations. Remarkably, when the magnetic field lies in [112] or [44more » $$\\bar{1}$$] axis, magnetoresistance oscillations with only single period are present. However, the oscillation shows double periods when the field is applied along [1$$\\bar{1}$$0] direction. Moreover, aligning the magnetic field at certain directions also gives rise to double period oscillations. We attribute the observed anomalous oscillation behavior to the sophisticated geometry of Fermi surface and illustrate a complete 3D Fermi surfaces with two nested anisotropic ellipsoids around the Dirac points. Additionally, a sub-millimeter mean free path at 6 K is found in Cd 3As 2 crystals, indicating ballistic transport in this material. By measuring the magnetoresistance up to 60 T, we reach the quantum limit (n = 1 Landau level) at about 43 T. Lastly, these results improve the knowledge of the Dirac semimetal material Cd 3As 2, and also pave the way for proposing new electronic applications based on 3D Dirac materials.« less

Solution of effective Hamiltonian of impurity hopping between two sites in a metal

NASA Astrophysics Data System (ADS)

Ye, Jinwu

1998-03-01

We analyze in detail all the possible fixed points of the effective Hamiltonian of a non-magnetic impurity hopping between two sites in a metal obtained by Moustakas and Fisher(MF). We find a line of non-fermi liquid fixed points which continuously interpolates between the 2-channel Kondo fixed point(2CK) and the one channel, two impurity Kondo (2IK) fixed point. There is one relevant direction with scaling dimension 1/2 and one leading irrelevant operator with dimension 3/2. There is also one marginal operator in the spin sector moving along this line. The additional non-fermi liquid fixed point found by MF has the same symmetry as the 2IK, it has two relevant directions with scaling dimension 1/2, therefore also unstable. The system is shown to flow to a line of fermi-liquid fixed points which continuously interpolates between the non-interacting fixed point and the 2 channel spin-flavor Kondo fixed point (2CSFK) discussed by the author previously. The effect of particle-hole symmetry breaking is discussed. The effective Hamiltonian in the external magnetic field is analysed. The scaling functions for the physical measurable quantities are derived in the different regimes; their predictions for the experiments are given. Finally the implications are given for a non-magnetic impurity hopping around three sites with triangular symmetry discussed by MF.

Redox Electrocatalysis of Floating Nanoparticles: Determining Electrocatalytic Properties without the Influence of Solid Supports.

PubMed

Peljo, Pekka; Scanlon, Micheál D; Olaya, Astrid J; Rivier, Lucie; Smirnov, Evgeny; Girault, Hubert H

2017-08-03

Redox electrocatalysis (catalysis of electron-transfer reactions by floating conductive particles) is discussed from the point-of-view of Fermi level equilibration, and an overall theoretical framework is given. Examples of redox electrocatalysis in solution, in bipolar configuration, and at liquid-liquid interfaces are provided, highlighting that bipolar and liquid-liquid interfacial systems allow the study of the electrocatalytic properties of particles without effects from the support, but only liquid-liquid interfaces allow measurement of the electrocatalytic current directly. Additionally, photoinduced redox electrocatalysis will be of interest, for example, to achieve water splitting.

Effects of temporally persistent ant nests of soil protozoan communities and the abundance of morphological types of amoeba

USDA-ARS?s Scientific Manuscript database

We compared soil protozoan communities near ant nests with soil protozoans in reference soils 5m from the edge of any mounds. We sampled three species of Chihuahuan Desert ants that construct nests that persist for more than a decade: a seed harvester, Pogonomymex rugosus, a liquid feeding honey-po...

Theory of Fermi Liquid with Flat Bands

NASA Astrophysics Data System (ADS)

Khodel, V. A.

2018-04-01

A self-consistent theory of Fermi systems hosting flat bands is developed. Compared with an original model of fermion condensation, its key point consists in proper accounting for mixing between condensate and non-condensate degrees of freedom that leads to formation of a non-BCS gap Υ (p) in the single-particle spectrum. The results obtained explain: (1) the two-gap structure of spectra of single-particle excitations of electron systems of copper oxides, revealed in ARPES studies, (2) the role of violation of the topological stability of the Landau state in the arrangement of the T-x phase diagram of this family of high-T_c superconductors, (3) the topological nature of a metal-insulator transition, discovered in homogeneous two-dimensional low-density electron liquid of MOSFETs more than 20 years ago.

Interface Superconductivity in Cuprates Defies Fermi-Liquid Description

DOE PAGES

Radović, Zoran; Vanević, Mihajlo; Wu, Jie; ...

2016-07-26

La 2-xSr xCuO 4/La 2CuO 4 bilayers show interface superconductivity that originates from accumulation and depletion of mobile charge carriers across the interface. Surprisingly, the doping level can be varied broadly (within the interval 0.15 < x < 0.47) without affecting the transition temperature, which stays essentially constant and equal to that in optimally doped material, T c ≈ 40 K. Here we argue that this finding implies that doping up to the optimum level does not shift the chemical potential, unlike in ordinary Fermi liquids. Lastly, we discuss possible physical scenarios that can give doping-independent chemical potential in themore » pseudogap regime: electronic phase separation, formation of charge-density waves, strong Coulomb interactions, or self-trapping of mobile charge carriers.« less

Antiferromagnetic fluctuations in a quasi-two-dimensional organic superconductor detected by Raman spectroscopy.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drichko, Natalia; Hackl, Rudi; Schlueter, John A.

2015-10-15

Using Raman scattering, the quasi-two-dimensional organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br (T-c = 11.8 K) and the related antiferromagnet kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl are studied. Raman scattering provides unique spectroscopic information about magnetic degrees of freedom that has been otherwise unavailable on such organic conductors. Below T = 200 K a broad band at about 500 cm(-1) develops in both compounds. We identify this band with two-magnon excitation. The position and the temperature dependence of the spectral weight are similar in the antiferromagnet and in the metallic Fermi liquid. We conclude that antiferromagnetic correlations are similarly present in the magnetic insulator and the Fermi-liquid state ofmore » the superconductor.« less

Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations

NASA Astrophysics Data System (ADS)

Wang, Yi X.; Wu, Q.; Chen, Xiang R.; Geng, Hua Y.

2016-09-01

The pressure-induced transition of vanadium from BCC to rhombohedral structures is unique and intriguing among transition metals. In this work, the stability of these phases is revisited by using density functional theory. At finite temperatures, a novel transition of rhombohedral phases back to BCC phase induced by thermal electrons is discovered. This reentrant transition is found not driven by phonons, instead it is the electronic entropy that stabilizes the latter phase, which is totally out of expectation. Parallel to this transition, we find a peculiar and strong increase of the shear modulus C44 with increasing temperature. It is counter-intuitive in the sense that it suggests an unusual harding mechanism of vanadium by temperature. With these stability analyses, the high-pressure and finite-temperature phase diagram of vanadium is proposed. Furthermore, the dependence of the stability of RH phases on the Fermi energy and chemical environment is investigated. The results demonstrate that the position of the Fermi level has a significant impact on the phase stability, and follows the band-filling argument. Besides the Fermi surface nesting, we find that the localization/delocalization of the d orbitals also contributes to the instability of rhombohedral distortions in vanadium.

Stripe Antiferromagnetic Spin Fluctuations in SrCo 2As 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jayasekara, Wageesha; Lee, Young-Jin; Pandey, Abhishek

Inelastic neutron scattering measurements of paramagnetic SrCo 2As 2 at T = 5 K reveal antiferromagnetic (AFM) spin fluctuations that are peaked at a wave vector of Q AFM = (1/2, 1/2, 1) and possess a large energy scale. These stripe spin fluctuations are similar to those found in AFe 2As 2 compounds, where spin-density wave AFM is driven by Fermi surface nesting between electron and hole pockets separated by Q AFM. SrCo 2As 2 has a more complex Fermi surface and band-structure calculations indicate a potential instability toward either a ferromagnetic or stripe AFM ground state. The results suggestmore » that stripe AFM magnetism is a general feature of both iron and cobalt-based arsenides and the search for spin fluctuation-induced unconventional superconductivity should be expanded to include cobalt-based compounds.« less

Concurrence and fidelity of a Bose-Fermi mixture in a one-dimensional optical lattice.

PubMed

Ning, Wen-Qiang; Gu, Shi-Jian; Chen, Yu-Guang; Wu, Chang-Qin; Lin, Hai-Qing

2008-06-11

We study the ground-state fidelity and entanglement of a Bose-Fermi mixture loaded in a one-dimensional optical lattice. It is found that the fidelity is able to signal quantum phase transitions between the Luttinger liquid phase, the density-wave phase, and the phase separation state of the system, and the concurrence, as a measure of the entanglement, can be used to signal the transition between the density-wave phase and the Ising phase.

Toward the theory of fermionic condensation

NASA Astrophysics Data System (ADS)

Khodel, V. A.

2017-04-01

The diagrammatic technique elaborated by Belyaev for the theory of a Fermi liquid has been implemented to analyze the behavior of Fermi systems beyond the topological phase transition point, where the fermionic condensate appears. It has been shown that the inclusion of the interaction between the condensate and above-condensate particles leads to the emergence of a gap in the single-particle excitation spectrum of these particles even in the absence of Cooper pairing. Hence, the emergence of this gap in homogeneous electron systems of silicon field-effect structures leads to a metal-insulator phase transition rather than to superconductivity. It has been shown that the same interaction explains the nature of the Fermi arc structure in twodimensional electron systems of cuprates.

Three superconducting phases with different categories of pairing in hole- and electron-doped LaFeAs1 -xPxO

NASA Astrophysics Data System (ADS)

Miyasaka, S.; Uekubo, M.; Tsuji, H.; Nakajima, M.; Tajima, S.; Shiota, T.; Mukuda, H.; Sagayama, H.; Nakao, H.; Kumai, R.; Murakami, Y.

2017-06-01

The phase diagram of the LaFeAs1 -xPxO system has been extensively studied through hole and electron doping as well as As/P substitution. It has been revealed that there are three different superconducting phases with different Fermi surface (FS) topologies and thus with possibly different pairing glues. One of them is well understood as spin fluctuation-mediated superconductivity within a FS nesting scenario. Another one with the FSs in a bad nesting condition must be explained in a different context such as orbital or spin fluctuation in a strongly correlated electronic system. In both phases, T -linear resistivity was commonly observed when the superconducting transition temperature Tc becomes the highest value, indicating that the strength of bosonic fluctuation determines Tc. In the last superconducting phase, the nesting condition of FSs and the related bosonic fluctuation are moderate. Variety of phase diagram characterizes the multiple orbital nature of the iron-based superconductors which are just near the boundary between weak and strong correlation regimes.

Quantum oscillations in vortex-liquids

NASA Astrophysics Data System (ADS)

Banerjee, Sumilan; Zhang, Shizhong; Randeria, Mohit

2012-02-01

Motivated by observations of quantum oscillations in underdoped cuprates [1], we examine the electronic density of states (DOS) in a vortex-liquid state, where long-range phase coherence is destroyed by an external magnetic field H but the local pairing amplitude survives. We note that this regime is distinct from that studied in most of the recent theories, which have focused on either a Fermi liquid with a competing order parameter or on a d-wave vortex lattice. The cuprate experiments are very likely in a resistive vortex-liquid state. We generalize the s-wave analysis of Maki and Stephen [2] to d-wave pairing and examine various regimes of the chemical potential, gap and field. We find that the (1/H) oscillations of the DOS at the chemical potential in a d-wave vortex-liquid are much more robust, i.e., have a reduced damping, compared to the s-wave case. We critically investigate the conventional wisdom relating the observed frequency to the area of an underlying Fermi surface. We also show that the oscillations in the DOS cross over to a √H behavior in the low field limit, in agreement with the recent specific heat measurements. [1] L. Taillefer, J. Phys. Cond. Mat. 21, 164212 (2009). [2] M. J. Stephen, Phys. Rev. B 45, 5481 (1992).

Superfluid 3He—the Early Days

NASA Astrophysics Data System (ADS)

Lee, D. M.; Leggett, A. J.

2011-08-01

A history is given of liquid 3He research from the time when 3He first became available following World War II through 1972 when the discovery of the superfluid phases was made. The Fermi liquid nature was established early on, and the Landau Fermi liquid theory provided a framework for understanding the interactions between the Fermions (quasiparticles). The theory's main triumph was to predict zero sound, which was soon discovered experimentally. Experimental techniques are treated, including adiabatic demagnetization, dilution refrigerator technology, and Pomeranchuk cooling. A description of the superfluid 3He discovery experiments using the latter two of these techniques is given. While existing theories provided a basis for understanding the newly discovered superfluid phases in terms of ℓ>0 Cooper pairs, the unexpected stability of the A phase in the high- P, high- T region of the phase diagram needed for its explanation a creative leap beyond the BCS paradigm. The use of sum rules to interpret some of the unusual magnetic resonance in liquid 3He is discussed. Eventually a complete theory of the spin dynamics of superfluid 3He was developed, which predicted many of the exciting phenomena subsequently discovered.

Fermi energy dependence of the optical emission in core/shell InAs nanowire homostructures

NASA Astrophysics Data System (ADS)

Möller, M.; Oliveira, D. S.; Sahoo, P. K.; Cotta, M. A.; Iikawa, F.; Motisuke, P.; Molina-Sánchez, A.; de Lima, M. M., Jr.; García-Cristóbal, A.; Cantarero, A.

2017-07-01

InAs nanowires grown by vapor-liquid-solid (VLS) method are investigated by photoluminescence. We observe that the Fermi energy of all samples is reduced by ˜20 meV when the size of the Au nanoparticle used for catalysis is increased from 5 to 20 nm. Additional capping with a thin InP shell enhances the optical emission and does not affect the Fermi energy. The unexpected behavior of the Fermi energy is attributed to the differences in the residual donor (likely carbon) incorporation in the axial (low) and lateral (high incorporation) growth in the VLS and vapor-solid (VS) methods, respectively. The different impurity incorporation rate in these two regions leads to a core/shell InAs homostructure. In this case, the minority carriers (holes) diffuse to the core due to the built-in electric field created by the radial impurity distribution. As a result, the optical emission is dominated by the core region rather than by the more heavily doped InAs shell. Thus, the photoluminescence spectra and the Fermi energy become sensitive to the core diameter. These results are corroborated by a theoretical model using a self-consistent method to calculate the radial carrier distribution and Fermi energy for distinct diameters of Au nanoparticles.

Filling-enforced nonsymmorphic Kondo semimetals in two dimensions

NASA Astrophysics Data System (ADS)

Pixley, J. H.; Lee, SungBin; Brandom, B.; Parameswaran, S. A.

2017-08-01

We study the competition between Kondo screening and frustrated magnetism on the nonsymmorphic Shastry-Sutherland Kondo lattice at a filling of two conduction electrons per unit cell. This model is known to host a set of gapless partially Kondo screened phases intermediate between the Kondo-destroyed paramagnet and the heavy Fermi liquid. Based on crystal symmetries, we argue that (i) both the paramagnet and the heavy Fermi liquid are semimetals protected by a glide symmetry; and (ii) partial Kondo screening breaks the symmetry, removing this protection and allowing the partially Kondo screened phase to be deformed into a Kondo insulator via a Lifshitz transition. We confirm these results using large-N mean-field theory and then use nonperturbative arguments to derive a generalized Luttinger sum rule constraining the phase structure of two-dimensional nonsymmorphic Kondo lattices beyond the mean-field limit.

Bell pair creation in current of Kondo-correlated dot

NASA Astrophysics Data System (ADS)

Sakano, Rui; Oguri, Akira; Nishikawa, Yunori; Abe, Eisuke

Recently, local-Fermi-liquid properties in non-linear currents and shot noises through the Kondo dot have been investigated both theoretically and experimentally. We suggest a new entangled-electron-pair generator utilizing mechanism of quasiparticle-pair creation which has been observed as enhancement of shot noise in the quantum dot. Using the renormalized perturbation theory for an orbital-degenerate impurity Anderson model and the full counting statistics, we calculate the Clauser-Horne-Shimony-Holt type Bell's correlator for currents through correlated two different channels of a Kondo correlated dot. It is shown that residual exchange-interactions of the local-Fermi-liquid create spin-entangled quasiparticle-pairs in nonlinear current and this results in violation of the Bell's inequality. This work was partially supported by JSPS KAKENHI Grant Numbers JP26220711, JP26400319, JP15K05181 and JP16K17723.

Non-Fermi Liquid Behavior and Continuously Tunable Resistivity Exponents in the Anderson-Hubbard Model at Finite Temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patel, Niravkumar D.; Mukherjee, Anamitra; Kaushal, Nitin

Here, we employ a recently developed computational many-body technique to study for the first time the half-filled Anderson-Hubbard model at finite temperature and arbitrary correlation U and disorder V strengths. Interestingly, the narrow zero temperature metallic range induced by disorder from the Mott insulator expands with increasing temperature in a manner resembling a quantum critical point. Our study of the resistivity temperature scaling T α for this metal reveals non-Fermi liquid characteristics. Moreover, a continuous dependence of α on U and V from linear to nearly quadratic is observed. We argue that these exotic results arise from a systematic changemore » with U and V of the “effective” disorder, a combination of quenched disorder and intrinsic localized spins.« less

Information scrambling at an impurity quantum critical point

NASA Astrophysics Data System (ADS)

Dóra, Balázs; Werner, Miklós Antal; Moca, Cǎtǎlin Paşcu

2017-10-01

The two-channel Kondo impurity model realizes a local non-Fermi-liquid state with finite residual entropy. The competition between the two channels drives the system to an impurity quantum critical point. We show that the out-of-time-ordered (OTO) commutator for the impurity spin reveals markedly distinct behavior depending on the low-energy impurity state. For the one-channel Kondo model with Fermi-liquid ground state, the OTO commutator vanishes for late times, indicating the absence of the butterfly effect. For the two channel case, the impurity OTO commutator is completely temperature independent and saturates quickly to its upper bound 1/4, and the butterfly effect is maximally enhanced. These compare favorably to numerics on spin chain representation of the Kondo model. Our results imply that a large late time value of the OTO commutator does not necessarily diagnose quantum chaos.

Many-body interactions in quasi-freestanding graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siegel, David; Park, Cheol-Hwan; Hwang, Choongyu

2011-06-03

The Landau-Fermi liquid picture for quasiparticles assumes that charge carriers are dressed by many-body interactions, forming one of the fundamental theories of solids. Whether this picture still holds for a semimetal such as graphene at the neutrality point, i.e., when the chemical potential coincides with the Dirac point energy, is one of the long-standing puzzles in this field. Here we present such a study in quasi-freestanding graphene by using high-resolution angle-resolved photoemission spectroscopy. We see the electron-electron and electron-phonon interactions go through substantial changes when the semimetallic regime is approached, including renormalizations due to strong electron-electron interactions with similarities tomore » marginal Fermi liquid behavior. These findings set a new benchmark in our understanding of many-body physics in graphene and a variety of novel materials with Dirac fermions.« less

Zero-field quantum critical point in Ce0.91Yb0.09CoIn5

NASA Astrophysics Data System (ADS)

Singh, Y. P.; Adhikari, R. B.; Haney, D. J.; White, B. D.; Maple, M. B.; Dzero, M.; Almasan, C. C.

2018-05-01

We present results of specific heat, electrical resistance, and magnetoresistivity measurements on single crystals of the heavy-fermion superconducting alloy Ce0.91Yb0.09CoIn5 . Non-Fermi-liquid to Fermi-liquid crossovers are clearly observed in the temperature dependence of the Sommerfeld coefficient γ and resistivity data. Furthermore, we show that the Yb-doped sample with x =0.09 exhibits universality due to an underlying quantum phase transition without an applied magnetic field by utilizing the scaling analysis of γ . Fitting of the heat capacity and resistivity data based on existing theoretical models indicates that the zero-field quantum critical point is of antiferromagnetic origin. Finally, we found that at zero magnetic field the system undergoes a third-order phase transition at the temperature Tc 3≈7 K.

Hidden Fermi liquid: Self-consistent theory for the normal state of high-Tc superconductors

NASA Astrophysics Data System (ADS)

Casey, Philip A.

The anomalous "strange metal" properties of the normal, non-superconducting state of the high-Tc cuprate superconductors have been extensively studied for over two decades. The resistivity is robustly T-linear at high temperatures, while at low T it appears to maintain linearity near optimal doping and is T2 at higher doping. The inverse Hall angle is strictly T2 and hence has a distinct scattering lifetime from the resistivity. The transport scattering lifetime is highly anisotropic as directly measured by angle-dependent magnetoresistance (ADMR) and indirectly in more traditional transport experiments. The IR conductivity exhibits a non-integer power-law in frequency, which we take as a defining characteristic of the "strange metal". A phenomenological theory of the transport and spectroscopic properties at a self-consistent and predictive level has been much sought after, yet elusive. Hidden Fermi liquid theory (HFL) explicitly accounts for the effects of Gutzwiller projection in the t-J Hamiltonian, widely believed to contain the essential physics of the high-Tc superconductors. We show this theory to be the first self-consistent description for the normal state of the cuprates based on transparent, fundamental assumptions. Our well-defined formalism also serves as a guide for further experimental confirmation. Chapter 1 reviews the "strange metal" properties and the relevant aspects of competing models. Chapter 2 presents the theoretical foundations of the formalism. Chapters 3 and 4 derive expressions for the entire normal state relating many of the properties, for example: angle-resolved photoemission, IR conductivity, resistivity, Hall angle, and by generalizing the formalism to include the Fermi surface topology---ADMR. Self-consistency is demonstrated with experimental comparisons, including the most recent laser-ARPES and ADMR. Chapter 5 discusses entropy transport, as in the thermal conductivity, thermal Hall conductivity, and consequent metrics of non-Fermi liquid behavior such as the Wiedemann-Franz and Kadowaki-Woods ratios.

Multiple charge density wave states at the surface of TbT e 3

DOE PAGES

Fu, Ling; Kraft, Aaron M.; Sharma, Bishnu; ...

2016-11-01

We studied TbTe 3 using scanning tunneling microscopy (STM) in the temperature range of 298–355 K. Our measurements detect a unidirectional charge density wave (CDW) state in the surface Te layer with a wave vector consistent with that of the bulk q CDW = 0.30 ± 0.01c*. However, unlike previous STM measurements, and differing from measurements probing the bulk, we detect two perpendicular orientations for the unidirectional CDW with no directional preference for the in-plane crystal axes (a or c axis) and no noticeable difference in wave vector magnitude. In addition, we find regions in which the bidirectional CDW statesmore » coexist. We propose that observation of two unidirectional CDW states indicates a decoupling of the surface Te layer from the rare-earth block layer below, and that strain variations in the Te surface layer drive the local CDW direction to the specific unidirectional or, in rare occurrences, bidirectional CDW orders observed. This indicates that similar driving mechanisms for CDW formation in the bulk, where anisotropic lattice strain energy is important, are at play at the surface. Furthermore, the wave vectors for the bidirectional order we observe differ from those theoretically predicted for checkerboard order competing with stripe order in a Fermi-surface nesting scenario, suggesting that factors beyond Fermi-surface nesting drive CDW order in TbTe 3. As a result, our temperature-dependent measurements provide evidence for localized CDW formation above the bulk transition temperature T CDW.« less

Quadratic Fermi node in a 3D strongly correlated semimetal

PubMed Central

Kondo, Takeshi; Nakayama, M.; Chen, R.; Ishikawa, J. J.; Moon, E.-G.; Yamamoto, T.; Ota, Y.; Malaeb, W.; Kanai, H.; Nakashima, Y.; Ishida, Y.; Yoshida, R.; Yamamoto, H.; Matsunami, M.; Kimura, S.; Inami, N.; Ono, K.; Kumigashira, H.; Nakatsuji, S.; Balents, L.; Shin, S.

2015-01-01

Strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour is predicted, for which we observe some evidence. Our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states. PMID:26640114

Gyrotropic Magnetic Effect and the Magnetic Moment on the Fermi Surface.

PubMed

Zhong, Shudan; Moore, Joel E; Souza, Ivo

2016-02-19

The current density j^{B} induced in a clean metal by a slowly-varying magnetic field B is formulated as the low-frequency limit of natural optical activity, or natural gyrotropy. Working with a multiband Pauli Hamiltonian, we obtain from the Kubo formula a simple expression for α_{ij}^{GME}=j_{i}^{B}/B_{j} in terms of the intrinsic magnetic moment (orbital plus spin) of the Bloch electrons on the Fermi surface. An alternate semiclassical derivation provides an intuitive picture of the effect, and takes into account the influence of scattering processes in dirty metals. This "gyrotropic magnetic effect" is fundamentally different from the chiral magnetic effect driven by the chiral anomaly and governed by the Berry curvature on the Fermi surface, and the two effects are compared for a minimal model of a Weyl semimetal. Like the Berry curvature, the intrinsic magnetic moment should be regarded as a basic ingredient in the Fermi-liquid description of transport in broken-symmetry metals.

Gyrotropic Magnetic Effect and the Magnetic Moment on the Fermi Surface

NASA Astrophysics Data System (ADS)

Zhong, Shudan; Moore, Joel E.; Souza, Ivo

2016-02-01

The current density jB induced in a clean metal by a slowly-varying magnetic field B is formulated as the low-frequency limit of natural optical activity, or natural gyrotropy. Working with a multiband Pauli Hamiltonian, we obtain from the Kubo formula a simple expression for αij GME=jiB/Bj in terms of the intrinsic magnetic moment (orbital plus spin) of the Bloch electrons on the Fermi surface. An alternate semiclassical derivation provides an intuitive picture of the effect, and takes into account the influence of scattering processes in dirty metals. This "gyrotropic magnetic effect" is fundamentally different from the chiral magnetic effect driven by the chiral anomaly and governed by the Berry curvature on the Fermi surface, and the two effects are compared for a minimal model of a Weyl semimetal. Like the Berry curvature, the intrinsic magnetic moment should be regarded as a basic ingredient in the Fermi-liquid description of transport in broken-symmetry metals.

Field-induced spin-density-wave phases in (TMTSF)2 Cl O4 at high magnetic field: Effect of anion ordering

NASA Astrophysics Data System (ADS)

Haddad, S.; Charfi-Kaddour, S.; Héritier, M.; Bennaceur, R.

2005-08-01

We study the high magnetic field-induced spin-density-wave (FISDW) phases of the relaxed (TMTSF)2ClO4 salt. Due to an orientational ordering of the ClO4 anions, a gap opens at the Fermi surface leading to a two band energy spectrum. We go through the different experimental and theoretical results related to the high field regime of the (TMTSF)2ClO4 phase diagram. We show that, in spite of intensive studies, this phase diagram is still the subject of controversies. We then tackle the issue of analyzing the exotic features of the high field spin-density-wave (SDW) phases. Based on a mean field theory and a renormalization group method, we study the consequences of anion ordering on the stability of the FISFW phases. We show that the presence of a two pairs of Fermi surface gives rise to two types of competing SDW phases. One is due to a single interband nesting process, as in a one band model, while the second originates from two intraband nesting vectors. The latter, for which we derive a generalized instability criterion, has the highest metal-SDW transition temperature and is described by two coexisting order parameters. As the temperature decreases, this coexistence puts at disadvantage the corresponding phase. Eventually, a first order transition takes place to a second SDW phase characterized by a single nesting vector and which appears inside the first one. Within the proposed model, we are able to label the different SDW phases with definite quantum numbers N related to the quantum Hall effect. We argue that the first SDW phase is nothing but the N=0 state whereas the inner phase is the N=1 state. The obtained results are consistent with recent experiments.

Role of degeneracy, hybridization, and nesting in the properties of multiorbital systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nicholson, Andrew D; Liu, Jia-Ming; Ge, Weihao

2011-01-01

To understand the role that degeneracy, hybridization, and nesting play in the magnetic and pairing properties of multiorbital Hubbard models we here study numerically two types of two-orbital models, both with holelike and electron-like Fermi surfaces (FS s) that are related by nesting vectors ( ,0) and (0, ). In one case the bands that determine the FS s arise from strongly hybridized degenerate dxz and dyz orbitals, while in the other the two bands are determined by nondegenerate and nonhybridized s-like orbitals. Using a variety of techniques, in the weak-coupling regime it is shown that only the model withmore » hybridized bands develops metallic magnetic order, while the other model exhibits an ordered excitonic orbital-transverse spin state that is insulating and does not have a local magnetization. However, both models display similar insulating magnetic stripe ordering in the strong-coupling limit. These results indicate that nesting is a necessary but not sufficient condition for the development of ordered states with finite local magnetization in multiorbital Hubbard systems; the additional ingredient appears to be that the nested portions of the bands need to have the same orbital flavor. This condition can be achieved via strong hybridization of the orbitals in weak coupling or via the FS reconstruction induced by the Coulomb interactions in the strong-coupling regime. This effect also affects the pairing symmetry as demonstrated by the study of the dominant pairing channels for the two models.« less

Exotic Quantum Phases and Phase Transitions of Strongly Interacting Electrons in Low-Dimensional Systems

NASA Astrophysics Data System (ADS)

Mishmash, Ryan V.

Experiments on strongly correlated quasi-two-dimensional electronic materials---for example, the high-temperature cuprate superconductors and the putative quantum spin liquids kappa-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2---routinely reveal highly mysterious quantum behavior which cannot be explained in terms of weakly interacting degrees of freedom. Theoretical progress thus requires the introduction of completely new concepts and machinery beyond the traditional framework of the band theory of solids and its interacting counterpart, Landau's Fermi liquid theory. In full two dimensions, controlled and reliable analytical approaches to such problems are severely lacking, as are numerical simulations of even the simplest of model Hamiltonians due to the infamous fermionic sign problem. Here, we attempt to circumvent some of these difficulties by studying analogous problems in quasi-one dimension. In this lower dimensional setting, theoretical and numerical tractability are on much stronger footing due to the methods of bosonization and the density matrix renormalization group, respectively. Using these techniques, we attack two problems: (1) the Mott transition between a Fermi liquid metal and a quantum spin liquid as potentially directly relevant to the organic compounds kappa-(BEDT-TTF)2Cu 2(CN)3 and EtMe3Sb[Pd(dmit)2] 2 and (2) non-Fermi liquid metals as strongly motivated by the strange metal phase observed in the cuprates. In both cases, we are able to realize highly exotic quantum phases as ground states of reasonable microscopic models. This lends strong credence to respective underlying slave-particle descriptions of the low-energy physics, which are inherently strongly interacting and also unconventional in comparison to weakly interacting alternatives. Finally, working in two dimensions directly, we propose a new slave-particle theory which explains in a universal way many of the intriguing experimental results of the triangular lattice organic spin liquid candidates kappa-(BEDT-TTF) 2Cu2(CN)3 and EtMe3Sb[Pd(dmit) 2]2. With use of large-scale variational Monte Carlo calculations, we show that this new state has very competitive trial energy in an effective spin model thought to describe the essential features of the real materials.

Itinerancy enhanced quantum fluctuation of magnetic moments in iron-based superconductors

DOE PAGES

Tam, Yu -T.; Ku, W.; Yao, D. -X.

2015-09-10

We investigate the influence of itinerant carriers on dynamics and fluctuation of local moments in Fe-based superconductors, via linear spin-wave analysis of a spin-fermion model containing both itinerant and local degrees of freedom. Surprisingly against the common lore, instead of enhancing the (π,0) order, itinerant carriers with well nested Fermi surfaces is found to induce significant amount of spatial and temporal quantum fluctuation that leads to the observed small ordered moment. Interestingly, the underlying mechanism is shown to be intra-pocket nesting-associated long-range coupling, rather than the previously believed ferromagnetic double-exchange effect. This challenges the validity of ferromagnetically compensated first-neighbor couplingmore » reported from short-range fitting to the experimental dispersion, which turns out to result instead from the ferro-orbital order that is also found instrumental in stabilizing the magnetic order.« less

Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi3 (A = Sr and Ba)

PubMed Central

Shao, D. F.; Luo, X.; Lu, W. J.; Hu, L.; Zhu, X. D.; Song, W. H.; Zhu, X. B.; Sun, Y. P.

2016-01-01

Recently, Bi-based compounds have attracted attentions because of the strong spin-orbit coupling (SOC). In this work, we figured out the role of SOC in ABi3 (A = Sr and Ba) by theoretical investigation of the band structures, phonon properties, and electron-phonon coupling. Without SOC, strong Fermi surface nesting leads to phonon instabilities in ABi3. SOC suppresses the nesting and stabilizes the structure. Moreover, without SOC the calculation largely underestimates the superconducting transition temperatures (Tc), while with SOC the calculated Tc are very close to those determined by measurements on single crystal samples. The SOC enhanced superconductivity in ABi3 is due to not only the SOC induced phonon softening, but also the SOC related increase of electron-phonon coupling matrix elements. ABi3 can be potential platforms to construct heterostructure of superconductor/topological insulator to realize topological superconductivity. PMID:26892681

Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi₃ (A = Sr and Ba).

PubMed

Shao, D F; Luo, X; Lu, W J; Hu, L; Zhu, X D; Song, W H; Zhu, X B; Sun, Y P

2016-02-19

Recently, Bi-based compounds have attracted attentions because of the strong spin-orbit coupling (SOC). In this work, we figured out the role of SOC in ABi3 (A = Sr and Ba) by theoretical investigation of the band structures, phonon properties, and electron-phonon coupling. Without SOC, strong Fermi surface nesting leads to phonon instabilities in ABi3. SOC suppresses the nesting and stabilizes the structure. Moreover, without SOC the calculation largely underestimates the superconducting transition temperatures (Tc), while with SOC the calculated Tc are very close to those determined by measurements on single crystal samples. The SOC enhanced superconductivity in ABi3 is due to not only the SOC induced phonon softening, but also the SOC related increase of electron-phonon coupling matrix elements. ABi3 can be potential platforms to construct heterostructure of superconductor/topological insulator to realize topological superconductivity.

Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations

PubMed Central

Wang, Yi X.; Wu, Q.; Chen, Xiang R.; Geng, Hua Y.

2016-01-01

The pressure-induced transition of vanadium from BCC to rhombohedral structures is unique and intriguing among transition metals. In this work, the stability of these phases is revisited by using density functional theory. At finite temperatures, a novel transition of rhombohedral phases back to BCC phase induced by thermal electrons is discovered. This reentrant transition is found not driven by phonons, instead it is the electronic entropy that stabilizes the latter phase, which is totally out of expectation. Parallel to this transition, we find a peculiar and strong increase of the shear modulus C44 with increasing temperature. It is counter-intuitive in the sense that it suggests an unusual harding mechanism of vanadium by temperature. With these stability analyses, the high-pressure and finite-temperature phase diagram of vanadium is proposed. Furthermore, the dependence of the stability of RH phases on the Fermi energy and chemical environment is investigated. The results demonstrate that the position of the Fermi level has a significant impact on the phase stability, and follows the band-filling argument. Besides the Fermi surface nesting, we find that the localization/delocalization of the d orbitals also contributes to the instability of rhombohedral distortions in vanadium. PMID:27581551

Spin–orbit coupling, minimal model and potential Cooper-pairing from repulsion in BiS2-superconductors

NASA Astrophysics Data System (ADS)

Cobo-Lopez, Sergio; Saeed Bahramy, Mohammad; Arita, Ryotaro; Akbari, Alireza; Eremin, Ilya

2018-04-01

We develop the realistic minimal electronic model for recently discovered BiS2 superconductors including the spin–orbit (SO) coupling based on the first-principles band structure calculations. Due to strong SO coupling, characteristic for the Bi-based systems, the tight-binding low-energy model necessarily includes p x , p y , and p z orbitals. We analyze a potential Cooper-pairing instability from purely repulsive interaction for the moderate electronic correlations using the so-called leading angular harmonics approximation. For small and intermediate doping concentrations we find the dominant instabilities to be {d}{x2-{y}2}-wave, and s ±-wave symmetries, respectively. At the same time, in the absence of the sizable spin fluctuations the intra and interband Coulomb repulsions are of the same strength, which yield the strongly anisotropic behavior of the superconducting gaps on the Fermi surface. This agrees with recent angle resolved photoemission spectroscopy findings. In addition, we find that the Fermi surface topology for BiS2 layered systems at large electron doping can resemble the doped iron-based pnictide superconductors with electron and hole Fermi surfaces maintaining sufficient nesting between them. This could provide further boost to increase T c in these systems.

Evolution and Control of Electronic Structures near the Interface of Complex Oxide Heterostructure SmTiO3/SrTiO3

NASA Astrophysics Data System (ADS)

Mori, Ryo; Marshall, Patrick; Isaac, Brandon; Denlinger, Jonathan; Stemmer, Susanne; Lanzara, Alessandra

The confined electron system in the quantum well of the transition metal oxide, SrTiO3, embedded in the rare earth titanate, SmTiO3, shows unique properties, such as high carrier density, fermi liquid to non-fermi liquid transition, and pseudo-gap, which can be controlled by changing the shape of the quantum well. We will present a distinct difference in the electronic structures between the different quantum well structures obtained by angle-resolved photoemission spectroscopy (ARPES) measurements, suggesting the possibility to control the orbital character and the electron correlation near the interface as well as carrier density. The work was supported by the Quantum Materials Program at LBNL, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231.

Low-Energy Electronic Properties of Clean CaRuO3: Elusive Landau Quasiparticles

NASA Astrophysics Data System (ADS)

Schneider, M.; Geiger, D.; Esser, S.; Pracht, U. S.; Stingl, C.; Tokiwa, Y.; Moshnyaga, V.; Sheikin, I.; Mravlje, J.; Scheffler, M.; Gegenwart, P.

2014-05-01

We have prepared high-quality epitaxial thin films of CaRuO3 with residual resistivity ratios up to 55. Shubnikov-de Haas oscillations in the magnetoresistance and a T2 temperature dependence in the electrical resistivity only below 1.5 K, the coefficient of which is substantially suppressed in large magnetic fields, establish CaRuO3 as a Fermi liquid (FL) with an anomalously low coherence scale. At T >1.5 K non-Fermi-liquid (NFL) behavior is found in the electrical resistivity. The high sample quality allows access to the intrinsic electronic properties via THz spectroscopy. For frequencies below 0.6 THz, the conductivity is Drude-like and can be modeled by FL concepts; for higher frequencies, non-Drude behavior is found, which is inconsistent with FL predictions. This establishes CaRuO3 as a prime example of optical NFL behavior in the THz range.

Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2.

PubMed

Dong, J K; Zhou, S Y; Guan, T Y; Zhang, H; Dai, Y F; Qiu, X; Wang, X F; He, Y; Chen, X H; Li, S Y

2010-02-26

The in-plane resistivity rho and thermal conductivity kappa of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior rho(T) approximately T{1.5} at H{c{2}}=5 T, and the development of a Fermi liquid state with rho(T) approximately T{2} when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field H{c{2}}. In zero field, there is a large residual linear term kappa{0}/T, and the field dependence of kappa_{0}/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.

Angular dependence of novel magnetic quantum oscillations in a quasi-two-dimensional multiband Fermi liquid with impurities

NASA Astrophysics Data System (ADS)

Bratkovsky, A. M.; Alexandrov, A. S.

2002-03-01

The semiclassical Lifshitz-Kosevich-type description is given for the angular dependence of quantum oscillations with combination frequencies in a multiband quasi-two-dimensional Fermi liquid with a constant number of electrons. The analytical expressions are found for the Dingle, thermal, spin, and amplitude (Yamaji) reduction factors of the novel combination harmonics, where the latter two strongly oscillate with the direction of the field [1]. At the magic angles those factors reduce to the purely two-dimensional expressions given earlier. The combination harmonics are suppressed in the presence of the nonquantized background states, and they decay exponentially faster with temperature and/or disorder compared to the standard harmonics, providing an additional tool for electronic structure determination. The theory is applied to Sr2RuO4. [1] A.M. Bratkovsky and A.S. Alexandrov, Phys. Rev. B 65, xxxx (2002); cond-mat/0104520.

Violation of Ohm's law in a Weyl metal.

PubMed

Shin, Dongwoo; Lee, Yongwoo; Sasaki, M; Jeong, Yoon Hee; Weickert, Franziska; Betts, Jon B; Kim, Heon-Jung; Kim, Ki-Seok; Kim, Jeehoon

2017-11-01

Ohm's law is a fundamental paradigm in the electrical transport of metals. Any transport signatures violating Ohm's law would give an indisputable fingerprint for a novel metallic state. Here, we uncover the breakdown of Ohm's law owing to a topological structure of the chiral anomaly in the Weyl metal phase. We observe nonlinear I-V characteristics in Bi 0.96 Sb 0.04 single crystals in the diffusive limit, which occurs only for a magnetic-field-aligned electric field (E∥B). The Boltzmann transport theory with the charge pumping effect reveals the topological-in-origin nonlinear conductivity, and it leads to a universal scaling function of the longitudinal magnetoconductivity, which completely describes our experimental results. As a hallmark of Weyl metals, the nonlinear conductivity provides a venue for nonlinear electronics, optical applications, and the development of a topological Fermi-liquid theory beyond the Landau Fermi-liquid theory.

Zero-Field Ambient-Pressure Quantum Criticality in the Stoichiometric Non-Fermi Liquid System CeRhBi

NASA Astrophysics Data System (ADS)

Anand, Vivek K.; Adroja, Devashibhai T.; Hillier, Adrian D.; Shigetoh, Keisuke; Takabatake, Toshiro; Park, Je-Geun; McEwen, Keith A.; Pixley, Jedediah H.; Si, Qimiao

2018-06-01

We present the spin dynamics study of a stoichiometric non-Fermi liquid (NFL) system CeRhBi, using low-energy inelastic neutron scattering (INS) and muon spin relaxation (μSR) measurements. It shows evidence for an energy-temperature (E/T) scaling in the INS dynamic response and a time-field (t/Hη) scaling of the μSR asymmetry function indicating a quantum critical behavior in this compound. The E/T scaling reveals a local character of quantum criticality consistent with the power-law divergence of the magnetic susceptibility, logarithmic divergence of the magnetic heat capacity and T-linear resistivity at low temperature. The occurrence of NFL behavior and local criticality over a very wide dynamical range at zero field and ambient pressure without any tuning in this stoichiometric heavy fermion compound is striking, making CeRhBi a model system amenable to in-depth studies for quantum criticality.

Distinct nature of orbital-selective Mott phases dominated by low-energy local spin fluctuations

NASA Astrophysics Data System (ADS)

Song, Ze-Yi; Jiang, Xiu-Cai; Lin, Hai-Qing; Zhang, Yu-Zhong

2017-12-01

Quantum orbital-selective Mott (OSM) transitions are investigated within dynamical mean-field theory based on a two-orbital Hubbard model with different bandwidth at half filling. We find two distinct OSM phases both showing coexistence of itinerant electrons and localized spins, dependent on whether the Hund's coupling is full or of Ising type. The critical values and the nature of the OSM transitions are efficiently determined by entanglement entropy. We reveal that vanishing of the Kondo energy scale evidenced by absence of local spin fluctuations at low frequency in local dynamical spin susceptibility is responsible for the appearance of non-Fermi-liquid OSM phase in Ising Hund's coupling case. We argue that this scenario can also be applied to account for emergent quantum non-Fermi liquid in the one-band Hubbard model when short-range antiferromagnetic order is considered.

Evidence for a New Intermediate Phase in a Strongly Correlated 2D System near Wigner Crystallization

NASA Astrophysics Data System (ADS)

Gao, Xuan; Qiu, Richard; Goble, Nicholas; Serafin, Alex; Yin, Liang; Xia, Jian-Sheng; Sullivan, Neil; Pfeiffer, Loren; West, Ken

How the two dimensional (2D) quantum Wigner crystal (WC) transforms into the metallic liquid phase remains an outstanding problem in physics. In theories considering the 2D WC to liquid transition in the clean limit, it was suggested that a number of intermediate phases might exist. We have studied the transformation between the metallic fluid phase and the low magnetic field reentrant insulating phase (RIP) which was interpreted as due to the WC [Qiu et al., PRL 108, 106404 (2012)], in a strongly correlated 2D hole system in GaAs quantum well with large interaction parameter rs (~20-30) and high mobility. Instead of a sharp transition, we found that increasing density (or lowering rs) drives the RIP into a state where the incipient RIP coexists with Fermi liquid. This apparent mixture phase intermediate between Fermi liquid and WC also exhibits a non-trivial temperature dependent resistivity behavior which can be qualitatively understood by the reversed melting of WC in the mixture, in analogy to the Pomeranchuk effect in the solid-liquid mixture of Helium-3. X.G. thanks NSF (DMR-0906415) for supporting work at CWRU. Experiments at the NHMFL High B/T Facility were supported by NSF Grant 0654118 and the State of Florida. L.P. thanks the Gordon and Betty Moore Foundation and NSF MRSEC (DMR-0819860) for support.

Spectroscopic views of high-Tc superconductors

NASA Astrophysics Data System (ADS)

Wendin, Göran

1989-01-01

Recent progress in the fields of photoelectron spectroscopy, electron energy loss spectroscopy, inverse photoemission, and infrared- and optical reflectivity applied to high-Tc superconductors is analyzed in terms of correlation effects, transport properties and Fermi liquid behaviour. For the CuO2 based materials, a picture emerges of localized holes in copper 3d levels and itinerant holes in oxygen 2p-like bands. A Fermi liquid picture and a superconducting gap is indicated by angle-resolved photo-emission, infrared absorption, and NMR. A Fermi surface is indicated by positron annihilation. Infrared absorption reveals strongly frequency and temperature dependent scattering and polaronic behaviour for frequencies below 0.1 eV. Infrared absorption indicates a maximum superconducting gap of 2Δ/kBTc = 8 and suggests that ordinary samples may show a range of gaps 2 < 2Δ/kBTc < 8 resulting in commonly measured average values of 2Δ/kBTc = 5. An interesting possibility in YBaCuO, suggested by infrared reflectivity and photoconductivity measurements, is that polarons in the CuO2 planes with 0.13 eV excitation energy mediate an attractive interaction between quasi-holes in O 2p-derived conduction bands. The polarons will involve important lattice distortions even if, as is frequently assumed, magnetic polaron effects may be the essential thing.

Evolution of Quasiparticle Excitations in a Doped Hubbard Model

NASA Astrophysics Data System (ADS)

Hess, D. W.; Deisz, J. J.; Serene, J. W.

1997-03-01

Self-consistent calculations in the fluctuation exchange approximation for the 2D Hubbard model at half-filling show the evolution of anomalous structure in the self-energy at low energy with decreasing temperature. This structure is inconsistent with a Fermi liquid interpretation of evolving quasiparticle excitations.(J.J. Deisz, D.W. Hess, J.W. Serene, Phys. Rev. Lett. 76), 1312 (1996). Here we present calculations for a doped 2D Hubbard model with U=4t, n = 0.87 and for temperatures down to ~ 0.01t. Unlike the self-energy of the half-filled case, the slope of Re Σ(k_F, \\varepsilon) remains negative and | Im Σ(k_F, \\varepsilon)| shows no anomalous structure and is roughly parabolic at low energy with a very small magnitude at \\varepsilon = 0. In contrast to the `shadows' of antiferromagnetic order observed for half-filling, structure observed in the single-particle spectral function for momenta not on the Fermi surface are consistent with the characteristic depression at \\varepsilon =0 expected for an evolving Fermi liquid.(See e.g.) P.G. Mc Queen, D.W. Hess, J.W. Serene, Phys. Rev. Lett. 71, 129 (1993). No anomalous structure associated with incipient antiferromagnetic order is evident in the momentum distribution function.

Luttinger theorem and imbalanced Fermi systems

NASA Astrophysics Data System (ADS)

Pieri, Pierbiagio; Strinati, Giancarlo Calvanese

2017-04-01

The proof of the Luttinger theorem, which was originally given for a normal Fermi liquid with equal spin populations formally described by the exact many-body theory at zero temperature, is here extended to an approximate theory given in terms of a "conserving" approximation also with spin imbalanced populations. The need for this extended proof, whose underlying assumptions are here spelled out in detail, stems from the recent interest in superfluid trapped Fermi atoms with attractive inter-particle interaction, for which the difference between two spin populations can be made large enough that superfluidity is destroyed and the system remains normal even at zero temperature. In this context, we will demonstrate the validity of the Luttinger theorem separately for the two spin populations for any "Φ-derivable" approximation, and illustrate it in particular for the self-consistent t-matrix approximation.

Dimensional crossover and thermoelectric properties in CeTe2-xSbx single crystals

NASA Astrophysics Data System (ADS)

Rhyee, Jong-Soo; Lee, Kyung Eun; Nyeong Kim, Jae; Shim, Ji Hoon; Min, Byeong Hun; Kwon, Yong Seung

2013-03-01

Several years before, we proposed that the charge density wave is a new pathway for high thermoelectric performance in In4Se3-x bulk crystalline materials. (Nature v.459, p. 965, 2009) Recently, from the increase of the chemical potential by halogen doped In4Se3-xH0.03 (H =Halogen elements) crystals, we achieved high ZT (maximum ZT 1.53) over a wide temperature range. (Adv. Mater. v.23, p.2191, 2011) Here we demonstrate the low dimensionality increases power factor in CeTe2-xSbx single crystals. The band structures of CeTe2 show the 2-dimensional (2D) Fermi surface nesting behavior as well as a 3-dimensional (3D) electron Fermi surface hindering the perfect charge density wave (CDW) gap opening. By hole doping with the substitution of Sb at the Te-site, the 3D-like Fermi surface disappears and the 2D perfect CDW gap opening enhances the power factor up to x = 0.1. With further hole doping, the Fermi surfaces become 3-dimensional structure with heavy hole bands. The enhancement of the power factor is observed near the dimensional crossover of CDW, at x = 0.1, where the CDW gap is maximized. This research was supported by Basic Science Research Program (2011-0021335), Mid-career Research Program (Strategy) (No. 2012R1A2A1A03005174) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology, and TJ Park Junior Faculty Fellowship funded by the POSCO TJ Park Foundation.

Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2 H – NbSe 2

DOE PAGES

Arguello, C. J.; Rosenthal, E. P.; Andrade, E. F.; ...

2015-01-21

We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe₂ that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe₂. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiologymore » and the interactions. In 2H-NbSe₂, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector.« less

Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H-NbSe2.

PubMed

Arguello, C J; Rosenthal, E P; Andrade, E F; Jin, W; Yeh, P C; Zaki, N; Jia, S; Cava, R J; Fernandes, R M; Millis, A J; Valla, T; Osgood, R M; Pasupathy, A N

2015-01-23

We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe2 that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe2. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe2, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector.

Entanglement in 3D Kitaev spin liquids

NASA Astrophysics Data System (ADS)

Matern, S.; Hermanns, M.

2018-06-01

Quantum spin liquids are highly fascinating quantum liquids in which the spin degrees of freedom fractionalize. An interesting class of spin liquids are the exactly solvable, three-dimensional Kitaev spin liquids. Their fractionalized excitations are Majonara fermions, which may exhibit a variety of topological band structures—ranging from topologically protected Weyl semi-metals over nodal semi-metals to systems with Majorana Fermi surfaces. We study the entanglement spectrum of such Kitaev spin liquids and verify that it is closely related to the topologically protected edge spectrum. Moreover, we find that in some cases the entanglement spectrum contains even more information about the topological features than the surface spectrum, and thus provides a simple and reliable tool to probe the topology of a system.

Positron-annihilation study of the electronic structure of URu2Si2

NASA Astrophysics Data System (ADS)

Rozing, G. J.; Mijnarends, P. E.; Menovsky, A. A.; de Chtel, P. F.

1991-04-01

Measurements of the two-dimensional angular correlation of annihilation radiation (2D-ACAR) were performed on oriented single crystals of URu2Si2. The spectra, obtained with integration along four different symmetry directions, display anisotropic structure in fair agreement with a previous calculation of the two-photon momentum distribution. In particular, the contribution of the f-ligand hybridized electron states is clearly observed and reasonably well described by the band calculation. The 2D-ACAR distribution remains unchanged as the temperature is increased from 6 K in the Fermi-liquid state to 72 K, which is just above the coherence temperature. The inhomogeneity of the positron density in the unit cell complicates the Lock-Crisp-West (LCW) analysis of the experiments in terms of Fermi-surface features. Nevertheless, the disagreement between theory and experiment after LCW folding indicates that the Fermi surface as predicted by local-density-approximation band theory does not apply.

Collective modes of an imbalanced unitary Fermi gas

NASA Astrophysics Data System (ADS)

Hofmann, Johannes; Chevy, Frédéric; Goulko, Olga; Lobo, Carlos

2018-03-01

We study theoretically the collective mode spectrum of a strongly imbalanced two-component unitary Fermi gas in a cigar-shaped trap, where the minority species forms a gas of polarons. We describe the collective breathing mode of the gas in terms of the Fermi-liquid kinetic equation taking collisions into account using the method of moments. Our results for the frequency and damping of the longitudinal in-phase breathing mode are in good quantitative agreement with an experiment by Nascimbène et al. [Phys. Rev. Lett. 103, 170402 (2009), 10.1103/PhysRevLett.103.170402] and interpolate between a hydrodynamic and a collisionless regime as the polarization is increased. A separate out-of phase breathing mode, which for a collisionless gas is sensitive to the effective mass of the polaron, however, is strongly damped at finite temperature, whereas the experiment observes a well-defined oscillation.

Specific heat in KFe2As2 in zero and applied magnetic field

NASA Astrophysics Data System (ADS)

Kim, J. S.; Kim, E. G.; Stewart, G. R.; Chen, X. H.; Wang, X. F.

2011-05-01

The specific heat down to 0.08 K of the iron pnictide superconductor KFe2As2 was measured on a single-crystal sample with a residual resistivity ratio of ˜650, with a Tconset determined by a specific heat of 3.7 K. The zero-field normal-state specific heat divided by temperature, C/T, was extrapolated from above Tc to T=0 by insisting on agreement between the extrapolated normal-state entropy at Tc, Snextrap(Tc), and the measured superconducting-state entropy at Tc, Ssmeas(Tc), since for a second-order phase transition the two entropies must be equal. This extrapolation would indicate that this rather clean sample of KFe2As2 exhibits non-Fermi-liquid behavior; i.e., C/T increases at low temperatures, in agreement with the reported non-Fermi-liquid behavior in the resistivity. However, specific heat as a function of magnetic field shows that the shoulder feature around 0.7 K, which is commonly seen in KFe2As2 samples, is not evidence for a second superconducting gap as has been previously proposed but instead is due to an unknown magnetic impurity phase, which can affect the entropy balance and the extrapolation of the normal-state specific heat. This peak (somewhat larger in magnitude) with similar field dependence is also found in a less pure sample of KFe2As2, with a residual resistivity ratio of only 90 and Tconset=3.1 K. These data, combined with the measured normal-state specific heat in field to suppress superconductivity, allow the conclusion that an increase in the normal-state specific heat as T→0 is in fact not seen in KFe2As2; i.e., Fermi-liquid behavior is observed.

Classification and properties of quantum spin liquids on the hyperhoneycomb lattice

NASA Astrophysics Data System (ADS)

Huang, Biao; Choi, Wonjune; Kim, Yong Baek; Lu, Yuan-Ming

2018-05-01

The family of "Kitaev materials" provides an ideal platform to study quantum spin liquids and their neighboring magnetic orders. Motivated by the possibility of a quantum spin liquid ground state in pressurized hyperhoneycomb iridate β -Li2IrO3 , we systematically classify and study symmetric quantum spin liquids on the hyperhoneycomb lattice, using the Abrikosov-fermion representation. Among the 176 symmetric U (1 ) spin liquids (and 160 Z2 spin liquids), we identify eight "root" U (1 ) spin liquids in proximity to the ground state of the solvable Kitave model on the hyperhonecyomb lattice. These eight states are promising candidates for possible U (1 ) spin liquid ground states in pressurized β -Li2IrO3 . We further discuss physical properties of these eight U (1 ) spin liquid candidates, and show that they all support nodal-line-shaped spinon Fermi surfaces.

Study of electronic structure of liquid Pb

NASA Astrophysics Data System (ADS)

Vora, A. M.; Gajjar, P. N.

2018-04-01

The Fiolhais et al.'s universal model potential in conjunction with the hard sphere technique of Percus and Yevick has been used for the study of electronic structure, Fermi energy and density of states of liquid Pb. The screening influence of the different forms of the local field correction functions proposed by Hartree (H) and Taylor (T) on the afore said properties is studied, which replicates the changing effects of screening and found suitable for the present study.

Violation of Ohm’s law in a Weyl metal [A hallmark of the Weyl metal state: Breakdown of Ohm's law

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, Dongwoo; Lee, Yongwoo; Sasaki, M.

Ohm’s law is a fundamental paradigm in the electrical transport of metals. Any transport signatures violating Ohm’s law would give an indisputable fingerprint for a novel metallic state. Here, we uncover the breakdown of Ohm’s law owing to a topological structure of the chiral anomaly in the Weyl metal phase. We observe nonlinear I–V characteristics in Bi 0.96Sb 0.04 single crystals in the diffusive limit, which occurs only for a magnetic-field-aligned electric field (E∥B). The Boltzmann transport theory with the charge pumping effect reveals the topological-in-origin nonlinear conductivity, and it leads to a universal scaling function of the longitudinal magnetoconductivity,more » which completely describes our experimental results. Furthermore, as a hallmark of Weyl metals, the nonlinear conductivity provides a venue for nonlinear electronics, optical applications, and the development of a topological Fermi-liquid theory beyond the Landau Fermi-liquid theory.« less

Local Criticality and non-Fermi Liquid Behavior in Heavy Fermions

NASA Astrophysics Data System (ADS)

Si, Qimiao

2002-03-01

Quantum criticality provides a means to understand the apparent non-Fermi liquid phenomena in strongly correlated metals. Heavy fermion metals have emerged as a prototype system; many of them explicitly display a magnetic QCP. Experiments have shown that the quantum critical behavior is much richer than expected. One surprise came from neutron scattering, which found that the spin dynamics is anomalous not only near the antiferromagnetic wavevectors but also essentially everywhere in the Brillouin zone. In this talk, I will review the experiments and describe our theoretical work on the subject [1,2,3]. The notion of "local criticality" will be introduced and will be argued to apply to the heavy fermions. Some broader implications of the results will also be discussed. [1] Q. Si, S. Rabello, K. Ingersent, and J. L. Smith, Nature 413, 804 (2001). [2] Q. Si, J. L. Smith and K. Ingersent, Int. Journ. Mod. Phys. B13, 2331 (1999). [3] J. L. Smith and Q. Si, Phys. Rev. B61, 5184 (2000).

Strongly Correlated Metal Built from Sachdev-Ye-Kitaev Models

NASA Astrophysics Data System (ADS)

Song, Xue-Yang; Jian, Chao-Ming; Balents, Leon

2017-11-01

Prominent systems like the high-Tc cuprates and heavy fermions display intriguing features going beyond the quasiparticle description. The Sachdev-Ye-Kitaev (SYK) model describes a (0 +1 )D quantum cluster with random all-to-all four-fermion interactions among N fermion modes which becomes exactly solvable as N →∞ , exhibiting a zero-dimensional non-Fermi-liquid with emergent conformal symmetry and complete absence of quasiparticles. Here we study a lattice of complex-fermion SYK dots with random intersite quadratic hopping. Combining the imaginary time path integral with real time path integral formulation, we obtain a heavy Fermi liquid to incoherent metal crossover in full detail, including thermodynamics, low temperature Landau quasiparticle interactions, and both electrical and thermal conductivity at all scales. We find linear in temperature resistivity in the incoherent regime, and a Lorentz ratio L ≡(κ ρ /T ) varies between two universal values as a function of temperature. Our work exemplifies an analytically controlled study of a strongly correlated metal.

Theoretical model of x-ray scattering as a dense matter probe.

PubMed

Gregori, G; Glenzer, S H; Rozmus, W; Lee, R W; Landen, O L

2003-02-01

We present analytical expressions for the dynamic structure factor, or form factor S(k,omega), which is the quantity describing the x-ray cross section from a dense plasma or a simple liquid. Our results, based on the random phase approximation for the treatment on the charged particle coupling, can be applied to describe scattering from either weakly coupled classical plasmas or degenerate electron liquids. Our form factor correctly reproduces the Compton energy down-shift and the known Fermi-Dirac electron velocity distribution for S(k,omega) in the case of a cold degenerate plasma. The usual concept of scattering parameter is also reinterpreted for the degenerate case in order to include the effect of the Thomas-Fermi screening. The results shown in this work can be applied to interpreting x-ray scattering in warm dense plasmas occurring in inertial confinement fusion experiments or for the modeling of solid density matter found in the interior of planets.

Non-Fermi-liquid behavior in nonequilibrium transport through Co-doped Au chains connected to fourfold symmetric leads

NASA Astrophysics Data System (ADS)

Di Napoli, S.; Roura-Bas, P.; Weichselbaum, Andreas; Aligia, A. A.

2014-09-01

We calculate the differential conductance as a function of temperature and bias voltage, G (T,V), through Au monatomic chains with a substitutional Co atom as a magnetic impurity, connected to a fourfold symmetric lead. The system was recently proposed as a possible scenario for observation of the overscreened Kondo physics. Stretching the chain, the system could be tuned through a quantum critical point (QCP) with three different regimes: overscreened, underscreened, and non-Kondo phases. We present calculations of the impurity spectral function by using the numerical renormalization group for the three different regimes characterizing the QCP. Nontrivial behavior of the spectral function is reported near the QCP. Comparison with results using the noncrossing approximation (NCA) shows that the latter is reliable in the overscreened regime, when the anisotropy is larger than the Kondo temperature. For these parameters, which correspond to realistic previous estimates, G (T,V) calculated within NCA exhibits clear signatures of the non-Fermi-liquid behavior within the overscreened regime.

Exact Solution of a Two-Species Quantum Dimer Model for Pseudogap Metals

NASA Astrophysics Data System (ADS)

Feldmeier, Johannes; Huber, Sebastian; Punk, Matthias

2018-05-01

We present an exact ground state solution of a quantum dimer model introduced by Punk, Allais, and Sachdev [Quantum dimer model for the pseudogap metal, Proc. Natl. Acad. Sci. U.S.A. 112, 9552 (2015)., 10.1073/pnas.1512206112], which features ordinary bosonic spin-singlet dimers as well as fermionic dimers that can be viewed as bound states of spinons and holons in a hole-doped resonating valence bond liquid. Interestingly, this model captures several essential properties of the metallic pseudogap phase in high-Tc cuprate superconductors. We identify a line in parameter space where the exact ground state wave functions can be constructed at an arbitrary density of fermionic dimers. At this exactly solvable line the ground state has a huge degeneracy, which can be interpreted as a flat band of fermionic excitations. Perturbing around the exactly solvable line, this degeneracy is lifted and the ground state is a fractionalized Fermi liquid with a small pocket Fermi surface in the low doping limit.

Correlation of normal and superconducting properties and unified approach to the description of high Tc oxides

NASA Technical Reports Server (NTRS)

Kresin, V. Z.; Wolf, S. A.

1991-01-01

We present a unified approach based on the Fermi liquid picture which allows us to describe the normal as well as the superconducting properties of the doped cuprates. The theory that is presented is for the doped compounds which are metallic. One can distinguish two interrelated, but nevertheless, different directions in the physics of high T(sub c): one involving the problem of carrier doping and the transition to the metallic state, and the second being the description of the metallic state. It is important that this metallic phase undergoes the transition into the superconducting state; as a result, our analysis is directly related to the origin of high T(sub c). We are using a quasi-2D Fermi liquid model to estimate the fundamental parameters of these very interesting materials. We find that this description is able to describe these materials and also that phonons and plasmons play a major role in the mechanism of high T(sub c).

Violation of Ohm’s law in a Weyl metal [A hallmark of the Weyl metal state: Breakdown of Ohm's law

DOE PAGES

Shin, Dongwoo; Lee, Yongwoo; Sasaki, M.; ...

2017-08-14

Ohm’s law is a fundamental paradigm in the electrical transport of metals. Any transport signatures violating Ohm’s law would give an indisputable fingerprint for a novel metallic state. Here, we uncover the breakdown of Ohm’s law owing to a topological structure of the chiral anomaly in the Weyl metal phase. We observe nonlinear I–V characteristics in Bi 0.96Sb 0.04 single crystals in the diffusive limit, which occurs only for a magnetic-field-aligned electric field (E∥B). The Boltzmann transport theory with the charge pumping effect reveals the topological-in-origin nonlinear conductivity, and it leads to a universal scaling function of the longitudinal magnetoconductivity,more » which completely describes our experimental results. Furthermore, as a hallmark of Weyl metals, the nonlinear conductivity provides a venue for nonlinear electronics, optical applications, and the development of a topological Fermi-liquid theory beyond the Landau Fermi-liquid theory.« less

The Thomas-Fermi model in the theory of systems of charged particles above the surface of liquid dielectrics

NASA Astrophysics Data System (ADS)

Lytvtnenko, D. M.; Slyusarenko, Yu. V.; Kirdin, A. I.

2012-10-01

A consistent theory of equilibrium states of same sign charges above the surface of liquid dielectric film located on solid substrate in the presence of external attracting constant electric field is proposed. The approach to the development of the theory is based on the Thomas-Fermi model generalized to the systems under consideration and on the variational principle. The using of self-consistent field model allows formulating a theory containing no adjustable constants. In the framework of the variational principle we obtain the self-consistency equations for the parameters describing the system: the distribution function of charges above the liquid dielectric surface, the electrostatic field potentials in all regions of the system and the surface profile of the liquid dielectric. The self-consistency equations are used to describe the phase transition associated with the formation of spatially periodic structures in the system of charges on liquid dielectric surface. Assuming the non-degeneracy of the gas of charges above the surface of liquid dielectric film the solutions of the self-consistency equations near the critical point are obtained. In the case of the symmetric phase we obtain the expressions for the potentials and electric fields in all regions of the studied system. The distribution of the charges above the surface of liquid dielectric film for the symmetric phase is derived. The system parameters of the phase transition to nonsymmetric phase - the states with a spatially periodic ordering are obtained. We derive the expression determining the period of two-dimensional lattice as a function of physical parameters of the problem - the temperature, the external attractive electric field, the number of electrons per unit of the flat surface area of the liquid dielectric, the density of the dielectric, its surface tension and permittivity, and the permittivity of the solid substrate. The possibility of generalizing the developed theory in the case of degenerate gas of like-charged particles above the liquid dielectric surface is discussed.

Holographic non-Fermi-liquid fixed points.

PubMed

Faulkner, Tom; Iqbal, Nabil; Liu, Hong; McGreevy, John; Vegh, David

2011-04-28

Techniques arising from string theory can be used to study assemblies of strongly interacting fermions. Via this 'holographic duality', various strongly coupled many-body systems are solved using an auxiliary theory of gravity. Simple holographic realizations of finite density exhibit single-particle spectral functions with sharp Fermi surfaces, of a form distinct from those of the Landau theory. The self-energy is given by a correlation function in an infrared (IR) fixed-point theory that is represented by a two-dimensional anti de Sitter space (AdS(2)) region in the dual gravitational description. Here, we describe in detail the gravity calculation of this IR correlation function.

One- and two-channel Kondo model with logarithmic Van Hove singularity: A numerical renormalization group solution

NASA Astrophysics Data System (ADS)

Zhuravlev, A. K.; Anokhin, A. O.; Irkhin, V. Yu.

2018-02-01

Simple scaling consideration and NRG solution of the one- and two-channel Kondo model in the presence of a logarithmic Van Hove singularity at the Fermi level is given. The temperature dependences of local and impurity magnetic susceptibility and impurity entropy are calculated. The low-temperature behavior of the impurity susceptibility and impurity entropy turns out to be non-universal in the Kondo sense and independent of the s-d coupling J. The resonant level model solution in the strong coupling regime confirms the NRG results. In the two-channel case the local susceptibility demonstrates a non-Fermi-liquid power-law behavior.

Persistent order due to transiently enhanced nesting in an electronically excited charge density wave

DOE PAGES

Rettig, L.; Cortés, R.; Chu, J. -H.; ...

2016-01-25

Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time-and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of themore » dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. In conclusion, our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order.« less

Crystal growth of Dirac semimetal ZrSiS with high magnetoresistance and mobility.

PubMed

Sankar, Raman; Peramaiyan, G; Muthuselvam, I Panneer; Butler, Christopher J; Dimitri, Klauss; Neupane, Madhab; Rao, G Narsinga; Lin, M-T; Chou, F C

2017-01-18

High quality single crystal ZrSiS as a theoretically predicted Dirac semimetal has been grown successfully using a vapor phase transport method. The single crystals of tetragonal structure are easy to cleave into perfect square-shaped pieces due to the van der Waals bonding between the sulfur atoms of the quintuple layers. Physical property measurement results including resistivity, Hall coefficient (R H ), and specific heat are reported. The transport and thermodynamic properties suggest a Fermi liquid behavior with two Fermi pockets at low temperatures. At T = 3 K and magnetic field of Hǁc up to 9 Tesla, large magneto-resistance up to 8500% and 7200% for Iǁ (100) and Iǁ (110) were found. Shubnikov de Haas (SdH) oscillations were identified from the resistivity data, revealing the existence of two Fermi pockets at the Fermi level via the fast Fourier transform (FFT) analysis. The Hall coefficient (R H ) showed hole-dominated carriers with a high mobility of 3.05 × 10 4  cm 2 V -1 s -1 at 3 K. ZrSiS has been confirmed to be a Dirac semimetal by the Dirac cone mapping near the X-point via angle resolved photoemission spectroscopy (ARPES) with a Dirac nodal line near the Fermi level identified using scanning tunneling spectroscopy (STS).

Measurement of a Neutrino-Induced Charged Current Single Neutral Pion Cross Section at MicroBooNE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hackenburg, Ariana

Micro Booster Neutrino Experiment (MicroBooNE) is a Liquid Argon Time Projection Chamber (LArTPC) operating in the Booster Neutrino Beamline at Fermi National Accelerator Laboratory. MicroBooNE's physics goals include studying short baslinemore » $$\

Is the Luttinger Liquid a New State of Matter?

NASA Astrophysics Data System (ADS)

Afonin, V. V.; Petrov, V. Y.

2010-02-01

We are demonstrating that the Luttinger model with short range interaction can be treated as a type of Fermi liquid. In line with the main dogma of Landau’s theory one can define a fermion excitation renormalized by interaction and show that in terms of these fermions any excited state of the system is described by free particles. The fermions are a mixture of renormalized right and left electrons. The electric charge and chirality of the Landau quasi-particle is discussed.

Latent instabilities in metallic LaNiO₃ films by strain control of Fermi-surface topology

DOE PAGES

Yoo, Hyang Keun; Hyun, Seung Ill; Moreschini, Luca; ...

2015-03-04

Strain control is one of the most promising avenues to search for new emergent phenomena in transition metal-oxide films. Here, we investigate the strain-induced changes of electronic structures in strongly correlated LaNiO₃ (LNO) films, using angle-resolved photoemission spectroscopy and the dynamical mean-field theory. The strongly renormalized e g-orbital bands are systematically rearranged by misfit strain to change its fermiology. As tensile strain increases, the hole pocket centered at the A point elongates along the k z-axis and seems to become open, thus changing Fermi-surface (FS) topology from three- to quasi-two-dimensional. Concomitantly, the FS shape becomes flattened to enhance FS nesting.more » A FS superstructure withQ₁ = (1/2,1/2,1/2) appears in all LNO films, while a tensile-strained LNO film has an additional Q₂ = (1/4,1/4,1/4) modulation, indicating that some instabilities are present in metallic LNO films. Charge disproportionation and spin-density-wave fluctuations observed in other nickelates might be their most probable origins« less

On Scaling Relations of Organic Antiferromagnets with Magnetic Anions

NASA Astrophysics Data System (ADS)

Shimahara, Hiroshi; Kono, Yuki

2017-04-01

We study a recently reported scaling relation of the specific heat of the organic compounds λ-(BETS)2FexGa1-xCl4. This relation suggests that the sublattice magnetization m of the π electrons and the antiferromagnetic transition temperature TN are proportional to x. Note that the scaling relation for TN can be explained by considering the effective interaction between the π electrons via the localized 3d spins on the FeCl4 anions. The effective interaction is analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, but the roles of the conductive electrons and the localized spins are interchanged. Using available energy scales, it is shown that the TN scaling relation indicates that the system is in the vicinity of the quantum critical point. It is argued that the scaling relation for m at low temperatures, i.e., below TN but excluding temperatures in the vicinity of TN, indicates that the mismatch between the Fermi surface and that shifted by the nesting vector is large, at least for a large part of the Fermi surface. We also discuss the scaling relation near TN.

Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe 1-xCo x)₂As₂

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chang; Palczewski, A. D.; Dhaka, R. S.

We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe 1-xCo x)₂As₂ high-temperature superconductor. Our data demonstrate that several Lifshitz transitions—topological changes of the Fermi surface—occur for large x. The central hole barrel changes to ellipsoids that are centered at Z at x~0.11 and subsequently disappear around x~0.2; changes in thermoelectric power occur at similar x values. T c decreases and goes to zero around x~0.15—between the two Lifshitz transitions. Beyond x=0.2 the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance ofmore » the underlying Fermiology in electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.« less

Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe 1-xCo x)₂As₂

DOE PAGES

Liu, Chang; Palczewski, A. D.; Dhaka, R. S.; ...

2011-07-25

We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe 1-xCo x)₂As₂ high-temperature superconductor. Our data demonstrate that several Lifshitz transitions—topological changes of the Fermi surface—occur for large x. The central hole barrel changes to ellipsoids that are centered at Z at x~0.11 and subsequently disappear around x~0.2; changes in thermoelectric power occur at similar x values. T c decreases and goes to zero around x~0.15—between the two Lifshitz transitions. Beyond x=0.2 the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance ofmore » the underlying Fermiology in electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.« less

Condensed Matter Theories - Volume 22

NASA Astrophysics Data System (ADS)

Reinholz, Heidi; Röpke, Gerd; de Llano, Manuel

2007-09-01

pt. A. Fermi liquids. Pressure comparison between the spherical cellular model and the Thomas-Fermi model / G.A. Baker, Jr. Pair excitations and vertex corrections in Fermi fluids and the dynamic structure function of two-dimension 3He / H.M. Böhm, H. Godfrin, E. Krotscheck, H.J. Lauter, M. Meschke and M. Panholzer. Condensation of helium in wedges / E.S. Hernádez ... [et al.]. Non-Fermi liquid behavior from the Fermi-liquid approach / V.A. Khodel ... [et al.]. Theory of third sound and stability of thin 3He-4He superfluid films / E. Krotscheck and M.D. Miller. Pairing in asymmetrical Fermi systems / K.F. Quader and R. Liao. Ground-state properties of small 3He drops from quantum Monte Carlo simulations / E. Sola, J. Casulleras and J. Boronat. Ground-state energy and compressibility of a disordered two-dimensional electron gas / Tanatar ... [et al.]. Quasiexcitons in photoluminescence of incompressible quantum liquids / A. Wójs, A.G ladysiewicz and J.J. Quinn -- pt. B. Bose liquids. Quantum Boltzmann liquids / K.A. Gernoth, M L. Ristig and T. Lindenau. Condensate fraction in the dynamic structure function of Bose fluids / M. Saarela, F. Mazzanti and V. Apaja -- pt. C. Strongly-correlated electronic systems. Electron gas in high-field nanoscopic transport: metallic carbon nanotubes / F. Green and D. Neilson. Evolution and destruction of the Kondo effect in a capacitively coupled double dot system / D.E. Logan and M.R. Galpin. The method of increments-a wavefunction-based Ab-Initio correlation method for solids / B. Paulus. Fractionally charged excitations on frustrated lattices / E. Runge, F. Pollmann and P. Fulde. 5f Electrons in actinides: dual nature and photoemission spectra / G. Zwicknagl -- pt. D. Magnetism. Magnetism in disordered two-dimensional Kondo-Necklace / W. Brenig. On the de Haas-can Alphen oscillation in 2D / S. Fujita and D.L. Morabito. Dynamics in one-dimensional spin systems-density matrix reformalization group study / S. Nishimoto and M. Arikawa. Frustrated quantum antiferromagnets: application of high-order coupled cluster method / J. Richter ... [et al.]. Vorticity and antivorticity in submicron ferromagnetic films / H. Wang, M. Yan and C.E. Campbell -- pt. E. Conductivity. D-wave checkerboard bose condensate of mobile bipolarons / A.S. Alexandrov. Five possible reasons why high-Tc superconductivity is stalled / M. Grether and M. de Llano. Multistability and Multi 2[Pie symbol]-Kinks in the Frenkel-Kontorova model: an application to arrays of Josephson junctions / K.E. Kürten and C. Krattenthaler. Lowering of Boson-Fermion system energy with a gapped cooper resonant-pair dispersion relation / T.A. Mamedov and M. de Llano. The concept of correlated density and its application / K. Morawetz ... [et al.]. Competing local and non-local phase correlations in Fermionic systems with resonant pairing: the Boson-Fermion scenario / J. Ranninger. Superconducting order parameters in the extended Hubbard model: a simple mean-field study / J.S. Thakur and M.P. Das -- pt. F. Nuclear systems. Distribution of maxima of the antisymmetized wave function for the nucleons of a closed-shell and for the nucleons of all closed-shells in a nucleus / G.S. Anagnostatos. Pairing of strongly correlated nucleons / W.H. Dickhoff. Short range correlations in relativistic nuclear models / P.K. Panda, C. Providência and J. da Providência. Quartetting in attractive Fermi-systems and alpha particle condensation in nuclear systems / P. Schuck ... [et al.]. Alpha-alpha and Alpha-nucleus potentials: an energy-density fucntional approach / Z.F. Shehadeh ... [et al.]. -- pt. G. Density functional theory and MD simulations. Dynamics of metal clusters in rare gas clusters / M. Baer ... [et al.]. Reinhard and E. Suraud. Kohn-Sham calculations combined with an average pair-density functional theory / P. Gori-Giorgi and A. Savin. Correlations, collision frequency and optical properties in laser excited clusters / H. Reinholz, T. Raitza and G. Röpke -- pt. H. Biophysics. Condensed matter physics of biomolecule systems in a differential geometric framework / H. Bohr, J.I. Ipsen and S. Markvorsen. The brain's view of the natural world in motion: computing structure from function using directional Fourier transformations / B.K. Dellen, J.W. Clark and R. Wessel -- pt. I. Quantum information. Control and error prevention in condensed matter quantum computing devices / M.S. Byrd and L.A. Wu. Maxent approaches to qubits / C.M. Sarris, A.N. Proto and F B. Malik -- pt. J. New formalisms. Thermal coherent states, a broader class of mixed coherent states, and generalized thermo-field dynamics / R.F. Bishop and A. Vourdas. Ergodic condition and magnetic models / M. Howard Lee. From thermodynamics to Maxent / A. Plastino and E. M.F. Curado. Recent progress in the density-matrix renormalization group / U. Schollwöck.

Mechanism of a strange metal state near a heavy-fermion quantum critical point

NASA Astrophysics Data System (ADS)

Chang, Yung-Yeh; Paschen, Silke; Chung, Chung-Hou

2018-01-01

Unconventional metallic or strange metal (SM) behavior with non-Fermi liquid (NFL) properties, generic features of heavy-fermion systems near quantum phase transitions, are yet to be understood microscopically. A paradigmatic example is the magnetic field-tuned quantum critical heavy-fermion metal YbRh2Si2 , revealing a possible SM state over a finite range of fields at low temperatures when substituted with Ge. Above a critical field, the SM state gives way to a heavy Fermi liquid with Kondo correlation. The NFL behavior, most notably a linear-in-temperature electrical resistivity and a logarithmic-in-temperature followed by a power-law singularity in the specific heat coefficient at low temperatures, still lacks a definite understanding. We propose the following mechanism as origin of the experimentally observed behavior: a quasi-2 d fluctuating short-ranged resonating-valence-bond spin liquid competing with the Kondo correlation. Applying a field-theoretical renormalization group analysis on an effective field theory beyond a large-N approach to an antiferromagnetic Kondo-Heisenberg model, we identify the critical point and explain remarkably well the SM behavior. Our theory goes beyond the well-established framework of quantum phase transitions and serves as a basis to address open issues in quantum critical heavy-fermion systems.

Ground-states for the liquid drop and TFDW models with long-range attraction

NASA Astrophysics Data System (ADS)

Alama, Stan; Bronsard, Lia; Choksi, Rustum; Topaloglu, Ihsan

2017-10-01

We prove that both the liquid drop model in R 3 with an attractive background nucleus and the Thomas-Fermi-Dirac-von Weizsäcker (TFDW) model attain their ground-states for all masses as long as the external potential V(x) in these models is of long range, that is, it decays slower than Newtonian (e.g., V ( x ) ≫ | x | - 1 for large |x|.) For the TFDW model, we adapt classical concentration-compactness arguments by Lions, whereas for the liquid drop model with background attraction, we utilize a recent compactness result for sets of finite perimeter by Frank and Lieb.

Mott transition between a spin-liquid insulator and a metal in three dimensions.

PubMed

Podolsky, Daniel; Paramekanti, Arun; Kim, Yong Baek; Senthil, T

2009-05-08

We study a bandwidth controlled Mott metal-insulator transition (MIT) from a Fermi-liquid metal to a quantum spin-liquid insulator in three dimensions. Using a slave rotor approach including gauge fluctuations, we obtain a continuous MIT and discuss finite temperature crossovers in its vicinity. We show that the specific heat C approximately Tlnln(1/T) at the MIT and that the metallic state near the MIT should exhibit a "conductivity minimum" as a function of temperature. We suggest Na4Ir3O8 as a candidate to test our predictions and compute its electron spectral function at the MIT.

Detection of low plasma estradiol concentrations in nesting green turtles (Chelonia mydas) by HPLC/Ms-Ms.

PubMed

Mahmoud, I Y; Alkindi, A Y; Khan, T; Al-Bahry, S N

2011-03-01

In previous studies on nesting green turtles under natural conditions from different geographical regions, 17-β-estradiol (E(2) ) was either undetectable or detected at very low levels. RIA and other related techniques were not sensitive enough to measure low E(2) values in the green turtles. In this study, a sensitive method was used in detecting low hormone concentrations: high performance liquid chromatography with tandem quadruple mass spectrometry (HPLC-MS/MS). Using this technique, estradiol for the first time was detected in nesting green turtles during the peak season (June-October) at Ras Al-Hadd Reserve, Oman. The E(2) values recorded from this study were the highest ever recorded from nesting green turtles in any geographical region, but the levels did not vary significantly throughout different phases of nesting. The presence of E(2) during nesting presumably plays a role in the physiology and behavior of this species. Ras Al-Hadd hosts one of the largest nesting populations of green turtles in the world, and an understanding of their nesting patterns may be of value in conservation and management programs for this endangered species. Copyright © 2011 Wiley-Liss, Inc., A Wiley Company.

Landau parameters for energy density functionals generated by local finite-range pseudopotentials

NASA Astrophysics Data System (ADS)

Idini, A.; Bennaceur, K.; Dobaczewski, J.

2017-06-01

In Landau theory of Fermi liquids, the particle-hole interaction near the Fermi energy in different spin-isospin channels is probed in terms of an expansion over the Legendre polynomials. This provides a useful and efficient way to constrain properties of nuclear energy density functionals in symmetric nuclear matter and finite nuclei. In this study, we present general expressions for Landau parameters corresponding to a two-body central local regularized pseudopotential. We also show results obtained for two recently adjusted NLO and N2LO parametrizations. Such pseudopotentials will be used to determine mean-field and beyond-mean-field properties of paired nuclei across the entire nuclear chart.

Phenomenological view at the two-component physics of cuprates

NASA Astrophysics Data System (ADS)

Teitel'baum, G. B.

2017-08-01

In the search for mechanisms of high- T c superconductivity it is critical to know the electronic spectrum in the pseudogap phase from which superconductivity evolves. The lack of ARPES data for every cuprate family precludes an agreement as to its structure, doping and temperature dependence and the role of charge ordering. No approach has been developed yet to address the issue theoretically, and we limit ourselves by the phenomenological analysis of the experimental data. We argue that, in the Fermi-liquid-like regime ubiquitous in underdoped cuprates, the spectrum consists of holes on the Fermi arcs and an electronic pocket in contrast to the idea of the Fermi surface reconstruction via charge ordering. At high temperatures, the electrons are dragged by holes while at lower temperatures they get decoupled. The longstanding issue of the origin of the negative Hall coefficient in YBCO and Hg1201 at low temperature is resolved: the electronic contribution prevails, as its mobility becomes temperature independent, while the mobility of holes, scattered by the shortwavelength charge density waves, decreases.

Sign Reversal of Coulom Interaction Between Two Quasiparticles in Momentum Space

NASA Astrophysics Data System (ADS)

Fan, J. D.; Malozovsky, Yuriy M.

2013-06-01

The main misconception regarding the interaction between quasiparticles stems from the assertion that the interaction energy between two quasiparticles is exactly identical to that of the renormalized interaction between two particles due to interparticle interaction in the Fermi system. If the main concept regarding the definition of quasiparticle as a weakly excited state of the Fermi system with conservation of charge and spin is paramount (except for the charge and spin separation models), the concept of the interaction between quasiparticles is very different from the assumption in the common sense. In this paper, we will prove a general theorem that the interaction between two quasiparticles is very much different from the renormalized interaction between two particles. The major difference lies in two places: the interaction between two quasiparticles is just negative to the renormalized interaction between two particles, and the interaction energy between the two particles is proportional to the product of two Fermi liquid renormalization factors. The result shed light on the reinterpretation of Cooper's pairing without invoking electron-photon interaction.

Bulk Fermi surface and momentum density in heavily doped La2-xSrxCuO4 using high-resolution Compton scattering and positron annihilation spectroscopies

NASA Astrophysics Data System (ADS)

Al-Sawai, W.; Barbiellini, B.; Sakurai, Y.; Itou, M.; Mijnarends, P. E.; Markiewicz, R. S.; Kaprzyk, S.; Wakimoto, S.; Fujita, M.; Basak, S.; Lin, H.; Wang, Yung Jui; Eijt, S. W. H.; Schut, H.; Yamada, K.; Bansil, A.

2012-03-01

We have observed the bulk Fermi surface (FS) in an overdoped (x=0.3) single crystal of La2-xSrxCuO4 by using Compton scattering. A two-dimensional (2D) momentum density reconstruction from measured Compton profiles yields a clear FS signature in the third Brillouin zone along [100]. The quantitative agreement between density functional theory (DFT) calculations and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. In particular the predicted FS topology is found to be in good accord with the corresponding experimental data. We find similar quantitative agreement between the measured 2D angular correlation of positron annihilation radiation (2D-ACAR) spectra and the DFT-based computations. However, 2D-ACAR does not give such a clear signature of the FS in the extended momentum space in either the theory or the experiment.

Quadratic Fermi node in a 3D strongly correlated semimetal

DOE PAGES

Kondo, Takeshi; Nakayama, M.; Chen, R.; ...

2015-12-07

We report that strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr 2Ir 2O 7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermimore » liquid behaviour is predicted, for which we observe some evidence. Lastly, our discovery implies that Pr 2Ir 2O 7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states.« less

Dynamical susceptibility near a long-wavelength critical point with a nonconserved order parameter

NASA Astrophysics Data System (ADS)

Klein, Avraham; Lederer, Samuel; Chowdhury, Debanjan; Berg, Erez; Chubukov, Andrey

2018-04-01

We study the dynamic response of a two-dimensional system of itinerant fermions in the vicinity of a uniform (Q =0 ) Ising nematic quantum critical point of d - wave symmetry. The nematic order parameter is not a conserved quantity, and this permits a nonzero value of the fermionic polarization in the d - wave channel even for vanishing momentum and finite frequency: Π (q =0 ,Ωm)≠0 . For weak coupling between the fermions and the nematic order parameter (i.e., the coupling is small compared to the Fermi energy), we perturbatively compute Π (q =0 ,Ωm)≠0 over a parametrically broad range of frequencies where the fermionic self-energy Σ (ω ) is irrelevant, and use Eliashberg theory to compute Π (q =0 ,Ωm) in the non-Fermi-liquid regime at smaller frequencies, where Σ (ω )>ω . We find that Π (q =0 ,Ω ) is a constant, plus a frequency-dependent correction that goes as |Ω | at high frequencies, crossing over to |Ω| 1 /3 at lower frequencies. The |Ω| 1 /3 scaling holds also in a non-Fermi-liquid regime. The nonvanishing of Π (q =0 ,Ω ) gives rise to additional structure in the imaginary part of the nematic susceptibility χ″(q ,Ω ) at Ω >vFq , in marked contrast to the behavior of the susceptibility for a conserved order parameter. This additional structure may be detected in Raman scattering experiments in the d - wave geometry.

Functional renormalization group approach to electronic structure calculations for systems without translational symmetry

NASA Astrophysics Data System (ADS)

Seiler, Christian; Evers, Ferdinand

2016-10-01

A formalism for electronic-structure calculations is presented that is based on the functional renormalization group (FRG). The traditional FRG has been formulated for systems that exhibit a translational symmetry with an associated Fermi surface, which can provide the organization principle for the renormalization group (RG) procedure. We here advance an alternative formulation, where the RG flow is organized in the energy-domain rather than in k space. This has the advantage that it can also be applied to inhomogeneous matter lacking a band structure, such as disordered metals or molecules. The energy-domain FRG (ɛ FRG) presented here accounts for Fermi-liquid corrections to quasiparticle energies and particle-hole excitations. It goes beyond the state of the art G W -BSE , because in ɛ FRG the Bethe-Salpeter equation (BSE) is solved in a self-consistent manner. An efficient implementation of the approach that has been tested against exact diagonalization calculations and calculations based on the density matrix renormalization group is presented. Similar to the conventional FRG, also the ɛ FRG is able to signalize the vicinity of an instability of the Fermi-liquid fixed point via runaway flow of the corresponding interaction vertex. Embarking upon this fact, in an application of ɛ FRG to the spinless disordered Hubbard model we calculate its phase boundary in the plane spanned by the interaction and disorder strength. Finally, an extension of the approach to finite temperatures and spin S =1 /2 is also given.

Excitonic Phase Diagram of the Three-Chain Hubbard Model for Semiconducting and Semimetallic Ta2NiSe5

NASA Astrophysics Data System (ADS)

Domon, Kaoru; Yamada, Takemi; Ōno, Yoshiaki

2018-05-01

Transition metal chalcogenide Ta2NiSe5, a promising material for the excitonic insulator, is investigated on the basis of the three-chain Hubbard model with two conduction (c) bands and one valence (f) band. In the semimetallic case where only one of two c bands and the f band cross the Fermi level, the transition from the c-f compensated semimetal to the uniform excitonic order, the so-called excitonic insulator, takes place at low temperature as the same as in the semiconducting case. On the other hand, when another c band also crosses the Fermi level, the system shows three types of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) excitonic orders characterized by the condensation of excitons with finite center-of-mass momentum q corresponding to the three types of nesting vectors between the imbalanced two c and one f Fermi surfaces. The obtained FFLO excitonic states are metallic in contrast to the excitonic insulator and are expected to be observed in the semimetallic Ta2NiSe5 under high pressure. The effect of the electron-lattice coupling is also discussed briefly and is found to induce the monoclinic distortion not only in the uniform excitonic state but also in the FFLO one resulting in the orthorhombic-monoclinic structural phase transition for both cases as observed in Ta2NiSe5 for both low-pressure semiconducting and high-pressure semimetallic regimes.

Electronic nature of the lock-in magnetic transition in Ce X Al4Si2

NASA Astrophysics Data System (ADS)

Gunasekera, J.; Harriger, L.; Dahal, A.; Maurya, A.; Heitmann, T.; Disseler, S. M.; Thamizhavel, A.; Dhar, S.; Singh, D. J.; Singh, D. K.

2016-04-01

We have investigated the underlying magnetism in newly discovered single crystal Kondo lattices Ce X Al4Si2 , where X = Rh, Ir. We show that the compound undergoes an incommensurate-to-commensurate magnetic transition at Tc=9.19 K (10.75 K in Ir). The spin correlation in the incommensurate phase is described by a spin density wave configuration of Ce ions, which locks in to the long-range antiferromagnetic order at T =Tc. The analysis of the experimental data, combined with the calculation of the electronic properties, suggests the role of the Fermi surface nesting as the primary mechanism behind this phenomenon.

Tunnel transport and interlayer excitons in bilayer fractional quantum Hall systems

NASA Astrophysics Data System (ADS)

Zhang, Yuhe; Jain, J. K.; Eisenstein, J. P.

2017-05-01

In a bilayer system consisting of a composite-fermion (CF) Fermi sea in each layer, the tunnel current is exponentially suppressed at zero bias, followed by a strong peak at a finite-bias voltage Vmax. This behavior, which is qualitatively different from that observed for the electron Fermi sea, provides fundamental insight into the strongly correlated non-Fermi-liquid nature of the CF Fermi sea and, in particular, offers a window into the short-distance high-energy physics of this highly nontrivial state. We identify the exciton responsible for the peak current and provide a quantitative account of the value of Vmax. The excitonic attraction is shown to be quantitatively significant, and its variation accounts for the increase of Vmax with the application of an in-plane magnetic field. We also estimate the critical Zeeman energy where transition occurs from a fully spin-polarized composite-fermion Fermi sea to a partially spin-polarized one, carefully incorporating corrections due to finite width and Landau level mixing, and find it to be in satisfactory agreement with the Zeeman energy where a qualitative change has been observed for the onset bias voltage [J. P. Eisenstein et al., Phys. Rev. B 94, 125409 (2016), 10.1103/PhysRevB.94.125409]. For fractional quantum Hall states, we predict a substantial discontinuous jump in Vmax when the system undergoes a transition from a fully spin-polarized state to a spin singlet or a partially spin-polarized state.

Transport signatures of topology protected quantum criticality in Majorana islands

NASA Astrophysics Data System (ADS)

Papaj, Michal; Zhu, Zheng; Fu, Liang

Using numerical renormalization group we study a topological superconductor island coupled to three metallic leads in the vicinity of the charge degeneracy point. We show that the system flows to a non-Fermi liquid fixed point at low temperatures with fractional quantized DC conductance of 2 / 3e2 / h . Our proposal is experimentally feasible due to a much larger crossover temperature than in the previously studied cases and the robustness of the setup against the channel coupling anisotropy and charge degeneracy detuning. Including Majorana hybridization drives the system into a Fermi liquid phase at very low temperatures. The two proposed experimental signatures of multi-terminal electron teleportation include nonmonotonic temperature dependence of DC conductance and emergence of a plateau at 2 / 3e2 / h in tunnel coupling dependence of DC conductance. This work is funded by the DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award de-sc0010526 (ZZ and LF) and the NSF STC ''Center for Integrated Quantum Materials'' under Cooperative Agreement No. DMR-1231319 (MP).

Role of four-fermion interaction and impurity in the states of two-dimensional semi-Dirac materials.

PubMed

Wang, Jing

2018-03-28

We study the effects of four-fermion interaction and impurity on the low-energy states of 2D semi-Dirac materials by virtue of the unbiased renormalization group approach. The coupled flow equations that govern the energy-dependent evolutions of all correlated interaction parameters are derived after taking into account one-loop corrections from the interplay between four-fermion interaction and impurity. Whether and how four-fermion interaction and impurity influence the low-energy properties of 2D semi-Dirac materials are discreetly explored and addressed attentively. After carrying out the standard renormalization group analysis, we find that both trivial insulating and nontrivial semimetal states are qualitatively stable against all four kinds of four-fermion interactions. However, while switching on both four-fermion interaction and impurity, certain insulator-semimetal phase transitions and the distance of Dirac nodal points can be respectively induced and modified due to their strong interplay and intimate competition. Moreover, several non-Fermi liquid behaviors that deviate from the conventional Fermi liquids are exhibited at the lowest-energy limit.

Controlled calculation of the thermal conductivity for a spinon Fermi surface coupled to a U(1) gauge field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Freire, Hermann, E-mail: hfreire@mit.edu

2014-10-15

Motivated by recent transport measurements on the candidate spin-liquid phase of the organic triangular lattice insulator EtMe{sub 3}Sb[Pd(dmit){sub 2}]{sub 2}, we perform a controlled calculation of the thermal conductivity at intermediate temperatures in a spin liquid system where a spinon Fermi surface is coupled to a U(1) gauge field. The present computation builds upon the double expansion approach developed by Mross et al. (2010) for small ϵ=z{sub b}−2 (where z{sub b} is the dynamical critical exponent of the gauge field) and large number of fermionic species N. Using the so-called memory matrix formalism that most crucially does not assume the existencemore » of well-defined quasiparticles at low energies in the system, we calculate the temperature dependence of the thermal conductivity κ of this model due to non-critical Umklapp scattering of the spinons for a finite N and small ϵ. Then we discuss the physical implications of such theoretical result in connection with the experimental data available in the literature.« less

Bond Order Correlations in the 2D Hubbard Model

NASA Astrophysics Data System (ADS)

Moore, Conrad; Abu Asal, Sameer; Yang, Shuxiang; Moreno, Juana; Jarrell, Mark

We use the dynamical cluster approximation to study the bond correlations in the Hubbard model with next nearest neighbor (nnn) hopping to explore the region of the phase diagram where the Fermi liquid phase is separated from the pseudogap phase by the Lifshitz line at zero temperature. We implement the Hirsch-Fye cluster solver that has the advantage of providing direct access to the computation of the bond operators via the decoupling field. In the pseudogap phase, the parallel bond order susceptibility is shown to persist at zero temperature while it vanishes for the Fermi liquid phase which allows the shape of the Lifshitz line to be mapped as a function of filling and nnn hopping. Our cluster solver implements NVIDIA's CUDA language to accelerate the linear algebra of the Quantum Monte Carlo to help alleviate the sign problem by allowing for more Monte Carlo updates to be performed in a reasonable amount of computation time. Work supported by the NSF EPSCoR Cooperative Agreement No. EPS-1003897 with additional support from the Louisiana Board of Regents.

Invalidity of the Fermi liquid theory and magnetic phase transition in quasi-1D dopant-induced armchair-edged graphene nanoribbons

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Davoudiniya, Masoumeh; Yarmohammadi, Mohsen

2018-04-01

Based on theoretically tight-binding calculations considering nearest neighbors and Green's function technique, we show that the magnetic phase transition in both semiconducting and metallic armchair graphene nanoribbons with width ranging from 9.83 Å to 69.3 Å would be observed in the presence of injecting electrons by doping. This transition is explained by the temperature-dependent static charge susceptibility through calculation of the correlation function of charge density operators. This work showed that charge concentration of dopants in such system plays a crucial role in determining the magnetic phase. A variety of multicritical points such as transition temperatures and maximum susceptibility are compared in undoped and doped cases. Our findings show that there exist two different transition temperatures and maximum susceptibility depending on the ribbon width in doped structures. Another remarkable point refers to the invalidity (validity) of the Fermi liquid theory in nanoribbons-based systems at weak (strong) concentration of dopants. The obtained interesting results of magnetic phase transition in such system create a new potential for magnetic graphene nanoribbon-based devices.

Pressure-induced shift of T c and structural transition in “122” type pnictide superconductor Ca 0.34Na 0.66Fe 2As 2

DOE PAGES

Zhang, Sijia; Zhao, Kan; Yu, Xiaohui; ...

2016-07-11

Here, the effect of pressure on superconductivity of “122” type Ca 1-xNa xFe 2As 2 (x=0.66 single crystal is investigated through the temperature dependence of resistanc measurement. Optimal Na doped (Ca 0.34Na 0.66)Fe 2As 2 shows a superconductin transition with T c ~ 33 K at ambient pressure. With application of pressure, T decreases nearly linearly with d Tc/d P ~ -1.7K/GPa at pressures lower than 2 GPa and disappears gradually at higher pressure. The disappearance of superconductivit is also companied with the recovery of standard Fermi liquid behaviors of th normal-state transport properties. Moreover, (Ca 0.34Na 0.66)Fe 2As 2more » exhibits a tetragona (T) to collapsed-tetragonal (c T) transition at about 3 GPa. The evolution o non-Fermi liquid behaviors and superconductivity under pressure are both relate to the interband fluctuations.« less

Peculiar phase diagram with isolated superconducting regions in ThFeAsN1‑x O x

NASA Astrophysics Data System (ADS)

Li, Bai-Zhuo; Wang, Zhi-Cheng; Wang, Jia-Lu; Zhang, Fu-Xiang; Wang, Dong-Ze; Zhang, Feng-Yuan; Sun, Yu-Ping; Jing, Qiang; Zhang, Hua-Fu; Tan, Shu-Gang; Li, Yu-Ke; Feng, Chun-Mu; Mei, Yu-Xue; Wang, Cao; Cao, Guang-Han

2018-06-01

ThFeAsN1‑x O x () system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T c value decreases rapidly to below 2 K for , and surprisingly, superconductivity re-appears in the range of with a maximum of 17.5 K at x  =  0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x  =  0.4 is , which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN1‑x O x presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

Non-Fermi-liquid and topological states with strong spin-orbit coupling.

PubMed

Moon, Eun-Gook; Xu, Cenke; Kim, Yong Baek; Balents, Leon

2013-11-15

We argue that a class of strongly spin-orbit-coupled materials, including some pyrochlore iridates and the inverted band gap semiconductor HgTe, may be described by a minimal model consisting of the Luttinger Hamiltonian supplemented by Coulomb interactions, a problem studied by Abrikosov and collaborators. It contains twofold degenerate conduction and valence bands touching quadratically at the zone center. Using modern renormalization group methods, we update and extend Abrikosov's classic work and show that interactions induce a quantum critical non-Fermi-liquid phase, stable provided time-reversal and cubic symmetries are maintained. We determine the universal power-law exponents describing various observables in this Luttinger-Abrikosov-Beneslavskii state, which include conductivity, specific heat, nonlinear susceptibility, and the magnetic Gruneisen number. Furthermore, we determine the phase diagram in the presence of cubic and/or time-reversal symmetry breaking perturbations, which includes a topological insulator and Weyl semimetal phases. Many of these phases possess an extraordinarily large anomalous Hall effect, with the Hall conductivity scaling sublinearly with magnetization σ(xy)∼M0.51.

Role of four-fermion interaction and impurity in the states of two-dimensional semi-Dirac materials

NASA Astrophysics Data System (ADS)

Wang, Jing

2018-03-01

We study the effects of four-fermion interaction and impurity on the low-energy states of 2D semi-Dirac materials by virtue of the unbiased renormalization group approach. The coupled flow equations that govern the energy-dependent evolutions of all correlated interaction parameters are derived after taking into account one-loop corrections from the interplay between four-fermion interaction and impurity. Whether and how four-fermion interaction and impurity influence the low-energy properties of 2D semi-Dirac materials are discreetly explored and addressed attentively. After carrying out the standard renormalization group analysis, we find that both trivial insulating and nontrivial semimetal states are qualitatively stable against all four kinds of four-fermion interactions. However, while switching on both four-fermion interaction and impurity, certain insulator-semimetal phase transitions and the distance of Dirac nodal points can be respectively induced and modified due to their strong interplay and intimate competition. Moreover, several non-Fermi liquid behaviors that deviate from the conventional Fermi liquids are exhibited at the lowest-energy limit.

Optical conductivity of an interacting Weyl liquid in the collisionless regime

NASA Astrophysics Data System (ADS)

Roy, Bitan; Juričić, Vladimir

2017-10-01

Optical conductivity (OC) can serve as a measure of correlation effects in a wide range of condensed-matter systems. We show that the long-range tail of the Coulomb interaction yields a universal correction to the OC in a three-dimensional Weyl semimetal σ (Ω ) =σ0(Ω ) [1 +1/N +1 ] , where σ0(Ω ) =N e02Ω /(12 h v ) is the OC in the noninteracting system, with v as the actual (renormalized) Fermi velocity of Weyl quasiparticles at frequency Ω , and e0 is the electron charge in vacuum. Such universal enhancement of OC, which depends only on the number of Weyl nodes near the Fermi level (N ), is a remarkable consequence of an intriguing conspiracy among the quantum-critical nature of an interacting Weyl liquid, marginal irrelevance of the long-range Coulomb interaction, and violation of hyperscaling in three dimensions, and can directly be measured in recently discovered Weyl as well as Dirac materials. By contrast, a local density-density interaction produces a nonuniversal correction to the OC, stemming from the nonrenormalizable nature of the corresponding interacting field theory.

Temperature dependence of superfluid density in YBa 2Cu 3O 7- δ and Y 0.7Ca 0.3Ba 2Cu 3O 7- δ thin films: A doping dependence study of the linear slope

NASA Astrophysics Data System (ADS)

Lai, L. S.; Juang, J. Y.; Wu, K. H.; Uen, T. M.; Gou, Y. S.

2005-11-01

By using a microstrip ring resonator to measure the temperature dependence of the in-plane magnetic penetration depth λ(T) in YBa2Cu3O7-δ (YBCO) and Y0.7Ca0.3Ba2Cu3O7-δ (Ca-YBCO) epitaxially grown thin films, the linear temperature dependence of the superfluid density ρs/m∗ ≡ 1/λ2(T) was observed from the under- to the overdoped regime at the temperatures below T/Tc ≈ 0.3 . For the underdoped regime of YBCO and Ca-YBCO thin films, the magnitude of the slope d(1/λ2(T))/dT is insensitive to doping, and it can be treated in the framework of projected d-density-wave model. Combining these slope values with the thermal conductivity measurements, the Fermi-liquid correction factor α2 from the Fermi-liquid model, suggested by Wen and Lee, was revealed here with various doping levels.

Your Retirement Nest Egg: A Goose Egg or a Golden Goose

ERIC Educational Resources Information Center

Stein, Lawrence

2010-01-01

For years, people have been taught that maintaining liquidity of assets, particularly at retirement, is beneficial. One's liquidity, that is, monies he/she controls and has ready access to for discretionary withdrawals, translates into uncertainty to the company holding those assets because they can be withdrawn at any time. If one can increase a…

Interplay of Coulomb interactions and disorder in three-dimensional quadratic band crossings without time-reversal symmetry and with unequal masses for conduction and valence bands

NASA Astrophysics Data System (ADS)

Mandal, Ipsita; Nandkishore, Rahul M.

2018-03-01

Coulomb interactions famously drive three-dimensional quadratic band crossing semimetals into a non-Fermi liquid phase of matter. In a previous work [Nandkishore and Parameswaran, Phys. Rev. B 95, 205106 (2017), 10.1103/PhysRevB.95.205106], the effect of disorder on this non-Fermi liquid phase was investigated, assuming that the band structure was isotropic, assuming that the conduction and valence bands had the same band mass, and assuming that the disorder preserved exact time-reversal symmetry and statistical isotropy. It was shown that the non-Fermi liquid fixed point is unstable to disorder and that a runaway flow to strong disorder occurs. In this paper, we extend that analysis by relaxing the assumption of time-reversal symmetry and allowing the electron and hole masses to differ (but continuing to assume isotropy of the low energy band structure). We first incorporate time-reversal symmetry breaking disorder and demonstrate that there do not appear any new fixed points. Moreover, while the system continues to flow to strong disorder, time-reversal-symmetry-breaking disorder grows asymptotically more slowly than time-reversal-symmetry-preserving disorder, which we therefore expect should dominate the strong-coupling phase. We then allow for unequal electron and hole masses. We show that whereas asymmetry in the two masses is irrelevant in the clean system, it is relevant in the presence of disorder, such that the `effective masses' of the conduction and valence bands should become sharply distinct in the low-energy limit. We calculate the RG flow equations for the disordered interacting system with unequal band masses and demonstrate that the problem exhibits a runaway flow to strong disorder. Along the runaway flow, time-reversal-symmetry-preserving disorder grows asymptotically more rapidly than both time-reversal-symmetry-breaking disorder and the Coulomb interaction.

Magnetic coupling between liquid 3He and a solid state substrate: a new approach

NASA Astrophysics Data System (ADS)

Klochkov, Alexander V.; Naletov, Vladimir V.; Tayurskii, Dmitrii A.; Tagirov, Murat S.; Suzuki, Haruhiko

2000-07-01

We suggest a new approach for solving the long-standing problem of a magnetic coupling between liquid 3He and a solid state substrate at temperatures above the Fermi temperature. The approach is based on our previous careful investigations of the physical state of a solid substrate by means of several experimental methods (EPR, NMR, conductometry, and magnetization measurements). The developed approach allows, first, to get more detailed information about the magnetic coupling phenomenon by varying the repetition time in pulse NMR investigations of liquid 3He in contact with the solid state substrate and, second, to compare the obtained dependences and the data of NMR-cryoporometry and AFM-microscopy.

Itinerancy-Enhanced Quantum Fluctuation of Magnetic Moments in Iron-Based Superconductors

NASA Astrophysics Data System (ADS)

Tam, Yu-Ting; Yao, Dao-Xin; Ku, Wei

We investigate the influence of itinerant carriers on dynamics and fluctuation of local moments in Fe-based superconductors, via linear spin-wave analysis of a spin-fermion model containing both itinerant and local degrees of freedom.Surprisingly against the common lore, instead of enhancing the (π,0) order, itinerant carriers with well nested Fermi surfaces are found to induce a significant amount of spatial and temporal quantum fluctuation that leads to the observed small ordered moment. Interestingly, the underlying mechanism is shown to be intra-pocket nesting-associated long-range coupling rather than the previously believed ferromagnetic double-exchange effect. This challenges the validity of ferromagnetically compensated first-neighbor coupling reported from short-range fitting to the experimental dispersion, which turns out to result instead from the ferro-orbital order that is also found instrumental in stabilizing the magnetic order. *Y.-T. Tam, D.-X. Yao and W. Ku, Phys. Rev. Lett. 115, 117001 (2015) Work supported by US DOE No.DE-AC02-98CH10886 and CHN No. NBRPC-2012CB821400, No. NSFC-11275279.

Theory of inhomogeneous quantum systems. III. Variational wave functions for Fermi fluids

NASA Astrophysics Data System (ADS)

Krotscheck, E.

1985-04-01

We develop a general variational theory for inhomogeneous Fermi systems such as the electron gas in a metal surface, the surface of liquid 3He, or simple models of heavy nuclei. The ground-state wave function is expressed in terms of two-body correlations, a one-body attenuation factor, and a model-system Slater determinant. Massive partial summations of cluster expansions are performed by means of Born-Green-Yvon and hypernetted-chain techniques. An optimal single-particle basis is generated by a generalized Hartree-Fock equation in which the two-body correlations screen the bare interparticle interaction. The optimization of the pair correlations leads to a state-averaged random-phase-approximation equation and a strictly microscopic determination of the particle-hole interaction.

Unconventional aspects of electronic transport in delafossite oxides

NASA Astrophysics Data System (ADS)

Daou, Ramzy; Frésard, Raymond; Eyert, Volker; Hébert, Sylvie; Maignan, Antoine

2017-12-01

The electronic transport properties of the delafossite oxides ? are usually understood in terms of two well-separated entities, namely the triangular ? and (? layers. Here, we review several cases among this extensive family of materials where the transport depends on the interlayer coupling and displays unconventional properties. We review the doped thermoelectrics based on ? and ?, which show a high-temperature recovery of Fermi-liquid transport exponents, as well as the highly anisotropic metals ?, ?, and ?, where the sheer simplicity of the Fermi surface leads to unconventional transport. We present some of the theoretical tools that have been used to investigate these transport properties and review what can and cannot be learned from the extensive set of electronic structure calculations that have been performed.

Recent ARPES experiments on quasi-1D bulk materials and artificial structures.

PubMed

Grioni, M; Pons, S; Frantzeskakis, E

2009-01-14

The spectroscopy of quasi-one-dimensional (1D) systems has been a subject of strong interest since the first experimental observations of unusual line shapes in the early 1990s. Angle-resolved photoemission (ARPES) measurements performed with increasing accuracy have greatly broadened our knowledge of the properties of bulk 1D materials and, more recently, of artificial 1D structures. They have yielded a direct view of 1D bands, of open Fermi surfaces, and of characteristic instabilities. They have also provided unique microscopic evidence for the non-conventional, non-Fermi-liquid, behavior predicted by theory, and for strong and singular interactions. Here we briefly review some of the remarkable experimental results obtained in the last decade.

Starting points for the study of non-Fermi liquid-like properties of FeCrAs

NASA Astrophysics Data System (ADS)

O'Brien, Patrick James

FeCrAs exhibits non-Fermi liquid-like behavior because of its odd combination of thermodynamic, transport, and magnetic properties. In particular, the resistivity of FeCrAs is not characteristic of a metal or an insulator and so remains a mystery. In this thesis, we seek a model to describe its properties. In FeCrAs, local moments reside on the Cr sites, and there is some conduction. We study the simplest possible model on the kagome lattice that features local moments and itinerant electrons, the kagome Kondo Lattice Model. We present the phase diagram of this model, which features a host of complex spin orders, one of which is the √3 x √3, the experimentally observed magnetic ground state in FeCrAs. The kagome Kondo Lattice Model, having one itinerant d-orbital band on the kagome lattice, does not fully capture the microscopic physics of FeCrAs. The kagome Kondo Lattice Model also will not de- scribe the mutilation of the Fermi surface. To investigate the microscopic properties, we calculated LDA and LDA+U results. These results and GGA results from another group all exhibit high d-orbital density of states at the Fermi energy as well as low p-orbital density of states at the Fermi energy. The DFT results motivated us to construct a model based on the chemistry and full geometry of the FeCrAs crystal. The model we construct is an effective hopping model consisting of only d-orbital operators that we call the Optimal Overlap Hopping Model (OOHM). We calculate the band structure that results from the OOHM, and this band structure can be compared to ARPES measurements. As an example of how one can use the OOHM, we calculate a dynamic spin structure factor from within the OOHM, and we compare it to neutron scattering data. We consider both the OOHM and the Kondo Lattice Model on the kagome lattice as starting points from which we can launch studies of FeCrAs, and we present the existing theories for FeCrAs on a metallicity spectrum to illustrate the various perspectives from which FeCrAs is studied.

Multipolar Kondo effect in a S10-P32 mixture of 173Yb atoms

NASA Astrophysics Data System (ADS)

Kuzmenko, Igor; Kuzmenko, Tetyana; Avishai, Yshai; Jo, Gyu-Boong

2018-02-01

Whereas in the familiar Kondo effect the exchange interaction is dipolar, there are systems in which the exchange interaction is multipolar, as has been realized in a recent experiment. Here, we study multipolar Kondo effect in a Fermi gas of cold 173Yb atoms. Making use of different ac polarizabilities of the electronic ground state Yb (S10 ) and the long-lived metastable state Yb*(P32 ), it is suggested that the latter atoms can be localized and serve as a dilute concentration of magnetic impurities while the former ones remain itinerant. The exchange mechanism between the itinerant Yb and the localized Yb* atoms is analyzed and shown to be antiferromagnetic. The quadrupole and octupole interactions act to enhance the Kondo temperature TK that is found to be experimentally accessible. The bare exchange Hamiltonian needs to be decomposed into dipole (d), quadrupole (q), and octupole (o) interactions in order to retain its form under renormalization group (RG) analysis, in which the corresponding exchange constants (λd,λq, and λo) flow independently. Numerical solution of the RG scaling equations reveals a few finite fixed points. Arguments are presented that the Fermi-liquid fixed point at low temperature is unstable, indicating that the impurity is overscreened, which suggests a non-Fermi-liquid phase. The impurity contributions to the specific heat, entropy, and the magnetic susceptibility are calculated in the weak coupling regime (T ≫TK ), and are compared with the analogous results obtained for the standard case of dipolar exchange interaction (the s -d Hamiltonian).

Spin-resolved band structure of a densely packed Pb monolayer on Si(111)

NASA Astrophysics Data System (ADS)

Brand, C.; Muff, S.; Fanciulli, M.; Pfnür, H.; Tringides, M. C.; Dil, J. H.; Tegenkamp, C.

2017-07-01

Monolayer structures of Pb on Si(111) attracted recently considerable interest as superconductivity was found in these truly two-dimensional (2D) structures. In this study, we analyzed the electronic surface band structure of the so-called striped incommensurate Pb phase with 4/3 ML coverage by means of spin-resolved photoemission spectroscopy. Our results fully agree with density functional theory calculations done by Ren et al. [Phys. Rev. B 94, 075436 (2016), 10.1103/PhysRevB.94.075436]. We observe a local Zeeman-type splitting of a fully occupied and spin-polarized surface band at the K¯√{3} points. The growth of this densely packed Pb structure results in the formation of imbalanced rotational domains, which triggered the detection of C3 v symmetry forbidden spin components for surface states around the Fermi energy. Moreover, the Fermi surface of the metallic surface state of this phase is Rashba spin split and revealed a pronounced warping. However, the 2D nesting vectors are incommensurate with the atomic structure, thus keeping this system rather immune against charge density wave formation and possibly enabling a superconducting behavior.

Superconductivity in SnO: a nonmagnetic analog to Fe-based superconductors?

PubMed

Forthaus, M K; Sengupta, K; Heyer, O; Christensen, N E; Svane, A; Syassen, K; Khomskii, D I; Lorenz, T; Abd-Elmeguid, M M

2010-10-08

We discovered that under pressure SnO with α-PbO structure, the same structure as in many Fe-based superconductors, e.g., β-FeSe, undergoes a transition to a superconducting state for p≳6 GPa with a maximum Tc of 1.4 K at p=9.3 GPa. The pressure dependence of Tc reveals a domelike shape and superconductivity disappears for p≳16 GPa. It is further shown from band structure calculations that SnO under pressure exhibits a Fermi surface topology similar to that reported for some Fe-based superconductors and that the nesting between the hole and electron pockets correlates with the change of Tc as a function of pressure.

Pressure Dependence of the Charge-Density-Wave Gap in Rare-Earth Tri-Tellurides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sacchetti, A.; /Zurich, ETH; Arcangeletti, E.

2009-12-14

We investigate the pressure dependence of the optical properties of CeTe{sub 3}, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe{submore » 3}.« less

Unconventional and conventional quantum criticalities in CeRh0.58Ir0.42In5

NASA Astrophysics Data System (ADS)

Luo, Yongkang; Lu, Xin; Dioguardi, Aadm P.; Rosa, Priscila F. S.; Bauer, Eric D.; Si, Qimiao; Thompson, Joe D.

2018-03-01

An appropriate description of the state of matter that appears as a second order phase transition is tuned toward zero temperature, viz. quantum-critical point (QCP), poses fundamental and still not fully answered questions. Experiments are needed both to test basic conclusions and to guide further refinement of theoretical models. Here, charge and entropy transport properties as well as AC specific heat of the heavy-fermion compound CeRh0.58Ir0.42In5, measured as a function of pressure, reveal two qualitatively different QCPs in a single material driven by a single non-symmetry-breaking tuning parameter. A discontinuous sign-change jump in thermopower suggests an unconventional QCP at pc1 accompanied by an abrupt Fermi-surface reconstruction that is followed by a conventional spin-density-wave critical point at pc2 across which the Fermi surface evolves smoothly to a heavy Fermi-liquid state. These experiments are consistent with some theoretical predictions, including the sequence of critical points and the temperature dependence of the thermopower in their vicinity.

Formation of an incoherent metallic state in Rh-doped Sr2IrO4

NASA Astrophysics Data System (ADS)

Louat, A.; Bert, F.; Serrier-Garcia, L.; Bertran, F.; Le Fèvre, P.; Rault, J.; Brouet, V.

2018-04-01

Sr2IrO4 is the archetype of the spin-orbit Mott insulator, but the nature of the metallic states that may emerge from this type of insulator is still not very well known. We study with angle-resolved photoemission the insulator-to-metal transition observed in Sr2Ir1 -xRhxO4 when Ir is substituted by Rh (0.02 0.07 , is not a Fermi liquid. It is characterized by the absence of quasiparticles, unrenormalized band dispersion compared to calculations, and an ˜30 -meV pseudogap on the entire Fermi surface.

Des proprietes de l'etat normal du modele de Hubbard bidimensionnel

NASA Astrophysics Data System (ADS)

Lemay, Francois

Depuis leur decouverte, les etudes experimentales ont demontre que les supra-conducteurs a haute temperature ont une phase normale tres etrange. Les proprietes de ces materiaux ne sont pas bien decrites par la theorie du liquide de Fermi. Le modele de Hubbard bidimensionnel, bien qu'il ne soit pas encore resolu, est toujours considere comme un candidat pour expliquer la physique de ces composes. Dans cet ouvrage, nous mettons en evidence plusieurs proprietes electroniques du modele qui sont incompatibles avec l'existence de quasi-particules. Nous montrons notamment que la susceptibilite des electrons libres sur reseau contient des singularites logarithmiques qui influencent de facon determinante les proprietes de la self-energie a basse frequence. Ces singularites sont responsables de la destruction des quasi-particules. En l'absence de fluctuations antiferromagnetiques, elles sont aussi responsables de l'existence d'un petit pseudogap dans le poids spectral au niveau de Fermi. Les proprietes du modele sont egalement etudiees pour une surface de Fermi similaire a celle des supraconducteurs a haute temperature. Un parallele est etabli entre certaines caracteristiques du modele et celles de ces materiaux.

Connection between Fermi contours of zero-field electrons and ν =1/2 composite fermions in two-dimensional systems

NASA Astrophysics Data System (ADS)

Ippoliti, Matteo; Geraedts, Scott D.; Bhatt, R. N.

2017-07-01

We investigate the relation between the Fermi sea (FS) of zero-field carriers in two-dimensional systems and the FS of the corresponding composite fermions which emerge in a high magnetic field at filling ν =1/2 , as the kinetic energy dispersion is varied. We study cases both with and without rotational symmetry and find that there is generally no straightforward relation between the geometric shapes and topologies of the two FSs. In particular, we show analytically that the composite Fermi liquid (CFL) is completely insensitive to a wide range of changes to the zero-field dispersion which preserve rotational symmetry, including ones that break the zero-field FS into multiple disconnected pieces. In the absence of rotational symmetry, we show that the notion of "valley pseudospin" in many-valley systems is generically not transferred to the CFL, in agreement with experimental observations. We also discuss how a rotationally symmetric band structure can induce a reordering of the Landau levels, opening interesting possibilities of observing higher-Landau-level physics in the high-field regime.

Direct observation of bulk Fermi surface at higher Brillouin zones in a heavily hole-doped cuprate

NASA Astrophysics Data System (ADS)

Al-Sawai, W.; Sakurai, Y.; Itou, M.; Barbiellini, B.; Mijnarends, P. E.; Markiewicz, R. S.; Kaprzyk, S.; Gillet, J.-M.; Wakimoto, S.; Fujita, M.; Basak, S.; Lin, H.; Bansil, A.; Yamada, K.

2010-03-01

We have observed the bulk Fermi surface (FS) in an overdoped (x=0.3) single crystal of La2-xSrxCuO4 by using Compton scattering. A 2-D momentum density reconstruction [1] from measured Compton profiles, yields a clear FS signature in a higher Brillouin zone centered at p=(1.5,1.5) a.u. The quantitative agreement with density functional theory (DFT) calculations [2] and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. We have also measured the 2-D angular correlation of positron annihilation radiation (2D-ACAR) [3] and noticed a similar quantitative agreement with the DFT simulations. However, 2D-ACAR does not give a clear signature of the FS in the extended momentum space in both theory and experiment. Work supported in part by the US DOE.[1] Y. Tanaka et al., Phys. Rev. B 63, 045120 (2001).[2] S. Sahrakorpi et al., Phys. Rev. Lett. 95, 157601 (2005).[3] L. C. Smedskjaer et al., J. Phys. Chem. Solids 52, 1541 (1991).

Noise and the statistical mechanics of distributed transport in a colony of interacting agents

NASA Astrophysics Data System (ADS)

Katifori, Eleni; Graewer, Johannes; Ronellenfitsch, Henrik; Mazza, Marco G.

Inspired by the process of liquid food distribution between individuals in an ant colony, in this work we consider the statistical mechanics of resource dissemination between interacting agents with finite carrying capacity. The agents move inside a confined space (nest), pick up the food at the entrance of the nest and share it with other agents that they encounter. We calculate analytically and via a series of simulations the global food intake rate for the whole colony as well as observables describing how uniformly the food is distributed within the nest. Our model and predictions provide a useful benchmark to assess which strategies can lead to efficient food distribution within the nest and also to what level the observed food uptake rates and efficiency in food distribution are due to stochastic fluctuations or specific food exchange strategies by an actual ant colony.

Interacting adiabatic quantum motor

NASA Astrophysics Data System (ADS)

Bruch, Anton; Kusminskiy, Silvia Viola; Refael, Gil; von Oppen, Felix

2018-05-01

We present a field-theoretic treatment of an adiabatic quantum motor. We explicitly discuss a motor called the Thouless motor which is based on a Thouless pump operating in reverse. When a sliding periodic potential is considered to be the motor degree of freedom, a bias voltage applied to the electron channel sets the motor in motion. We investigate a Thouless motor whose electron channel is modeled as a Luttinger liquid. Interactions increase the gap opened by the periodic potential. For an infinite Luttinger liquid the coupling-induced friction is enhanced by electron-electron interactions. When the Luttinger liquid is ultimately coupled to Fermi liquid reservoirs, the dissipation reduces to its value for a noninteracting electron system for a constant motor velocity. Our results can also be applied to a motor based on a nanomagnet coupled to a quantum spin Hall edge.

Holon Wigner Crystal in a Lightly Doped Kagome Quantum Spin Liquid

DOE PAGES

Jiang, Hong -Chen; Devereaux, T.; Kivelson, S. A.

2017-08-07

We address the problem of a lightly doped spin liquid through a large-scale density-matrix renormalization group study of the t–J model on a kagome lattice with a small but nonzero concentration δ of doped holes. It is now widely accepted that the undoped (δ = 0) spin-1/2 Heisenberg antiferromagnet has a spin-liquid ground state. Theoretical arguments have been presented that light doping of such a spin liquid could give rise to a high temperature superconductor or an exotic topological Fermi liquid metal. Instead, we infer that the doped holes form an insulating charge-density wave state with one doped hole permore » unit cell, i.e., a Wigner crystal. Spin correlations remain short ranged, as in the spin-liquid parent state, from which we infer that the state is a crystal of spinless holons, rather than of holes. In conclusion, our results may be relevant to kagome lattice herbertsmithite upon doping.« less

A New Approach to Determine the Density of Liquids and Solids without Measuring Mass and Volume: Introducing the "Solidensimeter"

ERIC Educational Resources Information Center

Kiriktas, Halit; Sahin, Mehmet; Eslek, Sinan; Kiriktas, Irem

2018-01-01

This study aims to design a mechanism with which the density of any solid or liquid can be determined without measuring its mass and volume in order to help students comprehend the concept of density more easily. The "solidensimeter" comprises of two scaled and nested glass containers (graduated cylinder or beaker) and sufficient water.…

Quantum states and optical responses of low-dimensional electron hole systems

NASA Astrophysics Data System (ADS)

Ogawa, Tetsuo

2004-09-01

Quantum states and their optical responses of low-dimensional electron-hole systems in photoexcited semiconductors and/or metals are reviewed from a theoretical viewpoint, stressing the electron-hole Coulomb interaction, the excitonic effects, the Fermi-surface effects and the dimensionality. Recent progress of theoretical studies is stressed and important problems to be solved are introduced. We cover not only single-exciton problems but also few-exciton and many-exciton problems, including electron-hole plasma situations. Dimensionality of the Wannier exciton is clarified in terms of its linear and nonlinear responses. We also discuss a biexciton system, exciton bosonization technique, high-density degenerate electron-hole systems, gas-liquid phase separation in an excited state and the Fermi-edge singularity due to a Mahan exciton in a low-dimensional metal.

Variational theory of valence fluctuations: Ground states and quasiparticle excitations of the Anderson lattice model

NASA Astrophysics Data System (ADS)

Brandow, B. H.

1986-01-01

A variational study of ground states of the orbitally nondegenerate Anderson lattice model, using a wave function with one variational parameter per Bloch state k, has been extended to deal with essentially metallic systems having a nonintegral number of electrons per site. Quasiparticle excitations are obtained by direct appeal to Landau's original definition for interacting Fermi liquids, scrEqp(k,σ)=δEtotal/δn qp(k,σ). This approach provides a simple and explicit realization of the Luttinger picture of a periodic Fermi liquid. A close correspondence is maintained between the ``interacting'' (U=∞) system and the corresponding ``noninteracting'' (U=0) case, i.e., ordinary band theory; the result can be described as a renormalized band or renormalized hybridization theory. The occupation-number distribution for the conduction orbitals displays a finite discontinuity at the Fermi surface. If the d-f hybridization is nonzero throughout the Brillouin zone, the quasiparticle spectrum will always exhibit a gap, although this gap becomes exponentially small (i.e., of order TK) in the Kondo-lattice regime. In the ``ionic'' case with precisely two electrons per site, such a system may therefore exhibit an insulating (semiconducting) gap. The quasiparticle state density exhibits a prominent spike on each side of the spectral gap, just as in the elementary hybridization model (the U=0 case). For the metallic case, with a nonintegral number of electrons per site, the Fermi level falls within one of the two sharp density peaks. The effective mass at the Fermi surface tends to be very large; enhancements by a factor >~102 are quite feasible. The foregoing variational theory has also been refined by means of a trial wave function having two variational parameters per Bloch state k. The above qualitative features are all retained, with some quantitative differences, but there are also some qualitatively new features. The most interesting of these is the appearance, within the Kondo regime, of a significant quasiparticle contribution to the f spectral weight in the vicinity of ɛf. The present ``one-parameter'' and ``two-parameter'' versions can be viewed as lattice generalizations of the first two approximations of the (1/Nf)-expansion school, although our treatment of lattice aspects departs from strict 1/Nf methodology. The two versions have Wilson ratios ≡1 and ≠1, respectively, consistent with (1/Nf)-expansion studies of the single-impurity model, and a number of other features likewise show good correspondence with (1/Nf)-expansion results. Implications are presented for the finite-temperature behaviors of several properties, especially the specific heat and electrical resistivity. Comparison with experiment then leads to some inferences about the band structures of heavy-fermion materials. A new mechanism is presented for breakup of the coherent Fermi-liquid behavior, as temperature is increased. There are two main approximations: (a) Neglect of the ``site exclusion'' problem, i.e., within cluster-expansion terms we ignore the requirement that interacting sites must all be distinct. (b) Assumption of a low density of excited quasiparticles (those excited from the ``far'' side of the hybridization gap) limits the present treatment to very low temperatures, T<

Peculiar phase diagram with isolated superconducting regions in ThFeAsN1-x O x.

PubMed

Li, Bai-Zhuo; Wang, Zhi-Cheng; Wang, Jia-Lu; Zhang, Fu-Xiang; Wang, Dong-Ze; Zhang, Feng-Yuan; Sun, Yu-Ping; Jing, Qiang; Zhang, Hua-Fu; Tan, Shu-Gang; Li, Yu-Ke; Feng, Chun-Mu; Mei, Yu-Xue; Wang, Cao; Cao, Guang-Han

2018-06-27

ThFeAsN 1-x O x ([Formula: see text]) system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at [Formula: see text] K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T c value decreases rapidly to below 2 K for [Formula: see text], and surprisingly, superconductivity re-appears in the range of [Formula: see text] with a maximum [Formula: see text] of 17.5 K at x  =  0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x  =  0.4 is [Formula: see text], which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN 1-x O x presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

Spin re-orientation in heavy fermion system α - YbAl1 - x FexB4

NASA Astrophysics Data System (ADS)

Wu, Shan; Broholm, C.; Kuga, K.; Suzuki, Shintaro; Nakatsuji, S.; Mourigal, M.; Stone, M.; Tian, Wei; Qiu, Y.; Rodriguez-Rivera, Jose

Non centro-symmetric α - YbAlB4 has a heavy Fermi liquid ground state and shares many characteristics with centro-symmetric β - YbAlB4 . Both isomorphs display intermediate valence, associated with a fluctuation scale of T0 = 200 K and a Kondo lattice scale of T* = 8 K. Unlike β - YbAlB4 , α - YbAlB4 is at the boundary of a transition from a Fermi liquid metallic state to an antiferromagnetic (AFM) insulating state, driven by Fe substitution of Al. Magnetization and specific heat measurements reveal two different antiferromagnetic phases with TN = 9 K and TN = 2 K for Fe concentration above and below x =0.07. We report single crystal neutron scattering experiments on Fe doped YbAlB4 with x =0.035 and x =0.125. While the ordering wave vector is identical, k -> = (1 , 0 , 0) , the spin orientation switches from c to a with increasing Fe concentration. This suggests different anisotropic hybridization between 4f and conduction electrons that we confirmed by determining the crystal field levels. Supported by DOE, BES through DE-FG02-08ER46544.

Abnormal specific heat enhancement and non-Fermi-liquid behavior in the heavy-fermion system U2Cu17 -xGax (5 ≤x ≤8 )

NASA Astrophysics Data System (ADS)

Svanidze, E.; Amon, A.; Prots, Yu.; Leithe-Jasper, A.; Grin, Yu.

2018-03-01

In the antiferromagnetic heavy-fermion compound U2Zn17 , the Sommerfeld coefficient γ can be enhanced if all Zn atoms are replaced by a combination of Cu and Al or Cu and Ga. In the former ternary phase, glassy behavior was observed, while for the latter, conflicting ground-state reports suggest material quality issues. In this work, we investigate the U2Cu17 -xGax substitutional series for 4.5 ≤x ≤9.5 . In the homogeneity range of the phase with the Th2Zn17 -type of crystal structure, all samples exhibit glassy behavior with 0.6 K ≤Tf≤1.8 K . The value of the electronic specific heat coefficient γ in this system exceeds 900 mJ/molUK2. Such a drastic effective-mass enhancement can possibly be attributed to the effects of structural disorder, since the role of electron concentration and lattice compression is likely minimal. Crystallographic disorder is also responsible for the emergence of non-Fermi-liquid behavior in these spin-glass materials, as evidenced by logarithmic divergence of magnetic susceptibility, specific heat, and electrical resistivity.

Automated Forensic Animal Family Identification by Nested PCR and Melt Curve Analysis on an Off-the-Shelf Thermocycler Augmented with a Centrifugal Microfluidic Disk Segment.

PubMed

Keller, Mark; Naue, Jana; Zengerle, Roland; von Stetten, Felix; Schmidt, Ulrike

2015-01-01

Nested PCR remains a labor-intensive and error-prone biomolecular analysis. Laboratory workflow automation by precise control of minute liquid volumes in centrifugal microfluidic Lab-on-a-Chip systems holds great potential for such applications. However, the majority of these systems require costly custom-made processing devices. Our idea is to augment a standard laboratory device, here a centrifugal real-time PCR thermocycler, with inbuilt liquid handling capabilities for automation. We have developed a microfluidic disk segment enabling an automated nested real-time PCR assay for identification of common European animal groups adapted to forensic standards. For the first time we utilize a novel combination of fluidic elements, including pre-storage of reagents, to automate the assay at constant rotational frequency of an off-the-shelf thermocycler. It provides a universal duplex pre-amplification of short fragments of the mitochondrial 12S rRNA and cytochrome b genes, animal-group-specific main-amplifications, and melting curve analysis for differentiation. The system was characterized with respect to assay sensitivity, specificity, risk of cross-contamination, and detection of minor components in mixtures. 92.2% of the performed tests were recognized as fluidically failure-free sample handling and used for evaluation. Altogether, augmentation of the standard real-time thermocycler with a self-contained centrifugal microfluidic disk segment resulted in an accelerated and automated analysis reducing hands-on time, and circumventing the risk of contamination associated with regular nested PCR protocols.

NMR studies of non-Fermi-liquid behavior in disordered Kondo systems

NASA Astrophysics Data System (ADS)

Liu, Chia-Ying

A number of heavy-fermion alloys have been discovered to have non-Fermi-liquid (NFL) properties in contrast to the Fermi-liquid behavior expected for normal metals. Since nuclear magnetic resonance (NMR) studies in the heavy-fermion UCusb{5-x}Pdsb{x} by our group, the "Kondo disorder" model has been recognized as one of the possible origins of NFL behavior. This dissertation describes the use of NMR to study NFL behavior in the two heavy-fermion systems Ce(Rusb{1-x}Rhsb{x})sb2Sisb2 (x = 0.5) and Usb{1-x}Thsb{x}Pdsb2Alsb3\\ (x > 0.6). The cerium compound is disordered on non-f atoms (ligand disordered), whereas the uranium system is disordered on the f sublattice. Both exhibit complex phase diagrams and NFL behavior. sp{29}Si powder-pattern NMR spectra from a randomly-oriented powder sample of CeRhRuSisb2 show broad linewidths at low temperature, consistent with disorder-induced NFL behavior. The spectra from a field-aligned sample further confirm that these broad linewidths are due to distributions of local susceptibilities. The NMR widths are in good agreement with the distribution P(Tsb{K}) of Kondo temperatures Tsb{K} derived from the previous analysis of Graf et al., Phys. Rev. Lett. 78, 3769 (1997), including a "hole" in P(Tsb{K}) for small Tsb{K}\\ lbrack P(Tsb{K} = 0) = 0rbrack which describes the return to Fermi-liquid behavior below 1 K observed in the specific heat. The Kondo disorder model successfully explains the NMR linewidth and the NFL behavior in CeRhRuSisb2 either with or without consideration of RKKY interaction between Ce moments. In Usb{1-x}Thsb{x}Pdsb2Alsb3 (x = 0.7, 0.8, 0.9) the sp{27}Al NMR spectra in unaligned powders were initially thought to indicate a metallugical problem, namely, the existence of a second phase. After careful comparison of the behavior of Knight shifts in different concentrations, those extra lines were recognized as impurity satellites instead of coming from a second phase. These impurity satellites are due to specific U near-neighbor configurations to Al sites and appear clearly in the field-aligned spectra. The intensities of the impurity satellites are proportional to the probabilities of finding occupied U sites in specific near-neighbor shells around an Al site. Comparison of the calculated and observed satellite intensities allows us to reconstruct the spectra taken from field-aligned powders with the c axis both perpendicular and parallel to the external field. The narrow linewidths observed at low temperatures suggests that "Kondo disorder" is not the cause of NFL behavior in these alloys. Several theoretical models have been proposed to explain the source of the NFL behavior in Usb{1-x}Thsb{x}Pdsb2Alsb3.

Crystal structure and properties of tetragonal EuAg{sub 4}In{sub 8} grown by metal flux technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Subbarao, Udumula; Sarkar, Sumanta; Peter, Sebastian C., E-mail: sebastiancp@jncasr.ac.in

The compound EuAg{sub 4}In{sub 8} has been obtained as single crystals in high yield from reactions run in liquid indium. X-ray diffraction on single crystals suggests that EuAg{sub 4}In{sub 8} crystallizes in the CeMn{sub 4}Al{sub 8} structure type, tetragonal space group I4/mmm with lattice constants a=b=9.7937(2) Å and c=5.7492(2) Å. Crystal structure of EuAg{sub 4}In{sub 8} is composed of pseudo Frank–Kasper cages occupied by one europium atom in each ring, which are shared through the corner along the ab plane resulting in a three dimensional network. The magnetic susceptibility of EuAg{sub 4}In{sub 8} was measured in the temperature range 2–300more » K, which obeyed Curie–Weiss law above 50 K. Magnetic moment value calculated from the fitting indicates the presence of divalent europium, which was confirmed by X-ray absorption near edge spectroscopy. Electrical resistivity measurements suggest that EuAg{sub 4}In{sub 8} is metallic in nature with a probable Fermi liquid behavior at low temperature. - Graphical abstract: The tetragonal EuAg{sub 4}In{sub 8} has been grown as single crystals from reactions run in liquid indium. Magnetic and XANES measurements suggest divalent nature of Eu and resistivity measurements suggest metallic nature. - Highlights: • EuAg{sub 4}In{sub 8} phase having tetragonal phase is grown by metal flux technique. • Magnetic and XANES measurements exhibit divalent nature of Eu in EuAg{sub 4}In{sub 8}. • Resistivity measurement suggests metallic nature and probable Fermi liquid behavior.« less

Elementary diagrams in nuclear and neutron matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiringa, R.B.

1995-08-01

Variational calculations of nuclear and neutron matter are currently performed using a diagrammatic cluster expansion with the aid of nonlinear integral equations for evaluating expectation values. These are the Fermi hypernetted chain (FHNC) and single-operator chain (SOC) equations, which are a way of doing partial diagram summations to infinite order. A more complete summation can be made by adding elementary diagrams to the procedure. The simplest elementary diagrams appear at the four-body cluster level; there is one such E{sub 4} diagram in Bose systems, but 35 diagrams in Fermi systems, which gives a level of approximation called FHNC/4. We developedmore » a novel technique for evaluating these diagrams, by computing and storing 6 three-point functions, S{sub xyz}(r{sub 12}, r{sub 13}, r{sub 23}), where xyz (= ccd, cce, ddd, dde, dee, or eee) denotes the exchange character at the vertices 1, 2, and 3. All 35 Fermi E{sub 4} diagrams can be constructed from these 6 functions and other two-point functions that are already calculated. The elementary diagrams are known to be important in some systems like liquid {sup 3}He. We expect them to be small in nuclear matter at normal density, but they might become significant at higher densities appropriate for neutron star calculations. This year we programmed the FHNC/4 contributions to the energy and tested them in a number of simple model cases, including liquid {sup 3}He and Bethe`s homework problem. We get reasonable, but not exact agreement with earlier published work. In nuclear and neutron matter with the Argonne v{sub 14} interaction these contributions are indeed small corrections at normal density and grow to only 5-10 MeV/nucleon at 5 times normal density.« less

Conditions for l =1 Pomeranchuk instability in a Fermi liquid

NASA Astrophysics Data System (ADS)

Wu, Yi-Ming; Klein, Avraham; Chubukov, Andrey V.

2018-04-01

We perform a microscopic analysis of how the constraints imposed by conservation laws affect q =0 Pomeranchuk instabilities in a Fermi liquid. The conventional view is that these instabilities are determined by the static interaction between low-energy quasiparticles near the Fermi surface, in the limit of vanishing momentum transfer q . The condition for a Pomeranchuk instability is set by Flc (s )=-1 , where Flc (s ) (a Landau parameter) is a properly normalized partial component of the antisymmetrized static interaction F (k ,k +q ;p ,p -q ) in a charge (c) or spin (s) subchannel with angular momentum l . However, it is known that conservation laws for total spin and charge prevent Pomeranchuk instabilities for l =1 spin- and charge-current order parameters. Our study aims to understand whether this holds only for these special forms of l =1 order parameters or is a more generic result. To this end we perform a diagrammatic analysis of spin and charge susceptibilities for charge and spin density order parameters, as well as perturbative calculations to second order in the Hubbard U . We argue that for l =1 spin-current and charge-current order parameters, certain vertex functions, which are determined by high-energy fermions, vanish at Fl=1 c (s )=-1 , preventing a Pomeranchuk instability from taking place. For an order parameter with a generic l =1 form factor, the vertex function is not expressed in terms of Fl=1 c (s ), and a Pomeranchuk instability may occur when F1c (s )=-1 . We argue that for other values of l , a Pomeranchuk instability may occur at Flc (s )=-1 for an order parameter with any form factor.

Casimir forces between defects in one-dimensional quantum liquids

NASA Astrophysics Data System (ADS)

Recati, A.; Fuchs, J. N.; Peça, C. S.; Zwerger, W.

2005-08-01

We discuss the effective interactions between two localized perturbations in one-dimensional quantum liquids. For noninteracting fermions, the interactions exhibit Friedel oscillations, giving rise to a Ruderman-Kittel-Kasuya-Yosida-type interaction familiar from impurity spins in metals. In the interacting case, at low energies, a Luttinger-liquid description applies. In the case of repulsive fermions, the Friedel oscillations of the interacting system are replaced, at long distances, by a universal Casimir-type interaction which depends only on the sound velocity and decays inversely with the separation. The Casimir-type interaction between localized perturbations embedded in a fermionic environment gives rise to a long-range coupling between quantum dots in ultracold Fermi gases, opening an alternative to couple qubits with neutral atoms. We also briefly discuss the case of bosonic quantum liquids in which the interaction between weak impurities turns out to be short ranged, decaying exponentially on the scale of the healing length.

Electrical and thermal transport in the quasiatomic limit of coupled Luttinger liquids

NASA Astrophysics Data System (ADS)

Szasz, Aaron; Ilan, Roni; Moore, Joel E.

2017-02-01

We introduce a new model for quasi-one-dimensional materials, motivated by intriguing but not yet well-understood experiments that have shown two-dimensional polymer films to be promising materials for thermoelectric devices. We consider a two-dimensional material consisting of many one-dimensional systems, each treated as a Luttinger liquid, with weak (incoherent) coupling between them. This approximation of strong interactions within each one-dimensional chain and weak coupling between them is the "quasiatomic limit." We find integral expressions for the (interchain) transport coefficients, including the electrical and thermal conductivities and the thermopower, and we extract their power law dependencies on temperature. Luttinger liquid physics is manifested in a violation of the Wiedemann-Franz law; the Lorenz number is larger than the Fermi liquid value by a factor between γ2 and γ4, where γ ≥1 is a measure of the electron-electron interaction strength in the system.

Higher-order Fermi-liquid corrections for an Anderson impurity away from half filling : Equilibrium properties

NASA Astrophysics Data System (ADS)

Oguri, Akira; Hewson, A. C.

2018-01-01

We study the low-energy behavior of the vertex function of a single Anderson impurity away from half filling for finite magnetic fields, using the Ward identities with careful consideration of the antisymmetry and analytic properties. The asymptotic form of the vertex function Γσσ';σ'σ(i ω ,i ω';i ω',i ω ) is determined up to terms of linear order with respect to the two frequencies ω and ω', as well as the ω2 contribution for antiparallel spins σ'≠σ at ω'=0 . From these results, we also obtain a series of the Fermi-liquid relations beyond those of Yamada-Yosida [Prog. Theor. Phys. 54, 316 (1975), 10.1143/PTP.54.316]. The ω2 real part of the self-energy Σσ(i ω ) is shown to be expressed in terms of the double derivative ∂2Σσ(0 ) /∂ ɛdσ 2 with respect to the impurity energy level ɛdσ, and agrees with the formula obtained recently by Filippone, Moca, von Delft, and Mora (FMvDM) in the Nozières phenomenological Fermi-liquid theory [Phys. Rev. B 95, 165404 (2017), 10.1103/PhysRevB.95.165404]. We also calculate the T2 correction of the self-energy and find that the real part can be expressed in terms of the three-body correlation function ∂ χ↑↓/∂ ɛd,-σ , where χ↑↓ is the static susceptibility between antiparallel spins. We also provide an alternative derivation of the asymptotic form of the vertex function. Specifically, we calculate the skeleton diagrams for the vertex function Γσσ ;σ σ(i ω ,0 ;0 ,i ω ) for parallel spins up to order U4 in the Coulomb repulsion U . It directly clarifies the fact that the analytic components of order ω vanish as a result of the cancellation of four related Feynman diagrams, which are related to each other through the antisymmetry operation.

Kohn Anomaly and Phase Stability in Group VB Transition Metals

DOE PAGES

Landa, Alexander; Soderlind, Per; Naumov, Ivan; ...

2018-03-26

In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being α-U and Cr. Whereas α-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs), Cr is known for its nesting-induced spin density waves (SDWs). Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals—materials with relatively high superconducting critical temperatures. Thismore » article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (ξ00) in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength.« less

Kohn Anomaly and Phase Stability in Group VB Transition Metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Landa, Alexander; Soderlind, Per; Naumov, Ivan

In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being α-U and Cr. Whereas α-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs), Cr is known for its nesting-induced spin density waves (SDWs). Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals—materials with relatively high superconducting critical temperatures. Thismore » article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (ξ00) in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength.« less

Pressure dependence of the Peierls transition in the quasi two-dimensional purple bronze KMo 6O 17

NASA Astrophysics Data System (ADS)

Rötger, A.; Beille, J.; Laurant, J. M.; Schlenker, C.

1993-09-01

The electrical resistivity and the lattice parameters have been studied as a function of pressure on the quasi-twodimensional purple bronze KMo 6O 17 which shows a Peierls transition towards a commensurate charge density wave state. The Peierls temperature is found to be first slightly decreased for pressures smaller than 6 kbar, then strongly increased above. This increase is associated to an anomalous contraction of the lattice parameters in the plane of the layers. The corresponding large increase of the compressibility above 16 kbar at 300 K is associated to the pretransitional regime of the Peierls transition as a function of pressure. These results are attributed mainly to an improved nesting of the Fermi surface under pressure.

Deep melting reveals liquid structural memory and anomalous ferromagnetism in bismuth.

PubMed

Shu, Yu; Yu, Dongli; Hu, Wentao; Wang, Yanbin; Shen, Guoyin; Kono, Yoshio; Xu, Bo; He, Julong; Liu, Zhongyuan; Tian, Yongjun

2017-03-28

As an archetypal semimetal with complex and anisotropic Fermi surface and unusual electric properties (e.g., high electrical resistance, large magnetoresistance, and giant Hall effect), bismuth (Bi) has played a critical role in metal physics. In general, Bi displays diamagnetism with a high volumetric susceptibility ([Formula: see text]10 -4 ). Here, we report unusual ferromagnetism in bulk Bi samples recovered from a molten state at pressures of 1.4-2.5 GPa and temperatures above [Formula: see text]1,250 K. The ferromagnetism is associated with a surprising structural memory effect in the molten state. On heating, low-temperature Bi liquid (L) transforms to a more randomly disordered high-temperature liquid (L') around 1,250 K. By cooling from above 1,250 K, certain structural characteristics of liquid L' are preserved in L. Bi clusters with characteristics of the liquid L' motifs are further preserved through solidification into the Bi-II phase across the pressure-independent melting curve, which may be responsible for the observed ferromagnetism.

Deep melting reveals liquid structural memory and anomalous ferromagnetism in bismuth

PubMed Central

Shu, Yu; Yu, Dongli; Hu, Wentao; Wang, Yanbin; Shen, Guoyin; Kono, Yoshio; Xu, Bo; He, Julong; Liu, Zhongyuan; Tian, Yongjun

2017-01-01

As an archetypal semimetal with complex and anisotropic Fermi surface and unusual electric properties (e.g., high electrical resistance, large magnetoresistance, and giant Hall effect), bismuth (Bi) has played a critical role in metal physics. In general, Bi displays diamagnetism with a high volumetric susceptibility (∼10−4). Here, we report unusual ferromagnetism in bulk Bi samples recovered from a molten state at pressures of 1.4–2.5 GPa and temperatures above ∼1,250 K. The ferromagnetism is associated with a surprising structural memory effect in the molten state. On heating, low-temperature Bi liquid (L) transforms to a more randomly disordered high-temperature liquid (L′) around 1,250 K. By cooling from above 1,250 K, certain structural characteristics of liquid L′ are preserved in L. Bi clusters with characteristics of the liquid L′ motifs are further preserved through solidification into the Bi-II phase across the pressure-independent melting curve, which may be responsible for the observed ferromagnetism. PMID:28289195

Metal insulator transition in nickel substituted FeSi

NASA Astrophysics Data System (ADS)

Krishnan, M.; Mishra, Ashish; Singh, Durgesh; Venkatesh, R.; Gangrade, Mohan; Ganesan, V.

2018-04-01

Resistivity of Fe1-xNixSi has been reported. Metal Insulator transition (MIT) is observed in Nickel (Ni) substituted FeSi for x in the range from 2 to 4 percentage. Two Band Model has been employed in order to calculate activation energy and to predict how band structure renormalized with substitution of nickel in FeSi. At sufficient level of nickel concentration an impurity band forms around Fermi level and contributes to the conduction heavily at low temperatures. Concentration around x = 0.04, displays metallic property below ˜ 70 K and is quantitatively similar to systems like Fe1-xTxSi (T = Co, Mn). Metallic component thus derived from Ni substituted FeSi seems to have an unconventional temperature dependence that may be attributed to the onset of departures from Fermi liquid picture.

Dynamical thermalization in isolated quantum dots and black holes

NASA Astrophysics Data System (ADS)

Kolovsky, Andrey R.; Shepelyansky, Dima L.

2017-01-01

We study numerically a model of quantum dot with interacting fermions. At strong interactions with small conductance the model is reduced to the Sachdev-Ye-Kitaev black-hole model while at weak interactions and large conductance it describes a Landau-Fermi liquid in a regime of quantum chaos. We show that above the Åberg threshold for interactions there is an onset of dynamical themalization with the Fermi-Dirac distribution describing the eigenstates of an isolated dot. At strong interactions in the isolated black-hole regime there is also the onset of dynamical thermalization with the entropy described by the quantum Gibbs distribution. This dynamical thermalization takes place in an isolated system without any contact with a thermostat. We discuss the possible realization of these regimes with quantum dots of 2D electrons and cold ions in optical lattices.

Metal-insulator quantum critical point beneath the high Tc superconducting dome.

PubMed

Sebastian, Suchitra E; Harrison, N; Altarawneh, M M; Mielke, C H; Liang, Ruixing; Bonn, D A; Hardy, W N; Lonzarich, G G

2010-04-06

An enduring question in correlated systems concerns whether superconductivity is favored at a quantum critical point (QCP) characterized by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high T(c) cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultrastrong magnetic fields to measure quantum oscillations in underdoped YBa(2)Cu(3)O(6+x), revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in T(c) in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centered at a critical Fermi surface instability.

Thermal Smearing of the Magneto-Kohn Anomaly for Dirac materials and comparison with the Two-dimensional electron Liquid

NASA Astrophysics Data System (ADS)

Dahal, Dipendra; Balassis, Antonios; Gumbs, Godfrey; Glasser, M. L.; graphene projects Collaboration

We compute and compare the effects due to a uniform perpendicular magnetic field and the temperature on the static polarization functions for monolayer graphene (MLG) associated with the Dirac point with that for the two-dimensional electron liquid (2DEL). Previous results for the 2DEL are discussed and we point out a flaw in reported analytic derivation to exhibit the smearing of the Fermi surface for 2DEL. The relevance of our study to the Kohn anomaly in low-dimensional structures and the Friedel oscillations for the screening of the potential for a dilute distribution of impurities is reported.

The Mott transition in the strong coupling perturbation theory

NASA Astrophysics Data System (ADS)

Sherman, A.

2015-01-01

Using the strong coupling diagram technique a self-consistent equation for the electron Green's function is derived for the repulsive Hubbard model. Terms of two lowest orders of the ratio of the bandwidth Δ to the Hubbard repulsion U are taken into account in the irreducible part of the Larkin equation. The obtained equation is shown to retain causality and reduces to Green's function of uncorrelated electrons in the limit U → 0. Calculations were performed for the semi-elliptical initial band. It is shown that the approximation describes the Mott transition, which occurs at Uc =√{ 3 } Δ / 2. This value coincides with that obtained in the Hubbard-III approximation. At half-filling, for 0 < U Uc the Mott gap disappears.

Superconductivity in the two-dimensional Hubbard model

NASA Astrophysics Data System (ADS)

Beenen, J.; Edwards, D. M.

1995-11-01

Quasiparticle bands of the two-dimensional Hubbard model are calculated using the Roth two-pole approximation to the one-particle Green's function. Excellent agreement is obtained with recent Monte Carlo calculations, including an anomalous volume of the Fermi surface near half-filling, which can possibly be explained in terms of a breakdown of Fermi liquid theory. The calculated bands are very flat around the (π,0) points of the Brillouin zone in agreement with photoemission measurements of cuprate superconductors. With doping there is a shift in spectral weight from the upper band to the lower band. The Roth method is extended to deal with superconductivity within a four-pole approximation allowing electron-hole mixing. It is shown that triplet p-wave pairing never occurs. A self-consistent solution with singlet dx2-y2-wave pairing is found and optimal doping occurs when the van Hove singularity, corresponding to the flat band part, lies at the Fermi level. Nearest-neighbor antiferromagnetic correlations play an important role in flattening the bands near the Fermi level and in favoring superconductivity. However, the mechanism for superconductivity is a local one, in contrast to spin-fluctuation exchange models. For reasonable values of the hopping parameter the transition temperature Tc is in the range 10-100 K. The optimum doping δc lies between 0.14 and 0.25, depending on the ratio U/t. The gap equation has a BCS-like form and 2Δmax/kTc~=4.

Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi gases

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Lianyi; Lu, Haifeng; Cao, Gaoqing

2015-08-14

We present a theoretical study of the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases. While the mean-field theory provides a simple and analytical equation of state, the pressure is equal to that of a noninteracting Fermi gas in the entire BCS-BEC crossover, which is not consistent with the features of a weakly interacting Bose condensate in the BEC limit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of the two-dimensional mean-field theory indicates that the quantum fluctuations are much more pronounced than those in three dimensions. In this work, we show thatmore » the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on the boson chemical potential is recovered by the quantum fluctuations. Near the quantum phase transition from the vacuum to the BEC phase, we compare our equation of state with the known grand canonical equation of state of two-dimensional Bose gases and determine the ratio of the composite boson scattering length a B to the fermion scattering length a 2D. We find a B ≃ 0.56a 2D, in good agreement with the exact four-body calculation. As a result, we compare our equation of state in the BCS-BEC crossover with recent results from the quantum Monte Carlo simulations and the experimental measurements and find good agreements.« less

Ultracold fermions in a one-dimensional bipartite optical lattice: Metal-insulator transitions driven by shaking

NASA Astrophysics Data System (ADS)

Di Liberto, M.; Malpetti, D.; Japaridze, G. I.; Morais Smith, C.

2014-08-01

We theoretically investigate the behavior of a system of fermionic atoms loaded in a bipartite one-dimensional optical lattice that is under the action of an external time-periodic driving force. By using Floquet theory, an effective model is derived. The bare hopping coefficients are renormalized by zeroth-order Bessel functions of the first kind with different arguments for the nearest-neighbor and next-nearest-neighbor hopping. The insulating behavior characterizing the system at half filling in the absence of driving is dynamically suppressed, and for particular values of the driving parameter the system becomes either a standard metal or an unconventional metal with four Fermi points. The existence of the four-Fermi-point metal relies on the fact that, as a consequence of the shaking procedure, the next-nearest-neighbor hopping coefficients become significant compared to the nearest-neighbor ones. We use the bosonization technique to investigate the effect of on-site Hubbard interactions on the four-Fermi-point metal-insulator phase transition. Attractive interactions are expected to enlarge the regime of parameters where the unconventional metallic phase arises, whereas repulsive interactions reduce it. This metallic phase is known to be a Luther-Emery liquid (spin-gapped metal) for both repulsive and attractive interactions, contrary to the usual Hubbard model, which exhibits a Mott-insulator phase for repulsive interactions. Ultracold fermions in driven one-dimensional bipartite optical lattices provide an interesting platform for the realization of this long-studied four-Fermi-point unconventional metal.

Field-induced superconducting phase of FeSe in the BCS-BEC cross-over

PubMed Central

Kasahara, Shigeru; Watashige, Tatsuya; Hanaguri, Tetsuo; Kohsaka, Yuhki; Yamashita, Takuya; Shimoyama, Yusuke; Mizukami, Yuta; Endo, Ryota; Ikeda, Hiroaki; Aoyama, Kazushi; Terashima, Taichi; Uji, Shinya; Wolf, Thomas; von Löhneysen, Hilbert; Shibauchi, Takasada; Matsuda, Yuji

2014-01-01

Fermi systems in the cross-over regime between weakly coupled Bardeen–Cooper–Schrieffer (BCS) and strongly coupled Bose–Einstein-condensate (BEC) limits are among the most fascinating objects to study the behavior of an assembly of strongly interacting particles. The physics of this cross-over has been of considerable interest both in the fields of condensed matter and ultracold atoms. One of the most challenging issues in this regime is the effect of large spin imbalance on a Fermi system under magnetic fields. Although several exotic physical properties have been predicted theoretically, the experimental realization of such an unusual superconducting state has not been achieved so far. Here we show that pure single crystals of superconducting FeSe offer the possibility to enter the previously unexplored realm where the three energies, Fermi energy εF, superconducting gap Δ, and Zeeman energy, become comparable. Through the superfluid response, transport, thermoelectric response, and spectroscopic-imaging scanning tunneling microscopy, we demonstrate that εF of FeSe is extremely small, with the ratio Δ/εF∼1(∼0.3) in the electron (hole) band. Moreover, thermal-conductivity measurements give evidence of a distinct phase line below the upper critical field, where the Zeeman energy becomes comparable to εF and Δ. The observation of this field-induced phase provides insights into previously poorly understood aspects of the highly spin-polarized Fermi liquid in the BCS-BEC cross-over regime. PMID:25378706

Electronic structure of charge-density-wave state in quasi-2D KMo6O17 purple bronze characterized by angle resolved photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Valbuena, M. A.; Avila, J.; Drouard, S.; Guyot, H.; Asensio, M. C.

2006-01-01

We report on an angle-resolved-photoemission spectroscopy (ARPES) investigation of layered quasi-two dimensional (2D) Molybdenum purple bronze KMo6O17 in order to study and characterizes the transition to a charge-density-wave (CDW) state. We have performed photoemission temperature dependent measurements cooling down from room temperature (RT) to 32 K, well below the Peierls transition for this material, with CDW transition temperature Tc =110 K. The spectra have been taken at a selected kF point of the Fermi surface (FS) that satisfies the nesting condition of the FS, looking for the characteristic pseudo-gap opening in this kind of materials. The pseudogap has been estimated and it result to be in agreement with our previous works. The shift to lower binding energy of crossing Fermi level ARPES feature have been also confirmed and studied as a function of temperature, showing a rough like BCS behaviour. Finally we have also focused on ARPES measurements along ΓM¯ high symmetry direction for both room and low temperature states finding some insight for ‘shadow’ or back folded bands indicating the new periodicity of real lattice after the CDW lattice distortion.

Enhanced superconductivity in the high pressure phase of SnAs studied from first principles

NASA Astrophysics Data System (ADS)

Sreenivasa Reddy, P. V.; Kanchana, V.; Millichamp, T. E.; Vaitheeswaran, G.; Dugdale, S. B.

2017-01-01

First principles calculations are performed using density functional theory and density functional perturbation theory for SnAs. Total energy calculations show the first order phase transition from an NaCl structure to a CsCl one at around 37 GPa, which is also confirmed from enthalpy calculations and agrees well with experimental work. Calculations of the phonon structure and hence the electron-phonon coupling, λep, and superconducting transition temperature, Tc, across the phase diagram are performed. These calculations give an ambient pressure Tc, in the NaCl structure, of 3.08 K, in good agreement with experiment whilst at the transition pressure, in the CsCl structure, a drastically increased value of Tc = 12.2 K is found. Calculations also show a dramatic increase in the electronic density of states at this pressure. The lowest energy acoustic phonon branch in each structure also demonstrates some softening effects. Electronic structure calculations of the Fermi surface in both phases are presented for the first time as well as further calculations of the generalised susceptibility with the inclusion of matrix elements. These calculations indicate that the softening is not derived from Fermi surface nesting and it is concluded to be due to a wavevector-dependent enhancement of the electron-phonon coupling.

Automated Forensic Animal Family Identification by Nested PCR and Melt Curve Analysis on an Off-the-Shelf Thermocycler Augmented with a Centrifugal Microfluidic Disk Segment

PubMed Central

Zengerle, Roland; von Stetten, Felix; Schmidt, Ulrike

2015-01-01

Nested PCR remains a labor-intensive and error-prone biomolecular analysis. Laboratory workflow automation by precise control of minute liquid volumes in centrifugal microfluidic Lab-on-a-Chip systems holds great potential for such applications. However, the majority of these systems require costly custom-made processing devices. Our idea is to augment a standard laboratory device, here a centrifugal real-time PCR thermocycler, with inbuilt liquid handling capabilities for automation. We have developed a microfluidic disk segment enabling an automated nested real-time PCR assay for identification of common European animal groups adapted to forensic standards. For the first time we utilize a novel combination of fluidic elements, including pre-storage of reagents, to automate the assay at constant rotational frequency of an off-the-shelf thermocycler. It provides a universal duplex pre-amplification of short fragments of the mitochondrial 12S rRNA and cytochrome b genes, animal-group-specific main-amplifications, and melting curve analysis for differentiation. The system was characterized with respect to assay sensitivity, specificity, risk of cross-contamination, and detection of minor components in mixtures. 92.2% of the performed tests were recognized as fluidically failure-free sample handling and used for evaluation. Altogether, augmentation of the standard real-time thermocycler with a self-contained centrifugal microfluidic disk segment resulted in an accelerated and automated analysis reducing hands-on time, and circumventing the risk of contamination associated with regular nested PCR protocols. PMID:26147196

Quantum phase transition and non-Fermi liquid behavior in Fe1-x Co x Si (x ⩾ 0.7).

PubMed

Samatham, S Shanmukharao; Suresh, K G; Ganesan, V

2018-04-11

We report on the nature of electron correlations in Fe 1-x Co x Si ([Formula: see text]) using combined results of magnetization, specific heat and transport properties. Doping driven quantum critical point is observed to occur at [Formula: see text]. The magnetically unstable regime is identified to be centered around [Formula: see text] [[Formula: see text

New Forms of Matter in Optical Lattices

DTIC Science & Technology

2016-05-19

Daley, A. M. Läuchli, and P. Zoller Thermal vs. Entanglement Entropy: A Measurement Protocol for Fermionic Atoms with a Quantum Gas Microscope...J. A. Edge, E. Taylor, S. Zhang, S. Trotzky, J. H. Thywissen Transverse Demagnetization Dynamics of a Unitary Fermi Gas Science 344, 722 (2014...Jiang, J Ignacio Cirac, Peter Zoller, Mikhail D Lukin, "Topologically Protected Quantum State Transfer in a Chiral Spin Liquid , "Nature Communications

Quantum phase transition and non-Fermi liquid behavior in Fe1-x Co x Si (x ⩾ 0.7)

NASA Astrophysics Data System (ADS)

Shanmukharao Samatham, S.; Suresh, K. G.; Ganesan, V.

2018-04-01

We report on the nature of electron correlations in Fe1-x Co x Si (0.7 ≤slant x < 1 ) using combined results of magnetization, specific heat and transport properties. Doping driven quantum critical point is observed to occur at x˜ 0.75 . The magnetically unstable regime is identified to be centered around x\\in [0.75, 0.95 ]. The emergence of non-Fermi liquid behaviors in x  =  0.8 (near to ferromagnetic quantum critical point) and x  =  0.9 (disorder-induced) compositions are discussed on the basis of the power-law dependence of susceptibility χ ˜ T-g (g ˜ 1.07 for x  =  0.8 and 0.55 for x  =  0.9), specific heat C/T ˜ T-1+λ (λ ˜ 1.52 for x  =  0.8 and 0.9) and resistivity Δρ ˜ Td (d ˜ 1.56 for x  =  0.8 and 1.38 for x  =  0.9). Further, a comprehensive classification of doping dependent physical properties of Fe1-x Co x Si is presented in the revisited temperature-composition (T-x) phase diagram.

Numerical Study of Quantum Hall Bilayers at Total Filling νT=1 : A New Phase at Intermediate Layer Distances

NASA Astrophysics Data System (ADS)

Zhu, Zheng; Fu, Liang; Sheng, D. N.

2017-10-01

We study the phase diagram of quantum Hall bilayer systems with total filing νT=1 /2 +1 /2 of the lowest Landau level as a function of layer distances d . Based on numerical exact diagonalization calculations, we obtain three distinct phases, including an exciton superfluid phase with spontaneous interlayer coherence at small d , a composite Fermi liquid at large d , and an intermediate phase for 1.1

Effect of Zn-site substitution with Ga on non-Fermi liquid behavior in PrIr2Zn20

NASA Astrophysics Data System (ADS)

Yamada, R. J.; Onimaru, T.; Uenishi, K.; Yamane, Y.; Wakiya, K.; Matsumoto, K. T.; Umeo, K.; Takabatake, T.

2018-05-01

PrIr2Zn20 exhibits an antiferroquadrupolar (AFQ) order at TQ = 0.11 K, above which temperature the electrical resistivity ρ(T) shows an upward curvature and the magnetic specific heat divided by temperature Cm/T follows - lnT dependence. The non-Fermi Liquid (NFL) behaviors have suggested formation of a quadrupole Kondo lattice. In the present work, we have studied the effect of Ga substitution for Zn on the NFL behavior by the measurements of the specific heat C, the magnetic susceptibility χ, and ρ of PrIr2Zn20-xGax (0 ≤ x ≤ 0.25). With increasing x, the characteristic temperature T0 defined as the temperature where the magnetic entropy Sm reaches (3/4)Rln2 is increased by a factor of 3.5. Similarly, another characteristic temperature TR below which ρ(T) starts decreasing with the upward curvature increases with x by a factor of 1.2. The increments of both T0 and TR may be attributed to the possible split of the Γ3 doublet by symmetry lowering of the Pr sites. Otherwise, the quadrupole Kondo lattice would be stabilized by the enhanced c-f hybridization due to the increment of the 4p electronic density and/or the chemical pressure effect.

Unconventional high-Tc superconductivity in fullerides.

PubMed

Takabayashi, Yasuhiro; Prassides, Kosmas

2016-09-13

A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter-the overlap between the outer wave functions of the constituent molecules-is controlled by the C60 (3-) molecular electronic structure via the on-molecule Jahn-Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott-Jahn-Teller state through chemical or physical pressurization yields an unconventional Jahn-Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen-Cooper-Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn-Teller and Fermi liquid metal when the Jahn-Teller distortion melts.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. © 2016 The Author(s).

Unconventional high-Tc superconductivity in fullerides

PubMed Central

Takabayashi, Yasuhiro; Prassides, Kosmas

2016-01-01

A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc. However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter—the overlap between the outer wave functions of the constituent molecules—is controlled by the C603− molecular electronic structure via the on-molecule Jahn–Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott–Jahn–Teller state through chemical or physical pressurization yields an unconventional Jahn–Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen–Cooper–Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn–Teller and Fermi liquid metal when the Jahn–Teller distortion melts. This article is part of the themed issue ‘Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene’. PMID:27501971

Stability of Dirac Liquids with Strong Coulomb Interaction.

PubMed

Tupitsyn, Igor S; Prokof'ev, Nikolay V

2017-01-13

We develop and apply the diagrammatic Monte Carlo technique to address the problem of the stability of the Dirac liquid state (in a graphene-type system) against the strong long-range part of the Coulomb interaction. So far, all attempts to deal with this problem in the field-theoretical framework were limited either to perturbative or random phase approximation and functional renormalization group treatments, with diametrically opposite conclusions. Our calculations aim at the approximation-free solution with controlled accuracy by computing vertex corrections from higher-order skeleton diagrams and establishing the renormalization group flow of the effective Coulomb coupling constant. We unambiguously show that with increasing the system size L (up to ln(L)∼40), the coupling constant always flows towards zero; i.e., the two-dimensional Dirac liquid is an asymptotically free T=0 state with divergent Fermi velocity.

Effect of Anharmonicity on the Kondo Phenomena of a Magnetic Ion Vibrating in a Confinement Potential

NASA Astrophysics Data System (ADS)

Yashiki, Satoshi; Ueda, Kazuo

2011-08-01

Effect of anharmonicity of a cage potential for a magnetic ion vibrating in a metal is investigated by the numerical renormalization group method. The cage potential is assumed to be one-dimensional and of the double-well type. In the absence of the Coulomb interaction, we find continuous crossover among the three limiting cases: Yu--Anderson-type Kondo regime, the double-well-type Kondo one, and the renormalized Fermi chain one. In the entire parameter space of the double-well potential, the ground state is described by a local Fermi liquid. In the Yu--Anderson-type Kondo regime, a quantum phase transition to the ground state with odd parity takes place passing through the two-channel Kondo fixed point when the Coulomb interaction increases. Therefore, the vibration of a magnetic ion in an oversized cage structure is a promising route to the two-channel Kondo effect.

Strong Quantum Coherence between Fermi Liquid Mahan Excitons

NASA Astrophysics Data System (ADS)

Paul, J.; Stevens, C. E.; Liu, C.; Dey, P.; McIntyre, C.; Turkowski, V.; Reno, J. L.; Hilton, D. J.; Karaiskaj, D.

2016-04-01

In modulation doped quantum wells, the excitons are formed as a result of the interactions of the charged holes with the electrons at the Fermi edge in the conduction band, leading to the so-called "Mahan excitons." The binding energy of Mahan excitons is expected to be greatly reduced and any quantum coherence destroyed as a result of the screening and electron-electron interactions. Surprisingly, we observe strong quantum coherence between the heavy hole and light hole excitons. Such correlations are revealed by the dominating cross-diagonal peaks in both one-quantum and two-quantum two-dimensional Fourier transform spectra. Theoretical simulations based on the optical Bloch equations where many-body effects are included phenomenologically reproduce well the experimental spectra. Time-dependent density functional theory calculations provide insight into the underlying physics and attribute the observed strong quantum coherence to a significantly reduced screening length and collective excitations of the many-electron system.

Strong Quantum Coherence between Fermi Liquid Mahan Excitons.

PubMed

Paul, J; Stevens, C E; Liu, C; Dey, P; McIntyre, C; Turkowski, V; Reno, J L; Hilton, D J; Karaiskaj, D

2016-04-15

In modulation doped quantum wells, the excitons are formed as a result of the interactions of the charged holes with the electrons at the Fermi edge in the conduction band, leading to the so-called "Mahan excitons." The binding energy of Mahan excitons is expected to be greatly reduced and any quantum coherence destroyed as a result of the screening and electron-electron interactions. Surprisingly, we observe strong quantum coherence between the heavy hole and light hole excitons. Such correlations are revealed by the dominating cross-diagonal peaks in both one-quantum and two-quantum two-dimensional Fourier transform spectra. Theoretical simulations based on the optical Bloch equations where many-body effects are included phenomenologically reproduce well the experimental spectra. Time-dependent density functional theory calculations provide insight into the underlying physics and attribute the observed strong quantum coherence to a significantly reduced screening length and collective excitations of the many-electron system.

Imaging the Formation of High-Energy Dispersion Anomalies in the Actinide UCoGa5

NASA Astrophysics Data System (ADS)

Das, Tanmoy; Durakiewicz, Tomasz; Zhu, Jian-Xin; Joyce, John J.; Sarrao, John L.; Graf, Matthias J.

2012-10-01

We use angle-resolved photoemission spectroscopy to image the emergence of substantial dispersion and spectral-weight anomalies in the electronic renormalization of the actinide compound UCoGa5 that was presumed to belong to a conventional Fermi-liquid family. Kinks or abrupt breaks in the slope of the quasiparticle dispersion are detected both at low (approximately 130 meV) and high (approximately 1 eV) binding energies below the Fermi energy, ruling out any significant contribution of phonons. We perform numerical calculations to demonstrate that the anomalies are adequately described by coupling between itinerant fermions and spin fluctuations arising from the particle-hole continuum of the spin-orbit-split 5f states of uranium. These anomalies resemble the “waterfall” phenomenon of the high-temperature copper-oxide superconductors, suggesting that spin fluctuations are a generic route toward multiform electronic phases in correlated materials as different as high-temperature superconductors and actinides.

Electron teleportation and statistical transmutation in multiterminal Majorana islands

NASA Astrophysics Data System (ADS)

Michaeli, Karen; Landau, L. Aviad; Sela, Eran; Fu, Liang

2017-11-01

We study a topological superconductor island with spatially separated Majorana modes coupled to multiple normal-metal leads by single-electron tunneling in the Coulomb blockade regime. We show that low-temperature transport in such a Majorana island is carried by an emergent charge-e boson composed of a Majorana mode and an electronic excitation in leads. This transmutation from Fermi to Bose statistics has remarkable consequences. For noninteracting leads, the system flows to a non-Fermi-liquid fixed point, which is stable against tunnel couplings anisotropy or detuning away from the charge-degeneracy point. As a result, the system exhibits a universal conductance at zero temperature, which is a fraction of the conductance quantum, and low-temperature corrections with a universal power-law exponent. In addition, we consider Majorana islands connected to interacting one-dimensional leads, and find different stable fixed points near and far from the charge-degeneracy point.

Specific heat and magnetic susceptibility of CeNiSn doped with Rh.

PubMed

Slebarski, A; Maple, M B; Fijałkowski, M; Goraus, J

2010-04-28

CeNiSn is known as a semimetallic system with a small pseudogap at the Fermi energy. We investigate the effect of Rh doping on the Kondo insulator CeNiSn by means of measurements of ac magnetic susceptibility and specific heat. We show that the formation of the Kondo insulator narrow gap in CeNi(1 - x)Rh(x)Sn is associated with disorder-induced f-electron localization. For doped CeNiSn with x ≤ 0.06, the electrical resistivity data follow an activation and variable range hopping behaviour at low T, consistent with weak disorder and localization, while C/T is large, which is not a common feature of Kondo insulators. For x > 0.06, the system is metallic and exhibits non-Fermi liquid behaviour with magnetic susceptibility χ ∼ T( - n) with n ∼ 0.4 and electrical resistivity ρ ∼ T.

Quantum Hall Ferroelectrics and Nematics in Multivalley Systems

NASA Astrophysics Data System (ADS)

Sodemann, Inti; Zhu, Zheng; Fu, Liang

2017-10-01

We study broken symmetry states at integer Landau-level fillings in multivalley quantum Hall systems whose low-energy dispersions are anisotropic. When the Fermi surface of individual pockets lacks twofold rotational symmetry, like in bismuth (111) [Feldman et al. , Observation of a Nematic Quantum Hall Liquid on the Surface of Bismuth, Science 354, 316 (2016), 10.1126/science.aag1715] and in Sn1 -xPbxSe (001) [Dziawa et al., Topological Crystalline Insulator States in Pb1 -xSnxSe , Nat. Mater. 11, 1023 (2012), 10.1038/nmat3449] surfaces, interactions tend to drive the formation of quantum Hall ferroelectric states. We demonstrate that the dipole moment in these states has an intimate relation to the Fermi surface geometry of the parent metal. In quantum Hall nematic states, like those arising in AlAs quantum wells, we demonstrate the existence of unusually robust Skyrmion quasiparticles.

Bias-induced modulation of ultrafast carrier dynamics in metallic single-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Maekawa, Keisuke; Yanagi, Kazuhiro; Minami, Yasuo; Kitajima, Masahiro; Katayama, Ikufumi; Takeda, Jun

2018-02-01

The gate bias dependence of excited-state relaxation dynamics in metallic single-walled carbon nanotubes (MCNTs) was investigated using pump-probe transient absorption spectroscopy coupled with electrochemical doping through an ionic liquid. The transient transmittance decayed exponentially with the pump-probe delay time, whose value could be tuned via the Fermi-level modulation of Dirac electrons under a bias voltage. The obtained relaxation time was the shortest when the Fermi level was at the Dirac point of the MCNTs, and exhibited a U-shaped dependence on the bias voltage. Because optical dipole transitions between the Dirac bands are forbidden in MCNTs, the observed dynamics were attributed to carrier relaxation from the E11 band to the Dirac band. Using a model that considers the suppression of electron-electron scattering (impact ionization) due to Pauli blocking, we could qualitatively explain the obtained bias dependence of the relaxation time.

Dynamics of optical matter creation and annihilation in colloidal liquids controlled by laser trapping power.

PubMed

Liu, Jin; Dai, Qiao-Feng; Huang, Xu-Guang; Wu, Li-Jun; Guo, Qi; Hu, Wei; Yang, Xiang-Bo; Lan, Sheng; Gopal, Achanta Venu; Trofimov, Vyacheslav A

2008-11-15

We investigate the dynamics of optical matter creation and annihilation in a colloidal liquid that was employed to construct an all-optical switch. It is revealed that the switching-on process can be characterized by the Fermi-Dirac distribution function, while the switching-off process can be described by a steady state followed by a single exponential decay. The phase transition times exhibit a strong dependence on trapping power. With an increasing trapping power, while the switching-on time decreases rapidly, the switch-off time increases significantly, indicating the effects of optical binding and van der Waals force on the lifetime of the optical matter.

Hidden One-Dimensional Electronic Structure of η-Mo_4O_11

NASA Astrophysics Data System (ADS)

Gweon, G.-H.; Mo, S.-K.; Allen, J. W.; Höchst, H.; Sarrao, J. L.; Fisk, Z.

2002-03-01

η-Mo_4O_11 is a layered metal that undergoes two charge density wave (CDW) transitions at 109 K and 30 K, and is unique in showing a bulk quantum Hall effect. Research so far indicates that this material has a ``hidden one-dimensional'' (hidden-1d) Fermi surface (FS) in the normal state (T > 109 K), whose nesting property drives the 109 K CDW formation. Here, we directly confirm this picture by angle resolved photoemission spectroscopy (ARPES). We also observe a gap opening associated with the 109 K transition. Most interesting, this material shows the same ARPES line shape anomalies that suggest electron fractionalization in other hidden-1d materials like NaMo_6O_17 and KMo_6O_17. Studies of the 30 K transition are in progress.

Feshbach resonance management for Bose-Einstein condensates.

PubMed

Kevrekidis, P G; Theocharis, G; Frantzeskakis, D J; Malomed, Boris A

2003-06-13

An experimentally realizable scheme of periodic sign-changing modulation of the scattering length is proposed for Bose-Einstein condensates similar to dispersion-management schemes in fiber optics. Because of controlling the scattering length via the Feshbach resonance, the scheme is named Feshbach-resonance management. The modulational-instability analysis of the quasiuniform condensate driven by this scheme leads to an analog of the Kronig-Penney model. The ensuing stable localized structures are found. These include breathers, which oscillate between the Thomas-Fermi and Gaussian configuration, or may be similar to the 2-soliton state of the nonlinear Schrödinger equation, and a nearly static state ("odd soliton") with a nested dark soliton. An overall phase diagram for breathers is constructed, and full stability of the odd solitons is numerically established.

Low temperatures shear viscosity of a two-component dipolar Fermi gas with unequal population

NASA Astrophysics Data System (ADS)

Darsheshdar, E.; Yavari, H.; Zangeneh, Z.

2016-07-01

By using the Green's functions method and linear response theory we calculate the shear viscosity of a two-component dipolar Fermi gas with population imbalance (spin polarized) in the low temperatures limit. In the strong-coupling Bose-Einstein condensation (BEC) region where a Feshbach resonance gives rise to tightly bound dimer molecules, a spin-polarized Fermi superfluid reduces to a simple Bose-Fermi mixture of Bose-condensed dimers and the leftover unpaired fermions (atoms). The interactions between dimer-atom, dimer-dimer, and atom-atom take into account to the viscous relaxation time (τη) . By evaluating the self-energies in the ladder approximation we determine the relaxation times due to dimer-atom (τDA) , dimer-dimer (τcDD ,τdDD) , and atom-atom (τAA) interactions. We will show that relaxation rates due to these interactions τDA-1 ,τcDD-1, τdDD-1, and τAA-1 have T2, T4, e - E /kB T (E is the spectrum of the dimer atoms), and T 3 / 2 behavior respectively in the low temperature limit (T → 0) and consequently, the atom-atom interaction plays the dominant role in the shear viscosity in this rang of temperatures. For small polarization (τDA ,τAA ≫τcDD ,τdDD), the low temperatures shear viscosity is determined by contact interaction between dimers and the shear viscosity varies as T-5 which has the same behavior as the viscosity of other superfluid systems such as superfluid neutron stars, and liquid helium.

Model for a Ferromagnetic Quantum Critical Point in a 1D Kondo Lattice

NASA Astrophysics Data System (ADS)

Komijani, Yashar; Coleman, Piers

2018-04-01

Motivated by recent experiments, we study a quasi-one-dimensional model of a Kondo lattice with ferromagnetic coupling between the spins. Using bosonization and dynamical large-N techniques, we establish the presence of a Fermi liquid and a magnetic phase separated by a local quantum critical point, governed by the Kondo breakdown picture. Thermodynamic properties are studied and a gapless charged mode at the quantum critical point is highlighted.

NEST: a comprehensive model for scintillation yield in liquid xenon

DOE PAGES

Szydagis, M.; Barry, N.; Kazkaz, K.; ...

2011-10-03

Here, a comprehensive model for explaining scintillation yield in liquid xenon is introduced. We unify various definitions of work function which abound in the literature and incorporate all available data on electron recoil scintillation yield. This results in a better understanding of electron recoil, and facilitates an improved description of nuclear recoil. An incident gamma energy range of O(1 keV) to O(1 MeV) and electric fields between 0 and O(10 kV/cm) are incorporated into this heuristic model. We show results from a Geant4 implementation, but because the model has a few free parameters, implementation in any simulation package should bemore » simple. We use a quasi-empirical approach, with an objective of improving detector calibrations and performance verification. The model will aid in the design and optimization of future detectors. This model is also easy to extend to other noble elements. In this paper we lay the foundation for an exhaustive simulation code which we call NEST (Noble Element Simulation Technique).« less

Adler Award Lecture: Fermi-Liquid Instabilities in Strongly Correlated f-Electron Materials.^*

NASA Astrophysics Data System (ADS)

Maple, M. Brian

1996-03-01

Strongly correlated f-electron materials are replete with novel electronic states and phenomena ; e. g. , a metallic ``heavy electron'' state with a quasiparticle effective mass of several hundred times the free electron mass, anisotropic superconductivity with an energy gap that may vanish at points or along lines on the Fermi surface, the coexistence of superconductivity and antiferromagnetism over different parts of the Fermi surface, multiple superconducting phases in the hyperspace of chemical composition, temperature, pressure, and magnetic field, and an insulating phase, in so-called ``hybridization gap semiconductors'' or ``Kondo insulators'', with a small energy gap of only a few meV. During the last several years, a new low temperature non-Fermi-liquid (NFL) state has been observed in a new class of strongly correlated f-electron materials which currently consists of certain Ce and U intermetallics into which a nonmagnetic element has been substituted.(M. B. Maple et al./) , J. Low Temp. Phys. 99 , 223 (1995). The Ce and U ions have partially-filled f-electron shells and carry magnetic dipole or electric quadrupole moments which interact with the spins and charges of the conduction electrons and can participate in magnetic or quadrupolar ordering at low temperatures. The physical properties of these materials exhibit weak power law or logarithmic divergences in temperature and suggest the existence of a critical point at T=0 K. Possible origins of the 0 K critical point include an unconventional moment compensation process, such as a multichannel Kondo effect, and fluctuations of the order parameter in the vicinity of a 0 K second order phase transition. In some systems, such as Y_1-xU_xPd 3 and U_1-xTh_xPd _2Al 3 , the NFL characteristics appear to be single ion effects since they persist to low concentrations of f-moments, whereas in other systems, such as CeCu _5.9Au _0.1 , the NFL behavior seems to be associated with interactions between the f-moments. In this talk, we review recent experimental efforts to determine the characteristics, establish the systematics, and develop an understanding of NFL behavior in f-electron materials. \\vspace*3mm ^* Research supported by the U.S. National Science Foundation under Grant No. DMR-94-08835 and the U.S. Department of Energy under Grant No. DE-FG03-86ER45230.

Terahertz Spectroscopy of Individual Single-Walled Carbon Nanotubes as a Probe of Luttinger Liquid Physics.

PubMed

Chudow, Joel D; Santavicca, Daniel F; Prober, Daniel E

2016-08-10

Luttinger liquid theory predicts that collective electron excitations due to strong electron-electron interactions in a one-dimensional (1D) system will result in a modification of the collective charge-propagation velocity. By utilizing a circuit model for an individual metallic single-walled carbon nanotube as a nanotransmission line, it has been shown that the frequency-dependent terahertz impedance of a carbon nanotube can probe this expected 1D Luttinger liquid behavior. We excite terahertz standing-wave resonances on individual antenna-coupled metallic single-walled carbon nanotubes. The terahertz signal is rectified using the nanotube contact nonlinearity, allowing for a low-frequency readout of the coupled terahertz current. The charge velocity on the nanotube is determined from the terahertz spectral response. Our measurements show that a carbon nanotube can behave as a Luttinger liquid system with charge-propagation velocities that are faster than the Fermi velocity. Understanding what determines the charge velocity in low-dimensional conductors is important for the development of next generation nanodevices.

Multiple chiral topological states in liquid crystals from unstructured light beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Loussert, Charles; Brasselet, Etienne, E-mail: e.brasselet@loma.u-bordeaux1.fr

2014-02-03

It is shown experimentally that unstructured light beams can generate a wealth of distinct metastable defect structures in thin films of chiral liquid crystals. Various kinds of individual chiral topological states are obtained as well as dimers and trimers, which correspond to the entanglement of several topological unit cells. Self-assembled nested assemblies of several metastable particle-like topological states can also be formed. Finally, we propose and experimentally demonstrate an opto-electrical approach to generate tailor-made architectures.

Thermodynamics and structural transition of binary atomic Bose-Fermi mixtures in box or harmonic potentials: A path-integral study

NASA Astrophysics Data System (ADS)

Kim, Tom; Chien, Chih-Chun

2018-03-01

Experimental realizations of a variety of atomic binary Bose-Fermi mixtures have brought opportunities for studying composite quantum systems with different spin statistics. The binary atomic mixtures can exhibit a structural transition from a mixture into phase separation as the boson-fermion interaction increases. By using a path-integral formalism to evaluate the grand partition function and the thermodynamic grand potential, we obtain the effective potential of binary Bose-Fermi mixtures. Thermodynamic quantities in a broad range of temperatures and interactions are also derived. The structural transition can be identified as a loop of the effective potential curve, and the volume fraction of phase separation can be determined by the lever rule. For 6Li-7Li and 6Li-41K mixtures, we present the phase diagrams of the mixtures in a box potential at zero and finite temperatures. Due to the flexible densities of atomic gases, the construction of phase separation is more complicated when compared to conventional liquid or solid mixtures where the individual densities are fixed. For harmonically trapped mixtures, we use the local density approximation to map out the finite-temperature density profiles and present typical trap structures, including the mixture, partially separated phases, and fully separated phases.

Thermoelectric Power in Bilayer Graphene Device with Ionic Liquid Gating.

PubMed

Chien, Yung-Yu; Yuan, Hongtao; Wang, Chang-Ran; Lee, Wei-Li

2016-02-08

The quest for materials showing large thermoelectric power has long been one of the important subjects in material science and technology. Such materials have great potential for thermoelectric cooling and also high figure of merit ZT thermoelectric applications. We have fabricated bilayer graphene devices with ionic-liquid gating in order to tune its band gap via application of a perpendicular electric field on a bilayer graphene. By keeping the Fermi level at charge neutral point during the cool-down, we found that the charge puddles effect can be greatly reduced and thus largely improve the transport properties at low T in graphene-based devices using ionic liquid gating. At (Vig, Vbg) = (-1 V, +23 V), a band gap of about 36.6 ± 3 meV forms, and a nearly 40% enhancement of thermoelectric power at T = 120 K is clearly observed. Our works demonstrate the feasibility of band gap tuning in a bilayer graphene using ionic liquid gating. We also remark on the significant influence of the charge puddles effect in ionic-liquid-based devices.

Exotic emergent phenomena in the fractional quantum Hall effect

NASA Astrophysics Data System (ADS)

Coimbatore Balram, Ajit

When two-dimensional electron systems are subjected to a perpendicular magnetic field, they exhibit the marvelous phenomenon known as the fractional quantum Hall effect (FQHE). This arises as a result of the formation of composite fermions (CFs), which are bound states of electrons and an even number of vortices. The FQHE of electrons is understood as arising from the integer QHE (IQHE) of CFs. Alongside superconductivity, Bose-Einstein condensation and spin-liquids, the CF quantum fluid provides a model system for understanding strongly correlated systems and their collective behavior. Although it has been more than three decades since the experimental discovery of FQHE, the field continues to produce profound insights and pose interesting problems some of which have been addressed in this thesis. A major unanswered question in the field of FQHE is the mechanism of FQHE for the 1/3 state in the second Landau level (7/3 state). Numerical studies of this state have brought out the following puzzle: exact diagonalization studies suggest that the ground state and excitations of 1/3 state in the second Landau level are different from its counterpart in the lowest Landau level (LLL), while entanglement spectra of the two states point to the fact that they fall in the same universality class. Using methods from CF theory we show that the excitations of the 7/3 FQHE lie in the same universality class as those of the 1/3 state but are strongly modified due to screening by CF excitons, thereby settling the above discrepancy. Armed with the exciton calculation, we illustrate that by imposing certain exclusion rules for CF excitons one can build the full spectrum of FQHE in the lowest Landau level. Equipped with the techniques to calculate the spectra of FQHE systems, we carry out an extensive study of FQHE of multi-component CFs (systems possessing degrees of freedom for eg: valley and spin degeneracy), which is applicable to FQHE in systems such as graphene, AlAs and GaAs quantum wells. We provide a comprehensive list of the possible fractions, their ground state energies and the critical "Zeeman" energies for the "spin" transitions between the states and compare them with the experimental observations. In the lowest Landau level of graphene, we find an excellent agreement between theory and experiments. However, in the second Landau level of graphene we find an unexpected spontaneous spin polarization of CFs. We predict that there are no spin transitions to be expected in the second Landau level of graphene, a result that could be tested out in experiments. We reanalyzed some old experimental data showing excitation modes below the Zeeman energy in the vicinity of 1/3 filling of the lowest Landau level whose theoretical origin was unexplained. Using methods of exact diagonalization and CF theory we demonstrate that these modes arise as a result of formation of trions of CFs which have sub-Zeeman energy due to skyrmion-like physics. In the past couple of years, the Fermi wave vector of CFs has been measured very accurately in pioneering experiments at Princeton University. Motivated by these experiments we address the issue of the validity of Luttinger's theorem (which is a fundamental tenet of Landau Fermi liquid theory) for the Fermi sea of CFs. Our calculations suggest that the CF Fermi sea may violate Luttinger's theorem slightly. This not only provides a nontrivial example of a non-Fermi liquid, but gives new insight into the nature of the CF Fermi sea state and opens a new line of inquiry in the field of FQHE.

Solution of the effective Hamiltonian of impurity hopping between two sites in a metal

NASA Astrophysics Data System (ADS)

Ye, Jinwu

1997-07-01

We analyze in detail all the possible fixed points of the effective Hamiltonian of a nonmagnetic impurity hopping between two sites in a metal obtained by Moustakas and Fisher (MF). We find a line of non-Fermi liquid fixed points which continuously interpolates between the two-channel Kondo fixed point (2CK) and the one-channel, two-impurity Kondo (2IK) fixed point. There is one relevant direction with scaling dimension 12 and one leading irrelevant operator with dimension 32. There is also one marginal operator in the spin sector moving along this line. The marginal operator, combined with the leading irrelevant operator, will generate the relevant operator. For the general position on this line, the leading low-temperature exponents of the specific heat, the hopping susceptibility and the electron conductivity Cimp,χhimp,σ(T) are the same as those of the 2CK, but the finite-size spectrum depends on the position on the line. No universal ratios can be formed from the amplitudes of the three quantities except at the 2CK point on this line where the universal ratios can be formed. At the 2IK point on this line, σ(T)~2σu(1+aT3/2), no universal ratio can be formed either. The additional non-Fermi-liquid fixed point found by MF has the same symmetry as the 2IK, it has two relevant directions with scaling dimension 12, and is therefore also unstable. The leading low-temperature behaviors are Cimp~T,χhimp~lnT,σ(T)~2σu(1+aT3/2) no universal ratios can be formed. The system is shown to flow to a line of Fermi-liquid fixed points which continuously interpolates between the noninteracting fixed point and the two-channel spin-flavor Kondo fixed point discussed by the author previously. The effect of particle-hole symmetry breaking is discussed. The effective Hamiltonian in the external magnetic field is analyzed. The scaling functions for the physical measurable quantities are derived in the different regimes; their predictions for the experiments are given. Finally the implications are given for a nonmagnetic impurity hopping around three sites with triangular symmetry discussed by MF.

Ground and Low-Lying Excited States of Interacting Electron Systems: A Survey and Some Critical Analyses

NASA Astrophysics Data System (ADS)

Farid, Behnam

1999-12-01

In this contribution we deal with a number of theoretical aspects concerning physics of systems of interacting electrons. Our discussions, although amenable to appropriate generalisations, are subject to some limitations. To name, we deal with systems of spin-less fermions — or those of spin-compensated fermions with spin —, with nondegenerate ground states, and those in which relativistic effects are negligible; we disregard ionic motions and deal with "normal" (not superconducting, for instance) systems that are in addition free from randomly distributed impurities. We restrict our considerations to the absolute zero of temperature. The Green and response functions feature in our theoretical considerations. Here we give especial attention to the analytic properties of these functions for complex values of energy. We discuss how, both fundamentally and from the practical viewpoint, ground and low-lying excited-states properties can be obtained from these correlation functions. Characterising low-lying excited states by means of elementary excitations, we deal with both those that are particle-like (the Landau quasi-particles) and those that are collective (plasmons, excitation in the total distribution of electrons). We devote some space to discussions concerning the domain of validity and breakdown of the many-body perturbation theory, specifically that for the single-particle Green function and the self-energy operator. Extensive analysis of the asymptotic behaviour of dynamic correlation functions in the limits of small and large energies reveal the significance of the Kohn-Sham-like Hamiltonians within the context of the many-body perturbation theory. In view of this, at places we pay especial attention to a number of the existing density-functional theories (including the ones for the single-particle reduced density matrix and time-dependent external potentials). We discuss in some detail a number of issues that are specific to the (phenomenological) Landau Fermi-liquid theory and their justification within the framework of the many-body perturbation theory. In doing so we touch upon a number of characteristic features specific to Fermi-liquid (as oppsed to marginal Fermi- and Luttinger-liquid) systems. Finally, we put one particular approximation scheme for the self-energy operator, known as the the GW scheme, under magnifying glass and observe it in many of its facets.

Chiral Luttinger liquids and a generalized Luttinger's theorem in fractional quantum Hall edges via finite-entanglement scaling

NASA Astrophysics Data System (ADS)

Varjas, Daniel; Zaletel, Michael; Moore, Joel

2014-03-01

We use bosonic field theories and the infinite system density matrix renormalization group (iDMRG) method to study infinite strips of fractional quantum Hall (FQH) states starting from microscopic Hamiltonians. Finite-entanglement scaling allows us to accurately measure chiral central charge, edge mode exponents and momenta without finite-size errors. We analyze states in the first and second level of the standard hierarchy and compare our results to predictions of the chiral Luttinger liquid (χLL) theory. The results confirm the universality of scaling exponents in chiral edges and demonstrate that renormalization is subject to universal relations in the non-chiral case. We prove a generalized Luttinger's theorem involving all singularities in the momentum-resolved density, which naturally arises when mapping Landau levels on a cylinder to a fermion chain and deepens our understanding of non-Fermi liquids in 1D.

Chiral Luttinger liquids and a generalized Luttinger theorem in fractional quantum Hall edges via finite-entanglement scaling

NASA Astrophysics Data System (ADS)

Varjas, Dániel; Zaletel, Michael P.; Moore, Joel E.

2013-10-01

We use bosonic field theories and the infinite system density matrix renormalization group method to study infinite strips of fractional quantum Hall states starting from microscopic Hamiltonians. Finite-entanglement scaling allows us to accurately measure chiral central charge, edge-mode exponents, and momenta without finite-size errors. We analyze states in the first and second levels of the standard hierarchy and compare our results to predictions of the chiral Luttinger liquid theory. The results confirm the universality of scaling exponents in chiral edges and demonstrate that renormalization is subject to universal relations in the nonchiral case. We prove a generalized Luttinger theorem involving all singularities in the momentum-resolved density, which naturally arises when mapping Landau levels on a cylinder to a fermion chain and deepens our understanding of non-Fermi liquids in one dimension.

Graphene plasmonic nanogratings for biomolecular sensing in liquid

NASA Astrophysics Data System (ADS)

Chorsi, Meysam T.; Chorsi, Hamid T.

2017-12-01

We design a surface plasmon resonance (SPR) molecular sensor based on graphene and biomolecule adsorption at graphene-liquid interfaces. The sensor configuration consists of two opposing arrays of graphene nanograting mounted on a substrate, with a liquid-phase sensing medium confined between them. We characterize the design in simulation on a variety of substrates by altering the refractive index of the sensing medium and varying the absorbance-transmittance characteristics. The influence of various parameters on the biosensor's performance, including the Fermi level of graphene, the dielectric constant of the substrate, and the incident angle for plasmon excitation, is investigated. Numerical simulations demonstrate the sensitivity higher than 3000 nm/RIU (refractive index unit). The device supports a wide range of substrates in which graphene can be epitaxially grown. The proposed biosensor works independent of the incident angle and can be tuned to cover a broadband wavelength range.

Evaluation of highly conserved hsp65-specific nested PCR primers for diagnosing Mycobacterium tuberculosis.

PubMed

Priyadarshini, P; Tiwari, K; Das, A; Kumar, D; Mishra, M N; Desikan, P; Nath, G

2017-02-01

To evaluate the sensitivity and specificity of a new nested set of primers designed for the detection of Mycobacterium tuberculosis complex targeting a highly conserved heat shock protein gene (hsp65). The nested primers were designed using multiple sequence alignment assuming the nucleotide sequence of the M. tuberculosis H37Rv hsp65 genome as base. Multidrug-resistant Mycobacterium species along with other non-mycobacterial and fungal species were included to evaluate the specificity of M. tuberculosis hsp65 gene-specific primers. The sensitivity of the primers was determined using serial 10-fold dilutions, and was 100% as shown by the bands in the case of M. tuberculosis complex. None of the other non M. tuberculosis complex bacterial and fungal species yielded any band on nested polymerase chain reaction (PCR). The first round of amplification could amplify 0.3 ng of the template DNA, while nested PCR could detect 0.3 pg. The present hsp65-specific primers have been observed to be sensitive, specific and cost-effective, without requiring interpretation of biochemical tests, real-time PCR, sequencing or high-performance liquid chromatography. These primer sets do not have the drawbacks associated with those protocols that target insertion sequence 6110, 16S rDNA, rpoB, recA and MPT 64.

Interplay of phase sequence and electronic structure in the modulated martensites of Mn2NiGa from first-principles calculations

NASA Astrophysics Data System (ADS)

Kundu, Ashis; Gruner, Markus E.; Siewert, Mario; Hucht, Alfred; Entel, Peter; Ghosh, Subhradip

2017-08-01

We investigate the relative stability, structural properties, and electronic structure of various modulated martensites of the magnetic shape memory alloy Mn2NiGa by means of density functional theory. We observe that the instability in the high-temperature cubic structure first drives the system to a structure where modulation shuffles with a period of six atomic planes are taken into account. The driving mechanism for this instability is found to be the nesting of the minority band Fermi surface, in a similar way to that established for the prototype system Ni2MnGa . In agreement with experiments, we find 14M modulated structures with orthorhombic and monoclinic symmetries having energies lower than other modulated phases with the same symmetry. In addition, we also find energetically favorable 10M modulated structures which have not been observed experimentally for this system yet. The relative stability of various martensites is explained in terms of changes in the electronic structures near the Fermi level, affected mostly by the hybridization of Ni and Mn states. Our results indicate that the maximum achievable magnetic field-induced strain in Mn2NiGa would be larger than in Ni2MnGa . However, the energy costs for creating nanoscale adaptive twin boundaries are found to be one order of magnitude higher than that in Ni2MnGa .

Separation of charge-order and magnetic QCPs in heavy fermions and high Tc cuprates

NASA Astrophysics Data System (ADS)

Harrison, Neil

2010-03-01

The Fermi surface topology of high temperature superconductors inferred from magnetic quantum oscillation measurements provides clues for the origin of unconventional pairing thus previously not accessed by other spectroscopy techniques. While the overdoped regime of the high Tc phase diagram has a large Fermi surface consistent with bandstructure calculations, the underdoped regime of YBa2Cu2O6+x is found to be composed of small pockets. There is considerable debate as to whether the small observed ``pocket'' is hole-like or electron-like- whether the Fermi surface is best described by a t-J model or a conventional band folding picture- whether or not a Fermi liquid description applies- or- whether bilayer coupling splits the degeneracy of the observed pockets. We (myself and collaborators) have now collected an extensive body of experimental data that brings this debate to rest, but raises new questions about the nature of itinerant magnetism in underdoped high Tc cuprates. Quantum oscillation measurements are performed on multiple samples in magnetic fields extending to 85 T, temperatures between 30 mK (dilution fridge in dc fields to 45 T) and 18 K, over a range of hole dopings and with samples rotated in-situ about multiple axes with respect to the magnetic field. We perform a topographical map of the Fermi surface, enabling the in-plane shape of one of the pockets to be determined- imposing stringent constraints on the origin of the Fermi surface. While quantum oscillations measurements are consistent with a topological Fermi surface change associated with magnetism near optimal doping, they also point to a secondary instability deep within the underdoped regime beneath a high Tc superconducting sub-dome. An steep upturn in the quasiparticle effective mass is observed on underdoping, suggestive of a quantum critical point near x= 0.46 separating the metallic regime (composed of small pockets) from a more underdoped insulating charge-ordered regime (earlier reported in neutron scattering measurements). Our findings suggest the importance of two critical instabilities affecting the Fermi surface beneath the high Tc superconducting dome(s). While one of these has been proposed to provide the likely origin of unconventional pairing in the cuprates, the other can be an important factor in boosting transition temperatures. [4pt] This work is supported by the DoE BES grant ``Science in 100 T''. The author would like to thank collaborators S. E. Sebastian, C. H. Mielke, P. A. Goddard, M. M. Altarawneh, R. Liang, D. A. Bonn, W. N. Hardy and G. G. Lonzarich, and supporting staff at the National High Magnetic Field Laboratory (NHMFL). Quantum oscillation experiments are performed at the NHMFL, which is funded by the NSF with support from the DoE and State of Florida.

Strange metal from local quantum chaos

NASA Astrophysics Data System (ADS)

Ben-Zion, Daniel; McGreevy, John

2018-04-01

How to make a model of a non-Fermi-liquid metal with efficient current dissipation is a long-standing problem. Results from holographic duality suggest a framework where local critical fermionic degrees of freedom provide both a source of decoherence for the Landau quasiparticle, and a sink for its momentum. This leads us to study a Kondo lattice type model with SYK models in place of the spin impurities. We find evidence for a stable phase at intermediate couplings.

Dyakonov-Shur instability across the ballistic-to-hydrodynamic crossover

NASA Astrophysics Data System (ADS)

Mendl, Christian B.; Lucas, Andrew

2018-03-01

We numerically solve semiclassical kinetic equations and compute the growth rate of the Dyakonov-Shur instability of a two-dimensional Fermi liquid in a finite length cavity. When electron-electron scattering is fast, we observe the well-understood hydrodynamic instability and its disappearance due to viscous dissipation. When electron-electron scattering is negligible, we find that the instability re-emerges for certain boundary conditions but not for others. We discuss the implications of these findings for experiments.

Dyakonov-Shur instability across the ballistic-to-hydrodynamic crossover

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mendl, Christian B.; Lucas, Andrew

Here, we numerically solve semiclassical kinetic equations and compute the growth rate of the Dyakonov-Shur instability of a two-dimensional Fermi liquid in a finite length cavity. When electron-electron scattering is fast, we observe the well-understood hydrodynamic instability and its disappearance due to viscous dissipation. When electron-electron scattering is negligible, we find that the instability re-emerges for certain boundary conditions but not for others. We discuss the implications of these findings for experiments.

Fermion dipole moment and holography

NASA Astrophysics Data System (ADS)

Kulaxizi, Manuela; Rahman, Rakibur

2015-12-01

In the background of a charged AdS black hole, we consider a Dirac particle endowed with an arbitrary magnetic dipole moment. For non-zero charge and dipole coupling of the bulk fermion, we find that the dual boundary theory can be plagued with superluminal modes. Requiring consistency of the dual CFT amounts to constraining the strength of the dipole coupling by an upper bound. We briefly discuss the implications of our results for the physics of holographic non-Fermi liquids.

Dyakonov-Shur instability across the ballistic-to-hydrodynamic crossover

DOE PAGES

Mendl, Christian B.; Lucas, Andrew

2018-03-19

Here, we numerically solve semiclassical kinetic equations and compute the growth rate of the Dyakonov-Shur instability of a two-dimensional Fermi liquid in a finite length cavity. When electron-electron scattering is fast, we observe the well-understood hydrodynamic instability and its disappearance due to viscous dissipation. When electron-electron scattering is negligible, we find that the instability re-emerges for certain boundary conditions but not for others. We discuss the implications of these findings for experiments.

Track structure simulations at relativistic energies: an update on cross section calculations

NASA Astrophysics Data System (ADS)

Dingfelder, Michael

Charged particle track structure simulations follow the primary, as well as all (produced) sec-ondary particles in an event-by-event matter, from starting or ejection energies down to total stopping. They provide detailed information on the spacial distributions of energy depositions, interaction types, and radical species produced. These quantities provide a starting point to describe the interaction of the radiation with matter of biological interest and to explore and estimate the effects of radiation quality on various biological responses of these systems. Of special interest is liquid water which serves as surrogate for soft tissue. Ionization and excitation cross sections for bare charged particles can be calculated within the framework of the (relativistic) plane-wave Born approximation or the (relativistic) Bethe approximation. Both theories rely on a realistic model of the dielectric response function of the material under consideration and need to address relativistic medium polarization effects like the Fermi-density effect in a consistent way. In this talk we will review and present new and updated aspects of charged particle cross section calculations for relativistic heavy ions with liquid water and other materials of biological interest. This includes an updated model for the dielectric response function of liquid water to better reflect new data from inelastic X-ray scattering (IXS) experiments using synchrotron radiation and a model for the dielectric response function of calcium, which serves as a bone surrogate. We will also discuss the implementation of relativistic effect, especially of the Fermi-density effect into the cross section calculations. This work is supported by the National Aeronautics and Space Administration (NASA), grant no. NNJ04HF39G.

Universal thermodynamics of the one-dimensional attractive Hubbard model

NASA Astrophysics Data System (ADS)

Cheng, Song; Yu, Yi-Cong; Batchelor, M. T.; Guan, Xi-Wen

2018-03-01

The one-dimensional (1D) Hubbard model, describing electrons on a lattice with an on-site repulsive interaction, provides a paradigm for the physics of quantum many-body phenomena. Here, by solving the thermodynamic Bethe ansatz equations, we study the universal thermodynamics, quantum criticality, and magnetism of the 1D attractive Hubbard model. We show that the compressibility and the susceptibility of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like state obey simple additivity rules at low temperatures, indicating an existence of two free quantum fluids. The magnetic properties, such as magnetization and susceptibility, reveal three physical regions: quantum fluids at low temperatures, a non-Fermi liquid at high temperatures, and the quantum fluid to non-Fermi liquid crossover in between. The lattice interaction is seen to significantly influence the nature of the FFLO-like state in 1D. Furthermore, we show that the dimensionless Wilson ratio provides an ideal parameter to map out the various phase boundaries and to characterize the two free fluids of the FLLO-like state. The quantum scaling functions for the thermal and magnetic properties yield the same dynamic critical exponent z =2 and correlation critical exponent ν =1 /2 in the quantum critical region whenever a phase transition occurs. Our results provide a rigorous understanding of quantum criticality and free fluids of many-body systems on a 1D lattice.

Dilution and non-Fermi-liquid effects in the CePtIn Kondo lattice.

PubMed

Ragel, F C; Plessis, P de V du; Strydom, A M

2009-01-28

Measurements of electrical resistivity (ρ(T)), magnetoresistivity (MR), magnetic susceptibility (χ(T)) and heat capacity (C(P)(T)) are presented for the (Ce(1-x)La(x))PtIn alloy system of which the CePtIn parent is a known dense Kondo compound that does not order magnetically down to 50 mK. χ(T) for alloys 0≤x≤0.8 exhibits Curie-Weiss behaviour. ρ(T) results indicate a transition from a dense Kondo behaviour for 0≤x≤0.2 to a single-ion Kondo region (0.3≤x≤0.8). The Kondo energy scale as given by T(K) values calculated from MR studies and by the temperature T(max)(ρ(mag)) where the magnetic contribution to ρ(T) exhibits a maximum value, is compared with theoretical models. It is shown that the experimental results not only depend on a volume effect as given by the compressible Kondo lattice model of Lavagna but in addition confirm the more complex behaviour recently presented by Burdin and Fulde for a Kondo alloy system in which the magnetic (Ce) and non-magnetic (La) atoms are distributed randomly. Non-Fermi-liquid behaviour is predicted by Burdin and Fulde at certain critical concentrations of the alloy system and experimental evidence for this is presented through χ(T), ρ(T) and C(P)(T) measurements.

Saturation and negative temperature coefficient of electrical resistivity in liquid iron-sulfur alloys at high densities from first-principles calculations

NASA Astrophysics Data System (ADS)

Wagle, Fabian; Steinle-Neumann, Gerd; de Koker, Nico

2018-03-01

We report results on electronic transport properties of liquid Fe-S alloys at conditions of planetary cores, computed using first-principle techniques in the Kubo-Greenwood formalism. We describe a combined effect of resistivity saturation due to temperature, compression, and chemistry by comparing the electron mean free path from the Drude response of optical conductivity to the mean interatomic distance. At high compression and high sulfur concentration the Ioffe-Regel condition is satisfied, and the temperature coefficient of resistivity changes sign from positive to negative. We show that this happens due to a decrease in the d density of states at the Fermi level in response to thermal broadening.

Charge Fractionalization in the Two-Channel Kondo Effect

NASA Astrophysics Data System (ADS)

Landau, L. Aviad; Cornfeld, Eyal; Sela, Eran

2018-05-01

The phenomenon of charge fractionalization describes the emergence of novel excitations with fractional quantum numbers, as predicted in strongly correlated systems such as spin liquids. We elucidate that precisely such an unusual effect may occur in the simplest possible non-Fermi liquid, the two-channel Kondo effect. To bring this concept down to experimental test, we study nonequilibrium transport through a device realizing the charge two-channel Kondo critical point in a recent experiment by Iftikhar et al. [Nature (London) 526, 233 (2015), 10.1038/nature15384]. The shot noise at low voltages is predicted to result in a universal Fano factor e*/e =1 /2 . This allows us to experimentally identify elementary transport processes of emergent fermions carrying half-integer charge.

Inelastic X-ray Scattering from Shocked Liquid Deuterium

DOE PAGES

Regan, S. P.; Falk, K.; Gregori, G.; ...

2012-12-28

The Fermi-degenerate plasma conditions created in liquid deuterium by a laser-ablation—driven shock wave were probed with noncollective, spectrally resolved, inelastic x-ray Thomson scattering employing Cl Ly α line emission at 2.96 keV. Thus, these first x-ray Thomson scattering measurements of the microscopic properties of shocked deuterium show an inferred spatially averaged electron temperature of 8±5 eV, an electron density of 2.2(±0.5)×10 23 cm -3, and an ionization of 0.8 (-0.25, +0.15). Our two-dimensional hydrodynamic simulations using equation-of-state models suited for the extreme parameters occurring in inertial confinement fusion research and planetary interiors are consistent with the experimental results.

Migdal's theorem and electron-phonon vertex corrections in Dirac materials

NASA Astrophysics Data System (ADS)

Roy, Bitan; Sau, Jay D.; Das Sarma, S.

2014-04-01

Migdal's theorem plays a central role in the physics of electron-phonon interactions in metals and semiconductors, and has been extensively studied theoretically for parabolic band electronic systems in three-, two-, and one-dimensional systems over the last fifty years. In the current work, we theoretically study the relevance of Migdal's theorem in graphene and Weyl semimetals which are examples of 2D and 3D Dirac materials, respectively, with linear and chiral band dispersion. Our work also applies to 2D and 3D topological insulator systems. In Fermi liquids, the renormalization of the electron-phonon vertex scales as the ratio of sound (vs) to Fermi (vF) velocity, which is typically a small quantity. In two- and three-dimensional quasirelativistic systems, such as undoped graphene and Weyl semimetals, the one loop electron-phonon vertex renormalization, which also scales as η =vs/vF as η →0, is, however, enhanced by an ultraviolet logarithmic divergent correction, arising from the linear, chiral Dirac band dispersion. Such enhancement of the electron-phonon vertex can be significantly softened due to the logarithmic increment of the Fermi velocity, arising from the long range Coulomb interaction, and therefore, the electron-phonon vertex correction does not have a logarithmic divergence at low energy. Otherwise, the Coulomb interaction does not lead to any additional renormalization of the electron-phonon vertex. Therefore, electron-phonon vertex corrections in two- and three-dimensional Dirac fermionic systems scale as vs/vF0, where vF0 is the bare Fermi velocity, and small when vs≪vF0. These results, although explicitly derived for the intrinsic undoped systems, should hold even when the chemical potential is tuned away from the Dirac points.

Impurity-induced modulations in PdxNbSe3 coupled to charge-density-wave formation

NASA Astrophysics Data System (ADS)

Xue, Q.; Gong, Y.; Drake, D. L.; Qian, J.; Coleman, R. V.

1996-01-01

Very dilute amounts of Pd in PdxNbSe3 introduce long-range electronic modulations of wavelength 7b0, 4b0, 3b0, and 2b0 at room temperature as the Pd concentration increases in the range x=0.002 to x=0.02 while the low-temperature charge-density waves (CDW's) initially remain unchanged. For x>=0.02 the low-temperature CDW's are quenched while the NbSe3 structure remains intact, and the high-temperature modulations disappear, indicating a clear correlation between the two effects. The magnetoquantum oscillations due to magnetic breakdown first detect the band-structure shift followed by the sudden quenching of the nested Fermi surface sheets. The atomic force microscope scans show substantial charge transfer between chains caused by the Pd doping.

Absolute Negative Resistance Induced by Directional Electron-Electron Scattering in a Two-Dimensional Electron Gas

NASA Astrophysics Data System (ADS)

Kaya, Ismet I.; Eberl, Karl

2007-05-01

A three-terminal device formed by two electrostatic barriers crossing an asymmetrically patterned two-dimensional electron gas displays an unusual potential depression at the middle contact, yielding absolute negative resistance. The device displays momentum and current transfer ratios that far exceed unity. The observed reversal of the current or potential in the middle terminal can be interpreted as the analog of Bernoulli’s effect in a Fermi liquid. The results are explained by directional scattering of electrons in two dimensions.

High-Tc superconductivity: The t-J-V model and its applications

NASA Astrophysics Data System (ADS)

Roy, K.; Pal, P.; Nath, S.; Ghosh, N. K.

2017-05-01

We present numerical results of the t-J-V model in an 8-site tilted square cluster using exact diagonalization (ED) method with periodic boundary conditions. Effective hopping amplitude initially increases with inter-site Coulomb repulsion (V), but decreases at larger V's. The hole-hole correlation decreases with inter-site distances at smaller V. With the increase of Coulomb repulsion, the system becomes ordered. The specific heat curves confirm the non-Fermi liquid behavior of the system under t-J-V model.

Vortices and quasiparticles near the superconductor-insulator transition in thin films.

PubMed

Galitski, Victor M; Refael, G; Fisher, Matthew P A; Senthil, T

2005-08-12

We study the low temperature behavior of an amorphous superconducting film driven normal by a perpendicular magnetic-field (B). For this purpose we introduce a new two-fluid formulation consisting of fermionized field-induced vortices and electrically neutralized Bogoliubov quasiparticles (spinons) interacting via a long-ranged statistical interaction. This approach allows us to access a novel non-Fermi-liquid phase, which naturally interpolates between the low B superconductor and the high B normal metal. We discuss the properties of the resulting "vortex metal" phase.

Impurity self-energy in the strongly-correlated Bose systems

NASA Astrophysics Data System (ADS)

Panochko, Galyna; Pastukhov, Volodymyr; Vakarchuk, Ivan

2018-02-01

We proposed the nonperturbative scheme for the calculation of the impurity spectrum in the Bose system at zero temperature. The method is based on the path-integral formulation and describes an impurity as a zero-density ideal Fermi gas interacting with Bose system for which the action is written in terms of density fluctuations. On the example of the 3He atom immersed in the liquid helium-4 a good consistency with experimental data and results of Monte Carlo simulations is shown.

First-order metal-insulator transitions in the extended Hubbard model due to self-consistent screening of the effective interaction

NASA Astrophysics Data System (ADS)

Schüler, M.; van Loon, E. G. C. P.; Katsnelson, M. I.; Wehling, T. O.

2018-04-01

While the Hubbard model is the standard model to study Mott metal-insulator transitions, it is still unclear to what extent it can describe metal-insulator transitions in real solids, where nonlocal Coulomb interactions are always present. By using a variational principle, we clarify this issue for short- and long-range nonlocal Coulomb interactions for half-filled systems on bipartite lattices. We find that repulsive nonlocal interactions generally stabilize the Fermi-liquid regime. The metal-insulator phase boundary is shifted to larger interaction strengths to leading order linearly with nonlocal interactions. Importantly, nonlocal interactions can raise the order of the metal-insulator transition. We present a detailed analysis of how the dimension and geometry of the lattice as well as the temperature determine the critical nonlocal interaction leading to a first-order transition: for systems in more than two dimensions with nonzero density of states at the Fermi energy the critical nonlocal interaction is arbitrarily small; otherwise, it is finite.

Strong quantum coherence between Fermi liquid Mahan excitons

DOE PAGES

Paul, J.; Stevens, C. E.; Liu, C.; ...

2016-04-14

In modulation doped quantum wells, the excitons are formed as a result of the interactions of the charged holes with the electrons at the Fermi edge in the conduction band, leading to the so-called “Mahan excitons.” The binding energy of Mahan excitons is expected to be greatly reduced and any quantum coherence destroyed as a result of the screening and electron-electron interactions. Surprisingly, we observe strong quantum coherence between the heavy hole and light hole excitons. Such correlations are revealed by the dominating cross-diagonal peaks in both one-quantum and two-quantum two-dimensional Fourier transform spectra. Theoretical simulations based on the opticalmore » Bloch equations where many-body effects are included phenomenologically reproduce well the experimental spectra. Furthermore, time-dependent density functional theory calculations provide insight into the underlying physics and attribute the observed strong quantum coherence to a significantly reduced screening length and collective excitations of the many-electron system.« less

Dispersive Sachdev-Ye-Kitaev model: Band structure and quantum chaos

NASA Astrophysics Data System (ADS)

Zhang, Pengfei

2017-11-01

The Sachdev-Ye-Kitaev (SYK) model is a concrete model for a non-Fermi liquid with maximally chaotic behavior in (0 +1 ) dimensions. In order to gain some insights into real materials in higher dimensions where fermions could hop between different sites, here we consider coupling a SYK lattice by constant hopping. We call this the dispersive SYK model. Focusing on (1 +1 ) -dimensional homogeneous hopping, by either tuning the temperature or the relative strength of the random interaction (hopping) and constant hopping, we find a crossover between a dispersive metal to an incoherent metal, where the dynamic exponent z changes from 1 to ∞ . We study the crossover by calculating the spectral function, charge density correlator, and the Lyapunov exponent. We further find the Lyapunov exponent becomes larger when the chemical potential is tuned to approach a van Hove singularity because of the large density of states near the Fermi surface. The effect of the topological nontrivial bands is also discussed.

Hallmarks of the Mott-metal crossover in the hole-doped pseudospin-1/2 Mott insulator Sr 2IrO 4

DOE PAGES

Cao, Yue; Wang, Qiang; Waugh, Justin A.; ...

2016-04-22

The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr 2 IrO 4 . The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observedmore » in doped cuprates - pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation.« less

Statistical mechanics of light elements at high pressure. VI - Liquid-state calculations with Thomas-Fermi-Dirac theory

NASA Technical Reports Server (NTRS)

Macfarlane, J. J.

1984-01-01

A model free energy is developed for hydrogen-helium mixtures based on solid-state Thomas-Fermi-Dirac calculations at pressures relevant to the interiors of giant planets. Using a model potential similar to that for a two-component plasma, effective charges for the nuclei (which are in general smaller than the actual charges because of screening effects) are parameterized, being constrained by calculations at a number of densities, compositions, and lattice structures. These model potentials are then used to compute the equilibrium properties of H-He fluids using a charged hard-sphere model. The results find critical temperatures of about 0 K, 500 K, and 1500 K, for pressures of 10, 100, and 1000 Mbar, respectively. These phase separation temperatures are considerably lower (approximately 6,000-10,000 K) than those found from calculations using free electron perturbation theory, and suggest that H-He solutions should be stable against phase separation in the metallic zones of Jupiter and Saturn.

The development of a cryogenic over-pressure pump

NASA Astrophysics Data System (ADS)

Alvarez, M.; Cease, H.; Flaugher, B.; Flores, R.; Garcia, J.; Lathrop, A.; Ruiz, F.

2014-01-01

A cryogenic over-pressure pump (OPP) was tested in the prototype telescope liquid nitrogen (LN2) cooling system for the Dark Energy Survey (DES) Project. This OPP consists of a process cylinder (PC), gas generator, and solenoid operated valves (SOVs). It is a positive displacement pump that provided intermittent liquid nitrogen (LN2) flow to an array of charge couple devices (CCDs) for the prototype Dark Energy Camera (DECam). In theory, a heater submerged in liquid would generate the drive gas in a closed loop cooling system. The drive gas would be injected into the PC to displace that liquid volume. However, due to limitations of the prototype closed loop nitrogen system (CCD cooling system) for DECam, a quasiclosed-loop nitrogen system was created. During the test of the OPP, the CCD array was cooled to its designed set point temperature of 173K. It was maintained at that temperature via electrical heaters. The performance of the OPP was captured in pressure, temperature, and flow rate in the CCD LN2 cooling system at Fermi National Accelerator Laboratory (FNAL).

Emergence of liquid crystalline order in the lowest Landau level of a quantum Hall system with internal anisotropy

NASA Astrophysics Data System (ADS)

Ciftja, Orion

2018-05-01

It has now become evident that interplay between internal anisotropy parameters (such as electron mass anisotropy and/or anisotropic coupling of electrons to the substrate) and electron-electron correlation effects can create a rich variety of possibilities especially in quantum Hall systems. The electron mass anisotropy or material substrate effects (for example, the piezoelectric effect in GaAs) can lead to an effective anisotropic interaction potential between electrons. For lack of knowledge of realistic ab-initio potentials that may describe such effects, we adopt a phenomenological approach and assume that an anisotropic Coulomb interaction potential mimics the internal anisotropy of the system. In this work we investigate the emergence of liquid crystalline order at filling factor ν = 1/6 of the lowest Landau level, a state very close to the point where a transition from the liquid to the Wigner solid happens. We consider small finite systems of electrons interacting with an anisotropic Coulomb interaction potential and study the energy stability of an anisotropic liquid crystalline state relative to its isotropic Fermi-liquid counterpart. Quantum Monte Carlo simulation results in disk geometry show stabilization of liquid crystalline order driven by an anisotropic Coulomb interaction potential at all values of the interaction anisotropy parameter studied.

The Effective Correlation Theory for Liquid 3He

NASA Astrophysics Data System (ADS)

Puoskari, M.; Kallio, A.

1981-09-01

We show that when the antisymmetry of liquid 3He is treated with the effective correlation theory of Lado, the optimal HNC solution gives very good agreement with the optimal FHNC theory when in the latter the long wave length properties due to Fermi cancellations are treated properly. When in addition elementary diagrams are calculated with the Pade approximation, we obtain ground state energies that agree quite well with the Monte-Carlo results of Ceperley, Chester and Kalos and Levesque, especially at low densities. In addition we calculate the contribution of the three-body factors in the variational wave function. For the expectation value of the ground state energy we obtain altogether - 1.62 ± 0.15 K at a saturation density 0.015 ± 0.001 Å-3.

Charge Density Waves and the Hidden Nesting of Purple Bronze KMo6O17

NASA Astrophysics Data System (ADS)

Su, Lei; Pereira, Vitor

The layered purple bronze KMo6O17, with its robust triple CDW phase up to high temperatures, became the emblematic example of the ''hidden nesting'' concept. Recent experiments suggest that, on the surface layers, its CDW phase can be stabilized at much higher temperatures, and with a tenfold increase in the electronic gap in comparison with the bulk. Despite such interesting fermiology and properties, the K and Na purple bronzes remain largely unexplored systems, most particularly so at the theoretical level. We introduce the first multi-orbital effective tight-binding model to describe the effect of electron-electron interactions in this system. Upon fixing all the effective hopping parameters in the normal state against an ab-initio band structure, and with only the overall scale of the interactions as sole adjustable parameter, we find that a self-consistent Hartree-Fock solution reproduces extremely well the experimental behavior of the charge density wave (CDW) order parameter in the full range 0 < T < Tc , as well as the precise reciprocal space locations of the partial gap opening and Fermi arc development. The interaction strengths extracted from fitting to the experimental CDW gap are consistent with those derived from an independent Stoner-type analysis This work was supported by the Singapore National Research Foundation under Grant NRF-CRP6-2010-05.

Entanglement entropies and fermion signs of critical metals

NASA Astrophysics Data System (ADS)

Kaplis, N.; Krüger, F.; Zaanen, J.

2017-04-01

The fermion sign problem is often viewed as a sheer inconvenience that plagues numerical studies of strongly interacting electron systems. Only recently has it been suggested that fermion signs are fundamental for the universal behavior of critical metallic systems and crucially enhance their degree of quantum entanglement. In this work we explore potential connections between emergent scale invariance of fermion sign structures and scaling properties of bipartite entanglement entropies. Our analysis is based on a wave-function Ansatz that incorporates collective, long-range backflow correlations into fermionic Slater determinants. Such wave functions mimic the collapse of a Fermi liquid at a quantum critical point. Their nodal surfaces, a representation of the fermion sign structure in many-particle configurations space, show fractal behavior up to a length scale ξ that diverges at a critical backflow strength. We show that the Hausdorff dimension of the fractal nodal surface depends on ξ , the number of fermions and the exponent of the backflow. For the same wave functions we numerically calculate the second Rényi entanglement entropy S2. Our results show a crossover from volume scaling, S2˜ℓθ (θ =2 in d =2 dimensions), to the characteristic Fermi-liquid behavior S2˜ℓ lnℓ on scales larger than ξ . We find that volume scaling of the entanglement entropy is a robust feature of critical backflow fermions, independent of the backflow exponent and hence the fractal dimension of the scale invariant sign structure.

Charge and spin in low-dimensional cuprates

NASA Astrophysics Data System (ADS)

Maekawa, Sadamichi; Tohyama, Takami

2001-03-01

One of the central issues in the study of high-temperature superconducting cuprates which are composed of two-dimensional (2D) CuO2 planes is whether the 2D systems with strong electron correlation behave as a Fermi liquid or a non-Fermi-liquid-like one-dimensional (1D) system with electron correlation. In this article, we start with the detailed examination of the electronic structure in cuprates and study theoretically the spin and charge dynamics in 1D and 2D cuprates. The theoretical background of spin-charge separation in the 1D model systems including the Hubbard and t-J models is presented. The first direct observation of collective modes of spin and charge excitations in a 1D cuprate, which are called spinons and holons respectively, in angle-resolved photoemission spectroscopy (ARPES) experiments is reviewed in the light of the theoretical results based on the numerically exact-diagonalization method. The charge and spin dynamics in 1D insulating cuprates is also discussed in connection with the spin-charge separation. The arguments are extended to the 2D cuprates, and the unique aspects of the electronic properties of high-temperature superconductors are discussed. Special emphasis is placed on the d-wave-like excitations in insulating 2D cuprates observed in ARPES experiments. We explain how the excitations are caused by the spin-charge separation. The charge stripes observed in the underdoped cuprates are examined in connection with spin-charge separation in real space.

Superconductivity in an almost localized Fermi liquid of quasiparticles with spin-dependent masses and effective-field induced by electron correlations

NASA Astrophysics Data System (ADS)

Kaczmarczyk, Jan; Spałek, Jozef

2009-06-01

Paired state of nonstandard quasiparticles is analyzed in detail in two model situations. Namely, we consider the Cooper-pair bound state and the condensed phase of an almost localized Fermi liquid composed of quasiparticles in a narrow band with the spin-dependent masses and an effective field, both introduced earlier and induced by strong electronic correlations. Each of these novel characteristics is calculated in a self-consistent manner. We analyze the bound states as a function of Cooper-pair momentum |Q| in applied magnetic field in the strongly Pauli limiting case (i.e., when the orbital effects of applied magnetic field are disregarded). The spin-direction dependence of the effective mass makes the quasiparticles comprising Cooper-pair spin distinguishable in the quantum-mechanical sense, whereas the condensed gas of pairs may still be regarded as composed of identical entities. The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) condensed phase of moving pairs is by far more robust in the applied field for the case with spin-dependent masses than in the situation with equal masses of quasiparticles. Relative stability of the Bardeen-Cooper-Schrieffer vs FFLO phase is analyzed in detail on temperature-applied field plane. Although our calculations are carried out for a model situation, we can conclude that the spin-dependent masses should play an important role in stabilizing high-field low-temperature unconventional superconducting phases (FFLO, for instance) in systems such as CeCoIn5 , organic metals, and possibly others.

Evidence against a charge density wave on Bi(111)

DOE PAGES

Kim, T. K.; Wells, J.; Kirkegaard, C.; ...

2005-08-18

The Bi(111) surface was studied by scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and angle-resolved photoemission (ARPES) in order to verify the existence of a recently proposed surface charge density wave (CDW). The STM and TEM results to not support a CDW scenario at low temperatures. Thus the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electronmore » pocket at the centre of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.« less

On the stability of the electronic system in transition metal dichalcogenides.

PubMed

Faraggi, M N; Zubizarreta, X; Arnau, A; Silkin, V M

2016-05-11

Based on first-principles calculations, we prove that the origin of charge-density wave formation in metallic layered transition metal dichalcogenides (TMDC) is not due to an electronic effect, like the Fermi surface (FS) nesting, as it had been proposed. In particular, we consider NbSe2, NbS2, TaSe2, and TaS2 as representative examples of 2H-TMDC polytypes. Our main result consists that explicit inclusion of the matrix elements in first-principles calculations of the electron susceptibility [Formula: see text] removes, due to strong momentum dependence of the matrix elements, almost all the information about the FS topologies in the resulting [Formula: see text]. This finding strongly supports an interpretation in which the momentum dependence of the electron-phonon interaction is the only reason why the phenomenon of charge-density waves appears in this class of materials.

Phase separation and long-wavelength charge instabilities in spin-orbit coupled systems

NASA Astrophysics Data System (ADS)

Seibold, G.; Bucheli, D.; Caprara, S.; Grilli, M.

2015-01-01

We investigate a two-dimensional electron model with Rashba spin-orbit interaction where the coupling constant g=g(n) depends on the electronic density. It is shown that this dependence may drive the system unstable towards a long-wavelength charge density wave (CDW) where the associated second-order instability occurs in close vicinity to global phase separation. For very low electron densities the CDW instability is nesting-induced and the modulation follows the Fermi momentum kF. At higher density the instability criterion becomes independent of kF and the system may become unstable in a broad momentum range. Finally, upon filling the upper spin-orbit split band, finite momentum instabilities disappear in favor of phase separation alone. We discuss our results with regard to the inhomogeneous phases observed at the LaAlO3/SrTiO3 or LaTiO3/SrTiO3 interfaces.

Electronic signatures of dimerization in IrTe2

NASA Astrophysics Data System (ADS)

Dai, Jixia; Wu, Weida; Oh, Yoon Seok; Cheong, S.-W.; Yang, J. J.

2014-03-01

Recently, the mysterious phase transition around Tc ~ 260 K in IrTe2 has been intensively studied. A structural supermodulation with q =1/5 was identified below Tc. A variety of microscopic mechanisms have been proposed to account for this transition, including charge-density wave due to Fermi surface nesting, Te p-orbital driven structure instability, anionic depolymerization, ionic dimerization, and so on. However, there has not been an unified picture on the nature of this transition. To address this issue, we have performed low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) experiments on IrTe2 and IrTe2-xSex. Our STM data clearly shows a strong bias dependence in both topography and local density of states (STS) maps. High resolution spectroscopic data further confirms the stripe-like electronic states modulation, which provides insight to the ionic dimerization revealed by X-ray diffraction.

Phonon triggered rhombohedral lattice distortion in vanadium at high pressure

DOE PAGES

Antonangeli, Daniele; Farber, Daniel L.; Bosak, Alexei; ...

2016-08-19

In spite of the simple body-centered-cubic crystal structure, the elements of group V, vanadium, niobium and tantalum, show strong interactions between the electronic properties and lattice dynamics. Further, these interactions can be tuned by external parameters, such as pressure and temperature. We used inelastic x-ray scattering to probe the phonon dispersion of single-crystalline vanadium as a function of pressure to 45 GPa. Our measurements show an anomalous high-pressure behavior of the transverse acoustic mode along the (100) direction and a softening of the elastic modulus C44 that triggers a rhombohedral lattice distortion occurring between 34 and 39 GPa. Lastly, ourmore » results provide the missing experimental confirmation of the theoretically predicted shear instability arising from the progressive intra-band nesting of the Fermi surface with increasing pressure, a scenario common to all transition metals of group V.« less

Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe4As4

NASA Astrophysics Data System (ADS)

Iida, Kazuki; Ishikado, Motoyuki; Nagai, Yuki; Yoshida, Hiroyuki; Christianson, Andrew D.; Murai, Naoki; Kawashima, Kenji; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Iyo, Akira

2017-09-01

The dynamical spin susceptibility in the new-structure-type iron-based superconductor CaKFe4As4 was investigated by using a combination of inelastic neutron scattering (INS) measurements and random phase approximation (RPA) calculations. Powder INS measurements show that the spin resonance at Qres = 1.17(1) Å-1, corresponding to the (π ,π ) nesting wave vector in tetragonal notation, evolves below Tc. The characteristic energy of the spin resonance Eres = 12.5 meV is smaller than twice the size of the superconducting gap (2Δ). The broad energy feature of the dynamical susceptibility of the spin resonance can be explained by the RPA calculations, in which the different superconducting gaps on different Fermi surfaces are taken into account. Our INS and PRA studies demonstrate that the superconducting pairing nature in CaKFe4As4 is the s± symmetry.

Motion of the guest ion as precursor to the first-order phase transition in the cage system GdB6

NASA Astrophysics Data System (ADS)

Iwasa, Kazuaki; Igarashi, Ryosuke; Saito, Kotaro; Laulhé, Claire; Orihara, Toshihiko; Kunii, Satoru; Kuwahara, Keitaro; Nakao, Hironori; Murakami, Youichi; Iga, Fumitoshi; Sera, Masafumi; Tsutsui, Satoshi; Uchiyama, Hiroshi; Baron, Alfred Q. R.

2011-12-01

The motion of guest Gd ions in oversized boron cages in GdB6 was investigated from phonon spectra measurements obtained by inelastic x-ray scattering. The measured phonon modes soften by about 10% from 300 K down to TN=16 K, in particular, the longitudinal phonon for the propagation vector q1=(1/2,0,0) that characterizes the distorted structure below TN. Besides, the dispersion relation curves show kinklike anomalies at qk=(0.38,0.38,0). The observed results imply that the motion of the guest Gd ion interplays with the f electrons magnetoelastically and with carriers via Fermi surface nesting. The anomalous properties previously reported for this material far above TN originate from the strong electron-phonon coupling, which causes the motion of guest ions as precursors to the first-order phase transition.

Enhanced electron-phonon coupling near the lattice instability of superconducting NbC1-xNx from density-functional calculations

NASA Astrophysics Data System (ADS)

Blackburn, Simon; Côté, Michel; Louie, Steven G.; Cohen, Marvin L.

2011-09-01

Using density-functional theory within the local-density approximation, we study the electron-phonon coupling in NbC1-xNx and NbN crystals in the rocksalt structure. The Fermi surface of these systems exhibits important nesting. The associated Kohn anomaly greatly increases the electron-phonon coupling and induces a structural instability when the electronic density of states reaches a critical value. Our results reproduce the observed rise in Tc from 11.2 to 17.3 K as the nitrogen doping is increased in NbC1-xNx. To further understand the contribution of the structural instability to the rise of the superconducting temperature, we develop a model for the Eliashberg spectral function in which the effect of the unstable phonons is set apart. We show that this model together with the McMillan formula can reproduce the increase of Tc near the structural phase transition.

A new approach to determine the density of liquids and solids without measuring mass and volume: introducing the solidensimeter

NASA Astrophysics Data System (ADS)

Kiriktaş, Halit; Şahin, Mehmet; Eslek, Sinan; Kiriktaş, İrem

2018-05-01

This study aims to design a mechanism with which the density of any solid or liquid can be determined without measuring its mass and volume in order to help students comprehend the concept of density more easily. The solidensimeter comprises of two scaled and nested glass containers (graduated cylinder or beaker) and sufficient water. In this method, the density measurement was made using the Archimedes’ principle stating that an object fully submerged in a liquid displaces the same amount of liquid as its volume, while an object partially submerged or floating displaces the same amount of liquid as its mass. Using this method, the density of any solids or liquids can be determined using a simple mathematical ratio. At the end of the process a mechanism that helps students to comprehend the density topic more easily was designed. The system is easy-to-design, uses low-cost equipment and enables one to determine the density of any solid or liquid without measuring its mass and volume.

Measuring the Density of Liquid Targets in the SeaQuest Experiment

NASA Astrophysics Data System (ADS)

Xi, Zhaojia; SeaQuest/E906 Collaboration

2015-10-01

The SeaQuest (E906) experiment, using the 120 GeV proton beam from the Main Injector at the Fermi National Accelerator Lab (FNAL), is studying the quark and antiquark structure of the nucleon using the Drell-Yan process. Based on the cross section ratios, σ (p + d) / σ (p + p) , SeaQuest will extract the Bjorken-x dependnce of the d / u ratio. The measurement will cover the large region (x > 0 . 25) with improved accuracy compared to the previous E866/Nusea experiment. Liquid D2 (LD2) and Liquid H2 (LH2) are the targets used in the SeaQuest experiment. The densities of LD2 and LH2 targets are two important quantities for the determination of the d / u ratio. We measure the pressure and temperature inside the flasks, from which the densities are calculated. The method, measurements and results of this study will be presented. This work is supported by U.S. DOE MENP Grant DE-FG02-03ER41243.

Bimodal behaviour of charge carriers in graphene induced by electric double layer

PubMed Central

Tsai, Sing-Jyun; Yang, Ruey-Jen

2016-01-01

A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid. PMID:27464986

VizieR Online Data Catalog: Fermi/non-Fermi blazars jet power and accretion (Chen+, 2015)

NASA Astrophysics Data System (ADS)

Chen, Y. Y.; Zhang, X.; Zhang, H. J.; Yu, X. L.

2017-11-01

We selected the sample using radio catalogues to get the widest possible sample of blazars based on their radio properties. We split them into Fermi-detected sources and non-Fermi detections. Massaro et al. (2009, J/A+A/495/691) created the "Multifrequency Catalogue of Blazars" (Roma-BZCAT), which classifies blazars into three main groups based on their spectral properties. In total, we have a sample containing 177 clean Fermi blazars (96 Fermi FSRQs and 81 Fermi BL Lacs) and 133 non-Fermi blazars (105 non-Fermi FSRQs and 28 non-Fermi BL Lacs). (2 data files).

Nesting habits shape feeding preferences and predatory behavior in an ant genus

NASA Astrophysics Data System (ADS)

Dejean, Alain; Labrière, Nicolas; Touchard, Axel; Petitclerc, Frédéric; Roux, Olivier

2014-04-01

We tested if nesting habits influence ant feeding preferences and predatory behavior in the monophyletic genus Pseudomyrmex (Pseudomyrmecinae) which comprises terrestrial and arboreal species, and, among the latter, plant-ants which are obligate inhabitants of myrmecophytes (i.e., plants sheltering so-called plant-ants in hollow structures). A cafeteria experiment revealed that the diet of ground-nesting Pseudomyrmex consists mostly of prey and that of arboreal species consists mostly of sugary substances, whereas the plant-ants discarded all the food we provided. Workers forage solitarily, detecting prey from a distance thanks to their hypertrophied eyes. Approach is followed by antennal contact, seizure, and the manipulation of the prey to sting it under its thorax (next to the ventral nerve cord). Arboreal species were not more efficient at capturing prey than were ground-nesting species. A large worker size favors prey capture. Workers from ground- and arboreal-nesting species show several uncommon behavioral traits, each known in different ant genera from different subfamilies: leaping abilities, the use of surface tension strengths to transport liquids, short-range recruitment followed by conflicts between nestmates, the consumption of the prey's hemolymph, and the retrieval of entire prey or pieces of prey after having cut it up. Yet, we never noted group ambushing. We also confirmed that Pseudomyrmex plant-ants live in a kind of food autarky as they feed only on rewards produced by their host myrmecophyte, or on honeydew produced by the hemipterans they attend and possibly on the fungi they cultivate.

Breakdown of the independent electron picture in mesoscopic samples at low temperatures: The hunt for the Unicorn

NASA Astrophysics Data System (ADS)

Webb, R. A.

1998-03-01

A variety of experiments are discussed where, at low temperatures, it appears that the non-interacting picture of electrons in a Fermi liquid description of a mesoscopic sample is breaking down. Specifically, experiments on the temperature dependence of the phase-coherence time, energy relaxation rate, spin-flip scattering time, persistent currents in normal metals and transmission through a barrier in the fractional quantum Hall regime all display low-temperature properties which can not be accounted for in the independent electron picture.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu Cenke

In this paper, we calculate the entanglement Renyi entropy of two coupled gapless systems in general spatial dimension d. The gapless systems can be either conformal field theories or Fermi liquids. We assume the two systems are coupled uniformly in an h-dimensional submanifold of the space, with 0{<=}h{<=}d. We will focus on the scaling of the Renyi entropy with the size of the system, and its scaling with the intersystem coupling constant g. Three approaches will be used for our calculation: (1) exact calculation with ground-state wave functional, (2) perturbative calculation with functional path integral, and (3) scaling argument.

Thermo-electric transport in gauge/gravity models with momentum dissipation

NASA Astrophysics Data System (ADS)

Amoretti, Andrea; Braggio, Alessandro; Maggiore, Nicola; Magnoli, Nicodemo; Musso, Daniele

2014-09-01

We present a systematic definition and analysis of the thermo-electric linear response in gauge/gravity systems focusing especially on models with massive gravity in the bulk and therefore momentum dissipation in the dual field theory. A precise treatment of finite counter-terms proves to be essential to yield a consistent physical picture whose hydrodynamic and beyond-hydrodynamics behaviors noticeably match with field theoretical expectations. The model furnishes a possible gauge/gravity description of the crossover from the quantum-critical to the disorder-dominated Fermi-liquid behaviors, as expected in graphene.

Kinetic Theory of Electronic Transport in Random Magnetic Fields

NASA Astrophysics Data System (ADS)

Lucas, Andrew

2018-03-01

We present the theory of quasiparticle transport in perturbatively small inhomogeneous magnetic fields across the ballistic-to-hydrodynamic crossover. In the hydrodynamic limit, the resistivity ρ generically grows proportionally to the rate of momentum-conserving electron-electron collisions at large enough temperatures T . In particular, the resulting flow of electrons provides a simple scenario where viscous effects suppress conductance below the ballistic value. This new mechanism for ρ ∝T2 resistivity in a Fermi liquid may describe low T transport in single-band SrTiO3 .

Kinetic Theory of Electronic Transport in Random Magnetic Fields.

PubMed

Lucas, Andrew

2018-03-16

We present the theory of quasiparticle transport in perturbatively small inhomogeneous magnetic fields across the ballistic-to-hydrodynamic crossover. In the hydrodynamic limit, the resistivity ρ generically grows proportionally to the rate of momentum-conserving electron-electron collisions at large enough temperatures T. In particular, the resulting flow of electrons provides a simple scenario where viscous effects suppress conductance below the ballistic value. This new mechanism for ρ∝T^{2} resistivity in a Fermi liquid may describe low T transport in single-band SrTiO_{3}.

Exploring excited eigenstates of many-body systems using the functional renormalization group

NASA Astrophysics Data System (ADS)

Klöckner, Christian; Kennes, Dante Marvin; Karrasch, Christoph

2018-05-01

We introduce approximate, functional renormalization group based schemes to obtain correlation functions in pure excited eigenstates of large fermionic many-body systems at arbitrary energies. The algorithms are thoroughly benchmarked and their strengths and shortcomings are documented using a one-dimensional interacting tight-binding chain as a prototypical testbed. We study two "toy applications" from the world of Luttinger liquid physics: the survival of power laws in lowly excited states as well as the spectral function of high-energy "block" excitations, which feature several single-particle Fermi edges.

Fermi surfaces and electronic topological transitions in metallic solid solutions

NASA Astrophysics Data System (ADS)

Bruno, E.; Ginatempo, B.; Guiliano, E. S.; Ruban, A. V.; Vekilov, Yu. Kh.

1994-12-01

Notwithstanding the substitutional disorder, the Fermi surface of metallic alloys can be measured and computed. We show that, from the theoretical point of view, it is defined as the locus of the peaks of the Bloch Spectral Function (BSF). Such Fermi surfaces, on varying the atomic concentrations, may undergo changes of their topology, known as Electronic Topological Transitions (ETT). Thus, for instance, pockets of electrons or holes may appear or disappear, necks may open or close. ETTs cause anomalous behaviours of thermodynamic, transport and elastic properties of metals and constitute a fascinating field in the study of Fermi liquid systems. Although ETTs could be studied on pure systems as a function of the thermodynamic variables, nevertheless such a study would often require extreme conditions, and would lead to experimental difficulties. On the other hand, it is possible to explore the variations of atomic concentration, i.e. the valence electron per atom ratio, in metallic solid solutions with a relative experimental ease. In this paper we review the theoretical techniques for the determination of Fermi surfaces in metallic solid solutions and discuss some examples of ETTs, namely LiMg, ZrNb, NbMo, MoRe, AgPd, CdMg, NiW and NiTi alloys, also in connection with experimental data as thermoelectric power, resistivity, elastic constants and electron-phonon coupling and with the determinations of the electron momentum distribution function from Compton scattering and positron annihilation experiments. We show that the ab initio calculations of the electronic structure for the quoted systems, together with a careful determination of the BSF, are able to predict quantitatively ETTs at those concentrations where physical quantities display anomalies, so confirming directly ETT theory. Although it is not the purpose of the present review to give a full account of electronic structure calculation schemes, however, we briefly discuss the ideas and the main physical approximations underlying theories of substitutional disorder in alloys. We shall pay some more attention to the Coherent Potential Approximation (CPA) in the Korringa-Kohn-Rostoker (KKR) multiple scattering framework and the Hohenberg and Kohn Density Functional Theory in the Local Density Approximation (LDA) for the exchange-correlation potential. The above choice is supported by the numerical versatility of the LDAKKRCPA theory, and, more important, by the a fortiori evidence that essentially equivalent results are obtained from different theoretical frameworks, provided the same basic physical approximations are used. Accordingly, when convenient, we present new LDAKKRCPA determinations of the Fermi surfaces, as for the ZrNbMoRe series.

Pressure-temperature phase diagram of a charge-ordered organic conductor studied by C13 NMR

NASA Astrophysics Data System (ADS)

Itou, T.; Miyagawa, K.; Nakamura, J.; Kanoda, K.; Hiraki, K.; Takahashi, T.

2014-07-01

We performed C13 NMR measurements on the quasi-one-dimensional (Q1D) charge-ordered system (DI-DCNQI)2Ag under ambient and applied pressure to clarify the pressure-temperature phase diagram. For pressures up to 15 kbar, the NMR spectra exhibit complicated splitting at low temperatures, indicating a "generalized 3D Wigner crystal" state. In this pressure region, we find that increased pressure causes a decrease in the charge disproportionation ratio, along with a decrease in the transition temperature of the generalized 3D Wigner crystal. In the high-pressure region, near 20 kbar, where a 1D confined liquid crosses over to a 3D Fermi liquid at high temperatures, the ground state is replaced by a nonmagnetic insulating state that is qualitatively different from the generalized 3D Wigner crystal.

Spray generators for absorption refrigeration systems

DOEpatents

Sibley, Howard W.

1979-06-19

A spray generator for an absorption refrigeration system that includes a heat exchanger comprised of a multiplicity of variably spaced heat exchange tubes. The tubes are spaced close together near the top of the heat exchanger and spaced more widely apart near the bottom of the heat exchanger. Dilute absorbent solution is sprayed down through the heat exchanger. The close nesting of the tubes in the top portion of the heat exchanger retards liquid flow and aids heating of the solution. The wide spacing of the tubes in the lower section of the heat exchanger facilitate vapor flow out of the heat exchanger and eliminates liquid "blow-off". The top tubes are covered by a baffle to prevent the liquid solution from splashing out of the heat exchanger off of these top tubes.

Observation of Spin-Polarons in a strongly interacting Fermi liquid

NASA Astrophysics Data System (ADS)

Zwierlein, Martin

2009-03-01

We have observed spin-polarons in a highly imbalanced mixture of fermionic atoms using tomographic RF spectroscopy. Feshbach resonances allow to freely tune the interactions between the two spin states involved. A single spin down atom immersed in a Fermi sea of spin up atoms can do one of two things: For strong attraction, it can form a molecule with exactly one spin up partner, but for weaker interaction it will spread its attraction and surround itself with a collection of majority atoms. This spin down atom ``dressed'' with a spin up cloud constitutes the spin-polaron. We have observed a striking spectroscopic signature of this quasi-particle for various interaction strengths, a narrow peak in the spin down spectrum that emerges above a broad background. The narrow width signals a long lifetime of the spin-polaron, much longer than the collision rate with spin up atoms, as it must be for a proper quasi-particle. The peak position allows to directly measure the polaron energy. The broad pedestal at high energies reveals physics at short distances and is thus ``molecule-like'': It is exactly matched by the spin up spectra. The comparison with the area under the polaron peak allows to directly obtain the quasi-particle weight Z. We observe a smooth transition from polarons to molecules. At a critical interaction strength of 1/kFa = 0.7, the polaron peak vanishes and spin up and spin down spectra exactly match, signalling the formation of molecules. This is the same critical interaction strength found earlier to separate a normal Fermi mixture from a superfluid molecular Bose-Einstein condensate. The spin-polarons determine the low-temperature phase diagram of imbalanced Fermi mixtures. In principle, polarons can interact with each other and should, at low enough temperatures, form a superfluid of p-wave pairs. We will present a first indication for interactions between polarons.

Tunneling spectroscopy of a spiral Luttinger liquid in contact with superconductors

NASA Astrophysics Data System (ADS)

Liu, Dong E.; Levchenko, Alex

2014-03-01

One-dimensional wires with Rashba spin-orbit coupling, magnetic field, and strong electron-electron interactions are described by a spiral Luttinger liquid model. We develop a theory to investigate the tunneling density of states into a spiral Luttinger liquid in contact with superconductors at its two ends. This approach provides a way to disentangle the delicate interplay between superconducting correlations and strong electron interactions. If the wire-superconductor boundary is dominated by Andreev reflection, we find that in the vicinity of the interface the zero-bias tunneling anomaly reveals a power law enhancement with the unusual exponent. This zero-bias due to Andreev reflections may coexist and thus mask possible peak due to Majorana bound states. Far away from the interface strong correlations inherent to the Luttinger liquid prevail and restore conventional suppression of the tunneling density of states at the Fermi level, which acquires a Friedel-like oscillatory envelope with the period renormalized by the strength of the interaction. D.E.L. was supported by Michigan State University and in part by ARO through Contract No. W911NF-12-1-0235. A.L. acknowledges support from NSF under Grant No. PHYS-1066293, and the hospitality of the Aspen Center for Physics.

Analyzing the equilibrium states of a quasi-neutral spatially inhomogeneous system of charges above a liquid dielectric film based on the first principles of quantum statistics

NASA Astrophysics Data System (ADS)

Lytvynenko, D. M.; Slyusarenko, Yu V.

2017-08-01

A theory of quasi-neutral equilibrium states of charges above a liquid dielectric surface is developed. This theory is based on the first principles of quantum statistics for systems comprising many identical particles. The proposed approach involves applying the variational principle, modified for the considered systems, and the Thomas-Fermi model. In the terms of the developed theory self-consistency equations are obtained. These equations provide the relation between the main parameters describing the system: the potential of the static electric field, the distribution function of charges and the surface profile of the liquid dielectric. The equations are used to study the phase transition in the system to a spatially periodic state. The proposed method can be applied in analyzing the properties of the phase transition in the system in relation to the spatially periodic states of wave type. Using the analytical and numerical methods, we perform a detailed study of the dependence of the critical parameters of such a phase transition on the thickness of the liquid dielectric film. Some stability criteria for the new asymmetric phase of the studied system are discussed.

Atomic Scale Control of Competing Electronic Phases in Ultrathin Correlated Oxides

NASA Astrophysics Data System (ADS)

Shen, Kyle

2015-03-01

Ultrathin epitaxial thin films offer a number of unique advantages for engineering the electronic properties of correlated transition metal oxides. For example, atomically thin films can be synthesized to artificially confine electrons in two dimensions. Furthermore, using a substrate with a mismatched lattice constant can impose large biaxial strains of larger than 3% (Δa / a), much larger than can achieved in bulk single crystals. Since these dimensionally confined or strained systems may necessarily be less than a few unit cells thick, investigating their properties and electronic structure can be particularly challenging. We employ a combination of reactive oxide molecular beam epitaxy (MBE) and angle-resolved photoemission spectroscopy (ARPES) to investigate how dimensional confinement and epitaxial strain can be used to manipulate electronic properties and structure in correlated transition metal oxide thin films. We describe some of our recent work manipulating and studying the electronic structure of ultrathin LaNiO3 through a thickness-driven metal-insulator transition between three and two unit cells (Nature Nanotechnology 9, 443, 2014), where coherent Fermi liquid-like quasiparticles are suppressed at the metal-insulator transition observed in transport. We also will describe some recent unpublished work using epitaxial strain to drive a Lifshitz transition in atomically thin films of the spin-triplet ruthenate superconductor Sr2RuO4, where we also can dramatically alter the quasiparticle scattering rates and drive the system towards non-Fermi liquid behavior near the critical point (B. Burganov, C. Adamo, in preparation). Funding provided by the Office of Naval Research and Air Force Office of Scientific Research.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koshelev, A. E.

Multiple-band electronic structure and proximity to antiferromagnetic (AF) instability are the key properties of iron-based superconductors. In this paper, we explore the influence of scattering by the AF spin fluctuations on transport of multiple-band metals above the magnetic transition. A salient feature of scattering on the AF fluctuations is that it is strongly enhanced at the Fermi surface locations where the nesting is perfect (“hot spots” or “hot lines”). We review derivation of the collision integral for the Boltzmann equation due to AF-fluctuations scattering. In the paramagnetic state, the enhanced scattering rate near the hot lines leads to anomalous behaviormore » of electronic transport in magnetic field. We explore this behavior by analytically solving the Boltzmann transport equation with approximate transition rates. This approach accounts for return scattering events and is more accurate than the relaxation-time approximation. The magnetic-field dependences are characterized by two very different field scales: the lower scale is set by the hot-spot width and the higher scale is set by the total scattering amplitude. A conventional magnetotransport behavior is limited to magnetic fields below the lower scale. In the wide range in-between these two scales, the longitudinal conductivity has linear dependence on the magnetic field and the Hall conductivity has quadratic dependence. The linear dependence of the diagonal component reflects growth of the Fermi-surface area affected by the hot spots proportional to the magnetic field. Finally, we discuss applicability of this theoretical framework for describing of anomalous magnetotransport properties in different iron pnictides and chalcogenides in the paramagnetic state.« less

Large optical conductivity of Dirac semimetal Fermi arc surface states

NASA Astrophysics Data System (ADS)

Shi, Li-kun; Song, Justin C. W.

2017-08-01

Fermi arc surface states, a hallmark of topological Dirac semimetals, can host carriers that exhibit unusual dynamics distinct from that of their parent bulk. Here we find that Fermi arc carriers in intrinsic Dirac semimetals possess a strong and anisotropic light-matter interaction. This is characterized by a large Fermi arc optical conductivity when light is polarized transverse to the Fermi arc; when light is polarized along the Fermi arc, Fermi arc optical conductivity is significantly muted. The large surface spectral weight is locked to the wide separation between Dirac nodes and persists as a large Drude weight of Fermi arc carriers when the system is doped. As a result, large and anisotropic Fermi arc conductivity provides a novel means of optically interrogating the topological surfaces states of Dirac semimetals.

Atomically precise lateral modulation of a two-dimensional electron liquid in anatase TiO 2 thin films

DOE PAGES

Wang, Zhiming; Zhong, Z.; Walker, S. McKeown; ...

2017-03-10

Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at the surface or interface of transition metal oxides is key to unlocking their full potential. Here we describe a new approach to tailoring the electronic structure of an oxide surface 2DEL demonstrating the lateral modulation of electronic states with atomic scale precision on an unprecedented length scale comparable to the Fermi wavelength. To this end, we use pulsed laser deposition to grow anatase TiO 2 films terminated by a (1 x 4) in-plane surface reconstruction. Employing photo-stimulated chemical surface doping we induce 2DELs with tunable carrier densities thatmore » are confined within a few TiO 2 layers below the surface. Subsequent in situ angle resolved photoemission experiments demonstrate that the (1 x 4) surface reconstruction provides a periodic lateral perturbation of the electron liquid. Furthermore, this causes strong backfolding of the electronic bands, opening of unidirectional gaps and a saddle point singularity in the density of states near the chemical potential.« less

Soft X-ray and cathodoluminescence measurement, optimisation and analysis at liquid nitrogen temperatures

NASA Astrophysics Data System (ADS)

MacRae, C. M.; Wilson, N. C.; Torpy, A.; Delle Piane, C.

2018-01-01

Advances in field emission gun electron microprobes have led to significant gains in the beam power density and when analysis at high resolution is required then low voltages are often selected. The resulting beam power can lead to damage and this can be minimised by cooling the sample down to cryogenic temperatures allowing sub-micrometre imaging using a variety of spectrometers. Recent advances in soft X-ray emission spectrometers (SXES) offer a spectral tool to measure both chemistry and bonding and when combined with spectral cathodoluminescence the complementary techniques enable new knowledge to be gained from both mineral and materials. Magnesium and aluminium metals have been examined at both room and liquid nitrogen temperatures by SXES and the L-emission Fermi-edge has been observed to sharpen at the lower temperatures directly confirming thermal broadening of the X-ray spectra. Gains in emission intensity and resolution have been observed in cathodoluminescence for liquid nitrogen cooled quartz grains compared to ambient temperature quartz. This has enabled subtle growth features at quartz to quartz-cement boundaries to be imaged for the first time.

Stokes parameter studies of spontaneous emission from chiral nematic liquid crystals as a one-dimensional photonic stopband crystal: experiment and theory.

PubMed

Woon, Kai L; O'Neill, Mary; Richards, Gary J; Aldred, Matthew P; Kelly, Stephen M

2005-04-01

The helical structure of uniformly aligned chiral nematic liquid crystals results in a photonic stopband for only one sense of circular polarization. The spectroscopic Stokes polarimeter is used to analyze spontaneous emission in the stopband. Highly polarized photoluminescence is found and the polarization properties vary with the excitation wavelength. Spontaneous emission is enhanced at the stopband edge and this Purcell effect is greater on excitation at wavelengths where the absorption coefficient is low. This is interpreted as greater overlap between the excited molecules and the electrical modal field of the resonant modes at the stopband edge. Photoluminescence detected from the excitation face of the liquid crystal cell is less polarized because of photon tunneling. Fermi's golden rule in conjunction with Stokes vectors is used to model the polarization of emission taking multiple reflections at the interfaces of the cell into account. The discrepancy between the experiment and the theoretical model is interpreted as direct experimental evidence that virtual photons, which originate from zero point fluctuations of quantum space, are randomly polarized.

Ionic Liquid Gating Control of RKKY Interaction in FeCoB/Ru/FeCoB and (Pt/Co) 2/Ru/(Co/Pt) 2 Multilayers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Qu; Wang, Lei; Zhou, Ziyao

To overcome the fundamental challenge of the weak natural response of antiferromagnetic materials under a magnetic field, voltage manipulation of antiferromagnetic interaction is developed to realize ultrafast, high-density, and power efficient antiferromagnetic spintronics. Here, we report a low voltage modulation of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction via ionic liquid gating in synthetic antiferromagnetic multilayers of FeCoB/Ru/FeCoB and (Pt/Co) 2/Ru/(Co/Pt) 2. At room temperature, the distinct voltage control of transition between antiferromagnetic and ferromagnetic ordering is realized and up to 80% of perpendicular magnetic moments manage to switch with a small-applied voltage bias of 2.5 V. We related this ionic liquid gating-induced RKKYmore » interaction modification to the disturbance of itinerant electrons inside synthetic antiferromagnetic heterostructure and the corresponding change of its Fermi level. Voltage tuning of RKKY interaction may enable the next generation of switchable spintronics between antiferromagnetic and ferromagnetic modes with both fundamental and practical perspectives.« less

Spin-dependent analysis of two-dimensional electron liquids

NASA Astrophysics Data System (ADS)

Bulutay, C.; Tanatar, B.

2002-05-01

Two-dimensional electron liquid (2D EL) at full Fermi degeneracy is revisited, giving special attention to the spin-polarization effects. First, we extend the recently proposed classical-map hypernetted-chain (CHNC) technique to the 2D EL, while preserving the simplicity of the original proposal. An efficient implementation of CHNC is given utilizing Lado's quadrature expressions for the isotropic Fourier transforms. Our results indicate that the paramagnetic phase stays to be the ground state until the Wigner crystallization density, even though the energy separation with the ferromagnetic and other partially polarized states become minute. We analyze compressibility and spin stiffness variations with respect to density and spin polarization, the latter being overlooked until now. Spin-dependent static structure factor and pair-distribution functions are computed; agreement with the available quantum Monte Carlo data persists even in the strong-coupling regime of the 2D EL.

Hydrodynamic pumping of a quantum Fermi liquid in a semiconductor heterostructure

NASA Astrophysics Data System (ADS)

Heremans, J. J.; Kantha, D.; Chen, H.; Govorov, A. O.

2003-03-01

We present experimental results for a pumping mechanism observed in mesoscopic structures patterned on two-dimensional electron systems in GaAs/AlGaAs heterostructures. The experiments are performed at low temperatures, in the ballistic regime. The effect is observed as a voltage or current signal corresponding to carrier extraction from sub-micron sized apertures, when these apertures are swept by a beam of ballistic electrons. The carrier extraction, phenomenologically reminiscent of the Bernoulli pumping effect in classical fluids, has been observed in various geometries. We ascertained linearity between measured voltage and injected current in all experiments, thereby excluding rectification effects. The linear response, however, points to a fundamental difference from the Bernoulli effect in classical liquids, where the response is nonlinear and quadratic in terms of the velocity. The temperature dependence of the effect will also be presented. We thank M. Shayegan (Princeton University) for the heterostructure growth, and acknowledge support from NSF DMR-0094055.

Ionic liquid gating reveals trap-filled limit mobility in low temperature amorphous zinc oxide

NASA Astrophysics Data System (ADS)

Bubel, S.; Meyer, S.; Kunze, F.; Chabinyc, M. L.

2013-10-01

In low-temperature solution processed amorphous zinc oxide (a-ZnO) thin films, we show the thin film transistor (TFT) characteristics for the trap-filled limit (TFL), when the quasi Fermi energy exceeds the conduction band edge and all tail-states are filled. In order to apply gate fields that are high enough to reach the TFL, we use an ionic liquid tape gate. Performing capacitance voltage measurements to determine the accumulated charge during TFT operation, we find the TFL at biases higher than predicted by the electronic structure of crystalline ZnO. We conclude that the density of states in the conduction band of a-ZnO is higher than in its crystalline state. Furthermore, we find no indication of percolative transport in the conduction band but trap assisted transport in the tail-states of the band.

Generalized Stoner criterion and versatile spin ordering in two-dimensional spin-orbit coupled electron systems

NASA Astrophysics Data System (ADS)

Liu, Weizhe Edward; Chesi, Stefano; Webb, David; Zülicke, U.; Winkler, R.; Joynt, Robert; Culcer, Dimitrie

2017-12-01

Spin-orbit coupling is a single-particle phenomenon known to generate topological order, and electron-electron interactions cause ordered many-body phases to exist. The rich interplay of these two mechanisms is present in a broad range of materials and has been the subject of considerable ongoing research and controversy. Here we demonstrate that interacting two-dimensional electron systems with strong spin-orbit coupling exhibit a variety of time reversal symmetry breaking phases with unconventional spin alignment. We first prove that a Stoner-type criterion can be formulated for the spin polarization response to an electric field, which predicts that the spin polarization susceptibility diverges at a certain value of the electron-electron interaction strength. The divergence indicates the possibility of unconventional ferromagnetic phases even in the absence of any applied electric or magnetic field. This leads us, in the second part of this work, to study interacting Rashba spin-orbit coupled semiconductors in equilibrium in the Hartree-Fock approximation as a generic minimal model. Using classical Monte Carlo simulations, we construct the complete phase diagram of the system as a function of density and spin-orbit coupling strength. It includes both an out-of-plane spin-polarized phase and in-plane spin-polarized phases with shifted Fermi surfaces and rich spin textures, reminiscent of the Pomeranchuk instability, as well as two different Fermi-liquid phases having one and two Fermi surfaces, respectively, which are separated by a Lifshitz transition. We discuss possibilities for experimental observation and useful application of these novel phases, especially in the context of electric-field-controlled macroscopic spin polarizations.

Exact Chiral Spin Liquid with Stable Spin Fermi Surface on the Kagome Lattice

DTIC Science & Technology

2011-05-17

REVIEW B 83, 180412(R) (2011) FIG. 3. (a) Band structure on a cylindrical geometry for J = J ′ = 1.0, J∇ = J ′∇ = 0.8, J5 = 0. There are two gapless...Grant No. DMR-0955778 (V.C. and G.A.F.) at Austin and DOE Grant No. DE -AC02- 05CH11231 (HY) at Berkeley. 1S. A. Kivelson, D. S. Rokhsar, and J. P...Helton et al., Phys. Rev. Lett. 98, 107204 (2007). 32D. F. Schroeter, E. Kapit , R. Thomale, and M. Greiter, Phys. Rev. Lett. 99, 97202 (2007). 33E. H

Note on tachyon moduli and closed strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carneiro da Cunha, Bruno

2008-07-15

The collective behavior of the SL(2,R) covariant brane states of noncritical c=1 string theory, found in a previous work, is studied in the Fermi liquid approximation. It is found that such states mimic the coset WZW model, whereas only by further restrictions one recovers the double-scaling limit which was purported to be equivalent to closed string models. Another limit is proposed, inspired by the tachyon condensation ideas, where the spectrum is the same of two-dimensional string theory. We close by noting some strange connections between vacuum states of the theory in their different interpretations.

Possible quantum valence criticality in CeCu6-xAux

NASA Astrophysics Data System (ADS)

Shiino, Takayuki; Nobe, Kohei; Imura, Keiichiro; Deguchi, Kazuhiko; Sato, Noriaki K.

2018-05-01

CeCu6-xAux is known as a heavy fermion compound that exhibits antiferromagnetism for x ≳ 0 . 1 and non-Fermi-liquid (NFL) behavior around the critical concentration xc ≈ 0 . 1. Although this material has been studied by means of a lot of experiments, the origin of its NFL is still veiled in mystery. In this study, we examine the magnetic properties of CeCu6-xAux for various values of x (0 ≤ x ≤ 0.8), and discuss the possibility that the quantum valence criticality might be responsible for the low-temperature magnetic properties.

Neutron diffraction, specific heat and magnetization studies on Nd{sub 2}CuTiO{sub 6}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rayaprol, S., E-mail: sudhindra@csr.res.in; Kaushik, S. D.; Kumar, Naresh

2016-05-23

Structural and physical properties of a double-perovskite compound, Nd{sub 2}CuTiO{sub 6} have been studied using neutron diffraction, magnetization and specific heat measurements. The compound crystallizes in an orthorhombic structure in space group Pnma. The interesting observation we make here is that, though no long range magnetic order is observed between 2 and 300 K, the low temperature specific heat and magnetic susceptibility behavior exhibits non-Fermi liquid like behavior in this insulating compound. The magnetization and specific heat data are presented and discussed in light of these observations.

Electronic and structural transitions in dense liquid sodium.

PubMed

Raty, Jean-Yves; Schwegler, Eric; Bonev, Stanimir A

2007-09-27

At ambient conditions, the light alkali metals are free-electron-like crystals with a highly symmetric structure. However, they were found recently to exhibit unexpected complexity under pressure. It was predicted from theory--and later confirmed by experiment--that lithium and sodium undergo a sequence of symmetry-breaking transitions, driven by a Peierls mechanism, at high pressures. Measurements of the sodium melting curve have subsequently revealed an unprecedented (and still unexplained) pressure-induced drop in melting temperature from 1,000 K at 30 GPa down to room temperature at 120 GPa. Here we report results from ab initio calculations that explain the unusual melting behaviour in dense sodium. We show that molten sodium undergoes a series of pressure-induced structural and electronic transitions, analogous to those observed in solid sodium but commencing at much lower pressure in the presence of liquid disorder. As pressure is increased, liquid sodium initially evolves by assuming a more compact local structure. However, a transition to a lower-coordinated liquid takes place at a pressure of around 65 GPa, accompanied by a threefold drop in electrical conductivity. This transition is driven by the opening of a pseudogap, at the Fermi level, in the electronic density of states--an effect that has not hitherto been observed in a liquid metal. The lower-coordinated liquid emerges at high temperatures and above the stability region of a close-packed free-electron-like metal. We predict that similar exotic behaviour is possible in other materials as well.

Electron Tunneling in Lithium Ammonia Solutions Probed by Frequency-Dependent Electron-Spin Relaxation Studies

PubMed Central

Maeda, Kiminori; Lodge, Matthew T.J.; Harmer, Jeffrey; Freed, Jack H.; Edwards, Peter P.

2012-01-01

Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multi-exponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10)×10−12 s over a temperature range 230–290K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a timescale of ca. 10−13 s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential of multi-frequency EPR measurements to interrogate the microscopic nature and dynamics of ultra fast electron transfer or quantum-tunneling processes in liquids. Our results also impact on the universal issue of the role of a host solvent (or host matrix, e.g. a semiconductor) in mediating long-range electron transfer processes and we discuss the implications of our results with a range of other materials and systems exhibiting the phenomenon of electron transfer. PMID:22568866

Bursting Bubbles and Bilayers

PubMed Central

Wrenn, Steven P.; Dicker, Stephen M.; Small, Eleanor F.; Dan, Nily R.; Mleczko, Michał; Schmitz, Georg; Lewin, Peter A.

2012-01-01

This paper discusses various interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. The paper begins with a review of microbubble physics models, developed to describe microbubble dynamic behavior in the presence of ultrasound, and follows this with a discussion of how such models can be used to predict inertial cavitation profiles. Predicted sensitivities of inertial cavitation to changes in the values of membrane properties, including surface tension, surface dilatational viscosity, and area expansion modulus, indicate that area expansion modulus exerts the greatest relative influence on inertial cavitation. Accordingly, the theoretical dependence of area expansion modulus on chemical composition - in particular, poly (ethylene glyclol) (PEG) - is reviewed, and predictions of inertial cavitation for different PEG molecular weights and compositions are compared with experiment. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on PEG molecular weight and mole fraction. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the “brush” regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power) with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. This is followed by a discussion of nesting microbubbles inside the aqueous core of microcapsules and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and other applications such as sonoporation. A review of putative sonoporation mechanisms is then presented, including those involving microbubbles to deliver cargo into a cell, and those - not necessarily involving microubbles - to release cargo from a phospholipid vesicle (or reverse sonoporation). It is shown that the rate of (reverse) sonoporation from liposomes correlates with phospholipid bilayer phase behavior, liquid-disordered phases giving appreciably faster release than liquid-ordered phases. Moreover, liquid-disordered phases exhibit evidence of two release mechanisms, which are described well mathematically by enhanced diffusion (possibly via dilation of membrane phospholipids) and irreversible membrane disruption, whereas liquid-ordered phases are described by a single mechanism, which has yet to be positively identified. The ability to tune release kinetics with bilayer composition makes reverse sonoporation of phospholipid vesicles a promising methodology for controlled drug delivery. Moreover, nesting of microbubbles inside vesicles constitutes a truly “theranostic” vehicle, one that can be used for both long-lasting, safe imaging and for controlled drug delivery. PMID:23382772

Bursting bubbles and bilayers.

PubMed

Wrenn, Steven P; Dicker, Stephen M; Small, Eleanor F; Dan, Nily R; Mleczko, Michał; Schmitz, Georg; Lewin, Peter A

2012-01-01

This paper discusses various interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. The paper begins with a review of microbubble physics models, developed to describe microbubble dynamic behavior in the presence of ultrasound, and follows this with a discussion of how such models can be used to predict inertial cavitation profiles. Predicted sensitivities of inertial cavitation to changes in the values of membrane properties, including surface tension, surface dilatational viscosity, and area expansion modulus, indicate that area expansion modulus exerts the greatest relative influence on inertial cavitation. Accordingly, the theoretical dependence of area expansion modulus on chemical composition-- in particular, poly (ethylene glyclol) (PEG)--is reviewed, and predictions of inertial cavitation for different PEG molecular weights and compositions are compared with experiment. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on PEG molecular weight and mole fraction. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the "brush" regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power) with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. This is followed by a discussion of nesting microbubbles inside the aqueous core of microcapsules and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and other applications such as sonoporation. A review of putative sonoporation mechanisms is then presented, including those involving microbubbles to deliver cargo into a cell, and those--not necessarily involving microubbles--to release cargo from a phospholipid vesicle (or reverse sonoporation). It is shown that the rate of (reverse) sonoporation from liposomes correlates with phospholipid bilayer phase behavior, liquid-disordered phases giving appreciably faster release than liquid-ordered phases. Moreover, liquid-disordered phases exhibit evidence of two release mechanisms, which are described well mathematically by enhanced diffusion (possibly via dilation of membrane phospholipids) and irreversible membrane disruption, whereas liquid-ordered phases are described by a single mechanism, which has yet to be positively identified. The ability to tune release kinetics with bilayer composition makes reverse sonoporation of phospholipid vesicles a promising methodology for controlled drug delivery. Moreover, nesting of microbubbles inside vesicles constitutes a truly "theranostic" vehicle, one that can be used for both long-lasting, safe imaging and for controlled drug delivery.

Spiral magnetism in the single-band Hubbard model: the Hartree-Fock and slave-boson approaches.

PubMed

Igoshev, P A; Timirgazin, M A; Gilmutdinov, V F; Arzhnikov, A K; Irkhin, V Yu

2015-11-11

The ground-state magnetic phase diagram is investigated within the single-band Hubbard model for square and different cubic lattices. The results of employing the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave-boson approach by Kotliar and Ruckenstein with correlation effects included are compared. We take into account commensurate ferromagnetic, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often lacking in previous investigations. It is found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistically large Hubbard U by the correlation effects if nesting is absent and van Hove singularities are well away from the paramagnetic phase Fermi level. The magnetic phase separation plays an important role in the formation of magnetic states, the corresponding phase regions being especially wide in the vicinity of half-filling. The details of non-collinear and collinear magnetic ordering for different cubic lattices are discussed.

Intertwined order in a frustrated four-leg t - J cylinder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dodaro, John F.; Jiang, Hong -Chen; Kivelson, Steven A.

Here, we report a density-matrix renormalization group study of the t–J model with nearest (t 1 and J 1) and next-nearest (t 2 and J 2) interactions on a four-leg cylinder with concentration δ=1/8 of doped holes. We observe an astonishingly complex interplay between uniform d-wave superconductivity (SC) and strong spin and charge-density wave ordering tendencies (SDW and CDW). Depending on parameters, the CDWs can be commensurate with period 4 or 8. By comparing the charge ordering vectors with 2k F, we rule out Fermi surface nesting-induced density wave order in our model. Magnetic frustration (i.e., J 2/J 1~1/2) significantlymore » quenches SDW correlations with little effect on the CDW. Typically, the SC order is strongly modulated at the CDW ordering vector and exhibits d-wave symmetry around the cylinder. There is no evidence of a near-degenerate tendency to pair-density wave (PDW) ordering, charge 4e SC, or orbital current order.« less

Intertwined order in a frustrated four-leg t - J cylinder

DOE PAGES

Dodaro, John F.; Jiang, Hong -Chen; Kivelson, Steven A.

2017-04-12

Here, we report a density-matrix renormalization group study of the t–J model with nearest (t 1 and J 1) and next-nearest (t 2 and J 2) interactions on a four-leg cylinder with concentration δ=1/8 of doped holes. We observe an astonishingly complex interplay between uniform d-wave superconductivity (SC) and strong spin and charge-density wave ordering tendencies (SDW and CDW). Depending on parameters, the CDWs can be commensurate with period 4 or 8. By comparing the charge ordering vectors with 2k F, we rule out Fermi surface nesting-induced density wave order in our model. Magnetic frustration (i.e., J 2/J 1~1/2) significantlymore » quenches SDW correlations with little effect on the CDW. Typically, the SC order is strongly modulated at the CDW ordering vector and exhibits d-wave symmetry around the cylinder. There is no evidence of a near-degenerate tendency to pair-density wave (PDW) ordering, charge 4e SC, or orbital current order.« less

Scanning tunnelling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets

DOE PAGES

Gastiasoro, Maria N.; Eremin, Ilya; Fernandes, Rafael M.; ...

2017-02-08

The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept bymore » computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors—one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability.« less

Observation of direct evolution from antiferromagnetism to superconductivity in C u1 -xL ixFeAs (0 ≤x ≤1.0 )

NASA Astrophysics Data System (ADS)

Li, Kunkun; Yuan, Duanduan; Guo, Jiangang; Chen, Xiaolong

2018-04-01

We report the structure, antiferromagnetism, and superconductivity in C u1 -xL ixFeAs (0 ≤x ≤1.0 ) samples. A direct evolution from antiferromagnetism to superconductivity is observed as increasing doping level of Li. A phase diagram is constructed to show this evolution, which features no coexistence region between superconductivity and antiferromagnetism. This behavior shows that antiferromagnetic CuFeAs can be regarded as a parent compound to the observed superconductivity by equivalent doping, which is different from the cases with other FeAs-based superconductors. Structural analyses and first-principles calculations indicate that the anion height of F e2A s2 tetrahedral layer plays a crucial role on the physical properties. Moreover, the simple Fermi surface nesting picture adopted to explain the evolution from spin-density wave to superconductor in other FeAs-based superconductors might be not applicable to C u1 -xL ixFeAs .

Strong Quantum Size Effects in Pb(111) Thin Films Mediated by Anomalous Friedel Oscillations

NASA Astrophysics Data System (ADS)

Jia, Yu; Wu, Biao; Li, Chong; Einstein, T. L.; Weitering, H. H.; Zhang, Zhenyu

2010-08-01

Using first-principles calculations within density functional theory, we study Friedel oscillations (FOs) in the electron density at different metal surfaces and their influence on the lattice relaxation and stability of ultrathin metal films. We show that the FOs at the Pb(111) surface decay as 1/x with the distance x from the surface, different from the conventional 1/x2 power law at other metal surfaces. The underlying physical reason for this striking difference is tied to the strong nesting of the two different Fermi sheets along the Pb(111) direction. The interference of the strong FOs emanating from the two surfaces of a Pb(111) film, in turn, not only results in superoscillatory interlayer relaxations around the center of the film, but also determines its stability in the quantum regime. As a simple and generic picture, the present findings also explain why quantum size effects are exceptionally robust in Pb(111) films.

Microscopic origin of magnetism and magnetic interactions in ferropnictides

NASA Astrophysics Data System (ADS)

Johannes, M. D.; Mazin, I. I.

2009-06-01

One year after their initial discovery, two schools of thought have crystallized regarding the electronic structure and magnetic properties of ferropnictide systems. One postulates that these are itinerant weakly correlated metallic systems that become magnetic by virtue of spin-Peierls-type transition due to near nesting between the hole and the electron Fermi-surface pockets. The other argues that these materials are strongly or at least moderately correlated and the electrons are considerably localized and close to a Mott-Hubbard transition, with the local magnetic moments interacting via short-range superexchange. In this Rapid Communication we argue that neither picture is fully correct. The systems are moderately correlated but with correlations driven by Hund’s rule coupling rather than by the on-site Hubbard repulsion. The iron moments are largely local, driven by Hund’s intra-atomic exchange. Superexchange is not operative, and the interactions between the Fe moments are considerably long range and driven mostly by one-electron energies of all occupied states.

Dinosaur origin of egg color: oviraptors laid blue-green eggs

PubMed Central

Yang, Tzu-Ruei; Sander, Philipp N.; Schneider, Marion; Engeser, Marianne; Kath-Schorr, Stephanie; Müller, Christa E.; Sander, P. Martin

2017-01-01

Protoporphyrin (PP) and biliverdin (BV) give rise to the enormous diversity in avian egg coloration. Egg color serves several ecological purposes, including post-mating signaling and camouflage. Egg camouflage represents a major character of open-nesting birds which accomplish protection of their unhatched offspring against visually oriented predators by cryptic egg coloration. Cryptic coloration evolved to match the predominant shades of color found in the nesting environment. Such a selection pressure for the evolution of colored or cryptic eggs should be present in all open nesting birds and relatives. Many birds are open-nesting, but protect their eggs by continuous brooding, and thus exhibit no or minimal eggshell pigmentation. Their closest extant relatives, crocodiles, protect their eggs by burial and have unpigmented eggs. This phylogenetic pattern led to the assumption that colored eggs evolved within crown birds. The mosaic evolution of supposedly avian traits in non-avian theropod dinosaurs, however, such as the supposed evolution of partially open nesting behavior in oviraptorids, argues against this long-established theory. Using a double-checking liquid chromatography ESI-Q-TOF mass spectrometry routine, we traced the origin of colored eggs to their non-avian dinosaur ancestors by providing the first record of the avian eggshell pigments protoporphyrin and biliverdin in the eggshells of Late Cretaceous oviraptorid dinosaurs. The eggshell parataxon Macroolithus yaotunensis can be assigned to the oviraptor Heyuannia huangi based on exceptionally preserved, late developmental stage embryo remains. The analyzed eggshells are from three Late Cretaceous fluvial deposits ranging from eastern to southernmost China. Reevaluation of these taphonomic settings, and a consideration of patterns in the porosity of completely preserved eggs support an at least partially open nesting behavior for oviraptorosaurs. Such a nest arrangement corresponds with our reconstruction of blue-green eggs for oviraptors. According to the sexual signaling hypothesis, the reconstructed blue-green eggs support the origin of previously hypothesized avian paternal care in oviraptorid dinosaurs. Preserved dinosaur egg color not only pushes the current limits of the vertebrate molecular and associated soft tissue fossil record, but also provides a perspective on the potential application of this unexplored paleontological resource. PMID:28875070

Dinosaur origin of egg color: oviraptors laid blue-green eggs.

PubMed

Wiemann, Jasmina; Yang, Tzu-Ruei; Sander, Philipp N; Schneider, Marion; Engeser, Marianne; Kath-Schorr, Stephanie; Müller, Christa E; Sander, P Martin

2017-01-01

Protoporphyrin (PP) and biliverdin (BV) give rise to the enormous diversity in avian egg coloration. Egg color serves several ecological purposes, including post-mating signaling and camouflage. Egg camouflage represents a major character of open-nesting birds which accomplish protection of their unhatched offspring against visually oriented predators by cryptic egg coloration. Cryptic coloration evolved to match the predominant shades of color found in the nesting environment. Such a selection pressure for the evolution of colored or cryptic eggs should be present in all open nesting birds and relatives. Many birds are open-nesting, but protect their eggs by continuous brooding, and thus exhibit no or minimal eggshell pigmentation. Their closest extant relatives, crocodiles, protect their eggs by burial and have unpigmented eggs. This phylogenetic pattern led to the assumption that colored eggs evolved within crown birds. The mosaic evolution of supposedly avian traits in non-avian theropod dinosaurs, however, such as the supposed evolution of partially open nesting behavior in oviraptorids, argues against this long-established theory. Using a double-checking liquid chromatography ESI-Q-TOF mass spectrometry routine, we traced the origin of colored eggs to their non-avian dinosaur ancestors by providing the first record of the avian eggshell pigments protoporphyrin and biliverdin in the eggshells of Late Cretaceous oviraptorid dinosaurs. The eggshell parataxon Macroolithus yaotunensis can be assigned to the oviraptor Heyuannia huangi based on exceptionally preserved, late developmental stage embryo remains. The analyzed eggshells are from three Late Cretaceous fluvial deposits ranging from eastern to southernmost China. Reevaluation of these taphonomic settings, and a consideration of patterns in the porosity of completely preserved eggs support an at least partially open nesting behavior for oviraptorosaurs. Such a nest arrangement corresponds with our reconstruction of blue-green eggs for oviraptors. According to the sexual signaling hypothesis, the reconstructed blue-green eggs support the origin of previously hypothesized avian paternal care in oviraptorid dinosaurs. Preserved dinosaur egg color not only pushes the current limits of the vertebrate molecular and associated soft tissue fossil record, but also provides a perspective on the potential application of this unexplored paleontological resource.

Gold-induced nanowires on the Ge(100) surface yield a 2D and not a 1D electronic structure

NASA Astrophysics Data System (ADS)

de Jong, N.; Heimbuch, R.; Eliëns, S.; Smit, S.; Frantzeskakis, E.; Caux, J.-S.; Zandvliet, H. J. W.; Golden, M. S.

2016-06-01

Atomic nanowires on semiconductor surfaces induced by the adsorption of metallic atoms have attracted a lot of attention as possible hosts of the elusive, one-dimensional Tomonaga-Luttinger liquid. The Au/Ge(100) system in particular is the subject of controversy as to whether the Au-induced nanowires do indeed host exotic, 1D (one-dimensional) metallic states. In light of this debate, we report here a thorough study of the electronic properties of high quality nanowires formed at the Au/Ge(100) surface. The high-resolution ARPES data show the low-lying Au-induced electronic states to possess a dispersion relation that depends on two orthogonal directions in k space. Comparison of the E (kx,ky) surface measured using high-resolution ARPES to tight-binding calculations yields hopping parameters in the two different directions that differ by approximately factor of two. Additionally, by pinpointing the Au-induced surface states in the first, second, and third surface Brillouin zones and analyzing their periodicity in k||, the nanowire propagation direction seen clearly in STM can be imported into the ARPES data. We find that the larger of the two hopping parameters corresponds, in fact, to the direction perpendicular to the nanowires (tperp). This proves that the Au-induced electron pockets possess a two-dimensional, closed Fermi surface, and this firmly places the Au/Ge(100) nanowire system outside potential hosts of a Tomonaga-Luttinger liquid. We combine these ARPES data with scanning tunneling spectroscopic measurements of the spatially resolved electronic structure and find that the spatially straight—wirelike—conduction channels observed up to energies of order one electron volt below the Fermi level do not originate from the Au-induced states seen in the ARPES data. The former are rather more likely to be associated with bulk Ge states that are localized to the subsurface region. Despite our proof of the 2D (two-dimentional) nature of the Au-induced nanowire and subsurface Ge-related states, an anomalous suppression of the density of states at the Fermi level is observed in both the STS and ARPES data, and this phenomenon is discussed in the light of the effects of disorder.

Soil moisture and excavation behaviour in the Chaco leaf-cutting ant (Atta vollenweideri): digging performance and prevention of water inflow into the nest.

PubMed

Pielström, Steffen; Roces, Flavio

2014-01-01

The Chaco leaf-cutting ant Atta vollenweideri is native to the clay-heavy soils of the Gran Chaco region in South America. Because of seasonal floods, colonies are regularly exposed to varying moisture across the soil profile, a factor that not only strongly influences workers' digging performance during nest building, but also determines the suitability of the soil for the rearing of the colony's symbiotic fungus. In this study, we investigated the effects of varying soil moisture on behaviours associated with underground nest building in A. vollenweideri. This was done in a series of laboratory experiments using standardised, plastic clay-water mixtures with gravimetric water contents ranging from relatively brittle material to mixtures close to the liquid limit. Our experiments showed that preference and group-level digging rate increased with increasing water content, but then dropped considerably for extremely moist materials. The production of vibrational recruitment signals during digging showed, on the contrary, a slightly negative linear correlation with soil moisture. Workers formed and carried clay pellets at higher rates in moist clay, even at the highest water content tested. Hence, their weak preference and low group-level excavation rate observed for that mixture cannot be explained by any inability to work with the material. More likely, extremely high moistures may indicate locations unsuitable for nest building. To test this hypothesis, we simulated a situation in which workers excavated an upward tunnel below accumulated surface water. The ants stopped digging about 12 mm below the interface soil/water, a behaviour representing a possible adaptation to the threat of water inflow field colonies are exposed to while digging under seasonally flooded soils. Possible roles of soil water in the temporal and spatial pattern of nest growth are discussed.

Europium mixed-valence, long-range magnetic order, and dynamic magnetic response in EuCu 2 ( Si x Ge 1 - x ) 2

DOE PAGES

Nemkovski, Krill S.; Kozlenko, D. P.; Alekseev, Pavel A.; ...

2016-11-01

In mixed-valence or heavy-fermion systems, the hybridization between local f orbitals and conduction band states can cause the suppression of long-range magnetic order, which competes with strong spin uctuations. Ce- and Yb-based systems have been found to exhibit fascinating physical properties (heavy-fermion superconductivity, non-Fermi-liquid states, etc.) when tuned to the vicinity of magnetic quantum critical points by use of various external control parameters (temperature, magnetic eld, chemical composition). Recently, similar effects (mixed-valence, Kondo uctuations, heavy Fermi liquid) have been reported to exist in some Eu-based compounds. Unlike Ce (Yb), Eu has a multiple electron (hole) occupancy of its 4f shell,more » and the magnetic Eu 2+ state (4f 7) has no orbital component in the usual LS coupling scheme, which can lead to a quite different and interesting physics. In the EuCu 2(Si xGe 1-x) 2 series, where the valence can be tuned by varying the Si/Ge ratio, it has been reported that a significant valence uctuation can exist even in the magnetic order regime. This paper presents a detailed study of the latter material using different microscopic probes (XANES, Mossbauer spectroscopy, elastic and inelastic neutron scattering), in which the composition dependence of the magnetic order and dynamics across the series is traced back to the change in the Eu valence state. In particular, the results support the persistence of valence uctuations into the antiferromagnetic state over a sizable composition range below the critical Si concentration x c ≈ 0:65. In conclusion, the sequence of magnetic ground states in the series is shown to re ect the evolution of the magnetic spectral response.« less

Systems with Many Degrees of Freedom: from Mean - Theories of Non-Fermi Liquid Behavior in Impurity Models to Implied Binomial Trees for Modeling Financial Markets

NASA Astrophysics Data System (ADS)

Barle, Stanko

In this dissertation, two dynamical systems with many degrees of freedom are analyzed. One is the system of highly correlated electrons in the two-impurity Kondo problem. The other deals with building a realistic model of diffusion underlying financial markets. The simplest mean-field theory capable of mimicking the non-Fermi liquid behavior of the critical point in the two-impurity Kondo problem is presented. In this approach Landau's adiabaticity assumption--of a one-to-one correspondence between the low-energy excitations of the interacting and noninteracting systems--is violated through the presence of decoupled local degrees of freedom. These do not couple directly to external fields but appear indirectly in the physical properties leading, for example, to the log(T, omega) behavior of the staggered magnetic susceptibility. Also, as observed previously, the correlation function <{bf S}_1 cdot{bf S}_2> = -1/4 is a consequence of the equal weights of the singlet and triplet impurity configurations at the critical point. In the second problem, a numerical model is developed to describe the diffusion of prices in the market. Implied binomial (or multinomial) trees are constructed to enable practical pricing of derivative securities in consistency with the existing market. The method developed here is capable of accounting for both the strike price and term structure of the implied volatility. It includes the correct treatment of interest rate and dividends which proves robust even if these quantities are unusually large. The method is explained both as a set of individual innovations and, from a different prospective, as a consequence of a single plausible transformation from the tree of spot prices to the tree of futures prices.

Evidence for a small hole pocket in the Fermi surface of underdoped YBa2Cu3Oy

PubMed Central

Doiron-Leyraud, N.; Badoux, S.; René de Cotret, S.; Lepault, S.; LeBoeuf, D.; Laliberté, F.; Hassinger, E.; Ramshaw, B. J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Park, J.-H..; Vignolles, D.; Vignolle, B.; Taillefer, L.; Proust, C.

2015-01-01

In underdoped cuprate superconductors, the Fermi surface undergoes a reconstruction that produces a small electron pocket, but whether there is another, as yet, undetected portion to the Fermi surface is unknown. Establishing the complete topology of the Fermi surface is key to identifying the mechanism responsible for its reconstruction. Here we report evidence for a second Fermi pocket in underdoped YBa2Cu3Oy, detected as a small quantum oscillation frequency in the thermoelectric response and in the c-axis resistance. The field-angle dependence of the frequency shows that it is a distinct Fermi surface, and the normal-state thermopower requires it to be a hole pocket. A Fermi surface consisting of one electron pocket and two hole pockets with the measured areas and masses is consistent with a Fermi-surface reconstruction by the charge–density–wave order observed in YBa2Cu3Oy, provided other parts of the reconstructed Fermi surface are removed by a separate mechanism, possibly the pseudogap. PMID:25616011

Tailoring graphene-based electrodes from semiconducting to metallic to increase the energy density in supercapacitors

NASA Astrophysics Data System (ADS)

Vatamanu, Jenel; Ni, Xiaojuan; Liu, Feng; Bedrov, Dmitry

2015-11-01

The semiconducting character of graphene and some carbon-based electrodes can lead to noticeably lower total capacitances and stored energy densities in electric double layer (EDL) capacitors. This paper discusses the chemical and electronic structure modifications that enhance the available energy bands, density of states and quantum capacitance of graphene substrates near the Fermi level, therefore restoring the conducting character of these materials. The doping of graphene with p or n dopants, such as boron and nitrogen atoms, or the introduction of vacancy defects that introduce zigzag edges, can significantly increase the quantum capacitance within the potential range of interest for the energy storage applications by either shifting the Dirac point away from the Fermi level or by eliminating the Dirac point. We show that a combination of doping and vacancies at realistic concentrations is sufficient to increase the capacitance of a graphene-based electrode to within 1 μF cm-2 from that of a metallic surface. Using a combination of ab initio calculations and classical molecular dynamics simulations we estimate how the changes in the quantum capacitance of these electrode materials affect the total capacitance stored by the open structure EDL capacitors containing room temperature ionic liquid electrolytes.

Optimized Hypernetted-Chain Solutions for Helium -4 Surfaces and Metal Surfaces

NASA Astrophysics Data System (ADS)

Qian, Guo-Xin

This thesis is a study of inhomogeneous Bose systems such as liquid ('4)He slabs and inhomogeneous Fermi systems such as the electron gas in metal films, at zero temperature. Using a Jastrow-type many-body wavefunction, the ground state energy is expressed by means of Bogoliubov-Born-Green-Kirkwood -Yvon and Hypernetted-Chain techniques. For Bose systems, Euler-Lagrange equations are derived for the one- and two -body functions and systematic approximation methods are physically motivated. It is shown that the optimized variational method includes a self-consistent summation of ladder- and ring-diagrams of conventional many-body theory. For Fermi systems, a linear potential model is adopted to generate the optimized Hartree-Fock basis. Euler-Lagrange equations are derived for the two-body correlations which serve to screen the strong bare Coulomb interaction. The optimization of the pair correlation leads to an expression of correlation energy in which the state averaged RPA part is separated. Numerical applications are presented for the density profile and pair distribution function for both ('4)He surfaces and metal surfaces. Both the bulk and surface energies are calculated in good agreement with experiments.

From the Old to the New World of Nuclear Physics

NASA Astrophysics Data System (ADS)

Stuewer, Roger H.

Physicists passed from the Old to the New World of Nuclear Physics in the two decades between the first and second world wars. The transition occurred against the background of the Great War, the postwar hyperinflation in Germany and Austria, and the greatest intellection migrations in history after the Nazi Civil Service law of 1933, the Anschlussof Austria in March 1938, and the Fascist anti-Semitic laws that fall. It involved Rutherford's discovery of artificial disintegration, Pettersson and Kirsch's challenge of it, and the concomitant rise and fall of Rutherford's satellite model of the nucleus; Gamow's quantum-mechanical theory of alpha decay and his liquid-drop model of the nucleus; the discoveries of deuterium and the deuteron, neutron, and positron, and the inventions of the Cockcroft-Walton accelerator and the cyclotron; the influence of the seventh Solvay Conference; Joliot and Curie's discovery of artificial radioactivity; Pauli's neutrino hypothesis, Fermi's theory of beta decay, and his discovery of the efficacy of slow neutrons in producing nuclear reactions; Bohr's theory of the compound nucleus and Breit and Wigner's theory of neutron-nucleus resonances; and the discovery of nuclear fission, Meitner and Frisch's interpretation of it, and Bohr and Fermi revelation of both in America.

Optical Asymmetry and Nonlinear Light Scattering from Colloidal Gold Nanorods.

PubMed

Lien, Miao-Bin; Kim, Ji-Young; Han, Myung-Geun; Chang, You-Chia; Chang, Yu-Chung; Ferguson, Heather J; Zhu, Yimei; Herzing, Andrew A; Schotland, John C; Kotov, Nicholas A; Norris, Theodore B

2017-06-27

A systematic study is presented of the intensity-dependent nonlinear light scattering spectra of gold nanorods under resonant excitation of the longitudinal surface plasmon resonance (SPR). The spectra exhibit features due to coherent second and third harmonic generation as well as a broadband feature that has been previously attributed to multiphoton photoluminescence arising primarily from interband optical transitions in the gold. A detailed study of the spectral dependence of the scaling of the scattered light with excitation intensity shows unexpected scaling behavior of the coherent signals, which is quantitatively accounted for by optically induced damping of the SPR mode through a Fermi liquid model of the electronic scattering. The broadband feature is shown to arise not from luminescence, but from scattering of the second-order longitudinal SPR mode with the electron gas, where efficient excitation of the second order mode arises from an optical asymmetry of the nanorod. The electronic-temperature-dependent plasmon damping and the Fermi-Dirac distribution together determine the intensity dependence of the broadband emission, and the structure-dependent absorption spectrum determines the spectral shape through the fluctuation-dissipation theorem. Hence a complete self-consistent picture of both coherent and incoherent light scattering is obtained with a single set of physical parameters.

Singularities of the dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field.

PubMed

Carmelo, J M P; Sacramento, P D; Machado, J D P; Campbell, D K

2015-10-14

We study the longitudinal and transverse spin dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field h, focusing in particular on the singularities at excitation energies in the vicinity of the lower thresholds. While the static properties of the model can be studied within a Fermi-liquid like description in terms of pseudoparticles, our derivation of the dynamical properties relies on the introduction of a form of the 'pseudofermion dynamical theory' (PDT) of the 1D Hubbard model suitably modified for the spin-only XXX chain and other models with two pseudoparticle Fermi points. Specifically, we derive the exact momentum and spin-density dependences of the exponents ζ(τ)(k) controlling the singularities for both the longitudinal (τ = l) and transverse (τ = t) dynamical structure factors for the whole momentum range k ∈ ]0,π[, in the thermodynamic limit. This requires the numerical solution of the integral equations that define the phase shifts in these exponents expressions. We discuss the relation to neutron scattering and suggest new experiments on spin-chain compounds using a carefully oriented crystal to test our predictions.

Singularities of the dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field

NASA Astrophysics Data System (ADS)

Carmelo, J. M. P.; Sacramento, P. D.; Machado, J. D. P.; Campbell, D. K.

2015-10-01

We study the longitudinal and transverse spin dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field h, focusing in particular on the singularities at excitation energies in the vicinity of the lower thresholds. While the static properties of the model can be studied within a Fermi-liquid like description in terms of pseudoparticles, our derivation of the dynamical properties relies on the introduction of a form of the ‘pseudofermion dynamical theory’ (PDT) of the 1D Hubbard model suitably modified for the spin-only XXX chain and other models with two pseudoparticle Fermi points. Specifically, we derive the exact momentum and spin-density dependences of the exponents {{\\zeta}τ}(k) controlling the singularities for both the longitudinal ≤ft(τ =l\\right) and transverse ≤ft(τ =t\\right) dynamical structure factors for the whole momentum range k\\in ]0,π[ , in the thermodynamic limit. This requires the numerical solution of the integral equations that define the phase shifts in these exponents expressions. We discuss the relation to neutron scattering and suggest new experiments on spin-chain compounds using a carefully oriented crystal to test our predictions.

--No Title--

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Effects of impurity and Bose-Fermi interactions on the transition temperature of a dilute dipolar Bose-Einstein condensation in trapped Bose-Fermi mixtures

NASA Astrophysics Data System (ADS)

Yavari, H.; Mokhtari, M.

2014-03-01

The effects of impurity and Bose-Fermi interactions on the transition temperature of a dipolar Bose-Einstein condensation in trapped Bose-Fermi mixture, by using the two-fluid model, are investigated. The shift of the transition temperature consists of four contributions due to contact, Bose-Fermi, dipole-dipole, and impurity interactions. We will show that in the presence of an anisotropic trap, the Bose-Fermi correction to the shift of transition temperature due to the excitation spectra of the thermal part is independent of anisotropy factor. Applying our results to trapped Bose-Fermi mixtures shows that, by knowing the impurity effect, the shift of the transition temperature due to Bose-Fermi interaction could be measured for isotropic trap (dipole-dipole contributions is zero) and Feshbach resonance technique (contact potential contribution is negligible).

Magnetotransport of multiple-band nearly antiferromagnetic metals due to hot-spot scattering

DOE PAGES

Koshelev, A. E.

2016-09-30

Multiple-band electronic structure and proximity to antiferromagnetic (AF) instability are the key properties of iron-based superconductors. In this paper, we explore the influence of scattering by the AF spin fluctuations on transport of multiple-band metals above the magnetic transition. A salient feature of scattering on the AF fluctuations is that it is strongly enhanced at the Fermi surface locations where the nesting is perfect (“hot spots” or “hot lines”). We review derivation of the collision integral for the Boltzmann equation due to AF-fluctuations scattering. In the paramagnetic state, the enhanced scattering rate near the hot lines leads to anomalous behaviormore » of electronic transport in magnetic field. We explore this behavior by analytically solving the Boltzmann transport equation with approximate transition rates. This approach accounts for return scattering events and is more accurate than the relaxation-time approximation. The magnetic-field dependences are characterized by two very different field scales: the lower scale is set by the hot-spot width and the higher scale is set by the total scattering amplitude. A conventional magnetotransport behavior is limited to magnetic fields below the lower scale. In the wide range in-between these two scales, the longitudinal conductivity has linear dependence on the magnetic field and the Hall conductivity has quadratic dependence. The linear dependence of the diagonal component reflects growth of the Fermi-surface area affected by the hot spots proportional to the magnetic field. Finally, we discuss applicability of this theoretical framework for describing of anomalous magnetotransport properties in different iron pnictides and chalcogenides in the paramagnetic state.« less

Homogeneous Atomic Fermi Gases

NASA Astrophysics Data System (ADS)

Mukherjee, Biswaroop; Yan, Zhenjie; Patel, Parth B.; Hadzibabic, Zoran; Yefsah, Tarik; Struck, Julian; Zwierlein, Martin W.

2017-03-01

We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state: the striking consequence of Pauli blocking in momentum space for a degenerate gas. Cooling a spin-balanced Fermi gas at unitarity, we create homogeneous superfluids and observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas.

Lev Landau: A View from the West

NASA Astrophysics Data System (ADS)

Hohenberg, Pierre

2009-03-01

The tragic accident which ended Landau's scientific career at an early age meant that Lev Landau was known personally to only a small number of western scientists. His remarkable influence on twentieth century physics thus came from his published work and indirectly from the members of the famed Landau school, who are so well represented at this Symposium. Regarding the published work, I would distinguish three distinct ways in which Landau's influence has been felt. The most obvious is the set of seminal papers on a broad set of topics ranging from Landau diamagnetism, to the phonon-roton theory and two-fluid hydrodynamics of ^4He, Fermi-liquid theory and zero sound, the theory of second-order phase transitions, the Landau-Hopf theory of fluid turbulence and many more. The second class of contributions consists of the famed Landau-Lifshitz Course of Theoretical Physics, which first appeared in the West in the late fifties and early sixties. In many ways the third aspect of Landau's influence, although more difficult to define, is probably even more significant. This is Landau's pervasive presence in a large number of the major theoretical advances in condensed matter and statistical physics throughout the second half of the twentieth century. So many major developments can be viewed as elaborations, advances and - yes - corrections to the foundational theories and points of view laid down by Landau. One example is the theory of superfluidity in Bose liquids, for which one may ask why Landau resisted London's explanation in terms of Bose condensation, which has turned out to be important after all. A second example is the Fermi liquid theory and important later developments stemming from superfluid transitions or effects of strong correlations. A third example is the theory of second-order phase transitions which lays the foundations for the study of critical phenomena using the renormalization group. In each case one marvels at the important foundational role played by Landau's work and one may ask to what extent he himself anticipated the later developments. It is hoped that the subsequent speakers might address some of these questions.

Unconventional superconductivity in magic-angle graphene superlattices.

PubMed

Cao, Yuan; Fatemi, Valla; Fang, Shiang; Watanabe, Kenji; Taniguchi, Takashi; Kaxiras, Efthimios; Jarillo-Herrero, Pablo

2018-04-05

The behaviour of strongly correlated materials, and in particular unconventional superconductors, has been studied extensively for decades, but is still not well understood. This lack of theoretical understanding has motivated the development of experimental techniques for studying such behaviour, such as using ultracold atom lattices to simulate quantum materials. Here we report the realization of intrinsic unconventional superconductivity-which cannot be explained by weak electron-phonon interactions-in a two-dimensional superlattice created by stacking two sheets of graphene that are twisted relative to each other by a small angle. For twist angles of about 1.1°-the first 'magic' angle-the electronic band structure of this 'twisted bilayer graphene' exhibits flat bands near zero Fermi energy, resulting in correlated insulating states at half-filling. Upon electrostatic doping of the material away from these correlated insulating states, we observe tunable zero-resistance states with a critical temperature of up to 1.7 kelvin. The temperature-carrier-density phase diagram of twisted bilayer graphene is similar to that of copper oxides (or cuprates), and includes dome-shaped regions that correspond to superconductivity. Moreover, quantum oscillations in the longitudinal resistance of the material indicate the presence of small Fermi surfaces near the correlated insulating states, in analogy with underdoped cuprates. The relatively high superconducting critical temperature of twisted bilayer graphene, given such a small Fermi surface (which corresponds to a carrier density of about 10 11 per square centimetre), puts it among the superconductors with the strongest pairing strength between electrons. Twisted bilayer graphene is a precisely tunable, purely carbon-based, two-dimensional superconductor. It is therefore an ideal material for investigations of strongly correlated phenomena, which could lead to insights into the physics of high-critical-temperature superconductors and quantum spin liquids.

Raman spectroscopic measurements of CO2 density: Experimental calibration with high-pressure optical cell (HPOC) and fused silica capillary capsule (FSCC) with application to fluid inclusion observations

USGS Publications Warehouse

Wang, X.; Chou, I-Ming; Hu, W.; Burruss, Robert; Sun, Q.; Song, Y.

2011-01-01

Raman spectroscopy is a powerful method for the determination of CO2 densities in fluid inclusions, especially for those with small size and/or low fluid density. The relationship between CO2 Fermi diad split (Δ, cm−1) and CO2 density (ρ, g/cm3) has been documented by several previous studies. However, significant discrepancies exist among these studies mainly because of inconsistent calibration procedures and lack of measurements for CO2fluids having densities between 0.21 and 0.75 g/cm3, where liquid and vapor phases coexist near room temperature.In this study, a high-pressure optical cell and fused silica capillary capsules were used to prepare pure CO2 samples with densities between 0.0472 and 1.0060 g/cm3. The measured CO2 Fermi diad splits were calibrated with two well established Raman bands of benzonitrile at 1192.6 and 1598.9 cm−1. The relationship between the CO2 Fermi diad split and density can be represented by: ρ = 47513.64243 − 1374.824414 × Δ + 13.25586152 × Δ2 − 0.04258891551 × Δ3(r2 = 0.99835, σ = 0.0253 g/cm3), and this relationship was tested by synthetic fluid inclusions and natural CO2-rich fluid inclusions. The effects of temperature and the presence of H2O and CH4 on this relationship were also examined.

From ultracold Fermi Gases to Neutron Stars

NASA Astrophysics Data System (ADS)

Salomon, Christophe

2012-02-01

Ultracold dilute atomic gases can be considered as model systems to address some pending problem in Many-Body physics that occur in condensed matter systems, nuclear physics, and astrophysics. We have developed a general method to probe with high precision the thermodynamics of locally homogeneous ultracold Bose and Fermi gases [1,2,3]. This method allows stringent tests of recent many-body theories. For attractive spin 1/2 fermions with tunable interaction (^6Li), we will show that the gas thermodynamic properties can continuously change from those of weakly interacting Cooper pairs described by Bardeen-Cooper-Schrieffer theory to those of strongly bound molecules undergoing Bose-Einstein condensation. First, we focus on the finite-temperature Equation of State (EoS) of the unpolarized unitary gas. Surprisingly, the low-temperature properties of the strongly interacting normal phase are well described by Fermi liquid theory [3] and we localize the superfluid phase transition. A detailed comparison with theories including recent Monte-Carlo calculations will be presented. Moving away from the unitary gas, the Lee-Huang-Yang and Lee-Yang beyond-mean-field corrections for low density bosonic and fermionic superfluids are quantitatively measured for the first time. Despite orders of magnitude difference in density and temperature, our equation of state can be used to describe low density neutron matter such as the outer shell of neutron stars. [4pt] [1] S. Nascimbène, N. Navon, K. Jiang, F. Chevy, and C. Salomon, Nature 463, 1057 (2010) [0pt] [2] N. Navon, S. Nascimbène, F. Chevy, and C. Salomon, Science 328, 729 (2010) [0pt] [3] S. Nascimbène, N. Navon, S. Pilati, F. Chevy, S. Giorgini, A. Georges, and C. Salomon, Phys. Rev. Lett. 106, 215303 (2011)

Unconventional superconductivity in magic-angle graphene superlattices

NASA Astrophysics Data System (ADS)

Cao, Yuan; Fatemi, Valla; Fang, Shiang; Watanabe, Kenji; Taniguchi, Takashi; Kaxiras, Efthimios; Jarillo-Herrero, Pablo

2018-04-01

The behaviour of strongly correlated materials, and in particular unconventional superconductors, has been studied extensively for decades, but is still not well understood. This lack of theoretical understanding has motivated the development of experimental techniques for studying such behaviour, such as using ultracold atom lattices to simulate quantum materials. Here we report the realization of intrinsic unconventional superconductivity—which cannot be explained by weak electron–phonon interactions—in a two-dimensional superlattice created by stacking two sheets of graphene that are twisted relative to each other by a small angle. For twist angles of about 1.1°—the first ‘magic’ angle—the electronic band structure of this ‘twisted bilayer graphene’ exhibits flat bands near zero Fermi energy, resulting in correlated insulating states at half-filling. Upon electrostatic doping of the material away from these correlated insulating states, we observe tunable zero-resistance states with a critical temperature of up to 1.7 kelvin. The temperature–carrier-density phase diagram of twisted bilayer graphene is similar to that of copper oxides (or cuprates), and includes dome-shaped regions that correspond to superconductivity. Moreover, quantum oscillations in the longitudinal resistance of the material indicate the presence of small Fermi surfaces near the correlated insulating states, in analogy with underdoped cuprates. The relatively high superconducting critical temperature of twisted bilayer graphene, given such a small Fermi surface (which corresponds to a carrier density of about 1011 per square centimetre), puts it among the superconductors with the strongest pairing strength between electrons. Twisted bilayer graphene is a precisely tunable, purely carbon-based, two-dimensional superconductor. It is therefore an ideal material for investigations of strongly correlated phenomena, which could lead to insights into the physics of high-critical-temperature superconductors and quantum spin liquids.

Fast quantum Monte Carlo on a GPU

NASA Astrophysics Data System (ADS)

Lutsyshyn, Y.

2015-02-01

We present a scheme for the parallelization of quantum Monte Carlo method on graphical processing units, focusing on variational Monte Carlo simulation of bosonic systems. We use asynchronous execution schemes with shared memory persistence, and obtain an excellent utilization of the accelerator. The CUDA code is provided along with a package that simulates liquid helium-4. The program was benchmarked on several models of Nvidia GPU, including Fermi GTX560 and M2090, and the Kepler architecture K20 GPU. Special optimization was developed for the Kepler cards, including placement of data structures in the register space of the Kepler GPUs. Kepler-specific optimization is discussed.

Absence of Cyclotron Resonance in the Anomalous Metallic Phase in InOx

NASA Astrophysics Data System (ADS)

Wang, Youcheng; Tamir, I.; Shahar, D.; Armitage, N. P.

2018-04-01

It is observed that many thin superconducting films with not too high disorder level (generally RN/□<2000 Ω ) placed in magnetic field show an anomalous metallic phase where the resistance is low but still finite as temperature goes to zero. Here we report in weakly disordered amorphous InOx thin films that this anomalous metal phase possesses no cyclotron resonance and hence non-Drude electrodynamics. The absence of a finite frequency resonant mode can be associated with a vanishing downstream component of the vortex current parallel to the supercurrent and an emergent particle-hole symmetry of this metal, which establishes its non-Fermi-liquid character.

Pasta phases in core-collapse supernova matter

NASA Astrophysics Data System (ADS)

Pais, Helena; Chiacchiera, Silvia; Providência, Constança

2016-04-01

The pasta phase in core-collapse supernova matter (finite temperatures and fixed proton fractions) is studied within relativistic mean field models. Three different calculations are used for comparison, the Thomas-Fermi (TF), the Coexisting Phases (CP) and the Compressible Liquid Drop (CLD) approximations. The effects of including light clusters in nuclear matter and the densities at which the transitions between pasta configurations and to uniform matter occur are also investigated. The free energy and pressure, in the space of particle number densities and temperatures expected to cover the pasta region, are calculated. Finally, a comparison with a finite temperature Skyrme-Hartree-Fock calculation is drawn.

Hawking radiation in sonic black holes.

PubMed

Giovanazzi, S

2005-02-18

I present a microscopic description of Hawking radiation in sonic black holes. A one-dimensional Fermi-degenerate liquid squeezed by a smooth barrier forms a transonic flow, a sonic analog of a black hole. The quantum treatment of the noninteracting case establishes a close relationship between sonic Hawking radiation and quantum tunneling through the barrier. Quasiparticle excitations appear at the barrier and are then radiated with a thermal distribution in exact agreement with Hawking's formula. The signature of the radiation can be found in the dynamic structure factor, which can be measured in a scattering experiment. The possibility for experimental verification of this new transport phenomenon for ultracold atoms is discussed.

Electronic Griffiths phase and quantum interference in disordered heavy-fermion systems

NASA Astrophysics Data System (ADS)

Gnida, Daniel

2018-02-01

We investigated the specific heat and electrical resistivity of disordered heavy-fermion systems Ce2Co0.8Si3.2 and Ce2Co0.4Rh0.4Si3.2 . Results show that pronounced non-Fermi-liquid behavior in these Kondo disordered compounds originates from approaching metal-insulator transition rather than from proximity to magnetic instability. Power-law divergence of the local Kondo temperature distribution, P (TK) , in the limit of TK→0 , and clear signature of the quantum interference corrections in the resistivity detected deep below the onset of Kondo coherent state, point to electronic Griffiths phase formation in the studied compounds.

The valence bond glass phase

NASA Astrophysics Data System (ADS)

Tarzia, M.; Biroli, G.

2008-06-01

We show that a new glassy phase can emerge in the presence of strong magnetic frustration and quantum fluctuations. It is a valence bond glass (VBG). We study its properties solving the Hubbard-Heisenberg model on a Bethe lattice within the large-N limit introduced by Affleck and Marston. We work out the phase diagram that contains Fermi liquid, dimer and valence bond glass phases. This new glassy phase has no electronic or spin gap (although a pseudo-gap is observed), it is characterized by long-range critical valence bond correlations and is not related to any magnetic ordering. As a consequence, it is quite different from both valence bond crystals and spin glasses.

Constant electrical resistivity of Ni along the melting boundary up to 9 GPa

NASA Astrophysics Data System (ADS)

Silber, Reynold E.; Secco, Richard A.; Yong, Wenjun

2017-07-01

Characterization of transport properties of liquid Ni at high pressures has important geophysical implications for terrestrial planetary interiors, because Ni is a close electronic analogue of Fe and it is also integral to Earth's core. We report measurements of the electrical resistivity of solid and liquid Ni at pressures 3-9 GPa using a 3000 t multianvil large volume press. A four-wire method, in conjunction with a rapid acquisition meter and polarity switch, was used to overcome experimental challenges such as melt containment and maintaining sample geometry and to mitigate the extreme reactivity/solubility of liquid Ni with most thermocouple and electrode materials. Thermal conductivity is calculated using the Wiedemann-Franz law. Electrical resistivity of solid Ni exhibits the expected P dependence and is consistent with earlier experimental values. Within experimental uncertainties, our results indicate that resistivity of liquid Ni remains invariant along the P-dependent melting boundary, which is in disagreement with earlier prediction for liquid transition metals. The potential reasons for such behavior are examined qualitatively through the impact of P-independent local short-range ordering on electron mean free path and the possibility of constant Fermi surface at the onset of Ni melting. Correlation among metals obeying the Kadowaki-Woods ratio and the group of late transition metals with unfilled d-electron band displaying anomalously shallow melting curves suggests that on the melting boundary, Fe may exhibit the same resistivity behavior as Ni. This could have important implications for the heat flow in the Earth's core.

Number of holes contained within the Fermi surface volume in underdoped high-temperature superconductors

DOE PAGES

Harrison, Neil

2016-08-16

Here, we provide a potential solution to the longstanding problem relating Fermi surface reconstruction to the number of holes contained within the Fermi surface volume in underdoped high T c superconductors. On considering uniaxial and biaxial charge-density wave order, we show that there exists a relationship between the ordering wave vector, the hole doping, and the cross-sectional area of the reconstructed Fermi surface whose precise form depends on the volume of the starting Fermi surface. We consider a “large” starting Fermi surface comprising 1+p hole carriers, as predicted by band structure calculations, and a “small” starting Fermi surface comprising pmore » hole carriers, as proposed in models in which the Coulomb repulsion remains the dominant energy. Using the reconstructed Fermi surface cross-sectional area obtained in quantum oscillation experiments in YBa 2Cu 3O 6+x and HgBa 2CuO 4+x and the established methods for estimating the chemical hole doping, we find the ordering vectors obtained from x-ray scattering measurements to show a close correspondence with those expected for the small starting Fermi surface. We therefore show the quantum oscillation frequency and charge-density wave vectors provide accurate estimates for the number of holes contributing to the Fermi surface volume in the pseudogap regime.« less

Number of holes contained within the Fermi surface volume in underdoped high-temperature superconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harrison, Neil

Here, we provide a potential solution to the longstanding problem relating Fermi surface reconstruction to the number of holes contained within the Fermi surface volume in underdoped high T c superconductors. On considering uniaxial and biaxial charge-density wave order, we show that there exists a relationship between the ordering wave vector, the hole doping, and the cross-sectional area of the reconstructed Fermi surface whose precise form depends on the volume of the starting Fermi surface. We consider a “large” starting Fermi surface comprising 1+p hole carriers, as predicted by band structure calculations, and a “small” starting Fermi surface comprising pmore » hole carriers, as proposed in models in which the Coulomb repulsion remains the dominant energy. Using the reconstructed Fermi surface cross-sectional area obtained in quantum oscillation experiments in YBa 2Cu 3O 6+x and HgBa 2CuO 4+x and the established methods for estimating the chemical hole doping, we find the ordering vectors obtained from x-ray scattering measurements to show a close correspondence with those expected for the small starting Fermi surface. We therefore show the quantum oscillation frequency and charge-density wave vectors provide accurate estimates for the number of holes contributing to the Fermi surface volume in the pseudogap regime.« less

Fermi surfaces in Kondo insulators

NASA Astrophysics Data System (ADS)

Liu, Hsu; Hartstein, Máté; Wallace, Gregory J.; Davies, Alexander J.; Ciomaga Hatnean, Monica; Johannes, Michelle D.; Shitsevalova, Natalya; Balakrishnan, Geetha; Sebastian, Suchitra E.

2018-04-01

We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB12 and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary quantities such as a finite linear specific heat capacity in YbB12 exhibit similarities with the Kondo insulator SmB6, yet also crucial differences. Small heavy Fermi sections are observed in YbB12 with similarities to the neighbouring heavy fermion semimetallic Fermi surface, in contrast to large light Fermi surface sections in SmB6 which are more similar to the conduction electron Fermi surface. A rich spectrum of theoretical models is suggested to explain the origin across different Kondo insulating families of a bulk Fermi surface potentially from novel itinerant quasiparticles that couple to magnetic fields, yet do not couple to weak DC electric fields.

Test report dot 7A type a liquid packaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ketusky, E. T.; Brandjes, C.; Benoit, T. J.

This test report documents the performance of Savannah River National Laboratory’s (SRNL’s) U.S. Department of Transportation (DOT) Specification 7A; General Packaging, Type A shielded liquid shipping packaging and compliance with the regulatory requirements of Title 49 of the Code of Federal Regulations (CFR). The primary use of this packaging design is for the transport of radioactive liquids of up to 1.3 liters in an unshielded configuration and up to 113 mL of radioactive liquids in a shielded configuration, with no more than an A2 quantity in either configuration, over public highways and/or commercial aircraft. The contents are liquid radioactive materialsmore » sufficiently shielded and within the activity limits specified in173.435 or 173.433 for A2 (normal form) materials, as well as within the analyzed thermal heat limits. Any contents must be compatibly packaged and must be compatible with the packaging. The basic packaging design is based on the U.S. Department of Energy’s (DOE’s) Model 9979 Type A fissile shipping packaging designed and tested by SRNL. The shielded liquid configuration consists of the outer and inner drums of the 9979 package with additional low density polyethylene (LDPE) dunnage nesting a tungsten shielded cask assembly (WSCA) within the 30-gallon inner drum. The packaging model for the DOT Specification 7A, Type A liquids packaging is HVYTAL.« less

Reprint of : Scattering theory approach to bosonization of non-equilibrium mesoscopic systems

NASA Astrophysics Data System (ADS)

Sukhorukov, Eugene V.

2016-08-01

Between many prominent contributions of Markus Büttiker to mesoscopic physics, the scattering theory approach to the electron transport and noise stands out for its elegance, simplicity, universality, and popularity between theorists working in this field. It offers an efficient way to theoretically investigate open electron systems far from equilibrium. However, this method is limited to situations where interactions between electrons can be ignored, or considered perturbatively. Fortunately, this is the case in a broad class of metallic systems, which are commonly described by the Fermi liquid theory. Yet, there exist another broad class of electron systems of reduced dimensionality, the so-called Tomonaga-Luttinger liquids, where interactions are effectively strong and cannot be neglected even at low energies. Nevertheless, strong interactions can be accounted exactly using the bosonization technique, which utilizes the free-bosonic character of collective excitations in these systems. In the present work, we use this fact in order to develop the scattering theory approach to the bosonization of open quasi-one dimensional electron systems far from equilibrium.

Scattering theory approach to bosonization of non-equilibrium mesoscopic systems

NASA Astrophysics Data System (ADS)

Sukhorukov, Eugene V.

2016-03-01

Between many prominent contributions of Markus Büttiker to mesoscopic physics, the scattering theory approach to the electron transport and noise stands out for its elegance, simplicity, universality, and popularity between theorists working in this field. It offers an efficient way to theoretically investigate open electron systems far from equilibrium. However, this method is limited to situations where interactions between electrons can be ignored, or considered perturbatively. Fortunately, this is the case in a broad class of metallic systems, which are commonly described by the Fermi liquid theory. Yet, there exist another broad class of electron systems of reduced dimensionality, the so-called Tomonaga-Luttinger liquids, where interactions are effectively strong and cannot be neglected even at low energies. Nevertheless, strong interactions can be accounted exactly using the bosonization technique, which utilizes the free-bosonic character of collective excitations in these systems. In the present work, we use this fact in order to develop the scattering theory approach to the bosonization of open quasi-one dimensional electron systems far from equilibrium.

LCLS-II 1.3 GHz cryomodule design - lessons learned from testing at Fermilab

NASA Astrophysics Data System (ADS)

Kaluzny, J.; Hurd, J.; Orlov, Y.; He, Y.; Bossert, R.; Grimm, C.; Schappert, W.; Atassi, O. Al; Wang, R.; Arkan, T.; Theilacker, J.; Klebaner, A.; White, M.; Wu, G.; Makara, J.; Ginsburg, C.; Pei, L.; Holzbauer, J.; Hansen, B.; Stanek, R.; Peterson, T.; Harms, E.

2017-12-01

Fermilab’s 1.3 GHz prototype cryomodule for the Linac Coherent Light Source Upgrade (LCLS-II) has been tested at Fermilab’s Cryomodule Test Facility (CMTF). Aspects of the cryomodule design have been studied and tested. The cooldown circuit was used to quickly cool the cavities through the transition temperature, and a heater on the circuit was used to heat incoming helium for warmup. Due to the 0.5% slope of the cryomodule, the liquid level is not constant along the length of the cryomodule. This slope as well as the pressure profile caused liquid level management to be a challenge. The microphonics levels in the cryomodule were studied and efforts were made to reduce them throughout testing. Some of the design approaches and studies performed on these aspects will be presented. Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy. This work was supported, in part, by the LCLS-II Project.

Band-edges and band-gap in few-layered transition metal dichalcogenides

NASA Astrophysics Data System (ADS)

Bhunia, Hrishikesh; Pal, Amlan J.

2018-05-01

We have considered liquid-exfoliated transition metal dichalcogenides (WS2, WSe2, MoS2, and MoSe2) and studied their band-edges and band-gap through scanning tunneling spectroscopy (STS) and density of states. A monolayer, bilayer (2L), and trilayer (3L) of each of the layered materials were characterized to derive the energies. Upon an increase in the number of layers, both the band-edges were found to shift towards the Fermi energy. The results from the exfoliated nanosheets have been compared with reported STS studies of MoS2 and WSe2 formed through chemical vapor deposition or molecular beam epitaxy methods; an uncontrolled lattice strain existed in such 2L and 3L nanoflakes due to mismatch in stacking-patterns between the monolayers affecting their energies. In the present work, the layers formed through the liquid-exfoliation process retained their interlayer coupling or stacking-sequence prevalent to the bulk and hence allowed determination of band-energies in these strain-free two-dimensional materials.

Fermi surface properties of NbAs2 studied by de Haas-van Alphen oscillation

NASA Astrophysics Data System (ADS)

Singha, Ratnadwip; Mandal, Prabhat

2018-04-01

We have grown high quality single crystal of NbAs2, a member of the transition metal dipnictide family and measured magnetotransport properties. Very large magnetoresistance ˜1.3×105 % has been observed at 2 K with 9 T magnetic field. The Fermi surface properties have been studied by de Haas-van Alphen oscillation technique. The Fermi surface is highly anisotropic and consists of multiple Fermi pockets. From quantum oscillation results, different Fermi surface related parameters have been quantified.

Single-Particle Properties of a Strongly Interacting Bose-Fermi Mixture Above the BEC Phase Transition Temperature

NASA Astrophysics Data System (ADS)

Kharga, D.; Inotani, D.; Hanai, R.; Ohashi, Y.

2017-06-01

We theoretically investigate the normal state properties of a Bose-Fermi mixture with a strong attractive interaction between Fermi and Bose atoms. We extend the ordinary T-matrix approximation (TMA) with respect to Bose-Fermi pairing fluctuations, to include the Hugenholtz-Pines' relation for all Bose Green's functions appearing in TMA self-energy diagrams. This extension is shown to be essentially important to correctly describe the physical properties of the Bose-Fermi mixture, especially near the Bose-Einstein condensation instability. Using this improved TMA, we clarify how the formation of composite fermions affects Bose and Fermi single-particle excitation spectra, over the entire interaction strength.

Quasiparticle lifetime in a mixture of Bose and Fermi superfluids.

PubMed

Zheng, Wei; Zhai, Hui

2014-12-31

In this Letter, we study the effect of quasiparticle interactions in a Bose-Fermi superfluid mixture. We consider the lifetime of a quasiparticle of the Bose superfluid due to its interaction with quasiparticles in the Fermi superfluid. We find that this damping rate, i.e., the inverse of the lifetime, has quite a different threshold behavior at the BCS and the BEC side of the Fermi superfluid. The damping rate is a constant near the threshold momentum in the BCS side, while it increases rapidly in the BEC side. This is because, in the BCS side, the decay process is restricted by the constraint that the fermion quasiparticle is located near the Fermi surface, while such a restriction does not exist in the BEC side where the damping process is dominated by bosonic quasiparticles of the Fermi superfluid. Our results are related to the collective mode experiment in the recently realized Bose-Fermi superfluid mixture.

Fermi-LAT detection of ongoing gamma-ray activity from the new gamma-ray source Fermi J1654-1055 (PMN J1632-1052)

NASA Astrophysics Data System (ADS)

Kocevski, D.; Ajello, M.; Buson, S.; Buehler, R.; Giomi, M.

2016-02-01

During the week between February 8 and 15, 2016, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, observed gamma-ray activity from a new transient source, Fermi J1654-1055.

Pseudogap-generated a coexistence of Fermi arcs and Fermi pockets in cuprate superconductors

NASA Astrophysics Data System (ADS)

Zhao, Huaisong; Gao, Deheng; Feng, Shiping

2017-03-01

One of the most intriguing puzzle is why there is a coexistence of Fermi arcs and Fermi pockets in the pseudogap phase of cuprate superconductors? This puzzle is calling for an explanation. Based on the t - J model in the fermion-spin representation, the coexistence of the Fermi arcs and Fermi pockets in cuprate superconductors is studied by taking into account the pseudogap effect. It is shown that the pseudogap induces an energy band splitting, and then the poles of the electron Green's function at zero energy form two contours in momentum space, however, the electron spectral weight on these two contours around the antinodal region is gapped out by the pseudogap, leaving behind the low-energy electron spectral weight only located at the disconnected segments around the nodal region. In particular, the tips of these disconnected segments converge on the hot spots to form the closed Fermi pockets, generating a coexistence of the Fermi arcs and Fermi pockets. Moreover, the single-particle coherent weight is directly related to the pseudogap, and grows linearly with doping. The calculated result of the overall dispersion of the electron excitations is in qualitative agreement with the experimental data. The theory also predicts that the pseudogap-induced peak-dip-hump structure in the electron spectrum is absent from the hot-spot directions.

3D Quantum Hall Effect of Fermi Arc in Topological Semimetals

NASA Astrophysics Data System (ADS)

Wang, C. M.; Sun, Hai-Peng; Lu, Hai-Zhou; Xie, X. C.

2017-09-01

The quantum Hall effect is usually observed in 2D systems. We show that the Fermi arcs can give rise to a distinctive 3D quantum Hall effect in topological semimetals. Because of the topological constraint, the Fermi arc at a single surface has an open Fermi surface, which cannot host the quantum Hall effect. Via a "wormhole" tunneling assisted by the Weyl nodes, the Fermi arcs at opposite surfaces can form a complete Fermi loop and support the quantum Hall effect. The edge states of the Fermi arcs show a unique 3D distribution, giving an example of (d -2 )-dimensional boundary states. This is distinctly different from the surface-state quantum Hall effect from a single surface of topological insulator. As the Fermi energy sweeps through the Weyl nodes, the sheet Hall conductivity evolves from the 1 /B dependence to quantized plateaus at the Weyl nodes. This behavior can be realized by tuning gate voltages in a slab of topological semimetal, such as the TaAs family, Cd3 As2 , or Na3Bi . This work will be instructive not only for searching transport signatures of the Fermi arcs but also for exploring novel electron gases in other topological phases of matter.

Semiclassical approaches to nuclear dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Magner, A. G., E-mail: magner@kinr.kiev.ua; Gorpinchenko, D. V.; Bartel, J.

The extended Gutzwiller trajectory approach is presented for the semiclassical description of nuclear collective dynamics, in line with the main topics of the fruitful activity of V.G. Solovjov. Within the Fermi-liquid droplet model, the leptodermous effective surface approximation was applied to calculations of energies, sum rules, and transition densities for the neutron–proton asymmetry of the isovector giant-dipole resonance and found to be in good agreement with the experimental data. By using the Strutinsky shell correction method, the semiclassical collective transport coefficients, such as nuclear inertia, friction, stiffness, and moments of inertia, can be derived beyond the quantum perturbation approximation ofmore » the response function theory and the cranking model. The averaged particle-number dependences of the low-lying collective vibrational states are described in good agreement with the basic experimental data, mainly due to the enhancement of the collective inertia as compared to its irrotational flow value. Shell components of the moment of inertia are derived in terms of the periodic-orbit free-energy shell corrections. A good agreement between the semiclassical extended Thomas–Fermi moments of inertia with shell corrections and the quantum results is obtained for different nuclear deformations and particle numbers. Shell effects are shown to be exponentially dampted out with increasing temperature in all the transport coefficients.« less

Tailoring graphene-based electrodes from semiconducting to metallic to increase the energy density in supercapacitors.

PubMed

Vatamanu, Jenel; Ni, Xiaojuan; Liu, Feng; Bedrov, Dmitry

2015-11-20

The semiconducting character of graphene and some carbon-based electrodes can lead to noticeably lower total capacitances and stored energy densities in electric double layer (EDL)capacitors. This paper discusses the chemical and electronic structure modifications that enhance the available energy bands, density of states and quantum capacitance of graphene substrates near the Fermi level, therefore restoring the conducting character of these materials. The doping of graphene with p or n dopants, such as boron and nitrogen atoms, or the introduction of vacancy defects that introduce zigzag edges, can significantly increase the quantum capacitance within the potential range of interest for the energy storage applications by either shifting the Dirac point away from the Fermi level or by eliminating the Dirac point. We show that a combination of doping and vacancies at realistic concentrations is sufficient to increase the capacitance of a graphene-based electrode to within 1 μF cm(−2) from that of a metallic surface.Using a combination of ab initio calculations and classical molecular dynamics simulations we estimate how the changes in the quantum capacitance of these electrode materials affect the total capacitance stored by the open structure EDL capacitors containing room temperature ionic liquid electrolytes.

Optical Asymmetry and Nonlinear Light Scattering from Colloidal Gold Nanorods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lien, Miao-Bin; Kim, Ji-Young; Han, Myung-Geun

A systematic study is presented of the intensity-dependent nonlinear light scattering spectra of gold nanorods under resonant excitation of the longitudinal surface plasmon resonance (SPR). The spectra exhibit features due to coherent second and third harmonic generation as well as a broadband feature that has been previously attributed to multiphoton photoluminescence arising primarily from interband optical transitions in the gold. A detailed study of the spectral dependence of the scaling of the scattered light with excitation intensity shows unexpected scaling behavior of the coherent signals, which is quantitatively accounted for by optically induced damping of the SPR mode through amore » Fermi liquid model of the electronic scattering. The broadband feature is shown to arise not from luminescence, but from scattering of the secondorder longitudinal SPR mode with the electron gas, where efficient excitation of the 2nd order mode arises from an optical asymmetry of the nanorod. The electronic-temperature-dependent plasmon damping and the Fermi-Dirac distribution together determine the intensity dependence of the broadband emission, and the structure-dependent absorption spectrum determines the spectral shape through the fluctuation-dissipation theorem. Hence a complete self-consistent picture of both coherent and incoherent light scattering is obtained with a single set of physical parameters.« less

Momentum distribution of the uniform electron gas: Improved parametrization and exact limits of the cumulant expansion

NASA Astrophysics Data System (ADS)

Gori-Giorgi, Paola; Ziesche, Paul

2002-12-01

The momentum distribution of the unpolarized uniform electron gas in its Fermi-liquid regime, n(k,rs), with the momenta k measured in units of the Fermi wave number kF and with the density parameter rs, is constructed with the help of the convex Kulik function G(x). It is assumed that n(0,rs),n(1±,rs), the on-top pair density g(0,rs), and the kinetic energy t(rs) are known (respectively, from accurate calculations for rs=1,…,5, from the solution of the Overhauser model, and from quantum Monte Carlo calculations via the virial theorem). Information from the high- and the low-density limit, corresponding to the random-phase approximation and to the Wigner crystal limit, is used. The result is an accurate parametrization of n(k,rs), which fulfills most of the known exact constraints. It is in agreement with the effective-potential calculations of Takada and Yasuhara [Phys. Rev. B 44, 7879 (1991)], is compatible with quantum Monte Carlo data, and is valid in the density range rs≲12. The corresponding cumulant expansions of the pair density and of the static structure factor are discussed, and some exact limits are derived.

Electrodynamics of the nodal metal state in weakly doped high- Tc cuprates

NASA Astrophysics Data System (ADS)

Lee, Y. S.; Segawa, Kouji; Li, Z. Q.; Padilla, W. J.; Dumm, M.; Dordevic, S. V.; Homes, C. C.; Ando, Yoichi; Basov, D. N.

2005-08-01

We report on the detailed analysis of the infrared (IR) conductivity of two prototypical high- Tc systems YBa2Cu3Oy and La2-xSrxCuO4 throughout the complex phase diagram of these compounds. Our focus in this work is to thoroughly document the electromagnetic response of the nodal metal state which is initiated with only a few holes doped in parent antiferromagnetic systems and extends up to the pseudogap boundary in the phase diagram. The key signature of the nodal metal is the two-component conductivity: the Drude mode at low energies followed by a resonance in mid-IR. The Drude component can be attributed to the response of coherent quasiparticles residing on the Fermi arcs detected in photoemission experiments. The microscopic origin of the mid-IR band is yet to be understood. A combination of transport and IR data uncovers fingerprints of the Fermi liquid behavior in the response of the nodal metal. The comprehensive nature of the data sets presented in this work allows us to critically re-evaluate common approaches to the interpretation of the optical data. Specifically we re-examine the role of magnetic excitations in generating electronic self-energy effects through the analysis of the IR data in a high magnetic field.

Conductance of closed and open long Aharonov-Bohm-Kondo rings

NASA Astrophysics Data System (ADS)

Shi, Zheng; Komijani, Yashar

2017-02-01

We calculate the finite temperature linear dc conductance of a generic single-impurity Anderson model containing an arbitrary number of Fermi liquid leads, and apply the formalism to closed and open long Aharonov-Bohm-Kondo (ABK) rings. We show that, as with the short ABK ring, there is a contribution to the conductance from the connected four-point Green's function of the conduction electrons. At sufficiently low temperatures this contribution can be eliminated, and the conductance can be expressed as a linear function of the T matrix of the screening channel. For closed rings we show that at temperatures high compared to the Kondo temperature, the conductance behaves differently for temperatures above and below vF/L , where vF is the Fermi velocity and L is the circumference of the ring. For open rings, when the ring arms have both a small transmission and a small reflection, we show from the microscopic model that the ring behaves like a two-path interferometer, and that the Kondo temperature is unaffected by details of the ring. Our findings confirm that ABK rings are potentially useful in the detection of the size of the Kondo screening cloud, the π /2 scattering phase shift from the Kondo singlet, and the suppression of Aharonov-Bohm oscillations due to inelastic scattering.

Optical Asymmetry and Nonlinear Light Scattering from Colloidal Gold Nanorods

DOE PAGES

Lien, Miao-Bin; Kim, Ji-Young; Han, Myung-Geun; ...

2017-05-16

A systematic study is presented of the intensity-dependent nonlinear light scattering spectra of gold nanorods under resonant excitation of the longitudinal surface plasmon resonance (SPR). The spectra exhibit features due to coherent second and third harmonic generation as well as a broadband feature that has been previously attributed to multiphoton photoluminescence arising primarily from interband optical transitions in the gold. A detailed study of the spectral dependence of the scaling of the scattered light with excitation intensity shows unexpected scaling behavior of the coherent signals, which is quantitatively accounted for by optically induced damping of the SPR mode through amore » Fermi liquid model of the electronic scattering. The broadband feature is shown to arise not from luminescence, but from scattering of the secondorder longitudinal SPR mode with the electron gas, where efficient excitation of the 2nd order mode arises from an optical asymmetry of the nanorod. The electronic-temperature-dependent plasmon damping and the Fermi-Dirac distribution together determine the intensity dependence of the broadband emission, and the structure-dependent absorption spectrum determines the spectral shape through the fluctuation-dissipation theorem. Hence a complete self-consistent picture of both coherent and incoherent light scattering is obtained with a single set of physical parameters.« less

Thermodynamics of phase formation in the quantum critical metal Sr3Ru2O7

PubMed Central

Rost, A. W.; Grigera, S. A.; Bruin, J. A. N.; Perry, R. S.; Tian, D.; Raghu, S.; Kivelson, Steven Allan; Mackenzie, A. P.

2011-01-01

The behavior of matter near zero temperature continuous phase transitions, or “quantum critical points” is a central topic of study in condensed matter physics. In fermionic systems, fundamental questions remain unanswered: the nature of the quantum critical regime is unclear because of the apparent breakdown of the concept of the quasiparticle, a cornerstone of existing theories of strongly interacting metals. Even less is known experimentally about the formation of ordered phases from such a quantum critical “soup.” Here, we report a study of the specific heat across the phase diagram of the model system Sr3Ru2O7, which features an anomalous phase whose transport properties are consistent with those of an electronic nematic. We show that this phase, which exists at low temperatures in a narrow range of magnetic fields, forms directly from a quantum critical state, and contains more entropy than mean-field calculations predict. Our results suggest that this extra entropy is due to remnant degrees of freedom from the highly entropic state above Tc. The associated quantum critical point, which is “concealed” by the nematic phase, separates two Fermi liquids, neither of which has an identifiable spontaneously broken symmetry, but which likely differ in the topology of their Fermi surfaces. PMID:21933961

The DarkSide-50 outer detectors

NASA Astrophysics Data System (ADS)

Westerdale, S.; Agnes, P.; Agostino, L.; Albuquerque, I. F. M.; Alexander, T.; Alton, A. K.; Arisaka, K.; Back, H. O.; Baldin, B.; Biery, K.; Bonfini, G.; Bossa, M.; Bottino, B.; Brigatti, A.; Brodsky, J.; Budano, F.; Bussino, S.; Cadeddu, M.; Cadonati, L.; Cadoni, M.; Calaprice, F.; Canci, N.; Candela, A.; Cao, H.; Cariello, M.; Carlini, M.; Catalanotti, S.; Cavalcante, P.; Chepurnov, A.; Cocco, A. G.; Covone, G.; D'Angelo, D.; D'Incecco, M.; Davini, S.; De Cecco, S.; De Deo, M.; De Vincenzi, M.; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, G.; Edkins, E.; Empl, A.; Fan, A.; Fiorillo, G.; Fomenko, K.; Foster, G.; Franco, D.; Gabriele, F.; Galbiati, C.; Giganti, C.; Goretti, A. M.; Granato, F.; Grandi, L.; Gromov, M.; Guan, M.; Guardincerri, Y.; Hackett, B. R.; Herner, K. R.; Hungerford, E. V.; Aldo, Ianni; Andrea, Ianni; James, I.; Jollet, C.; Keeter, K.; Kendziora, C. L.; Kobychev, V.; Koh, G.; Korablev, D.; Korga, G.; Kubankin, A.; Li, X.; Lissia, M.; Lombardi, P.; Luitz, S.; Ma, Y.; Machulin, I. N.; Mandarano, A.; Mari, S. M.; Maricic, J.; Marini, L.; Martoff, C. J.; Meregaglia, A.; Meyers, P. D.; Miletic, T.; Milincic, R.; Montanari, D.; Monte, A.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B. J.; Muratova, V. N.; Musico, P.; Napolitano, J.; Orsini, M.; Ortica, F.; Pagani, L.; Pallavicini, M.; Pantic, E.; Parmeggiano, S.; Pelczar, K.; Pelliccia, N.; Perasso, S.; Pocar, A.; Pordes, S.; Pugachev, D. A.; Qian, H.; Randle, K.; Ranucci, G.; Razeto, A.; Reinhold, B.; Renshaw, A. L.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Sablone, D.; Saggese, P.; Saldanha, R.; Sands, W.; Sangiorgio, S.; Savarese, C.; Segreto, E.; Semenov, D. A.; Shields, E.; Singh, P. N.; DSkorokhvatov, M.; Smirnov, O.; Sotnikov, A.; Stanford, C.; Suvorov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Tonazzo, A.; Trinchese, P.; Unzhakov, E. V.; Vishneva, A.; Vogelaar, B.; Wada, M.; Walker, S.; Wang, H.; Wang, Y.; Watson, A. W.; Wilhelmi, J.; Wojcik, M. M.; Xiang, X.; Xu, J.; Yang, C.; Yoo, J.; Zavatarelli, S.; Zec, A.; Zhong, W.; Zhu, C.; Zuzel, G.; DarkSide Collaboration

2016-05-01

DarkSide-50 is a dark matter detection experiment searching for Weakly Interacting Massive Particles (WIMPs), in Gran Sasso National Laboratory. For experiments like DarkSide-50, neutrons are one of the primary backgrounds that can mimic WIMP signals. The experiment consists of three nested detectors: a liquid argon time projection chamber surrounded by two outer detectors. The outermost detector is a 10 m by 11 m cylindrical water Cherenkov detector with 80 PMTs, designed to provide shielding and muon vetoing. Inside the water Cherenkov detector is the 4 m diameter spherical boron-loaded liquid scintillator veto, with a cocktail of pseudocumene, trimethyl borate, and PPO wavelength shifter, designed to provide shielding, neutron vetoing, and in situ measurements of the TPC backgrounds. We present design and performance details of the DarkSide-50 outer detectors.

Spin-orbital quantum liquid on the honeycomb lattice

NASA Astrophysics Data System (ADS)

Corboz, Philippe

2013-03-01

The symmetric Kugel-Khomskii can be seen as a minimal model describing the interactions between spin and orbital degrees of freedom in transition-metal oxides with orbital degeneracy, and it is equivalent to the SU(4) Heisenberg model of four-color fermionic atoms. We present simulation results for this model on various two-dimensional lattices obtained with infinite projected-entangled pair states (iPEPS), an efficient variational tensor-network ansatz for two dimensional wave functions in the thermodynamic limit. This approach can be seen as a two-dimensional generalization of matrix product states - the underlying ansatz of the density matrix renormalization group method. We find a rich variety of exotic phases: while on the square and checkerboard lattices the ground state exhibits dimer-Néel order and plaquette order, respectively, quantum fluctuations on the honeycomb lattice destroy any order, giving rise to a spin-orbital liquid. Our results are supported from flavor-wave theory and exact diagonalization. Furthermore, the properties of the spin-orbital liquid state on the honeycomb lattice are accurately accounted for by a projected variational wave-function based on the pi-flux state of fermions on the honeycomb lattice at 1/4-filling. In that state, correlations are algebraic because of the presence of a Dirac point at the Fermi level, suggesting that the ground state is an algebraic spin-orbital liquid. This model provides a good starting point to understand the recently discovered spin-orbital liquid behavior of Ba3CuSb2O9. The present results also suggest to choose optical lattices with honeycomb geometry in the search for quantum liquids in ultra-cold four-color fermionic atoms. We acknowledge the financial support from the Swiss National Science Foundation.

Soil Moisture and Excavation Behaviour in the Chaco Leaf-Cutting Ant (Atta vollenweideri): Digging Performance and Prevention of Water Inflow into the Nest

PubMed Central

Pielström, Steffen; Roces, Flavio

2014-01-01

The Chaco leaf-cutting ant Atta vollenweideri is native to the clay-heavy soils of the Gran Chaco region in South America. Because of seasonal floods, colonies are regularly exposed to varying moisture across the soil profile, a factor that not only strongly influences workers' digging performance during nest building, but also determines the suitability of the soil for the rearing of the colony's symbiotic fungus. In this study, we investigated the effects of varying soil moisture on behaviours associated with underground nest building in A. vollenweideri. This was done in a series of laboratory experiments using standardised, plastic clay-water mixtures with gravimetric water contents ranging from relatively brittle material to mixtures close to the liquid limit. Our experiments showed that preference and group-level digging rate increased with increasing water content, but then dropped considerably for extremely moist materials. The production of vibrational recruitment signals during digging showed, on the contrary, a slightly negative linear correlation with soil moisture. Workers formed and carried clay pellets at higher rates in moist clay, even at the highest water content tested. Hence, their weak preference and low group-level excavation rate observed for that mixture cannot be explained by any inability to work with the material. More likely, extremely high moistures may indicate locations unsuitable for nest building. To test this hypothesis, we simulated a situation in which workers excavated an upward tunnel below accumulated surface water. The ants stopped digging about 12 mm below the interface soil/water, a behaviour representing a possible adaptation to the threat of water inflow field colonies are exposed to while digging under seasonally flooded soils. Possible roles of soil water in the temporal and spatial pattern of nest growth are discussed. PMID:24748382

Quasiclassical Theory of Spin Dynamics in Superfluid ^3He: Kinetic Equations in the Bulk and Spin Response of Surface Majorana States

NASA Astrophysics Data System (ADS)

Silaev, M. A.

2018-06-01

We develop a theory based on the formalism of quasiclassical Green's functions to study the spin dynamics in superfluid ^3He. First, we derive kinetic equations for the spin-dependent distribution function in the bulk superfluid reproducing the results obtained earlier without quasiclassical approximation. Then, we consider spin dynamics near the surface of fully gapped ^3He-B-phase taking into account spin relaxation due to the transitions in the spectrum of localized fermionic states. The lifetimes of longitudinal and transverse spin waves are calculated taking into account the Fermi-liquid corrections which lead to a crucial modification of fermionic spectrum and spin responses.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rice, T. Maurice; Robinson, Neil J.; Tsvelik, Alexei M.

Here, the high-temperature normal state of the unconventional cuprate superconductors has resistivity linear in temperature T, which persists to values well beyond the Mott-Ioffe-Regel upper bound. At low temperatures, within the pseudogap phase, the resistivity is instead quadratic in T, as would be expected from Fermi liquid theory. Developing an understanding of these normal phases of the cuprates is crucial to explain the unconventional superconductivity. We present a simple explanation for this behavior, in terms of the umklapp scattering of electrons. This fits within the general picture emerging from functional renormalization group calculations that spurred the Yang-Rice-Zhang ansatz: Umklapp scatteringmore » is at the heart of the behavior in the normal phase.« less

A method for atomic-level noncontact thermometry with electron energy distribution

NASA Astrophysics Data System (ADS)

Kinoshita, Ikuo; Tsukada, Chiharu; Ouchi, Kohei; Kobayashi, Eiichi; Ishii, Juntaro

2017-04-01

We devised a new method of determining the temperatures of materials with their electron-energy distributions. The Fermi-Dirac distribution convoluted with a linear combination of Gaussian and Lorentzian distributions was fitted to the photoelectron spectrum measured for the Au(110) single-crystal surface at liquid N2-cooled temperature. The fitting successfully determined the surface-local thermodynamic temperature and the energy resolution simultaneously from the photoelectron spectrum, without any preliminary results of other measurements. The determined thermodynamic temperature was 99 ± 2.1 K, which was in good agreement with the reference temperature of 98.5 ± 0.5 K measured using a silicon diode sensor attached to the sample holder.

Safety approach to the selection of design criteria for the CRBRP reactor refueling system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meisl, C J; Berg, G E; Sharkey, N F

1979-01-01

The selection of safety design criteria for Liquid Metal Fast Breeder Reactor (LMFBR) refueling systems required the extrapolation of regulations and guidelines intended for Light Water Reactor refueling systems and was encumbered by the lack of benefit from a commercially licensed predecessor other than Fermi. The overall approach and underlying logic are described for developing safety design criteria for the reactor refueling system (RRS) of the Clinch River Breeder Reactor Plant (CRBRP). The complete selection process used to establish the criteria is presented, from the definition of safety functions to the finalization of safety design criteria in the appropriate documents.more » The process steps are illustrated by examples.« less

Fractional Wigner Crystal in the Helical Luttinger Liquid.

PubMed

Traverso Ziani, N; Crépin, F; Trauzettel, B

2015-11-13

The properties of the strongly interacting edge states of two dimensional topological insulators in the presence of two-particle backscattering are investigated. We find an anomalous behavior of the density-density correlation functions, which show oscillations that are neither of Friedel nor of Wigner type: they, instead, represent a Wigner crystal of fermions of fractional charge e/2, with e the electron charge. By studying the Fermi operator, we demonstrate that the state characterized by such fractional oscillations still bears the signatures of spin-momentum locking. Finally, we compare the spin-spin correlation functions and the density-density correlation functions to argue that the fractional Wigner crystal is characterized by a nontrivial spin texture.

Theory of superconductivity in oxides. Final technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, P.W.

1988-05-18

Progress was made towards a final theory of high-Tc superconductivity. The key elements are the work on normal-state properties and the actual mechanism for Tc. With the understanding (ZA) of the large anisotropy and other transport properties in the normal state, the model is uniquely determined: one must have one version or another of a holon-spinon quantum-fluid state, which is not a normal Fermi liquid. And with the recognition (HWA) of the large-repulsion holon-holon interactions, the author has the first way of thinking quantitatively about the superconducting state. Work on the pure Heisenberg system, which is related but not necessarilymore » crucial to understanding the superconducting properties is described.« less

Search for the Acoustic Faraday Effect in Superfluid ^3He-B

NASA Astrophysics Data System (ADS)

Lee, Y.; Haard, T. M.; Kycia, J. B.; Halperin, W. P.

1997-03-01

Transverse zero sound is another propagating mode predicted to exist in Fermi liquids by Landau. However, it has been difficult to achieve clear experimental evidence for propagating transverse zero sound in ^3He. A recent theoretical calculation(G.F. Moores and J.A. Sauls, JLTP 91), 13 (1993). showed that this mode may be rather easily detected at very low temperatures in the B-phase of superfluid ^3He. Futhermore, in the presence of a magnetic field the polarization of the sound wave rotates as it propagates, which is analogous to the Faraday effect in optics. We report our preliminary experimental results on the acoustic Faraday effect in ^3He-B.

Electric resistivity and thermoelectricity of Ni-Nb-Zr and Ni-Nb-Zr-H glassy alloys

NASA Astrophysics Data System (ADS)

Fukuhara, Mikio; Inoue, Akihisa

2010-09-01

Electric resistivity ρ and thermoelectric power S of Ni 36Nb 24Zr 40 and (Ni 0.36Nb 0.24Zr 0.4) 90H 10 glassy alloys were investigated in temperature region between 1.5 and 300 K. After resistivity curves of both alloys increase gradually with decreasing temperature down to around 6 K, they dropped suddenly and then reached zero resistivity at 2.1 K, leading to superconductivity. Linear curve with negative TCR of ρ vs T2 and slight increase of S/ T in temperature region down to around 6 K clearly reveal Fermi-liquid phenomenon in electronic state for both alloys independent of hydrogen content.

75 FR 24755 - DTE ENERGY; Enrico Fermi Atomic Power Plant Unit 1; Exemption From Certain Low-Level Waste...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-05-05

... NUCLEAR REGULATORY COMMISSION [Docket No. 50-16; NRC-2009-0073] DTE ENERGY; Enrico Fermi Atomic... License No. DPR-9 issued for Enrico Fermi Atomic Power Plant, Unit 1 (Fermi-1), located in Monroe County... undue hazard to life or property. There are no provisions in the Atomic Energy Act (or in any other...

Understanding and Using the Fermi Science Tools

NASA Astrophysics Data System (ADS)

Asercion, Joseph

2018-01-01

The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.

Fermi arc mediated entropy transport in topological semimetals

NASA Astrophysics Data System (ADS)

McCormick, Timothy M.; Watzman, Sarah J.; Heremans, Joseph P.; Trivedi, Nandini

2018-05-01

The low-energy excitations of topological Weyl semimetals are composed of linearly dispersing Weyl fermions that act as monopoles of Berry curvature in the bulk momentum space. Furthermore, on the surface there exist topologically protected Fermi arcs at the projections of these Weyl points. We propose a pathway for entropy transport involving Fermi arcs on one surface connecting to Fermi arcs on the other surface via the bulk Weyl monopoles. We present results for the temperature and magnetic field dependence of the magnetothermal conductance of this conveyor belt channel. The circulating currents result in a net entropy transport without any net charge transport. We provide results for the Fermi arc mediated magnetothermal conductivity in the low-field semiclassical limit as well as in the high-field ultraquantum limit, where only chiral Landau levels are involved. Our work provides a proposed signature of Fermi arc mediated magnetothermal transport and sets the stage for utilizing and manipulating the topological Fermi arcs in thermal applications.

Phonon Dispersion and the Competition between Pairing and Charge Order

NASA Astrophysics Data System (ADS)

Costa, N. C.; Blommel, T.; Chiu, W.-T.; Batrouni, G.; Scalettar, R. T.

2018-05-01

The Holstein model describes the interaction between fermions and a collection of local (dispersionless) phonon modes. In the dilute limit, the phonon degrees of freedom dress the fermions, giving rise to polaron and bipolaron formation. At higher densities, the phonons mediate collective superconducting (SC) and charge-density wave (CDW) phases. Quantum Monte Carlo (QMC) simulations have considered both these limits but have not yet focused on the physics of more general phonon spectra. Here we report QMC studies of the role of phonon dispersion on SC and CDW order in such models. We quantify the effect of finite phonon bandwidth and curvature on the critical temperature Tcdw for CDW order and also uncover several novel features of diagonal long-range order in the phase diagram, including a competition between charge patterns at momenta q =(π ,π ) and q =(0 ,π ) which lends insight into the relationship between Fermi surface nesting and the wave vector at which charge order occurs. We also demonstrate SC order at half filling in situations where a nonzero bandwidth sufficiently suppresses Tcdw.

Theory of Magnetic Ordering in the Heavy Rare Earths: Ab Initio Electronic Origin of Pair- and Four-Spin Interactions

NASA Astrophysics Data System (ADS)

Mendive-Tapia, Eduardo; Staunton, Julie B.

2017-05-01

We describe a disordered local moment theory for long-period magnetic phases and investigate the temperature and magnetic field dependence of the magnetic states in the heavy rare earth elements (HREs), namely, paramagnetic, conical and helical antiferromagnetic (HAFM), fan, and ferromagnetic (FM) states. We obtain a generic HRE magnetic phase diagram which is consequent on the response of the common HRE valence electronic structure to f -electron magnetic moment ordering. The theory directly links the first-order HAFM-FM transition to the loss of Fermi surface nesting, induced by this magnetic ordering, as well as provides a template for analyzing the other phases and exposing where f -electron correlation effects are particularly intricate. Gadolinium, for a range of hexagonal, close-packed lattice constants c and a , is the prototype, described ab initio, and applications to other HREs are made straightforwardly by scaling the effective pair and quartic local moment interactions that emerge naturally from the theory with de Gennes factors and choosing appropriate lanthanide-contracted c and a values.

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe2 -xTxAs2 (T =Co,Ni )

NASA Astrophysics Data System (ADS)

Tam, David W.; Song, Yu; Man, Haoran; Cheung, Sky C.; Yin, Zhiping; Lu, Xingye; Wang, Weiyi; Frandsen, Benjamin A.; Liu, Lian; Gong, Zizhou; Ito, Takashi U.; Cai, Yipeng; Wilson, Murray N.; Guo, Shengli; Koshiishi, Keisuke; Tian, Wei; Hitti, Bassam; Ivanov, Alexandre; Zhao, Yang; Lynn, Jeffrey W.; Luke, Graeme M.; Berlijn, Tom; Maier, Thomas A.; Uemura, Yasutomo J.; Dai, Pengcheng

2017-02-01

We use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe2As2 and its Co- and Ni-substituted members near optimal superconductivity. In the low-temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11% increase under 40 MPa for BaFe1.9Co0.1As2 , and a 15% increase for BaFe1.915Ni0.085As2 . We also observe an increase of the AF ordering temperature (TN) of about 0.25 K/MPa in all compounds, consistent with density functional theory calculations that reveal better Fermi surface nesting for itinerant electrons under uniaxial pressure. The doping dependence of the magnetic ordered moment is captured by combining dynamical mean field theory with density functional theory, suggesting that the pressure-induced moment increase near optimal superconductivity is closely related to quantum fluctuations and the nearby electronic nematic phase.

Magnetism and electronic structures of novel layered CaFeAs{sub 2} and Ca{sub 0.75}(Pr/La){sub 0.25}FeAs{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Yi-Na; Zou, Liang-Jian, E-mail: zou@theory.issp.ac.cn; University of Science and Technology of China, Hefei, Anhui 230026

2015-05-07

The magnetic and electronic properties of the parent material CaFeAs{sub 2} of new superconductors are investigated using first-principles calculations. We predict that the ground state of CaFeAs{sub 2} is a spin-density-wave (SDW)-type striped antiferromagnet driven by Fermi surface nesting. The magnetic moment around each Fe atom is about 2.1 μ{sub B}. We also present electronic and magnetic structures of electron-doped phase Ca{sub 0.75}(Pr/La){sub 0.25}FeAs{sub 2}, the SDW order was suppressed by La/Pr substitution. The As in arsenic layers is negative monovalent and acts as blocking layers enhancing two-dimensional character by increasing the spacing distance between the FeAs layers. This favorsmore » strong antiferromagnetic fluctuations mediated pairing, implying higher T{sub c} in Ca{sub 0.75}(Pr/La){sub 0.25}FeAs{sub 2} than Ca{sub 0.75}(Pr/La){sub 0.25}Fe{sub 2}As{sub 2}.« less

Hubbard physics in the PAW GW approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Booth, J. M., E-mail: jamie.booth@rmit.edu.au; Smith, J. S.; Russo, S. P.

It is demonstrated that the signatures of the Hubbard Model in the strongly interacting regime can be simulated by modifying the screening in the limit of zero wavevector in Projector-Augmented Wave GW calculations for systems without significant nesting. This modification, when applied to the Mott insulator CuO, results in the opening of the Mott gap by the splitting of states at the Fermi level into upper and lower Hubbard bands, and exhibits a giant transfer of spectral weight upon electron doping. The method is also employed to clearly illustrate that the M{sub 1} and M{sub 2} forms of vanadium dioxidemore » are fundamentally different types of insulator. Standard GW calculations are sufficient to open a gap in M{sub 1} VO{sub 2}, which arise from the Peierls pairing filling the valence band, creating homopolar bonds. The valence band wavefunctions are stabilized with respect to the conduction band, reducing polarizability and pushing the conduction band eigenvalues to higher energy. The M{sub 2} structure, however, opens a gap from strong on-site interactions; it is a Mott insulator.« less

Effects of Co and Mn doping in K0.8Fe2-ySe2 revisited.

PubMed

Zhou, Tingting; Chen, Xiaolong; Guo, Jiangang; Jin, Shifeng; Wang, Gang; Lai, Xiaofang; Ying, Tianping; Zhang, Han; Shen, Shijie; Wang, Shunchong; Zhu, Kaixing

2013-07-10

Accumulated evidence indicates that phase separation occurs in potassium intercalated iron selenides, a superconducting phase coexisting with the antiferromagnetic phase K2Fe4Se5, the so-called '245 phase'. Here, we report a comparative study of substitution effects by Co and Mn for Fe sites in K0.8Fe2-ySe2 within the phase separation scenario. Our results demonstrate that Co and Mn dopants have distinct differences in occupancy and hence in the suppression mechanism of superconductivity upon doping of Fe sites. In K0.8Fe2-xCoxSe2, Co prefers to occupy the lattice of the superconducting phase and suppresses superconductivity very quickly, obeying the magnetic pair-breaking mechanism or the collapse of the Fermi surface nesting mechanism. In contrast, in K0.8Fe1.7-xMnxSe2, Mn shows no preferential occupancy in the superconducting phase or the 245 phase. The suppression of superconductivity can be attributed to restraining of the superconducting phase and meanwhile inducing another non-superconducting phase by Mn doping.

ARPES study of the evolution of band structure and charge density wave properties in RTe3 ( R=Y , La, Ce, Sm, Gd, Tb, and Dy)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hussain, Zahid; Brouet, Veronique; Yang, Wanli

2008-01-16

We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the RTe3 family, which sets this system as an ideal"textbook" example for the formation of a nesting driven charge density wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDWinstabilities, from the opening of large gaps on the best nested parts of Fermi surface (up to 0.4 eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k space. An additional advantage of RTe3more » is that theband structure can be very accurately described by a simple two dimensional tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure by comparing our ARPES measurements with the linear muffin-tinorbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k space, the evolution of the CDW wave vector with R, and the shape of the residual metallic pockets. Finally, we give an estimation of the CDWinteraction parameters and find that the change in the electronic density of states n (EF), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.« less

The interplay of long-range magnetic order and single-ion anisotropy in rare earth nickel germanides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Islam, Z.

1999-05-10

This dissertation is concerned with the interplay of long-range order and anisotropy in the tetragonal RNi{sub 2}Ge{sub 2} (R = rare earth) family of compounds. Microscopic magnetic structures were studied using both neutron and x-ray resonant exchange scattering (XRES) techniques. The magnetic structures of Tb, Dy, Eu and Gd members have been determined using high-quality single-crystal samples. This work has correlated a strong Fermi surface nesting to the magnetic ordering in the RNi{sub 2}Ge{sub 2} compounds. Generalized susceptibility, {chi}{sub 0}(q), calculations found nesting to be responsible for both incommensurate ordering wave vector in GdNi{sub 2}Ge{sub 2}, and the commensurate structuremore » in EuNi{sub 2}Ge{sub 2}. A continuous transition from incommensurate to commensurate magnetic structures via band filling is predicted. The surprisingly higher T{sub N} in EuNi{sub 2}Ge{sub 2} than that in GdNi{sub 2}Ge{sub 2} is also explained. Next, all the metamagnetic phases in TbNi{sub 2}Ge{sub 2} with an applied field along the c axis have been characterized with neutron diffraction measurements. A mixed phase model for the first metamagnetic structure consisting of fully-saturated as well as reduced-moment Tb ions is presented. The moment reduction may be due to moment instability which is possible if the exchange is comparable to the low-lying CEF level splitting and the ground state is a singlet. In such a case, certain Tb sites may experience a local field below the critical value needed to reach saturation.« less

Nonlocal Poisson-Fermi model for ionic solvent.

PubMed

Xie, Dexuan; Liu, Jinn-Liang; Eisenberg, Bob

2016-07-01

We propose a nonlocal Poisson-Fermi model for ionic solvent that includes ion size effects and polarization correlations among water molecules in the calculation of electrostatic potential. It includes the previous Poisson-Fermi models as special cases, and its solution is the convolution of a solution of the corresponding nonlocal Poisson dielectric model with a Yukawa-like kernel function. The Fermi distribution is shown to be a set of optimal ionic concentration functions in the sense of minimizing an electrostatic potential free energy. Numerical results are reported to show the difference between a Poisson-Fermi solution and a corresponding Poisson solution.

Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La) 2CuO 6+δ (Bi2201)

DOE PAGES

Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; ...

2015-06-18

Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. Here, we show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Finally, our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping.

Fermi surfaces of the pyrite-type cubic AuSb2 compared with split Fermi surfaces of the ullmannite-type cubic chiral NiSbS and PdBiSe

NASA Astrophysics Data System (ADS)

Nishimura, K.; Kakihana, M.; Nakamura, A.; Aoki, D.; Harima, H.; Hedo, M.; Nakama, T.; Ōnuki, Y.

2018-05-01

We grew high-quality single crystals of AuSb2 with the pyrite (FeS2)-type cubic structure by the Bridgman method and studied the Fermi surface properties by the de Haas-van Alphen (dHvA) experiment and the full potential LAPW band calculation. The Fermi surfaces of AuSb2 are found to be similar to those of NiSbS and PdBiSe with the ullmannite (NiSbS)-type cubic chiral structure because the crystal structures are similar each other and the number of valence electrons is the same between two different compounds. Note that each Fermi surface splits into two Fermi surfaces in NiSbS and PdBiSe, reflecting the non-centrosymmetric crystal structure.

Spin liquid state in the 3D frustrated antiferromagnet PbCuTe 2 O 6 : NMR and muon spin relaxation studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khuntia, P.; Bert, F.; Mendels, P.

In this study, PbCuTe 2O 6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu 2+ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointingmore » to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T 1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.« less

Spin liquid state in the 3D frustrated antiferromagnet PbCuTe 2 O 6 : NMR and muon spin relaxation studies

DOE PAGES

Khuntia, P.; Bert, F.; Mendels, P.; ...

2016-03-11

In this study, PbCuTe 2O 6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu 2+ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointingmore » to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T 1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.« less

The fermi paradox is neither Fermi's nor a paradox.

PubMed

Gray, Robert H

2015-03-01

The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth--and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked "Where is everybody?"--apparently suggesting that we do not see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist or suggesting its absence is paradoxical. The claim "they are not here; therefore they do not exist" was first published by Michael Hart, claiming that interstellar travel and colonization of the Galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence--cited in the U.S. Congress as a reason for killing NASA's SETI program on one occasion. But evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox.