Vortexlike excitations in the heavy-fermion superconductor CeIrIn5
NASA Astrophysics Data System (ADS)
Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; Thompson, J. D.
2016-05-01
We report a systematic study of temperature- and field-dependent charge (ρ ) and entropy (S ) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sx x is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sx y. By separating the off-diagonal Peltier coefficient αx y from Sx y, we find that αx y becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity of heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.
Vortexlike excitations in the heavy-fermion superconductor CeIrIn5
Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; Thompson, J. D.
2016-05-05
Here, we report a systematic study of temperature- and field-dependent charge (ρ) and entropy (S) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sxx is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sxy. By separating the off-diagonal Peltier coefficient αxy from Sxy, we find that αxy becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity ofmore » heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.« less
Electrical resistivity under extreme conditions in the Ce3Ir4Sn13 heavy fermion compound
NASA Astrophysics Data System (ADS)
Collave, J. R.; Borges, H. A.; Ramos, S. M.; Hering, E. N.; Fontes, M. B.; Baggio-Saitovitch, E.; Eichler, A.; Bittar, E. M.; Pagliuso, P. G.
2014-01-01
We have performed measurements of temperature dependent electrical resistivity ρ(T) under pressures up to 27 kbar and down to 0.1 K on single crystals of the Ce3Ir4Sn13 heavy fermion compound. At ambient pressure (P=0) we have identified in the ρ(T) data interesting features associated with the presence of crystalline field effects, magnetic correlations, Kondo single impurity scattering and, possibly, a low temperature structural phase transition. All these features were mapped as a function of pressure which allowed us to construct a pressure-temperature phase diagram with these temperature scales. We have also carried out measurements of ρ(T) as a function of magnetic fields up to H=8 T and the important temperature scales in ρ(T) were followed with field. Enlightened also by temperature dependent specific heat experiments we discuss the possible microscopic origins of the features found in our ρ(T) data.
NASA Astrophysics Data System (ADS)
Rai, Binod K.; Oswald, Iain W. H.; Chan, Julia Y.; Morosan, E.
2016-01-01
Single crystals of Yb3(Rh 1 -xTx )4Ge13 (T =Co ,Ir ) have been grown using the self-flux method. Powder x-ray diffraction data on these compounds are consistent with the cubic structure with space group P m 3 ¯n . Intermediate-valence behavior is observed in Yb3(Rh 1 -xTx )4Ge13 upon T = Co doping, while T = Ir doping drives the system into a heavy-fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb3(Rh 1 -xTx )4Ge13 for 0.5
NASA Astrophysics Data System (ADS)
Rai, Binod; Morosan, Emilia
Single crystals of Yb3(Rh1-x Tx)4Ge13 (T = Co, Ir) have been grown using the self-flux method. Powder X-ray diffraction data on these compounds are consistent with the cubic structure with space group Pm 3 n . Intermediate valence behavior is observed in Yb3(Rh1-x Tx)4Ge13 upon T = Co doping, while T = Ir doping drives the system into a heavy fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb3(Rh1-x Tx)4Ge13 for 0.5 < x <= 1 with TN = 0.96 K for Yb3Ir4Ge13. With decreasing x, the magnetic order is suppressed towards a quantum critical point around xc = 0.5, accompanied by non-Fermi liquid behavior evidenced by logarithmic divergence of the specific heat and linear temperature dependence of the resistivity. The Fermi liquid behavior is recovered with the application of large magnetic fields. Gordon and Betty Moore Foundation EPiQS initiative through Grant GBMF4417 and Welch Foundation.
NASA Astrophysics Data System (ADS)
Ghimire, Nirmal; Cary, Samantha; Albrecht-Schmitt, Thomas; Brown, Craig; Eley, Serena; Wakeham, Nicholas; Rosa, Priscila; Janoschek, Marc; Civale, Leonardo; Thompson, Joe; Ronning, Filip; Bauer, Eric
Ce-based intermetallic compounds provide a fascinating ground to study several exotic physical phenomena due to the presence of competing low Kondo and RKKY interactions. One widely explored entity in these compounds is the quantum phase transition that is accessed by the suppression of the magnetic order down to absolute temperature by an external parameter such as magnetic field, chemical substitution, or pressure. Exotic phenomena like unconventional superconductivity and non-Fermi liquid behavior are ubiquitous in the vicinity of the quantum critical point. Quantum criticality in these Ce-based materials is often observed in layered, tetragonal systems such as the CeM2X2 (M =transition metal; X =Si, Ge) or CeMIn5 (M =Co, Rh, Ir) compounds. We present the structural and physical properties of a new family of heavy fermion compounds Ce2MAl7Ge4 (M = Co, Ir, Ni, Pd) that crystallize in the tetragonal space group P-421m. Ce2MAl7Ge4 (M =Co, Ir, Ni) show complex magnetic order below 2 K, while Ce2PdAl7Ge4 does not order magnetically down to 400 mK, and, instead, shows quantum critical behavior at low temperature. Present affiliation: Argonne National Laboratory.
Physical properties of the Ce2M Al 7Ge4 heavy-fermion compounds (M =Co,Ir,Ni,Pd)
NASA Astrophysics Data System (ADS)
Ghimire, N. J.; Cary, S. K.; Eley, S.; Wakeham, N. A.; Rosa, P. F. S.; Albrecht-Schmitt, T.; Lee, Y.; Janoschek, M.; Brown, C. M.; Civale, L.; Thompson, J. D.; Ronning, F.; Bauer, E. D.
2016-05-01
We report the synthesis, crystal structure, and characterization by means of single-crystal x-ray diffraction, neutron powder diffraction, and magnetic, thermal, and transport measurements of the new heavy-fermion compounds Ce2MAl 7Ge4 (M =Co,Ir,Ni,Pd). These compounds crystallize in a noncentrosymmetric tetragonal space group P 4 ¯21m , consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce2CoAl7Ge4,Ce2IrAl7Ge4 , and Ce2NiAl7Ge4 order magnetically below TM= 1.8 , 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce2PdAl7Ge4 down to 0.4 K. The small amount of entropy released in the magnetic state of Ce2M Al7Ge4 (M = Co, Ir, Ni) and the reduced specific heat jump at TM suggest a strong Kondo interaction in these materials. Ce2PdAl7Ge4 shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point.
NASA Astrophysics Data System (ADS)
Forker, M.; Silva, P. R. J.; Cavalcante, J. T. P. D.; Cavalcante, F. H. M.; Ramos, S. M.; Saitovitch, H.; Baggio-Saitovitch, E.; Alonso, R.; Taylor, M.; Errico, L. A.
2013-04-01
The electric field gradient (EFG) at the highly dilute nuclear probe 111Cd in the heavy fermion systems CeMIn5, M= Co, Rh, and Ir and YCoIn5 has been investigated by perturbed angular correlation (PAC) measurements of the nuclear electric quadrupole interaction (QI) of 111Cd on In sites. Pure and Sn-doped single crystals prepared by In-flux synthesis and polycrystalline samples prepared by arc melting have been studied. The samples were doped with the PAC probe 111Cd by diffusion of the mother isotope 111In. In all samples, several fractions of 111Cd probe nuclei subject to different QI's have been observed, among them a large fraction of 111Cd in unreacted In metal. Detailed calculations of the EFG at In nuclei and at Cd probes on In sites of pure and Sn-doped CeMIn5 were preformed, using the full-potential augmented plane wave+local orbital (APW+lo) formalism and taking into account different variables such as the electronic structure of the hyperfine probes, probe induced structural distortions, and impurity doping. The excellent agreement between the predicted EFG's and the experimental results allows us to assign two of the observed EFG components to the lattice sites 1c and 4i of the CeMIn5 compounds and to explain the pronounced difference of the EFG at In and Cd probes on the same lattice position. Structural distortions induced by the Cd probe and Sn-doping were found to have little effect on the EFG at the Cd probes. We also show that the local spin density approximation (LSDA) and LDA+U calculations predict very similar equilibrium structures and EFG's at the In/Cd sites. The extension of the experiments and the calculations from CeMIn5 to YCoIn5 and LaCoIn5 have established that the influence of the 4f electrons on the EFG's at impurity sites is negligibly small.
Danzenbacher, S.; Kucherenko, Y.; Vyalikh, D.V.; Holder, M.; Laubschat, C.; Yaresko, A.N.; Krellner, C.; Hossain, Z.; Geibel, C.; Zhou, X.J.; Yang, W.L.; Mannella, N.; Hussain, Z.; Shen, Z.X.; Shi, M.; Patthey, L.; Molodtsov, S.L.
2010-04-15
Heavy-fermion compounds YbIr2Si2 and YbRh2Si2 were studied by means of angle-resolved photoemission (PE). The splittings and dispersions of the 4f13 bulk and surface PE signals in the region of the expected energy crossings of the 4f final states and the valence bands in the Brillouin zone are observed. The experimental results are explained in terms of a simplified periodic Anderson model by a momentum dependence of the electron hopping matrix element between the 4f and valence-band states.
Plutonium-Based Heavy-Fermion Systems
NASA Astrophysics Data System (ADS)
Bauer, E. D.; Thompson, J. D.
2015-03-01
An effective mass of charge carriers that is significantly larger than the mass of a free electron develops at low temperatures in certain lanthanide- and actinide-based metals, including those formed with plutonium, owing to strong electron-electron interactions. This heavy-fermion mass is reflected in a substantially enhanced electronic coefficient of specific heat Î³, which for elemental Pu is much larger than that of normal metals. By our definition, there are twelve Pu-based heavy-fermion compounds, most discovered recently, whose basic properties are known and discussed. Relative to other examples, these Pu-based heavy-fermion systems are particularly complex owing in part to the possible simultaneous presence of multiple, nearly degenerate 5fn configurations. This complexity poses significant opportunities as well as challenges, including understanding the origin of unconventional superconductivity in some of these materials.
Heavy fermion behavior explained by bosons
NASA Technical Reports Server (NTRS)
Kallio, A.; Poykko, S.; Apaja, V.
1995-01-01
Conventional heavy fermion (HF) theories require existence of massive fermions. We show that heavy fermion phenomena can also be simply explained by existence of bosons with moderate mass but temperature dependent concentration below the formation temperature T(sub B), which in turn is close to room temperature. The bosons B(++) are proposed to be in chemical equilibrium with a system of holes h(+): B(++) = h(+) + h(+). This equilibrium is governed by a boson breaking function f(T), which determines the decreasing boson density and the increasing fermion density with increasing temperature. Since HF-compounds are hybridized from minimum two elements, we assume in addition existence of another fermion component h(sub s)(+) with temperature independent density. This spectator component is thought to be the main agent in binding the bosons in analogy with electronic or muonic molecules. Using a linear boson breaking function we can explain temperature dependence of the giant linear specific heat coefficient gamma(T) coming essentially from bosons. The maxima in resistivity, Hall coefficient, and susceptibility are explained by boson localization effects due to the Wigner crystallization. The antiferromagnetic transitions in turn are explained by similar localization of the pairing fermion system when their density n(sub h)(T(sub FL)) becomes lower than n(sub WC), the critical density of Wigner crystallization. The model applies irrespective whether a compound is superconducting or not. The same model explains the occurrence of low temperature antiferromagnetism also in high-T(sub c) superconductors. The double transition in UPt3 is proposed to be due to the transition of the pairing fermion liquid from spin polarized to unpolarized state.
Unconventional superconductivity in heavy-fermion compounds
White, B. D.; Thompson, J. D.; Maple, M. B.
2015-02-27
Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion com- pounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates and iron-based superconductors. Lastly, we conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.
Unconventional superconductivity in heavy-fermion compounds
White, B. D.; Thompson, J. D.; Maple, M. B.
2015-02-27
Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion com- pounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates andmore » iron-based superconductors. Lastly, we conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.« less
Heavy fermions in an optical lattice
Foss-Feig, Michael; Hermele, Michael; Gurarie, Victor; Rey, Ana Maria
2010-11-15
We employ a mean-field theory to study ground-state properties and transport of a two-dimensional gas of ultracold alkaline-earth-metal atoms governed by the Kondo lattice Hamiltonian plus a parabolic confining potential. In a homogenous system, this mean-field theory is believed to give a qualitatively correct description of heavy-fermion metals and Kondo insulators: It reproduces the Kondo-like scaling of the quasiparticle mass in the former and the same scaling of the excitation gap in the latter. In order to understand ground-state properties in a trap, we extend this mean-field theory via local-density approximation. We find that the Kondo insulator gap manifests as a shell structure in the trapped density profile. In addition, a strong signature of the large Fermi surface expected for heavy-fermion systems survives the confinement and could be probed in time-of-flight experiments. From a full self-consistent diagonalization of the mean-field theory, we are able to study dynamics in the trap. We find that the mass enhancement of quasiparticle excitations in the heavy-Fermi liquid phase manifests as slowing of the dipole oscillations that result from a sudden displacement of the trap center.
Angle-resolved heat capacity of heavy fermion superconductors.
Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige
2016-09-01
Owing to a strong Coulomb repulsion, heavy electron superconductors mostly have anisotropic gap functions which have nodes for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is of primary importance. This article discusses the experimental methods of the gap determination by bulk heat capacity measurements in a rotating magnetic field. The basic idea is based on the fact that the quasiparticle density of states in the vortex state of nodal superconductors is field and direction dependent. We present our recent experimental results of the field-orientation dependence of the heat capacity in heavy fermion superconductors CeTIn5 (T = Co, Ir), UPt3, CeCu2Si2, and UBe13 and discuss their gap structures. PMID:27482621
Angle-resolved heat capacity of heavy fermion superconductors
NASA Astrophysics Data System (ADS)
Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige
2016-09-01
Owing to a strong Coulomb repulsion, heavy electron superconductors mostly have anisotropic gap functions which have nodes for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is of primary importance. This article discusses the experimental methods of the gap determination by bulk heat capacity measurements in a rotating magnetic field. The basic idea is based on the fact that the quasiparticle density of states in the vortex state of nodal superconductors is field and direction dependent. We present our recent experimental results of the field-orientation dependence of the heat capacity in heavy fermion superconductors CeTIn5 (T = Co, Ir), UPt3, CeCu2Si2, and UBe13 and discuss their gap structures.
NASA Astrophysics Data System (ADS)
Yamaoka, H.; Yamamoto, Y.; Schwier, E. F.; Honda, F.; Zekko, Y.; Ohta, Y.; Lin, J.-F.; Nakatake, M.; Iwasawa, H.; Arita, M.; Shimada, K.; Hiraoka, N.; Ishii, H.; Tsuei, K.-D.; Mizuki, J.
2015-12-01
Pressure- and temperature-induced changes in the Ce valence and c -f hybridization of the Ce115 superconductors have been studied systematically. Resonant x-ray-emission spectroscopy indicated that the increase of the Ce valence with pressure was significant for CeCoIn5, and moderate for CeIr (In0.925Cd0.075)5 . We found no abrupt change of the Ce valence in the Kondo regime for CeIr (In0.925Cd0.075)5 , which suggests that valence fluctuations are unlikely to mediate the superconductivity in this material. X-ray-diffraction results were consistent with the pressure-induced change in the Ce valence. High-resolution photoelectron spectroscopy revealed a temperature-dependent reduction of the spectral intensity at the Fermi level, indicating enhanced c -f hybridization on cooling.
Carrier relaxation dynamics in heavy fermion compounds
Demsar, J.; Tracy, L. A.; Averitt, R. D.; Trugman, S. A.; Sarrao, John L.,; Taylor, Antoinette J.,
2002-01-01
The first femtosecond carrier relaxation dynamics studies in heavy fermion compounds are presented. The carrier relaxation time shows a dramatic hundred-fold increase below the Kondo temperature revealing a dramatic sensitivity to the electronic density of states near the Fermi level. Femtosecond time-resolved optical spectroscopy is an excellent experimental alternative to conventional spectroscopic methods that probe the low energy electronic structure in strongly correlated electron systems. In particular, it has been shown that carrier relaxation dynamics are very sensitive to changes in the low energy density of states (e.g. associated with the formation of a low energy gap or pseudogap) providing new insights into the low energy electronic structure in these materials. In this report we present the first studies of carrier relaxation dynamics in heavy fermion (HF) systems by means of femtosecond time-resolved optical spectroscopy. Our results show that the carrier relaxation dynamics, below the Kondo temperature (T{sub K}), are extremely sensitive to the low energy density of states (DOS) near the Ferini level to which localized f-moments contribute. Specifically, we have performed measurements of the photoinduced reflectivity {Delta}R/R dynamics as a function of temperature and excitation intensity on the series of HF compounds YbXCu{sub 4} (X = Ag, Cd, In) in comparison to their non-magnetic counterparts LuXCu{sub 4}.
Routes to heavy-fermion superconductivity
NASA Astrophysics Data System (ADS)
Steglich, F.; Stockert, O.; Wirth, S.; Geibel, C.; Yuan, H. Q.; Kirchner, S.; Si, Q.
2013-07-01
Superconductivity in lanthanide- and actinide-based heavy-fermion (HF) metals can have different microscopic origins. Among others, Cooper pair formation based on fluctuations of the valence, of the quadrupole moment or of the spin of the localized 4f/5f shell have been proposed. Spin-fluctuation mediated superconductivity in CeCu2Si2 was demonstrated by inelastic neutron scattering to exist in the vicinity of a spin-density-wave (SDW) quantum critical point (QCP). The isostructural HF compound YbRh2Si2 which is prototypical for a Kondo-breakdown QCP has so far not shown any sign of superconductivity down to T ≈ 10 mK. In contrast, results of de-Haas-van-Alphen experiments by Shishido et al. (J. Phys. Soc. Jpn. 74, 1103 (2005)) suggest superconductivity in CeRhIn5 close to an antiferromagnetic QCP beyond the SDW type, at which the Kondo effect breaks down. For the related compound CeCoIn5 however, a field-induced QCP of SDW type is extrapolated to exist inside the superconducting phase.
Millikelvin cooling by heavy-fermion-based tunnel junctions
Prest, Martin; Min, Gao; Whall, Terry
2015-12-28
This paper addresses a high-performance electron-tunneling cooler based on a novel heavy-fermion/insulator/superconductor junction for millikelvin cooling applications. We show that the cooling performance of an electronic tunneling refrigerator could be significantly improved using a heavy-fermion metal to replace the normal metal in a conventional normal metal/insulator/superconductor junction. The calculation, based on typical parameters, indicates that, for a bath temperature of 300 mK, the minimum cooling temperature of an electron tunneling refrigerator is reduced from around 170 mK to below 50 mK if a heavy-fermion metal is employed in place of the normal metal. The improved cooling is attributed to an enhancement in electron tunneling due to the existence of a resonant density of states at the Fermi level.
The electronic structure of heavy fermions: Narrow temperature independent bands
Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B.
1996-08-01
The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from photoemission for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable.
Magnitude of the magnetic exchange interaction in the heavy-fermion antiferromagnet CeRhIn₅.
Das, Pinaki; Lin, S-Z; Ghimire, N J; Huang, K; Ronning, F; Bauer, E D; Thompson, J D; Batista, C D; Ehlers, G; Janoschek, M
2014-12-12
We have used high-resolution neutron spectroscopy experiments to determine the complete spin wave spectrum of the heavy-fermion antiferromagnet CeRhIn₅. The spin wave dispersion can be quantitatively reproduced with a simple frustrated J₁-J₂ model that also naturally explains the magnetic spin-spiral ground state of CeRhIn₅ and yields a dominant in-plane nearest-neighbor magnetic exchange constant J₀=0.74(3) meV. Our results pave the way to a quantitative understanding of the rich low-temperature phase diagram of the prominent CeTIn₅ (T=Co, Rh, Ir) class of heavy-fermion materials.
Magnitude of the magnetic exchange interaction in the heavy-fermion antiferromagnet CeRhIn5
Das, Pinaki; Lin, S. -Z.; Ghimire, N. J.; Huang, K.; Ronning, F.; Bauer, E. D.; Thompson, J. D.; Batista, C. D.; Ehlers, G.; Janoschek, M.
2014-12-08
We have used high-resolution neutron spectroscopy experiments to determine the complete spin wave spectrum of the heavy-fermion antiferromagnet CeRhIn₅. The spin wave dispersion can be quantitatively reproduced with a simple frustrated J₁-J₂ model that also naturally explains the magnetic spin-spiral ground state of CeRhIn₅ and yields a dominant in-plane nearest-neighbor magnetic exchange constant J₀=0.74(3) meV. Our results lead the way to a quantitative understanding of the rich low-temperature phase diagram of the prominent CeTIn₅ (T = Co, Rh, Ir) class of heavy-fermion materials.
Magnitude of the magnetic exchange interaction in the heavy-fermion antiferromagnet CeRhIn_{5}
Das, Pinaki; Lin, S. -Z.; Ghimire, N. J.; Huang, K.; Ronning, F.; Bauer, E. D.; Thompson, J. D.; Batista, C. D.; Ehlers, G.; Janoschek, M.
2014-12-08
We have used high-resolution neutron spectroscopy experiments to determine the complete spin wave spectrum of the heavy-fermion antiferromagnet CeRhIn₅. The spin wave dispersion can be quantitatively reproduced with a simple frustrated J₁-J₂ model that also naturally explains the magnetic spin-spiral ground state of CeRhIn₅ and yields a dominant in-plane nearest-neighbor magnetic exchange constant J₀=0.74(3) meV. Our results lead the way to a quantitative understanding of the rich low-temperature phase diagram of the prominent CeTIn₅ (T = Co, Rh, Ir) class of heavy-fermion materials.
LiV204: frustration induced heavy fermion metal
NASA Astrophysics Data System (ADS)
Hopkinson, John
2004-03-01
How does the interplay of mixed valence and geometric frustration result in a heavy fermion state for LiV2O4?. I will briefly review the experimental evidence for the heavy fermion state realized in this compound in contrast to that seen in isostructural ZnV204 and LiTi2O4. This motivates the introduction of a hole doped S=1 t-J model whose key features are a high temperature mixed valent spin quenching and a frustrated antiferromagnetic coupling on the pyrochlore lattice which is treated at a mean field level. Unlike in conventional heavy fermions, 'conduction electrons' and 'localized electrons' here both originate from the d-electrons of the magnetic sites, leading to unusual properties of the resistivity at high temperatures as the 'conduction electrons' begin to localize. Within our proposed [1,2] two-stage spin-quenching scenario, local valence fluctuations are responsible for the formation of partially quenched, spin-1/2 moments below room temperature. Frustration of the intersite spin couplings then drives the system to realize the heavy Fermi liquid seen at low temperatures, providing a natural explanation for the sign change of the Hall coefficient along the way. [1]J. Hopkinson and P. Coleman, Phys. Rev. Lett. 89, 267201 (2002); [2]J. Hopkinson and P. Coleman, Physica B 312-313, 711 (2002).
(Strongly interacting fermion systems: Emphasis on heavy fermions: Annual performance report)
Not Available
1987-01-01
The research has been concentrated into two areas: heavy fermions and development of new methods for electronic properties (henceforth referred to as the ''electronic structure program''). This first area is going into deep hibernation due to the new interest in the high-T/sub c/ materials; notwithstanding this development, there has been significant progress. On the other hand, in the electronic structure program there has been a period of intense development which is just starting to yield results.
High-pressure studies on heavy fermion systems
NASA Astrophysics Data System (ADS)
Ye, Chen; Zongfa, Weng; Smidman, Michael; Xin, Lu; Huiqiu, Yuan
2016-07-01
In this review article, we give a brief overview of heavy fermions, which are prototype examples of strongly correlated electron systems. We introduce the application of physical pressure in heavy fermion systems to construct their pressure phase diagrams and to study the close relationship between superconductivity (SC) and other electronic instabilities, such as antiferromagnetism (AFM), ferromagnetism (FM), and valence transitions. Field-angle dependent heat capacity and point-contact spectroscopic measurements under pressure are taken as examples to illustrate their ability to investigate novel physical properties of the emergent electronic states. Project supported by the National Basic Research Program of China (Grant No. 2011CBA00103), the National Natural Science Foundation of China (Grant Nos. 11174245 and 11374257), the Science Challenge Program of China, and the Fundamental Research Funds for the Central Universities of China.
New heavy-fermion antiferromagnet UPd2Cd20
NASA Astrophysics Data System (ADS)
Hirose, Yusuke; Doto, Hiroshi; Honda, Fuminori; Li, Dexin; Aoki, Dai; Haga, Yoshinori; Settai, Rikio
2016-10-01
We succeeded in growing a new high quality single crystal of a ternary uranium compound UPd2Cd20. From the electrical resistivity, magnetization, magnetic susceptibility, and specific heat experiments, UPd2Cd20 is found to be an antiferromagnetic heavy-fermion compound with the Néel temperature {{T}\\text{N}} = 5 K and exhibits the large electronic specific heat coefficient γ exceeding 500 mJ (K2· mol)-1. This compound is the first one that exhibits the magnetic ordering with the magnetic moments of the U atom in a series of UT2X20 (T: transition metal, X = Al, Zn, Cd). UPd2Cd20 shows typical characteristic features in heavy-fermion systems such as a broad maximum in the magnetic susceptibility at {{T}{{χ\\text{max}}}} and a large coefficient A of T 2 term in the resistivity.
Visualizing heavy fermions emerging in a quantum critical Kondo lattice
NASA Astrophysics Data System (ADS)
Aynajian, Pegor
2013-03-01
In solids containing elements with f orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass. These excitations are fundamental to the appearance of unconventional superconductivity and non-Fermi-liquid behavior observed in actinide- and lanthanide-based compounds. We use spectroscopic mapping with the scanning tunneling microscope to detect the emergence of heavy excitations with lowering of temperature in a prototypical family of cerium-based heavy-fermion compounds. We demonstrate the sensitivity of the tunneling process to the composite nature of these heavy quasiparticles, which arises from quantum entanglement of itinerant conduction and f electrons. Scattering and interference of the composite quasiparticles is used to resolve their energy-momentum structure and to extract their mass enhancement, which develops with decreasing temperature. The lifetime of the emergent heavy quasiparticles reveals signatures of enhanced scattering and their spectral lineshape shows evidence of energy-temperature scaling. These findings demonstrate that proximity to a quantum critical point results in critical damping of the emergent heavy excitation of our Kondo lattice system. This work is funded by a DOE-BES grant. Partial support for instrumentation is provided by NSF-DMR, Keck Foundation, and NSF-MRSEC. PA also acknowledges support of a fellowship through the PCCM funded by NSF MERSEC.
Two-dimensional Confinement of Heavy Fermions in Artificial Superlattices
NASA Astrophysics Data System (ADS)
Shishido, Hiroaki
2011-03-01
Low dimensionality and strong electron-electron Coulomb interactions are both key parameters for novel quantum states of condensed matter. A metallic system with the strongest electron correlations is reported in rare-earth and actinide compounds with f electrons, known as heavy-fermion compounds, where the effective mass of the conduction electrons are strikingly enhanced by the electron correlations up to some hundreds times the free electron mass. To date the electronic structure of all heavy-fermion compounds is essentially three-dimensional. We realized experimentally a two-dimensional heavy fermion system, adjusting the dimensionality in a controllable fashion. We grew artificial superlattices of CeIn 3 (m)/ LaIn 3 (n), in which m -layers of heavy-fermion antiferromagnet CeIn 3 and n -layers of a non-magnetic isostructual compound LaIn 3 are stacked alternately, by a molecular beam epitaxy. By reducing the thickness of the CeIn 3 layers, the magnetic order was suppressed and the effective electron mass was further enhanced. The Néel temperature becomes zero at around m = 2 , concomitant with striking deviations from the standard Fermi liquid low-temperature electronic properties. Standard Fermi liquid behaviors are, however, recovered under high magnetic field. These behaviors imply new ``dimensional tuning'' towards a quantum critical point. We also succeeded to fabricate artificial superlattices of a heavy fermion superconductor CeCoIn 5 and non-magnetic divalent Yb-compound YbCoIn 5 . Superconductivity survives even in CeCoIn 5 (3)/ YbCoIn 5 (5) films, while the thickness of CeCoIn 5 layer, 2.3 nm, is comparable to the c -axis coherence length ξc ~ 2 nm. This work has been done in collaboration with Y. Mizukami, S. Yasumoto, M. Shimozawa, H. Kontani, T. Shibauchi, T. Terashima and Y. Matsuda.superconductivity is realized in the artificial superlattices. This work has been done in collaboration with Y. Mizukami, S. Yasumoto, M. Shimozawa, H. Kontani, T
Unconventional Quantum Criticality in Heavy-Fermion Compounds
NASA Astrophysics Data System (ADS)
Stockert, O.; Steglich, F.
2011-03-01
We review magnetic quantum-critical points (QPCs) in heavy-fermion compounds separating at zero temperature: an antiferromagnetically ordered state and a nonordered ground state. At the magnetic instability, the Fermi-liquid (FL) description valid for normal metals breaks down, giving rise to unusual, non-Fermi-liquid (NFL) low-temperature behavior. After a short introduction to phase transitions and to T = 0 phase transitions in general as well as to the physics of heavy-fermion systems, the two main theoretical scenarios describing the physics at QPCs in these systems are presented, the conventional spin-density-wave (SDW) scenario and the unconventional Kondo-breakdown scenario. Whereas for the conventional scenario experimental data for CeCu2Si2 and Ce1-xLaxRu2Si2 are discussed only briefly, we focus in more detail on the unusual behavior of CeCu6-xAux and YbRh2Si2 at their respective QPCs and show that these systems are best described within the unconventional scenario.
Exploring heavy fermions from macroscopic to microscopic length scales
NASA Astrophysics Data System (ADS)
Wirth, Steffen; Steglich, Frank
2016-10-01
Strongly correlated systems present fundamental challenges, especially in materials in which electronic correlations cause a strong increase of the effective mass of the charge carriers. Heavy fermion metals — intermetallic compounds of rare earth metals (such as Ce, Sm and Yb) and actinides (such as U, Np and Pu) — are prototype systems for complex and collective quantum states; they exhibit both a lattice Kondo effect and antiferromagnetic correlations. These materials show unexpected phenomena; for example, they display unconventional superconductivity (beyond Bardeen–Cooper–Schrieffer (BCS) theory) and unconventional quantum criticality (beyond the Landau framework). In this Review, we focus on systems in which Landau's Fermi-liquid theory does not apply. Heavy fermion metals and semiconductors are well suited for the study of strong electronic correlations, because the relevant energy scales (for charge carriers, magnetic excitations and lattice dynamics) are well separated from each other, allowing the exploration of concomitant physical phenomena almost independently. Thus, the study of these materials also provides valuable insight for the understanding — and tailoring — of other correlated systems.
Not Available
1993-02-01
During this period, 1/N expansions have been systematically applied to the calculation of the properties of highly correlated electron systems. These studies include examinations of (a) the class of materials known as heavy fermion semi-conductors, (b) the high energy spectra of heavy fermion systems, and (c) the doped oxide superconductors.
Optical spectroscopy and ultrafast pump-probe studies on the heavy-fermion compound CePt2In7
NASA Astrophysics Data System (ADS)
Chen, R. Y.; Zhang, S. J.; Bauer, E. D.; Thompson, J. D.; Wang, N. L.
2016-07-01
We report optical spectroscopy and ultrafast pump-probe measurements on the antiferromagnetic heavy-fermion compound CePt2In7 , a member showing stronger two dimensionality than other compounds in the CeIn3-derived heavy-fermion family. We identify clear and typical hybridization spectral structures at low temperature from the two different spectroscopy probes. However, the strength and related energy scale of the hybridization are much weaker and smaller than that in the superconducting compounds CeCoIn5 and CeIrIn5. The features are more similar to observations on the antiferromagnetic compounds CeIn3 and CeRhIn5 in the same family. The results clearly indicate that the Kondo interaction and hybridizations exist in the antiferromagnetic compounds but with weaker strength.
The magnitude of the magnetic exchange interaction in the heavy fermion antiferromagnet CeRhIn5
NASA Astrophysics Data System (ADS)
Das, P.; Lin, S.-Z.; Ghimire, N. J.; Ronning, F.; Bauer, E. D.; Thompson, J. D.; Batista, C. D.; Janoschek, M.; Huang, K.; Ehlers, G.
2015-03-01
The family of heavy fermion compounds Ce TIn5 (T = Co, Rh, Ir) has been a fertile ground to explore and understand the interplay between magnetism, unconventional superconductivity and quantum criticality due to their tunability by pressure, substitution and magnetic field. CeRhIn5 is a heavy fermion antiferromagent which can be tuned to quantum criticality under pressure. The strength of the magnetic exchange interaction, which is a key parameter to understand its complex properties, however remained unknown. We have used high-resolution neutron spectroscopy to determine the complete spin wave spectrum in CeRhIn5. The spin wave dispersion can be quantitatively reproduced with a simple frustrated J1 -J2 model that also naturally explains the magnetic spin-spiral ground state of CeRhIn5 and yields a dominant in-plane nearest-neighbor magnetic exchange constant J0 = 0 . 74 (3) meV. Our results pave the way to a quantitative understanding of the rich low-temperature phase diagram of the prominent Ce TIn5 class of heavy fermion materials. Work at LANL was performed under the auspices of the US DOE, OBES, MSE division and partly funded by LDRD.
Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model
Joyce, J.J.; Arko, A.J.; Andrews, A.B.
1993-09-01
The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show massive disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give very strong indications of core-like characteristics and compare favorable to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 3} were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl{sub 3}, the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f fineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work.
Spin gap in heavy fermion compound UBe13
NASA Astrophysics Data System (ADS)
Storchak, V. G.; Brewer, J. H.; Eshchenko, D. G.; Mengyan, P. W.; Parfenov, O. E.; Tokmachev, A. M.; Dosanjh, P.; Fisk, Z.; Smith, J. L.
2016-08-01
Heavy fermion (HF) compounds are well known for their unique properties, such as narrow bandwidths, loss of coherence in a metal, non-Fermi-liquid behaviour, unconventional superconductivity, huge magnetoresistance etc. While these materials have been known since the 1970s, there is still considerable uncertainty regarding the fundamental mechanisms responsible for some of these features. Here we report transverse-field muon spin rotation (μ +SR) experiments on the canonical HF compound UBe13 in the temperature range from 0.025 to 300 K and in magnetic fields up to 7 T. The μ +SR spectra exhibit a sharp anomaly at 180 K. We present a simple explanation of the experimental findings identifying this anomaly with a gap in the spin excitation spectrum of f-electrons opening near 180 K. It is consistent with anomalies discovered in heat capacity, NMR and optical conductivity measurements of UBe13, as well as with the new resistivity data presented here. The proposed physical picture may explain several long-standing mysteries of UBe13 (as well as other HF systems).
Inhomogeneous disorder Dirac Fermions: from heavy fermion superconductors to graphene. Final report
Vekhter, Ilya
2013-08-11
This is the final report on the award designed to foster a partnership between Louisiana State University and Los Alamos National Laboratory (LANL) in conducting fundamental research in support of energy needs. The general focus of the research effort was on developing a better understanding of materials with new functionalities. We investigated two distinct and very promising classes of new materials, which serve as a testing ground for many of the novel phenomena in condensed matter physics: the heavy fermion 115 series, where the interplay of strong interactions between the electrons leads to a rich variety of competing phases and anomalous properties, and newly discovered pnictide superconductors. The former focus was planned; the latter emerged during the collaborative effort with LANL. Our objective was to determine the origin, and to establish a functional effective theory description of the phases in these systems, and transitions between them. We report on the main accomplishments under the award that serves to clarify the nature of superconductivity in both families of materials. In particular, we collaborated with experimentalists to predict and analyze the magnetic field and temperature dependence of the bulk thermodynamic and transport properties and to determine the gap shape in CeCoIn₅ and in Ba(Fe_{1-x}Co_{x})₂As₂, investigated the Kondo temperature in the presence of spin-orbit coupling in the conduction band, and provided theoretical guidance for local probes such as scanning tunneling spectroscopy of vortex cores and impurity resonances, and magnetic force microscopy of the superconducting states.
Fine tuning the heavy fermion ground state: A new handle on cerium cobalt indium
NASA Astrophysics Data System (ADS)
Pham, Long D.
A Two Fluid Description of the Kondo Lattice CeCoIn5 has been extended to include additional entropy terms that were not considered in the original work by S. Nakatsuji et al. [1]. The use of a Matlab computer code was successful at iteratively solving for f, the fraction of itinerant interacting heavy quasiparticles, and showed that it converges to a temperature dependent function invariant under successive iterations. The linear specific heat coefficient, gamma, was extracted from transport consideration in conjunction with f(T) and the Kadowacki-Woods ratio to be 204mJ/mole-K2, in good agreement from heat capacity measurements of 290mJ/mole-K2 for CeCoIn 5 [32]. Antiferromagnetism has been induced in CeCoIn5 as well as its two isostructural, isovalent sister compounds CeRhIn5 and CeIrIn 5. Cadmium-doping the heavy-fermion superconductor CeCoIn5 at the percent level acts as an electronic tuning agent, sensitively shifting the balance between superconductivity and antiferromagnetism and opening new ambient-pressure phase space in the study of heavy-fermion ground states. At nominal concentrations of x>0.070, CeCo(In1-xCd x)5 displays a two phase region of antiferromagnetism coexisting with superconductivity up to x<0.15, above which no trace of superconductivity persists in specific heat. Similar results was seen in CeIr(In1-xCd x)5 where a quantum critical point (QCP) was observed, separating superconductivity from antiferromagnetism at a nominal critical concentration of x≈0.0475, while CeRh(In1-xCdx)5 goes through an incommensurate to commensurate antiferromagnetic transition nominally at x≈0.10. Amazingly, pressure completely recovers Tc in CeCo(In1-x Cdx)5 measured at nominal concentrations of x=0.10, and 0.15. Phase diagrams were constructed from specific heat and confirmed with resistivity and magnetization. An introduction to strongly correlated physics, relevant to the 115 family, will be worked out followed by a description of general techniques of
Scalar Resonance at 750 GeV as Composite of Heavy Vector-Like Fermions
NASA Astrophysics Data System (ADS)
Liao, Wei; Zheng, Han-Qing
2016-08-01
We study a model of scalars which includes both the SM Higgs and a scalar singlet as composites of heavy vector-like fermions. The vector-like fermions are bounded by the super-strong four-fermion interactions. The scalar singlet decays to SM vector bosons through loop of heavy vector-like fermions. We show that the surprisingly large production cross section of di-photon events at 750 GeV resonance and the odd decay properties can all be explained. This model serves as a good model for both SM Higgs and a scalar resonance at 750 GeV. Supported by National Natural Science Foundation of China (NSFC) under Grant Nos. 11135009, 11375065 and 10925522
Investigation of quantum criticality in the new heavy fermion compound Ce2PdAl7Ge4
NASA Astrophysics Data System (ADS)
Bauer, Eric; Wakeham, N. A.; Kim, D.; Ghimire, N. J.; Ronning, F.; Movshovich, R.; Thompson, J. D.
Ce-based intermetallic compounds exhibit a variety of interesting ground states including magnetic order, heavy fermion behavior, unconventional superconductivity, and non-Fermi liquid behavior. When magnetic order is suppressed to T = 0 K, or quantum critical point, by chemical substitution, pressure, or magnetic field, a dome of unconventional superconductivity is often found. Close to the quantum critical point, non-Fermi liquid temperature dependencies of the thermodynamic and transport properties are observed. Recently, a new family of tetragonal Ce2MAl7Ge4 (M =Co, Ni, Pd, Ir) compounds was discovered. While the Ce2MAl7Ge4 (M =Co, Ir, Ni) materials order magnetically between Tm = 0.8 - 1.6 K, Ce2PdAl7Ge4 exhibits non-Fermi liquid behavior at low temperature. Here, we discuss the quantum criticality in Ce2PdAl7Ge4.
Issues in heavy fermions and in high-T c superconductive materials raised at this conference
NASA Astrophysics Data System (ADS)
Varma, C. M.
1991-05-01
In this closing session at the conference I would like, in the light of the presentations at this conference to briefly summarize the remarkable progress achieved in the heavy-fermion and heavy-fermion superconductivity problems, and point to what seem to me the principal problems remaining. The situation in the theory of high- Tc materials, on the face of it, appears much less bright. Unlike the heavy fermions, there is no agreement on what model represents the essentials of the problem. I believe, the difficulty in achieving a consensus here is only partly scientific. It is also sociological. I will paint a rather sanguine picture of the scientific developments there as well.
NASA Astrophysics Data System (ADS)
Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Zhang, Wen; Lai, Xinchun; Donglai Feng Team; Huiqiu Yuan Team
One basic concept in heavy fermions systems is the entanglement of localized spin state and itinerant electron state. It can be tuned by two competitive intrinsic mechanisms, Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction, with external disturbances. The key issue regarding heavy fermions properties is how the two mechanisms work in the same phase region. To investigate the relation of the two mechanisms, the cubic antiferromagnetic heavy fermions compound CeIn3 was investigated by soft x-ray angle resolved photoemission spectroscopy. The hybridization between f electrons and conduction bands in the paramagnetic state was observed directly, providing compelling evidence for Kondo screening scenario and coexistence of two mechanisms. The hybridization strength shows slight and regular anisotropy in K space, implying that the two mechanisms are competitive and anisotropic. This work illuminates the concomitant and competitive relation between the two mechanisms and supplies some evidences for the anisotropic superconductivity of CeIn3
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics
NASA Astrophysics Data System (ADS)
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a ‘conventional’, itinerant QCP can be well understood within Landau’s paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an ‘unconventional’, local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts. PMID:27376190
Tuning the Hybridization at the Surface of a Heavy-Fermion System
NASA Astrophysics Data System (ADS)
Vyalikh, D. V.; Danzenbächer, S.; Kucherenko, Yu.; Krellner, C.; Geibel, C.; Laubschat, C.; Shi, M.; Patthey, L.; Follath, R.; Molodtsov, S. L.
2009-09-01
Electron-hybridization phenomena in YbRh2Si2 were probed by angle-resolved photoemission. It was shown that the Yb 4f-Rh 4d hybridization strength in the surface region of this heavy-fermion material can be varied by deposition of Ag. Site-specific charge transfer from adatoms leads to change of the energy overlap of the interacting states close to the Fermi energy. Our study demonstrates a new way to tune the hybridization between 4f and valence electrons as well as the induced strong correlation effects at the surface of heavy-fermion systems.
Schlottmann, P.
1998-10-12
Properties of highly correlated electrons, such as heavy fermion compounds, metal-insulator transitions, one-dimensional conductors and systems of restricted dimensionality are studied theoretically. The main focus is on Kondo insulators and impurity bands due to Kondo holes, the low-temperature magnetoresistivity of heavy fermion alloys, the n-channel Kondo problem, mesoscopic systems and one-dimensional conductors.
Correlation between ground state and orbital anisotropy in heavy fermion materials
Willers, Thomas; Strigari, Fabio; Hu, Zhiwei; Sessi, Violetta; Brookes, Nicholas B.; Bauer, Eric D.; Sarrao, John L.; Thompson, J. D.; Tanaka, Arata; Wirth, Steffen; Tjeng, Liu Hao; Severing, Andrea
2015-02-09
The interplay of structural, orbital, charge, and spin degrees of freedom is at the heart of many emergent phenomena, including superconductivity. We find that unraveling the underlying forces of such novel phases is a great challenge because it not only requires understanding each of these degrees of freedom, it also involves accounting for the interplay between them. Cerium-based heavy fermion compounds are an ideal playground for investigating these interdependencies, and we present evidence for a correlation between orbital anisotropy and the ground states in a representative family of materials. We have measured the 4f crystal-electric field ground-state wave functions of the strongly correlated materials CeRh_{1₋x}Ir_{x}In_{5} with great accuracy using linear polarization-dependent soft X-ray absorption spectroscopy. These measurements show that these wave functions correlate with the ground-state properties of the substitution series, which covers long-range antiferromagnetic order, unconventional superconductivity, and coexistence of these two states.
PARTICLES AND FIELDS Two loop electroweak corrections from heavy fermions to b → s + γ
NASA Astrophysics Data System (ADS)
Yang, Xiu-Yi; Feng, Tai-Fu
2010-12-01
Applying an effective Lagrangian method and an on-shell scheme, we analyze the electroweak corrections to the rare decay b → s + γ from some special two loop diagrams in which a closed heavy fermion loop is attached to the virtual charged gauge bosons or Higgs. At the decoupling limit where the virtual fermions in the inner loop are much heavier than the electroweak scale, we verify the final results satisfying the decoupling theorem explicitly when the interactions among Higgs and heavy fermions do not contain the nondecoupling couplings. Adopting the universal assumptions on the relevant couplings and mass spectrum of new physics, we find that the relative corrections from those two loop diagrams to the SM theoretical prediction on the branching ratio of B → Xsγ can reach 5% as the energy scale of new physics ΛNP = 200 GeV.
Heavy fermions and two loop electroweak corrections to b → s + γ
NASA Astrophysics Data System (ADS)
Yang, Xiu-Yi; Feng, Tai-Fu
2010-05-01
Applying effective Lagrangian method and on-shell scheme, we analyze the electroweak corrections to the rare decay b → s + γ from some special two loop diagrams in which a closed heavy fermion loop is attached to the virtual charged gauge bosons or Higgs. At the decoupling limit where the virtual fermions in inner loop are much heavier than the electroweak scale, we verify the final results satisfying the decoupling theorem explicitly when the interactions among Higgs and heavy fermions do not contain the nondecoupling couplings. Adopting the universal assumptions on the relevant couplings and mass spectrum of new physics, we find that the relative corrections from those two loop diagrams to the SM theoretical prediction on the branching ratio of B → X s γ can reach 5% as the energy scale of new physics ΛNP = 200GeV.
Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.
Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q
2016-09-01
Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology. PMID:27533524
Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.
Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q
2016-09-01
Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.
Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions
NASA Astrophysics Data System (ADS)
Weng, Z. F.; Smidman, M.; Jiao, L.; Lu, Xin; Yuan, H. Q.
2016-09-01
Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.
Magnetism and superconductivity in heavy fermion superconductor CeCo (In0.97Cd0/03)5
Heffner, R H; Ohishi, K; Spehling, J; Macdougall, G J; Ito, T U; Higemoto, W; Amato, D; Andreica, D; Nieuwenhuys, G; Klauss, H H; Luke, G M; Thompson, J D; Bianchi, A D; Fisk, Z
2008-01-01
Zero field (ZF) and transverse field (TF) muon spin relaxtion and rotation ({mu}SR) experiments have been carried out in the Cd-doped heavy fermion super conductor CeCoIn{sub 5} to investigate its superconducting state.
Riseborough, Peter S.
2002-05-01
A theoretical investigation of many-body effects in Cerium and Uranium Heavy Fermion and Mixed Valent Compounds and their experimental manifestations in thermodynamic, transport, and spectroscopic properties is discussed in this report.
Spin fluctations and heavy fermions in the Kondo lattice
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 periodic 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.
Infrared properties of heavy fermions: evolution from weak to strong hybridizations
NASA Astrophysics Data System (ADS)
Chen, R. Y.; Wang, N. L.
2016-06-01
In this article, we review the charge excitations of heavy fermion compounds probed by infrared spectroscopy. The article is not meant to be a comprehensive survey of experimental investigations. Rather it focuses on the dependence of charge excitations on the hybridization strength. In this context, the infrared properties of the Ce m M n In3m+2n family are discussed in detail since the hybridization strengths differ dramatically in different members despite their similar lattice structures. Investigations on some mixed valent compounds are also presented, aiming to elucidate the generic trend of the evolution. In particular, we address the scaling between hybridization energy gap {{Δ }\\text{dir}} and hybridization strength \\tilde{V} (\\propto \\sqrt{W{{T}\\text{K}}} ) in a wide range of heavy fermion compounds, which demonstrates that the periodic Anderson model can generally and quantitatively describe the low-energy charge excitations.
Evidence for fully-gapped superconductivity in heavy-fermion CeCu2Si2
NASA Astrophysics Data System (ADS)
Kasahara, Y.; Terazawa, D.; Yamashita, T.; Onishi, T.; Tokiwa, Y.; Terashima, T.; Matsuda, Y.; Takenaka, T.; Mizukami, Y.; Shibauchi, T.; Wilcox, J.; Putzke, C.; Carrington, A.; Kittaka, S.; Sakakibara, T.; Jeevan, H. S.; Seiro, S.; Geibel, C.; Haga, Y.
The discovery of superconductivity in heavy-fermion CeCu2Si2 in 1979 has opened a new playground for unconventional superconductivity in strongly-correlated systems. However, even in this archetypal heavy-fermion superconductor, the symmetry and the structure of the superconducting gap, which are intimately related to the paring mechanism, are still elusive. Here, to investigate the low-energy quasiparticle excitations in the superconducting state of CeCu2Si2(Tc = 0 . 6 K), we performed specific heat, thermal conductivity, and penetration depth measurements down to 60 mK. We found that specific heat and penetration depth exhibit exponential T-dependence at low T. Moreover, thermal conductivity has no residual T-linear term and shows little H-dependence. These behavior are in marked contrast to nodal superconductors. From the data taken with different experimental configurations, the detailed superconducting gap structure will be discussed.
Yb-based heavy fermion compounds and field tuned quantum chemistry
Mun, Eundeok
2010-01-01
The motivation of this dissertation was to advance the study of Yb-based heavy fermion (HF) compounds especially ones related to quantum phase transitions. One of the topics of this work was the investigation of the interaction between the Kondo and crystalline electric field (CEF) energy scales in Yb-based HF systems by means of thermoelectric power (TEP) measurements. In these systems, the Kondo interaction and CEF excitations generally give rise to large anomalies such as maxima in ρ(T) and as minima in S(T). The TEP data were use to determine the evolution of Kondo and CEF energy scales upon varying transition metals for YbT_{2}Zn_{20} (T = Fe, Ru, Os, Ir, Rh, and Co) compounds and applying magnetic fields for YbAgGe and YbPtBi. For YbT_{2}Zn_{20} and YbPtBi, the Kondo and CEF energy scales could not be well separated in S(T), presumably because of small CEF level splittings. A similar effect was observed for the magnetic contribution to the resistivity. For YbAgGe, S(T) has been successfully applied to determine the Kondo and CEF energy scales due to the clear separation between the ground state and thermally excited CEF states. The Kondo temperature, T_{K}, inferred from the local maximum in S(T), remains finite as magnetic field increases up to 140 kOe. In this dissertation we have examined the heavy quasi-particle behavior, found near the field tuned AFM quantum critical point (QCP), with YbAgGe and YbPtBi. Although the observed nFL behaviors in the vicinity of the QCP are different between YbAgGe and YbPtBi, the constructed H-T phase diagram including the two crossovers are similar. For both YbAgGe and YbPtBi, the details of the quantum criticality turn out to be complicated. We expect that YbPtBi will provide an additional example of field tuned quantum criticality, but clearly there are further experimental investigations left and more ideas needed to understand the basic physics of field-induced quantum
NASA Astrophysics Data System (ADS)
Hall, Donavan; Palm, E. C.; Murphy, T. P.; Tozer, S. W.; Fisk, Z.; Alver, U.; Goodrich, R. G.; Sarrao, J. L.; Pagliuso, P. G.; Ebihara, Takao
2001-12-01
Measurements of the de Haas-van Alphen effect in the normal state of the heavy-fermion superconductor CeCoIn5 have been carried out using a torque cantilever at temperatures ranging from 20 to 500 mK and in fields up to 18 T. Angular-dependent measurements of the extremal Fermi surface areas reveal a more extreme two-dimensional sheet than is found in either CeRhIn5 or CeIrIn5. The effective masses of the measured frequencies range from 9 to 20m*/m0.
Heavy fermion Ce{sub 3}Co{sub 4}Sn{sub 13} compound under pressure
Collave, J. R.; Borges, H. A.; Ramos, S. M.; Hering, E. N.; Mendonça-Ferreira, L.; Pagliuso, P. G.
2015-05-07
The non-magnetic heavy fermion compound Ce{sub 3}Co{sub 4}Sn{sub 13} was studied under pressure. We report single crystalline measurements of electrical resistivity as a function of temperature ρ(T) under pressure. Some characteristic features related to a structural transition (T{sub S}), crystalline field effects (T{sub CEF}), and a low temperature maximum (T{sub max}), possibly connected simultaneously to the onset of Kondo lattice coherence and short range magnetic correlations, were identified in the ρ(T) data. A pressure-temperature phase diagram with T{sub S} and T{sub max} was constructed by mapping these features. Like for most Ce-based heavy fermion compounds, T{sub max} moves to higher temperatures with pressure, indicating that it is related to the Kondo energy scale, due to the increase of hybridization induced by pressure. On the other hand, T{sub S}, associated to a superlattice distortion and probably combined with a charge density wave transition, decreases as a function of pressure. However, differently from the Sr{sub 3−x}Ca{sub x}Ir{sub 4}Sn{sub 13} system, where a superlattice quantum phase transition is observed [L. E. Klintberg et al., Phys. Rev. Lett. 109, 237 008 (2012)], in Ce{sub 3}Co{sub 4}Sn{sub 13} T{sub S} ∼ 154 K, at ambient pressure (P = 0), seems to stabilize at around 143 K for P ≥ 19 kilobars. We also investigated ρ(T) in external magnetic fields, at P = 0. Negative magnetoresistance and increase of T{sub max} are observed, suggesting suppression of low temperature short range magnetic correlations.
Hall effect indicates destruction of large Fermi surface at a heavy-fermion quantum critical point
NASA Astrophysics Data System (ADS)
Paschen, Silke
2005-03-01
Quantum critical points (QCPs) - phase transitions at absolute zero in temperature -- are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. To accommodate the heavy electrons, the Fermi surface of the heavy-fermion paramagnet is larger than that of an antiferromagnet [1]. An important unsolved question concerns whether the Fermi surface transformation at the QCP develops gradually, as expected if the magnetism is of spin density wave type [2], or suddenly as expected if the heavy electrons are abruptly localized by magnetism [3]. Here we report measurements of the low-temperature Hall coefficient (RH) -- a measure of the Fermi surface volume -- in the heavy-fermion metal YbRh2Si2 upon field-tuning it from an antiferromagnetic to a paramagnetic state. RH undergoes an increasingly rapid change near the QCP as the temperature is lowered, extrapolating to a sudden jump in the zero temperature limit. We interpret these results in terms of a collapse of the large Fermi surface and of the heavy-fermion state itself precisely at the QCP [4].[0.2cm] [1] R. M. Martin, Phys. Rev. Lett. 48, 362-- 365 (1982); P. Fulde, in Narrow-Band Phenomena -- Influence of Electrons with both Band and Localized Character (ed. Fuggle, J. C.) 27--29 (Plenum Press, New York, 1988); M. Oshikawa, Phys. Rev. Lett. 84, 3370--3373 (2000).[0.2cm] [2] J. A. Hertz, Phys. Rev. B 14, 1165--1184 (1976); A. J. Millis, Phys. Rev. B 48, 7183-- 7196 (1993).[0.2cm] [3] A. Schröder et al., Nature 407, 351- -355 (2000); P. Coleman et al., J. Phys.: Condens. Matter 13, R723--R738 (2001); Q. Si et al., Nature 413, 804--808 (2001).[0.2cm] [4] S. Paschen et al., to appear in Nature.[0.2cm] In collaboration with: T. Lühmann, S. Wirth, P. Gegenwart, O. Trovarelli, C. Geibel, F. Steglich, P. Coleman, and Q. Si.
Bi-layer ^3He: a simple two dimensional heavy fermion system with quantum criticality
NASA Astrophysics Data System (ADS)
Saunders, John
2008-03-01
Two dimensional helium films provide simple model systems for the investigation of quantum phase transitions in two dimensions. Monolayer ^3He absorbed on graphite, with various pre-platings, behaves as a two dimensional Mott-Hubbard system, complete with a density driven ``metal-insulator'' transition [1, 2] into what appears to be a gapless spin-liquid. In two dimensions the corrections to the temperature dependence of the fluid heat capacity, beyond the term linear in T, are anomalous and attributed to quasi-1D scattering [3]. On the other hand, bi-layer ^3He films adsorbed on the surface of graphite show evidence of two-band heavy-fermion behavior and quantum criticality [4, 5]. The relevant control parameter is the total density of the ^3He film. The ^3He bilayer system can be driven toward a quantum critical point (QCP) at which the effective mass appears to diverge, the effective inter-band hybridization vanishes, and a local moment state appears. A theoretical model in terms of a ``Kondo breakdown selective Mott transition'' has recently been suggested [6]. * In collaboration with: A Casey, M Neumann, J Nyeki, B Cowan. [1] Evidence for a Mott-Hubbard Transition in a Two-Dimensional ^3He Fluid Monolayer, A. Casey, H. Patel, J. Ny'eki, B. P. Cowan, and J. Saunders Phys. Rev. Lett. 90, 115301 (2003) [2] D Tsuji et al. J. Low Temp. Phys. 134, 31 (2004) [3] A V Chubukov et al. Phys. Rev. B71, 205112 (2005) [4] Bilayer ^3He; a simple two dimensional heavy fermion system with quantum criticality, Michael Neumann, Jan Nyeki, Brian Cowan, John Saunders. Science 317, 1356 (2007) [5] Heavy fermions in the original Fermi liquid. Christopher A Hooley and Andrew P Mackenzie. Science 317, 1332 (2007) [6] C Pepin, Phys. Rev. Lett. 98, 206401 (2007) and A Benlagra and C Pepin, arXiv: 0709.0354
Incommensurate magnetic order in the heavy fermion superconductor UNi2Al3
NASA Astrophysics Data System (ADS)
Schröder, A.; Lussier, J. G.; Gaulin, B. D.; Garrett, J. D.; Buyers, W. J. L.; Rebelsky, L.; Shapiro, S. M.
1994-01-01
Neutron scattering measurements show UNi2Al3 to be unique among heavy fermion superconductors in that below TN~5.2 K it displays long range magnetic order which is incommensurate with its chemical lattice. The ordering wave vector is (1/2+/-δ, 0, 1/2) where δ=0.110+/-0.003. The measured superlattice intensities are well described by the presence of a longitudinal spin density wave within the hexagonal basal plane, polarized along a*. The magnitude of the maximum ordered moment is found to be very small; μord=(0.24+/-0.10)μB.
Heat conduction in the heavy fermion superconductor UPd 2Al 3
NASA Astrophysics Data System (ADS)
Chiao, May; Lussier, Benoit; Ellman, Brett; Taillefer, Louis
1997-02-01
We present preliminary measurements of the thermal conductivity of the heavy fermion superconductor UPd 2Al 3 for the normal and superconducting states at low temperatures. As T → 0, the superconducting state is characterized by a finite linear term, about 10% of the normal state value, which suggests a residual density of low-energy quasiparticle states. This agrees qualitatively with resonant impurity scattering theories applied to exotic superconductors with nodes in the gap structure. Comparisons are made with theory and with other U-based superconductors, such as URu 2Si 2 and UPt 3.
Anisotropy of heat conduction in the heavy fermion superconductor UPt3
NASA Astrophysics Data System (ADS)
Lussier, Benoit; Ellman, Brett; Taillefer, Louis
1994-12-01
We report on the first measurement of the anisotropy of heat conduction in a heavy fermion superconductor, performed on a single crystal of UPt3 with a current parallel and perpendicular to the hexagonal axis. Beyond the temperature-independent anisotropy of the normal state, a clear additional anisotropy develops in the superconducting state. This direct measure of gap anisotropy places precise constraints on the possible states for the two zero-field phases. An axial gap is excluded for both, and a comparison with existing calculations favors a d-wave gap for the low-temperature phase.
Cerium heavy-fermion compounds near their T = 0 magnetic-non-magnetic boundary
Thompson, J.D.; Hundley, M.F.; Movshovich, R.; Sarrao, J.L.; Graf, T.; Uwatoko, Y.; Fisk, Z.; Fisher, R.A.; Phillips, N.E. |
1997-12-01
Measurements of the temperature-dependent specific heat and thermal expansion coefficient near a T = 0 magnetic-non-magnetic boundary, accessed in CeRh{sub 2}Si{sub 2} by application of pressure and in CeRh{sub 2{minus}x}Ru{sub x}Si{sub 2} at ambient pressure by chemical substitution, emphasize the role of disorder in producing non-Fermi-liquid behavior. Interestingly, superconductivity also develops near this boundary in some crystallographically-ordered Ce-based heavy-fermion compounds.
Energy and momentum relaxation of heavy fermion in dense and warm plasma
Sarkar, Sreemoyee; Dutt-Mazumder, Abhee K.
2010-09-01
We determine the drag and the momentum diffusion coefficients of heavy fermion in dense plasma. It is seen that in degenerate matter the drag coefficient at the leading order mediated by the transverse photon is proportional to (E-{mu}){sup 2} while for the longitudinal exchange this goes as (E-{mu}){sup 3}. We also calculate the longitudinal diffusion coefficient to obtain the Einstein relation in a relativistic degenerate plasma. Finally, finite temperature corrections are included both for the drag and the diffusion coefficients.
Effect of electron-phonon interaction on resistivity of some heavy fermion (HF) systems
Sahoo, J.; Shadangi, N.; Nayak, P.
2014-04-24
Here, we have analyzed the electron-phonon interaction in the Periodic Anderson Model (PAM) to describe the temperature dependence of resistivity in some heavy fermion (HF) systems for finite wave vector (q) and for finite temperature (T). Since the resistivity is related to the imaginary part of the electron self energy, the expression for the same is evaluated through double time temperature dependant Green function technique of the Zubarev type. The effect of different system parameters namely the position of 4f level, E{sub 0} and the electron - phonon coupling strengths on resistivity have been studied. The results obtained give satisfactory explanations to the experimental observations.
Heavy-fermion superconductivity in the quadrupole ordered state of PrV2Al20.
Tsujimoto, Masaki; Matsumoto, Yosuke; Tomita, Takahiro; Sakai, Akito; Nakatsuji, Satoru
2014-12-31
PrV2Al20 is a rare example of a heavy-fermion system based on strong hybridization between conduction electrons and nonmagnetic quadrupolar moments of the cubic Γ3 ground doublet. Here, we report that a high-quality single crystal of PrV2Al20 exhibits superconductivity at Tc=50 mK in the antiferroquadrupole-ordered state under ambient pressure. The heavy-fermion character of the superconductivity is evident from the specific heat jump of ΔC/T∼0.3 J/mol K(2) and the effective mass m*/m0∼140 estimated from the temperature dependence of the upper critical field. Furthermore, the high-quality single crystals exhibit double transitions at TQ=0.75 K and T*=0.65 K associated with quadrupole and octupole degrees of freedom of the Γ3 doublet. In the ordered state, the specific heat C/T shows a T(3) dependence, indicating the gapless mode associated with the quadrupole order, the octupole order, or both. The strong sensitivity to impurity of the superconductivity suggests unconventional character due to significant quadrupolar fluctuations.
Study of ultrasonic attenuation for the Kondo and magnetic effects in heavy fermion systems
NASA Astrophysics Data System (ADS)
Baral, Purna Chandra; Rout, Govind Chandra
2013-05-01
The heavy fermion (HF) systems draw considerable attention due to their cooperative phenomena and anomalous properties arising out of the huge effective mass. A heavy fermion system is described by a model Hamiltonian consisting of the Kondo lattice model in addition to the Heisenberg-type spin-spin interaction among the localised electrons. The Hamiltonian is treated in the mean-field approximation to find the Kondo singlet parameter λ and the short-ranged f-electron correlation parameter Γ. In order to investigate ultrasonic absorption in the system, we consider the phonon interaction with the bare f-electrons, and the phonon coupling to the Kondo singlets. Further, the phonon Hamiltonian is considered in the harmonic approximation. The phonon Green's function is calculated in closed form. The imaginary part of the phonon self-energy describes the ultrasonic attenuation for the HF systems. The calculated ultrasonic attenuation clearly displays the f-electron correlation region separated by the Kondo singlet state at low temperatures. The correlation transition temperature and the Kondo temperature are located at dips in the temperature-dependent ultrasonic attenuation. The parameter dependence of the attenuation is investigated by varying the physical parameters of the HF systems and the wave frequency, and the experimental observations are explained on the basis of the model calculations.
Extended nuclear quadrupole resonance study of the heavy-fermion superconductor PuCoGa5
NASA Astrophysics Data System (ADS)
Koutroulakis, G.; Yasuoka, H.; Tobash, P. H.; Mitchell, J. N.; Bauer, E. D.; Thompson, J. D.
2016-10-01
PuCoGa5 has emerged as a prototypical heavy-fermion superconductor, with its transition temperature (Tc≃18.5 K) being the highest amongst such materials. Nonetheless, a clear description as to what drives the superconducting pairing is still lacking, rendered complicated by the notoriously intricate nature of plutonium's 5 f valence electrons. Here, we present a detailed Ga,7169 nuclear quadrupole resonance (NQR) study of PuCoGa5, concentrating on the system's normal state properties near to Tc and aiming to detect distinct signatures of possible pairing mechanisms. In particular, the quadrupole frequency and spin-lattice relaxation rate were measured for the two crystallographically inequivalent Ga sites and for both Ga isotopes, in the temperature range 1.6-300 K. No evidence of significant charge fluctuations is found from the NQR observables. On the contrary, the low-energy dynamics is dominated by anisotropic spin fluctuations with strong, nearly critical, in-plane character, which are effectively identical to the case of the sister compound PuCoIn5. These findings are discussed within the context of different theoretical proposals for the unconventional pairing mechanism in heavy-fermion superconductors.
Quantum oscillations in the heavy-fermion compound YbPtBi
Mun, E.; Bud'ko, S. L.; Lee, Y.; Martin, C.; Tanatar, M. A.; Prozorov, R.; Canfield, P. C.
2015-08-01
We present quantum oscillations observed in the heavy-fermion compound YbPtBi in magnetic fields far beyond its field-tuned, quantum critical point. Quantum oscillations are observed in magnetic fields as low as 60 kOe at 60 mK and up to temperatures as high as 3 K, which confirms the very high quality of the samples as well as the small effective mass of the conduction carriers far from the quantum critical point. Although the electronic specific heat coefficient of YbPtBi reaches ~7.4 J/molK^{2} in zero field, which is one of the highest effective mass values among heavy-fermion systems, we suppress it quickly by an applied magnetic field. The quantum oscillations were used to extract the quasiparticle effective masses of the order of the bare electron mass, which is consistent with the behavior observed in specific heat measurements. Furthermore, such small effective masses at high fields can be understood by considering the suppression of Kondo screening.
Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickel oxypnictide.
Luo, Yongkang; Pourovskii, Leonid; Rowley, S E; Li, Yuke; Feng, Chunmu; Georges, Antoine; Dai, Jianhui; Cao, Guanghan; Xu, Zhu'an; Si, Qimiao; Ong, N P
2014-08-01
A quantum critical point arises at a continuous transformation between distinct phases of matter at zero temperature. Studies in antiferromagnetic heavy-fermion materials have revealed that quantum criticality has several classes, with an unconventional type that involves a critical destruction of the Kondo entanglement. To understand such varieties, it is important to extend the materials basis beyond the usual setting of intermetallic compounds. Here we show that a nickel oxypnictide, CeNiAsO, exhibits a heavy-fermion antiferromagnetic quantum critical point as a function of either pressure or P/As substitution. At the quantum critical point, non-Fermi-liquid behaviour appears, which is accompanied by a divergent effective carrier mass. Across the quantum critical point, the low-temperature Hall coefficient undergoes a rapid sign change, suggesting a sudden jump of the Fermi surface and a destruction of the Kondo effect. Our results imply that the enormous materials basis for the oxypnictides, which has been so crucial in the search for high-temperature superconductivity, will also play a vital role in the effort to establish the universality classes of quantum criticality in strongly correlated electron systems. PMID:24859644
Heavy Fermion Superconductivity in Non-magnetic Cage Compound PrV2Al20
NASA Astrophysics Data System (ADS)
Matsumoto, Yosuke; Tsujimoto, Masaki; Tomita, Takahiro; Sakai, Akito; Nakatsuji, Satoru
2016-02-01
PrT2Al20 (T = Ti, V) are ideal systems to study the quadrupole Kondo effect and quantum criticality arising from orbital degrees of freedom. Both systems have the nonmagnetic cubic Γ3 crystal electric field ground doublet with the well separated excited state. In particular, PrV2Al20 exhibits anomalous metallic behavior above and below the multipolar ordering temperatures, reflecting the even stronger hybridization between f and conduction electrons possibly due to a proximity to a orbital quantum critical point. Here, we discuss the heavy fermion superconductivity (SC) of PrV2Al20 in detail. The SC appears at Tc = 0.05 K with the highly enhanced effective mass (m* /m0 ∼ 140) estimated using the temperature dependence of the upper critical field. In addition, large electronic specific heat coefficient of γ ∼ 0.9 J/mol K2 above Tc and the large specific heat jump at Tc of ΔC/Tc ∼ 0.3 J/mol K2 provide direct evidences of the heavy fermion SC. This observation indicates the first realization of the novel SC arising from the orbital fluctuation of the f electrons at ambient pressure.
Quantum oscillations in the heavy-fermion compound YbPtBi
Mun, E.; Bud'ko, S. L.; Lee, Y.; Martin, C.; Tanatar, M. A.; Prozorov, R.; Canfield, P. C.
2015-08-01
We present quantum oscillations observed in the heavy-fermion compound YbPtBi in magnetic fields far beyond its field-tuned, quantum critical point. Quantum oscillations are observed in magnetic fields as low as 60 kOe at 60 mK and up to temperatures as high as 3 K, which confirms the very high quality of the samples as well as the small effective mass of the conduction carriers far from the quantum critical point. Although the electronic specific heat coefficient of YbPtBi reaches ~7.4 J/molK2 in zero field, which is one of the highest effective mass values among heavy-fermion systems, we suppress it quicklymore » by an applied magnetic field. The quantum oscillations were used to extract the quasiparticle effective masses of the order of the bare electron mass, which is consistent with the behavior observed in specific heat measurements. Furthermore, such small effective masses at high fields can be understood by considering the suppression of Kondo screening.« less
Fragile antiferromagnetism in the heavy-fermion compound YbBiPt
Ueland, Benjamin G.; Kreyssig, Andreas; Prokes, K.; Lynn, J. W.; Harriger, L. W.; Pratt, D. K.; Singh, D. K.; Heitmann, T. W.; Sauerbrei, Samantha; Saunders, Scott M.; Mun, E. D.; Budko, Serguei L.; McQueeney, Robert J.; Canfield, Paul C.; Goldman, Alan I.
2014-05-08
We report results from neutron scattering experiments on single crystals of YbBiPt that demonstrate antiferromagnetic order characterized by a propagation vector, τAFM = (121212), and ordered moments that align along the [1 1 1] direction of the cubic unit cell. We describe the scattering in terms of a two-Gaussian peak fit, which consists of a narrower component that appears below TN≈0.4 K and corresponds to a magnetic correlation length of ξn≈ 80 Å, and a broad component that persists up to T*≈ 0.7 K and corresponds to antiferromagnetic correlations extending over ξb≈ 20 Å. Our results illustrate the fragile magnetic order present in YbBiPt and provide a path forward for microscopic investigations of the ground states and fluctuations associated with the purported quantum critical point in this heavy-fermion compound.
NASA Astrophysics Data System (ADS)
Gritsan, Andrei V.; Röntsch, Raoul; Schulze, Markus; Xiao, Meng
2016-09-01
In this paper, we investigate anomalous interactions of the Higgs boson with heavy fermions, employing shapes of kinematic distributions. We study the processes p p →t t ¯+H , b b ¯+H , t q +H , and p p →H →τ+τ- and present applications of event generation, reweighting techniques for fast simulation of anomalous couplings, as well as matrix element techniques for optimal sensitivity. We extend the matrix element likelihood approach (MELA) technique, which proved to be a powerful matrix element tool for Higgs boson discovery and characterization during Run I of the LHC, and implement all analysis tools in the JHU generator framework. A next-to-leading-order QCD description of the p p →t t ¯+H process allows us to investigate the performance of the MELA in the presence of extra radiation. Finally, projections for LHC measurements through the end of Run III are presented.
Dynamical Electroweak Symmetry Breaking with a Heavy Fermion in Light of Recent LHC Results
Hung, Pham Q.
2013-01-01
The recent announcement of a discovery of a possible Higgs-like particle—its spin and parity are yet to be determined—at the LHC with a mass of 126 GeV necessitates a fresh look at the nature of the electroweak symmetry breaking, in particular if this newly-discovered particle will turn out to have the quantum numbers of a Standard Model Higgs boson. Even if it were a 0 + scalar with the properties expected for a SM Higgs boson, there is still the quintessential hierarchy problem that one has to deal with and which, by itself, suggests a new physics energy scale aroundmore » 1 TeV. This paper presents a minireview of one possible scenario: the formation of a fermion-antifermion condensate coming from a very heavy fourth generation, carrying the quantum number of the SM Higgs field, and thus breaking the electroweak symmetry.« less
Grüneisen parameter studies on heavy fermion quantum criticality
NASA Astrophysics Data System (ADS)
Gegenwart, Philipp
2016-11-01
The Grüneisen parameter, experimentally determined from the ratio of thermal expansion to specific heat, quantifies the pressure dependence of characteristic energy scales of matter. It is highly enhanced for Kondo lattice systems, whose properties are strongly dependent on the pressure sensitive antiferromagnetic exchange interaction between f- and conduction electrons. In this review, we focus on the divergence of the Grüneisen parameter and its magnetic analogue, the adiabatic magnetocaloric effect, for heavy-fermion metals near quantum critical points. We compare experimental results with current theoretical models, including the effect of strong geometrical frustration. We also discuss the possibility of using materials with the divergent magnetic Grüneisen parameter for adiabatic demagnetization cooling to very low temperatures.
Magnetism and superconductivity driven by identical 4f states in a heavy-fermion metal
Thompson, Joe E; Nair, S; Stockert, O; Witte, U; Nicklas, M; Schedler, R; Bianchi, A; Fisk, Z; Wirth, S; Steglich, K
2009-01-01
The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity.
Magnetic properties of nearly stoichiometric CeAuBi{sub 2} heavy fermion compound
Adriano, C.; Jesus, C. B. R.; Pagliuso, P. G.; Rosa, P. F. S.; Grant, T.; Fisk, Z.; Garcia, D. J.
2015-05-07
Motivated by the interesting magnetic anisotropy found in the heavy fermion family CeTX{sub 2} (T = transition metal and X = pnictogen), here, we study the novel parent compound CeAu{sub 1−x}Bi{sub 2−y} by combining magnetization, pressure dependent electrical resistivity, and heat-capacity measurements. The magnetic properties of our nearly stoichiometric single crystal sample of CeAu{sub 1−x}Bi{sub 2−y} (x = 0.92 and y = 1.6) revealed an antiferromagnetic ordering at T{sub N} = 12 K with an easy axis along the c-direction. The field dependent magnetization data at low temperatures reveal the existence of a spin-flop transition when the field is applied along the c-axis (H{sub c} ∼ 7.5 T and T = 5 K). The heat capacity and pressure dependent resistivity data suggest that CeAu{sub 0.92}Bi{sub 1.6} exhibits a weak heavy fermion behavior with strongly localized Ce{sup 3+} 4f electrons. Furthermore, the systematic analysis using a mean field model including anisotropic nearest-neighbors interactions and the tetragonal crystalline electric field (CEF) Hamiltonian allows us to extract a CEF scheme and two different values for the anisotropic J{sub RKKY} exchange parameters between the Ce{sup 3+} ions in this compound. Thus, we discuss a scenario, considering both the anisotropic magnetic interactions and the tetragonal CEF effects, in the CeAu{sub 1−x}Bi{sub 2−y} compounds, and we compare our results with the isostructural compound CeCuBi{sub 2}.
Spatial interferences in the electron transport of heavy-fermion materials
NASA Astrophysics Data System (ADS)
Zhang, Shu-feng; Liu, Yu; Song, Hai-Feng; Yang, Yi-feng
2016-08-01
The scanning tunneling microscopy/spectroscopy and the point contact spectroscopy represent major progress in recent heavy-fermion research. Both have revealed important information on the composite nature of the emergent heavy-electron quasiparticles. However, a detailed and thorough microscopic understanding of the similarities and differences in the underlying physical processes of these techniques is still lacking. Here we study the electron transport in the normal state of the periodic Anderson lattice by using the Keldysh nonequilibrium Green's function technique. In addition to the well-known Fano interference between the conduction and f -electron channels, our results further reveal the effect of spatial interference between different spatial paths at the interface on the differential conductance and their interesting interplay with the band features such as the hybridization gap and the Van Hove singularity. We find that the spatial interference leads to a weighted average in the momentum space for the electron transport and could cause suppression of the electronic band features under certain circumstances. In particular, it reduces the capability of probing the f -electron spectral weight near the edges of the hybridization gap for large interface depending on the Fermi surface of the lead. Our results indicate an intrinsic inefficiency of the point contact spectroscopy in probing the f electrons.
Quasi-particle interference of heavy fermions in resonant x-ray scattering
Gyenis, András; da Silva Neto, Eduardo H.; Sutarto, Ronny; Schierle, Enrico; He, Feizhou; Weschke, Eugen; Kavai, Mariam; Baumbach, Ryan E.; Thompson, Joe D.; Bauer, Eric D.; Fisk, Zachary; Damascelli, Andrea; Yazdani, Ali; Aynajian, Pegor
2016-01-01
Resonant x-ray scattering (RXS) has recently become an increasingly important tool for the study of ordering phenomena in correlated electron systems. Yet, the interpretation of RXS experiments remains theoretically challenging because of the complexity of the RXS cross section. Central to this debate is the recent proposal that impurity-induced Friedel oscillations, akin to quasi-particle interference signals observed with a scanning tunneling microscope (STM), can lead to scattering peaks in RXS experiments. The possibility that quasi-particle properties can be probed in RXS measurements opens up a new avenue to study the bulk band structure of materials with the orbital and element selectivity provided by RXS. We test these ideas by combining RXS and STM measurements of the heavy fermion compound CeMIn5 (M = Co, Rh). Temperature- and doping-dependent RXS measurements at the Ce-M4 edge show a broad scattering enhancement that correlates with the appearance of heavy f-electron bands in these compounds. The scattering enhancement is consistent with the measured quasi-particle interference signal in the STM measurements, indicating that the quasi-particle interference can be probed through the momentum distribution of RXS signals. Overall, our experiments demonstrate new opportunities for studies of correlated electronic systems using the RXS technique. PMID:27757422
Hidden Orbital Order in the Heavy Fermion Metal URu_2Si_2
NASA Astrophysics Data System (ADS)
Chandra, Premi
2003-03-01
When matter is cooled from high temperatures, collective instabilities develop amongst its constituent particles that lead to new kinds of order. An anomaly in the specific heat, due to a sudden loss of entropy, is a classic signature of this phenomenon. Usually the associated order is easily identified, but sometimes its nature remains elusive. The heavy fermion metal URu_2Si2 is one such example, where the order responsible for the sharp specific heat anomaly at T_0=17 K has remained unidentified despite more than seventeen years of effort. It belongs to a class of ``strongly correlated'' materials where competing interactions lead to correlated electron motion and hence to the possibility of many exotic types of magnetic, charge and superconducting order. The coexistence of large electron-electron repulsion and antiferromagnetic fluctuations in URu_2Si2 leads to an almost incompressible heavy electron fluid, where anisotropically paired quasiparticle states are energetically favored and lead to superconductivity with nodes at 1.5 K. My collaborators(P. Chandra, P. Coleman, J.A. Mydosh and V. Tripathi, Nature, 417, 831 (2002).) and I have developped a detailed proposal for the hidden order in URu_2Si_2. We show that incommensurate orbital antiferromagnetism,associated with circulating currents between the uranium ions, can account for the local fields and entropy loss observed at the 17 K transition; furthermore we make detailed predictions for neutron scattering measurements.
Coexistence of Antiferromagnetism and Superconductivity in Heavy Fermion Cerium Compound Ce3PdIn11
Kratochvílová, M.; Prokleška, J.; Uhlířová, K.; Tkáč, V.; Dušek, M.; Sechovský, V.; Custers, J.
2015-01-01
Many current research efforts in strongly correlated systems focus on the interplay between magnetism and superconductivity. Here we report on coexistence of both cooperative ordered states in recently discovered stoichiometric and fully inversion symmetric heavy fermion compound Ce3PdIn11 at ambient pressure. Thermodynamic and transport measurements reveal two successive magnetic transitions at T1 = 1.67 K and TN = 1.53 K into antiferromagnetic type of ordered states. Below Tc = 0.42 K the compound enters a superconducting state. The large initial slope of dBc2/dT ≈ – 8.6 T/K indicates that heavy quasiparticles form the Cooper pairs. The origin of the two magnetic transitions and the coexistence of magnetism and superconductivity is briefly discussed in the context of the coexistence of the two inequivalent Ce-sublattices in the unit cell of Ce3PdIn11 with different Kondo couplings to the conduction electrons. PMID:26514364
LiV{sub 2}O{sub 4}: A heavy fermion transition metal oxide
Kondo, Shinichiro
1999-02-12
The format of this dissertation is as follows. In the remainder of Chapter 1, brief introductions and reviews are given to the topics of frustration, heavy fermions and spinels including the precedent work of LiV{sub 2}O{sub 4}. In Chapter 2, as a general overview of this work the important publication in Physical Review Letters by the author of this dissertation and collaborators regarding the discovery of the heavy fermion behavior in LiV{sub 2}O{sub 4} is introduced [removed for separate processing]. The preparation methods employed by the author for nine LiV{sub 2}O{sub 4} and two Li{sub 1+x}Ti{sub 2{minus}x}O{sub 4} (x = 0 and 1/3) polycrystalline samples are introduced in Chapter 3. The subsequent structural characterization of the LiV{sub 2}O{sub 4} and Li{sub 1+x}Ti{sub 2{minus}x}O{sub 4} samples was done by the author using thermogravimetric analysis (TGA), x-ray diffraction measurements and their structural refinements by the Rietveld analysis. The results of the characterization are detailed in Chapter 3. In Chapter 4 magnetization measurements carried out by the author are detailed. In Chapter 5, after briefly discussing the resistivity measurement results including the single-crystal work by Rogers et al., for the purpose of clear characterization of LiV{sub 2}O{sub 4} it is of great importance to introduce in the following chapters the experiments and subsequent data analyses done by his collaborators. Heat capacity measurements (Chapter 6) were carried out and analyzed by Dr. C.A. Swenson, and modeled theoretically by Dr. D.C. Johnston. In Chapter 7 a thermal expansion study using neutron diffraction by Dr. O. Chmaissem et al. and capacitance dilatometry measurements by Dr. C.A. Swenson are introduced. The data analyses for the thermal expansion study were mainly done by Dr. O. Chmaissem (for neutron diffraction) and Dr. C.A. Swendon (for dilatometry), with assistances by Dr. J.D. Jorgensen, Dr. D.C. Johnston, and S. Kondo the author of this
Superconducting gap and vortex lattice of the heavy-fermion compound CeCu2Si2
NASA Astrophysics Data System (ADS)
Enayat, Mostafa; Sun, Zhixiang; Maldonado, Ana; Suderow, Hermann; Seiro, Silvia; Geibel, Christoph; Wirth, Steffen; Steglich, Frank; Wahl, Peter
2016-01-01
The order parameter and pairing mechanism for superconductivity in heavy-fermion compounds are still poorly understood. Scanning tunneling microscopy and spectroscopy at ultralow temperatures can yield important information about the superconducting order parameter and the gap structure. Here, we study the first heavy-fermion superconductor, CeCu2Si2 . Our data show the superconducting gap which is not fully formed and exhibits features that point to a multigap order parameter. Spatial mapping of the zero-bias conductance in magnetic field reveals the vortex lattice, which allows us to unequivocally link the observed conductance gap to superconductivity in CeCu2Si2 . The vortex lattice is found to be predominantly triangular with distortions at fields close to ˜0.7 Hc 2 .
NASA Astrophysics Data System (ADS)
Wasser, S.; Nowack, A.; Schlabitz, W.; Freimuth, A.; Kvitnitskaya, O. E.; Menovsky, A. A.; Bruder, C.
1998-07-01
Point contacts between the heavy-fermion superconductor URu2Si2 and Nb are studied. A finite dc Josephson current is found in contacts aligned parallel to the a- b directions of URu2Si2, whereas it is absent in contacts aligned along the c direction. We attribute this extreme anisotropy of the Josephson current to an unconventional superconducting order parameter in URu2Si2, with a symmetry leading to destructive interference for Josephson currents along the c direction.
Resonant magnetic X-ray scattering studies of heavy fermion superconductors
NASA Astrophysics Data System (ADS)
Gaulin, B. D.; Isaacs, E. D.; Lussier, J. G.; Reimers, J. N.; Gibbs, D.; Zschack, P.; Schröder, A.; Taillefer, L.; Garrett, J. D.
1994-04-01
The uranium-based heavy fermion superconductors which are known to display weak antiferromagnetism at low temperatures are well suited to study by the newly developed resonant magnetic X-ray scattering technique. We review recent synchrotron X-ray scattering studies of the magnetic behavior of UPd 2Al 3 and URu 2Si 2 and the interaction between magnetism and superconductivity in these materials. These measurements show resolution-limited magnetic Bragg peaks in UPd 2Al 3 in contrast to those in URu 2Si 2. The order parameter as measured at the (0 0 {1}/{2}) magnetic reciprocal lattice position in UPd 2Al 3 is different from that at (0, 0, {3}/{2}), the latter of which indicates a strong anomaly at TNI ∼ 11.8 K below the sharp onset of the antiferromagnetic phase at TN ∼ 14.5 K. Finally, the behavior of the (0 0 {1}/{2}) order parameter is smooth for T ≤ Tc = 2.00 ± 0.04 K.
Complex magnetic phases in non-centrosymmetric heavy fermion CeCoGe3
NASA Astrophysics Data System (ADS)
Wu, Shan; Stock, Chris; Petrovic, Cedomir; Rodriguez-Rivera, J. A.; Broholm, Collin
The non-centrosymmetric nature of the tetragonal heavy fermion system CeCoGe3 has attracted much interest in the high pressure superconducting state of the material. We have explored the related ambient pressure magnetism using neutron scattering. There are three successive phase transitions at TN 1 ~ 21 K , TN 2 ~ 12 K and TN 3 ~ 8 K. The upper transition greatly enhances the susceptibility and there are meta-magnetic transitions in the lower T phases. We confirmed the previously determined AFM spin structure for TN 2 < T
Correlation between ground state and orbital anisotropy in heavy fermion materials
Willers, Thomas; Strigari, Fabio; Hu, Zhiwei; Sessi, Violetta; Brookes, Nicholas B.; Bauer, Eric D.; Sarrao, John L.; Thompson, J. D.; Tanaka, Arata; Wirth, Steffen; et al
2015-02-09
The interplay of structural, orbital, charge, and spin degrees of freedom is at the heart of many emergent phenomena, including superconductivity. We find that unraveling the underlying forces of such novel phases is a great challenge because it not only requires understanding each of these degrees of freedom, it also involves accounting for the interplay between them. Cerium-based heavy fermion compounds are an ideal playground for investigating these interdependencies, and we present evidence for a correlation between orbital anisotropy and the ground states in a representative family of materials. We have measured the 4f crystal-electric field ground-state wave functions ofmore » the strongly correlated materials CeRh1₋xIrxIn5 with great accuracy using linear polarization-dependent soft X-ray absorption spectroscopy. These measurements show that these wave functions correlate with the ground-state properties of the substitution series, which covers long-range antiferromagnetic order, unconventional superconductivity, and coexistence of these two states.« less
Heavy fermion and Kondo lattice behavior in the itinerant ferromagnet CeCrGe3.
Das, Debarchan; Gruner, T; Pfau, H; Paramanik, U B; Burkhardt, U; Geibel, C; Hossain, Z
2014-03-12
Physical properties of polycrystalline CeCrGe3 and LaCrGe3 have been investigated by x-ray absorption spectroscopy, magnetic susceptibility χ(T), isothermal magnetization M(H), electrical resistivity ρ(T), specific heat C(T) and thermoelectric power S(T) measurements. These compounds are found to crystallize in the hexagonal perovskite structure (space group P63/mmc), as previously reported. The ρ(T), χ(T) and C(T) data confirm the bulk ferromagnetic ordering of itinerant Cr moments in LaCrGe3 and CeCrGe3 with TC = 90 K and 70 K respectively. In addition, a weak anomaly is also observed near 3 K in the C(T) data of CeCrGe3. The T dependences of ρ and finite values of Sommerfeld coefficient γ obtained from the specific heat measurements confirm that both the compounds are of metallic character. Further, the T dependence of ρ of CeCrGe3 reflects a Kondo lattice behavior. An enhanced γ of 130 mJ mol(-1) K(-2) together with the Kondo lattice behavior inferred from the ρ(T) establish CeCrGe3 as a moderate heavy fermion compound with a quasi-particle mass renormalization factor of ∼45. PMID:24553355
Quantum bicriticality in the heavy-fermion metamagnet YbAgGe.
Tokiwa, Y; Garst, M; Gegenwart, P; Bud'ko, S L; Canfield, P C
2013-09-13
Bicritical points, at which two distinct symmetry-broken phases become simultaneously unstable, are typical for spin-flop metamagnetism. Interestingly, the heavy-fermion compound YbAgGe also possesses such a bicritical point (BCP) with a low temperature T(BCP)≈0.3 K at a magnetic field of μH(BCP)≈4.5 T. In its vicinity, YbAgGe exhibits anomalous behavior that we attribute to the influence of a quantum bicritical point that is close in parameter space yet can be reached by tuning T(BCP) further to zero. Using high-resolution measurements of the magnetocaloric effect, we demonstrate that the magnetic Grüneisen parameter ΓH indeed both changes sign and diverges as required for quantum criticality. Moreover, ΓH displays a characteristic scaling behavior but only on the low-field side H≲H(BCP), indicating a pronounced asymmetry with respect to the critical field. We speculate that the small value of T(BCP) is related to the geometric frustration of the Kondo lattice of YbAgGe. PMID:24074108
Andraka, Bohdan
2015-05-14
The main goal of this program was to explore the possibility of novel states and behaviors in Pr-based system exhibiting quantum critical behavior, PrOs₄Sb₁₂. Upon small changes of external parameter, such as magnetic field, physical properties of PrOs₄Sb₁₂ are drastically altered from those corresponding to a superconductor, to heavy fermion, to field-induced ordered phase with primary quadrupolar order parameter. All these states are highly unconventional and not understood in terms of current theories thus offer an opportunity to expand our knowledge and understanding of condensed matter. At the same time, these novel states and behaviors are subjects to intense international controversies. In particular, two superconducting phases with different transition temperatures were observed in some samples and not observed in others leading to speculations that sample defects might be partially responsible for these exotic behaviors. This work clearly established that crystal disorder is important consideration, but contrary to current consensus this disorder suppresses exotic behavior. Superconducting properties imply unconventional inhomogeneous state that emerges from unconventional homogeneous normal state. Comprehensive structural investigations demonstrated that upper superconducting transition is intrinsic, bulk, and unconventional. The high quality of in-house synthesized single crystals was indirectly confirmed by de Haas-van Alphen quantum oscillation measurements. These measurements, for the first time ever reported, spanned several different phases, offering unprecedented possibility of studying quantum oscillations across phase boundaries.
Simple model for coupled magnetic and quadrupolar instabilities in uranium heavy-fermion materials
Libero, V.L. ); Cox, D.L. )
1993-08-01
We present a mean-field calculation of the phase diagram of a simple model of localized moments, in the hexagonal uranium heavy-fermion compounds. The model considers a non-Kramers quadrupolar doublet ground state magnetically coupled with a singlet excited state, favoring in-plane van Vleck magnetism, as has been conjectured for UPt[sub 3]. The Hamiltonian that defines the model is Heisenberg-like in both magnetic and quadrupolar moments. No Kondo-effect physics is included in the calculations. Among our main results are (i) for zero intersite quadrupolar coupling, the magnetic order is achieved by a first-order transition above a critical intersite magnetic coupling value, which becomes second order at higher coupling strengths (ii) for finite intersite quadrupolar coupling, at temperatures below a second-order quadrupolar ordering transition, the minimal magnetic coupling value is increased, but (a) the magnetic ordering temperature is enhanced above this value, and (b) the ordering of first- and second-order transitions in the phase diagram is reversed. By considering the general structure of the Ginsburg-Landau free energy, we argue that the Kondo effect will not modify the shape of the phase diagram, but will modify the quantitative values at which transitions occur.
NASA Astrophysics Data System (ADS)
Coqblin, B.
2006-07-01
After an introduction on the different cases of anomalous rare-earth systems, we start to present the case of intermediate valence, with the example of the phase diagram of Cerium and the study of the Anderson Hamiltonian. Then, we discuss the Kondo effect for a single impurity, with a perturbation calculation above the Kondo temperature and the exact single-impurity solution showing a heavy fermion behaviour below it. Then, the Kondo effect for Ce, Yb and other anomalous rare-earth impurities and their different transport properties arc discussed, with in particular a description of the Schrieffer-Wolff transformation and of the "Coqblin-Schrieffer" Hamiltonian without and with crystalline field effects. The properties of actinide metals and compounds are also discussed and both the spin fluctuation model applied to Plutonium or Neptunium metals or compounds and the undercreened Kondo-lattice model applied to Uranium Kondo and ferromagnetic compounds are presented. The Kondo-lattice problem is also discussed, with a special emphasis on the Doniach diagram, the mean-field approximations, the competition between the Kondo effect and the magnetic order, the spin glass-Kondo competition and the multi-channel Kondo effect. A brief summary of the superconductivity occurring in Ce, U or even Pu systems is finally presented.
Quest for the Origin of Heavy Fermion Behavior in d-Electron Systems
NASA Astrophysics Data System (ADS)
Miyazaki, Masanori; Yamauchi, Ichihiro; Kadono, Ryosuke
2016-09-01
Spin fluctuation is presumed to be one of the key properties in understanding the microscopic origin of heavy-fermion-like behavior in the class of transition-metal compounds, including LiV2O4, Y(Sc)Mn2, and YMn2Zn20. In this review, we demonstrate by our recent study of muon spin rotation/relaxation that the temperature (T) dependence of the longitudinal spin relaxation rate (λ ≡ 1/T1) in these compounds exhibits a common trend of leveling off to a constant value (λ ˜ const.) below a characteristic temperature, T*. This is in marked contrast to the behavior predicted for normal metals from the Korringa relation, λ ∝ T/ν, where the spin fluctuation rate (ν) in the Pauli paramagnetic state is given as a constant, ν ≃ 1/[hD(EF)] [with D(EF) being the density of states at the Fermi energy]. Thus, the observed behavior of λ implies that the spin fluctuation rate becomes linearly dependent on temperature, ν ∝ T, suggesting that heavy quasiparticles develop in a manner satisfying D(EF) ∝ (m*)σ ∝ 1/T at lower temperatures (σ determined by the electronic dispersion). Considering that the theory of spin correlation for intersecting Hubbard chains as a model of pyrochlore lattice predicts ν ∝ T, our finding strongly indicates the crucial role of t2g bands which preserve the one-dimensional character at low energies due to the geometrical frustration specific to the undistorted pyrochlore lattice.
Evidence of f-electron localization at a heavy-fermion quantum critical point
NASA Astrophysics Data System (ADS)
Steglich, Frank
2014-03-01
The prototypical heavy-fermion compound YbRh2Si2 exhibits a magnetic-field (B) induced antiferromagnetic quantum critical point (QCP) at Bc (⊥c) ~ 60 mT. As inferred from transport and thermodynamic measurements a quantum-critical energy scale, kB T *(B) , indicating a crossover of the Fermi surface, has been established for this system. Upon extrapolating finite-temperature (T) data to T = 0, one concludes (i) a vanishing of T*(B) and (ii) an abrupt drop in the (normal) Hall coefficient RH(B) at B =Bc , verifying the proposal of a Kondo destroying QCP. The dynamical processes underlying this apparent break-up of the Kondo singlets have been explored by studying the Lorenz ratio L/L0 as a function of Tand B. Here, L = ρ / w is the ratio of the electrical (ρ) and thermal (w = L0 T / κ) resistivities, with κ being the thermal conductivity and L0 = (πkB)2 /3e2 Sommerfeld's constant. By properly taking care of bosonic (magnon/paramagnon) contributions to the heat current which exist at finite temperature only, extrapolation of the measured data to T = 0 yields a purely electronic Lorenz ratio L/L0 = 1 at B ≠Bc . At B = Bc, we extrapolate L/L0 ~ 0.9. Therefore, the Wiedemann Franz (WF) law holds at any value of the control parameter B, except for the field-induced QCP, as is also illustrated by a pronounced heating of the sample when measuring the low - T electrical resistivity in the vicinity of the critical magnetic field. This violation of the WF law is ascribed to scatterings of the electronic heat carriers from fermionic quantum-critical fluctuations, namely those of the Fermi surface. Work done in collaboration with H. Pfau, S. Lausberg, P. Sun, U. Stockert, M. Brando, S. Friedemann, C. Krellner, C. Geibel, S. Wirth, S. Kirchner, E. Abrahams and Q. Si.
Thermodynamic behavior of the heavy-fermion compounds Ce3X (X=Al,In,Sn)
NASA Astrophysics Data System (ADS)
Chen, Y.-Y.; Lawrence, J. M.; Thompson, J. D.; Willis, J. O.
1989-12-01
We have measured the resistivity ρ(T) and susceptibility χ(T) of Ce3Al, Ce3In, and Ce3Sn in the temperature range 1-350 K, the specific heat C(T) for 1-25 K and the pressure dependence of the resistivity ρ(P,T) for 0
heavy-fermion systems that show no superconductivity above 0.4 K. In the ground state the linear coefficients of the specific heat γ are 0.70 and 0.26 J/mol Ce K2 for Ce3In and Ce3Sn, respectively. The magnetic specific heat of Ce3In shows two separated maxima: one at 4.3 K due to the heavy fermions and a second Schottky peak at 23 K arising from a Γ7-Γ8 crystal-field splitting of order TCF=65 K. For Ce3Sn the crystal-field splitting is comparable. From χ(0) we obtain values of the Wilson ratio of 11.5 and 7.0 for Ce3In and Ce3Sn. We argue that these large values represent the presence of ferromagnetic correlations in the ground state. For Ce3In the enhancement of the susceptibility and specific-heat coefficient and the rapid decrease of the resistivity all occur below the same temperature (7 K), suggesting that the onset of the heavy mass coincides with the onset of magnetic correlations and coherence. In addition, for Ce3In an inflection point occurs in ρ(T) at Tinf=2.2 K, below which ρ varies as T2, and there may be a peak in C(T)/T at 2 K. Thus, it appears that there are two temperature scales for the onset of interaction effects: One coincides with the single-ion Kondo temperature TK, and the other, a low-temperature scale TL, obeys a rule TL=TK/Ndeg, where Ndeg is the degeneracy of the ground-state multiplet. The ground state of Ce3Al is antiferromagnetic with TN=2.5 K. The specific-heat anomaly makes it impossible to determine γ but for 10
Heavy Dirac fermions in a graphene/topological insulator hetero-junction
NASA Astrophysics Data System (ADS)
Cao, Wendong; Zhang, Rui-Xing; Tang, Peizhe; Yang, Gang; Sofo, Jorge; Duan, Wenhui; Liu, Chao-Xing
2016-09-01
The low energy physics of both graphene and surface states of three-dimensional topological insulators (TIs) is described by gapless Dirac fermions with linear dispersion. In this work, we predict the emergence of a ‘heavy’ Dirac fermion in a graphene/TI hetero-junction, where the linear term almost vanishes and the corresponding energy dispersion becomes highly nonlinear. By combining ab initio calculations and an effective low-energy model, we show explicitly how strong hybridization between Dirac fermions in graphene and the surface states of TIs can reduce the Fermi velocity of Dirac fermions. Due to the negligible linear term, interaction effects will be greatly enhanced and can drive ‘heavy’ Dirac fermion states into the half quantum Hall state with non-zero Hall conductance.
Magnetic field tuned quantum criticality of heavy fermion system YbPtBi
NASA Astrophysics Data System (ADS)
Mun, Eundeok
2014-03-01
Quantum criticality triggers an emergence of new quantum phase of matters due to the critical behavior of quantum fluctuations. Heavy fermion (HF) compounds have provided the cleanest evidence for the quantum phase transition. The face-centered cubic YbPtBi is one of the few frustrated stoichiometric Yb-based HF compounds. Measurements of magnetic field and temperature dependent resistivity, specific heat, thermal expansion, Hall effect, and thermoelectric power indicate that the antiferromagnetic (AFM) order (TN ~ 0.4 K) can be suppressed by applied magnetic field of Hc ~ 4 kOe. In the H- T phase diagram of YbPtBi, three regimes of its low temperature states emerges: (I) AFM state, characterized by spin density wave (SDW) like feature, which can be suppressed to T = 0 by the relatively small magnetic field of Hc ~ 4 kOe, (II) field induced anomalous state in which the electrical resistivity follows ρ(T) ~T 1 . 5 between Hc and ~ 8 kOe, and (III) Fermi liquid (FL) state in which ρ(T) ~T2 for H >8 kOe. Regions I and II are separated at T = 0 by what appears to be a quantum critical point. Whereas region III appears to be a FL associated with the hybridized 4 f states of Yb, region II may be a manifestation of a spin liquid state. Work was supported by the US Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.
Van Dyke, John S; Massee, Freek; Allan, Milan P; Davis, J C Séamus; Petrovic, Cedomir; Morr, Dirk K
2014-08-12
To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of high-temperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable. Here, we use a novel approach based on precision measurements of the heavy-fermion band structure using quasiparticle interference imaging to reveal quantitatively the momentum space (k-space) structure of the f-electron magnetic interactions of CeCoIn5. Then, by solving the superconducting gap equations on the two heavy-fermion bands Ek(α,β) with these magnetic interactions as mediators of the Cooper pairing, we derive a series of quantitative predictions about the superconductive state. The agreement found between these diverse predictions and the measured characteristics of superconducting CeCoIn5 then provides direct evidence that the heavy-fermion Cooper pairing is indeed mediated by f-electron magnetism.
Van Dyke, John S.; Massee, Freek; Allan, Milan P.; Davis, J. C. Séamus; Petrovic, Cedomir; Morr, Dirk K.
2014-01-01
To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of high-temperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable. Here, we use a novel approach based on precision measurements of the heavy-fermion band structure using quasiparticle interference imaging to reveal quantitatively the momentum space (k-space) structure of the f-electron magnetic interactions of CeCoIn5. Then, by solving the superconducting gap equations on the two heavy-fermion bands Ekα,β with these magnetic interactions as mediators of the Cooper pairing, we derive a series of quantitative predictions about the superconductive state. The agreement found between these diverse predictions and the measured characteristics of superconducting CeCoIn5 then provides direct evidence that the heavy-fermion Cooper pairing is indeed mediated by f-electron magnetism. PMID:25062692
Min Li; Huey-Wen Lin
2007-10-01
We present a preliminary calculation of the charmonium spectrum using the dynamical 2+1 flavor $24^3\\times 64$ domain wall fermion lattice configurations generated by the RBC and UKQCD collaborations. We use the relativistic heavy quark action with 3 parameters non-perturbatively determined by matching to experimental quantities. Chiral extrapolation is done on four light sea quark masses from 0.005 to 0.03, with $m_s=0.04$ and $m_{res}=0.003$. We can either predict meson masses assuming the lattice spacing is known from other methods, or calculate the lattice spacing using those quantities.
NASA Astrophysics Data System (ADS)
Reber, Theodore; Rameau, Jonathon; Hu, Rongwei; Petrovic, Cedomir; Johnson, Peter
2015-03-01
With the highest Tc of the non-radioactive heavy fermion materials, CeCoIn5 has been extensively studied by a host of techniques. However direct measurements of the band structure via angle resolved photo-emission spectroscopy has been limited to just a few experiments. We will present our studies of the momentum, temperature, photon energy and polarization dependence of the band structure of CeCoIn5. We will compare our results with theory and other experimental results. Present address: Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University
NASA Astrophysics Data System (ADS)
Frederick, Neil Adam
A thorough investigation of the Pr(Os1- xRux)4Sb12 series of compounds is presented. The compound PrOs4Sb12 is the first known Pr-based heavy fermion superconductor, with an electronic specific heat coefficient gamma ˜ 500 mJ/mol K2 and a superconducting transition temperature Tc ≈ 1.8 K. PrOs4Sb12 displays unconventional superconductivity which may be driven by quadrupolar fluctuations, and also exhibits a unique phase in high magnetic fields. Multiple superconducting transitions, structure in the energy gap, and time reversal symmetry breaking have all been observed in the superconducting state of PrOs4Sb12. In contrast, PrRu4Sb12 is a more conventional superconductor with Tc ≈ 1.0 K. Substitution of Ru for Os to form Pr(Os 1-xRux) 4Sb12 has resulted in several very interesting findings. Crystalline electric field (CEF) effects play a strong and important role in the physical properties of PrOs4Sb12. In Chapter III, we present CEF fits to zero-field electrical resistivity which, when extrapolated to higher magnetic fields, display a similar shape to that of the measured rho(H) data. The Pr(Os1-xRu x)4Sb12 system has been extensively studied. In Chapter IV, we present x-ray, magnetic susceptibility, electrical resistivity, and specific heat data for the Pr(Os1-xRu x)4Sb12 series of compounds. A minimum in Tc is observed near x = 0.6, while the CEF splitting between the ground state and first excited state is found to increase monotonically between the end member compounds. The electronic specific heat coefficient gamma increases to a maximum near x ≈ 0.02, after which it drops rapidly and stabilizes at a more conventional value above x = 0.6. The jump in specific heat at the superconducting transition DeltaC/Tc, however, drops abruptly with Ru doping and stabilizes by x = 0.1. Structure in the specific heat jump at Tc appears to persist up to x ≈ 0.04, although fits to C(T) below Tc may indicate a change in the superconducting energy gap upon any Ru
Transport properties in heavy fermion system PrOs 4Sb 12 probed by radiation-induced disordering
NASA Astrophysics Data System (ADS)
Karkin, A.; Naumov, S.; Kostromitina, N.; Goshchitskii, B.
2004-08-01
The influence of atomic disordering induced by fast neutron irradiation on resistivity ρ and Hall coefficient RH was studied in single crystal samples of heavy fermion system PrOs 4Sb 12. Both ρ( T) and RH( T) of the initial samples can be described by a two-band model with conductivities in the form of ( σi) -1= ρi0 + AiT2 (indexes i=1,2 correspond to heavy and light holes), where A1≫ A2. Disordering leads to the appearance of electronic-like band as well as Kondo-like term in the resistivity. In both cases the essential decrease in charge carrier concentration under influence of the magnetic field is observed.
Magnetic Structure of the Heavy-fermion Compound CeAuSb2 in Zero-field
NASA Astrophysics Data System (ADS)
Marcus, Guy G.; Kim, Dae-Jeong; Lee, Hannoh; Fisk, Zachary; Rodriguez-Rivera, Jose A.; Broholm, Collin L.
2015-03-01
We have used neutron diffraction to determine the zero-field magnetic structure of the heavy-fermion compound CeAuSb2. Below TN ~ 6 . 2 K, we observe the development of antiferromagnetic Bragg diffraction consistent with previous transport and magnetization measurements. The intensities observed at 7 magnetic satellite locations indicate the staggered magnetization is predominantly along the c-axis. The maximum moment size is 1 . 15 +/- 0 . 08μB which is large compared with the 0 . 4μB moment in the iso-structural heavy fermion ferromagnet CeAgSb2. This suggests that the antiferromagnetic CeAuSb2 is deeper into a magnetic phase. The spin structure, due mainly to the Ce-4f sites, is described as a transverse polarized spin density wave with an incommensurate component of the wave vector in the basal plane. We will discuss these results and bulk measurements in terms of an ANNNI model and effective near neighbor exchange interactions. The work at IQM was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences and Engineering under Grant No. DE-FG02-08ER46544. GGM also acknowledges support from the NSF-GRFP Grant No. DGE-1232825.
Point-Contact Spectroscopy of Heavy Fermion Compounds CeCu6 and CeAl3 in Magnetic Field
NASA Astrophysics Data System (ADS)
Motoyama, G.; Ogawa, S.; Matsubayashi, K.; Fujiwara, K.; Miyoshi, K.; Nishigori, S.; Mutou, T.; Yamaguchi, A.; Sumiyama, A.; Uwatoko, Y.
We have carried out point-contact spectroscopy measurements on CeCu6 and CeAl3 to study these heavy fermion states. Temperature and magnetic field dependences of the point-contact spectra were observed in detail. At the lowest temperature of 0.4 K, differential resistance spectra of CeCu6 and CeAl3 as function of bias voltage exhibit each distinct minimum structure and additional small peak structure. Temperature evolutions of these spectra started at temperatures related to the Kondo effect, although the minimum and the peak structure emerged in reverse between both spectra of two compounds. In magnetic fields, both structures monotonically change with no distinct change without a change of curvature of magnetic field dependence of magnitude of differential resistance at zero bias voltage at critical magnetic field of meta-magnetization. This behavior in magnetic field is different from that of CeAl2, which shows antiferromagnetic ordering. This result may suggest that PCS is able to discriminate between heavy fermion state and antiferromagnetic state.
A Cu NQR study in a d-electron heavy-fermion system, CaCu3Ru4O12
NASA Astrophysics Data System (ADS)
Kato, Harukazu; Tsuruta, Takuya; Nishioka, Takashi; Matsumura, Masahiro; Sakai, Hironori; Kambe, Shinsaku
2007-11-01
Cu nuclear quadrupole resonance (NQR) studies have been carried out for CaCu3Ru4O12, which has been suggested to show a heavy-fermion-like behavior although it possess no f electron. A Lorentzian shape of the Cu NQR line with a narrow width implies that no magnetic ordering appears, at least, down to 5 K. The spin lattice relaxation rate of the Cu nuclei probes a change of the Cu 3d electron nature, resulting in the Fermi liquid state at a low temperature. These facts strongly support that the heavy fermion picture is available in the concerned compound.
Scanning Tunneling Microscopy and Spectroscopy of the Heavy Fermion Compounds URu2 Si 2 and CeCoIn5
NASA Astrophysics Data System (ADS)
Aynajian, Pegor
2011-03-01
Heavy electronic states originating from the f atomic orbitals underlie a rich variety of quantum phases of matter. We use atomic scale imaging and spectroscopy with the scanning tunneling microscope (STM) to examine the novel electronic states that emerge from the uranium f states in URu 2 Si 2. We find that as the temperature is lowered, partial screening of the f electrons' spins gives rise to a spatially modulated Kondo-Fano resonance that is maximal between the surface U atoms. At T=17.5 K, URu 2 Si 2 is known to undergo a 2nd order phase transition from the Kondo lattice state into a phase with a hidden order parameter. From tunneling spectroscopy, we identify a spatially modulated, bias-asymmetric energy gap with a mean-field temperature dependence that develops in the hidden order state. Spectroscopic imaging further reveals a spatial correlation between the hidden order gap and the Kondo resonance, suggesting that the two phenomena involve the same electronic states. We further study the behavior of the Kondo lattice in a model heavy fermion compound CeCoIn 5 as a function of temperature and establish a direct comparison between the two heavy fermion compounds. This work is funded by a DOE-BES grant. Infrastructure at the Princeton Nanoscale Microscopy Laboratory are also supported by grants from NSF-DMR, Keck Foundation, and NSF-MRSEC. PA also acknowledges support of a fellowship through the PCCM funded by NSF MERSEC. Work done in collaboration with Eduardo H. da Silva Neto, Colin V. Parker, Yingkai Huang, Abhay Pasupathy, John Mydosh, Eric Bauer, Paul Tobash, and Ali Yazdani.
High-magnetic-fields thermodynamics of the heavy-fermion metal YbRh2Si2
NASA Astrophysics Data System (ADS)
Shaginyan, V. R.; Popov, K. G.; Stephanovich, V. A.; Fomichev, V. I.; Kirichenko, E. V.
2011-01-01
We perform a comprehensive theoretical analysis of the high-magnetic-field behavior of the heavy-fermion (HF) compound YbRh2Si2. At low magnetic fields B, YbRh2Si2 has a quantum critical point related to the suppression of antiferromagnetic ordering at a critical magnetic field B⊥c of B=Bc0sime0.06 T. Our calculations of the thermodynamic properties of YbRh2Si2 in wide magnetic field range from Bc0sime0.06 T to Bsime18 T allow us to straddle a possible metamagnetic transition region and probe the properties of both low-field HF liquid and high-field fully polarized one. Namely, high magnetic fields B~B*~10 T fully polarize the corresponding quasiparticle band generating a Landau-Fermi-liquid (LFL) state and suppressing the HF (actually NFL) one, while at increasing temperatures both the HF state and the corresponding NFL properties are restored. Our calculations are in good agreement with experimental facts and show that the fermion condensation quantum phase transition is indeed responsible for the observed NFL behavior and quasiparticles survive both high temperatures and high magnetic fields.
Tuning the electronic hybridization in the heavy fermion cage compound YbFe2Zn20 with Cd doping
NASA Astrophysics Data System (ADS)
Cabrera-Baez, M.; Ribeiro, R. A.; Avila, M. A.
2016-09-01
The tuning of the electronic properties of heavy fermion compounds by chemical substitution provides excellent opportunities for further understanding the physics of hybridized ions in crystal lattices. Here we present an investigation on the effects of Cd doping in flux-grown single crystals of the complex intermetallic cage compound YbFe2Zn20, which has been described as a heavy fermion with a Sommerfeld coefficient of 535 mJ mol‑1 · K‑2. The substitution of Cd for Zn disturbs the system by expanding the unit cell and, in this case, the size of the Zn cages that surround the Yb and Fe. With an increasing amount of Cd, the hybridization between the Yb 4f electrons and the conduction electrons is weakened, as shown by a decrease in the Sommerfeld coefficient, which should be accompanied by a valence shift of the Yb3+ due to the negative chemical pressure effect. This scenario is also supported by the low temperature DC magnetic susceptibility, which is gradually suppressed and shows an increment of the Kondo temperature, based on a shift to higher temperatures of the characteristic broad susceptibility peak. Furthermore, the DC resistivity decreases with the isoelectronic substitution of Cd for Zn, contrary to expectations in an increasingly disordered system, and implying that the valence shift is not related to charge carrier doping. The combined results demonstrate the excellent complementarity between positive physical pressure and negative chemical pressure, and point to a rich playground for exploring the physics and chemistry of strongly correlated electron systems in the general family of Zn20 compounds, despite their structural complexity.
Tuning the electronic hybridization in the heavy fermion cage compound YbFe2Zn20 with Cd doping
NASA Astrophysics Data System (ADS)
Cabrera-Baez, M.; Ribeiro, R. A.; Avila, M. A.
2016-09-01
The tuning of the electronic properties of heavy fermion compounds by chemical substitution provides excellent opportunities for further understanding the physics of hybridized ions in crystal lattices. Here we present an investigation on the effects of Cd doping in flux-grown single crystals of the complex intermetallic cage compound YbFe2Zn20, which has been described as a heavy fermion with a Sommerfeld coefficient of 535 mJ mol-1 · K-2. The substitution of Cd for Zn disturbs the system by expanding the unit cell and, in this case, the size of the Zn cages that surround the Yb and Fe. With an increasing amount of Cd, the hybridization between the Yb 4f electrons and the conduction electrons is weakened, as shown by a decrease in the Sommerfeld coefficient, which should be accompanied by a valence shift of the Yb3+ due to the negative chemical pressure effect. This scenario is also supported by the low temperature DC magnetic susceptibility, which is gradually suppressed and shows an increment of the Kondo temperature, based on a shift to higher temperatures of the characteristic broad susceptibility peak. Furthermore, the DC resistivity decreases with the isoelectronic substitution of Cd for Zn, contrary to expectations in an increasingly disordered system, and implying that the valence shift is not related to charge carrier doping. The combined results demonstrate the excellent complementarity between positive physical pressure and negative chemical pressure, and point to a rich playground for exploring the physics and chemistry of strongly correlated electron systems in the general family of Zn20 compounds, despite their structural complexity.
Superconductivity in a heavy fermion system: CeCu2Si2
NASA Astrophysics Data System (ADS)
Kapoor, Charu; Tewari, S. P.
2016-09-01
Electron elementary excitations in certain inter-metallic rare-earth compounds are heavy electrons with physical characteristics completely different from that of metallic electrons. Using this knowledge, superconductivity has been studied exploiting heavy electron-phonon interaction brought about by Kondo volume collapse. Superconducting transition temperature, Tc, has been computed, in particular, for CeCu2Si2 under different values of observed Kondo temperature and Gruneisen parameter. It is found that one can explain the experimental Tc = 0.6 K, which is consistent with the description of heavy electron elementary excitations.
Spin-orbit Coupled Fermi Gases and Heavy Solitons in Fermionic Superfluids
NASA Astrophysics Data System (ADS)
Cheuk, Lawrence
2013-05-01
The coupling of the spin of electrons to their motional state lies at the heart of topological phases of matter. We have created and detected spin-orbit coupling in an atomic Fermi gas via spin-injection spectroscopy, which characterizes the energy-momentum dispersion and spin composition of the quantum states. For energies within the spin-orbit gap, the system acts as a spin diode. To fully inhibit transport, we open an additional spin gap with radio-frequency coupling, thereby creating a spin-orbit coupled lattice whose spinful band structure we probe. In the presence of s-wave interactions, spin-orbit coupled fermion systems should display induced p-wave pairing and consequently topological superfluidity. Such systems can be described by a relativistic Dirac theory with a mass term that can be made to vary spatially. Topologically protected edge states are expected to occur whenever the mass term changes sign. A system that similarly supports edges states is the strongly interacting atomic Fermi gas near a Feshbach resonance. Topological excitations, such as vortices - line defects - or solitons - planar defects - have been described theoretically for decades in many different physical contexts. In superconductivity and superfluidity they represent a defect in the order parameter and give rise to localized bound states. We have created and directly observed solitons in a fermionic superfluid by imprinting a phase step into the superfluid wavefunction. These are found to be stable for many seconds, allowing us to track their oscillatory motion in the trapped superfluid. Their trapping period increases dramatically as the interactions are tuned from the BEC to the BCS regime. At the Feshbach resonance, their period is an order of magnitude larger than expectations from mean-field Bogoliubov-de Gennes theory, signaling strong effects of bosonic quantum fluctuations and possible filling of Andreev bound states. Our work opens the study of fermionic edge states in
Zhu, Jian-xin; Dai, Jianhui; Si, Qimiao
2009-01-01
Some of the high {Tc} iron pnictides contain rare-earth elements, raising the question of how the existence and tunability of a d-electron antiferromagnetic order influences the heavy fermion behavior of the f-moments. With CeOFeP and CeOFeAs in mind as prototypes, we derive an extended Anderson lattice model appropriate for these quaternary systems. We show that the Kondo screening of the f-moments are efficiently suppressed by the d-electron ordering. We also argue that, inside the d-electron ordered state (as in CeOFeAs), the f-moments provide a rare realization of a quantum frustrated magnet with competing J{sub 1}-J{sub 2}-J{sub 3} interactions in an effective square lattice. Implications ofr the heavy fermion physics in broader contexts are also discussed.
NASA Astrophysics Data System (ADS)
Wagman, Jerod; Gaudet, Jonathan; Broholm, Collin; Rodriguez, Jose; Winn, Barry; Graves-Brook, Melissa; Garrett, Jim; Gaulin, Bruce
2015-03-01
We present neutron scattering data identifying a superconducting spin resonance in the heavy fermion, antiferromagnetic superconductor UNi2 Al3 . This resolves a longstanding issue in the comparison of UNi2 Al3 to its isostructural sister UPd2 Al3 . Theses material both undergo antiferromagnetic phase transitions at relatively high temperatures, TN = 4.6 K and 14.5 K respectively, before respectively superconducting below 1.2 and 2 K(B. D. Gaulin, et al, PRB 66, 174520 (2002)). However, previous reports suggest that only the magnetic fluctuations in UPd2 Al3 display sensitivity to superconductivity via a superconducting spin resonance - the build up in the superconducting ground state of excess scattered intensity at a well defined resonance energy centered on a magnetic wave-vector. We resolve this disparity by clearly identifying a superconducting spin resonance in UNi2 Al3 at the incommensurate wavevector Q = (1/2 +/- 0.11 0 1/2). This re-establishes the relationship between these sister compounds and further evidences the intimate correlation of magnetism and superconductivity. NSERC, National Science Foundation, Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE.
High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt
NASA Astrophysics Data System (ADS)
Ueland, B. G.; Saunders, S. M.; Bud'Ko, S. L.; Schmiedeshoff, G. M.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.
YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below T* = 0 . 7 K, fragile antiferromagnetic order below TN = 0 . 4 K, a Kondo temperature of TK ~ 1 K, and crystalline-electric-field splitting (CEF) on the order of E /kB = 1 - 10 K. Its lattice is face-centered cubic at ambient temperature, but certain data, particularly those from studies aimed at determining the CEF level scheme, suggest that the lattice distorts at lower temperature. Here, we present results from high-energy x-ray diffraction experiments which show that, within our experimental resolution of ~ 6 - 10 ×10-5 Å, no structural phase transition occurs between 1 . 5 and 50 K. Despite this result, we demonstrate that the compound's thermal expansion may be modeled using CEF level schemes appropriate for Yb3+ residing on a site with either cubic or less than cubic point symmetry. Work at the Ames Laboratory was supported by the US DOE, BES, DMSE, under Contract No. DE-AC02-07CH11358. Work at Occidental College was supported by the NSF under DMR-1408598. This research used resources at the Advanced Photon Source a US DOE, Office of Science, User Facility.
NASA Astrophysics Data System (ADS)
Dunne, Gerald V.
2006-05-01
This talk reports work done in collaboration with Jin Hur, Choonkyu Lee and Hyunsoo Min concerning the computation of the precise mass dependence of the fermion determinant for quarks in the presence of an instanton background. The result interpolates smoothly between the previously known chiral and heavy quark limits of extreme small and large mass. The computational method makes use of the fact that the single instanton background has radial symmetry, so that the computation can be reduced to a sum over partial waves of logarithms of radial determinants, each of which can be computed numerically in an efficient manner using a theorem of Gelfand and Yaglom. The bare sum over partial waves is divergent and must be regulated and renormalized. We use the angular momentum cutoff regularization and renormalization scheme. Our results provide an extension of the Gelfand-Yaglom result to higher-dimensional separable differential operators. I also comment on the application of this approach to a wide variety of fluctuation determinant computations in quantum field theory.
Scaling behavior of the thermopower of the archetypal heavy-fermion metal YbRh2Si2
NASA Astrophysics Data System (ADS)
Shaginyan, V. R.; Msezane, A. Z.; Japaridze, G. S.; Popov, K. G.; Clark, J. W.; Khodel, V. A.
2016-04-01
We reveal and explain the scaling behavior of the thermopower S/T exhibited by the archetypal heavy-fermion (HF) metal YbRh2Si2 under the application of magnetic field B at temperature T. We show that the same scaling is demonstrated by different HF compounds such as ß-YbAlB4 and the strongly correlated layered cobalt oxide [BiBa0.66K0.36O2]CoO2. Using YbRh2Si2 as an example, we demonstrate that the scaling behavior of S/T is violated at the antiferromagnetic phase transition, while both the residual resistivity ρ 0 and the density of states, N, experience jumps at the phase transition, causing the thermopower to make two jumps and change its sign. Our elucidation is based on flattening of the single-particle spectrum that profoundly affects ρ 0 and N. To depict the main features of the S/T behavior, we construct a T-B schematic phase diagram of YbRh2Si2. Our calculated S/T for the HF compounds are in good agreement with experimental facts and support our observations.
Crossover from a heavy fermion to intermediate valence state in noncentrosymmetric Yb2Ni12(P,As)7
Jiang, W. B.; Yang, L.; Guo, C. Y.; Hu, Z.; Lee, J. M.; Smidman, M.; Wang, Y. F.; Shang, T.; Cheng, Z. W.; Gao, F.; Ishii, H.; Tsuei, K. D.; Liao, Y. F.; Lu, X.; Tjeng, L. H.; Chen, J. M.; Yuan, H. Q.
2015-01-01
We report measurements of the physical properties and electronic structure of the hexagonal compounds Yb2Ni12Pn7 (Pn = P, As) by measuring the electrical resistivity, magnetization, specific heat and partial fluorescence yield x-ray absorption spectroscopy (PFY-XAS). These demonstrate a crossover upon reducing the unit cell volume, from an intermediate valence state in Yb2Ni12As7 to a heavy-fermion paramagnetic state in Yb2Ni12P7, where the Yb is nearly trivalent. Application of pressure to Yb2Ni12P7 suppresses TFL, the temperature below which Fermi liquid behavior is recovered, suggesting the presence of a quantum critical point (QCP) under pressure. However, while there is little change in the Yb valence of Yb2Ni12P7 up to 30 GPa, there is a strong increase for Yb2Ni12As7 under pressure, before a near constant value is reached. These results indicate that any magnetic QCP in this system is well separated from strong valence fluctuations. The pressure dependence of the valence and lattice parameters of Yb2Ni12As7 are compared and at 1 GPa, there is an anomaly in the unit cell volume as well as a change in the slope of the Yb valence, indicating a correlation between structural and electronic changes. PMID:26626431
Goncharov, A; Struzhkin, V V
2003-11-12
During the past years, the Co-PI's have been responsible for the development and operation of optical techniques (Raman, IR, fluorescence, absorption and reflectance spectroscopy at ultrahigh pressures and high and low temperatures) which have proven to be extremely powerful for studying low-Z, molecular solids including hydrogen, ice, etc. (see results below). Meanwhile, it has become increasingly clear that optical spectroscopy has an equally extraordinary potential for studying metals and superconductors at ultrahigh pressures, thus the result will have a major impact on material research. However, because of the extreme difference in optical properties of opaque metals and transparent insulating molecular solids, successful accomplishment of the present project will require substantial effort in improving the present equipment and developing new techniques, and funds for this are requested here. Below we provide a short description of the work done and techniques developed during the last years. We also propose to explore new frontiers in compressed materials close to the insulator-metal boundaries, spin-crossover, and other quantum critical points.
Li NMR study of heavy-fermion LiV2O4 containing magnetic defects
Zong, X.; Das, S.; Borsa, F.; Vannette, M.; Prozorov, R.; Schmalian, J.; Johnston, D.
2008-04-21
We present a systematic study of the variations of the {sup 7}Li NMR properties versus magnetic defect concentration up to 0.83 mol% within the spinel structure of polycrystalline powder samples and a collection of small single crystals of LiV2O4 in the temperature range from 0.5 to 4.2 K. We also report static magnetization measurements and ac magnetic susceptibility measurements at 14 MHz on the samples at low temperatures. Both the NMR spectrum and nuclear spin-lattice relaxation rate are inhomogeneous in the presence of the magnetic defects. The NMR data for the powders are well explained by assuming that (i) there is a random distribution of magnetic point defects, (ii) the same heavy Fermi liquid is present in the samples containing the magnetic defects as in magnetically pure LiV2O4, and (iii) the influences of the magnetic defects and of the Fermi liquid on the magnetization and NMR properties are separable. In the single crystals, somewhat different behaviors are observed. Remarkably, the magnetic defects in the powder samples show evidence of spin freezing below T {approx} 1.0 K, whereas in the single crystals with similar magnetic defect concentration no spin freezing was found down to 0.5 K. Thus different types of magnetic defects and/or interactions between them appear to arise in the powders versus the crystals, possibly due to the substantially different synthesis conditions of the powders and crystals.
NASA Astrophysics Data System (ADS)
Lussier, Jean-Guy
UPt_3, URu_2 Si_2, UNi_2 Al_3 and UPd_2 Al_3 form a special group among the uranium alloys because they exhibit heavy fermion character, magnetic order and superconductivity. This main interest in the study of this group of compounds resides in the simultaneous occurrence of magnetism and superconductivity at low temperature. Such a state could potentially involve an unconventional superconducting pairing mechanism, different from that contained in standard BCS theory. In this thesis, the magnetic states of three of these materials (URu_2Si _2, UNi_2Al _3 and UPd_2Al _3) is investigated with neutron and the relatively new resonant magnetic X-ray scattering techniques. The work presented here on URu_2Si _2 follows an earlier effort that demonstrated the applicabililty of the resonant X-ray technique to this weak magnetic system. Access to reciprocal space was extended in order to confirm the multipolar form of the resonant X-ray cross-section and to explore the limits of the technique compared to neutron scattering. The situation with the newly discovered UNi_2Al _3 and UPd_2Al _3 was different since their magnetic structure and phases needed first to be established. This task was achieved using two magnetic probes (neutron and X-ray scattering). Several magnetic order parameters in the normal and in the superconducting phase were also measured. The incommensurate magnetic order found in UNi_2Al_3 by neutron scattering constitutes the first observation of long range order in this compound. Other measurements on this compound provided some clues about the evolution of the magnetic structure in high magnetic fields.
NASA Astrophysics Data System (ADS)
Lussier, J. G.; Mao, M.; Schröder, A.; Garrett, J. D.; Gaulin, B. D.; Shapiro, S. M.; Buyers, W. J. L.
1997-11-01
Elastic neutron scattering from a single-crystal sample of the heavy-fermion superconductor UNi2Al3 has revealed the onset of long-range magnetic order below TN=4.6 K. This order is characterized by an incommensurate (IC) ordering wave vector given by (12+/-τ, 0, 12) with τ=0.11+/-0.003. The intensity of several magnetic satellite Bragg peaks within the (h,0,l) plane is well described by a model in which the spins lie within the basal plane and are modulated in amplitude from site to site. By applying a magnetic field to select from all the possible domains, we find that the moment is polarized along the a direction, with a maximum amplitude of 0.21+/-0.1μB per uranium atom. The order-parameter exponent β associated with this transition is 0.34+/-.03, which is typical of three-dimensional ordering transitions. Measurements down to ~0.3 K show that the magnetic order coexists with superconductivity below TC~1.2 K, and that these states are coupled as shown by anomalous behavior of the magnetic order parameter around TC. Measurements were also made in magnetic fields of up to 8 T applied perpendicular to the (h,0,l) plane, along (-1,1,0), a near-neighbor direction within the hexagonal basal plane. While the field does not influence TN, it does increase the intensity of the magnetic Bragg peaks by a factor of ~1.5, as well as increase the IC part of the ordering wave vector at low temperatures.
High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt
Ueland, B. G.; Saunders, S. M.; Bud'ko, S. L.; Schmiedeshoff, G. M.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.
2015-11-30
In this study, YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of T*=0.7K, fragile antiferromagnetic order below T_{N} = 0.4K, a Kondo temperature of T_{K} ≈ 1K, and crystalline-electric-field splitting on the order of E/k_{B} = 1 – 10K. Whereas the compound has a face-centered-cubic lattice at ambient temperature, certain experimental data, particularly those from studies aimed at determining its crystalline-electric-field scheme, suggest that the lattice distorts at lower temperature. Here, we present results from high-resolution, high-energy x-ray diffraction experiments which show that, within our experimental resolution of ≈ 6 – 10 × 10^{–5} Å, no structural phase transition occurs between T = 1.5 and 50 K. In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at ≈ 18 K and a region of negative thermal expansion for 9 ≲ T ≲ 18 K. Despite diffraction patterns taken at 1.6 K which indicate that the lattice is face-centered cubic and that the Yb resides on a crystallographic site with cubic point symmetry, we demonstrate that the linear thermal expansion may be modeled using crystalline-electric-field level schemes appropriate for Yb^{3+} residing on a site with either cubic or less than cubic point symmetry.
Crystal-field states of Kondo lattice heavy fermions CeRuSn3 and CeRhSn3
NASA Astrophysics Data System (ADS)
Anand, V. K.; Adroja, D. T.; Britz, D.; Strydom, A. M.; Taylor, J. W.; Kockelmann, W.
2016-07-01
Inelastic neutron scattering experiments have been carried out to determine the crystal-field states of the Kondo lattice heavy fermions CeRuSn3 and CeRhSn3. Both the compounds crystallize in LaRuSn3-type cubic structure (space group P m 3 ¯n ) in which the Ce atoms occupy two distinct crystallographic sites with cubic (m 3 ¯ ) and tetragonal (4 ¯m .2 ) point symmetries. The INS data of CeRuSn3 reveal the presence of a broad excitation centered around 6-8 meV, which is accounted by a model based on crystal electric field (CEF) excitations. On the other hand, the INS data of isostructural CeRhSn3 reveal three CEF excitations around 7.0, 12.2, and 37.2 meV. The neutron intensity sum rule indicates that the Ce ions at both cubic and tetragonal Ce sites are in Ce3 + state in both CeRuSn3 and CeRhSn3. The CEF level schemes for both the compounds are deduced. We estimate the Kondo temperature TK=3.1 (2 ) K for CeRuSn3 from neutron quasielastic linewidth in excellent agreement with that determined from the scaling of magnetoresistance which gives TK=3.2 (1 ) K. For CeRhSn3, the neutron quasielastic linewidth gives TK≈4.6 K. For both CeRuSn3 and CeRhSn3, the ground state of Ce3 + turns out to be a quartet for the cubic site and a doublet for the tetragonal site.
Quantum Critical Behavior in Heavy-Fermion Iron Oxypnictide Ce(Ru1-xFex) PO
NASA Astrophysics Data System (ADS)
Ishida, Kenji
2014-03-01
Quantum phase transition in itinerant ferromagnets is one of the major topics in a strongly correlated electron system, since it has been suggested to be always first order when the ferromagnetic (FM) order is suppressed by pressure or chemical doping. In order to obtain universal features of the FM quantum criticality, we have studied the two-dimensional heavy-fermion (HF) system Ce(Ru1-xFex) PO from microscopic 31P-NMR measurements. A HF ferromagnet CeRuPO turns into a HF paramagnet by an isovalent Fe substitution for Ru. We found that Ce(Ru0.15Fe0.85) PO shows critical fluctuations down to ~ 0.3 K, as well as the continuous suppression of Curie temperature and the ordered moments by the Fe substitution. These experimental results suggest the presence of a FM quantum critical point (QCP) at around x = 0.86, which is a rare example among itinerant ferromagnets. In addition, we point out that the critical behaviors in Ce(Ru0.15Fe0.85) PO share a similarity with those in YbRh2Si2, where the local criticality of f electrons has been discussed. We reveal that Ce(Ru1-xFex) PO is a new system to study FM quantum criticality in HF compound. This work has been done in collaboration with Shunsaku Kitagawa in Kyoto Univ. and T, Nakamura, M. Matoba, and Y. Kamihara, in Department of Applied Physics and Physico-informatics, Keio University.
High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt
Ueland, B. G.; Iowa State Univ., Ames, IA; Saunders, S. M.; Iowa State Univ., Ames, IA; Bud'ko, S. L.; Iowa State Univ., Ames, IA; Schmiedeshoff, G. M.; Canfield, P. C.; Iowa State Univ., Ames, IA; Kreyssig, A.; et al
2015-11-30
In this study, YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of T*=0.7K, fragile antiferromagnetic order below TN = 0.4K, a Kondo temperature of TK ≈ 1K, and crystalline-electric-field splitting on the order of E/kB = 1 – 10K. Whereas the compound has a face-centered-cubic lattice at ambient temperature, certain experimental data, particularly those from studies aimed at determining its crystalline-electric-field scheme, suggest that the lattice distorts at lower temperature. Here, we present results from high-resolution, high-energy x-ray diffraction experiments which show that, within our experimental resolution of ≈ 6 – 10 × 10–5 Å,more » no structural phase transition occurs between T = 1.5 and 50 K. In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at ≈ 18 K and a region of negative thermal expansion for 9 ≲ T ≲ 18 K. Despite diffraction patterns taken at 1.6 K which indicate that the lattice is face-centered cubic and that the Yb resides on a crystallographic site with cubic point symmetry, we demonstrate that the linear thermal expansion may be modeled using crystalline-electric-field level schemes appropriate for Yb3+ residing on a site with either cubic or less than cubic point symmetry.« less
Fermion damping in a fermion-scalar plasma
Boyanovsky, D.; Wang, S.; de Vega, H.J.; Lee, D.; Ng, Y.J.
1999-05-01
In this article we study the dynamics of fermions in a fermion-scalar plasma. We begin by obtaining the effective in-medium Dirac equation in real time which is fully renormalized and causal and leads to the initial value problem. For a heavy scalar we find the novel result that the {ital decay} of the scalar into fermion pairs in the medium leads to damping of the fermionic excitations and their in-medium propagation as quasiparticles. That is, the fermions acquire a width due to the decay of the heavier scalar in the medium. We find the damping rate to lowest order in the Yukawa coupling for arbitrary values of scalar and fermion masses, temperature and fermion momentum. An all-order expression for the damping rate in terms of the exact quasiparticle wave functions is established. A kinetic Boltzmann approach to the relaxation of the fermionic distribution function confirms the damping of fermionic excitations as a consequence of the induced decay of heavy scalars in the medium. A linearization of the Boltzmann equation near equilibrium clearly displays the relationship between the damping rate of fermionic mean fields and the fermion interaction rate to lowest order in the Yukawa coupling directly in real time. {copyright} {ital 1999} {ital The American Physical Society}
Christianson, Andrew D; Goremychkin, E. A.; Gardner, J. S.; Kang, H. J.; Chung, J.-H.; Manuel, P.; Thompson, J. D.; Sarrao, J. L.; Lawrence, J. M.
2008-01-01
The specific heat of Ce3Co4Sn13 exhibits a crossover from heavy Fermion behavior with antiferromagnetic correlations at low field to single impurity Kondo behavior above 2 T. We have performed neutron diffraction measurements in magnetic fields up to 6 Tesla on single crystal samples. The (001) position shows a dramatic increase in intensity in field which appears to arise from static polarization of the 4f level and which at 0.14 K also exhibits an anomaly near 2T reflecting the crossover to single impurity behavior.
FT-IR Spectra of Antifreeze Glycoproteins in Heavy Water and D2O Ice.
NASA Astrophysics Data System (ADS)
Tsvetkova, N. M.; Crowe, J. H.; Feeney, R. H.; Fink, W. H.; Yeh, Yin
2000-03-01
This work presents FT-IR studies on the antifreeze glycoprotein (AFGP)/heavy water (D2O) mixtures during freezing and melting. AFGP in the blood serum of polar fish are known to prevent ice crystal growth by a non-colligative mechanism. There are 8 known fractions of AFGP (1 8) that range in molecular mass from 33.7 to 2.6 kD respectively, each composed of alanine-alanine-threonine repeats, with a disaccharide attached to the threonine residue. The smallest peptide (AFGP-8) is structurally different from fractions 1-5 in that it contains proline substituting for alanine in certain positions. Substantial linewidth change of the D20 bending mode (ca. 1210 cm-1) was measured with solutions containing fractions 2-5 during both freezing and thawing cycles, suggesting significant coupling between protein and water molecules. At the same time, the Amide I band between 1620 and 1675 cm-1 shows that 310 helix and random coils are the main conformations of fractions 2-5 and fraction 8 in the presence of ice. In liquid state, b-sheet dominates the secondary structure of AFGP 8, whereas b-sheet and random coil are the main conformations of AFGP 2-5. These results are discussed in terms of the ability of AFGP 2-5 to affect the surface states of ice.
Song, Yu; Van Dyke, John; Lum, I. K.; White, B. D.; Jang, Sooyoung; Yazici, Duygu; Shu, L.; Schneidewind, A.; Čermák, Petr; Qiu, Y.; Maple, M. B.; Morr, Dirk K.; Dai, Pengcheng
2016-01-01
The neutron spin resonance is a collective magnetic excitation that appears in the unconventional copper oxide, iron pnictide and heavy fermion superconductors. Although the resonance is commonly associated with a spin-exciton due to the d(s±)-wave symmetry of the superconducting order parameter, it has also been proposed to be a magnon-like excitation appearing in the superconducting state. Here we use inelastic neutron scattering to demonstrate that the resonance in the heavy fermion superconductor Ce1−xYbxCoIn5 with x=0, 0.05 and 0.3 has a ring-like upward dispersion that is robust against Yb-doping. By comparing our experimental data with a random phase approximation calculation using the electronic structure and the momentum dependence of the -wave superconducting gap determined from scanning tunnelling microscopy (STM) for CeCoIn5, we conclude that the robust upward-dispersing resonance mode in Ce1−xYbxCoIn5 is inconsistent with the downward dispersion predicted within the spin-exciton scenario. PMID:27677397
Characterization of the heavy metal pyrochlore lattice superconductor CaIr2.
Haldolaarachchige, Neel; Gibson, Quinn; Schoop, Leslie M; Luo, Huixia; Cava, R J
2015-05-13
We report the electronic properties of the cubic laves phase superconductor CaIr2(Tc = 5.8 K), in which the Ir atoms have a pyrochlore lattice. The estimated superconducting parameters obtained from magnetization and specific heat measurements indicate that CaIr2 is a weakly coupled BCS superconductor. Electronic band structure calculations show that the Ir d-states are dominant at the Fermi level, creating a complex Fermi surface that is impacted substantially by spin-orbit coupling.
NASA Astrophysics Data System (ADS)
Xing, Guangxi; Zhu, Jianguo; Xiong, Zhengqin; Yamasaki, Shin-Ichi
2004-03-01
No observation has so far been reported that heavy metal elements from atmospheric deposition were accumulated widely in the surface soil layers. In this research, 28 soil profiles from different climate zones and agro-ecosystems in China were studied, and obvious enrichment of Ag, Ta, Ru, and Ir in the surface soils was discovered. It indicates that pollution of heavy metals emitted into the atmosphere from industrial activities is no longer limited to soils in the vicinity of power, metallurgic, metalworking, and machine-making industries, and they may settle down extensively on land besides cities and industrial regions.
Lopez-Aguilar, F.; Balle, S.; Costa-Quintana, J.
1988-07-01
A self-energy approximation is applied for obtaining the electronic structure of these two superconducting heavy-fermion systems and we explain some of their main experimental features by analyzing the calculated total and partial density of states. The superconducting mechanism is discussed and we determine relations between the density of states and the superconducting parameters.
NASA Astrophysics Data System (ADS)
Shaginyan, V. R.; Msezane, A. Z.; Popov, K. G.; Clark, J. W.; Khodel, V. A.; Zverev, M. V.
2016-05-01
Informative recent measurements on the heavy-fermion metal β -YbAlB4 performed with applied magnetic field and pressure as control parameters are analyzed with the goal of establishing a sound theoretical explanation for the inferred scaling laws and non-Fermi-liquid (NFL) behavior, which demonstrate some unexpected features. Most notably, the robustness of the NFL behavior of the thermodynamic properties and of the anomalous T3 /2 temperature dependence of the electrical resistivity under applied pressure P in zero magnetic field is at variance with the fragility of the NFL phase under application of a field B . We show that a consistent topological basis for this combination of observations, as well as the empirical scaling laws, may be found within fermion-condensation theory in the emergence and destruction of a flat band, and explains that the paramagnetic NFL phase takes place without magnetic criticality, not from quantum critical fluctuations. Schematic T -B and T -P phase diagrams are presented to illuminate this scenario.
Howald, Ludovic; Stilp, Evelyn; de Réotier, Pierre Dalmas; Yaouanc, Alain; Raymond, Stéphane; Piamonteze, Cinthia; Lapertot, Gérard; Baines, Christopher; Keller, Hugo
2015-07-30
In the generic phase diagram of heavy fermion systems, tuning an external parameter such as hydrostatic or chemical pressure modifies the superconducting transition temperature. The superconducting phase forms a dome in the temperature-tuning parameter phase diagram, which is associated with a maximum of the superconducting pairing interaction. Proximity to antiferromagnetism suggests a relation between the disappearance of antiferromagnetic order and superconductivity. We combine muon spin rotation, neutron scattering, and x-ray absorption spectroscopy techniques to gain access to the magnetic and electronic structure of CeCo(In(1-x)Cdx)5 at different time scales. Different magnetic structures are obtained that indicate a magnetic order of itinerant character, coexisting with bulk superconductivity. The suppression of the antiferromagnetic order appears to be driven by a modification of the bandwidth/carrier concentration, implying that the electronic structure and consequently the interplay of superconductivity and magnetism is strongly affected by hydrostatic and chemical pressure.
Howald, Ludovic; Stilp, Evelyn; de Réotier, Pierre Dalmas; Yaouanc, Alain; Raymond, Stéphane; Piamonteze, Cinthia; Lapertot, Gérard; Baines, Christopher; Keller, Hugo
2015-01-01
In the generic phase diagram of heavy fermion systems, tuning an external parameter such as hydrostatic or chemical pressure modifies the superconducting transition temperature. The superconducting phase forms a dome in the temperature—tuning parameter phase diagram, which is associated with a maximum of the superconducting pairing interaction. Proximity to antiferromagnetism suggests a relation between the disappearance of antiferromagnetic order and superconductivity. We combine muon spin rotation, neutron scattering, and x-ray absorption spectroscopy techniques to gain access to the magnetic and electronic structure of CeCo(In1−xCdx)5 at different time scales. Different magnetic structures are obtained that indicate a magnetic order of itinerant character, coexisting with bulk superconductivity. The suppression of the antiferromagnetic order appears to be driven by a modification of the bandwidth/carrier concentration, implying that the electronic structure and consequently the interplay of superconductivity and magnetism is strongly affected by hydrostatic and chemical pressure. PMID:26224422
NASA Astrophysics Data System (ADS)
Martiny, Johannes H. J.; Gastiasoro, Maria N.; Vekhter, I.; Andersen, Brian M.
2015-12-01
We investigate the properties of the coexistence phase of itinerant antiferromagnetism and nodal d -wave superconductivity (Q phase) discovered in heavy-fermion CeCoIn5 under applied magnetic field. We solve the minimal model that includes d -wave superconductivity and underlying magnetic correlations in real space to elucidate the structure of the Q phase in the presence of an externally applied magnetic field. We further focus on the role of magnetic impurities, and show that they nucleate the Q phase at lower magnetic fields. Our most crucial finding is that, even at zero applied field, dilute magnetic impurities cooperate via RKKY-like exchange interactions to generate a long-range ordered coexistence state identical to the Q phase. This result is in agreement with recent neutron scattering measurements [S. Raymond et al., J. Phys. Soc. Jpn. 83, 013707 (2014), 10.7566/JPSJ.83.013707].
Howald, Ludovic; Stilp, Evelyn; de Réotier, Pierre Dalmas; Yaouanc, Alain; Raymond, Stéphane; Piamonteze, Cinthia; Lapertot, Gérard; Baines, Christopher; Keller, Hugo
2015-01-01
In the generic phase diagram of heavy fermion systems, tuning an external parameter such as hydrostatic or chemical pressure modifies the superconducting transition temperature. The superconducting phase forms a dome in the temperature-tuning parameter phase diagram, which is associated with a maximum of the superconducting pairing interaction. Proximity to antiferromagnetism suggests a relation between the disappearance of antiferromagnetic order and superconductivity. We combine muon spin rotation, neutron scattering, and x-ray absorption spectroscopy techniques to gain access to the magnetic and electronic structure of CeCo(In(1-x)Cdx)5 at different time scales. Different magnetic structures are obtained that indicate a magnetic order of itinerant character, coexisting with bulk superconductivity. The suppression of the antiferromagnetic order appears to be driven by a modification of the bandwidth/carrier concentration, implying that the electronic structure and consequently the interplay of superconductivity and magnetism is strongly affected by hydrostatic and chemical pressure. PMID:26224422
NASA Astrophysics Data System (ADS)
Yano, K.; Nishimura, K.; Ohta, T.; Sato, K.
2012-12-01
Small amounts of Ce were substituted by Gd and the (Ce-Gd)Ni heavy fermion compounds were investigated in detail from viewpoint of magnetism in Gd-poor region between 3 at% and 20 at%. Magnetizations showed peculiar linear relationship as a function temperature and were sensitive to the applied magnetic field in common. These characteristic natures were analyzes employing molecular field analysis by changing three exchange interaction energies, JGd-Gd, JGd-Ni and JNi-Ni. The unique solution for the linear relationship in the temperature dependence of magnetization M(T) was found to be attributed to the collapselike decrease of JGd-Gd and the decrease of JGd-Gd can explain the sensitivity to applied magnetic field. However this peculiar decrease of JGd-Gd did not effect on the inverse susceptibilities above the Curie temperatures and the χ-1(T) behaved normally as ferri-magnet.
CeCu sub 4 A ell and CeCu sub 2 Zn sub 2 A ell : Very heavy fermion systems in high magnetic fields
Andraka, B.; Kim, J.S. . Dept. of Physics); Stewart, G.R. . Dept. of Physics Augsburg Univ. ); Fisk, Z. )
1990-01-01
CeCu{sub 4}A{ell} and CeCu{sub 2}Zn{sub 2}A{ell} are heavy fermion systems with extremely enhanced C/T (specific heat divided by temperature) values of 2.3 and 1.8 J/K{sup 2} respectively as T {yields} 0 K. The field dependence of the low temperature specific heat is also extreme; 11 T reduces C of CeCu{sub 4}A{ell} by more than a factor of five, 12.5 T suppresses C of CeCu{sub 2}Zn{sub 2}A{ell} about seven times. Magnetic field caused changes of the specific heat of CeCu{sub 4}A{ell} are consistent with a single ion Kondo model. Magnetic correlations are at least partially responsible for the enhanced low temperature specific heat of CeCu{sub 2}Zn{sub 2}A{ell}.
Adaptive sequential algorithms for detecting targets in a heavy IR clutter
NASA Astrophysics Data System (ADS)
Tartakovsky, Alexander G.; Kligys, Skirmantas; Petrov, Anton
1999-10-01
Cruise missiles over land and sea cluttered background are serious threats to search and track systems. In general, these threats are stealth in both the IR and radio frequency bands. That is, their thermal IR signature and their radar cross section can be quite small. This paper discusses adaptive sequential detection methods which exploit 'track- before-detect' technology for detection glow-SNR targets in IR search and track (IRST) systems. Despite the fact that we focus on an IRST against cruise missiles over land and sea cluttered backgrounds, the results are applicable to other sensors and other kinds of targets.
Fermion production during and after axion inflation
Adshead, Peter; Sfakianakis, Evangelos I.
2015-11-11
We study derivatively coupled fermions in axion-driven inflation, specifically m{sub ϕ}{sup 2}ϕ{sup 2} and monodromy inflation, and calculate particle production during the inflationary epoch and the post-inflationary axion oscillations. During inflation, the rolling axion acts as an effective chemical potential for helicity which biases the gravitational production of one fermion helicity over the other. This mechanism allows for efficient gravitational production of heavy fermion states that would otherwise be highly suppressed. Following inflation, the axion oscillates and fermions with both helicities are produced as the effective frequency of the fermion field changes non-adiabatically. For certain values of the fermion mass and axion-fermion coupling strength, the two helicity states are produced asymmetrically, resulting in unequal number-densities of left- and right-helicity fermions.
Heavy-impurity resonance, hybridization, and phonon spectral functions in Fe1-xMxSi (M =Ir , Os )
NASA Astrophysics Data System (ADS)
Delaire, O.; Al-Qasir, I. I.; May, A. F.; Li, C. W.; Sales, B. C.; Niedziela, J. L.; Ma, J.; Matsuda, M.; Abernathy, D. L.; Berlijn, T.
2015-03-01
The vibrational behavior of heavy substitutional impurities (M = Ir,Os) in Fe1-xMxSi (x =0 ,0.02 ,0.04 ,0.1 ) was investigated with a combination of inelastic neutron scattering (INS), transport measurements, and first-principles simulations. Our INS measurements on single crystals mapped the four-dimensional dynamical structure factor, S (Q ,E ) , for several compositions and temperatures. Our results show that both Ir and Os impurities lead to the formation of a weakly dispersive resonance vibrational mode, in the energy range of the acoustic phonon dispersions of the FeSi host. We also show that Ir doping, which introduces free carriers, leads to softened interatomic force constants compared to doping with Os, which is isoelectronic to Fe. We analyze the phonon S (Q ,E ) from INS through a Green's-function model incorporating the phonon self-energy based on first-principles density functional theory simulations, and we study the disorder-induced lifetimes on large supercells. Calculations of the quasiparticle spectral functions in the doped system reveal the hybridization between the resonance and the acoustic phonon modes. Our results demonstrate a strong interaction of the host acoustic dispersions with the resonance mode, likely leading to the large observed suppression in lattice thermal conductivity.
Heavy-impurity resonance, hybridization, and phonon spectral functions in Fe1-xMxSi, M=Ir,Os
Delaire, O.; Al-Qasir, Iyad I.; May, Andrew F.; Sales, Brian C.; Niedziela, Jennifer L.; Ma, Jie; Matsuda, Masaaki; Abernathy, Douglas L.; Berlijn, Tom
2015-03-31
The vibrational behavior of heavy substitutional impurities (M=Ir,Os) in Fe1-xMxSi (x = 0, 0.02, 0.04, 0.1) was investigated with a combination of inelastic neutron scattering (INS), transport measurements, and first-principles simulations. In this paper, our INS measurements on single-crystals mapped the four-dimensional dynamical structure factor, S(Q;E), for several compositions and temperatures. Our results show that both Ir and Os impurities lead to the formation of a weakly dispersive resonance vibrational mode, in the energy range of the acoustic phonon dispersions of the FeSi host. We also show that Ir doping, which introduces free carriers and increases electron-phonon coupling, leads tomore » softened interatomic force-constants compared to doping with Os, which is isoelectronic to Fe. We analyze the phonon S(Q,E) from INS through a Green's function model incorporating the phonon self-energy based on first-principles density functional theory (DFT) simulations. Calculations of the quasiparticle spectral functions in the doped system reveal the hybridization between the resonance and the acoustic phonon modes. Finally, our results demonstrate a strong interaction of the host acoustic dispersions with the resonance mode, likely leading to the large observed suppression in lattice thermal conductivity.« less
NASA Astrophysics Data System (ADS)
Nishiyama, Shinya; Matsuura, Hiroyasu; Miyake, Kazumasa
2010-10-01
In f2-based heavy fermion systems with a crystalline-electric-field (CEF) singlet ground state, the non-Fermi liquid (NFL) arises around the quantum critical point (QCP) due to the competition between the CEF singlet and the Kondo-Yosida singlet states. In such a case, the characteristic temperature TF* at which the entropy starts to decrease toward zero is suppressed by the effect of the competition, compared to both energy scales characterizing each singlet state, the lower Kondo temperature (TK2) and the CEF splitting (Δ). We show that in the case of tetragonal symmetry TF* is not affected by the magnetic field up to Hz* which is determined by the distance from the QCP or characteristic energy scales of each singlet states, not by TF* itself. As a result, in the vicinity of QCP, there are parameter regions where the NFL is robust against the magnetic field, at an observable temperature range T > TF*, up to Hz* which is far larger than TF* and less than \\min(TK2,Δ). Our result suggests that such an anomalous NFL behavior can arise also in systems with other CEF symmetry, which might provide us with the basis to understand the anomalous behaviors of UBe13.
Norman, M.R.; Koelling, D.D.
1985-05-01
The materials CeSn/sub 3/, USn/sub 3/, and NpSn/sub 3/ are all moderately heavy Fermion compounds with electronic specific heat coefficients of 73, 169, and 242 mJ/mole K/sup 2/. CeSn/sub 3/ is known as a mixed valent system and NpSn/sub 3/ is a weak itinerant antiferromagnet. All three are strongly enhanced. Being in the relatively simple Au/sub 3/Cu structure, they form an excellent set of materials to study as representatives of strongly enhanced systems. One would like to ascertain what properties can be determined from band calculations based on density functional theory in the local density approximation. It has already been shown that the Fermi surface topology of CeSn/sub 3/ can be well described in this way even though the experimental masses are much larger than the band results. The enhancement factor for USn/sub 3/ is even larger and NpSN/sub 3/ is indeed predicted to go magnetic. We present here fully relativistic SCF calculations for these materials and discuss the relation between our results and what is known experimentally.
Multipolar phases and magnetically hidden order: review of the heavy-fermion compound Ce1‑x La x B6
NASA Astrophysics Data System (ADS)
Cameron, Alistair S.; Friemel, Gerd; Inosov, Dmytro S.
2016-06-01
Cerium hexaboride is a cubic f-electron heavy-fermion compound that displays a rich array of low-temperature magnetic ordering phenomena which have been the subject of investigation for more than 50 years. Its complex behaviour is the result of competing interactions, with both itinerant and local electrons playing important roles. Investigating this material has proven to be a substantial challenge, in particular because of the appearance of a ‘magnetically hidden order’ phase, which remained elusive to neutron-scattering investigations for many years. It was not until the development of modern x-ray scattering techniques that the long suspected multipolar origin of this phase was confirmed. Doping with non-magnetic lanthanum dilutes the magnetic cerium sublattice and reduces the f-electron count, bringing about substantial changes to the ground state with the emergence of new phases and quantum critical phenomena. To this day, Ce1‑x La x B6 and its related compounds remain a subject of intense interest. Despite the substantial progress in understanding their behaviour, they continue to reveal new and unexplained physical phenomena. Here we present a review of the accumulated body of knowledge on this family of materials in order to provide a firm standpoint for future investigations.
Jiang, Rui; Mou, Daixing; Liu, Chang; Zhao, Xin; Yao, Yongxin; Ryu, Hyejin; Petrovic, C.; Ho, Kai -Ming; Kaminski, Adam
2015-04-01
We use angle-resolved photoemission spectroscopy (ARPES) to study the 2D heavy fermion superconductor, Ce₂RhIn₈. The Fermi surface is rather complicated and consists of several hole and electron pockets with one of the sheets displaying strong nesting properties with a q-vector of (0.32, 0.32) π/a. We do not observe kz dispersion of the Fermi sheets, which is consistent with the expected 2D character of the electronic structure. Comparison of the ARPES data to band structure calculations suggests that a localized picture of the f-electrons works best. While there is some agreement in the overall band dispersion and location of the Fermimore » sheets, the model does not reproduce all observed bands and is not completely accurate for those it does. As a result, our data paves the way for improving the band structure calculations and the general understanding of the transport and thermodynamical properties of this material.« less
NASA Astrophysics Data System (ADS)
Lu, Haiyan; Huang, Li
2016-08-01
The localized-itinerant nature of Ce -4 f valence electrons in heavy fermion compound CeIn3 under pressure is studied thoroughly by means of the combination of density functional theory and single-site dynamical mean-field theory. The detailed evolutions of electronic structures of CeIn3, including total and partial density of states, momentum-resolved spectral functions, and valence state histograms, are calculated in a wide pressure range where the corresponding volume compression V /V0∈[0.6 ,1.0 ] (here V0 is the experimental crystal volume) at T ≅116 K. Upon increasing pressure, two strong peaks associated with the Ce -4 f states emerge near the Fermi level, and the c -f hybridization and valence state fluctuation are enhanced remarkably. Moreover, the kinetic and potential energies rise, while the occupancy, total angular momentum, and low-energy scattering rate of the Ce -4 f electrons decline with respect to pressure. All the physical observables considered here exhibit prominent kinks or fluctuations in V /V0∈[0.80 ,0.90 ] , which are probably the desired fingerprints for the Ce -4 f localized-itinerant crossover.
Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2
Wang, C. H.; Poudel, L.; Taylor, Alice E.; Lawrence, J M.; Christianson, Andrew D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, Andrey A.; Ehlers, G.; et al
2014-12-03
Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to research the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. In addition, despite the factmore » that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. In conclusion, we suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.« less
NASA Astrophysics Data System (ADS)
Kittaka, Shunichiro; Aoki, Yuya; Shimura, Yasuyuki; Sakakibara, Toshiro; Seiro, Silvia; Geibel, Christoph; Steglich, Frank; Tsutsumi, Yasumasa; Ikeda, Hiroaki; Machida, Kazushige
2016-08-01
This paper presents the results of specific-heat and magnetization measurements, in particular their field-orientation dependence, on the first discovered heavy-fermion superconductor CeCu2Si2 (Tc˜0.6 K). We discuss the superconducting gap structure and the origin of the anomalous pair-breaking phenomena, leading, e.g., to the suppression of the upper critical field Hc 2, found in the high-field region. The data show that the anomalous pair breaking becomes prominent below about 0.15 K in any field direction, but occurs closer to Hc 2 for H ∥c . The presence of this anomaly is confirmed by the fact that the specific-heat and magnetization data satisfy standard thermodynamic relations. Concerning the gap structure, field-angle dependencies of the low-temperature specific heat within the a b and a c planes do not show any evidence for gap nodes. From microscopic calculations in the framework of a two-band full-gap model, the power-law-like temperature dependencies of C and 1 /T1 , reminiscent of nodal superconductivity, have been reproduced reasonably. These facts further support multiband full-gap superconductivity in CeCu2Si2 .
NASA Astrophysics Data System (ADS)
Javarone, Marco Alberto
2016-08-01
We study the structure of fermionic networks, i.e. a model of networks based on the behavior of fermionic gases, and we analyze dynamical processes over them. In this model, particle dynamics have been mapped to the domain of networks, hence a parameter representing the temperature controls the evolution of the system. In doing so, it is possible to generate adaptive networks, i.e. networks whose structure varies over time. As shown in previous works, networks generated by quantum statistics can undergo critical phenomena as phase transitions and, moreover, they can be considered as thermodynamic systems. In this study, we analyze fermionic networks and opinion dynamics processes over them, framing this network model as a computational model useful to represent complex and adaptive systems. Results highlight that a strong relation holds between the gas temperature and the structure of the achieved networks. Notably, both the degree distribution and the assortativity vary as the temperature varies, hence we can state that fermionic networks behave as adaptive networks. On the other hand, it is worth to highlight that we did not finding relation between outcomes of opinion dynamics processes and the gas temperature. Therefore, although the latter plays a fundamental role in gas dynamics, on the network domain, its importance is related only to structural properties of fermionic networks.
PM-GCD - a combined IR-MW satellite technique for frequent retrieval of heavy precipitation
NASA Astrophysics Data System (ADS)
Casella, D.; Dietrich, S.; di Paola, F.; Formenton, M.; Mugnai, A.; Porcù, F.; Sanò, P.
2012-01-01
Precipitation retrievals based on measurements from microwave (MW) radiometers onboard low-Earth-orbit (LEO) satellites can reach high level of accuracy - especially regarding convective precipitation. At the present stage though, these observations cannot provide satisfactory coverage of the evolution of intense and rapid precipitating systems. As a result, the obtained precipitation retrievals are often of limited use for many important applications - especially in supporting authorities for flood alerts and weather warnings. To tackle this problem, over the past two decades several techniques have been developed combining accurate MW estimates with frequent infrared (IR) observations from geosynchronous (GEO) satellites, such as the European Meteosat Second Generation (MSG). In this framework, we have developed a new fast and simple precipitation retrieval technique which we call Passive Microwave - Global Convective Diagnostic, (PM-GCD). This method uses MW retrievals in conjunction with the Global Convective Diagnostic (GCD) technique which discriminates deep convective clouds based on the difference between the MSG water vapor (6.2 μm) and thermal-IR (10.8 μm) channels. Specifically, MSG observations and the GCD technique are used to identify deep convective areas. These areas are then calibrated using MW precipitation estimates based on observations from the Advanced Microwave Sounding Unit (AMSU) radiometers onboard operational NOAA and Eumetsat satellites, and then finally propagated in time with a simple tracking algorithm. In this paper, we describe the PM-GCD technique, analyzing its results for a case study that refers to a flood event that struck the island of Sicily in southern Italy on 1-2 October 2009.
Improved IR detectors to swap heavy systems for SWaP
NASA Astrophysics Data System (ADS)
Manissadjian, Alain; Rubaldo, Laurent; Rebeil, Yann; Kerlain, Alexandre; Brellier, Delphine; Mollard, Laurent
2012-06-01
Cooled IR technologies are challenged for answering new system needs like the compactness and the reduction of cryopower which is a key feature for the SWaP (Size, Weight and Power) requirements. Over the last years, SOFRADIR has improved its HgCdTe technology, with effect on dark current reduction, opening the way for High Operating Temperature (HOT) systems that can get rid of the 80K temperature constraint, and therefore releases the Stirling cooler engine power consumption. Performances of the 640×512 15μm pitch LW detector working above 100K will be presented. A compact 640×512 15μm pitch MW detector presenting high EO performance above 130K with cut-off wavelength above 5.0μm has been developed. Its different performances with respect to the market requirements for SWaP will be discussed. High performance compact systems will make no compromise on detector resolution. The pixel pitch reduction is the answer for resolution enhancement with size reduction. We will therefore also discuss the ongoing developments and market needs for SWaP systems.
NASA Astrophysics Data System (ADS)
Loewenhaupt, M.; Geselbracht, P.; Faulhaber, E.; Rotter, M.; Doerr, M.; Schmalzl, K.; Schneidewind, A.
CeCu2Ge2, the counterpart of the heavy-fermion superconductor CeCu2Si2, exhibits an in-commensurate antiferromagnetically long-range ordered ground state with τ = (0.28 0.28 0.54) below TN = 4.15K. The magnetism is strongly affected by a Kondo screening of the Ce 4f-moments by conduction electrons. The similar energy scale of both, Kondo and exchange interactions, results in a complex magnetic phase diagram and gives rise to potential quantum critical phenomena at very low temperatures. We present elastic neutron diffraction data obtained on a CeCu2Ge2 single crystal employing the cold triple axis spectrometer PANDA at MLZ and the diffractometer D23 at ILL. The field dependence of the magnetic propagation vector was measured at T ≤ 400 mK in the [110]/[001] plane with vertical magnetic fields applied along [1¯10]. We observe a low-field incommensurate magnetic phase AF1, a first order phase transition around 7.8 T with the coexistence of two phases AF1 and AF2 with slightly different propagation vectors, the disappearance of AF1 at 8 T and the existence of AF2 up to 12 T with a possible modification at 10 T. At 12.6 T, yet still well below the value of 26 T of the saturation for magnetic fields in [110] direction, the AF2-type magnetic order is lost and magnetic intensities are not to be found at incommensurate positions in the [110]/[001] plane any more. These new results contradict a previously suggested scenario with a QCP located at 8 T and contribute new information to the B - T phase diagram of CeCu2Ge2 in [110] direction.
Quantum Critical Behavior in the Heavy Fermion Single Crystal Ce(Ni0.935Pd0.065)2Ge2
Wang, Cuihuan; Lawrence, J M; Christianson, Andrew D; Chang, S; Bauer, E D; Gofryk, K; Ronning, F; Thompson, J D; McClellan, K J; Rodriguez-Rivera, J A; Lynn, J W
2011-01-01
We have performed magnetic susceptibility, specific heat, resistivity, and inelastic neutron scattering measurements on a single crystal of the heavy Fermion compound Ce(Ni{sub 0.935}Pd{sup 0.065}){sub 2}Ge{sub 2}, which is believed to be close to a quantum critical point (QCP) at T = 0. At lowest temperature (1.8--3.5 K), the magnetic susceptibility behaves as {chi}(T)-{chi} (0) {proportional_to} T{sup -1/6} with {chi} (0) = 0.032 x 10{sup -6} m{sup 3}/mole (0.0025 emu/mole). For T < 1 K, the specific heat can be fit to the formula {Delta} C/T = {gamma}{sub 0} - T{sup 1/2} with {gamma}{sub 0} of order 700 mJ/mole-K{sup 2}. The resistivity behaves as {rho} = {rho}{sub 0} + AT{sup 3/2} for temperatures below 2 K. This low temperature behavior for {gamma} (T) and {rho} (T) is in accord with the SCR theory of Moriya and Takimoto. The inelastic neutron scattering spectra show a broad peak near 1.5 meV that appears to be independent of Q; we interpret this as Kondo scattering with T{sub K} = 17 K. In addition, the scattering is enhanced near Q=(1/2, 1/2, 0) with maximum scattering at {Delta} E = 0.45 meV{sup -}; we interpret this as scattering from antiferromagnetic fluctuations near the antiferromagnetic QCP.
Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo1-xNixIn5
NASA Astrophysics Data System (ADS)
Otaka, Ryo; Yokoyama, Makoto; Mashiko, Hiroaki; Hasegawa, Takeshi; Shimizu, Yusei; Ikeda, Yoichi; Tenya, Kenichi; Nakamura, Shota; Ueta, Daichi; Yoshizawa, Hideki; Sakakibara, Toshiro
2016-09-01
The effect of off-plane impurity on superconductivity and non-Fermi-liquid (NFL) behavior in the layered heavy-fermion compound CeCo1-xNixIn5 is investigated by specific heat, magnetization, and electrical resistivity measurements. These measurements reveal that the superconducting (SC) transition temperature Tc monotonically decreases from 2.3 K (x = 0) to 0.8 K (x = 0.20) with increasing x, and then the SC order disappears above x = 0.25. At the same time, the Ni substitution yields the NFL behavior at zero field for x = 0.25, characterized by the -ln T divergence in specific heat divided by temperature, Cp/T, and magnetic susceptibility, M/B. The NFL behavior in magnetic fields for x = 0.25 is quite similar to that seen at around the SC upper critical field in pure CeCoIn5, suggesting that both compounds are governed by the same antiferromagnetic quantum criticality. The resemblance of the doping effect on the SC order among Ni-, Sn-, and Pt-substituted CeCoIn5 supports the argument that the doped carriers are primarily responsible for the breakdown of the SC order. The present investigation further reveals the quantitative differences in the trends of the suppression of superconductivity between Ce(Co,Ni)In5 and the other alloys, such as the rates of decrease in Tc, dTc/dx, and specific heat jump at Tc, d(ΔCp/Tc)/dx. We suggest that the occupied positions of the doped ions play an important role in the origin of these differences.
Murayama, S.; Sekine, C.; Yokoyanagi, A.; Hoshi, K.; Onuki, Y.
1997-11-01
Resistivity parallel and perpendicular to the tetragonal c axis of the antiferromagnetic heavy-fermion compound Ce(Ru{sub 1{minus}x}Rh{sub x}){sub 2}Si{sub 2} for x=0.15 has been measured in various fields along the c axis of the single crystal. A sharp upturn is observed just below the N{acute e}el temperature T{sub N} only in the parallel direction. This is interpreted in terms of partial gapping of the Fermi surface along the uniaxial c direction. The specific heat and susceptibility below T{sub N} are, respectively, analyzed into two independent contributions in the low-temperature limit: one is an exponential contribution of the gapped part of the Fermi surface with the energy gap about 10 K, and the other is a residual heavy-fermion contribution due to the remaining ungapped part of about 65{percent}. These facts suggest an itinerant spin-density-wave transition based on Fermi-surface nesting in a heavy-electron band. {copyright} {ital 1997} {ital The American Physical Society}
Wang, Zhijun; Alexandradinata, A; Cava, R J; Bernevig, B Andrei
2016-04-14
Spatial symmetries in crystals may be distinguished by whether they preserve the spatial origin. Here we study spatial symmetries that translate the origin by a fraction of the lattice period, and find that these non-symmorphic symmetries protect an exotic surface fermion whose dispersion relation is shaped like an hourglass; surface bands connect one hourglass to the next in an unbreakable zigzag pattern. These 'hourglass' fermions are formed in the large-gap insulators, KHgX (X = As, Sb, Bi), which we propose as the first material class whose band topology relies on non-symmorphic symmetries. Besides the hourglass fermion, another surface of KHgX manifests a three-dimensional generalization of the quantum spin Hall effect, which has previously been observed only in two-dimensional crystals. To describe the bulk topology of non-symmorphic crystals, we propose a non-Abelian generalization of the geometric theory of polarization. Our non-trivial topology originates from an inversion of the rotational quantum numbers, which we propose as a criterion in the search for topological materials.
Wang, Zhijun; Alexandradinata, A; Cava, R J; Bernevig, B Andrei
2016-04-14
Spatial symmetries in crystals may be distinguished by whether they preserve the spatial origin. Here we study spatial symmetries that translate the origin by a fraction of the lattice period, and find that these non-symmorphic symmetries protect an exotic surface fermion whose dispersion relation is shaped like an hourglass; surface bands connect one hourglass to the next in an unbreakable zigzag pattern. These 'hourglass' fermions are formed in the large-gap insulators, KHgX (X = As, Sb, Bi), which we propose as the first material class whose band topology relies on non-symmorphic symmetries. Besides the hourglass fermion, another surface of KHgX manifests a three-dimensional generalization of the quantum spin Hall effect, which has previously been observed only in two-dimensional crystals. To describe the bulk topology of non-symmorphic crystals, we propose a non-Abelian generalization of the geometric theory of polarization. Our non-trivial topology originates from an inversion of the rotational quantum numbers, which we propose as a criterion in the search for topological materials. PMID:27075096
NASA Astrophysics Data System (ADS)
Le Drogoff, B.; El Khakani, M. A.; Silva, P. R. M.; Chaker, M.; Ross, G. G.
1999-11-01
Pulsed laser deposition (PLD) of iridium, rhodium, and Ir 0.9Rh 0.1 thin films onto a-SiC:H-coated silicon substrates for use in heavy metal sensors has been achieved by ablating iridium and/or rhodium targets with a KrF excimer laser. The deposited films are polycrystalline and exhibited very smooth surfaces with an average roughness value ( Ra) of ˜1 nm. The wettability by mercury of their surface was investigated by means of the contact angle measurement technique, and compared to that of Ag and Pt films. The PLD films (whether Ir, Rh, or Ir 0.9Rh 0.1) were found to present an almost identical Hg-wetting behavior, which is characterized by a high static contact angle of 132±2°. Moreover, in contrast to the cases of Pt or Ag films, where amalgamation with Hg rapidly occurs during the contact angle measurements, no evident interaction of Hg with the surface of the PLD films was observed. Microelectrode arrays of each of the three films (Ir, Rh and Ir 0.9Rh 0.1) were fabricated and used as a conducting base onto which Hg microdrops are electroplated. Reproducible and uniform Hg deposits on the microelectrode arrays were obtained. The electroanalytical performance of these Hg-electroplated microelectrode arrays based sensors was then evaluated by means of Square Wave Anodic Stripping Voltammetry (SWASV), in synthetic solutions containing Zn, Cd and Pb ion traces. Over a concentration range as wide as 0.2-20 ppb, the detected signals are found to exhibit a strong linear correlation with ion concentration. For a preconcentration time of only 5 min, detection limits as low as 0.2 ppb for both Cd and Pb, and 0.5 ppb for Zn were achieved.
The Categorification of Fermions
NASA Astrophysics Data System (ADS)
Wang, Na; Wang, Rui; Wang, Zhi-Xi; Wu, Ke; Yang, Jie; Yang, Zi-Feng
2015-02-01
In this paper, we lift Fermions to functors acting on some homotopy category by the Boson-Fermion correspondence and get the categorified relations of Fermions. In this way, both the categorified Bosons and the categorified Fermions can be viewed as functors on the same category. We also give actions of these functors on the charged Young diagrams (or equivalently Maya diagrams), so that the classical theory of Boson-Fermion correspondence is very well recovered as a result of such a categorification.
Searches for Fourth Generation Fermions
Ivanov, A.; /Fermilab
2011-09-01
We present the results from searches for fourth generation fermions performed using data samples collected by the CDF II and D0 Detectors at the Fermilab Tevatron p{bar p} collider. Many of these results represent the most stringent 95% C. L. limits on masses of new fermions to-date. A fourth chiral generation of massive fermions with the same quantum numbers as the known fermions is one of the simplest extensions of the SM with three generations. The fourth generation is predicted in a number of theories, and although historically have been considered disfavored, stands in agreement with electroweak precision data. To avoid Z {yields} {nu}{bar {nu}} constraint from LEP I a fourth generation neutrino {nu}{sub 4} must be heavy: m({nu}{sub 4}) > m{sub Z}/2, where m{sub Z} is the mass of Z boson, and to avoid LEP II bounds a fourth generation charged lepton {ell}{sub 4} must have m({ell}{sub 4}) > 101 GeV/c{sup 2}. At the same time due to sizeable radiative corrections masses of fourth generation fermions cannot be much higher the current lower bounds and masses of new heavy quarks t' and b' should be in the range of a few hundred GeV/c{sup 2}. In the four-generation model the present bounds on the Higgs are relaxed: the Higgs mass could be as large as 1 TeV/c{sup 2}. Furthermore, the CP violation is significantly enhanced to the magnitude that might account for the baryon asymmetry in the Universe. Additional chiral fermion families can also be accommodated in supersymmetric two-Higgs-doublet extensions of the SM with equivalent effect on the precision fit to the Higgs mass. Another possibility is heavy exotic quarks with vector couplings to the W boson Contributions to radiative corrections from such quarks with mass M decouple as 1/M{sup 2} and easily evade all experimental constraints. At the Tevatron p{bar p} collider 4-th generation chiral or vector-like quarks can be either produced strongly in pairs or singly via electroweak production, where the latter can be
Dynamical symmetries for fermions
Guidry, M.
1989-01-01
An introduction is given to the Fermion Dynamical Symmetry Model (FDSM). The analytical symmetry limits of the model are then applied to the calculation of physical quantities such as ground-state masses and B(E{sub 2}) values in heavy nuclei. These comparisons with data provide strong support for a new principle of collective motion, the Dynamical Pauli Effect, and suggest that dynamical symmetries which properly account for the pauli principle are much more persistent in nuclear structure than the corresponding boson symmetries. Finally, we present an assessment of criticisms which have been voiced concerning the FDSM, and a discussion of new phenomena and exotic spectroscopy'' which may be suggested by the model. 14 refs., 8 figs., 4 tabs.
CeCu{sub 4}A{ell} and CeCu{sub 2}Zn{sub 2}A{ell}: Very heavy fermion systems in high magnetic fields
Andraka, B.; Kim, J.S.; Stewart, G.R. |; Fisk, Z.
1990-12-31
CeCu{sub 4}A{ell} and CeCu{sub 2}Zn{sub 2}A{ell} are heavy fermion systems with extremely enhanced C/T (specific heat divided by temperature) values of 2.3 and 1.8 J/K{sup 2} respectively as T {yields} 0 K. The field dependence of the low temperature specific heat is also extreme; 11 T reduces C of CeCu{sub 4}A{ell} by more than a factor of five, 12.5 T suppresses C of CeCu{sub 2}Zn{sub 2}A{ell} about seven times. Magnetic field caused changes of the specific heat of CeCu{sub 4}A{ell} are consistent with a single ion Kondo model. Magnetic correlations are at least partially responsible for the enhanced low temperature specific heat of CeCu{sub 2}Zn{sub 2}A{ell}.
On the origin of the conductance assymetry in CeMIn5 (N=Co, Rh, Ir)
Bauer, E D; Sarrao, J L; Thompson, J D; Park, W K; Green, L H
2008-01-01
Asymmetric differential conductance has been frequently observed in heavy fermion point contact junctions. We report such data obtained from the Ce-based 1-1-5 compounds CeMIn{sub 5} (M = Co, Rh, Ir). Apart from the characteristics due to superconductivity or antiferromagnetism, a striking common feature is an asymmetry in the background conductance, which shows nontrivial temperature and bias dependencies. These behaviors cannot be explained by the local heating model combined with large Seebeck effect in heavy fermions. We propose that a Fano-like interference effect may cause the asymmetry. The interference can occur between two conductance channels, one into the conduction band and the other into the heavy electron band formed by the hybridization of conduction electrons with localized f-electrons.
On the origin of the conductance asymmetry in CeMin5(M=Co, Rh, Ir)
Bauer, Eric D; Sarrao, J L; Thompson, Joe D; Park, W K; Greene, L H
2008-01-01
Asymmetric differential conductance has been frequently observed in heavy fermion point-contact junctions. We report such data obtained from the Ce-based 1-1-5 compounds CeMIn5 (M=Co, Rh, Ir). Apart from characteristics due to superconductivity or antiferromagnetism, a striking common feature is an asymmetry in the background conductance, which shows nontrivial temperature and voltage dependencies. These behaviors cannot be explained by the local heating model combined with large Seebeck effect in heavy fermions. We propose that a Fana-like interference may cause the asymmetry. The interference can occur between two conductance channels, one into the conduction b<'lJld and the other into the heavy electron band formed by the hybridization of conduction electrons with localized f-electrons.
Heavy-impurity resonance, hybridization, and phonon spectral functions in Fe_{1-x}M_{x}Si, M=Ir,Os
Delaire, O.; Al-Qasir, Iyad I.; May, Andrew F.; Sales, Brian C.; Niedziela, Jennifer L.; Ma, Jie; Matsuda, Masaaki; Abernathy, Douglas L.; Berlijn, Tom
2015-03-31
The vibrational behavior of heavy substitutional impurities (M=Ir,Os) in Fe_{1-x}M_{x}Si (x = 0, 0.02, 0.04, 0.1) was investigated with a combination of inelastic neutron scattering (INS), transport measurements, and first-principles simulations. In this paper, our INS measurements on single-crystals mapped the four-dimensional dynamical structure factor, S(Q;E), for several compositions and temperatures. Our results show that both Ir and Os impurities lead to the formation of a weakly dispersive resonance vibrational mode, in the energy range of the acoustic phonon dispersions of the FeSi host. We also show that Ir doping, which introduces free carriers and increases electron-phonon coupling, leads to softened interatomic force-constants compared to doping with Os, which is isoelectronic to Fe. We analyze the phonon S(Q,E) from INS through a Green's function model incorporating the phonon self-energy based on first-principles density functional theory (DFT) simulations. Calculations of the quasiparticle spectral functions in the doped system reveal the hybridization between the resonance and the acoustic phonon modes. Finally, our results demonstrate a strong interaction of the host acoustic dispersions with the resonance mode, likely leading to the large observed suppression in lattice thermal conductivity.
Ferromagnetism and crystalline electric field effects in cubic UX2Zn20 (X=Co, Rh, Ir)
NASA Astrophysics Data System (ADS)
Bauer, E. D.; Thompson, J. D.; Sarrao, J. L.; Hundley, M. F.
2007-03-01
The physical properties of a new family of cubic UX2Zn20 (X=Co, Rh, Ir) heavy-fermion compounds are presented. Both UCo2Zn20 and URh2Zn20 show peaks in specific heat and magnetic susceptibility at ˜5-10 K suggesting the presence of crystalline electric field (CEF) effects in these materials, i.e., a localized 5f2 configuration of uranium. UIr2Zn20 exhibits a first-order ferromagnetic transition at Tc=2.1 K with a saturation moment μsat=0.4 μB at 2 K indicating itinerant ferromagnetism. All compounds in this series are heavy-fermion materials with enhanced electronic specific heat coefficients γ˜100-450 mJ/mol K2.
Global analysis of fermion mixing with exotics
NASA Technical Reports Server (NTRS)
Nardi, Enrico; Roulet, Esteban; Tommasini, Daniele
1991-01-01
The limits are analyzed on deviation of the lepton and quark weak-couplings from their standard model values in a general class of models where the known fermions are allowed to mix with new heavy particles with exotic SU(2) x U(1) quantum number assignments (left-handed singlets or right-handed doublets). These mixings appear in many extensions of the electroweak theory such as models with mirror fermions, E(sub 6) models, etc. The results update previous analyses and improve considerably the existing bounds.
NASA Astrophysics Data System (ADS)
Nasreen, Farzana; Antonio, Daniel; VanGennep, Derrick; Booth, Corwin H.; Kothapalli, Karunakar; Bauer, Eric D.; Sarrao, John L.; Lavina, Barbara; Iota-Herbei, Valentin; Sinogeikin, Stanislav; Chow, Paul; Xiao, Yuming; Zhao, Yusheng; Cornelius, Andrew L.
2016-03-01
We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0-28.2 GPa) and single crystal x-ray diffraction (SXD) (0-20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K 0 = 62(1) GPa and its pressure derivative, K0\\prime = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.
NASA Astrophysics Data System (ADS)
Nishiyama, Shinya; Matsuura, Hiroyasu; Miyake, Kazumasa
2011-01-01
In f2-based heavy fermion systems with a tetragonal symmetry, we investigate the magnetic field dependence of a non-fermi liquid (NFL) which arises related to the quantum critical point (QCP) due to the competition between the crystalline-electric field (CEF) singlet and the Kondo-Yosida singlet states. On the basis of the Wilson numerical renormalization group method, we find that the magnetic field less than a characteristic magnetic field Hz* does not affect the characteristic temperature TF* at which the specific heat takes a maximum value. Since such Hz* increases as the deviation from the QCP increases, slightly off the QCP, there are parameter regions where NFL behaviors are robust at an observable temperature range T > TF*against a magnetic field of up to Hz* which is far larger than TF*. Our result suggests that such robust NFL behaviors can arise also in systems with other CEF symmetries; e.g., magnetically robust NFL behaviors observed in UBe13 may be understood on this basis.
Quantum critical fluctuations in the heavy fermion compound Ce(Ni_{0.935} Pd_{0.065})_{2}Ge_{2}
Wang, C. H.; Poudel, L.; Taylor, A. E.; Lawrence, J. M.; Christianson, A. D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, A. A.; Ehlers, G.; Baumbach, R. E.; Bauer, E. D.; Gofryk, K.; Ronning, F.; McClellan, K. J.; Thompson, J. D.
2015-01-14
Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experi- ments were performed on a single crystal of the heavy fermion compound Ce(Ni_{0.935} Pd_{0.065})_{2}Ge_{2} in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T^{3/2} and γ(T) ~ γ_{0} - bT^{1/2}). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.
NASA Astrophysics Data System (ADS)
Storr, Kevin; Purcell, Kenneth; Rasco, Torrance; Schwartz, Sarah; Petrovic, Cedomir
2014-03-01
The Nd1-xCexCoIn5 alloys evolve from local moment magnetism x = 0 to heavy fermion superconductivity x = 1, as the Nd substitution alters the level of 4f-conduction electron coupling. Superconductivity has been shown to exist in Nd concentrations between x = 0 and x = 0.22. We report the temperature and angular dependence of the critical field of the superconducting state of the x = 0.98, 0.95, and 0.90 doping levels at temperatures ranging from 20 - 500 mK, investigating the evolution of the phase diagram for different concentrations of Nd at these previously unexplored low temperatures. No evidence of a low temperature mixed superconducting and magnetic mixed state was observed such that as that seen in CeCoIn5. The suppression of the critical field is more dramatic than the application of pressure and was observed to be rather anisotropic in line with the higher temperature measurements. Department of Defense ARO W911NF1110155.
Quantum critical fluctuations in the heavy fermion compound Ce(Ni_{0.935}Pd_{0.065})_{2}Ge_{2}
Wang, C. H.; Poudel, L.; Taylor, Alice E.; Lawrence, J M.; Christianson, Andrew D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, Andrey A.; Ehlers, G.; Baumbach, R. E.; Bauer, E. D.; Gofryk, Krzysztof; Ronning, F.; Mcclellan, K. J.; Thompson, J. D.
2014-12-03
Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni_{0.935}Pd_{0.065})_{2}Ge_{2} in order to research the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T^{3/2} and γ(T) ~ γ_{0} - bT^{1/2}). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. In addition, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. In conclusion, we suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.
NASA Astrophysics Data System (ADS)
Walker, H. C.; McEwen, K. A.; Griveau, J.-C.; Eloirdi, R.; Amador, P.; Maldonado, P.; Oppeneer, P. M.; Colineau, E.
2015-05-01
We present bulk property measurements of NpIr, a newly synthesized member of the Np-Ir binary phase diagram, which is isostructural to the noncentrosymmetric pressure-induced ferromagnetic superconductor UIr. Magnetic susceptibility, electronic transport properties at ambient and high pressure, and heat capacity measurements have been performed for temperatures T =0.55 -300 K in a range of magnetic fields up to 14 T and under pressure up to 17.3 GPa. These reveal that NpIr is a moderately heavy fermion Kondo system with strong antiferromagnetic interactions, but there is no evidence of any phase transition down to 0.55 K or at the highest pressure achieved. Experimental results are compared with ab initio calculations of the electronic band structure and lattice heat capacity. An extremely low lattice thermal conductivity is predicted for NpIr at temperatures above 300 K.
NASA Astrophysics Data System (ADS)
Onimaru, T.; Izawa, K.; Matsumoto, K. T.; Yoshida, T.; Machida, Y.; Ikeura, T.; Wakiya, K.; Umeo, K.; Kittaka, S.; Araki, K.; Sakakibara, T.; Takabatake, T.
2016-08-01
Orbital degrees of freedom in condensed matter could play important roles in forming a variety of exotic electronic states by interacting with conduction electrons. In 4 f -electron systems, because of strong intra-atomic spin-orbit coupling, an orbitally degenerate state inherently carries quadrupolar degrees of freedom. The present work has focused on a purely quadrupole-active system PrIr2Zn20 showing superconductivity in the presence of an antiferroquadrupole order at TQ=0.11 K. We observed non-Fermi-liquid (NFL) behaviors emerging in the electrical resistivity ρ and the 4 f contribution to the specific heat, C4 f, in the paramagnetic state at T > TQ. Moreover, in magnetic fields B ≤6 T, all data sets of ρ (T ) and C4 f(T ) are well scaled with characteristic temperatures T0's. This observation of the NFL state in the nonmagnetic quadrupole-active system has an origin intrinsically different from that observed in the vicinity of the conventional quantum critical point. It implies possible formation of a quadrupole Kondo lattice resulting from hybridization between the quadrupoles and the conduction electrons with an energy scale of kBT0 . At T ≤0.13 K, ρ (T ) and C4 f(T ) exhibit anomalies as B approaches 5 T. This is the manifestation of a field-induced crossover toward a Fermi-liquid ground state in the quadrupole Kondo lattice.
Bold Diagrammatic Monte Carlo for Fermionic and Fermionized Systems
NASA Astrophysics Data System (ADS)
Svistunov, Boris
2013-03-01
In three different fermionic cases--repulsive Hubbard model, resonant fermions, and fermionized spins-1/2 (on triangular lattice)--we observe the phenomenon of sign blessing: Feynman diagrammatic series features finite convergence radius despite factorial growth of the number of diagrams with diagram order. Bold diagrammatic Monte Carlo technique allows us to sample millions of skeleton Feynman diagrams. With the universal fermionization trick we can fermionize essentially any (bosonic, spin, mixed, etc.) lattice system. The combination of fermionization and Bold diagrammatic Monte Carlo yields a universal first-principle approach to strongly correlated lattice systems, provided the sign blessing is a generic fermionic phenomenon. Supported by NSF and DARPA
Shimizu, Yusei; Kittaka, Shunichiro; Sakakibara, Toshiro; Tsutsumi, Yasumasa; Nomoto, Takuya; Ikeda, Hiroaki; Machida, Kazushige; Homma, Yoshiya; Aoki, Dai
2016-07-15
Quasiparticle excitations in UPd_{2}Al_{3} were studied by means of heat-capacity (C) measurements under rotating magnetic fields using a high-quality single crystal. The field dependence shows C(H)∝H^{1/2}-like behavior at low temperatures for both two hexagonal crystal axes, i.e., H∥[0001] (c axis) and H∥[112[over ¯]0] (a axis), suggesting the presence of nodal quasiparticle excitations from heavy bands. At low temperatures, the polar-angle (θ) dependence of C exhibits a maximum along H∥[0001] with a twofold symmetric oscillation below 0.5 T, and an unusual shoulder or hump anomaly has been found around 30°-60° from the c axis in C(θ) at intermediate fields (1≲μ_{0}H≲2 T). These behaviors in UPd_{2}Al_{3} purely come from the superconducting nodal quasiparticle excitations, and can be successfully reproduced by theoretical calculations assuming the gap symmetry with a horizontal linear line node. We demonstrate the whole angle-resolved heat-capacity measurements done here as a novel spectroscopic method for nodal gap determination, which can be applied to other exotic superconductors. PMID:27472129
Is there an upper limit to fermion masses
Einhorn, M.B.; Goldberg, G.J.
1986-10-27
A fermion mass generated by spontaneous symmetry breaking is proportional to its Yukawa coupling y to a Higgs field. Like the Higgs-field self-coupling, y may well be trivial and diverge at a finite energy scale ..lambda../sub f/, corresponding to an upper limit on fermion masses. We verify this by solving a simple model by means of a 1/N expansion. Applied to the standard model, this suggests that there is an upper limit to quark and lepton masses. These results have implications for the ''decoupling'' of heavy fermions and bear on the issue of whether apparently ''anomalous'' gauge theories can be consistently quantized.
Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran
2016-03-17
We study the conformal bootstrap for a 4-point function of fermions <ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge CT. We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N. Finally, we also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.
Valence State in CeIrIn5 at High Magnetic Fields of up to 42 T
NASA Astrophysics Data System (ADS)
Matsuda, Yasuhiro H.; Terashima, Taku T.; Kindo, Koichi; Tsunoda, Ryoma; Settai, Rikio; Kawamura, Naomi; Mizumaki, Masaichiro; Inami, Toshiya
2016-11-01
High-magnetic-field X-ray absorption spectroscopy of the heavy-fermion compound CeIrIn5 has been conducted to clarify the valence state of Ce at the metamagnetic transition. The field-induced change in the X-ray absorption spectrum near the Ce-L3 edge is found to be smaller than the resolution limit of the measurement, suggesting that no field-induced valence change larger than 0.005 takes place at 2 K up to 42 T.
NASA Astrophysics Data System (ADS)
Marino, Eduardo
The electron, discovered by Thomson by the end of the nineteenth century, was the first experimentally observed particle. The Weyl fermion, though theoretically predicted since a long time, was observed in a condensed matter environment in an experiment reported only a few weeks ago. Is there any linking thread connecting the first and the last observed fermion (quasi)particles? The answer is positive. By generalizing the method known as bosonization, the first time in its full complete form, for a spacetime with 3+1 dimensions, we are able to show that both electrons and Weyl fermions can be expressed in terms of the same boson field, namely the Kalb-Ramond anti-symmetric tensor gauge field. The bosonized form of the Weyl chiral currents lead to the angle-dependent magneto-conductance behavior observed in these systems.
Cold asymmetrical fermion superfluids
Caldas, Heron
2003-12-19
The recent experimental advances in cold atomic traps have induced a great amount of interest in fields from condensed matter to particle physics, including approaches and prospects from the theoretical point of view. In this work we investigate the general properties and the ground state of an asymmetrical dilute gas of cold fermionic atoms, formed by two particle species having different densities. We have show in a recent paper, that a mixed phase composed of normal and superfluid components is the energetically favored ground state of such a cold fermionic system. Here we extend the analysis and verify that in fact, the mixed phase is the preferred ground state of an asymmetrical superfluid in various situations. We predict that the mixed phase can serve as a way of detecting superfluidity and estimating the magnitude of the gap parameter in asymmetrical fermionic systems.
Bifurcations in dissipative fermionic dynamics
NASA Astrophysics Data System (ADS)
Napolitani, Paolo; Colonna, Maria; Di Prima, Mariangela
2014-05-01
The Boltzmann-Langevin One-Body model (BLOB), is a novel one-body transport approach, based on the solution of the Boltzmann-Langevin equation in three dimensions; it is used to handle large-amplitude phase-space fluctuations and has a broad applicability for dissipative fermionic dynamics. We study the occurrence of bifurcations in the dynamical trajectories describing heavy-ion collisions at Fermi energies. The model, applied to dilute systems formed in such collisions, reveals to be closer to the observation than previous attempts to include a Langevin term in Boltzmann theories. The onset of bifurcations and bimodal behaviour in dynamical trajectories, determines the fragment-formation mechanism. In particular, in the proximity of a threshold, fluctuations between two energetically favourable mechanisms stand out, so that when evolving from the same entrance channel, a variety of exit channels is accessible. This description gives quantitative indications about two threshold situations which characterise heavy-ion collisions at Fermi energies. First, the fusion-to-multifragmentation threshold in central collisions, where the system either reverts to a compact shape, or splits into several pieces of similar sizes. Second, the transition from binary mechanisms to neck fragmentation (in general, ternary channels), in peripheral collisions.
NASA Astrophysics Data System (ADS)
Combescure, Monique; Robert, Didier
2012-06-01
The aim of this paper is to give a self-contained and unified presentation of a fermionic coherent state theory with the necessary mathematical details, discussing their definition, properties and some applications. After defining Grassmann algebras, it is possible to get a classical analog for the fermionic degrees of freedom in a quantum system. Following the basic work of Berezin (1966 The Method of Second Quantization (New York: Academic); 1987 Introduction to Superanalysis (Dordrecht: Reidel Publishing Company)), we show that we can compute with Grassmann numbers as we do with complex numbers: derivation, integration, Fourier transform. After that we show that we have quantization formulas for fermionic observables. In particular, there exists a Moyal product formula. As an application, we consider explicit computations for propagators with quadratic Hamiltonians in annihilation and creation operators. We prove a Mehler formula for the propagator and Mehlig-Wilkinson-type formulas for the covariant and contravariant symbols of ‘metaplectic’ transformations for fermionic states. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Coherent states: mathematical and physical aspects’.
NASA Astrophysics Data System (ADS)
Onimaru, Takahiro; Kusunose, Hiroaki
2016-08-01
This paper reviews experimental evidence and the related theoretical background on exotic phenomena arising from local quadrupolar degrees of freedom. Recent extensive studies on praseodymium-based cubic systems, PrT2X20, have revealed that the active quadrupoles in the non-Kramers doublet ground state play a vital role in exhibiting quadrupole orders and superconductivity with underlying peculiar normal paramagnetic electronic states. We focus on four prototype compounds of PrT2X20 (T = Ir, Rh, X = Zn; T = V, Ti, X = Al). Detailed comprehensive comparisons of these compounds have revealed a universal feature of the non-Fermi liquid state emerging from a lattice quadrupolar Kondo effect, and the commonality and individuality of the quadrupolar and superconducting phases. It may be possible to develop a new class of heavy-fermion systems beyond the classic view of heavy fermions on the basis of a concrete understanding of these phenomena.
Gusiatin, Zygmunt Mariusz; Kulikowska, Dorota
2014-07-01
To assess the environmental quality of compost, it is insufficient to use only total metal concentration. Therefore in this study, the stability of metals in compost and the environmental risk they pose were assessed by three indices that have been proposed for soils or sediments: the IR, the RAC and the MRI. In mature composts, the highest bonding intensity was for Ni (0.79<IR<0.93), then for Cu (0.56<IR<0.65) and Pb (0.55<IR<0.73), and the lowest for Zn (0.19<IR<0.25). Although, both the IR and the RAC are useful indices for evaluating the mobility of metals, they do not take into account their toxicity. Therefore, the overall classification of compost should also include the MRI, at which metal toxicity from the most available fractions is considered. Based on the MRI ranged between 10.0 and 11.6, all composts evaluated posed a low risk.
NASA Astrophysics Data System (ADS)
Wang, Rui; Lu, Hong-Yan; Wang, Baigeng; Ting, C. S.
2016-09-01
A realization of Majorana fermions is proposed in the frustrated magnets via the topological proximity effect. Specifically, we consider a theoretical model, where a topological insulator is coupled to a frustrated magnetic material through the spin exchange interaction. Using the renormalization group-based self-consistent mean-field approach, and calculating the self-energy correction due to the topological insulator, we find that the spin texture and the spin-momentum locking of the Dirac cone will be inherited by the spinons in the nearby frustrated magnets. This leads to a particular topological state of matter that supports the Majorana excitations. Unlike the conventional realization in superconductor systems, these Majorana fermions are the combination of spinons and antispinons, rather than electrons and holes. They can participate in the transport of spinons, leading to nontrivial properties of the spin transport.
NASA Astrophysics Data System (ADS)
Wang, Rui; Lu, Hong-Yan; Wang, Baigeng; Ting, Chin-Sen
A new realization of Majorana fermions is proposed in the frustrated magnets via the topological proximity effect. Specifically, we consider the interface between a topological insulator and a frustrated magnetic material. Using the renormalization group-based mean-field theory, and calculating the self-energy correction due to the topological insulator, we find that the spin texture and the spin-momentum locking of the Dirac cone will be inherited by the spinons in the nearby frustrated magnets. This leads to a particular topological state of matter that supports the Majorana excitation. Unlike the conventional ones, these Majorana fermions are the composite states of spinons and anti-spinons, rather than electrons and holes. They can also participate in the transport of spinons, resulting in nontrivial spin current, while the charge current is completely frozen.
NASA Astrophysics Data System (ADS)
Agrawal, Jyoti; Frampton, Paul H.; Jack Ng, Y.; Nishino, Hitoshi; Yasuda, Osamu
1991-03-01
An extension of the standard model is proposed. The gauge group is SU(2) X ⊗ SU(3) C ⊗ SU(2) S ⊗ U(1) Q, where all gauge symmetries are unbroken. The colour and electric charge are combined with SU(2) S which becomes strongly coupled at approximately 500 GeV and binds preons to form fermionic and vector bound states. The usual quarks and leptons are singlets under SU(2) X but additional fermions, called sarks. transform under it and the electroweak group. The present model explains why no more than three light quark-lepton families can exist. Neutral sark baryons, called narks, are candidates for the cosmological dark matter having the characteristics designed for WIMPS. Further phenomenological implications of sarks are analyzed i including electron-positron annihilation. Z 0 decay, flavor-changing neutral currents. baryon-number non-conservation, sarkonium and the neutron electric dipole moment.
Leptogenesis from split fermions
Nagatani, Yukinori; Perez, Gilad
2004-01-11
We present a new type of leptogenesis mechanism based on a two-scalar split-fermions framework. At high temperatures the bulk scalar vacuum expectation values (VEVs) vanish and lepton number is strongly violated. Below some temperature, T{sub c}, the scalars develop extra dimension dependent VEVs. This transition is assumed to proceed via a first order phase transition. In the broken phase the fermions are localized and lepton number violation is negligible. The lepton-bulk scalar Yukawa couplings contain sizable CP phases which induce lepton production near the interface between the two phases. We provide a qualitative estimation of the resultant baryon asymmetry which agrees with current observation. The neutrino flavor parameters are accounted for by the above model with an additional approximate U(1) symmetry.
Ferromagnetism and Crystalline Electric Field Effects in Cubic UX2Zn20 (X=Co, Rh, Ir)
NASA Astrophysics Data System (ADS)
Bauer, E. D.; Ronning, F.; Silhanek, A.; Harrison, N.; Thompson, J. D.; Sarrao, J. L.; Movshovich, R.; Hundley, M. F.; Jaime, M.; Daniel, E.; Booth, C. H.
2006-03-01
The properties of a new class of cubic UX2Zn20 (X=Co, Rh, Ir) heavy fermion compounds have been investigated by means of magnetic susceptibility, specific heat, electrical resistivity, and x-ray absorption spectroscopy. Both UCo2Zn20 and URh2Zn20 show peaks in C(T) and χ(T) at ˜5-10 K suggesting the presence of crystalline electric field (CEF) effects in these materials, i.e., a localized 5f^2 configuration of uranium. In addition, measurements in high magnetic fields up to 40 T are consistent with a CEF model of a nonmagnetic ground state and a magnetic first excited state separated by ˜ 20 K. In contrast, UIr2Zn20 exhibits a first-order ferromagnetic transition at Tc=2.75 K with a saturation moment μsat=0.5 μB in the ferromagnetic state. All compounds in this series are heavy fermion materials with enhanced electronic specific heat coefficients γ˜ 150-300 mJ/molK^2. The physical properties of UX2Zn20 (X=Co, Rh, Ir) will be discussed.
Linear dependencies between composite fermion states
NASA Astrophysics Data System (ADS)
Meyer, M. L.; Liabøtrø, O.; Viefers, S.
2016-09-01
The formalism of composite fermions (CFs) has been one of the most prominent and successful approaches to describing the fractional quantum Hall effect, in terms of trial many-body wave functions. Testing the accuracy of the latter typically involves rather heavy numerical comparison to exact diagonalization results. Thus, optimizing computational efficiency has been an important technical issue in this field. One generic (and not yet fully understood) property of the CF approach is that it tends to overcount the number of linearly independent candidate states for fixed sets of quantum numbers. Technically speaking, CF Slater determinants that are orthogonal before projection to the lowest Landau level, may lead to wave functions that are identical, or possess linear dependencies, after projection. This leads to unnecessary computations, and has been pointed out in the literature both for fermionic and bosonic systems. We here present a systematic approach that enables us to reveal all linear dependencies between bosonic compact states in the lowest CF ‘cyclotron energy’ sub-band, and almost all dependencies in higher sub-bands, at the level of the CF Slater determinants, i.e. before projection, which implies a major computational simplification. Our approach is introduced for so-called simple states of two-species rotating bosons, and then generalized to generic compact bosonic states, both one- and two-species. Some perspectives also apply to fermionic systems. The identities and linear dependencies we find, are analytically exact for ‘brute force’ projection in the disk geometry.
Wang, S.-Y.; Boyanovsky, D.; Vega, H. J. de; Lee, D.-S.; Ng, Y. J.
2000-03-15
We study the transport coefficients, damping rates, and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar plasma with the goal of understanding the main physical mechanisms that determine transport of chirality in scenarios of nonlocal electroweak baryogenesis. The focus is on identifying the different transport coefficients for the different branches of soft collective excitations of the fermion spectrum. These branches correspond to collective excitations with opposite ratios of chirality to helicity and different dispersion relations. By combining results from the hard thermal loop (HTL) resummation program with a novel mechanism of fermion damping through heavy scalar decay, we obtain a robust description of the different damping rates and mean free paths for the soft collective excitations to leading order in HTL and lowest order in the Yukawa coupling. The space-time evolution of wave packets of collective excitations unambiguously reveals the respective mean free paths. We find that whereas both the gauge and scalar contribution to the damping rates are different for the different branches, the difference of mean free paths for both branches is mainly determined by the decay of the heavy scalar into a hard fermion and a soft collective excitation. We argue that these mechanisms are robust and are therefore relevant for nonlocal scenarios of baryogenesis either in the standard model or extensions thereof. (c) 2000 The American Physical Society.
Hadron Properties with FLIC Fermions
James Zanotti; Wolodymyr Melnitchouk; Anthony Williams; J Zhang
2003-07-01
The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of nonperturbative O(a)-improvement in lattice fermion actions offering near continuum results at finite lattice spacing. It provides computationally inexpensive access to the light quark mass regime of QCD where chiral nonanalytic behavior associated with Goldstone bosons is revealed. The motivation and formulation of FLIC fermions, its excellent scaling properties and its low-lying hadron mass phenomenology are presented.
Cloaking two-dimensional fermions
Lin, De-Hone
2011-09-15
A cloaking theory for a two-dimensional spin-(1/2) fermion is proposed. It is shown that the spinor of the two-dimensional fermion can be cloaked perfectly through controlling the fermion's energy and mass in a specific manner moving in an effective vector potential inside a cloaking shell. Different from the cloaking of three-dimensional fermions, the scaling function that determines the invisible region is uniquely determined by a nonlinear equation. It is also shown that the efficiency of the cloaking shell is unaltered under the Aharonov-Bohm effect.
Probing the fermionic Higgs portal at lepton colliders
Fedderke, Michael A.; Lin, Tongyan; Wang, Lian -Tao
2016-04-26
Here, we study the sensitivity of future electron-positron colliders to UV completions of the fermionic Higgs portal operator H†Hχ¯χ. Measurements of precision electroweak S and T parameters and the e+e– → Zh cross-section at the CEPC, FCC-ee, and ILC are considered. The scalar completion of the fermionic Higgs portal is closely related to the scalar Higgs portal, and we summarize existing results. We devote the bulk of our analysis to a singlet-doublet fermion completion. Assuming the doublet is sufficiently heavy, we construct the effective field theory (EFT) at dimension-6 in order to compute contributions to the observables. We also providemore » full one-loop results for S and T in the general mass parameter space. In both completions, future precision measurements can probe the new states at the (multi-)TeV scale, beyond the direct reach of the LHC.« less
Nucleon Resonances from FLIC Fermions
Derek Leinweber; J. Hedditch; Wally Melnitchouk; Anthony Williams
2003-01-01
The Fat Link Irrelevant Glover (FL1C) fermion action and its associated phenomenology is described. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative O(a) improvement where near-continuum results are obtained at finite lattice spacing spin-1/2 and spin-3/2 , even and odd parity nucleon resonances are investigated.
NASA Astrophysics Data System (ADS)
Casella, Daniele; Dietrich, Stefano; di Paola, Francesco; Formenton, Marco; Mugnai, Alberto; Sanò, Paolo
2010-05-01
Precipitation retrievals based on measurements from microwave (MW) radiometers onboard low-Earth-orbit (LEO) satellites can reach a high level of accuracy - and especially so, for deep convective precipitating systems. However, these observations do not provide a satisfactorily coverage of the rapid evolution of intense precipitating systems. As a result, the obtained precipitation retrievals are often of limited use for many important applications -- including support to authorities in activating flood alarms. To avoid this problem, several techniques have been developed that combine accurate MW estimates with frequent infrared (IR) observations from geosynchronous (GEO) satellites, such as the European Meteosat Second Generation (MSG). Within the European Union FP6 FLASH project, we have developed a new combined MW-IR technique for producing frequent precipitation retrievals from space (which we call PM-GCD technique). This technique uses passive-microwave (PM) retrievals in conjunction with the Global Convection Detection (GCD) technique that discriminates deep convective clouds within the GEO observations, based on the difference between the water vapor (6.2 μm ) and thermal-IR (10.8 μm ) channels. In essence, within the PM-GCD technique, deep convective areas are defined from MSG observations, then calibrated using MW-AMSU precipitation retrievals and finally propagated over time with a simple tracking algorithm. In this paper, we describe the PM-GCD technique and discuss the results of its application to a flood event that occurred on September 12-15, 2006 over the north-western Mediterranean coastal areas, and that has been selected for joint research by the EU FLASH and HYDRATE projects.
Unlocking fermionic mode entanglement
NASA Astrophysics Data System (ADS)
Friis, Nicolai
2016-06-01
Aside from other puzzling features of entanglement, it has been debated whether a physically meaningful notion of entanglement requires two (or more) particles as carriers of the correlated degrees-of-freedom, or if a single particle could be considered to be entangled as well. While the usefulness of single-boson entanglement has been demonstrated some time ago, the restrictions of superselection rules have previously thwarted attempts at similar arguments for single fermions. In Dasenbrook et al (2016 New J. Phys. 18 043036) this obstacle is overcome. The authors propose a scheme for a Bell test on two copies of single-electron states whose entanglement is individually not accessible. The discussed scheme, which makes use of recent progress in electronic quantum optics, provides an experimentally viable and theoretically unambiguous way to assert that certain single-electron states can be considered to be entangled.
Fernández-Varela, R; Andrade, J M; Muniategui, S; Prada, D; Ramírez-Villalobos, F
2009-03-01
This paper compares the weathering patterns of two similar fuel oils: a fuel oil spilled after a ship accident (Prestige-Nassau, off the Galician coast -NW Spain-) and a fuel designed to cope with the numerous quests for samples to carry out scientific studies (IFO). Comparative studies were made to evaluate the capability of common fingerprinting analytical techniques to differentiate the fuels, as well as their capabilities to monitor their weathering. The two products were spilled under controlled conditions during ca. four months to assess how they evolved on time. Mid-IR spectrometry and gas chromatography (flame ionization and mass spectrometry detectors) were used. IR indexes related to total aromaticity, type of substituents (branched or linear chains) and degree of aromatic substitution reflected well the differences between the fuels during weathering. Regarding the chromatographic measurements, the n-alkanes became highly reduced for both fuel oils and it was found that the PAHs of the synthetic fuel (IFO) were more resistant to weathering. Regarding biomarkers, the different profiles of the steranes, diasteranes and triaromatic steroids allowed for a simple differentiation amongst the two products. The %D2/P2 ratio differentiated both products whereas the %N3/P2 one ordered the samples according to the extent of their weathering.
Effective fermion kinematics from modified quantum gravity
NASA Astrophysics Data System (ADS)
Alexandre, J.; Leite, J.
2016-10-01
We consider a classical fermion and a classical scalar, propagating on two different kinds of four-dimensional diffeomorphism breaking gravity backgrounds, and we derive the one-loop effective dispersion relation for matter, after integrating out gravitons. One gravity model involves quadratic divergences at one-loop, as in Einstein gravity, and the other model is the z = 3 non-projectable Horava-Lifshitz gravity, which involves logarithmic divergences only. Although these two models behave differently in the ultraviolet, the IR phenomenology for matter fields is comparable: (i) for generic values for the parameters, both models identify 1010 GeV as the characteristic scale above which they are not consistent with current upper bounds on Lorentz symmetry violation; (ii) for both models, there is always a fine-tuning of parameters which allows the cancellation of the indicator for Lorentz symmetry violation.
FLIC Fermions and Hadron Phenomenology
D. Leinweber; J.N. Hedditch; W. Melnitchouk; A.W. Thomas; A.G. Williams; R.D. Young; J.M. Zanotti; J.B. Zhang
2002-06-01
A pedagogical overview of the formulation of the Fat Link Irrelevant Clover (FLIC) fermion action and its associated phenomenology is described. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative order (a) improvement where near-continuum results are obtained at finite lattice spacing. Spin-1/2 and spin-3/2, even and odd parity baryon resonances are investigated in quenched QCD, where the nature of the Roper resonance and Lambda (1405) are of particular interest. FLIC fermions allow efficient access to the light quark-mass regime, where evidence of chiral nonanalytic behavior in the Delta mass is observed.
X-ray absorption studies of the local structure and f-level occupancy in CeIr(1-x)Rh(x)In(5)
Daniel, M.; Han, S.-W.; Booth, C.H.; Cornelius, A.L.; Pagliuso, P.G.; Sarrao, J.L.; Thompson, J.D.
2004-04-15
The CeIr{sub 1-x}Rh{sub x}In{sub 5} series exhibits a range of interesting phenomena, including heavy-fermion superconductivity, non-Fermi liquid behavior, and concomitant antiferromagnetism (AF) and superconductivity (SC). In the low-Rh concentration range (0.1 {ge} x {ge} 0.5), specific heat measurements show a broad anomaly, suggestive of gross phase separation. We have performed x-ray absorption experiments at the Ce L{sub III}, Ir L{sub III}, and Rh K-edges as a function of Rh concentration and temperature. X-ray absorption near-edge structure (XANES) measurements indicate that cerium is close to trivalent in this system, with no measurable change with temperature from 20-300 K, consistent with a heavy-fermion material. Extended x-ray absorption fine structure (EXAFS) measurements as a function of temperature from all measured edges indicate the local crystal structure of all samples is well ordered, with no gross phase separation observed, even for samples with x = 0.125 and x = 0.25. These results therefore suggest that the anomalous specific heat behavior in the 0.1 {ge} x {ge} 0.5 range have some other explanation, and some possibilities are discussed.
Relativistic spectra of bound fermions
Giachetti, Riccardo; Sorace, Emanuele
2007-02-27
A two fermion relativistic invariant wave equation is used for numerical calculations of the hyperfine shifts of the Positronium levels in a Breit interaction scheme. The results agree with known data up to the order {alpha}4.
Dynamical fermions with fat links
NASA Astrophysics Data System (ADS)
Knechtli, Francesco; Hasenfratz, Anna
2001-06-01
We present and test a new method for simulating dynamical fermions with fat links. Our construction is based on the introduction of auxiliary but dynamical gauge fields and works with any fermionic action and can be combined with any fermionic updating. In our simulation we use an overrelaxation step which makes it effective. For four flavors of staggered fermions the first results indicate that flavor symmetry at a lattice spacing a~0.2 fm is restored to a few percent. With the standard action this amount of flavor symmetry restoration is achieved at a~0.07 fm. We estimate that the overall computational cost is reduced by at least a factor of 10.
Observing remnants by fermions' tunneling
Chen, D.Y.; Wu, H.W.; Yang, H. E-mail: iverwu@uestc.edu.cn
2014-03-01
The standard Hawking formula predicts the complete evaporation of black holes. In this paper, we introduce effects of quantum gravity into fermions' tunneling from Reissner-Nordstrom and Kerr black holes. The quantum gravity effects slow down the increase of Hawking temperatures. This property naturally leads to a residue mass in black hole evaporation. The corrected temperatures are affected by the quantum numbers of emitted fermions. Meanwhile, the temperature of the Kerr black hole is a function of θ due to the rotation.
Božin, E. S.; Knox, K. R.; Juhás, P.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.
2014-01-01
Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood. Despite their ubiquity, they are hard to study because they produce weak diffuse signals in most measurements. Here we propose Cu(Ir1 − xCrx)2S4 as a model system, where robust local structural signals lead to key new insights. We demonstrate a hitherto unobserved coexistence of an Ir4+ charge-localized dimer phase and Cr-ferromagnetism. The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates. We suggest that the presence of quenched strain from dopant ions acts as an arbiter deciding between the competing ground states. PMID:24518384
NASA Astrophysics Data System (ADS)
Božin, E. S.; Knox, K. R.; Juhás, P.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.
2014-02-01
Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood. Despite their ubiquity, they are hard to study because they produce weak diffuse signals in most measurements. Here we propose Cu(Ir1 - xCrx)2S4 as a model system, where robust local structural signals lead to key new insights. We demonstrate a hitherto unobserved coexistence of an Ir4+ charge-localized dimer phase and Cr-ferromagnetism. The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates. We suggest that the presence of quenched strain from dopant ions acts as an arbiter deciding between the competing ground states.
NASA Astrophysics Data System (ADS)
Riess, Adam
2010-09-01
Observing asterisms for photometric calibration provides a "happy medium" between observing single stars which areobservable from the ground but lack statistics, and star clusters which have excellent statistics but are too crowded to observe from the ground.Asterisms in the IR for calibration have been less available than in the optical, e.g., Landolt's standard fields.While ad-hoc asterisms for calibration could be formed from 2MASS calibration, the photometric precision of 2MASSis relatively low, 0.02-0.05, for the fainter stars, m=9-13, that can still be observed without saturation in WFC3-IR.However, IR monitoring of variable phenomena {e.g., AGN SNe, stellar variables} from the ground has produced calibration of stars in asterisms with m=9-13 with a relative uncertainty of 0.001 to 0.01 mag due to the high frequency of monitoring. We have selected 4 such asterisms to observe. Because the stars are bright we need to use subarrays of 64x64 or 128x128 to get read out short enough to avoid saturation. The observations are obtained in pairs of 3 close stars, i.e., 2x3=6 stars per orbit in F125W and F160W as well as a F555W full frame to verify astrometry. In all we expect to measure 24 stars with m=9 to 14. The goal is to provide 2 calibrations, an independent zeropoint and its uncertainty as well as a measure of count rate non linearity. For the latter, an expected CRNL over 2 dex {5 mag} is expected tobe 0.02 mag.
Fermion localization on thick branes
Melfo, Alejandra; Pantoja, Nelson; Tempo, Jose David
2006-02-15
We consider chiral fermion confinement in scalar thick branes, which are known to localize gravity, coupled through a Yukawa term. The conditions for the confinement and their behavior in the thin-wall limit are found for various different BPS branes, including double walls and branes interpolating between different AdS{sub 5} spacetimes. We show that only one massless chiral mode is localized in all these walls, whenever the wall thickness is keep finite. We also show that, independently of wall's thickness, chiral fermionic modes cannot be localized in dS{sub 4} walls embedded in a M{sub 5} spacetime. Finally, massive fermions in double wall spacetimes are also investigated. We find that, besides the massless chiral mode localization, these double walls support quasilocalized massive modes of both chiralities.
Acoustoelectric current for composite fermions
NASA Astrophysics Data System (ADS)
Bergli, J.; Galperin, Y. M.
2001-07-01
The acoustoelectric current for composite fermions in a two-dimensional electron gas (2DEG) close to the half-filled Landau level is calculated in the random phase approximation. The Boltzmann equation is used to find the nonequilibrium distribution of composite fermions to second order in the acoustic field. It is shown that the oscillating Chern-Simons field created by the induced density fluctuations in the 2DEG is important for the acoustoelectric current. This leads to a violation of the Weinreich relation between the acoustoelectric current and acoustic intensity. The deviations from the Weinreich relation can be detected by measuring the angle between the longitudinal and the Hall components of the acoustoelectric current. This departure from the Weinreich relation gives additional information on the properties of the composite fermion fluid.
A Model of Fermion Masses and Flavor Mixings with Family Symmetry SU(3) otimes U(1)
NASA Astrophysics Data System (ADS)
Yang, Wei-Min; Wang, Qi; Zhong, Jin-Jin
2012-01-01
The family symmetry SU(3) otimes U(1) is proposed to solve flavor problems about fermion masses and flavor mixings. It is breaking is implemented by some flavon fields at the high-energy scale. In addition a discrete group Z2 is introduced to generate tiny neutrino masses, which is broken by a real singlet scalar field at the middle-energy scale. The low-energy effective theory is elegantly obtained after all of super-heavy fermions are integrated out and decoupling. All the fermion mass matrices are regularly characterized by four fundamental matrices and thirteen parameters. The model can perfectly fit and account for all the current experimental data about the fermion masses and flavor mixings, in particular, it finely predicts the first generation quark masses and the values of θl13 and JlCP in neutrino physics. All of the results are promising to be tested in the future experiments.
Jiang, Rui; Mou, Daixing; Liu, Chang; Zhao, Xin; Yao, Yongxin; Ryu, Hyejin; Petrovic, C.; Ho, Kai -Ming; Kaminski, Adam
2015-04-01
We use angle-resolved photoemission spectroscopy (ARPES) to study the 2D heavy fermion superconductor, Ce₂RhIn₈. The Fermi surface is rather complicated and consists of several hole and electron pockets with one of the sheets displaying strong nesting properties with a q-vector of (0.32, 0.32) π/a. We do not observe k_{z} dispersion of the Fermi sheets, which is consistent with the expected 2D character of the electronic structure. Comparison of the ARPES data to band structure calculations suggests that a localized picture of the f-electrons works best. While there is some agreement in the overall band dispersion and location of the Fermi sheets, the model does not reproduce all observed bands and is not completely accurate for those it does. As a result, our data paves the way for improving the band structure calculations and the general understanding of the transport and thermodynamical properties of this material.
Wilson fermions at finite temperature
Creutz, M.
1996-09-17
The author conjectures on the phase structure expected for lattice gauge theory with two flavors of Wilson fermions, concentrating on large values of the hopping parameter. Numerous phases are expected, including the conventional confinement and deconfinement phases, as well as an Aoki phase with spontaneous breaking of flavor and parity and a large hopping phase corresponding to negative quark masses.
Reflection Relations and Fermionic Basis
NASA Astrophysics Data System (ADS)
Negro, S.; Smirnov, F.
2013-12-01
There are two approaches to computing the one-point functions for sine-Gordon model in infinite volume. One is based on the use of the reflection relations, this is a bootstrap type procedure. Another is based on using the fermionic basis which originated in the study of lattice model. We show that the two procedures are deeply interrelated.
Chronometric cosmology and fundamental fermions
Segal, I. E.
1982-01-01
It is proposed that the fundamental fermions of nature are modeled by fields on the chronometric cosmos that are not precisely spinors but become such only in the nonchronometric limit. The imbedding of the scale-extended Poincaré group in the linearizer of the Minkowskian conformal group defines such fields, by induction. PMID:16593266
Fermion bag approach to lattice field theories
Chandrasekharan, Shailesh
2010-07-15
We propose a new approach to the fermion sign problem in systems where there is a coupling U such that when it is infinite the fermions are paired into bosons, and there is no fermion permutation sign to worry about. We argue that as U becomes finite, fermions are liberated but are naturally confined to regions which we refer to as fermion bags. The fermion sign problem is then confined to these bags and may be solved using the determinantal trick. In the parameter regime where the fermion bags are small and their typical size does not grow with the system size, construction of Monte Carlo methods that are far more efficient than conventional algorithms should be possible. In the region where the fermion bags grow with system size, the fermion bag approach continues to provide an alternative approach to the problem but may lose its main advantage in terms of efficiency. The fermion bag approach also provides new insights and solutions to sign problems. A natural solution to the ''silver blaze problem'' also emerges. Using the three-dimensional massless lattice Thirring model as an example, we introduce the fermion bag approach and demonstrate some of these features. We compute the critical exponents at the quantum phase transition and find {nu}=0.87(2) and {eta}=0.62(2).
NASA Technical Reports Server (NTRS)
2005-01-01
[figure removed for brevity, see original site]
Windstreaks are features caused by the interaction of wind and topographic landforms. The raised rims and bowls of impact craters causes a complex interaction such that the wind vortex in the lee of the crater can both scour away the surface dust and deposit it back in the center of the lee. If you look closely, you will see evidence of this in a darker 'rim' enclosing a brighter interior.
This infrared image shows windstreaks in the region between Gordii Dorsum and Amazonis Mensa.
Image information: IR instrument. Latitude -15.8, Longitude 215 East (145 West). 97 meter/pixel resolution.
Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.
NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.
Pinning of fermionic occupation numbers.
Schilling, Christian; Gross, David; Christandl, Matthias
2013-01-25
The Pauli exclusion principle is a constraint on the natural occupation numbers of fermionic states. It has been suspected since at least the 1970s, and only proved very recently, that there is a multitude of further constraints on these numbers, generalizing the Pauli principle. Here, we provide the first analytic analysis of the physical relevance of these constraints. We compute the natural occupation numbers for the ground states of a family of interacting fermions in a harmonic potential. Intriguingly, we find that the occupation numbers are almost, but not exactly, pinned to the boundary of the allowed region (quasipinned). The result suggests that the physics behind the phenomenon is richer than previously appreciated. In particular, it shows that for some models, the generalized Pauli constraints play a role for the ground state, even though they do not limit the ground-state energy. Our findings suggest a generalization of the Hartree-Fock approximation.
Quantum Algorithms for Fermionic Simulations
NASA Astrophysics Data System (ADS)
Ortiz, Gerardo
2001-06-01
The probabilistic simulation of quantum systems in classical computers is known to be limited by the so-called sign or phase problem, a problem believed to be of exponential complexity. This ``disease" manifests itself by the exponentially hard task of estimating the expectation value of an observable with a given error. Therefore, probabilistic simulations on a classical computer do not seem to qualify as a practical computational scheme for general quantum many-body problems. The limiting factors, for whatever reasons, are negative or complex-valued probabilities whether the simulations are done in real or imaginary time. In 1981 Richard Feynman raised some provocative questions in connection to the ``exact imitation'' of such systems using a special device named a ``quantum computer.'' Feynman hesitated about the possibility of imitating fermion systems using such a device. Here we address some of his concerns and, in particular, investigate the simulation of fermionic systems. We show how quantum algorithms avoid the sign problem by reducing the complexity from exponential to polynomial. Our demonstration is based upon the use of isomorphisms of *-algebras (spin-particle transformations) which connect different models of quantum computation. In particular, we present fermionic models (the fabled ``Grassmann Chip''); but, of course, these models are not the only ones since our spin-particle connections allow us to introduce more ``esoteric'' models of computation. We present specific quantum algorithms that illustrate the main points of our algebraic approach.
Superdeformations and fermion dynamical symmetries
Wu, Cheng-Li . Dept. of Physics and Atmospheric Science Tennessee Univ., Knoxville, TN . Dept. of Physics and Astronomy Joint Inst. for Heavy Ion Research, Oak Ridge, TN )
1990-01-01
In this talk, I will present a link between nuclear collective motions and their underlying fermion dynamical symmetries. In particular, I will focus on the microscopic understanding of deformations. It is shown that the SU{sub 3} of the one major shell fermion dynamical symmetry model (FDSM) is responsible for the physics of low and high spins in normal deformation. For the recently observed phenomena of superdeformation, the physics of the problem dictates a generalization to a supershell structure (SFDSM), which also has an SU{sub 3} fermion dynamical symmetry. Many recently discovered feature of superdeformation are found to be inherent in such an SU{sub 3} symmetry. In both cases the dynamical Pauli effect plays a vital role. A particularly noteworthy discovery from this model is that the superdeformed ground band is not the usual unaligned band but the D-pair aligned (DPA) band, which sharply crosses the excited bands. The existence of such DPA band is a key point to understand many properties of superdeformation. Our studies also poses new experimental challenge. This is particularly interesting since there are now plans to build new and exciting {gamma}-ray detecting systems, like the GAMMASPHERE, which could provide answers to some of these challenges. 34 refs., 11 figs., 5 tabs.
Light scattering of degenerate fermions
NASA Astrophysics Data System (ADS)
Aubin, S.; Leblanc, L. J.; Myrskog, S.; Extavour, M. H. T.; McKay, D.; Stummer, A.; Thywissen, J. H.
2006-05-01
We report on progress in measuring the suppression of resonant light scattering in a gas of degenerate fermions. A gas of trapped degenerate fermions is expected to exhibit narrower optical linewidths and longer excited state lifetimes than single atoms when the Fermi energy is larger than the photon recoil energy [1-3]. In this case, the number of available states into which a scattered atom can recoil is significantly reduced due to the filling of the Fermi sea. We produce a degenerate gas of 4x10^4 ultra-cold fermionic ^40K atoms by sympathetic cooling with bosonic ^87Rb in a micro-magnetic chip trap. The atoms can then be loaded into a tight dipole trap just above the surface of the chip and probed with a near resonance laser pulse. [1] Th. Busch, J. R. Anglin, J. I. Cirac, and P. Zoller, Europhys. Lett. 44, 1 (1998). [2] B. DeMarco and D. S. Jin, Phys. Rev. A 58, R4267 (1998). [3] J. Javanainen and J. Ruostekosky, Phys. Rev. A 52, 3033 (1995). Work supported by NSERC, CFI, OIT, Research Corporation, and PRO.
Aharonov-Bohm radiation of fermions
Chu Yizen; Mathur, Harsh; Vachaspati, Tanmay
2010-09-15
We analyze Aharonov-Bohm radiation of charged fermions from oscillating solenoids and cosmic strings. We find that the angular pattern of the radiation has features that differ significantly from that for bosons. For example, fermionic radiation in the lowest harmonic is approximately isotropically distributed around an oscillating solenoid, whereas for bosons the radiation is dipolar. We also investigate the spin polarization of the emitted fermion-antifermion pair. Fermionic radiation from kinks and cusps on cosmic strings is shown to depend linearly on the ultraviolet cutoff, suggesting strong emission at an energy scale comparable to the string energy scale.
Fermion mass hierarchy from the soft wall
Delgado, Antonio; Diego, David
2009-07-15
We develop a five-dimensional model for electroweak physics based on a noncompact warped extra dimension of finite length, known as the soft wall scenario, where all the dynamical degrees of freedom propagate in the five-dimensional bulk. We solve the equations of motion and find the allowed spectra, showing that the mass of the lightest fermionic mode behaves as a power law of the effective four-dimensional Yukawa coupling constant, with the exponent being the corresponding fermionic five-dimensional bulk mass. Precisely this nonuniversal behavior allows us to reproduce the hierarchy between the standard model fermion masses (from neutrinos to the top quark) with nonhierarchical fermionic bulk masses.
Light quark simulations with FLIC fermions
J.M. Zanotti; D.B. Leinweber; W. Melnitchouk; A.G. Williams; J.B. Zhang
2002-06-01
Hadron masses are calculated in quenched lattice QCD in order to probe the scaling behavior of a novel fat-link clover fermion action in which only the irrelevant operators of the fermion action are constructed using APE-smeared links. Light quark masses corresponding to an m{sub pi}/m{sub p} ratio of 0.35 are considered to assess the exceptional configuration problem of clover-fermion actions. This Fat-Link Irrelevant Clover (FLIC) fermion action provides scaling which is superior to mean-field improvement and offers advantages over nonperturbative improvement, including reduced exceptional configurations.
Undoubled Chiral Fermions on a Lattice
NASA Astrophysics Data System (ADS)
Xue, She-Sheng
1997-02-01
We analyze the dynamics of an SU L(2)⊗ U R(1) chiral theory on the lattice with a strong multifermion coupling. It is shown that no spontaneous symmetry breaking occurs; the "spectator" fermion ψR is a free mode; doublers are decoupled as massive Dirac fermions consistently with the chiral symmetries. In 1+1 dimension, we show that the right-handed three-fermion state disappears at the threshold and an undoubled left-handed chiral fermion remains in the continuum limit.
STOUT SMEARING FOR TWISTED FERMIONS.
SCHOLZ,W.; JANSEN, K.; McNEILE, C.; MONTVAY, I.; RICHARDS, C.; URBACH, C.; WENGER, U.
2007-07-30
The effect of Stout smearing is investigated in numerical simulations with twisted mass Wilson quarks. The phase transition near zero quark mass is studied on 12{sup 3} x 24, 16{sup 3} x 32 and 24{sup 3} x 48 lattices at lattice spacings a {approx_equal} 0.1-0.125 fm. The phase structure of Wilson fermions with twisted mass ({mu}) has been investigated in [1,2]. As it is explained there, the observed first order phase transition limits the minimal pion mass which can be reached in simulations at a given lattice spacing: m{sub k}{sup min} {approx_equal} {theta}(a). The phase structure is schematically depicted in the left panel of Fig. I . The phase transition can be observed in simulations with twisted mass fermions, for instance, as a ''jump'' or even metastabilities in the average plaquette value as a function of the hopping parameter ({kappa}). One possibility to weaken the phase transition and therefore allow for lighter pion masses at a given lattice spacing is to use an improved gauge action like the DBW2, Iwasaki, or tree-level Symanzik (tlSym) improved gauge action instead of the simple Wilson gauge action. This has been successfully demonstrated in [3,4,5]. Here we report on our attempts to use a smeared gauge field in the fermion lattice Dirac operator to further reduce the strength of the phase transition. This is relevant in simulations with N{sub f} = 2 + 1 + 1 (u,d,s,c) quark flavors [6] where the first order phase transition becomes stronger compared to N{sub f} = 2 simulations. The main impact of the above mentioned improved gauge actions on the gauge fields occurring in simulations is to suppress short range fluctuations (''dislocations'') and the associated ''exceptionally small'' eigenvalues of the fermion matrix. The same effect is expected from smearing the gauge field links in the fermion action. The cumulated effect of the improved gauge action and smeared links should allow for a smaller pion mass at a given lattice spacing and volume. Our
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.
Light fermions in composite models
NASA Astrophysics Data System (ADS)
Khlebnikov, S. Yu.; Peccei, R. D.
1993-07-01
In preon models based on chiral gauge theories, we show that light composite fermions can ensue as a result of gauging a subset of preons in a vectorlike manner. After demonstrating how this mechanism works in a toy example, we construct a one-generation model of quarks which admits a hierarchy between the up and down quark masses as well as between these masses and the compositeness scale. In simple extensions of this model to more generations we discuss the challenges of obtaining any quark mixing. Some possible phenomenological implications of scenarios where quarks and leptons which are heavier are also less pointlike are also considered.
Coulomb interactions and fermion condensation
Capstick, S.; Cutkosky, R.E.; Joensen, M.A. ); Wang, K.C. )
1990-08-15
The influence of the Coulomb interaction in states containing massless and flavorless fermion-antifermion pairs is studied, using a continuum formulation within the finite volume {ital S}{sup 3}. Several different forms for the Coulomb interaction are examined, including confining potentials as well as nonconfining potentials. The calculations show that if the interaction is strong enough, the Coulomb interaction leads to condensation of pairs, and that this condensation has a chiral character. The condensation does not depend on whether the interaction is confining. It is found that simplified variational approximations are not accurate enough for an adequate description of the states.
Local Hamiltonian Monte Carlo study of the massive schwinger model, the decoupling of heavy flavours
NASA Astrophysics Data System (ADS)
Ranft, J.
1983-12-01
The massive Schwinger model with two flavours is studied using the local hamiltonian lattice Monte Carlo method. Chiral symmetry breaking is studied using the fermion condensate as order parameter. For a small ratio of the two fermion masses, degeneracy of the two flavours is found. For a large ratio of the masses, the heavy flavour decouples and the light fermion behaves like in the one flavour Schwinger model. On leave from Sektion Physik, Karl-Marx-Universität, Leipzig, GDR.
Mass-induced transition in fermion number
Aragao de Carvalho, C.; Pureza, J. M.
1989-05-15
We show that if we increase the mass of fermions in interaction with a topological (kink) scalar background in 1+1 dimensions, the fractional fermion number of the system will eventually vanish. The transition is sharp and corresponds to the disappearance of localized states from the spectrum of a Dirac operator which is exactly solvable. Possible applications to different physical systems are discussed.
Superalgebra and fermion-boson symmetry
Miyazawa, Hironari
2010-01-01
Fermions and bosons are quite different kinds of particles, but it is possible to unify them in a supermultiplet, by introducing a new mathematical scheme called superalgebra. In this article we discuss the development of the concept of symmetry, starting from the rotational symmetry and finally arriving at this fermion-boson (FB) symmetry. PMID:20228617
Tunable Dirac fermion dynamics in topological insulators.
Chen, Chaoyu; Xie, Zhuojin; Feng, Ya; Yi, Hemian; Liang, Aiji; He, Shaolong; Mou, Daixiang; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Yu, Li; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Zhou, X J
2013-01-01
Three-dimensional topological insulators are characterized by insulating bulk state and metallic surface state involving relativistic Dirac fermions which are responsible for exotic quantum phenomena and potential applications in spintronics and quantum computations. It is essential to understand how the Dirac fermions interact with other electrons, phonons and disorders. Here we report super-high resolution angle-resolved photoemission studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3 topological insulators. We have directly revealed signatures of the electron-phonon coupling and found that the electron-disorder interaction dominates the scattering process. The Dirac fermion dynamics in Bi2(Te3-xSex) topological insulators can be tuned by varying the composition, x, or by controlling the charge carriers. Our findings provide crucial information in understanding and engineering the electron dynamics of the Dirac fermions for fundamental studies and potential applications.
Fermion hierarchy from sfermion anarchy
Altmannshofer, Wolfgang; Frugiuele, Claudia; Harnik, Roni
2014-12-31
We present a framework to generate the hierarchical flavor structure of Standard Model quarks and leptons from loops of superpartners. The simplest model consists of the minimal supersymmetric standard model with tree level Yukawa couplings for the third generation only and anarchic squark and slepton mass matrices. Agreement with constraints from low energy flavor observables, in particular Kaon mixing, is obtained for supersymmetric particles with masses at the PeV scale or above. In our framework both the second and the first generation fermion masses are generated at 1-loop. Despite this, a novel mechanism generates a hierarchy among the first and second generations without imposing a symmetry or small parameters. A second-to-first generation mass ratio of order 100 is typical. The minimal supersymmetric standard model thus includes all the necessary ingredients to realize a fermion spectrum that is qualitatively similar to observation, with hierarchical masses and mixing. The minimal framework produces only a few quantitative discrepancies with observation, most notably the muon mass is too low. Furthermore, we discuss simple modifications which resolve this and also investigate the compatibility of our model with gauge and Yukawa coupling Unification.
Fermion hierarchy from sfermion anarchy
Altmannshofer, Wolfgang; Frugiuele, Claudia; Harnik, Roni
2014-12-31
We present a framework to generate the hierarchical flavor structure of Standard Model quarks and leptons from loops of superpartners. The simplest model consists of the minimal supersymmetric standard model with tree level Yukawa couplings for the third generation only and anarchic squark and slepton mass matrices. Agreement with constraints from low energy flavor observables, in particular Kaon mixing, is obtained for supersymmetric particles with masses at the PeV scale or above. In our framework both the second and the first generation fermion masses are generated at 1-loop. Despite this, a novel mechanism generates a hierarchy among the first andmore » second generations without imposing a symmetry or small parameters. A second-to-first generation mass ratio of order 100 is typical. The minimal supersymmetric standard model thus includes all the necessary ingredients to realize a fermion spectrum that is qualitatively similar to observation, with hierarchical masses and mixing. The minimal framework produces only a few quantitative discrepancies with observation, most notably the muon mass is too low. Furthermore, we discuss simple modifications which resolve this and also investigate the compatibility of our model with gauge and Yukawa coupling Unification.« less
Superconductivity in Pd, Ir, and Pt chalcogenide
NASA Astrophysics Data System (ADS)
Oh, Yoon Seok; Yang, Junjie; Choi, Y. J.; Hogan, A.; Horibe, Y.; Cheong, S.-W.
2012-02-01
Large spin-orbit coupling in materials with heavy chalcogens can result in unique quantum states or functional properties such as topological insulator, giant thermoelectric power, and superconductivity. When materials contain heavy cations in addition to heavy chalcogens, spin-orbit coupling can be further enhanced. For these reasons, we have studied the superconductivity of Pd, Ir, and Pt tellurides and selenides. In the exploration of these chalcogenides, we have focused on the competition between superconductivity and charge density wave that is associated with superlattice reflections.
Heavy fermions. Unconventional Fermi surface in an insulating state.
Tan, B S; Hsu, Y-T; Zeng, B; Hatnean, M Ciomaga; Harrison, N; Zhu, Z; Hartstein, M; Kiourlappou, M; Srivastava, A; Johannes, M D; Murphy, T P; Park, J-H; Balicas, L; Lonzarich, G G; Balakrishnan, G; Sebastian, Suchitra E
2015-07-17
Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.
TRANSPORT IN THE HEAVY FERMION SUPERCONDUCTOR UPT3
M. GRAF; ET AL
1999-04-01
We report new theoretical results and analysis for the transport properties of superconducting UPt{sub 3}based on the leading models for the pairing symmetry. We use Fermi surface data and the measured inelastic scattering rate to show that the low-temperature thermal conductivity and transverse sound attenuation in the A and B phase of UPt3 are in excellent agreement with pairing states belonging to the two-dimensional orbital E{sub 2u} representation.
Kondo Lattice and Antiferromagnetic Behavior in Quaternary CeTAl4Si2 (T = Rh, Ir) Single Crystals
NASA Astrophysics Data System (ADS)
Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; Paudyal, Durga; Dhar, Sudesh Kumar
2016-03-01
We have explored in detail the anisotropic magnetic properties of CeRhAl4Si2 and CeIrAl4Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4Si2 and CeIrAl4Si2, respectively, classifying these materials as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two compounds.
Kondo lattice and antiferromagnetic behavior in quaternary CeTAl4Si2 (T = Rh, Ir) single crystals
Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; Paudyal, Durga; Dhar, Sudesh Kumar
2016-02-26
Here, we have explored in detail the anisotropic magnetic properties of CeRhAl4Si2 and CeIrAl4Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4Si2 and CeIrAl4Si2, respectively, classifying these materialsmore » as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two compounds.« less
NASA Astrophysics Data System (ADS)
de Brito, K. P. S.; da Rocha, Roldão
2016-10-01
The spinor fields on 5-dimensional Lorentzian manifolds are classified according to the geometric Fierz identities, which involve their bilinear covariants. Based upon this classification, which generalises the celebrated 4-dimensional Lounesto classification of spinor fields, new non-trivial classes of 5-dimensional spinor fields are hence found, with important potential applications regarding bulk fermions and their subsequent localisation on brane-worlds. In addition, quaternionic bilinear covariants are used to derive the quaternionic spin density through the truncated exterior bundle. In order to accomplish the realisation of these new spinors, a Killing vector field is constructed on the horizon of a 5-dimensional Kerr black hole. This Killing vector field is shown to reach the time-like Killing vector field at spatial infinity through a current 1-form density, constructed with the new derived spinor fields. The current density is, moreover, expressed as the fünfbein component, assuming a condensed form.
QCD with rooted staggered fermions
NASA Astrophysics Data System (ADS)
Goltermann, M.
In this talk, I will give an overview of the theoretical status of staggered Lattice QCD with the “fourth-root trick.” In this regularization of QCD, a separate staggered quark field is used for each physical flavor, and the inherent four-fold multiplicity that comes with the use of staggered fermions is removed by taking the fourth root of the staggered determinant for each flavor. At nonzero lattice spacing, the resulting theory is nonlocal and not unitary, but there are now strong arguments that this disease is cured in the continuum limit. In addition, the approach to the continuum limit can be understood in detail in the framework of effective field theories such as staggered chiral perturbation theory.
Fermion tunneling from dynamical horizons
NASA Astrophysics Data System (ADS)
Di Criscienzo, R.; Vanzo, L.
2008-06-01
The instability against emission of fermionic particles by the trapping horizon of an evolving black hole is analyzed and confirmed using the Hamilton-Jacobi tunneling method. This method automatically selects one special expression for the surface gravity of a changing horizon. The results also apply to point masses embedded in an expanding universe. As a bonus of the tunneling method, we gain the insight that the surface gravity still defines a temperature parameter as long as the evolution is sufficiently slow that the black-hole pass through a sequence of quasi-equilibrium states, and that black holes should be semi-classically unstable even in a hypothetical world without bosonic fields.
Flavor symmetries and fermion masses
Rasin, A.
1994-04-01
We introduce several ways in which approximate flavor symmetries act on fermions and which are consistent with observed fermion masses and mixings. Flavor changing interactions mediated by new scalars appear as a consequence of approximate flavor symmetries. We discuss the experimental limits on masses of the new scalars, and show that the masses can easily be of the order of weak scale. Some implications for neutrino physics are also discussed. Such flavor changing interactions would easily erase any primordial baryon asymmetry. We show that this situation can be saved by simply adding a new charged particle with its own asymmetry. The neutrality of the Universe, together with sphaleron processes, then ensures a survival of baryon asymmetry. Several topics on flavor structure of the supersymmetric grand unified theories are discussed. First, we show that the successful predictions for the Kobayashi-Maskawa mixing matrix elements, V{sub ub}/V{sub cb} = {radical}m{sub u}/m{sub c} and V{sub td}/V{sub ts} = {radical}m{sub d}/m{sub s}, are a consequence of a large class of models, rather than specific properties of a few models. Second, we discuss how the recent observation of the decay {beta} {yields} s{gamma} constrains the parameter space when the ratio of the vacuum expectation values of the two Higgs doublets, tan{Beta}, is large. Finally, we discuss the flavor structure of proton decay. We observe a surprising enhancement of the branching ratio for the muon mode in SO(10) models compared to the same mode in the SU(5) model.
Fermionic Schwinger effect and induced current in de Sitter space
NASA Astrophysics Data System (ADS)
Hayashinaka, Takahiro; Fujita, Tomohiro; Yokoyama, Jun'ichi
2016-07-01
We explore Schwinger effect of spin 1/2 charged particles with static electric field in 1+3 dimensional de Sitter spacetime. We analytically calculate the vacuum expectation value of the spinor current which is induced by the produced particles in the electric field. The renormalization is performed with the adiabatic subtraction scheme. We find that the current becomes negative, namely it flows in the direction opposite to the electric field, if the electric field is weaker than a certain threshold value depending on the fermion mass, which is also known to happen in the case of scalar charged particles in 1+3 de Sitter spacetime. Contrary to the scalar case, however, the IR hyperconductivity is absent in the spinor case.
Instantons and Massless Fermions in Two Dimensions
DOE R&D Accomplishments Database
Callan, C. G. Jr.; Dashen, R.; Gross, D. J.
1977-05-01
The role of instantons in the breakdown of chiral U(N) symmetry is studied in a two dimensional model. Chiral U(1) is always destroyed by the axial vector anomaly. For N = 2 chiral SU(N) is also spontaneously broken yielding massive fermions and three (decoupled) Goldstone bosons. For N greater than or equal to 3 the fermions remain massless. Realistic four dimensional theories are believed to behave in a similar way but the critical N above which the fermions cease to be massive is not known in four dimensions.
Fermion localization on a split brane
Chumbes, A. E. R.; Vasquez, A. E. O.; Hott, M. B.
2011-05-15
In this work we analyze the localization of fermions on a brane embedded in five-dimensional, warped and nonwarped, space-time. In both cases we use the same nonlinear theoretical model with a nonpolynomial potential featuring a self-interacting scalar field whose minimum energy solution is a soliton (a kink) which can be continuously deformed into a two-kink. Thus a single brane splits into two branes. The behavior of spin 1/2 fermions wave functions on the split brane depends on the coupling of fermions to the scalar field and on the geometry of the space-time.
On orbifolds and free fermion constructions
NASA Astrophysics Data System (ADS)
Donagi, Ron; Wendland, Katrin
2009-07-01
This work develops the correspondence between orbifolds and free fermion models. A complete classification is obtained for orbifolds X/G with X the product of three elliptic curves and G an abelian extension of a group ( of twists acting on X. Each such quotient X/G is shown to give a geometric interpretation to an appropriate free fermion model, including the geometric NAHE+ model. However, the semi-realistic NAHE free fermion model is proved to be non-geometric: its Hodge numbers are not reproduced by any orbifold X/G. In particular cases it is shown that X/G can agree with some Borcea-Voisin threefolds, an orbifold limit of the Schoen threefold, and several further orbifolds thereof. This yields free fermion models with geometric interpretations on such special threefolds.
Quantum-Gas Microscope for Fermionic Atoms
NASA Astrophysics Data System (ADS)
Cheuk, Lawrence W.; Nichols, Matthew A.; Okan, Melih; Gersdorf, Thomas; Ramasesh, Vinay V.; Bakr, Waseem S.; Lompe, Thomas; Zwierlein, Martin W.
2015-05-01
We realize a quantum-gas microscope for fermionic 40K atoms trapped in an optical lattice, which allows one to probe strongly correlated fermions at the single-atom level. We combine 3D Raman sideband cooling with high-resolution optics to simultaneously cool and image individual atoms with single-lattice-site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site-resolved imaging of fermions enables the direct observation of magnetic order, time-resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement.
Quantum Materials: Weyl fermions go into orbit
NASA Astrophysics Data System (ADS)
Dai, Xi
2016-08-01
Due to their chirality, the massless fermions inside Weyl semimetals can take unusual paths that are governed by chiral dynamics, potentially providing a direct method to explore their topological nature.
Quantum-gas microscope for fermionic atoms.
Cheuk, Lawrence W; Nichols, Matthew A; Okan, Melih; Gersdorf, Thomas; Ramasesh, Vinay V; Bakr, Waseem S; Lompe, Thomas; Zwierlein, Martin W
2015-05-15
We realize a quantum-gas microscope for fermionic ^{40}K atoms trapped in an optical lattice, which allows one to probe strongly correlated fermions at the single-atom level. We combine 3D Raman sideband cooling with high-resolution optics to simultaneously cool and image individual atoms with single-lattice-site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site-resolved imaging of fermions enables the direct observation of magnetic order, time-resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement. PMID:26024169
Majorana Fermions and Topology in Superconductors
NASA Astrophysics Data System (ADS)
Sato, Masatoshi; Fujimoto, Satoshi
2016-07-01
Topological superconductors are novel classes of quantum condensed phases, characterized by topologically nontrivial structures of Cooper pairing states. On the surfaces of samples and in vortex cores of topological superconductors, Majorana fermions, which are particles identified with their own anti-particles, appear as Bogoliubov quasiparticles. The existence and stability of Majorana fermions are ensured by bulk topological invariants constrained by the symmetries of the systems. Majorana fermions in topological superconductors obey a new type of quantum statistics referred to as non-Abelian statistics, which is distinct from bose and fermi statistics, and can be utilized for application to topological quantum computation. Also, Majorana fermions give rise to various exotic phenomena such as "fractionalization", non-local correlation, and "teleportation". A pedagogical review of these subjects is presented. We also discuss interaction effects on topological classification of superconductors, and the basic properties of Weyl superconductors.
Dissipation coefficients from scalar and fermion quantum field interactions
Bastero-Gil, Mar; Berera, Arjun; Ramos, Rudnei O. E-mail: ab@ph.ed.ac.uk
2011-09-01
Dissipation coefficients are calculated in the adiabatic, near thermal equilibrium regime for a large class of renormalizable interaction configurations involving a two-stage mechanism, where a background scalar field is coupled to heavy intermediate scalar or fermion fields which in turn are coupled to light scalar or fermion radiation fields. These interactions are typical of warm inflation microscopic model building. Two perturbative regimes are shown where well defined approximations for the spectral functions apply. One regime is at high temperature, when the masses of both intermediate and radiation fields are less than the temperature scale and where the poles of the spectral functions dominate. The other regime is at low temperature, when the intermediate field masses are much bigger than the temperature and where the low energy and low three-momentum regime dominate the spectral functions. The dissipation coefficients in these two regimes are derived. However, due to resummation issues for the high temperature case, only phenomenological approximate estimates are provided for the dissipation in this regime. In the low temperature case, higher loop contributions are suppressed and so no resummation is necessary. In addition to inflationary cosmology, the application of our results to cosmological phase transitions is also discussed.
Fermionic Subspaces of the Bosonic String
NASA Astrophysics Data System (ADS)
Chattaraputi, A.; Englert, F.; Houart, L.; Taormina, A.
A universal symmetric truncation of the bosonic string Hilbert space yields all known closed fermionic string theories in ten dimensions, their D-branes and their open descendants. We highlight the crucial role played by group theory and two-dimensional conformal field theory in the construction and emphasize the predictive power of the truncation. Such circumstantial evidence points towards the existence of a mechanism which generates space-time fermions out of bosons dynamically within the framework of bosonic string theory.
Fermionic subspaces of the bosonic string
NASA Astrophysics Data System (ADS)
Chattaraputi, Auttakit; Englert, François; Houart, Laurent; Taormina, Anne
2003-06-01
A universal symmetric truncation of the bosonic string Hilbert space yields all known closed fermionic string theories in ten dimensions, their D-branes and their open descendants. We highlight the crucial role played by group theory and two-dimensional conformal field theory in the construction and emphasize the predictive power of the truncation. Such circumstantial evidence points towards the existence of a mechanism which generates spacetime fermions out of bosons dynamically within the framework of bosonic string theory.
Quantum Gas Microscope for Fermionic Atoms
NASA Astrophysics Data System (ADS)
Okan, Melih; Cheuk, Lawrence; Nichols, Matthew; Lawrence, Katherine; Zhang, Hao; Zwierlein, Martin
2016-05-01
Strongly interacting fermions define the properties of complex matter throughout nature, from atomic nuclei and modern solid state materials to neutron stars. Ultracold atomic Fermi gases have emerged as a pristine platform for the study of many-fermion systems. In this poster we demonstrate the realization of a quantum gas microscope for fermionic 40 K atoms trapped in an optical lattice and the recent experiments which allows one to probe strongly correlated fermions at the single atom level. We combine 3D Raman sideband cooling with high- resolution optics to simultaneously cool and image individual atoms with single lattice site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site resolved imaging of fermions enables the direct observation of magnetic order, time resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement. NSF, AFOSR-PECASE, AFOSR-MURI on Exotic Phases of Matter, ARO-MURI on Atomtronics, ONR, a Grant from the Army Research Office with funding from the DARPA OLE program, and the David and Lucile Packard Foundation.
Iterants, Fermions and Majorana Operators
NASA Astrophysics Data System (ADS)
Kauffman, Louis H.
Beginning with an elementary, oscillatory discrete dynamical system associated with the square root of minus one, we study both the foundations of mathematics and physics. Position and momentum do not commute in our discrete physics. Their commutator is related to the diffusion constant for a Brownian process and to the Heisenberg commutator in quantum mechanics. We take John Wheeler's idea of It from Bit as an essential clue and we rework the structure of that bit to a logical particle that is its own anti-particle, a logical Marjorana particle. This is our key example of the amphibian nature of mathematics and the external world. We show how the dynamical system for the square root of minus one is essentially the dynamics of a distinction whose self-reference leads to both the fusion algebra and the operator algebra for the Majorana Fermion. In the course of this, we develop an iterant algebra that supports all of matrix algebra and we end the essay with a discussion of the Dirac equation based on these principles.
Adams, David H.
2008-05-15
To investigate the viability of the 4th root trick for the staggered fermion determinant in a simpler setting, we consider a 2-taste (flavor) lattice fermion formulation with no taste mixing but with exact taste-nonsinglet chiral symmetries analogous to the taste-nonsinglet U(1){sub A} symmetry of staggered fermions. Creutz's objections to the rooting trick apply just as much in this setting. To counter them we show that the formulation has robust would-be zero modes in topologically nontrivial gauge backgrounds, and that these manifest themselves in a viable way in the rooted fermion determinant and also in the disconnected piece of the pseudoscalar meson propagator as required to solve the U(1) problem. Also, our rooted theory is heuristically seen to be in the right universality class for QCD if the same is true for an unrooted mixed fermion action theory.
Proposal of Unified Fermion Texture
NASA Astrophysics Data System (ADS)
Krolikowski, W.
1998-03-01
unified form of mass matrix is proposed for neutrinos, charged leptons, up quarks and down quarks. Some constraints for the parameters involved are tentatively postulated. Then, the predictions are neatly consistent with available experimental data. Among the predictions are: (i) mτ ~1776.80 MeV (with the inputs of me and mμ ), (ii) mν_0 ≪ mν_1~(0.6 to )× 10-2 eV and mν_2~ (0.2 to 1)× 10-1 eV (with the atmospheric-neutrino inputs of |mν_22 - mν_12| × (0.0003 to 0.01) eV2 and the νμ → ντ oscillation amplitude × 0.8), and also ( iii) ms ~270 MeV, |Vub/Vcb| ~0.082 and argVub ~-640 (with the inputs of mc = 1.3 GeV, mb = 4.5 GeV, |Vus| = 0.221 and |Vcb| = 0.041, where mu ≪ mc ≪ mt and md ≪ ms ≪ mb ). All elements of the Cabibbo--Kobayashi--Maskawa matrix are evaluated. All elements of its lepton counterpart are calculated up to an unknown phase (Appendix B). Some items related to dynamical aspects of the proposed fermion ``texture'' are briefly commented on (Appendix A). In particular, the notion of a novel dark matter, free of any Standard Model interactions (and their supersymmetric variants), appears in the case of preon option.
Heat transport study of field-tuned quantum criticality in CeIrIn5
NASA Astrophysics Data System (ADS)
Shakeripour, H.; Tanatar, M. A.; Petrovic, C.; Taillefer, Louis
2016-02-01
The in-plane electrical resistivity, ρ , and thermal conductivity, κ , of the heavy-fermion superconductor CeIrIn5 were measured down to 40 mK in magnetic fields up to 11 T applied along the c axis. For all fields above Hc 2=4 T of filamentary superconductivity, we find that the ratio of heat and charge conductivities in the T →0 limit obeys the Wiedemann-Franz law, κ /T =L0/ρ , where L0=2.45 ×10-8 WΩ K-2 is the Sommerfeld value of the Lorenz number. The temperature-dependent parts of both the electrical and thermal resistivity, w ≡T /L0κ , follow the functional dependence expected for the Fermi liquid theory of metals with ρ -ρ0=A T2 , w -w0=B T2 , with ρ0=w0 and B ≈2 A . The coefficient B does not show a significant field dependence even upon approaching Hc 2=0.4 T of the bulk superconducting state. The weak response to the magnetic field is in stark contrast with the behavior found in the closely related CeCoIn5, in which the field-tuned quantum critical point coincides with Hc 2. The value of the electron-electron mass enhancement, as judged by the A and B coefficients, is about one order of magnitude reduced in CeIrIn5 as compared to CeCoIn5 (in spite of the fact that the zero field γ0 in CeIrIn5 is twice as large as γ0 in CeCoIn5), which suggests that the material is significantly farther away from the magnetic quantum critical point at bulk Hc 2 and at all of the studied fields. A suppressed Kadowaki-Woods ratio in CeIrIn5 compared to CeCoIn5 suggests a notably more localized nature of f electrons in the compound.
Fermions on one or fewer kinks
Chu Yizen; Vachaspati, Tanmay
2008-01-15
We find the full spectrum of fermion bound states on a Z{sub 2} kink. In addition to the zero mode, there are int[2m{sub f}/m{sub s}] bound states, where m{sub f} is the fermion and m{sub s} the scalar mass. We also study fermion modes on the background of a well-separated kink-antikink pair. Using a variational argument, we prove that there is at least one bound state in this background, and that the energy of this bound state goes to zero with increasing kink-antikink separation, 2L, and faster than e{sup -a2L} where a=min(m{sub s},2m{sub f}). By numerical evaluation, we find some of the low lying bound states explicitly.
Pseudoscalar flavor-singlets and staggered fermions
NASA Astrophysics Data System (ADS)
Gregory, Eric
2006-12-01
The Asqtad improved staggered fermion formalism has been a valuable tool in successfully cal- culating the non-singlet parts of the hadronic spectrum. We are engaged in a project to calculate the spectrum of the pseudoscalar singlet mesons with 2 + 1-flavor Asqtad staggered gauge con- figurations. Propagators of flavor-singlet states incorporate contributions from both disconnected and connected diagrams, and hence are sensitive to any differences in the actions governing the sea and valence fermions on the lattice. As such, they also present the possibility of a probe of the validity of the "fourth-root trick" in the staggered fermion formulation. We present an update on our progress toward measuring the η mass on 2 + 1-flavor Asqtad staggered gauge configura- tions, including a review of methods and preliminary results. We also show a strong correlation between Tr(γ5 ⊗ 1) and the topological charge in these configurations, as predicted by the index theorem.
Realizing universal Majorana fermionic quantum computation
NASA Astrophysics Data System (ADS)
Wu, Ya-Jie; He, Jing; Kou, Su-Peng
2014-08-01
Majorana fermionic quantum computation (MFQC) was proposed by S. B. Bravyi and A. Yu. Kitaev [Ann. Phys. (NY) 298, 210 (2002), 10.1006/aphy.2002.6254], who indicated that a (nontopological) fault-tolerant quantum computer built from Majorana fermions may be more efficient than that built from distinguishable two-state systems. However, until now scientists have not known how to realize a MFQC in a physical system. In this paper we propose a possible realization of MFQC. We find that the end of a line defect of a p-wave superconductor or superfluid in a honeycomb lattice traps a Majorana zero mode, which becomes the starting point of MFQC. Then we show how to manipulate Majorana fermions to perform universal MFQC, which possesses possibilities for high-level local controllability through individually addressing the quantum states of individual constituent elements by using timely cold-atom technology.
Apparatus for Ultra-Cold Fermion Interferometry
NASA Astrophysics Data System (ADS)
Aubin, Seth; Garcia, Aiyana; Desalvo, Brian
2008-05-01
We present progress on the construction of an apparatus for ultra-cold fermion interferometry experiments. The apparatus consists of two connected glass vacuum cells: Fermionic potassium (^40K) and bosonic rubidium (^87Rb) atoms are cooled and collected in a dual-species magneto-optical trap (MOT) in the first cell and are then transported magnetically to the second cell, where they are loaded into a micro-magnetic chip trap. We use radio-frequency (RF) evaporation to cool the rubidium atoms, which in turn sympathetically cool the potassium atoms. The apparatus takes advantage of the rapid cooling inherent to micro-magnetic traps, while also benefiting from the ultra high vacuum achievable with a two chamber vacuum system. In describing our experimental approach, we address the experimental challenges and possible force-sensing applications of fermion interferometers on chips.
Fermion boson metamorphosis in field theory
Ha, Y.K.
1982-01-01
In two-dimensional field theories many features are especially transparent if the Fermi fields are represented by non-local expressions of the Bose fields. Such a procedure is known as boson representation. Bilinear quantities appear in the Lagrangian of a fermion theory transform, however, as simple local expressions of the bosons so that the resulting theory may be written as a theory of bosons. Conversely, a theory of bosons may be transformed into an equivalent theory of fermions. Together they provide a basis for generating many interesting equivalences between theories of different types. In the present work a consistent scheme for constructing a canonical Fermi field in terms of a real scalar field is developed and such a procedure is valid and consistent with the tenets of quantum field theory is verified. A boson formulation offers a unifying theme in understanding the structure of many theories. This is illustrated by the boson formulation of a multifermion theory with chiral and internal symmetries. The nature of dynamical generation of mass when the theory undergoes boson transmutation and the preservation of continuous chiral symmetry in the massive case are examined. The dynamics of the system depends to a great extent on the specific number of fermions and different models of the same system can have very different properties. Many unusual symmetries of the fermion theory, such as hidden symmetry, duality and triality symmetries, are only manifest in the boson formulation. The underlying connections between some models with U(N) internal symmetry and another class of fermion models built with Majorana fermions which have O(2N) internal symmetry are uncovered.
NASA Astrophysics Data System (ADS)
Mason, E.
In this instrument review chapter the calibration plans of ESO IR instruments are presented and briefly reviewed focusing, in particular, on the case of ISAAC, which has been the first IR instrument at VLT and whose calibration plan served as prototype for the coming instruments.
Fermion-fermion scattering in quantum field theory with superconducting circuits.
García-Álvarez, L; Casanova, J; Mezzacapo, A; Egusquiza, I L; Lamata, L; Romero, G; Solano, E
2015-02-20
We propose an analog-digital quantum simulation of fermion-fermion scattering mediated by a continuum of bosonic modes within a circuit quantum electrodynamics scenario. This quantum technology naturally provides strong coupling of superconducting qubits with a continuum of electromagnetic modes in an open transmission line. In this way, we propose qubits to efficiently simulate fermionic modes via digital techniques, while we consider the continuum complexity of an open transmission line to simulate the continuum complexity of bosonic modes in quantum field theories. Therefore, we believe that the complexity-simulating-complexity concept should become a leading paradigm in any effort towards scalable quantum simulations. PMID:25763944
Fermion-fermion scattering in quantum field theory with superconducting circuits.
García-Álvarez, L; Casanova, J; Mezzacapo, A; Egusquiza, I L; Lamata, L; Romero, G; Solano, E
2015-02-20
We propose an analog-digital quantum simulation of fermion-fermion scattering mediated by a continuum of bosonic modes within a circuit quantum electrodynamics scenario. This quantum technology naturally provides strong coupling of superconducting qubits with a continuum of electromagnetic modes in an open transmission line. In this way, we propose qubits to efficiently simulate fermionic modes via digital techniques, while we consider the continuum complexity of an open transmission line to simulate the continuum complexity of bosonic modes in quantum field theories. Therefore, we believe that the complexity-simulating-complexity concept should become a leading paradigm in any effort towards scalable quantum simulations.
NASA Astrophysics Data System (ADS)
Quack, Martin
1995-01-01
Recent progress in IR laser chemistry is reviewed with stress on the conceptual background and experimental advances from our research group. In particular we discuss various experimental schemes in laser chemistry as related to thermal reactions and ordinary photochemistry, and new results in time and frequency resolved kinetic IR spectroscopy at the limit defined by the uncertainty relation. The recent detection of hyperfine effects in IR laser chemistry is reviewed as well as nonlinear intensity dependence over many orders of magnitude including observations of nonlinear intensity fall-off and IR laser ionization of molecules. An outlook is presented on different time scales for intramolecular processes and the resulting future possibilities of IR laser chemical reaction control.
Graham, T. B.
2010-04-01
The IR Hot Wave{trademark} furnace is a breakthrough heat treatment system for manufacturing metal components. Near-infrared (IR) radiant energy combines with IR convective heating for heat treating. Heat treatment is an essential process in the manufacture of most components. The controlled heating and cooling of a metal or metal alloy alters its physical, mechanical, and sometimes chemical properties without changing the object's shape. The IR Hot Wave{trademark} furnace offers the simplest, quickest, most efficient, and cost-effective heat treatment option for metals and metal alloys. Compared with other heat treatment alternatives, the IR Hot Wave{trademark} system: (1) is 3 to 15 times faster; (2) is 2 to 3 times more energy efficient; (3) is 20% to 50% more cost-effective; (4) has a {+-}1 C thermal profile compared to a {+-}10 C thermal profile for conventional gas furnaces; and (5) has a 25% to 50% smaller footprint.
Topological susceptibility in staggered fermion chiral perturbation theory
Billeter, Brian; DeTar, Carleton; Osborn, James
2004-10-01
The topological susceptibility of the vacuum in quantum chromodynamics has been simulated numerically using the Asqtad improved staggered fermion formalism. At nonzero lattice spacing, the residual fermion doublers (fermion tastes) in the staggered fermion formalism give contributions to the susceptibility that deviate from conventional continuum chiral perturbation theory. In this brief report, we estimate the taste-breaking artifact and compare it with results of recent simulations, finding that it accounts for roughly half of the scaling violation.
The bosonic mother of fermionic D-branes
NASA Astrophysics Data System (ADS)
Chattaraputi, Auttakit; Englert, François; Houart, Laurent; Taormina, Anne
2002-09-01
We extend the search for fermionic subspaces of the bosonic string compactified on E8 × SO(16) lattices to include all fermionic D-branes. This extension constraints the truncation procedure previously proposed and relates the fermionic strings, supersymmetric or not, to the global structure of the SO(16) group. The specific properties of all the fermionic D-branes are found to be encoded in its universal covering, whose maximal toroid defines the configuration space torus of their mother bosonic theory.
Fermionic superfluidity with imbalanced spin populations.
Zwierlein, Martin W; Schirotzek, André; Schunck, Christian H; Ketterle, Wolfgang
2006-01-27
We established superfluidity in a two-state mixture of ultracold fermionic atoms with imbalanced state populations. This study relates to the long-standing debate about the nature of the superfluid state in Fermi systems. Indicators for superfluidity were condensates of fermion pairs and vortices in rotating clouds. For strong interactions, near a Feshbach resonance, superfluidity was observed for a broad range of population imbalances. We mapped out the superfluid regime as a function of interaction strength and population imbalance and characterized the quantum phase transition to the normal state, known as the Pauli limit of superfluidity.
Novel Fat-Link Fermion Actions
J. M. Zanotti; S. Bilson-Thompson; F. D. R. Bonnet; P. D. Coddington; D. B. Leinweber; A. G. Williams; J. B. Zhang; W. Melnitchouk; F. X. Lee
2001-07-01
The hadron mass spectrum is calculated in lattice QCD using a novel fat-link clover fermion action in which only the irrelevant operators in the fermion action are constructed using smeared links. The simulations are performed on a 16{sup 3} x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link Irrelevant Clover (FLIC) action provides scaling which is superior to mean-field improvement, and offers advantages over nonperturbative 0(a) improvement.
Condensation of gauge interacting massless fermions
Siringo, Fabio
2004-09-15
A single massless fermionic field with an Abelian U(1) gauge interaction (electrodynamics of a massless Dirac fermion) is studied by a variational method. Even without the insertion of any extra interaction the vacuum is shown to be unstable towards a particle-antiparticle condensate. The single particle excitations do acquire a mass and behave as massive Fermi particles. An explicit low-energy gap equation has been derived and numerically solved. Some consequences of condensation and mass generation are discussed in the framework of the standard model.
Massless rotating fermions inside a cylinder
Ambruş, Victor E.; Winstanley, Elizabeth
2015-12-07
We study rotating thermal states of a massless quantum fermion field inside a cylinder in Minkowski space-time. Two possible boundary conditions for the fermion field on the cylinder are considered: the spectral and MIT bag boundary conditions. If the radius of the cylinder is sufficiently small, rotating thermal expectation values are finite everywhere inside the cylinder. We also study the Casimir divergences on the boundary. The rotating thermal expectation values and the Casimir divergences have different properties depending on the boundary conditions applied at the cylinder. This is due to the local nature of the MIT bag boundary condition, while the spectral boundary condition is nonlocal.
Fermion path integrals and topological phases
NASA Astrophysics Data System (ADS)
Witten, Edward
2016-07-01
Symmetry-protected topological (SPT) phases of matter have been interpreted in terms of anomalies, and it has been expected that a similar picture should hold for SPT phases with fermions. Here a description is given in detail of what this picture means for phases of quantum matter that can be understood via band theory and free fermions. The main examples considered are time-reversal invariant topological insulators and superconductors in two or three space dimensions. Along the way, the precise meaning of the statement that in the bulk of a 3D topological insulator, the electromagnetic θ angle is equal to π , is clarified.
Glamazda, A; Lemmens, P; Do, S-H; Choi, Y S; Choi, K-Y
2016-01-01
The fractionalization of elementary excitations in quantum spin systems is a central theme in current condensed matter physics. The Kitaev honeycomb spin model provides a prominent example of exotic fractionalized quasiparticles, composed of itinerant Majorana fermions and gapped gauge fluxes. However, identification of the Majorana fermions in a three-dimensional honeycomb lattice remains elusive. Here we report spectroscopic signatures of fractional excitations in the harmonic-honeycomb iridates β- and γ-Li2IrO3. Using polarization-resolved Raman spectroscopy, we find that the dynamical Raman response of β- and γ-Li2IrO3 features a broad scattering continuum with distinct polarization and composition dependence. The temperature dependence of the Raman spectral weight is dominated by the thermal damping of fermionic excitations. These results suggest the emergence of Majorana fermions from spin fractionalization in a three-dimensional Kitaev-Heisenberg system. PMID:27457278
Glamazda, A.; Lemmens, P.; Do, S. -H.; Choi, Y. S.; Choi, K. -Y.
2016-01-01
The fractionalization of elementary excitations in quantum spin systems is a central theme in current condensed matter physics. The Kitaev honeycomb spin model provides a prominent example of exotic fractionalized quasiparticles, composed of itinerant Majorana fermions and gapped gauge fluxes. However, identification of the Majorana fermions in a three-dimensional honeycomb lattice remains elusive. Here we report spectroscopic signatures of fractional excitations in the harmonic-honeycomb iridates β- and γ-Li2IrO3. Using polarization-resolved Raman spectroscopy, we find that the dynamical Raman response of β- and γ-Li2IrO3 features a broad scattering continuum with distinct polarization and composition dependence. The temperature dependence of the Raman spectral weight is dominated by the thermal damping of fermionic excitations. These results suggest the emergence of Majorana fermions from spin fractionalization in a three-dimensional Kitaev–Heisenberg system. PMID:27457278
Fermion-fermion interaction in a dilute gas-mixture Bose condensate
Mogilyuk, T. I.
2011-11-15
A mixture of a one-component Bose gas and two-component Fermi gas is considered at temperatures at which the Bose gas is completely condensed. Two fermions in such a mixture can interact with each other exchanging bosons from the condensate or supercondensate. The interaction potential, a change in the effective mass, the decay, and fermion spectrum are calculated in this quantum Fermi-Bose mixture.
Path integral and boson-fermion expansion in many-fermion systems: Lipkin model
Kaneko, K. )
1989-11-01
In a previous paper, a quantum-mechanical formulation involving both mean fields and independent-particle fields in many-fermion systems was proposed using the path-integral technique. Then the semiclassical calculation of the energy spectra was performed, and the quantization rule was derived by applying a stationary phase approximation on the path integral. In this paper, a boson-fermion expansion is derived from our formulation using Dirac quantization. As an illustration, the Lipkin model is utilized.
Fermions Living in a Flat World
Jesus Anguiano-Galicia, Ma. de; Bashir, A.
2006-09-25
In a plane, parity transformation, which changes the sign of only one spatial coordinate, swaps the fermion fields living in two inequivalent representations. A parity invariant Lagrangian thus contains fields corresponding to both the representations. For such a Lagrangian, we show that we can also define a chiral symmetry.
Fermionic entanglement ambiguity in noninertial frames
Montero, Miguel; Martin-Martinez, Eduardo
2011-06-15
We analyze an ambiguity in previous works on entanglement of fermionic fields in noninertial frames. This ambiguity, related to the anticommutation properties of field operators, leads to nonunique results when computing entanglement measures for the same state. We show that the ambiguity disappears when we introduce detectors, which are in any case necessary as a means to probe the field entanglement.
Reflection positivity of free overlap fermions
Kikukawa, Yoshio; Usui, Kouta
2010-12-01
It is shown that free lattice fermions defined by overlap Dirac operator fulfill the Osterwalder-Schrader reflection positivity condition with respect to the link-reflection. The proof holds true in nongauge models with interactions such as chiral Yukawa models.
Ideal fermion delocalization in Higgsless models
Chivukula, R. Sekhar; Simmons, Elizabeth H.; He, Hong-Jian; Kurachi, Masafumi; Tanabashi, Masaharu
2005-07-01
In this note we examine the properties of deconstructed Higgsless models for the case of a fermion whose SU(2) properties arise from delocalization over many sites of the deconstructed lattice. We derive expressions for the correlation functions and use these to establish a generalized consistency relation among correlation functions. We discuss the form of the W boson wavefunction and show that if the probability distribution of the delocalized fermions is appropriately related to the W wavefunction, then deviations in precision electroweak parameters are minimized. In particular, we show that this ''ideal fermion delocalization'' results in the vanishing of three of the four leading zero-momentum electroweak parameters defined by Barbieri et al. We then discuss ideal fermion delocalization in the context of two continuum Higgsless models, one in Anti-deSitter space and one in flat space. Our results may be applied to any Higgsless linear moose model with multiple SU(2) groups, including those with only a few extra vector bosons.
Finite volume renormalization scheme for fermionic operators
Monahan, Christopher; Orginos, Kostas
2013-11-01
We propose a new finite volume renormalization scheme. Our scheme is based on the Gradient Flow applied to both fermion and gauge fields and, much like the Schr\\"odinger functional method, allows for a nonperturbative determination of the scale dependence of operators using a step-scaling approach. We give some preliminary results for the pseudo-scalar density in the quenched approximation.
Kaon decay amplitudes using staggered fermions
Sharpe, S.R.
1986-12-01
A status report is given of an attempt, using staggered fermions to calculate the real and imaginary parts of the amplitudes for K ..-->.. ..pi pi..,. Semi-quantitative results are found for the imaginary parts, and these suggest that epsilon' might be smaller than previously expected in the standard model.
Precision Constraints on Extra Fermion Generations
Erler, Jens; Langacker, Paul
2010-07-16
There has been recent renewed interest in the possibility of additional fermion generations. At the same time there have been significant changes in the relevant electroweak precision constraints, in particular, in the interpretation of several of the low energy experiments. We summarize the various motivations for extra families and analyze them in view of the latest electroweak precision data.
Variational approach to cold fermionic atom superfluidity
NASA Astrophysics Data System (ADS)
Parish, Meera; Mihaila, Bogdan; Blagoev, Krastan; Gaudio, Sergio; Timmermans, Eddy; Szymanska, Marzena; Littlewood, Peter
2004-03-01
We study a system of ultra-cold, dilute, fermionic atoms close to a Feshbach resonance. By using a variational approach, we avoid making the approximation of preformed molecular pairs. This enables us to follow the crossover from BCS to Blatt-Schafroth pairs.
Odd frequency pairing of interacting Majorana fermions
NASA Astrophysics Data System (ADS)
Huang, Zhoushen; Woelfle, Peter; Balatsky, Alexandar
Majorana fermions are rising as a promising key component in quantum computation. While the prevalent approach is to use a quadratic (i.e. non-interacting) Majorana Hamiltonian, when expressed in terms of Dirac fermions, generically the Hamiltonian involves interaction terms. Here we focus on the possible pair correlations in a simple model system. We study a model of Majorana fermions coupled to a boson mode and show that the anomalous correlator between different Majorana fermions, located at opposite ends of a topological wire, exhibits odd frequency behavior. It is stabilized when the coupling strength g is above a critical value gc. We use both, conventional diagrammatic theory and a functional integral approach, to derive the gap equation, the critical temperature, the gap function, the critical coupling, and a Ginzburg-Landau theory allowing to discuss a possible subleading admixture of even-frequency pairing. Work supported by USDOE DE-AC52-06NA25396 E304, Knut and Alice Wallenberg Foundation, and ERC DM-321031.
On the decoupling of mirror fermions
NASA Astrophysics Data System (ADS)
Chen, Chen; Giedt, Joel; Poppitz, Erich
2013-04-01
An approach to the formulation of chiral gauge theories on the lattice is to start with a vector-like theory, but decouple one chirality (the "mirror" fermions) using strong Yukawa interactions with a chirally coupled "Higgs" field. While this is an attractive idea, its viability needs to be tested with nonperturbative studies. The model that we study here, the so-called "3-4-5" model, is anomaly free and the presence of massless states in the mirror sector is not required by anomaly matching arguments, in contrast to the "1-0" model that was studied previously. We have computed the polarization tensor in this theory and find a directional discontinuity that appears to be nonzero in the limit of an infinite lattice, which is equivalent to the continuum limit at fixed physical volume. We show that a similar behavior occurs for the free massless Ginsparg-Wilson fermion, where the polarization tensor is known to have a directional discontinuity in the continuum limit. We thus find support for the conclusion that in the continuum limit of the 3-4-5 model, there are massless charged modes in the mirror sector so that it does not decouple from the light sector. The value of the discontinuity we obtain allows for two interpretations: either a chiral gauge theory does not emerge and mirror-sector fermions in a chiral anomaly free representation remain massless, or a massless vectorlike mirror fermion appears. We end by discussing some questions for future study.
Fermionic-mode entanglement in non-Markovian environment
Cheng, Jiong; Han, Yan; An, Qing-zhi; Zhou, Ling
2015-03-15
We evaluate the non-Markovian effects on the entanglement dynamics of a fermionic system interacting with two dissipative vacuum reservoirs. The exact solution of density matrix is derived by utilizing the Feynman–Vernon influence functional theory in the fermionic coherent state representation and the Grassmann calculus, which are valid for both the fermionic and bosonic baths, and their difference lies in the dependence of the parity of the initial states. The fermionic entanglement dynamics is presented by adding an additional restriction to the density matrix known as the superselection rules. Our analysis shows that the usual decoherence suppression schemes implemented in qubits systems can also be achieved for systems of identical fermions, and the initial state proves its importance in the evolution of fermionic entanglement. Our results provide a potential way to decoherence controlling of identical fermions.
Resonance spectrum of a bulk fermion on branes
NASA Astrophysics Data System (ADS)
Zhang, Yu-Peng; Du, Yun-Zhi; Guo, Wen-Di; Liu, Yu-Xiao
2016-03-01
It is known that there are two mechanisms for localizing a bulk fermion on a brane: one is the well-known Yukawa coupling, and the other is the new coupling proposed in [Phys. Rev. D 89, 086001 (2014)]. In this paper, we investigate the localization and resonance spectrum of a bulk fermion on the same branes with the two localization mechanisms. It is found that both of the two mechanisms can result in a volcano-like effective potential of the fermion Kaluza-Klein modes. The left-chiral fermion zero mode can be localized on the brane, and there exist some discrete massive-fermion Kaluza-Klein modes that quasilocalized on the branes (also called fermion resonances). The number of the fermion resonances increases linearly with the coupling parameter.
Jets plus same-sign dileptons signatures from fermionic leptoquarks at the LHC
NASA Astrophysics Data System (ADS)
Alves, Alexandre; Barreto, E. Ramirez; Dias, A. G.
2012-09-01
Within the 3-3-1 model framework, we consider the production and decay of fermionic leptoquarks into a striking experimental signature at the LHC: a narrow resonance at the b jet plus same-sign dileptons channel. The data already accumulated by the LHC collaborations may hide a large number of events associated to the production and decay of such exotic quarks, allowing one to investigate large portions of the parameters space of the model. The observation or not of such events would shed light on the construction of models presenting heavy exotic quarks.
Decay of a Yukawa fermion at finite temperature and applications to leptogenesis
Kiessig, Clemens P.; Pluemacher, Michael; Thoma, Markus H.
2010-08-01
We calculate the decay rate of a Yukawa fermion in a thermal bath using finite-temperature cutting rules and effective Green's functions according to the hard thermal loop resummation technique. We apply this result to the decay of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach where thermal masses are inserted into the kinematics of final states, we find that deviations arise through two different leptonic dispersion relations. The decay rate differs from the usual approach by more than 1 order of magnitude in the temperature range which is interesting for the weak washout regime. We discuss how to arrive at consistent finite-temperature treatments of leptogenesis.
Peltier cooling of fermionic quantum gases.
Grenier, Ch; Georges, A; Kollath, C
2014-11-14
We propose a cooling scheme for fermionic quantum gases, based on the principles of the Peltier thermoelectric effect and energy filtering. The system to be cooled is connected to another harmonically trapped gas acting as a reservoir. The cooling is achieved by two simultaneous processes: (i) the system is evaporatively cooled, and (ii) cold fermions from deep below the Fermi surface of the reservoir are injected below the Fermi level of the system, in order to fill the "holes" in the energy distribution. This is achieved by a suitable energy dependence of the transmission coefficient connecting the system to the reservoir. The two processes can be viewed as simultaneous evaporative cooling of particles and holes. We show that both a significantly lower entropy per particle and faster cooling rate can be achieved in this way than by using only evaporative cooling. PMID:25432033
A closer look at the elementary fermions
Goldhaber, Maurice
2002-01-01
Although there have been many experimental and theoretical efforts to measure and interpret small deviations from the standard model of particle physics, the gap that the model leaves in understanding why there are only three generations of the elementary fermions, with hierarchical masses, has not received the attention it deserves. I present here an attempt to fill this gap. Although our findings are mostly only qualitative, they nevertheless may be of heuristic value. Rules concerning the elementary fermions, some previously known and some new, lead to a number of conclusions and questions that seem worth pursuing. Some clarify the standard model, and others suggest possible modifications, the implications of which are discussed. PMID:11773637
Fermion dark matter from SO(10) GUTs
NASA Astrophysics Data System (ADS)
Arbeláez, Carolina; Longas, Robinson; Restrepo, Diego; Zapata, Oscar
2016-01-01
We construct and analyze nonsupersymmetric SO(10) standard model extensions which explain dark matter (DM) through the fermionic Higgs portal. In these SO(10)-based models the DM particle is naturally stable since a Z2 discrete symmetry, the matter parity, is left at the end of the symmetry breaking chain to the standard model. Potentially realistic models contain the 10 and 45 fermionic representations from which a neutralino-like mass matrix with arbitrary mixings can be obtained. Two different SO(10) breaking chains will be analyzed in light of gauge coupling unification: the standard path SU (5 )×U (1 )X and the left-right symmetry intermediate chain. The former opens the possibility of a split supersymmetric-like spectrum with an additional (inert) scalar doublet, while the later requires additional exotic scalar representations associated to the breaking of the left-right symmetry.
Playing with fermion couplings in Higgsless models
Casalbuoni, R.; De Curtis, S.; Dolce, D.; Dominici, D.
2005-04-01
We discuss the fermion couplings in a four dimensional SU(2) linear moose model by allowing for direct couplings between the left-handed fermions on the boundary and the gauge fields in the internal sites. This is realized by means of a product of nonlinear {sigma}-model scalar fields which, in the continuum limit, is equivalent to a Wilson line. The effect of these new nonlocal couplings is a contribution to the {epsilon}{sub 3} parameter which can be of opposite sign with respect to the one coming from the gauge fields along the string. Therefore, with some fine-tuning, it is possible to satisfy the constraints from the electroweak data.
Possible Aoki phase for staggered fermions
Aubin, C.; Wang Qinghai
2004-12-01
The phase diagram for staggered fermions is discussed in the context of the staggered chiral Lagrangian, extending previous work on the subject. When the discretization errors are significant, there may be an Aoki-like phase for staggered fermions, where the remnant SO(4) taste-symmetry is broken down to SO(3). We solve explicitly for the mass spectrum in the 3-flavor degenerate mass case and discuss qualitatively the 2+1-flavor case. From numerical results we find that current simulations are outside the staggered-Aoki phase. As for near-future simulations with more-improved versions of the staggered action, it seems unlikely that these will be in the Aoki phase for any realistic value of the quark mass, although the evidence is not conclusive.
A Quantum Gas Microscope for Fermionic Potassium
NASA Astrophysics Data System (ADS)
Cheuk, Lawrence; Nichols, Matthew; Okan, Melih; Lawrence, Katherine; Zhang, Hao; Zwierlein, Martin
2016-05-01
Ultracold atoms in optical lattices have enabled experimental studies of quantum many-body physics in Hubbard-type lattice systems in a clean and well-controlled environment. In particular, the advent of quantum gas microscopes has made available new experimental probes ideally suited for observing magnetic order and spatial correlations. In the past year, several groups, including ours, first realized quantum gas microscopes for fermionic atoms. In this talk, we describe our experimental setup, which combines high-resolution imaging with Raman sideband cooling to achieve single-site-resolved fluorescent imaging of fermionic 40 K atoms. We also report on recent progress towards observing quantum phases of the Fermi-Hubbard model with single-site resolution.
Chiral fermions as classical massless spinning particles
NASA Astrophysics Data System (ADS)
Duval, C.; Horváthy, P. A.
2015-02-01
Semiclassical chiral fermion models with Berry term are studied in a symplectic framework. In the free case, the system can be obtained from Souriau's model for a relativistic massless spinning particle by "enslaving" the spin. The Berry term is identified with the classical spin two-form of the latter model. The Souriau model carries a natural Poincaré symmetry that we highlight, but spin enslavement breaks the boost symmetry. However the relation between the models allows us to derive a Poincaré symmetry of unconventional form for chiral fermions. Then we couple our system to an external electromagnetic field. For gyromagnetic ratio g =0 we get curious superluminal Hall-type motions; for g =2 and in a pure constant magnetic field in particular, we find instead spiraling motions.
Supersymmetry in Rydberg-dressed lattice fermions
NASA Astrophysics Data System (ADS)
Weimer, Hendrik; Huijse, Liza; Gorshkov, Alexey; Pupillo, Guido; Zoller, Peter; Lukin, Mikhail; Demler, Eugene
2012-06-01
Supersymmetry is a powerful tool that allows the characterization of strongly correlated many-body systems, in particular in the case of supersymmetric extensions of the fermionic Hubbard model [1]. At the same time, these models can exhibit rich and exotic physics on their own, such as flat bands with a vanishing dispersion relation. We show that such lattice models can be realized with Rydberg-dressed fermions in optical lattices. Strong interactions within the ground state manifold of the atoms can be realized by admixing a weak contribution of a highly excited Rydberg state [2]. We discuss the unique possbilities of ultracold atoms for the detection of supersymmetry and the effects of tuning the system away from the supersymmetric point.[4pt] [1] P. Fendley, K. Schoutens, J. de Boer, PRL 90, 120402 (2003).[0pt] [2] J. Honer, H. Weimer, T. Pfau, H. P. B"uchler, PRL 105, 160404 (2010).
The holographic fermions dual to massive gravity
NASA Astrophysics Data System (ADS)
Fang, Li-Qing; Kuang, Xiao-Mei; Wu, Jian-Pin
2016-10-01
We investigate the properties of the spectral function of the fermionic operator in the field theory which is dual to a 4-dimensional massive gravity. We first study the Fermi surface and the dispersion relation in the dual boundary theory. We find that as the massive parameters is decreased, the Fermi momentum becomes lower and the low energy excitation near Fermi surface behaves more like non-Fermi liquid. Then, we introduce a dipole coupling in the bulk theory and explore the emergence of a gap in the fermionic spectral function. It is found that larger critical dipole coupling is needed to open the gap than that in Einstein gravity. Accordingly, in the field theory dual to massive gravity, it requires stronger negative dipole coupling to generate the marginal Fermi liquid.
Strong coupling QED with two fermionic flavors
Wang, K.C.
1990-11-01
We report the recent results of our simulation of strong coupling QED, with non-compact action, on lattices 10{sup 4} and 16{sup 4}. Since we are dealing with two staggered fermionic flavors, we use hybrid algorithm to do the simulation. In addition to the measurement of the chiral order parameter {l angle}{bar {psi}}{psi}{r angle}, we also measure magnetic monopole susceptibility, {chi}, throughout the region of chiral transition. 6 refs., 6 figs.
Microcavity array IR photodetector
Esman, A K; Kuleshov, V K; Zykov, G L
2009-12-31
An original microcavity array IR photodetector is proposed and the sensitivity and response time of its pixels are calculated. A photosensitive element represents a composite silicon microcavity made of two optically coupled closed waveguides on a dielectric substrate whose resonance wave depends on its temperature. This dependence is used to detect IR radiation which heats an absorbing element and the composite microcavity thermally coupled with this element. It is shown that for a spatial resolution of 45 {mu}m, the time response is 30 ms and the sensitivity is 10{sup -3} K at the IR radiation power of {approx} 4.7 x 10{sup -8} W element{sup -1}. (photodetectors)
Type-III seesaw fermionic triplets at high energy e+e- collider
NASA Astrophysics Data System (ADS)
Goswami, Deepanjali; Poulose, Poulose
2016-03-01
We investigate the signature of heavy fermionic triplets belonging to Type-III seesaw model through their direct production at the high energy e+e- collider. Single and pair production of the charged (Σ+/-) and neutral (Σ0) triplets through the processes, e+e- -->Σ+Σ- ,Σ0Σ0 ,Σ0 ν ,Σ+/- l are considered for the study. The subsequent decay of the triplets to the detector level final states are studied with the corresponding Standard Model (SM) background processes. The decay distributions are considered in details to identify the significant channels, after devising and employing suitable methods to reduce backgrounds and enhance the signal significance. Advantage of single triplet production in association with the charged SM leptons to investigate the mixing of the triplet with the SM leptons is exploited. Preliminary results show the presence of charged fermionic triplets up to a mass of ~ 950 GeV could be established through the single production at 1 TeV ILC, assuming a fermionic triplet electron mixing of 0.05 and a moderate integrated luminosity of 300 fb-1 . Further, constraints in the mass-mixing are obtained for different CM energies assuming different luminosities.
Fermion mass hierarchy and nonhierarchical mass ratios in SU(5)xU(1){sub F}
Duque, Luis F.; Gutierrez, Diego A.; Nardi, Enrico; Norena, Jorge
2008-08-01
We consider a SU(5)xU(1){sub F} grand unified theory (GUT)-flavor model in which the number of effects that determine the charged fermions Yukawa matrices is much larger than the number of observables, resulting in a hierarchical fermion spectrum with no particular regularities. The GUT-flavor symmetry is broken by flavons in the adjoint of SU(5), realizing a variant of the Froggatt-Nielsen mechanism that gives rise to a large number of effective operators. By assuming a common mass for the heavy fields and universality of the fundamental Yukawa couplings, we reduce the number of free parameters to one. The observed fermion mass spectrum is reproduced thanks to selection rules that discriminate among various contributions. Bottom-tau Yukawa unification is preserved at leading order, but there is no unification for the first two families. Interestingly, U(1){sub F} charges alone do not determine the hierarchy, and can only give upper bounds on the parametric suppression of the Yukawa operators.
Mixtures of Ultracold Fermions with Unequal Masses
NASA Astrophysics Data System (ADS)
de Melo, Carlos A. R. Sa
2008-05-01
The quantum phases of ultracold fermions with unequal masses are discussed in continuum and lattice models for a wide variety of mixtures which exhibit Feshbach resonances, e.g., mixtures of ^6Li and ^40K. The evolution of superfluidity from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein condensation (BEC) regime in the continuum is analyzed as a function of scattering parameter, population imbalance and mass anisotropy. In the continuum case, regions corresponding to normal, phase-separated or coexisting uniform-superfluid/excess-fermion phases are identified and the possibility of topological phase transitions is discussed [1]. For optical lattices, the phase diagrams as a function of interaction strength, population imbalance, filling fraction and tunneling parameters are presented [2]. In addition to the characteristic phases of the continuum, a series of insulating phases emerge in the phase diagrams of optical lattices, including a Bose-Mott insulator (BMI), a Fermi-Pauli insulator (FPI), a phase-separated BMI/FPI mixture, and a Bose-Fermi checkerboard (BFC) phase. Lastly, the effects of harmonic traps and the emergence of unusual shell structures are discussed for mixtures of fermions with unequal masses. [1] M. Iskin, and C. A. R. S' a de Melo, Phys. Rev. Lett 97, 100404 (2006); [2] M. Iskin, and C. A. R. S' a de Melo, Phys. Rev. Lett. 99, 080403 (2007).
Composite gauge-bosons made of fermions
NASA Astrophysics Data System (ADS)
Suzuki, Mahiko
2016-07-01
We construct a class of Abelian and non-Abelian local gauge theories that consist only of matter fields of fermions. The Lagrangian is local and does not contain an auxiliary vector field nor a subsidiary condition on the matter fields. It does not involve an extra dimension nor supersymmetry. This Lagrangian can be extended to non-Abelian gauge symmetry only in the case of SU(2) doublet matter fields. We carry out an explicit diagrammatic computation in the leading 1 /N order to show that massless spin-one bound states appear with the correct gauge coupling. Our diagram calculation exposes the dynamical features that cannot be seen in the formal auxiliary vector-field method. For instance, it shows that the s -wave fermion-antifermion interaction in the 3S1 channel (ψ ¯ γμψ ) alone cannot form the bound gauge bosons; the fermion-antifermion pairs must couple to the d -wave state too. One feature common to our class of Lagrangian is that the Noether current does not exist. Therefore it evades possible conflict with the no-go theorem of Weinberg and Witten on the formation of the non-Abelian gauge bosons.
Scalar meson spectroscopy with lattice staggered fermions
Bernard, Claude; DeTar, Carleton; Fu Ziwen; Prelovsek, Sasa
2007-11-01
With sufficiently light up and down quarks the isovector (a{sub 0}) and isosinglet (f{sub 0}) scalar meson propagators are dominated at large distance by two-meson states. In the staggered-fermion formulation of lattice quantum chromodynamics, taste-symmetry breaking causes a proliferation of two-meson states that further complicates the analysis of these channels. Many of them are unphysical artifacts of the lattice approximation. They are expected to disappear in the continuum limit. The staggered-fermion fourth-root procedure has its purported counterpart in rooted staggered chiral perturbation theory (rS{chi}PT). Fortunately, the rooted theory provides a strict framework that permits the analysis of scalar meson correlators in terms of only a small number of low-energy couplings. Thus the analysis of the point-to-point scalar meson correlators in this context gives a useful consistency check of the fourth-root procedure and its proposed chiral realization. Through numerical simulation we have measured correlators for both the a{sub 0} and f{sub 0} channels in the 'Asqtad' improved staggered-fermion formulation in a lattice ensemble with lattice spacing a=0.12 fm. We analyze those correlators in the context of rS{chi}PT and obtain values of the low-energy chiral couplings that are reasonably consistent with previous determinations.
Strong CP, Flavor, and Twisted Split Fermions
Harnik, Roni; Perez, Gilad; Schwartz, Matthew D.; Shirman, Yuri
2004-11-10
We present a natural solution to the strong CP problem in the context of split fermions. By assuming CP is spontaneously broken in the bulk, a weak CKM phase is created in the standard model due to a twisting in flavor space of the bulk fermion wavefunctions. But the strong CP phase remains zero, being essentially protected by parity in the bulk and CP on the branes. As always in models of spontaneous CP breaking, radiative corrections to theta bar from the standard model are tiny, but even higher dimension operators are not that dangerous. The twisting phenomenon was recently shown to be generic, and not to interfere with the way that split fermions naturally weaves small numbers into the standard model. It follows that out approach to strong CP is compatible with flavor, and we sketch a comprehensive model. We also look at deconstructed version of this setup which provides a viable 4D model of spontaneous CP breaking which is not in the Nelson-Barr class.
NASA Astrophysics Data System (ADS)
Lannon, J.; Grego, S.; Solomon, S.
2007-04-01
We have evaluated several methods for generating multi-color emission for IR scene projector applications. The baseline requirements we employed were the ability to simulate color temperatures in the range 300-3000 K, minimum radiance levels consistent with existing IR sensor requirements, 1000 Hz frame rates and manufacturability. The analysis led us to down select two independent approaches that are capable of meeting HWIL multicolor requirements. We describe and discuss each of the approaches, their expected performance as well as their limitations.
Fermion localization on two-field thick branes
Castro, L. B.
2011-02-15
In a recent paper published in this journal, Almeida and collaborators [Phys. Rev. D 79, 125022 (2009)] analyze the issue of fermion localization of fermions on a brane constructed from two scalar fields coupled with gravity (Bloch brane model). In that meritorious research the simplest Yukawa coupling {eta}{Psi}{phi}{chi}{Psi} was considered. That work does not analyze the zero mode in details. In this paper, the localization of fermions on two-field thick branes is reinvestigated. It is found that the simplest Yukawa coupling does not support the localization of fermions on the brane. In addition, the problem of fermion localization for some other Yukawa couplings are analyzed. It is shown that the zero mode for left-handed and right-handed fermions can be localized on the brane depending on the values for the coupling constant {eta} and the Bloch brane's parameter a.
Drone-fermions in the two-dimensional antiferromagnet
NASA Astrophysics Data System (ADS)
Krivenko, S.; Khaliullin, G.
1995-02-01
Two different representations of spins - via the conventional fermions, or via the Mattis drone-fermions - are compared considering the planar antiferromagnetic Heisenberg model as an example. Mean-field spin correlation functions calculated for the uniform and flux RVB states show that the drone-fermion approach has an advantage in giving the lower energy and the enhanced AF correlations, because of the absence of unphysical spinless states in this representation.
Semiclassical fermion pair creation in de Sitter spacetime
Stahl, Clément Eckhard, Strobel
2015-12-17
We present a method to semiclassically compute the pair creation rate of bosons and fermions in de Sitter spacetime. The results in the bosonic case agree with the ones in the literature. We find that for the constant electric field the fermionic and bosonic pair creation rate are the same. This analogy of bosons and fermions in the semiclassical limit is known from several flat spacetime examples.
Mixtures of Bosonic and Fermionic atoms
NASA Astrophysics Data System (ADS)
Albus, Alexander
2003-12-01
The theory of atomic Boson-Fermion mixtures in the dilute limit beyond mean-field is considered in this thesis. Extending the formalism of quantum field theory we derived expressions for the quasi-particle excitation spectra, the ground state energy, and related quantities for a homogenous system to first order in the dilute gas parameter. In the framework of density functional theory we could carry over the previous results to inhomogeneous systems. We then determined to density distributions for various parameter values and identified three different phase regions: (i) a stable mixed regime, (ii) a phase separated regime, and (iii) a collapsed regime. We found a significant contribution of exchange-correlation effects in the latter case. Next, we determined the shift of the Bose-Einstein condensation temperature caused by Boson-Fermion interactions in a harmonic trap due to redistribution of the density profiles. We then considered Boson-Fermion mixtures in optical lattices. We calculated the criterion for stability against phase separation, identified the Mott-insulating and superfluid regimes both, analytically within a mean-field calculation, and numerically by virtue of a Gutzwiller Ansatz. We also found new frustrated ground states in the limit of very strong lattices. ----Anmerkung: Der Autor ist Träger des durch die Physikalische Gesellschaft zu Berlin vergebenen Carl-Ramsauer-Preises 2004 für die jeweils beste Dissertation der vier Universitäten Freie Universität Berlin, Humboldt-Universität zu Berlin, Technische Universität Berlin und Universität Potsdam. Ziel der Arbeit war die systematische theoretische Behandlung von Gemischen aus bosonischen und fermionischen Atomen in einem Parameterbereich, der sich zur Beschreibung von aktuellen Experimenten mit ultra-kalten atomaren Gasen eignet. Zuerst wurde der Formalismus der Quantenfeldtheorie auf homogene, atomare Boson-Fermion Gemische erweitert, um grundlegende Größen wie Quasiteilchenspektren
Quantum Hall Effect of Massless Dirac Fermions and Free Fermions in Hofstadter's Butterfly
NASA Astrophysics Data System (ADS)
Yoshioka, Nobuyuki; Matsuura, Hiroyasu; Ogata, Masao
2016-06-01
We propose a new physical interpretation of the Diophantine equation of σxy for the Hofstadter problem. First, we divide the energy spectrum, or Hofstadter's butterfly, into smaller self-similar areas called "subcells", which were first introduced by Hofstadter to describe the recursive structure. We find that in the energy gaps between subcells, there are two ways to account for the quantization rule of σxy, that are consistent with the Diophantine equation: Landau quantization of (i) massless Dirac fermions or (ii) free fermions in Hofstadter's butterfly.
Chiral lattice fermions with correct vacuum polarization and chiral anomaly
Pryor, C. )
1991-04-15
An action for chiral lattice fermions is proposed, which avoids the Nielsen-Ninomiya theorem by virtue of its nonlocality and nonbilinearity. The action is constructed by eliminating the extra fermion modes with a gauge-violating Majorana-type Wilson mass, which is then rendered invariant by an integration over gauge transformations. The free propagator is calculated, and the one-loop vacuum polarization is shown to be identical to that for Wilson fermions, even at nonzero lattice spacing. Also the chiral anomaly is shown to be the same as for Wilson fermions in the continuum limit.
Oscillatory pairing of fermions in spin-split traps
Sun Kuei; Vishveshwara, Smitha; Meyer, Julia S.; Sheehy, Daniel E.
2011-03-15
As a means of realizing oscillatory pairing between fermions, we study superfluid pairing between two fermion ''spin'' species that are confined to adjustable spin-dependent trapping potentials. Focusing on the one-dimensional limit, we find that with increasing separation between the spin-dependent traps, the fermions exhibit distinct phases, including a fully paired phase, a spin-imbalanced phase with oscillatory pairing, and an unpaired fully spin-polarized phase. We obtain the phase diagram of fermions in such a spin-split trap and discuss signatures of these phases in cold-atom experiments.
Wilson fermions and axion electrodynamics in optical lattices.
Bermudez, A; Mazza, L; Rizzi, M; Goldman, N; Lewenstein, M; Martin-Delgado, M A
2010-11-01
We show that ultracold Fermi gases in optical superlattices can be used as quantum simulators of relativistic lattice fermions in 3+1 dimensions. By exploiting laser-assisted tunneling, we find an analogue of the so-called naive Dirac fermions, and thus provide a realization of the fermion doubling problem. Moreover, we show how to implement Wilson fermions, and discuss how their mass can be inverted by tuning the laser intensities. In this regime, our atomic gas corresponds to a phase of matter where Maxwell electrodynamics is replaced by axion electrodynamics: a 3D topological insulator.
Four-fermion interaction from torsion as dark energy
NASA Astrophysics Data System (ADS)
Popławski, Nikodem J.
2012-02-01
The observed small, positive cosmological constant may originate from a four-fermion interaction generated by the spin-torsion coupling in the Einstein-Cartan-Sciama-Kibble gravity if the fermions are condensing. In particular, such a condensation occurs for quark fields during the quark-gluon/hadron phase transition in the early Universe. We study how the torsion-induced four-fermion interaction is affected by adding two terms to the Dirac Lagrangian density: the parity-violating pseudoscalar density dual to the curvature tensor and a spinor-bilinear scalar density which measures the nonminimal coupling of fermions to torsion.
Wilson Fermions and Axion Electrodynamics in Optical Lattices
Bermudez, A.; Martin-Delgado, M. A.; Mazza, L.; Rizzi, M.; Goldman, N.; Lewenstein, M.
2010-11-05
We show that ultracold Fermi gases in optical superlattices can be used as quantum simulators of relativistic lattice fermions in 3+1 dimensions. By exploiting laser-assisted tunneling, we find an analogue of the so-called naive Dirac fermions, and thus provide a realization of the fermion doubling problem. Moreover, we show how to implement Wilson fermions, and discuss how their mass can be inverted by tuning the laser intensities. In this regime, our atomic gas corresponds to a phase of matter where Maxwell electrodynamics is replaced by axion electrodynamics: a 3D topological insulator.
Low Power Polysilicon Sources for IR Applications
NASA Technical Reports Server (NTRS)
Das, N. C.; Jhabvala, M.; Shu, P.
1998-01-01
We have designed and fabricated polysilicon thin film infrared (IR) sources by micromachining technology. These sources are made with a lightly doped middle region for light emission and heavy doping of the supporting legs. The sources are fabricated on a 10 mm thick, low temperature process parameters in the fabrication of these silicon dioxide layer. Different doping levels were used to achieve various source resistances. From the power requirement to reach the required light emission versus source resistance curve it is seen that there exists a resistance value which minimizes the necessary input power.
NASA Astrophysics Data System (ADS)
Lan, Tian; Kong, Liang; Wen, Xiao-Gang
2016-10-01
We propose a systematic framework to classify (2+1)-dimensional (2+1D) fermionic topological orders without symmetry and 2+1D fermionic/bosonic topological orders with symmetry G . The key is to use the so-called symmetric fusion category E to describe the symmetry. Here, E =sRep (Z2f) describing particles in a fermionic product state without symmetry, or E =sRep (Gf) [E =Rep (G )] describing particles in a fermionic (bosonic) product state with symmetry G . Then, topological orders with symmetry E are classified by nondegenerate unitary braided fusion categories over E , plus their modular extensions and total chiral central charges. This allows us to obtain a list that contains all 2+1D fermionic topological orders without symmetry. For example, we find that, up to p +i p fermionic topological orders, there are only four fermionic topological orders with one nontrivial topological excitation: (1) the K =( -1 0 0 2) fractional quantum Hall state, (2) a Fibonacci bosonic topological order stacking with a fermionic product state, (3) the time-reversal conjugate of the previous one, and (4) a fermionic topological order with chiral central charge c =1/4 , whose only topological excitation has non-Abelian statistics with spin s =1/4 and quantum dimension d =1 +√{2 } .
Strongly Interacting Fermions in Optical Lattices
NASA Astrophysics Data System (ADS)
Koetsier, A. O.
2009-07-01
This thesis explores certain extraordinary phenomena that occur when a gas of neutral atoms is cooled to the coldest temperatures in the universe --- much colder, in fact, than the electromagnetic radiation that permeates the vacuum of interstellar space. At those extreme temperatures, quantum effects dominate and the collective behaviour of the atoms can have unexpected consequences. For example, Bose-Einstein condensation may occur where the atoms lose their individual identities to coalesce into a macroscopic quantum particle. Although such ultracold atomic gases are interesting in their own right, much of the excitement generated in this field is due to the possibility that studying these gases could shed light on intractable problems in other areas of physics. This is predominantly due to the uniquely high degree of control over various physical parameters that ultracold atomic gases afford to experimentalists. Recent technological advances exploit this advantage to study quantum phenomena in a detail that would not be possible in other systems. For instance, atoms can be made to attract or repel each other, the strength of this interaction can be set to almost any value, and external potentials of various geometries and periodicities can be introduced. In this way, atoms can be used to model phenomena as diverse as the quark-gluon plasmas arising in high-energy particle physics, the colour superfluids conjectured to exist in the core of neutron stars, and the high-temperature superconductivity exhibited by electrons on the ion lattice of certain compounds. Indeed, ultracold atomic gases also have a demonstrated applicability to quantum information and computation. Due to a subtle interplay between electronic and nuclear spins known as the hyperfine interaction, atoms can have either an integer or half-integer total spin quantum number, making them either bosonic or fermionic at low temperatures, respectively. With the exception of chapter 7, the work
Reiss, Krzysztof; Valle, Luis Del; Lassak, Adam; Trojanek, Joanna
2011-01-01
The family of insulin receptor substrates (IRS) consists of four proteins (IRS-1 - IRS-4), which were initially characterized as typical cytosolic adaptor proteins involved in insulin receptor (IR) and insulin-like growth factor I receptor (IGF-IR) signaling. The first cloned and characterized member of the IRS family, IRS-1, has predicted molecular weight of 132 kDa, however, as a result of its extensive serine phosphorylation it separates on a SDS gel as a band of approximately 160–185 kDa. In addition to its metabolic and growth-promoting functions, IRS-1 is also suspected to play a role in malignant transformation. The mechanism by which IRS-1 supports tumor growth is not fully understood, and the argument that IRS-1 merely amplifies the signal from the IGF-1R and/or IR requires further investigation. Almost a decade ago, we reported the presence of nuclear IRS-1 in medulloblastoma clinical samples, which express viral oncoprotein, large T-antigen of human polyomavirus JC (JCV T-antigen). This first demonstration of nuclear IRS-1 was confirmed in several other laboratories. The nuclear IRS-1 was also detected by cells expressing the SV40 T-antigen, v-Src, in immortalized fibroblasts stimulated with IGF-I, in hepatocytes, 32D cells, and in an osteosarcoma cell line. More recently, nuclear IRS-1 was detected in breast cancer cells in association with estrogen receptor alpha (ERα), and in JC virus negative medulloblastoma cells expressing ERβ, further implicating nuclear IRS-1 in cellular transformation. Here, we discuss how nuclear IRS-1 acting on DNA repair fidelity, transcriptional activity, and cell growth can support tumor development and progression. PMID:22454254
NASA Astrophysics Data System (ADS)
Vinson, R. J.; Passwater, R. D.
1981-03-01
The Army simulator facilities are presently configured to conduct hardware-in-the-loop mission tasks on the HELLFIRE and COPPERHEAD missile systems. These systems presently use a LASER seeker. The facility is an ideal candidate to be converted to include infrared (IR) seekers used on the TGSM system. This study investigates the possibility and impact of a facility update. This report documents the feasibility of developing a hardware-in-the-loop (HWIL) hybrid simulation incorporating infrared IR seekers used for the Assault Breaker program. Other hardware to be considered are the autopilot, signal conditioning, signal processing, and actuators which may be integrated into the system simulation. Considerations are given to replacing all or elements of hardware while substituting math models in the system simulation.
Discovering correlated fermions using quantum Monte Carlo
NASA Astrophysics Data System (ADS)
Wagner, Lucas K.; Ceperley, David M.
2016-09-01
It has become increasingly feasible to use quantum Monte Carlo (QMC) methods to study correlated fermion systems for realistic Hamiltonians. We give a summary of these techniques targeted at researchers in the field of correlated electrons, focusing on the fundamentals, capabilities, and current status of this technique. The QMC methods often offer the highest accuracy solutions available for systems in the continuum, and, since they address the many-body problem directly, the simulations can be analyzed to obtain insight into the nature of correlated quantum behavior.
Boson formulation of fermion field theories
Ha, Y.K.
1984-04-15
The nonperturbative connection between a canonical Fermi field and a canonical Bose field in two dimensions is developed and its validity verified according to the tenets of quantum field theory. We advocate the point of view that a boson formulation offers a unifying theme in understanding the structure of many theories. This is illustrated by the boson formulation of a multifermion theory with chiral and internal symmetries. Many features of the massless theory, such as dynamical mass generation with asymptotic-freedom behavior, hidden chiral symmetry, and connections with models of apparently different internal symmetries, are readily transparent through such fermion-boson metamorphosis.
Universal fermionic spectral functions from string theory.
Gauntlett, Jerome P; Sonner, Julian; Waldram, Daniel
2011-12-01
We carry out the first holographic calculation of a fermionic response function for a strongly coupled d=3 system with an explicit D=10 or D=11 supergravity dual. By considering the supersymmetry current, we obtain a universal result applicable to all d=3 N=2 SCFTs with such duals. Surprisingly, the spectral function does not exhibit a Fermi surface, despite the fact that the system is at finite charge density. We show that it has a phonino pole and at low frequencies there is a depletion of spectral weight with a power-law scaling which is governed by a locally quantum critical point.
Continuum regularization of gauge theory with fermions
Chan, H.S.
1987-03-01
The continuum regularization program is discussed in the case of d-dimensional gauge theory coupled to fermions in an arbitrary representation. Two physically equivalent formulations are given. First, a Grassmann formulation is presented, which is based on the two-noise Langevin equations of Sakita, Ishikawa and Alfaro and Gavela. Second, a non-Grassmann formulation is obtained by regularized integration of the matter fields within the regularized Grassmann system. Explicit perturbation expansions are studied in both formulations, and considerable simplification is found in the integrated non-Grassmann formalism.
Some Improved Nonperturbative Bounds for Fermionic Expansions
NASA Astrophysics Data System (ADS)
Lohmann, Martin
2016-06-01
We reconsider the Gram-Hadamard bound as it is used in constructive quantum field theory and many body physics to prove convergence of Fermionic perturbative expansions. Our approach uses a recursion for the amplitudes of the expansion, discovered in a model problem by Djokic (2013). It explains the standard way to bound the expansion from a new point of view, and for some of the amplitudes provides new bounds, which avoid the use of Fourier transform, and are therefore superior to the standard bounds for models like the cold interacting Fermi gas.
Generating functions for canonical systems of fermions
NASA Astrophysics Data System (ADS)
Pain, Jean-Christophe; Gilleron, Franck; Porcherot, Quentin
2011-06-01
The method proposed by Pratt to derive recursion relations for systems of degenerate fermions [S. Pratt, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.84.4255 84, 4255 (2000)] relies on diagrammatic techniques. This efficient formalism assumes no explicit two-body interactions, makes possible the inclusion of conservation laws, and requires low computational time. In this Brief Report, we show that such recursion relations can be obtained from generating functions, without any restriction in relation to the number of conservation laws (e.g., total energy or angular momentum).
Quantum mechanics of two relativistic bound fermions
Giachetti, R.; Sorace, E.
2006-11-15
This presentation shows how a joint use of symbolic and numerical programming makes it possible the construction of new quantum mechanical models and the explicit solution for their spectra. Similar methods can be used for investigating quantum systems of different nature with the highest accuracy, as it can be required by the development of new technologies. In particular we deal with the quantization of two relativistic fermions of arbitrary masses interacting by means of a radial potential. The numerical results are given for the Coulomb interaction.
Entanglement and algebraic independence in fermion systems
NASA Astrophysics Data System (ADS)
Benatti, Fabio; Floreanini, Roberto
2014-04-01
In the case of systems composed of identical particles, a typical instance in quantum statistical mechanics, the standard approach to separability and entanglement ought to be reformulated and rephrased in terms of correlations between operators from subalgebras localized in spatially disjoint regions. While this algebraic approach is straightforward for bosons, in the case of fermions it is subtler since one has to distinguish between micro-causality, that is the anti-commutativity of the basic creation and annihilation operators, and algebraic independence that is the commutativity of local observables. We argue that a consistent algebraic formulation of separability and entanglement should be compatible with micro-causality rather than with algebraic independence.
Complete Boson-Fermion Model of Superconductivity
NASA Astrophysics Data System (ADS)
de Llano, Manuel
2003-03-01
The unification of the 1957 BCS theory with that of Bose-Einstein condensation (BEC) that gives roughly good first-principles transition temperature Tc predictions in either 2D or 3D for all of the ``Uemura plot'' ``exotic'' or conventional superconductors without abandoning the much-maligned phonon interaction mechanism has recently been achieved [1]-[3]. The same dynamical mechanism also allows for room-temperature superconductivity. The only condition is that one depart moderately from the perfect electron (e)-/hole (h)-Cooper-pair (CP) symmetry to which BCS (and indeed also the somewhat more general BCS-Bose crossover) theory are restricted by construction. It now becomes feasible to explain, among other things, why largely all superconductors empirically have substantially higher T_c's if their normal-state charge carriers are holes rather than electrons. A complete (in the sense that 2h-CPs are not ignored) boson-fermion model (CBFM) has been developed that reduces in the appropriate special cases to: a) ordinary BCS theory for weak boson-fermion coupling; b) the BCS-Bose ``crossover'' theory dating back to 1967; and, for no 2h-CPs to: c) the 1989 boson-fermion (BF) BEC model by T.D. Lee et al. of superconductors which without 2h-CPs is unrelated to BCS theory; d) an ideal BF binary-gas model [4] predicting nonzero BEC T_c's even in 2D; and finally to e) ordinary BEC (1925). The CBFM is a BF statistical model similar to those developed in the mid-50's by Schafroth, Blatt & Butler but which now includes 2h-CPs on an equal footing with 2e-CPs, and which unlike these models also contains the empirically well-established fermionic energy gap. [1] V.V. Tolmachev, Phys. Lett. A 266, 400 (2000). [2] M. Fortes, M.A. Solis, M. de Llano & V.V. Tolmachev, Physica C 364, 95 (2001). [3] M. de Llano & V.V. Tolmachev, Physica A 317, 546 (2003). [4] M. Casas, N.J. Davidson, M. de Llano, T.A. Mamedov, A. Puente, R.M. Quick, A. Rigo & M.A. Solis, Physica A 295, 146 (2001
Discovering correlated fermions using quantum Monte Carlo.
Wagner, Lucas K; Ceperley, David M
2016-09-01
It has become increasingly feasible to use quantum Monte Carlo (QMC) methods to study correlated fermion systems for realistic Hamiltonians. We give a summary of these techniques targeted at researchers in the field of correlated electrons, focusing on the fundamentals, capabilities, and current status of this technique. The QMC methods often offer the highest accuracy solutions available for systems in the continuum, and, since they address the many-body problem directly, the simulations can be analyzed to obtain insight into the nature of correlated quantum behavior. PMID:27518859
Recent Progress in Fermion Monte Carlo
Kalos, M H; Pederiva, F
2006-01-24
Our approach to the solution of the Schroedinger Equation for many-fermion systems has been extensively revised. We have devised a generalization of ''acceptance/rejection'' that applies to signed random walkers. We have introduced a new class of importance functions for two walkers that better reflects the structure of the enlarged Euclidean space of the pair. For greater flexibility, we no longer rely on the ''local energy'' of the importance function to determine the dynamics of the walk. We sketch these technical changes and give new results for the two-dimensional electron gas.
NASA Technical Reports Server (NTRS)
2004-01-01
[figure removed for brevity, see original site]
Today's crater is slightly older than one shown yesterday. The ballistically emplaced ejecta is now a uniform gray tone in this nighttime IR image. With time dust will cover young surfaces and control the IR image tone. This crater is located east of Huygens Crater.
Image information: IR instrument. Latitude -10.6, Longitude 64.3 East (295.7 West). 100 meter/pixel resolution.
Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.
NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.
A streamlined method for chiral fermions on the lattice
Bodwin, G.T.; Kovacs, E.V.
1992-11-10
We discussed the use of renormalization counterterms to restore the chiral gauge symmetry in a lattice theory of Wilson fermions. We show that a large class of counterterms can be implemented automatically by making a simple modification to the fermion determinant.
Supersymmetric Chern-Simons vortex systems and fermion zero modes
Lee, B. ); Lee, C. ); Min, H. )
1992-06-15
Fermion zero modes around a general multivortex background are analyzed in supersymmetrized self-dual (Maxwell--) Chern-Simons Higgs systems, using the index theorem and other means. In the models with an {ital N}=2 extended supersymmetry, a simple connection is established between all independent fermion zero modes and corresponding bosonic zero modes. We provide a supersymmetry-based explanation of the result.
IR nanoscale spectroscopy and imaging
NASA Astrophysics Data System (ADS)
Kennedy, Eamonn; Yarrow, Fiona; Rice, James H.
2011-10-01
Sub diffraction limited infrared absorption imaging was applied to hemoglobin by coupling IR optics with an atomic force microscope. Comparisons between the AFM topography and IR absorption images of micron sized hemoglobin features are presented, along with nanoscale IR spectroscopic analysis of the metalloprotein.
Cox, B.; Gilman, F.J.; Gottschalk, T.D.
1986-11-01
A range of issues pertaining to heavy flavors at the SSC is examined including heavy flavor production by gluon-gluon fusion and by shower evolution of gluon jets, flavor tagging, reconstruction of Higgs and W bosons, and the study of rare decays and CP violation in the B meson system. A specific detector for doing heavy flavor physics and tuned to this latter study at the SSC, the TASTER, is described. 36 refs., 10 figs.
Superfluid and Insulating Phases of Fermion Mixtures in Optical Lattices
NASA Astrophysics Data System (ADS)
Iskin, M.; de Melo, C. A. R. Sá
2007-08-01
The ground state phase diagram of fermion mixtures in optical lattices is analyzed as a function of interaction strength, fermion filling factor, and tunneling parameters. In addition to standard superfluid, phase-separated or coexisting superfluid excess-fermion phases found in homogeneous or harmonically trapped systems, fermions in optical lattices have several insulating phases, including a molecular Bose-Mott insulator (BMI), a Fermi-Pauli (band) insulator (FPI), a phase-separated BMI-FPI mixture or a Bose-Fermi checkerboard (BFC). The molecular BMI phase is the fermion mixture counterpart of the atomic BMI found in atomic Bose systems, the BFC or BMI-FPI phases exist in Bose-Fermi mixtures, and lastly the FPI phase is particular to the Fermi nature of the constituent atoms of the mixture.
Fermion tunneling from higher-dimensional black holes
Lin Kai; Yang Shuzheng
2009-03-15
Via the semiclassical approximation method, we study the 1/2-spin fermion tunneling from a higher-dimensional black hole. In our work, the Dirac equations are transformed into a simple form, and then we simplify the fermion tunneling research to the study of the Hamilton-Jacobi equation in curved space-time. Finally, we get the fermion tunneling rates and the Hawking temperatures at the event horizon of higher-dimensional black holes. We study fermion tunneling of a higher-dimensional Schwarzschild black hole and a higher-dimensional spherically symmetric quintessence black hole. In fact, this method is also applicable to the study of fermion tunneling from four-dimensional or lower-dimensional black holes, and we will take the rainbow-Finsler black hole as an example in order to make the fact explicit.
Beyond Dirac and Weyl fermions: Unconventional quasiparticles in conventional crystals.
Bradlyn, Barry; Cano, Jennifer; Wang, Zhijun; Vergniory, M G; Felser, C; Cava, R J; Bernevig, B Andrei
2016-08-01
In quantum field theory, we learn that fermions come in three varieties: Majorana, Weyl, and Dirac. Here, we show that in solid-state systems this classification is incomplete, and we find several additional types of crystal symmetry-protected free fermionic excitations. We exhaustively classify linear and quadratic three-, six-, and eight-band crossings stabilized by space group symmetries in solid-state systems with spin-orbit coupling and time-reversal symmetry. Several distinct types of fermions arise, differentiated by their degeneracies at and along high-symmetry points, lines, and surfaces. Some notable consequences of these fermions are the presence of Fermi arcs in non-Weyl systems and the existence of Dirac lines. Ab initio calculations identify a number of materials that realize these exotic fermions close to the Fermi level. PMID:27445310
LETTERS AND COMMENTS: Noninteracting fermions in infinite dimensions
NASA Astrophysics Data System (ADS)
Acharyya, Muktish
2010-11-01
Usually, we study the statistical behaviour of noninteracting fermions in finite (mainly two and three) dimensions. For a fixed number of fermions, the average energy per fermion is calculated in two and in three dimensions, and it becomes equal to 50% and 60% of the Fermi energy respectively. However, in higher dimensions this percentage increases as the dimensionality increases, and in infinite dimensions it becomes 100%. This is an interesting result, at least pedagogically, which implies that all fermions are moving with Fermi momentum. This result is not yet discussed in standard text books of quantum statistics. Here this fact is discussed and explained. I hope that this letter will be helpful for graduate students to study the behaviours of free fermions in generalized dimensionality.
Observing fermionic statistics with photons in arbitrary processes
Matthews, Jonathan C. F.; Poulios, Konstantinos; Meinecke, Jasmin D. A.; Politi, Alberto; Peruzzo, Alberto; Ismail, Nur; Wörhoff, Kerstin; Thompson, Mark G.; O'Brien, Jeremy L.
2013-01-01
Quantum mechanics defines two classes of particles-bosons and fermions-whose exchange statistics fundamentally dictate quantum dynamics. Here we develop a scheme that uses entanglement to directly observe the correlated detection statistics of any number of fermions in any physical process. This approach relies on sending each of the entangled particles through identical copies of the process and by controlling a single phase parameter in the entangled state, the correlated detection statistics can be continuously tuned between bosonic and fermionic statistics. We implement this scheme via two entangled photons shared across the polarisation modes of a single photonic chip to directly mimic the fermion, boson and intermediate behaviour of two-particles undergoing a continuous time quantum walk. The ability to simulate fermions with photons is likely to have applications for verifying boson scattering and for observing particle correlations in analogue simulation using any physical platform that can prepare the entangled state prescribed here. PMID:23531788
Fermion tunneling from higher-dimensional black holes
NASA Astrophysics Data System (ADS)
Lin, Kai; Yang, Shu-Zheng
2009-03-01
Via the semiclassical approximation method, we study the 1/2-spin fermion tunneling from a higher-dimensional black hole. In our work, the Dirac equations are transformed into a simple form, and then we simplify the fermion tunneling research to the study of the Hamilton-Jacobi equation in curved space-time. Finally, we get the fermion tunneling rates and the Hawking temperatures at the event horizon of higher-dimensional black holes. We study fermion tunneling of a higher-dimensional Schwarzschild black hole and a higher-dimensional spherically symmetric quintessence black hole. In fact, this method is also applicable to the study of fermion tunneling from four-dimensional or lower-dimensional black holes, and we will take the rainbow-Finsler black hole as an example in order to make the fact explicit.
Pairing instabilities of Dirac composite fermions
NASA Astrophysics Data System (ADS)
Milovanović, M. V.; Ćirić, M. Dimitrijević; Juričić, V.
2016-09-01
Recently, a Dirac (particle-hole symmetric) description of composite fermions in the half-filled Landau level (LL) was proposed [D. T. Son, Phys. Rev. X 5, 031027 (2015), 10.1103/PhysRevX.5.031027], and we study its possible consequences on BCS (Cooper) pairing of composite fermions (CFs). One of the main consequences is the existence of anisotropic states in single-layer and bilayer systems, which was previously suggested in Jeong and Park [J. S. Jeong and K. Park, Phys. Rev. B 91, 195119 (2015), 10.1103/PhysRevB.91.195119]. We argue that in the half-filled LL in the single-layer case the gapped states may sustain anisotropy, because isotropic pairings may coexist with anisotropic ones. Furthermore, anisotropic pairings with the addition of a particle-hole symmetry-breaking mass term may evolve into rotationally symmetric states, i.e., Pfaffian states of Halperin-Lee-Read (HLR) ordinary CFs. On the basis of the Dirac formalism, we argue that in the quantum Hall bilayer at total filling factor 1, with decreasing distance between the layers, weak pairing of p -wave paired CFs is gradually transformed from Dirac to ordinary, HLR-like, with a concomitant decrease in the CF number. Global characterization of low-energy spectra based on the Dirac CFs agrees well with previous calculations performed by exact diagonalization on a torus. Finally, we discuss features of the Dirac formalism when applied in this context.
Rooted staggered fermions: good, bad or ugly?
NASA Astrophysics Data System (ADS)
Sharpe, Stephen
2006-12-01
I give a status report on the validity of the so-called "fourth-root trick", i.e. the procedure of representing the determinant for a single fermion by the fourth root of the staggered fermion determinant. This has been used by the MILC collaboration to create a large ensemble of lattices using which many quantities of physical interest have been and are being calculated. It is also used extensively in studies of QCD thermodynamics. The main question is whether the theory so defined has the correct continuum limit. There has been significant recent progress towards answering this question. After recalling the issue, and putting it into a broader context of results from statistical mechanics, I critically review the new work. I also address the related issue of the impact of treating valence and sea quarks differently in rooted simulations, discuss whether rooted simulations at finite temperature and density are subject to additional concerns, and briefly update results for quark masses using the MILC configurations. An answer to the question in the title is proposed in the summary.
New Fermionic Soft Theorems for Supergravity Amplitudes.
Chen, Wei-Ming; Huang, Yu-Tin; Wen, Congkao
2015-07-10
Soft limits of a massless S matrix are known to reflect the symmetries of the theory. In particular, for theories with Goldstone bosons, the double-soft limit of scalars reveals the coset structure of the vacuum manifold. In this Letter, we propose that such universal double-soft behavior is not only true for scalars, but also for spin-1/2 particles in four dimensions and fermions in three dimensions. We first consider the Akulov-Volkov theory and demonstrate that the double-soft limit of Goldstinos yields the supersymmetry algebra. More surprisingly, we also find that amplitudes in 4≤N≤8 supergravity theories in four dimensions as well as N=16 supergravity in three dimensions behave universally in the double-soft-fermion limit, analogous to the scalar ones. The validity of the new soft theorems at loop level is also studied. The results for supergravity are beyond what is implied by supersymmetry Ward identities and may impose nontrivial constraints on the possible counterterms for supergravity theories.
Feshbach molecule production in fermionic atomic gases
NASA Astrophysics Data System (ADS)
Gurarie, V.
2009-08-01
This paper examines the problem of molecule production in an atomic fermionic gas close to an s -wave Feshbach resonance by means of a magnetic field sweep through the resonance. In the solvable case of a narrow resonance, the density of molecules at the end of the process is derived for a slow sweep. It is shown that the density of the produced molecules is lower than what an application of a naive Landau-Zener formula for level crossing would imply. However, in the limit of a very slow sweep it is still possible to achieve full conversion of fermions into the molecules. It appears that the origin of the failure of the Landau-Zener picture of the molecule production is due to the fact that the sweep goes through a quantum phase transition in the limit of an infinitely narrow resonance, in agreement with general results recently discussed in the literature. However, the precise connection of this problem to other problems with this feature is not established.
Staggered fermion matrix elements using smeared operators
NASA Astrophysics Data System (ADS)
Kilcup, Greg; Gupta, Rajan; Sharpe, Stephen R.
1998-02-01
We investigate the use of two kinds of staggered fermion operators, smeared and unsmeared. The smeared operators extend over a 44 hypercube, and tend to have smaller perturbative corrections than the corresponding unsmeared operators. We use these operators to calculate kaon weak matrix elements on quenched ensembles at β=6.0, 6.2, and 6.4. Extrapolating to the continuum limit, we find BK(NDR,2 GeV)=0.62+/-0.02(stat)+/-0.02(syst). The systematic error is dominated by the uncertainty in the matching between lattice and continuum operators due to the truncation of perturbation theory at one loop. We do not include any estimate of the errors due to quenching or to the use of degenerate s and d quarks. For the ΔI=3/2 electromagnetic penguin operators we find B(3/2)7=0.62+/-0.03+/-0.06 and B(3/2)8=0.77+/-0.04+/-0.04. We also use the ratio of unsmeared to smeared operators to make a partially nonperturbative estimate of the renormalization of the quark mass for staggered fermions. We find that tadpole improved perturbation theory works well if the coupling is chosen to be αMS¯(q*=1/a).
Dynamical model for light composite fermions
NASA Astrophysics Data System (ADS)
Derman, Emanuel
1981-04-01
A simple dynamical model for the internal structure of the three light lepton and quark generations (νe,e,u,d), (νμ,μ,c,s), and (ντ,τ,t,b) is proposed. Each generation is constructed of only one fundamental massive generation F=(L∘,L-,U,D) with the same (SU3)c×SU2×U1 quantum numbers as the light generations, bound to a core of one or more massive Higgs bosons H, where H is the single physical Higgs boson necessary for spontaneous symmetry breaking in the standard model. For example, e-=[L-H], μ-=[L-HH], τ-=[L-HHH]. It is shown that the known binding force due to H exchange is attractive and strong enough to produce light bound states. Dynamical calculations for the bound-state composite fermions using the Bethe-Salpeter equation, together with some phenomenological imput, suggest MH~16 TeV and MF~100 GeV. It is likely that such bound states can have properties compatible with the up to now apparently elementary appearance of known fermions, for example, their Dirac magnetic moments and absence of intergeneration radiative decays (such as μ-->eδ). Phenomenological consequences and tests of the model are discussed.
Quantum phases of AB 2 fermionic chains
NASA Astrophysics Data System (ADS)
Murcia-Correa, L. S.; Franco, R.; Silva-Valencia, J.
2016-02-01
A fermionic chain is a one-dimensional system with fermions that interact locally and can jump between sites in the lattice, in particular an AB n chain type, where A and B are sites that exhibit a difference in energy level of Δ and site B is repeated n-times, such that the unit cell has n +1 sites. A limit case of this model, called the ionic Hubbard model (n = 1), has been widely studied due to its interesting physics and applications. In this paper, we study the ground state of an AB 2 chain, which describes the material R 4[Pt 2(P 2O5H2)4X] · nH 2 O. Specifically, we consider a filling with two electrons per unit cell, and using the density matrix renormalization group method we found that the system exhibits the band insulator and Mott correlated insulator phases, as well as an intermediate phase between them. For couplings of Δ = 2,10 and 20, we estimate the critical points that separate these phases through the structure factor and the energy gap in the sector of charge and spin, finding that the position of the critical point rises as a function of Δ.
Search for Majorana fermions in topological superconductors.
Pan, Wei; Shi, Xiaoyan; Hawkins, Samuel D.; Klem, John Frederick
2014-10-01
The goal of this project is to search for Majorana fermions (a new quantum particle) in a topological superconductor (a new quantum matter achieved in a topological insulator proximitized by an s-wave superconductor). Majorana fermions (MFs) are electron-like particles that are their own anti-particles. MFs are shown to obey non-Abelian statistics and, thus, can be harnessed to make a fault-resistant topological quantum computer. With the arrival of topological insulators, novel schemes to create MFs have been proposed in hybrid systems by combining a topological insulator with a conventional superconductor. In this LDRD project, we will follow the theoretical proposals to search for MFs in one-dimensional (1D) topological superconductors. 1D topological superconductor will be created inside of a quantum point contact (with the metal pinch-off gates made of conventional s-wave superconductors such as niobium) in a two-dimensional topological insulator (such as inverted type-II InAs/GaSb heterostructure).
White, M F
1994-02-01
IRS-1 is a principal substrate of the insulin receptor tyrosine kinase. It undergoes multi-site tyrosine phosphorylation and mediates the insulin signal by associating with various signaling molecules containing Src homology 2 domains. Interleukin-4 also stimulates IRS-1 phosphorylation, and it is suspected that a few more growth factors or cytokines will be added to form a select group of receptors that utilize the IRS-1 signaling pathway. More IRS-1-like adapter molecules, such as 4PS (IRS-2), may remain to be found.
2014-01-01
In automotive industry, destructive inspection of spot welds is still the mandatory quality assurance method due to the lack of efficient non-destructive evaluation (NDE) tools. However, it is costly and time-consuming. Recently at ORNL, a new NDE prototype system for spot weld inspection using infrared (IR) thermography has been developed to address this problem. This software contains all the key functions that ensure the NDE system to work properly: system input/output control, image acquisition, datamore » analysis, weld quality database generation and weld quality prediction, etc.« less
Chen, Jian; Feng, Zhili
2014-01-01
In automotive industry, destructive inspection of spot welds is still the mandatory quality assurance method due to the lack of efficient non-destructive evaluation (NDE) tools. However, it is costly and time-consuming. Recently at ORNL, a new NDE prototype system for spot weld inspection using infrared (IR) thermography has been developed to address this problem. This software contains all the key functions that ensure the NDE system to work properly: system input/output control, image acquisition, data analysis, weld quality database generation and weld quality prediction, etc.
Stability and collapse of fermions in a binary dipolar boson-fermion 164Dy-161Dy mixture
NASA Astrophysics Data System (ADS)
Adhikari, S. K.
2013-10-01
We suggest a time-dependent mean-field hydrodynamic model for a binary dipolar boson-fermion mixture to study the stability and collapse of fermions in the 164Dy-161Dy mixture. The condition of stability of the dipolar mixture is illustrated in terms of phase diagrams. A collapse is induced in a disk-shaped stable binary mixture by jumping the interspecies contact interaction from repulsive to attractive by the Feshbach resonance technique. The subsequent dynamics is studied by solving the time-dependent mean-field model including three-body loss due to molecule formation in boson-fermion and boson-boson channels. Collapse and fragmentation in the fermions after subsequent explosions are illustrated. The anisotropic dipolar interaction leads to anisotropic fermionic density distribution during collapse. This study is carried out in three-dimensional space using realistic values of dipolar and contact interactions.
SU(8) family unification with boson-fermion balance
NASA Astrophysics Data System (ADS)
Adler, Stephen L.
2014-08-01
We formulate an SU(8) family unification model motivated by requiring that the theory should incorporate the graviton, gravitinos, and the fermions and gauge fields of the standard model, with boson-fermion balance. Gauge field SU(8) anomalies cancel between the gravitinos and spin ½ fermions. The 56 of scalars breaks SU(8) to SU(3)family × SU(5) × U(1)/Z5, with the fermion representation content needed for "flipped" SU(5) with three families, and with residual scalars in the 10 and /line{10} representations that break flipped SU(5) to the standard model. Dynamical symmetry breaking can account for the generation of 5 representation scalars needed to break the electroweak group. Yukawa couplings of the 56 scalars to the fermions are forbidden by chiral and gauge symmetries, so in the first stage of SU(8) breaking fermions remain massless. In the limit of vanishing gauge coupling, there are N = 1 and N = 8 supersymmetries relating the scalars to the fermions, which restrict the form of scalar self-couplings and should improve the convergence of perturbation theory, if not making the theory finite and "calculable." In an Appendix we give an analysis of symmetry breaking by a Higgs component, such as the (1, 1)(-15) of the SU(8) 56 under SU(8) ⊃ SU(3) × SU(5) × U(1), which has nonzero U(1) generator.
SU(8) Family Unification with Boson Fermion Balance
NASA Astrophysics Data System (ADS)
Adler, Stephen L.
2015-03-01
We formulate an SU(8) family unification model motivated by requiring that the theory should incorporate the graviton, gravitinos, and the fermions and gauge fields of the standard model, with boson.fermion balance. Gauge field SU(8) anomalies cancel between the gravitinos and spin 1/2 fermions. The 56 of scalars breaks SU(8) to SU(3)family×SU(5)×U(1)/Z5, with the fermion representation content needed for "flipped" SU(5) with three families, and with residual scalars in the 10 and overline {10} representations that break flipped SU(5) to the standard model. Dynamical symmetry breaking can account for the generation of 5 representation scalars needed to break the electroweak group. Yukawa couplings of the 56 scalars to the fermions are forbidden by chiral and gauge symmetries, so in the first stage of SU(8) breaking fermions remain massless. In the limit of vanishing gauge coupling, there are N = 1 and N = 8 supersymmetries relating the scalars to the fermions, which restrict the form of scalar self-couplings and should improve the convergence of perturbation theory, if not making the theory finite and "calculable." In an Appendix we give an analysis of symmetry breaking by a Higgs component, such as the (1, 1)(-15) of the SU(8) 56 under SU(8) ⊃ SU(3) × SU(5) × U(1), which has nonzero U(1) generator.
Polarization of massive fermions in a vortical fluid
NASA Astrophysics Data System (ADS)
Fang, Ren-hong; Pang, Long-gang; Wang, Qun; Wang, Xin-nian
2016-08-01
Fermions become polarized in a vortical fluid due to spin-vorticity coupling. Such a polarization can be calculated from the Wigner function in a quantum kinetic approach. By extending previous results for chiral fermions, we derive the Wigner function for massive fermions up to next-to-leading order in spatial gradient expansion. The polarization density of fermions can be calculated from the axial vector component of the Wigner function and is found to be proportional to the local vorticity ω . The polarizations per particle for fermions and antifermions decrease with the chemical potential and increase with energy (mass). Both quantities approach the asymptotic value ℏ ω /4 in the large energy (mass) limit. The polarization per particle for fermions is always smaller than that for antifermions, whose ratio of fermions to antifermions also decreases with the chemical potential. The polarization per particle on the Cooper-Frye freeze-out hypersurface can also be formulated and is consistent with the previous result of Becattini et al.
Matrix elements of four-fermion operators with quenched Wilson fermions
NASA Astrophysics Data System (ADS)
Gupta, Rajan; Bhattacharya, Tanmoy; Sharpe, Stephen R.
1997-04-01
We present results for the matrix elements of a variety of four-fermion operators calculated using quenched Wilson fermions. Our simulations are done on 170 lattices of size 323×64 at β=6.0. We find BK=0.74+/-0.04+/-0.05, BD=0.78+/-0.01, B3/27=0.58+/-0.02+0.07-0.03, B3/28=0.81+/-0.03+0.03-0.02, with all results being in the NDR scheme at μ=2 GeV. We also calculate the B parameter for the operator Qs, which is needed in the study of the difference of B-meson lifetimes. Our best estimate is BS(NDR,μ=1/a=2.33 GeV) =0.80+/-0.01. This is given at the lattice scale since the required two-loop anomalous dimension matrix is not known. In all these estimates, the first error is statistical, while the second is due to the use of truncated perturbation theory to match continuum and lattice operators. Errors due to quenching and lattice discretization are not included. We also present new results for the perturbative matching coefficients, extending the calculation to all Lorentz scalar four-fermion operators, and using NDR as the continuum scheme.
Dynamics of domain-wall Dirac fermions on a topological insulator: A chiral fermion beam splitter
NASA Astrophysics Data System (ADS)
Hammer, René; Pötz, Walter
2013-12-01
The intersection of two ferromagnetic domain walls placed on the surface of topological insulators provides a one-way beam splitter for domain-wall Dirac fermions. Based on an analytic expression for a static two-soliton magnetic texture we perform a systematic numerical study of the propagation of Dirac wave packets along such intersections. A single-cone staggered-grid finite difference lattice scheme is employed in the numerical analysis. It is shown that the angle of intersection plays a decisive role in determining the splitting ratio of the fermion beam. For a nonrectangular intersection, the width and, to a lesser extent, the type of domain walls, e.g., Bloch or Néel, determine the properties of the splitter. As the ratio between domain-wall width and transverse localization length of the Dirac fermion is increased its propagation behavior changes from quantum-mechanical (wavelike) to classical ballistic (particlelike). An electric gate placed near the intersection offers a dynamic external control knob for adjusting the splitting ratio.
Charged fermions tunneling from regular black holes
Sharif, M. Javed, W.
2012-11-15
We study Hawking radiation of charged fermions as a tunneling process from charged regular black holes, i.e., the Bardeen and ABGB black holes. For this purpose, we apply the semiclassical WKB approximation to the general covariant Dirac equation for charged particles and evaluate the tunneling probabilities. We recover the Hawking temperature corresponding to these charged regular black holes. Further, we consider the back-reaction effects of the emitted spin particles from black holes and calculate their corresponding quantum corrections to the radiation spectrum. We find that this radiation spectrum is not purely thermal due to the energy and charge conservation but has some corrections. In the absence of charge, e = 0, our results are consistent with those already present in the literature.
Tomography of Majorana fermions with STM tips
NASA Astrophysics Data System (ADS)
Chevallier, Denis; Klinovaja, Jelena
2016-07-01
We investigate numerically the possibility to detect the spatial profile of Majorana fermions (MFs) by using STM tips that are made of either normal or superconducting material. In both cases, we are able to resolve the localization length and the oscillation period of the MF wave function. We show that the tunneling between the substrate and the tip, necessary to get the information on the wave-function oscillations, has to be weaker in the case of a superconducting probe. In the strong tunneling regime, the differential conductance saturates making it more difficult to observe the exponential decay of MFs. The temperature broadening of the profile is strongly suppressed in the case of the superconducting tip resulting, generally, in better resolution.
Majorana fermions in nanowires without gating superconductors
NASA Astrophysics Data System (ADS)
Lin, Chien-Hung; Hui, Hoi Yin; Sau, Jay; Das Sarma, Sankar
2011-03-01
Majorana fermions have been proposed to be realizable at the end of the semiconductor nanowire on top of an s-wave superconductor [1,2]. These proposals require gating the nanowire directly in contact with a superconductor which may be difficult in experiments. We analyze [1,2] in configurations where the wire is only gated away from the superconductor. We show that some signatures of the Majorana mode remain but the Majorana mode is not localized and hence not suitable for quantum computation. Therefore we propose an 1D periodic heterostructure which can support localized Majorana modes at the end of the wire without gating on the superconductor. This work is supported by DARPA-QuEST, JQI-NSF-PFC, and LPS-NSA.
Dynamical Arrest of Ultracold Lattice Fermions
NASA Astrophysics Data System (ADS)
Schmidt, Bernd; Bakhtiari, M. Reza; Titvinidze, Irakli; Schneider, Ulrich; Snoek, Michiel; Hofstetter, Walter
2013-02-01
We theoretically investigate the thermodynamics of an interacting inhomogeneous two-component Fermi gas in an optical lattice. Motivated by a recent experiment by L. Hackermüller , Science 327, 1621 (2010)SCIEAS0036-8075, we study the effect of the interplay between thermodynamics and strong correlations on the size of the fermionic cloud. We use dynamical mean-field theory to compute the cloud size, which in the experiment shows an anomalous expansion behavior upon increasing attractive interaction. We confirm this qualitative effect but, assuming adiabaticity, we find quantitative agreement only for weak interactions. For strong interactions we observe significant nonequilibrium effects which we attribute to a dynamical arrest of the particles due to increasing correlations.
Reasonable fermionic quantum information theories require relativity
NASA Astrophysics Data System (ADS)
Friis, Nicolai
2016-03-01
We show that any quantum information theory based on anticommuting operators must be supplemented by a superselection rule deeply rooted in relativity to establish a reasonable notion of entanglement. While quantum information may be encoded in the fermionic Fock space, the unrestricted theory has a peculiar feature: the marginals of bipartite pure states need not have identical entropies, which leads to an ambiguous definition of entanglement. We solve this problem, by proving that it is removed by relativity, i.e., by the parity superselection rule that arises from Lorentz invariance via the spin-statistics connection. Our results hence unveil a fundamental conceptual inseparability of quantum information and the causal structure of relativistic field theory.
Topological phases of fermions in one dimension
NASA Astrophysics Data System (ADS)
Fidkowski, Lukasz; Kitaev, Alexei
2011-02-01
In this paper we show how the classification of topological phases in insulators and superconductors is changed by interactions, in the case of one-dimensional systems. We focus on the time-reversal-invariant Majorana chain (BDI symmetry class). While the band classification yields an integer topological index k, it is known that phases characterized by values of k in the same equivalence class modulo 8 can be adiabatically transformed one to another by adding suitable interaction terms. Here we show that the eight equivalence classes are distinct and exhaustive, and provide a physical interpretation for the interacting invariant modulo 8. The different phases realize different Altland-Zirnbauer classes of the reduced density matrix for an entanglement bipartition into two half chains. We generalize these results to the classification of all one-dimensional gapped phases of fermionic systems with possible antiunitary symmetries, utilizing the algebraic framework of central extensions. We use matrix product state methods to prove our results.
Penguin diagrams for improved staggered fermions
Lee, Weonjong
2005-01-01
We calculate, at the one-loop level, penguin diagrams for improved staggered fermion operators constructed using various fat links. The main result is that diagonal mixing coefficients with penguin operators are identical between the unimproved operators and the improved operators using such fat links as Fat7, Fat7+Lepage, Fat7, HYP (I) and HYP (II). In addition, it turns out that the off-diagonal mixing vanishes for those constructed using fat links of Fat7, Fat7 and HYP (II). This is a consequence of the fact that the improvement by various fat links changes only the mixing with higher dimension operators and off-diagonal operators. The results of this paper, combined with those for current-current diagrams, provide complete matching at the one-loop level with all corrections of O(g{sup 2}) included.
Topological Thouless pumping of ultracold fermions
NASA Astrophysics Data System (ADS)
Nakajima, Shuta; Tomita, Takafumi; Taie, Shintaro; Ichinose, Tomohiro; Ozawa, Hideki; Wang, Lei; Troyer, Matthias; Takahashi, Yoshiro
2016-04-01
An electron gas in a one-dimensional periodic potential can be transported even in the absence of a voltage bias if the potential is slowly and periodically modulated in time. Remarkably, the transferred charge per cycle is sensitive only to the topology of the path in parameter space. Although this so-called Thouless charge pump was first proposed more than thirty years ago, it has not yet been realized. Here we report the demonstration of topological Thouless pumping using ultracold fermionic atoms in a dynamically controlled optical superlattice. We observe a shift of the atomic cloud as a result of pumping, and extract the topological invariance of the pumping process from this shift. We demonstrate the topological nature of the Thouless pump by varying the topology of the pumping path and verify that the topological pump indeed works in the quantum regime by varying the speed and temperature.
Fermionic path integrals and local anomalies
NASA Astrophysics Data System (ADS)
Roepstorff, G.
2003-05-01
No doubt, the subject of path integrals proved to be an immensely fruitful human, i.e. Feynman's idea. No wonder it is more timely than ever. Some even claim that it is the most daring, innovative and revolutionary idea since the days of Heisenberg and Bohr. It is thus likely to generate enthusiasm, if not addiction among physicists who seek simplicity together with perfection. Professor Devreese's long-lasting interest in, if not passion on the subject stems from his firm conviction that, beyond being the tool of choice, path integration provides the key to all quantum phenomena, be it in solid state, atomic, molecular or particle physics as evidenced by the impressive list of publications at the address http://lib.ua.ac.be/AB/a867.html. In this note, I review a pitfall of fermionic path integrals and a way to get around it in situations relevant to the Standard Model of particle physics.
Controlling interactions in ultracold fermionic ytterbium-173
NASA Astrophysics Data System (ADS)
Höfer, Moritz; Riegger, Luis; Hofrichter, Chrisitian; Rio Fernandes, Diogo; Bloch, Immanuel; Fölling, Simon
2016-05-01
The possibility to tune the interactions of ultracold atomic gases with an external magnetic field has become a vital tool for many quantum gas experiments. For fermionic ytterbium-173 both the 1 S0 ground state and 3 P0 metastable state have vanishing angular momentum J = 0 and therefore no magnetic Feshbach resonances are expected. Here we report on the discovery of a novel type of Feshbach resonance, which was predicted to exist due to orbital-mixing interactions. It occurs universally for all hyperfine-state combinations of ytterbium-173 and is located at experimentally accessible magnetic fields. The scattering properties are characterized by inter-orbital cross-thermalization measurements in the bulk as well as high resolution clock-line spectroscopy in a three-dimensional lattice. Furthermore, we study the dynamics of a strongly interacting two-orbital quantum gas in two dimensions.
Correlations between Majorana Fermions Through a Superconductor
NASA Astrophysics Data System (ADS)
Zyuzin, A. A.; Rainis, Diego; Klinovaja, Jelena; Loss, Daniel
2013-08-01
We consider a model of ballistic quasi-one-dimensional semiconducting wire with intrinsic spin-orbit interaction placed on the surface of a bulk s-wave superconductor (SC), in the presence of an external magnetic field. This setup has been shown to give rise to a topological superconducting state in the wire, characterized by a pair of Majorana-fermion (MF) bound states formed at the two ends of the wire. Here, we demonstrate that besides the well-known direct-overlap-induced energy splitting, the two MF bound states may hybridize via elastic tunneling processes through virtual quasiparticle states in the SC, giving rise to an additional energy splitting between MF states from the same as well as from different wires.
Heavy snow: IR spectroscopy of isotope mixed crystalline water ice.
Wong, Andy; Shi, Liang; Auchettl, Rebecca; McNaughton, Don; Appadoo, Dominique R T; Robertson, Evan G
2016-02-14
Mid-infrared spectra have been measured for crystalline water ice aerosols of widely varied H/D isotopic composition. Particles with diameters ranging from 10-200 nm were generated via rapid collisional cooling with a cold buffer gas over a range of temperatures from 7-200 K. In near isotopically pure ices, the νL band position is slightly red-shifted with increasing temperature whilst in the ν2 region apparently anomalous shifts in peak maxima are explained by the contribution of a broad 2νL band of H2O and a 3νL band of D2O together with ν2 intensity that is particularly weak in low temperature crystalline ice. The hydrogen bonded OH (or OD) oscillator bands of near pure H2O (or D2O) ices are blue-shifted with temperature, with a gradient very similar to that of the corresponding band in isotope diluted samples, HOD in D2O (or H2O). It implies that this observed temperature trend is predominantly due to the intrinsic change in local hydride stretch potential energy, rather than to changes in intermolecular coupling. However, it is also observed that the narrow hydride stretch bands of an isotope diluted sample rapidly develop sub-band structure as the oscillator concentration increases, evidence of strong intermolecular coupling and a high degree of delocalisation. Anomalous blue-shifts in the OD stretch profile as D2O concentration grows is attributable to Fermi resonance with 2ν2 of D2O, in much closer proximity than the corresponding H2O levels. Theoretical results from a mixed quantum/classical approach are used to validate these findings in the hydride stretching region. Theory qualitatively reproduces the experimental trends as a function of temperature and isotopic variance.
Heavy snow: IR spectroscopy of isotope mixed crystalline water ice.
Wong, Andy; Shi, Liang; Auchettl, Rebecca; McNaughton, Don; Appadoo, Dominique R T; Robertson, Evan G
2016-02-14
Mid-infrared spectra have been measured for crystalline water ice aerosols of widely varied H/D isotopic composition. Particles with diameters ranging from 10-200 nm were generated via rapid collisional cooling with a cold buffer gas over a range of temperatures from 7-200 K. In near isotopically pure ices, the νL band position is slightly red-shifted with increasing temperature whilst in the ν2 region apparently anomalous shifts in peak maxima are explained by the contribution of a broad 2νL band of H2O and a 3νL band of D2O together with ν2 intensity that is particularly weak in low temperature crystalline ice. The hydrogen bonded OH (or OD) oscillator bands of near pure H2O (or D2O) ices are blue-shifted with temperature, with a gradient very similar to that of the corresponding band in isotope diluted samples, HOD in D2O (or H2O). It implies that this observed temperature trend is predominantly due to the intrinsic change in local hydride stretch potential energy, rather than to changes in intermolecular coupling. However, it is also observed that the narrow hydride stretch bands of an isotope diluted sample rapidly develop sub-band structure as the oscillator concentration increases, evidence of strong intermolecular coupling and a high degree of delocalisation. Anomalous blue-shifts in the OD stretch profile as D2O concentration grows is attributable to Fermi resonance with 2ν2 of D2O, in much closer proximity than the corresponding H2O levels. Theoretical results from a mixed quantum/classical approach are used to validate these findings in the hydride stretching region. Theory qualitatively reproduces the experimental trends as a function of temperature and isotopic variance. PMID:26812598
Two-dimensional thermofield bosonization II: Massive fermions
Amaral, R.L.P.G.
2008-11-15
We consider the perturbative computation of the N-point function of chiral densities of massive free fermions at finite temperature within the thermofield dynamics approach. The infinite series in the mass parameter for the N-point functions are computed in the fermionic formulation and compared with the corresponding perturbative series in the interaction parameter in the bosonized thermofield formulation. Thereby we establish in thermofield dynamics the formal equivalence of the massive free fermion theory with the sine-Gordon thermofield model for a particular value of the sine-Gordon parameter. We extend the thermofield bosonization to include the massive Thirring model.
Hidden Fermionic Excitation Boosting High-Temperature Superconductivity in Cuprates.
Sakai, Shiro; Civelli, Marcello; Imada, Masatoshi
2016-02-01
The dynamics of a microscopic cuprate model, namely, the two-dimensional Hubbard model, is studied with a cluster extension of the dynamical mean-field theory. We find a nontrivial structure of the frequency-dependent self-energies, which describes an unprecedented interplay between the pseudogap and superconductivity. We show that these properties are well described by quasiparticles hybridizing with (hidden) fermionic excitations, emergent from the strong electronic correlations. The hidden fermion enhances superconductivity via a mechanism distinct from a conventional boson-mediated pairing, and originates the normal-state pseudogap. Though the hidden fermion is elusive in experiments, it can solve many experimental puzzles.
s-Wave collisional frequency shift of a fermion clock.
Hazlett, Eric L; Zhang, Yi; Stites, Ronald W; Gibble, Kurt; O'Hara, Kenneth M
2013-04-19
We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, θ(1). The fermion shift instead depends strongly on the second pulse area θ(2). It allows the shift to be canceled, nominally at θ(2)=π/2, but correlations perturb the null to slightly larger θ(2). The frequency shift is relevant for optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally larger at optical frequencies. PMID:23679589
Expansion of a quantum degenerate boson-fermion mixture
Hu, Hui; Liu, Xia-Ji; Modugno, Michele
2003-06-01
We study the expansion of an ultracold boson-fermion mixture released from an elongated magnetic trap, by using a scaling approach. We discuss in detail the role of the boson-fermion interaction on the evolution of the radial-to-axial aspect ratio of the condensate, and show that the latter depends crucially on the relative dynamics of the condensate and degenerate Fermi gas in the radial direction, which is characterized by the ratio between the trapping frequencies for fermions and bosons. The numerical solution of the scaling equations provides a reasonable agreement with the recent experiment [G. Roati et al., Phys. Rev. Lett. 89, 150403 (2002)].
Feshbach resonance described by boson-fermion coupling
Domanski, T.
2003-07-01
We consider a possibility to describe the Feshbach resonance in terms of the boson-fermion (BF) model. Using such a model, we show that after a gradual disentangling of the boson from fermion subsystem, the resonant-type scattering between fermions is indeed generated. We decouple the subsystems via (a) the single step and (b) the continuous canonical transformation. With the second one, we investigate the feedback effects effectively leading to the finite amplitude of the scattering strength. We study them in detail in the normal T>T{sub c} and superconducting T{<=}T{sub c} states.
Collective Interference of Composite Two-Fermion Bosons
NASA Astrophysics Data System (ADS)
Tichy, Malte C.; Bouvrie, Peter Alexander; Mølmer, Klaus
2012-12-01
The composite character of two-fermion bosons manifests itself in the interference of many composites as a deviation from the ideal bosonic behavior. A state of many composite bosons can be represented as a superposition of different numbers of perfect bosons and fermions, which allows us to provide the full Hong-Ou-Mandel-like counting statistics of interfering composites. Our theory quantitatively relates the deviation from the ideal bosonic interference pattern to the entanglement of the fermions within a single composite boson.
Hidden Fermionic Excitation Boosting High-Temperature Superconductivity in Cuprates.
Sakai, Shiro; Civelli, Marcello; Imada, Masatoshi
2016-02-01
The dynamics of a microscopic cuprate model, namely, the two-dimensional Hubbard model, is studied with a cluster extension of the dynamical mean-field theory. We find a nontrivial structure of the frequency-dependent self-energies, which describes an unprecedented interplay between the pseudogap and superconductivity. We show that these properties are well described by quasiparticles hybridizing with (hidden) fermionic excitations, emergent from the strong electronic correlations. The hidden fermion enhances superconductivity via a mechanism distinct from a conventional boson-mediated pairing, and originates the normal-state pseudogap. Though the hidden fermion is elusive in experiments, it can solve many experimental puzzles. PMID:26894730
On the Modified Palatini Action Coupled to Fermionic Matter
Lagraa, Meriem Hadjer
2010-10-31
From the generalized Palatini's action proposed recently in [1], we show that we can obtain the standard effective action of the theory of Einstein-Cartan coupled to the fermionic matter without the usual current-current interaction. Therefore, an effective action which is free from the Barbero-Immirzi parameter [2] and the non-vanishing torsion resulting from the presence of the minimal coupling of fermionic matter. This establishes the equivalence between the theories of general relativity and Einstein-Cartan minimally coupled to fermions [3].
Trapped fermions with density imbalance in the Bose-Einstein condensate limit.
Pieri, P; Strinati, G C
2006-04-21
We analyze the effects of imbalancing the populations of two-component trapped fermions, in the Bose-Einstein condensate limit of the attractive interaction between different fermions. Starting from the gap equation with two fermionic chemical potentials, we derive a set of coupled equations that describe composite bosons and excess fermions. We include in these equations the processes leading to the correct dimer-dimer and dimer-fermion scattering lengths. The coupled equations are then solved in the Thomas-Fermi approximation to obtain the density profiles for composite bosons and excess fermions, which are relevant to the recent experiments with trapped fermionic atoms.
Myers, M G; Sun, X J; White, M F
1994-07-01
Insulin-receptor substrate 1 (IRS-1) is a principal substrate of the receptor tyrosine kinase for insulin and insulin-like growth factor 1, and a substrate for a tyrosine kinase activated by interleukin 4. IRS-1 undergoes multisite tyrosine phosphorylation and mediates downstream signals by 'docking' various proteins that contain Src homology 2 domains. IRS-1 appears to be a unique molecule; however, 4PS, a protein found mainly in hemopoietic cells, may represent another member of this family.
Kawarabayashi, Tohru; Honda, Takahiro; Aoki, Hideo; Hatsugai, Yasuhiro
2013-12-04
The effect of disorder on the Landau levels of massless Dirac fermions is examined for the cases with and without the fermion doubling. To tune the doubling a tight-binding model having a complex transfer integral is adopted to shift the energies of two Dirac cones, which is theoretically proposed earlier and realizable in cold atoms in an optical lattice. In the absence of the fermion doubling, the n = 0 Landau level is shown to exhibit an anomalous sharpness even if the disorder is uncorrelated in space (i.e., large K-K' scattering). This anomaly occurs when the disorder respects the chiral symmetry of the Dirac cone.
Fermionic collective modes of an anisotropic quark-gluon plasma
Schenke, Bjoern; Strickland, Michael
2006-09-15
We determine the fermionic collective modes of a quark-gluon plasma which is anisotropic in momentum space. We calculate the fermion self-energy in both the imaginary- and real-time formalisms and find that numerically and analytically (for two special cases) there are no unstable fermionic modes. In addition we demonstrate that in the hard-loop limit the Kubo-Martin-Schwinger condition, which relates the off-diagonal components of the real-time fermion self-energy, holds even for the anisotropic, and therefore nonequilibrium, quark-gluon plasma considered here. The results obtained here set the stage for the calculation of the nonequilibrium photon production rate from an anisotropic quark-gluon plasma.
Instability-induced fermion production in quantum field theory
Berges, Juergen; Pruschke, Jens; Rothkopf, Alexander
2009-07-15
Nonequilibrium instabilities are known to lead to exponential amplification of boson occupation numbers for low-momentum modes on time scales much shorter than the asymptotic thermal equilibration time. We show for Yukawa-type interactions that this growth induces very efficient fermion production, which proceeds with the maximum primary boson growth rate. The description is based on a 1/N expansion of the 2PI effective action to next-to-leading order including boson-fermion loops, which are crucial to observe this phenomenon. For long enough amplification in the boson sector, fermion production terminates when the thermal occupancy is reached in the infrared. At higher momenta, where boson occupation numbers are low, the fermion modes exhibit a power-law regime with exponent two.
Odd-frequency pairing of interacting Majorana fermions
Huang, Zhoushen; Wolfle, P.; Balatsky, Alexander V.
2015-09-14
In this study, Majorana fermions are rising as a promising key component in quantum computation. Although the prevalent approach is to use a quadratic (i.e., noninteracting) Majorana Hamiltonian, when expressed in terms of Dirac fermions, generically the Hamiltonian involves interaction terms. Here we focus on the possible pair correlations in a simple model system. We study a model of Majorana fermions coupled to a boson mode and show that the anomalous correlator between different Majorana fermions, located at opposite ends of a topological wire, exhibits odd-frequency behavior. It is stabilized when the coupling strength g is above a critical valuemore » gc. We use both, conventional diagrammatic theory and a functional integral approach, to derive the gap equation, the critical temperature, the gap function, the critical coupling, and a Ginzburg-Landau theory that allows discussing a possible subleading admixture of even-frequency pairing.« less
Odd-frequency pairing of interacting Majorana fermions
Huang, Zhoushen; Wolfle, P.; Balatsky, Alexander V.
2015-09-14
In this study, Majorana fermions are rising as a promising key component in quantum computation. Although the prevalent approach is to use a quadratic (i.e., noninteracting) Majorana Hamiltonian, when expressed in terms of Dirac fermions, generically the Hamiltonian involves interaction terms. Here we focus on the possible pair correlations in a simple model system. We study a model of Majorana fermions coupled to a boson mode and show that the anomalous correlator between different Majorana fermions, located at opposite ends of a topological wire, exhibits odd-frequency behavior. It is stabilized when the coupling strength g is above a critical value g_{c}. We use both, conventional diagrammatic theory and a functional integral approach, to derive the gap equation, the critical temperature, the gap function, the critical coupling, and a Ginzburg-Landau theory that allows discussing a possible subleading admixture of even-frequency pairing.
Classical simulation of noninteracting-fermion quantum circuits
NASA Astrophysics Data System (ADS)
Terhal, Barbara M.; Divincenzo, David P.
2002-03-01
We show that a class of quantum computations that was recently shown to be efficiently simulatable on a classical computer by Valiant [in Proceedings of the 33rd ACM Symposium on the Theory of Computing (2001), p. 114] corresponds to a physical model of noninteracting fermions in one dimension. We give an alternative proof of his result using the language of fermions and extend the result to noninteracting fermions with arbitrary pairwise interactions, where gates can be conditioned on outcomes of complete von Neumann measurements in the computational basis on other fermionic modes in the circuit. This last result is in remarkable contrast with the case of noninteracting bosons where universal quantum computation can be achieved by allowing gates to be conditioned on classical bits [E. Knill, R. Laflamme, and G. Milburn, Nature (London) 409, 46 (2001)].
B-parameters of 4-fermion operators from lattice QCD
NASA Astrophysics Data System (ADS)
Gupta, Rajan
1998-04-01
This talk summarizes the status of the calculations of BK, B7, B8 and Bs, done in collaboration with T. Bhattacharya, G. Kilcup, and S. Sharpe. Results for staggered, Wilson, and Clover fermions are presented.
High-order correlation of chaotic bosons and fermions
NASA Astrophysics Data System (ADS)
Liu, Hong-Chao
2016-08-01
We theoretically study the high-order correlation functions of chaotic bosons and fermions. Based on the different parity of the Stirling number, the products of the first-order correlation functions are well classified and employed to represent the high-order correlation function. The correlation of bosons conduces a bunching effect, which will be enhanced as order N increases. Different from bosons, the anticommutation relation of fermions leads to the parity of the Stirling number, which thereby results in a mixture of bunching and antibunching behaviors in high-order correlation. By further investigating third-order ghost diffraction and ghost imaging, the differences between the high-order correlations of bosons and fermions are discussed in detail. A larger N will dramatically improve the ghost image quality for bosons, but a good strategy should be carefully chosen for the fermionic ghost imaging process due to its complex correlation components.
Skyrmion Superfluidity in Two-Dimensional Interacting Fermionic Systems.
Palumbo, Giandomenico; Cirio, Mauro
2015-06-17
In this article we describe a multi-layered honeycomb lattice model of interacting fermions which supports a new kind of parity-preserving skyrmion superfluidity. We derive the low-energy field theory describing a non-BCS fermionic superfluid phase by means of functional fermionization. Such effective theory is a new kind of non-linear sigma model, which we call double skyrmion model. In the bi-layer case, the quasiparticles of the system (skyrmions) have bosonic statistics and replace the Cooper-pairs role. Moreover, we show that the model is also equivalent to a Maxwell-BF theory, which naturally establishes an effective Meissner effect without requiring a breaking of the gauge symmetry. Finally, we map effective superfluidity effects to identities among fermionic observables for the lattice model. This provides a signature of our theoretical skyrmion superfluidy that can be detected in a possible implementation of the lattice model in a real quantum system.
A note on the loop formula for the fermionic determinant
NASA Astrophysics Data System (ADS)
Seiler, Erhard; Stamatescu, Ion-Olimpiu
2016-08-01
A formula expressing the fermionic determinant as an infinite product of smaller determinants is derived and discussed. These smaller determinants are of a fixed size, independent of the size of the lattice and are indexed by loops of increasing length.
Finite pulse effects on fermion pair creation from strong electric fields
NASA Astrophysics Data System (ADS)
Taya, Hidetoshi; Fujii, Hirotsugu; Itakura, Kazunori
2014-09-01
In the early stage of heavy ion collisions, there appear extraordinarily strong (color) EM fields. In the presence of such strong fields, we encounter essentially new phenomena that are not observed in the vacuum: Among those is fermion pair creation from the vacuum. In this talk, we consider fermion pair creation from the vacuum in a strong electric field with finite duration. Employing the Sauter-type pulsed electric field with height E0 and width τ, we demonstrate explicitly the interplay between the non-perturbative and perturbative aspects of the pair creation in a strong field with finite duration. We identify that two dimensionless parameters ν = | g E0 | τ2 and γ = | g E0 | τ / m characterize the importance of multiple interactions with the field and the transition from the perturbative to the non-perturbative regime. We also show that the pair creation is enhanced compared to Schwinger's formula when the field strength is relativity weak | g E0 | / m2 < 1 and the pulse duration is relatively short mτ < 1 , and reveal that the enhancement is predominantly described by the lowest order perturbation with a single photon. We also discuss some recent developments and applications.
Search strategies for TeV scale fermionic top partners with charge 2/3
NASA Astrophysics Data System (ADS)
Backović, Mihailo; Flacke, Thomas; Kim, Jeong Han; Lee, Seung J.
2016-04-01
Searches for fermionic top partners at the TeV scale will bring forward a new final state kinematic regime and event topologies, where Run I search strategies will inevitably fail. We propose concrete search strategies for singly produced charge 2/3 fermionic top partners ( T ') adequate for LHC Run II. Our analysis spans over all of the T' decay modes (i.e. tZ, th and Wb) where we present detailed discussion of the search performances, signal efficiencies and backgrounds rates. Our LHC Run II search proposals utilize signatures with large missing energy and leptons, as well as jet substructure observables for tagging of boosted heavy SM states, customized b-tagging tactics and forward jet tagging. We analyze the prospects for discovery and exclusion of T ' models within the framework of partially composite quarks at the LHC Run II. Our results show that the LHC Run II has good prospects for observing T ' models which predict single production cross section of σ T ' ˜ 70 - 140 (30 - 65) fb for M T ' = 1 (1 .5) TeV respectively with 100 fb-1 of integrated luminosity, depending on the branching ratios of the T '. Similarly, we find that cross sections of σ T ' ˜ 27 - 60 (13 - 24) fb for M T ' = 1 (1 .5) TeV respectively can be excluded with the same amount of data. Our results are minimally model dependent and can be applied to most T ' models where Γ T ' ≪ M T '.
Gravitational four-fermion interaction in the early Universe
NASA Astrophysics Data System (ADS)
Rudenko, A. S.; Khriplovich, I. B.
2014-02-01
If torsion exists, it generates gravitational four-fermion interaction (GFFI), essential on the Planck scale. We analyze the influence of this interaction on the Friedmann-Lemaitre-Robertson-Walker cosmology. An explicit analytic solution is derived for the problem where both the energy-momentum tensor generated by GFFI and the common ultrarelativistic energy-momentum tensor are included. We demonstrate that gravitational four-fermion interaction does not result in a Big Bounce.
Gravitational Four-Fermion Interaction in the Early Universe
NASA Astrophysics Data System (ADS)
Khriplovich, I.; Rudenko, A.
If torsion exists, it generates gravitational four-fermion interaction (GFFI), essential on the Planck scale. We analyze the influence of this interaction on the Friedmann-Lemaitre-Robertson-Walker cosmology. Explicit analytical solution is derived for the problem where both the energy-momentum tensor generated by GFFI and the common ultrarelativistic energy-momentum tensor are included. We demonstrate that gravitational four-fermion interaction does not result in Big Bounce.
Gravitational four-fermion interaction in the early Universe
NASA Astrophysics Data System (ADS)
Khriplovich, I. B.; Rudenko, A. S.
2014-07-01
If torsion exists, it generates gravitational four-fermion interaction (GFFI), essential on the Planck scale. We analyze the influence of this interaction on the Friedmann-Lemaitre-Robertson-Walker cosmology. Explicit analytical solution is derived for the problem where both the energy-momentum tensor generated by GFFI and the common ultrarelativistic energy-momentum tensor are included. We demonstrate that gravitational four-fermion interaction does not result in Big Bounce.
Species doubling and transfer matrices for fermionic fields
NASA Astrophysics Data System (ADS)
Creutz, Michael
1987-02-01
The transfer-matrix formalism for relating Hamiltonian quantum mechanics and Euclidean path integrals is discussed in the context of fermionic fields. Particular emphasis is placed on the extra fermionic species encountered with the naive discretization of time. When both particles and antiparticles are present, the Wilson projection-operator formalism arises naturally for the temporal coordinate. We discuss in detail how the Hilbert space must be enlarged to remove these projections.
A Comparative Study on q-Deformed Fermion Oscillators
NASA Astrophysics Data System (ADS)
Algin, Abdullah
2011-05-01
In this paper, the algebras, representations, and thermostatistics of four types of fermionic q-oscillator models, called fermionic Newton (FN), Chaichian-Kulish-Ng (CKN), Parthasarathy-Viswanathan-Chaichian (PVC), Viswanathan-Parthasarathy-Jagannathan-Chaichian (VPJC), are discussed. Similarities and differences among the properties of these models are revealed. Particular emphasis is given to the VPJC-oscillators model so that its Fock space representation is analyzed in detail. Possible physical applications of these models are concisely pointed out.
A gauge field theory of fermionic continuous-spin particles
NASA Astrophysics Data System (ADS)
Bekaert, X.; Najafizadeh, M.; Setare, M. R.
2016-09-01
In this letter, we suggest a local covariant action for a gauge field theory of fermionic Continuous-Spin Particles (CSPs). The action is invariant under gauge transformations without any constraint on both the gauge field and the gauge transformation parameter. The Fang-Fronsdal equations for a tower of massless fields with all half-integer spins arise as a particular limit of the equation of motion of fermionic CSPs.
Reprint of : Floquet Majorana fermions in superconducting quantum dots
NASA Astrophysics Data System (ADS)
Benito, Mónica; Platero, Gloria
2016-08-01
We consider different configurations of ac driven quantum dots coupled to superconductor leads where Majorana fermions can exist as collective quasiparticles. The main goal is to tune the existence, localization and properties of these zero energy quasiparticles by means of periodically driven external gates. In particular, we analyze the relevance of the system and driving symmetry. We predict the existence of different sweet spots with Floquet Majorana fermions in configurations where they are not present in the undriven system.
Fermions in the U(1) Y hypercharge theory
NASA Astrophysics Data System (ADS)
Lee, I.-Hsiu
1991-05-01
The U(1) Y hypercharge sector of the standard electroweak theory is studied on the lattice. It is shown that, for fermions with both nonsinglet ψL and ψR, the doubler modes can be removed in the continuum limit while the masses of the physical fermions can be tuned appropriately. Data from simulations will be discussed and compared with recent analytic calculations.
Chiral fermions in noncommutative electrodynamics: Renormalizability and dispersion
Buric, Maja; Latas, Dusko; Radovanovic, Voja; Trampetic, Josip
2011-02-15
We analyze quantization of noncommutative chiral electrodynamics in the enveloping algebra formalism in linear order in noncommutativity parameter {theta}. Calculations show that divergences exist and cannot be removed by ordinary renormalization; however, they can be removed by the Seiberg-Witten redefinition of fields. Performing redefinitions explicitly, we obtain renormalizable Lagrangian and discuss the influence of noncommutativity on field propagation. Noncommutativity affects the propagation of chiral fermions only: half of the fermionic modes become massive and birefringent.
Gauge covariant fermion propagator in quenched, chirally symmetric quantum electrodynamics
Roberts, C.D.; Dong, Z.; Munczek, H.J.
1995-08-01
The chirally symmetric solution of the massless, quenched, Dyson-Schwinger equation (DSE) for the fermion propagator in three- and four-dimensional quantum electrodynamics was obtained. The DSEs are a valuable nonperturbative tool for studying field theories. In recent years a good deal of progress was made in addressing the limitations of the DSE approach in the study of Abelian gauge theories. Key to this progress is an understanding of the role of the dressed fermion/gauge-boson vertex in ensuring gauge covariance and multiplicative renormalizability of the solution of the fermion DSE. The solutions we obtain are manifestly gauge covariant and a general gauge covariance constraint on the fermion/gauge-boson vertex is presented, which motivates a vertex Ansatz that, for the first time, both satisfies the Ward identity when the fermion self-mass is zero and ensures gauge covariance of the fermion propagator. This research facilitates gauge-invariant, nonperturbative studies of continuum quantum electrodynamics and has already been used by others in studies of the chiral phase transition.
A note on the path integral representation for Majorana fermions
NASA Astrophysics Data System (ADS)
Greco, Andrés
2016-04-01
Majorana fermions are currently of huge interest in the context of nanoscience and condensed matter physics. Different to usual fermions, Majorana fermions have the property that the particle is its own anti-particle thus, they must be described by real fields. Mathematically, this property makes nontrivial the quantization of the problem due, for instance, to the absence of a Wick-like theorem. In view of the present interest on the subject, it is important to develop different theoretical approaches in order to study problems where Majorana fermions are involved. In this note we show that Majorana fermions can be studied in the context of field theories for constrained systems. Using the Faddeev-Jackiw formalism for quantum field theories with constraints, we derived the path integral representation for Majorana fermions. In order to show the validity of the path integral we apply it to an exactly solvable problem. This application also shows that it is rather simple to perform systematic calculations on the basis of the present framework.
Anyonic behavior of an intermediate-statistics fermion gas model.
Algin, Abdullah; Irk, Dursun; Topcu, Gozde
2015-06-01
We study the high-temperature behavior of an intermediate-statistics fermionic gas model whose quantum statistical properties enable us to effectively deduce the details about both the interaction among deformed (quasi)particles and their anyonic behavior. Starting with a deformed fermionic grand partition function, we calculate, in the thermodynamical limit, several thermostatistical functions of the model such as the internal energy and the entropy by means of a formalism of the fermionic q calculus. For high temperatures, a virial expansion of the equation of state for the system is obtained in two and three dimensions and the first five virial coefficients are derived in terms of the model deformation parameter q. From the results obtained by the effect of fermionic deformation, it is found that the model parameter q interpolates completely between bosonlike and fermionic systems via the behaviors of the third and fifth virial coefficients in both two and three spatial dimensions and in addition it characterizes effectively the interaction among quasifermions. Our results reveal that the present deformed (quasi)fermion model could be very efficient and effective in accounting for the nonlinear behaviors in interacting composite particle systems.
Symmetry-improved 2PI approach to the Goldstone-boson IR problem of the SM effective potential
NASA Astrophysics Data System (ADS)
Pilaftsis, Apostolos; Teresi, Daniele
2016-05-01
The effective potential of the Standard Model (SM), from three loop order and higher, suffers from infrared (IR) divergences arising from quantum effects due to massless would-be Goldstone bosons associated with the longitudinal polarizations of the W± and Z bosons. Such IR pathologies also hinder accurate evaluation of the two-loop threshold corrections to electroweak quantities, such as the vacuum expectation value of the Higgs field. However, these divergences are an artifact of perturbation theory, and therefore need to be consistently resummed in order to obtain an IR-safe effective potential. The so-called Two-Particle-Irreducible (2PI) effective action provides a rigorous framework to consistently perform such resummations, without the need to resort to ad hoc subtractions or running into the risk of over-counting contributions. By considering the recently proposed symmetry-improved 2PI formalism, we address the problem of the Goldstone-boson IR divergences of the SM effective potential in the gaugeless limit of the theory. In the same limit, we evaluate the IR-safe symmetry-improved 2PI effective potential, after taking into account quantum loops of chiral fermions, as well as the renormalization of spurious custodially breaking effects triggered by fermionic Yukawa interactions. Finally, we compare our results with those obtained with other methods presented in the literature.
Standard Model fermion masses and mixing angles generated in 3HDM
NASA Astrophysics Data System (ADS)
Ibarra, A.; Solaguren-Beascoa, A.
2016-05-01
We present a framework to generate the mass hierarchies and mixing angles of the fermionic sector of the Standard Model with two extra Higgs doublets and one right-handed neutrino. The masses of the first and second generation are generated by small quantum effects, explaining the hierarchy with the third generation. The model also generates a natural hierarchy between the first and second generation after the assumption that the Yukawa couplings are of rank 1. All the quark and lepton mixing matrices can also be generated by quantum effects, reproducing the hierarchies of the experimental values. The parameters generated radiatively depend logarithmically on the heavy Higgs masses. Therefore this framework can be reconciled with the stringent limits on flavour violation by postulating a sufficiently large new physics scale.
Topological aspects of fermions on hyperdiamond
Saidi, E. H.; Fassi-Fehri, O.; Bousmina, M.
2012-07-15
Motivated by recent results on the index of the Dirac operator D={gamma}{sup {mu}}D{sub {mu}} of QCD on lattice and also by results on topological features of electrons and holes of two-dimensional graphene, we compute in this paper the index of D for fermions living on a family of even-dimensional lattices denoted as L{sub 2N} and describing the 2N-dimensional generalization of the graphene honeycomb. The calculation of this topological index is done by using the direct method based on solving explicitly the gauged Dirac equation and also by using specific properties of the lattices L{sub 2N}, which are shown to be intimately linked with the weight lattices of SU(2N+ 1). The index associated with the two leading N= 1 and N= 2 elements of this family describe precisely the chiral anomalies of graphene and QCD{sub 4}. Comments on the method using the spectral flow approach as well as the computation of the topological charges on 2-cycles of 2N-dimensional compact supercell in L{sub 2N} and applications to QCD{sub 4} are also given.
Composite fermions for fractionally filled Chern bands
NASA Astrophysics Data System (ADS)
Shankar, R.
2012-02-01
We consider fractionally filled bands with a non-zero Chern index that exhibit the Fractional Quantum Hall Effect in zero external fieldootnotetextR. Roy and S. Sondhi, Physics 4, 46 (2011) and papers reviewed therein. a possibility supported by numerical work.ootnotetextIbid. Analytic treatments are complicated by a non-constant Berry flux and the absence of Composite Fermions (CF), which would not only single out preferred fractions, but also allow us compute numerous response functions at nonzero frequencies, wavelengths and temperature using either Chern-Simons field theory or our Hamiltonian formalism.ootnotetextG. Murthy and R. Shankar, Rev. Mod. Phys., 75, 1101, (2003) We describe a way to introduce CF's by embedding the Chern band in an auxiliary problem involving Landau levels. The embedded band can be designed to approximate a prescribed Chern density in k space which determines the commutation relations of the charge densities and hence preserve all dynamical and algebraic aspects of the original problem. We find some states for which the filling fraction and dimensionless Hall conductance are not equal. The approach extends to two-dimensional time-reversal invariant topological insulators and to composite bosons.
Majorana fermions in condensed-matter physics
NASA Astrophysics Data System (ADS)
Leggett, A. J.
2016-06-01
It is an honor and a pleasure to have been invited to give a talk in this conference celebrating the memory of the late Professor Abdus Salam. To my regret, I did not know Professor Salam personally, but I am very aware of his work and of his impact on my area of specialization, condensed matter physics, both intellectually through his ideas on spontaneously broken symmetry and more practically through his foundation of the ICTP. Since I assume that most of this audience are not specialized in condensed-matter physics, I thought I would talk about one topic which to some extent bridges this field and the particle-physics interests of Salam, namely Majorana fermions (M.F.s). However, as we shall see, the parallels which are often drawn in the current literature may be a bit too simplistic. I will devote most of this talk to a stripped-down exposition of the current orthodoxy concerning M.F.s. in condensed-matter physics and their possible applications to topological quantum computing (TQC), and then at the end briefly indicate why I believe this orthodoxy may be seriously misleading.
Non-perturbative Renormalization with Staggered Fermions
NASA Astrophysics Data System (ADS)
Lytle, Andrew
Lattice studies of Standard Model phenomenology frequently require knowledge of matching factors, or "Z-factors," that convert lattice operators defined at the lattice scale to operators in a continuum scheme at a scale mu. We make the first non-perturbative determinations of Z-factors for improved, fully dynamical staggered fermions. We compute the mass renormalization factor Zm for the Asqtad action, which is the action used by the MILC collaboration[1]. We find the strange quark mass to be mMSs (2 GeV) = 103(3) MeV; significantly larger than the result obtained using the perturbative Z-factor[2]. We compute all 256 bilinear Z-factors for the HYP-smeared action, which provides a laboratory for comparison to the results of one-loop perturbation theory[3]. Our results indicate broad agreement for ratios of Z-factors, at the few percent level, while the Z-factors themselves differ at around the ten percent level. The bilinear calculations are a stepping stone towards computation of the four-Fermi Z-factors relevant for an ongoing precision calculation of BK[4, 5, 6, 7], the knowledge of which is used to constrain the CKM matrix. Uncertainty in the required matching factors constitutes the dominant source of error.
Topological aspects of fermions on hyperdiamond
NASA Astrophysics Data System (ADS)
Saidi, E. H.; Fassi-Fehri, O.; Bousmina, M.
2012-07-01
Motivated by recent results on the index of the Dirac operator D = γμDμ of QCD on lattice and also by results on topological features of electrons and holes of two-dimensional graphene, we compute in this paper the index of D for fermions living on a family of even-dimensional lattices denoted as {L}_{2N} and describing the 2N-dimensional generalization of the graphene honeycomb. The calculation of this topological index is done by using the direct method based on solving explicitly the gauged Dirac equation and also by using specific properties of the lattices {L} _{2N}, which are shown to be intimately linked with the weight lattices of SU(2N + 1). The index associated with the two leading N = 1 and N = 2 elements of this family describe precisely the chiral anomalies of graphene and QCD4. Comments on the method using the spectral flow approach as well as the computation of the topological charges on 2-cycles of 2N-dimensional compact supercell in {L}_{2N} and applications to QCD4 are also given.
Goldstone bosons and fermions in QCD
Zwanziger, Daniel
2010-06-15
We consider the version of QCD in Euclidean Landau gauge in which the restriction to the Gribov region is implemented by a local, renormalizable action. This action depends on the Gribov parameter {gamma}, with dimensions of (mass){sup 4}, whose value is fixed in terms of {Lambda}{sub QCD}, by the gap equation, known as the horizon condition, ({partial_derivative}{Gamma}/{partial_derivative}{gamma})=0, where {Gamma} is the quantum effective action. The restriction to the Gribov region suppresses gluons in the infrared, which nicely explains why gluons are not in the physical spectrum, but this only makes more mysterious the origin of the long-range force between quarks. In the present article we exhibit the symmetries of {Gamma}, and show that the solution to the gap equation, which defines the classical vacuum, spontaneously breaks some of the symmetries of {Gamma}. This implies the existence of massless Goldstone bosons and fermions that do not appear in the physical spectrum. Some of the Goldstone bosons may be exchanged between quarks, and are candidates for a long-range confining force. As an exact result we also find that in the infrared limit the gluon propagator vanishes like k{sup 2}.
Path Integral Monte Carlo Methods for Fermions
NASA Astrophysics Data System (ADS)
Ethan, Ethan; Dubois, Jonathan; Ceperley, David
2014-03-01
In general, Quantum Monte Carlo methods suffer from a sign problem when simulating fermionic systems. This causes the efficiency of a simulation to decrease exponentially with the number of particles and inverse temperature. To circumvent this issue, a nodal constraint is often implemented, restricting the Monte Carlo procedure from sampling paths that cause the many-body density matrix to change sign. Unfortunately, this high-dimensional nodal surface is not a priori known unless the system is exactly solvable, resulting in uncontrolled errors. We will discuss two possible routes to extend the applicability of finite-temperatue path integral Monte Carlo. First we extend the regime where signful simulations are possible through a novel permutation sampling scheme. Afterwards, we discuss a method to variationally improve the nodal surface by minimizing a free energy during simulation. Applications of these methods will include both free and interacting electron gases, concluding with discussion concerning extension to inhomogeneous systems. Support from DOE DE-FG52-09NA29456, DE-AC52-07NA27344, LLNL LDRD 10- ERD-058, and the Lawrence Scholar program.
A novel and economical explanation for SM fermion masses and mixings
NASA Astrophysics Data System (ADS)
Hernández, A. E. Cárcamo
2016-09-01
I propose the first multiscalar singlet extension of the standard model (SM), which generates tree level top quark and exotic fermion masses as well as one and three loop level masses for charged fermions lighter than the top quark and for light active neutrinos, respectively, without invoking electrically charged scalar fields. That model, which is based on the S3× Z8 discrete symmetry, successfully explains the observed SM fermion mass and mixing pattern. The charged exotic fermions induce one loop level masses for charged fermions lighter than the top quark. The Z8 charged scalar singlet χ generates the observed charged fermion mass and quark mixing pattern.
Baiz, Carlos R.; Schach, Denise; Tokmakoff, Andrei
2014-01-01
We describe a microscope for measuring two-dimensional infrared (2D IR) spectra of heterogeneous samples with μm-scale spatial resolution, sub-picosecond time resolution, and the molecular structure information of 2D IR, enabling the measurement of vibrational dynamics through correlations in frequency, time, and space. The setup is based on a fully collinear “one beam” geometry in which all pulses propagate along the same optics. Polarization, chopping, and phase cycling are used to isolate the 2D IR signals of interest. In addition, we demonstrate the use of vibrational lifetime as a contrast agent for imaging microscopic variations in molecular environments. PMID:25089490
Study of Majorana fermionic dark matter
NASA Astrophysics Data System (ADS)
Chua, Chun-Khiang; Wong, Gwo-Guang
2016-08-01
We construct a generic model of Majorana fermionic dark matter (DM). Starting with two Weyl spinor multiplets η1 ,2˜(I ,∓Y ) coupled to the Standard Model Higgs, six additional Weyl spinor multiplets with (I ±1 /2 ,±(Y ±1 /2 )) are needed in general. It has 13 parameters in total, five mass parameters and eight Yukawa couplings. The DM sector of the minimal supersymmetric Standard Model is a special case of the model with (I ,Y )=(1 /2 ,1 /2 ). Therefore, this model can be viewed as an extension of the neutralino DM sector. We consider three typical cases: the neutralinolike, the reduced, and the extended cases. For each case, we survey the DM mass mχ in the range of (1,2500) GeV by random sampling from the model parameter space and study the constraints from the observed DM relic density; the direct search of LUX, XENON100, and PICO experiments; and the indirect search of Fermi-LAT data. We investigate the interplay of these constraints and the differences among these cases. It is found that the direct detection of spin-independent DM scattering off nuclei and the indirect detection of DM annihilation to the W+W- channel will be more sensitive to the DM searches in the near future. The allowed mass for finding H ˜-, B ˜-, W ˜-, and non-neutralino-like DM particles and the predictions on ⟨σ (χ χ →Z Z ,Z H ,t t ¯)v ⟩ in the indirect search are given.
Effective fermion couplings in warped 5D Higgsless theories
Bechi, J.; Casalbuoni, R.; De Curtis, S.; Dominici, D.
2006-11-01
We consider a 5-dimensional SU(2) gauge theory with fermions in the bulk and with additional SU(2) and U(1) kinetic terms on the branes. The electroweak breaking is obtained by boundary conditions. After deconstruction, fermions in the bulk are eliminated by using their equations of motion. In this way, standard model fermion mass terms and direct couplings to the internal gauge bosons of the moose are generated. The presence of these new couplings gives a new contribution to the {epsilon}{sub 3} parameter in addition to the gauge boson term. This allows the possibility of a cancellation between the two contributions, which can be local (site by site) or global. Going back to the continuum, we show that the implementation of local cancellation in any generic warped metric leaves massless fermions. This is due to the presence of one horizon on the infrared brane. However, we can require a global cancellation of the new physics contributions to the {epsilon}{sub 3} parameter. This fixes relations among the warp factor and the parameters of the fermion and gauge sectors. It turns out that the warping of the metric does not substantially modify the results obtained in the flat case.
Effective fermion couplings in warped 5D Higgsless theories
NASA Astrophysics Data System (ADS)
Bechi, J.; Casalbuoni, R.; de Curtis, S.; Dominici, D.
2006-11-01
We consider a 5-dimensional SU(2) gauge theory with fermions in the bulk and with additional SU(2) and U(1) kinetic terms on the branes. The electroweak breaking is obtained by boundary conditions. After deconstruction, fermions in the bulk are eliminated by using their equations of motion. In this way, standard model fermion mass terms and direct couplings to the internal gauge bosons of the moose are generated. The presence of these new couplings gives a new contribution to the γ3 parameter in addition to the gauge boson term. This allows the possibility of a cancellation between the two contributions, which can be local (site by site) or global. Going back to the continuum, we show that the implementation of local cancellation in any generic warped metric leaves massless fermions. This is due to the presence of one horizon on the infrared brane. However, we can require a global cancellation of the new physics contributions to the γ3 parameter. This fixes relations among the warp factor and the parameters of the fermion and gauge sectors. It turns out that the warping of the metric does not substantially modify the results obtained in the flat case.
Extra neutral scalars with vectorlike fermions at the LHC
NASA Astrophysics Data System (ADS)
Gopalakrishna, Shrihari; Mukherjee, Tuhin Subhra; Sadhukhan, Soumya
2016-03-01
Many theories beyond the standard model (BSM) contain new C P -odd and C P -even neutral scalars ϕ ={A ,H } , and new vectorlike fermions (ψV L). The couplings of the C P -odd scalar A to two standard model (SM) gauge bosons cannot occur from renormalizable operators in a C P -conserving sector, but can be induced at the quantum loop level. We compute these effective couplings at the 1-loop level induced by the SM fermions and vectorlike fermions, present analytical expressions for them, and plot them numerically. Using the 8 TeV Large Hadron Collider (LHC) γ γ , τ+τ- and t t ¯ channel data, we derive constraints on the effective couplings of the ϕ to standard model gauge bosons and fermions. We present the gluon-fusion channel cross sections of the ϕ at the 8 and 14 TeV LHC, and its branching ratios into SM fermion and gauge-boson pairs. We first present our results in a model independent manner, and then we provide results for some simple models containing ϕ and ψV L in the singlet and doublet representations of S U (2 ). In the doublet case, we focus on the two-Higgs-doublet (2HDM) Type-II and Type-X models in the alignment limit.
Signatures of Majorana fermions in an elliptical quantum ring
NASA Astrophysics Data System (ADS)
Ghazaryan, Areg; Manaselyan, Aram; Chakraborty, Tapash
2016-06-01
We have investigated the signatures of zero-energy Majorana fermions in an anisotropic semiconductor quantum ring that contains a few electrons, has a strong spin-orbit interaction, and proximity coupled to an s -wave superconductor. We have found that for rings with sizes of few hundred angstroms and for certain range of values of the chemical potential and an applied magnetic field, the system is very likely in a topological phase with possible indications of the presence of Majorana fermions. In particular, the ground-state energies and the average electron numbers for the states with even and odd electron numbers are almost identical. We have analyzed the wave functions of Majorana fermions in the ring and have shown that Majorana fermions are well separated from each other in the angular coordinates. We have also determined the charge-density jumps due to the presence of the Majoranas, that are found to be uniformly distributed along the ring and can perhaps be detected by scanning charge measurements. While a definitive proof of the existence of these exotic particles in a ring has not been provided here, our study indicates the likelihood of the presence of these objects in our chosen system. As the semiconductor quantum rings with a few interacting electrons are available in the laboratories, we believe that the long sought-after Majorana fermions could perhaps be observed in such a system.
Holographic fermions in asymptotically scaling geometries with hyperscaling violation
NASA Astrophysics Data System (ADS)
Fan, ZhongYing
2013-07-01
We investigate holographic fermions in general asymptotically scaling geometries with hyperscaling violation exponent θ, which is a natural generalization of fermions in Lifshitz space-time. We prove that the retarded Green functions in this background satisfy the angle-resolved photoemission spectroscopy sum rules by introducing a dynamical source on a UV brane for zero density fermionic systems. The big difference from the Lifshitz case is that the mass of probe fermions decoupled from the UV theory and thus has no longer been restricted by the unitarity bound. We also study finite density fermions at finite temperature, with dynamical exponent z=2. We find that the dispersion relation is linear, but the logarithm of the spectral function is not linearly related to the logarithm of k⊥=k-kF, independent of charge q and θ. Furthermore, we show that, with the increasing of charge, new branches of Fermi surfaces emerge and tend to gather together to form a shell-like structure when the charge reaches some critical value beyond which a wide band pattern appears in the momentum-charge plane. However, all sharp peaks will be smoothed out when θ increases, no matter how much large the charge is.
NASA Technical Reports Server (NTRS)
Strom, Stephen; Sargent, Wallace L. W.; Wolff, Sidney; Ahearn, Michael F.; Angel, J. Roger; Beckwith, Steven V. W.; Carney, Bruce W.; Conti, Peter S.; Edwards, Suzan; Grasdalen, Gary
1991-01-01
Optical/infrared (O/IR) astronomy in the 1990's is reviewed. The following subject areas are included: research environment; science opportunities; technical development of the 1980's and opportunities for the 1990's; and ground-based O/IR astronomy outside the U.S. Recommendations are presented for: (1) large scale programs (Priority 1: a coordinated program for large O/IR telescopes); (2) medium scale programs (Priority 1: a coordinated program for high angular resolution; Priority 2: a new generation of 4-m class telescopes); (3) small scale programs (Priority 1: near-IR and optical all-sky surveys; Priority 2: a National Astrometric Facility); and (4) infrastructure issues (develop, purchase, and distribute optical CCDs and infrared arrays; a program to support large optics technology; a new generation of large filled aperture telescopes; a program to archive and disseminate astronomical databases; and a program for training new instrumentalists)
Ritson, D. |
1992-03-01
The IP luminosity at the Eloisatron will direct very large fluxes of hadronic debris into the IR quads. For instance at 1.10{sup 35} cm{sup 2}/sec the flux corresponds to 180 kilowatts. Already at the SSC fluxes in the neighborhood of 2 kilowatts are expected to require special handling. Scaling from SSC design experience we propose a configuration for the first IR quads at the Eloisatron capable of handling the heat load and radiation problems.
NASA Astrophysics Data System (ADS)
Deustua, Susana
2013-10-01
This program's goals are : A} Monitor the photometric throughput in all WFC3 UVIS and IR filters during Cycle 21 GO programs, measure zeropoints and determine color term corrections. The data provide a monitor of the UVIS/IR flux stability as a function of time, wavelength and source brightness. This is a continuation of Program 13089.B} Monitor effects of contamination in all WFC3 IR filters. This is a continuation of Cy17-Cy20 contamination monitor programs. WFC3 UVIS:Observations of stars GD153 and P330E are obtained in subarrays at each of the four corners of the UVIS imager to monitor changes in the filter transmission in all the UV filters and to provide a monitor for the zeropoints, and color transformation terms2 stars, Amps B & CWFC3 IR: Observations of GD153 and P330E are obtained in subarray mode for all IR filters 2 stars, subarray mode, 1 orbit each, interleaved with observations of GRW+70Observations of GRW+70 are obtained in subarray mode for all IR filters1 star, subarray mode, 2 orbits separated by 6 months.Orbits required: 17 orbits for zeropoints, 2 orbits for contamination monitor.
IR fiber sources for scene projection
NASA Astrophysics Data System (ADS)
Shaw, L. B.; Sanghera, J. S.; Aggarwal, I. D.
2007-04-01
Naval Research Laboratory has developed IR transmitting fiber and IR fiber sources which can be used for HWIL testing. IR transmitting fiber is capable of broad transmission from near IR to LWIR and can be formed into bundles for imaging. IR fiber sources are based on rare earth doped glass or nonlinear processes in the glass and are cable of high brightness IR emission. Recently, NRL developed a four emitter MWIR fiber source which is capable of high temperature simulation, high dynamic range, and fast response. New broadband fiber sources based upon IR supercontinuum generation in IR fibers are also being developed. In this paper, we will report on these technologies.
Fermion-induced quantum critical points: beyond Landau criterion
NASA Astrophysics Data System (ADS)
Yao, Hong; Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai
According to Landau criterion, phase transitions must be first-order when cubic terms of order parameters in the Landau-Ginzburg free energy are allowed by symmetry. Here, from both renormalization group analysis and sign-problem-free quantum Monte Carlo simulations, we show that second-order quantum phase transitions can occur at such putatively-first-order quantum phase transitions in strongly-interacting Dirac semimetals in two spatial dimensions. Such type of Landau-criterion-violating quantum critical points are induced by massless fermionic modes at the quantum phase transitions. We call them ``fermion-induced quantum critical points''. From Majorana-quantum-Monte-Carlo simulations and renormalization analysis, we find that the critical exponentials at the kekule valence-bond-solid transition of the Dirac fermions on the honeycomb lattice are highly-nonclassical. We also discuss experimental signatures of the kekule quantum critical point which may be realized in graphene-like systems.
Quenched dynamics of superconducting Dirac fermions on honeycomb lattice
NASA Astrophysics Data System (ADS)
Lu, Ming; Xie, X. C.; X. C. Xie's group Team
We study the BCS paring dynamics for the superconducting Dirac fermions on honeycomb lattice after a sudden quench of pairing strength. We observe two distinct phases, one is the synchronized phase with undamped oscillations of paring amplitude; the other phase has the paring amplitude oscillates from positive to negative. The exact phase transition point is given by investigating the integrability of the system. Different from the previous work on normal superconducting fermions, which has three distinct phases, our results shows the absence of the Landau damped phase and over damped phase. Moreover, we present a linear analysis in the weakly quenched regime, showing that in a rather long time scale, the dynamics can be approximated as the periodic oscillation with 2Δ∞ angular frequency along with the logarithmic decay of the pairing amplitude, in contrast of the t - 1 / 2 decay for the normal fermions, namely the Landau damped phase. The presenter's advisor.
Landau Levels of Majorana Fermions in a Spin Liquid.
Rachel, Stephan; Fritz, Lars; Vojta, Matthias
2016-04-22
Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels-highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles-for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudomagnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation.
On the nature of fermion-monopole supersymmetry
NASA Astrophysics Data System (ADS)
Plyushchay, M. S.
2000-07-01
It is shown that the generator of the nonstandard fermion-monopole supersymmetry uncovered by De Jonghe, Macfarlane, Peeters and van Holten, and the generator of its standard /N=1/2 supersymmetry have to be supplemented by their product operator to be treated as independent supercharge. As a result, the fermion-monopole system possesses the nonlinear /N=3/2 supersymmetry having the nature of the 3D spin-1/2 free particle's supersymmetry generated by the supercharges represented in a scalar form. Analyzing the supercharges' structure, we trace how under reduction of the fermion-monopole system to the spherical geometry the nonlinear /N=3/2 superalgebra comprising the Hamiltonian and the total angular momentum as even generators is transformed into the standard linear /N=1 superalgebra with the Hamiltonian to be the unique even generator.
Boson representations of fermion systems: Proton-neutron systems
Sambataro, M.
1988-05-01
Applications of a procedure recently proposed to construct boson images of fermion Hamiltonians are shown for proton-neutron systems. First the mapping from SD fermion onto sd boson spaces is discussed and a Q/sub ..pi../xQ/sub ..nu../ interaction investigated. A Hermitian one-body Q boson operator is derived and analytical expressions for its coefficients are obtained. A (Q/sub ..pi../+Q/sub ..nu../)x(Q/sub ..pi../+Q/sub ..nu../) interaction is, then, studied for particle-hole systems and the connections with the SU/sup */(3) dynamical symmetry of the neutron-proton interacting boson model are discussed. Finally, an example of mapping from SDG onto sdg spaces is analyzed. Fermion spectra and E2 matrix elements are well reproduced in the boson spaces.
Optimal Slater-determinant approximation of fermionic wave functions
NASA Astrophysics Data System (ADS)
Zhang, J. M.; Mauser, Norbert J.
2016-09-01
We study the optimal Slater-determinant approximation of an N -fermion wave function analytically. That is, we seek the Slater-determinant (constructed out of N orthonormal single-particle orbitals) wave function having largest overlap with a given N -fermion wave function. Some simple lemmas have been established and their usefulness is demonstrated on some structured states, such as the Greenberger-Horne-Zeilinger state. In the simplest nontrivial case of three fermions in six orbitals, which the celebrated Borland-Dennis discovery is about, the optimal Slater approximation wave function is proven to be built out of the natural orbitals in an interesting way. We also show that the Hadamard inequality is useful for finding the optimal Slater approximation of some special target wave functions.
A Three Higgs Doublet Model for Fermion Masses
NASA Astrophysics Data System (ADS)
Chao, Wei
2016-09-01
In this paper we propose a possible explanation to the Fermion mass hierarchy problem by fitting the type-II seesaw mechanism into the Higgs doublet sector, such that their vacuum expectation values are hierarchal. We extend the Standard Model with two extra Higgs doublets as well as a spontaneously broken UX (1) gauge symmetry. All the fermion Yukawa couplings except that of the top quark are of O}(10-2) in our model. Constraints on the parameter space of the model from low energy processes are studied. Besides, the lightest one of the neutral fermion fields, which is introduced to cancel the anomalies of the U(1)X gauge symmetry can be the cold dark matter candidate. We investigate its signature in the dark matter direct detection. Supported in part by the Wisconsin Alumni Research Foundation
Experiments with Ultracold Quantum-degenerate Fermionic Lithium Atoms
NASA Technical Reports Server (NTRS)
Ketterle, Wolfgang
2003-01-01
Experimental methods of laser and evaporative cooling, used in the production of atomic Bose-Einstein condensates have recently been extended to realize quantum degeneracy in trapped Fermi gases. Fermi gases are a new rich system to explore the implications of Pauli exclusion on scattering properties of the system, and ultimately fermionic superfluidity. We have produced a new macroscopic quantum system, in which a degenerate Li-6 Fermi gas coexists with a large and stable Na-23 BEC. This was accomplished using inter-species sympathetic cooling of fermionic 6Li in a thermal bath of bosonic Na-23. We have achieved high numbers of both fermions (less than 10(exp 5) and bosons (less than 10(exp 6), and Li-6 quantum degeneracy corresponding to one half of the Fermi temperature. This is the first time that a Fermi sea was produced with a condensate as a "refrigerator".
Fermions and Goldstone bosons in an asymptotically safe model
NASA Astrophysics Data System (ADS)
Bazzocchi, F.; Fabbrichesi, M.; Percacci, R.; Tonero, A.; Vecchi, L.
2011-11-01
We consider a model in which Goldstone bosons, described by a SU (N) chiral nonlinear σ model, are coupled to an N-plet of colored fermions by means of a Yukawa interaction. We study the one-loop renormalization group flow and show that the non-Gaussian UV fixed point, which is present in the purely bosonic model, is lost because of fermion loop effects unless N is sufficiently large. We then add four-fermion contact interactions to the Lagrangian and show that in this case there exist several non-Gaussian fixed points. The strength of the contact interactions, predicted by the requirement that the theory flows towards a fixed point in the UV, is compared to the current experimental bounds. This toy model could provide an important building block of an asymptotically safe model of the weak interactions.
Staggered fermions, zero modes, and flavor-singlet mesons
Donald, Gordon C; Davies, Christine T.H.; Follana, Eduardo; Kronfeld, Andreas S.
2011-09-12
We examine the taste structure of eigenvectors of the staggered-fermion Dirac operator. We derive a set of conditions on the eigenvectors of modes with small eigenvalues (near-zero modes), such that staggered fermions reproduce the 't Hooft vertex in the continuum limit. We also show that, assuming these conditions, the correlators of flavor-singlet mesons are free of contributions singular in 1/m, where m is the quark mass. This conclusion holds also when a single flavor of sea quark is represented by the fourth root of the staggered-fermion determinant. We then test numerically, using the HISQ action, whether these conditions hold on realistic lattice gauge fields. We find that the needed structure does indeed emerge.
Staggered fermions, zero modes, and flavor-singlet mesons
Donald, Gordon C; Davies, Christine T.H.; Follana, Eduardo; Kronfeld, Andreas S.
2011-09-12
We examine the taste structure of eigenvectors of the staggered-fermion Dirac operator. We derive a set of conditions on the eigenvectors of modes with small eigenvalues (near-zero modes), such that staggered fermions reproduce the 't Hooft vertex in the continuum limit. We also show that, assuming these conditions, the correlators of flavor-singlet mesons are free of contributions singular in 1/m, where m is the quark mass. This conclusion holds also when a single flavor of sea quark is represented by the fourth root of the staggered-fermion determinant. We then test numerically, using the HISQ action, whether these conditions hold onmore » realistic lattice gauge fields. We find that the needed structure does indeed emerge.« less
Majorana Fermion Surface Code for Universal Quantum Computation
NASA Astrophysics Data System (ADS)
Vijay, Sagar; Hsieh, Tim; Fu, Liang
We introduce an exactly solvable model of interacting Majorana fermions realizing Z2 topological order with a Z2 fermion parity grading and lattice symmetries permuting the three fundamental anyon types. We propose a concrete physical realization by utilizing quantum phase slips in an array of Josephson-coupled mesoscopic topological superconductors, which can be implemented in a wide range of solid state systems, including topological insulators, nanowires or two-dimensional electron gases, proximitized by s-wave superconductors. Our model finds a natural application as a Majorana fermion surface code for universal quantum computation, with a single-step stabilizer measurement requiring no physical ancilla qubits, increased error tolerance, and simpler logical gates than a surface code with bosonic physical qubits. We thoroughly discuss protocols for stabilizer measurements, encoding and manipulating logical qubits, and gate implementations.
Majorana Fermion Surface Code for Universal Quantum Computation
NASA Astrophysics Data System (ADS)
Vijay, Sagar; Hsieh, Timothy H.; Fu, Liang
2015-10-01
We introduce an exactly solvable model of interacting Majorana fermions realizing Z2 topological order with a Z2 fermion parity grading and lattice symmetries permuting the three fundamental anyon types. We propose a concrete physical realization by utilizing quantum phase slips in an array of Josephson-coupled mesoscopic topological superconductors, which can be implemented in a wide range of solid-state systems, including topological insulators, nanowires, or two-dimensional electron gases, proximitized by s -wave superconductors. Our model finds a natural application as a Majorana fermion surface code for universal quantum computation, with a single-step stabilizer measurement requiring no physical ancilla qubits, increased error tolerance, and simpler logical gates than a surface code with bosonic physical qubits. We thoroughly discuss protocols for stabilizer measurements, encoding and manipulating logical qubits, and gate implementations.
Fermion masses without symmetry breaking in two spacetime dimensions
NASA Astrophysics Data System (ADS)
BenTov, Yoni
2015-07-01
I study the prospect of generating mass for symmetry-protected fermions without breaking the symmetry that forbids quadratic mass terms in the Lagrangian. I focus on 1+1 spacetime dimensions in the hope that this can provide guidance for interacting fermions in 3+1 dimensions. I first review the SO(8) Gross-Neveu model and emphasize a subtlety in the triality transformation. Then I focus on the " m = 0" manifold of the SO(7) Kitaev-Fidkowski model. I argue that this theory exhibits a phenomenon similar to "parity doubling" in hadronic physics, and this leads to the conclusion that the fermion propagator vanishes when p μ = 0. I also briefly explore a connection between this model and the two-channel, single-impurity Kondo effect. This paper may serve as an introduction to topological superconductors for high energy theorists, and perhaps as a taste of elementary particle physics for condensed matter theorists.
Heterotic free fermionic and symmetric toroidal orbifold models
NASA Astrophysics Data System (ADS)
Athanasopoulos, P.; Faraggi, A. E.; Nibbelink, S. Groot; Mehta, V. M.
2016-04-01
Free fermionic models and symmetric heterotic toroidal orbifolds both constitute exact backgrounds that can be used effectively for phenomenological explorations within string theory. Even though it is widely believed that for Z_2× Z_2 orbifolds the two descriptions should be equivalent, a detailed dictionary between both formulations is still lacking. This paper aims to fill this gap: we give a detailed account of how the input data of both descriptions can be related to each other. In particular, we show that the generalized GSO phases of the free fermionic model correspond to generalized torsion phases used in orbifold model building. We illustrate our translation methods by providing free fermionic realizations for all Z_2× Z_2 orbifold geometries in six dimensions.
Birefringent breakup of Dirac fermions on a square optical lattice
Kennett, Malcolm P.; Komeilizadeh, Nazanin; Kaveh, Kamran; Smith, Peter M.
2011-05-15
We introduce a lattice model for fermions in a spatially periodic magnetic field that also has spatially periodic hopping amplitudes. We discuss how this model might be realized with cold atoms in an artificial magnetic field on a square optical lattice. When there is an average flux of half a flux quantum per plaquette, the spectrum of low-energy excitations can be described by massless Dirac fermions in which the usually doubly degenerate Dirac cones split into cones with different ''speeds of light.'' These gapless birefringent Dirac fermions arise because of broken chiral symmetry in the kinetic energy term of the effective low-energy Hamiltonian. We characterize the effects of various perturbations to the low-energy spectrum, including staggered potentials, interactions, and domain-wall topological defects.
A possible scaling region of chiral fermions on a lattice
NASA Astrophysics Data System (ADS)
Xue, She-Sheng
1997-02-01
We present the details of analyzing an SUL(2) ⊗ UR(1) chiral theory with multifermion couplings on a lattice. The existence of a possible scaling region in the phase space of multifermion couplings for defining the continuum limit of chiral fermions is advocated. In this scaling region, no spontaneous symmetry breaking occurs; the "spectator" fermion ψR( x) is a free mode and decoupled; doublers are decoupled as massive Dirac fermions consistently with the SUL(2) ⊗ UR(1) chiral symmetry, whereas the normal mode of ψLi( x) is plausibly speculated to be chiral in the continuum limit. This is not in agreement with the general belief of the definite failure of theories so constructed.
Slave fermion formalism for the tetrahedral spin chain
NASA Astrophysics Data System (ADS)
Mohan, Priyanka; Rao, Sumathi
2016-09-01
We use the SU(2) slave fermion approach to study a tetrahedral spin 1/2 chain, which is a one-dimensional generalization of the two dimensional Kitaev honeycomb model. Using the mean field theory, coupled with a gauge fixing procedure to implement the single occupancy constraint, we obtain the phase diagram of the model. We then show that it matches the exact results obtained earlier using the Majorana fermion representation. We also compute the spin-spin correlation in the gapless phase and show that it is a spin liquid. Finally, we map the one-dimensional model in terms of the slave fermions to the model of 1D p-wave superconducting model with complex parameters and show that the parameters of our model fall in the topological trivial regime and hence does not have edge Majorana modes.
Fermion Mass Renormalization Using Time-dependent Relativistic Quantum Mechanics
NASA Astrophysics Data System (ADS)
Kutnink, Timothy; Santrach, Amelia; Hocket, Sarah; Barcus, Scott; Petridis, Athanasios
2015-10-01
The time-dependent electromagnetically self-coupled Dirac equation is solved numerically by means of the staggered-leap-frog algorithm with refcecting boundary conditions. The stability region of the method versus the interaction strength and the spatial-grid size over time-step ratio is established. The expectation values of several dynamic operators are then evaluated as functions of time. These include the fermion and electromagnetic energies and the fermion dynamic mass, as the self-interacting spinors are no longer mass-eigenfunctions. There is a characteristic, non-exponential, oscillatory dependence leading to asymptotic constants of these expectation values. In the case of the fermion mass this amounts to renormalization. The dependence of the expectation values on the spatial-grid size is evaluated in detail. Statistical regularization is proposed to remove the grid-size dependence.
Yang-Mills theory and fermionic path integrals
NASA Astrophysics Data System (ADS)
Fujikawa, Kazuo
2016-01-01
The Yang-Mills gauge field theory, which was proposed 60 years ago, is extremely successful in describing the basic interactions of fundamental particles. The Yang-Mills theory in the course of its developments also stimulated many important field theoretical machinery. In this brief review I discuss the path integral techniques, in particular, the fermionic path integrals which were developed together with the successful applications of quantized Yang-Mills field theory. I start with the Faddeev-Popov path integral formula with emphasis on the treatment of fermionic ghosts as an application of Grassmann numbers. I then discuss the ordinary fermionic path integrals and the general treatment of quantum anomalies. The contents of this review are mostly pedagogical except for a recent analysis of path integral bosonization.
Yang-Mills Theory and Fermionic Path Integrals
NASA Astrophysics Data System (ADS)
Fujikawa, Kazuo
The Yang-Mills gauge field theory, which was proposed 60 years ago, is extremely successful in describing the basic interactions of fundamental particles. The Yang-Mills theory in the course of its developments also stimulated many important field theoretical machinery. In my talk I discuss the path integral techniques, in particular, the fermionic path integrals which were developed together with the successful applications of quantized Yang-Mills field theory. I start with the Faddeev-Popov path integral formula with emphasis on the treatment of fermionic ghosts as an application of Grassmann numbers. I then discuss the ordinary fermionic path integrals and the general treatment of quantum anomalies. The contents of this talk are mostly pedagogical except for a recent analysis of path integral bosonization.
Three Extra Mirror or Sequential Families: Case for a Heavy Higgs Boson and Inert Doublet
Martinez, Homero; Melfo, Alejandra; Nesti, Fabrizio; Senjanovic, Goran
2011-05-13
We study the possibility of the existence of extra fermion families and an extra Higgs doublet. We find that requiring the extra Higgs doublet to be inert leaves space for three extra families, allowing for mirror fermion families and a dark matter candidate at the same time. The emerging scenario is very predictive: It consists of a standard model Higgs boson, with a mass above 400 GeV, heavy new quarks between 340 and 500 GeV, light extra neutral leptons, and an inert scalar with a mass below M{sub Z}.
Spin-orbit coupling induced semi-metallic state in the 1/3 hole-doped hyper-kagome Na3Ir3O8
Takayama, Tomohiro; Yaresko, Alexander; Matsumoto, Akiyo; Nuss, Jürgen; Ishii, Kenji; Yoshida, Masahiro; Mizuki, Junichiro; Takagi, Hidenori
2014-01-01
The complex iridium oxide Na3Ir3O8 with a B-site ordered spinel structure was synthesized in single crystalline form, where the chiral hyper-kagome lattice of Ir ions, as observed in the spin-liquid candidate Na4Ir3O8, was identified. The average valence of Ir is 4.33+ and, therefore, Na3Ir3O8 can be viewed as a doped analogue of the hyper-kagome spin liquid with Ir4+. The transport measurements, combined with the electronic structure calculations, indicate that the ground state of Na3Ir3O8 is a low carrier density semi-metal. We argue that the semi-metallic state is produced by a competition of the molecular orbital splitting of t2g orbitals on Ir3 triangles with strong spin-orbit coupling inherent to heavy Ir ions. PMID:25351992
Spin-orbit coupling induced semi-metallic state in the 1/3 hole-doped hyper-kagome Na3Ir3O8.
Takayama, Tomohiro; Yaresko, Alexander; Matsumoto, Akiyo; Nuss, Jürgen; Ishii, Kenji; Yoshida, Masahiro; Mizuki, Junichiro; Takagi, Hidenori
2014-10-29
The complex iridium oxide Na3Ir3O8 with a B-site ordered spinel structure was synthesized in single crystalline form, where the chiral hyper-kagome lattice of Ir ions, as observed in the spin-liquid candidate Na4Ir3O8, was identified. The average valence of Ir is 4.33+ and, therefore, Na3Ir3O8 can be viewed as a doped analogue of the hyper-kagome spin liquid with Ir(4+). The transport measurements, combined with the electronic structure calculations, indicate that the ground state of Na3Ir3O8 is a low carrier density semi-metal. We argue that the semi-metallic state is produced by a competition of the molecular orbital splitting of t2g orbitals on Ir3 triangles with strong spin-orbit coupling inherent to heavy Ir ions.
Composite Fermion Theory for Bosonic Quantum Hall States on Lattices
NASA Astrophysics Data System (ADS)
Möller, G.; Cooper, N. R.
2009-09-01
We study the ground states of the Bose-Hubbard model in a uniform magnetic field, motivated by the physics of cold atomic gases on lattices at high vortex density. Mapping the bosons to composite fermions (CF) leads to the prediction of quantum Hall fluids that have no counterpart in the continuum. We construct trial states for these phases and test numerically the predictions of the CF model. We establish the existence of strongly correlated phases beyond those in the continuum limit and provide evidence for a wider scope of the composite fermion approach beyond its application to the lowest Landau level.
The Emergence of Fermions and the E11 Content
NASA Astrophysics Data System (ADS)
Englert, François; Houart, Laurent
Claudio's warm and endearing personality adds to our admiration for his achievements in physics a sense of friendliness. His constant interest in fundamental questions motivated the following presentation of our attempt to understand the nature of fermions. This problem is an essential element of the quantum world and might be related to the quest for quantum gravity. We shall review how space-time fermions can emerge out of bosons in string theory and how this fact affects the extended Kac-Moody approach to the M-theory project.
Charmonium Spectrum from Quenched QCD with Overlap Fermions
S. Tamhankar; A. Alexandru; Y. Chen; S.J. Dong; T. Draper; I. Horvath; F.X. Lee; K.F. Liu; N. Mathur; J.B. Zhang
2005-07-20
We present the first study of the charmonium spectrum using overlap fermions, on quenched configurations. Simulations are performed on 16{sup 3} x 72 lattices, with Wilson gauge action at {beta} = 6.3345. We demonstrate that we have discretization errors under control at about 5%. We obtain 88(4) MeV for hyperfine splitting using the {sub 0} scale, and 121(6) MeV using the (1{bar P}-1{bar S}) scale. This paper raises the possibility that the discrepancy between the lattice results and the experimental value for charmonium hyperfine splitting can be resolved using overlap fermions to simulate the charm quark on lattice.
Condensation of fermion zero modes in the vortex
NASA Astrophysics Data System (ADS)
Volovik, G. E.
2016-08-01
The energy levels of the fermions bound to the vortex are considered for vortices in the superfluid/superconducting systems which contain the symmetry protected plane of zeroes in the gap function in bulk. The Caroli-de Gennes-Matricon branches with different n approach zero energy level at p z → 0. The density of states of the bound fermions diverges at zero energy giving rise to the √ Ω dependence of DoS in the polar phase of superfluid 3He rotating with the angular velocity Ω and to the √ B dependence of DoS for superconductors in the (d xz + id yz )-wave pairing state.
Entanglement in algebraic quantum mechanics: Majorana fermion systems
NASA Astrophysics Data System (ADS)
Benatti, F.; Floreanini, R.
2016-07-01
Many-body entanglement is studied within the algebraic approach to quantum physics in systems made of Majorana fermions. In this framework, the notion of separability stems from partitions of the algebra of observables and properties of the associated correlation functions, rather than on particle tensor products. This allows a complete characterization of non-separable Majorana fermion states to be obtained. These results may have direct application in quantum metrology: using Majorana systems, sub-shot-noise accuracy in parameter estimations can be achieved without preliminary resource-consuming, state entanglement operations.
Relativistic confinement of neutral fermions with a trigonometric tangent potential
NASA Astrophysics Data System (ADS)
Castro, Luis B.; de Castro, Antonio S.
2007-01-01
The problem of neutral fermions subject to a pseudoscalar potential is investigated. Apart from the solutions for E = ±mc2, the problem is mapped into the Sturm-Liouville equation. The case of a singular trigonometric tangent potential (~tan γx) is exactly solved and the complete set of solutions is discussed in some detail. It is revealed that this intrinsically relativistic and true confining potential is able to localize fermions into a region of space arbitrarily small without the menace of particle-antiparticle production.
Magnetic domain walls of relic fermions as Dark Energy
Yajnik, Urjit A.
2005-12-02
We show that relic fermions of the Big Bang can enter a ferromagnetic state if they possess a magnetic moment and satisfy the requirements of Stoner theory of itinerant ferromagnetism. The domain walls of this ferromagnetism can successfully simulate Dark Energy over the observable epoch spanning {approx} 10 billion years. We obtain conditions on the anomalous magnetic moment of such fermions and their masses. Known neutrinos fail to satisfy the requirements thus pointing to the possibility of a new ultralight sector in Particle Physics.
Scaling analysis of fat-link irrelevant clover fermion actions
Kamleh, Waseem; Lasscock, Ben; Leinweber, Derek B.; Williams, Anthony G.
2008-01-01
The fat-link irrelevant clover fermion action is a variant of the O(a)-improved Wilson action where the irrelevant operators are constructed using smeared links. While the use of such smearing allows for the use of highly improved definitions of the field strength tensor F{sub {mu}}{sub {nu}}, we show that the standard 1-loop clover term with a mean field improved coefficient c{sub sw} is sufficient to remove the O(a) errors, avoiding the need for nonperturbative tuning. This result enables efficient dynamical simulations in QCD with the fat-link irrelevant clover fermion action.
Digital quantum simulation of fermionic models with a superconducting circuit.
Barends, R; Lamata, L; Kelly, J; García-Álvarez, L; Fowler, A G; Megrant, A; Jeffrey, E; White, T C; Sank, D; Mutus, J Y; Campbell, B; Chen, Yu; Chen, Z; Chiaro, B; Dunsworth, A; Hoi, I-C; Neill, C; O'Malley, P J J; Quintana, C; Roushan, P; Vainsencher, A; Wenner, J; Solano, E; Martinis, John M
2015-01-01
One of the key applications of quantum information is simulating nature. Fermions are ubiquitous in nature, appearing in condensed matter systems, chemistry and high energy physics. However, universally simulating their interactions is arguably one of the largest challenges, because of the difficulties arising from anticommutativity. Here we use digital methods to construct the required arbitrary interactions, and perform quantum simulation of up to four fermionic modes with a superconducting quantum circuit. We employ in excess of 300 quantum logic gates, and reach fidelities that are consistent with a simple model of uncorrelated errors. The presented approach is in principle scalable to a larger number of modes, and arbitrary spatial dimensions. PMID:26153660
Observation of Dynamical Fermionization in 1D Bose Gases
NASA Astrophysics Data System (ADS)
Malvania, Neel; Xia, Lin; Xu, Wei; Wilson, Joshua M.; Zundel, Laura A.; Rigol, Marcos; Weiss, David S.
2016-05-01
The momentum distribution of a harmonically trapped 1D Bose gases in the Tonks-Girardeau limit is expected to undergo dynamical fermionization. That is, after the harmonic trap is suddenly turned off, the momentum distribution steadily transforms into that of an ideal Fermi gas in the same initial trap. We measure 1D momentum distributions at variable times after such a quench, and observe the predicted dynamical fermionization. In addition to working in the strong coupling limit, we also perform the experiment with intermediate coupling, where theoretical calculations are more challenging.
Hadron Masses From Novel Fat-Link Fermion Actions
J. M. Zanotti; S. Bilson-Thompson; F. D. R. Bonnet; P. D. Coddington; D. B. Leinweber; A. G. Williams; J. B. Zhang; W. Melnitchouk; F. X. Lee
2001-11-01
The hadron mass spectrum is calculated in lattice QCD using a novel fat-link clover fermion action in which only the irrelevant operators in the fermion action are constructed using smeared links. The simulations are performed on a 16{sup 3} x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link Irrelevant Clover (FLIC) action provides scaling which is superior to mean-field improvement, and offers advantages over nonperturbative 0(a) improvement, including a reduced exceptional configuration problem.
Fermion excitations of a tense brane black hole
Cho, H. T.; Cornell, A. S.; Doukas, Jason; Naylor, Wade
2008-02-15
By finding the spinor eigenvalues for a single deficit angle (d-2)-sphere, we derive the radial potential for fermions on a d-dimensional black hole background that is embedded on a codimension-two brane with conical singularity, where the deficit angle is related to the brane tension. From this we obtain the quasinormal mode spectrum for bulk fermions on such a background. As a by-product of our method, this also gives a rigorous proof for integer spin fields on the deficit 2-sphere.
Digital quantum simulation of fermionic models with a superconducting circuit
Barends, R.; Lamata, L.; Kelly, J.; García-Álvarez, L.; Fowler, A. G.; Megrant, A; Jeffrey, E; White, T. C.; Sank, D.; Mutus, J. Y.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Hoi, I.-C.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Vainsencher, A.; Wenner, J.; Solano, E.; Martinis, John M.
2015-01-01
One of the key applications of quantum information is simulating nature. Fermions are ubiquitous in nature, appearing in condensed matter systems, chemistry and high energy physics. However, universally simulating their interactions is arguably one of the largest challenges, because of the difficulties arising from anticommutativity. Here we use digital methods to construct the required arbitrary interactions, and perform quantum simulation of up to four fermionic modes with a superconducting quantum circuit. We employ in excess of 300 quantum logic gates, and reach fidelities that are consistent with a simple model of uncorrelated errors. The presented approach is in principle scalable to a larger number of modes, and arbitrary spatial dimensions. PMID:26153660
Digital quantum simulation of fermionic models with a superconducting circuit
NASA Astrophysics Data System (ADS)
Barends, R.; Lamata, L.; Kelly, J.; García-Álvarez, L.; Fowler, A. G.; Megrant, A.; Jeffrey, E.; White, T. C.; Sank, D.; Mutus, J. Y.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Hoi, I.-C.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Vainsencher, A.; Wenner, J.; Solano, E.; Martinis, John M.
2015-07-01
One of the key applications of quantum information is simulating nature. Fermions are ubiquitous in nature, appearing in condensed matter systems, chemistry and high energy physics. However, universally simulating their interactions is arguably one of the largest challenges, because of the difficulties arising from anticommutativity. Here we use digital methods to construct the required arbitrary interactions, and perform quantum simulation of up to four fermionic modes with a superconducting quantum circuit. We employ in excess of 300 quantum logic gates, and reach fidelities that are consistent with a simple model of uncorrelated errors. The presented approach is in principle scalable to a larger number of modes, and arbitrary spatial dimensions.
Ward identities and chiral anomalies for coupled fermionic chains
Costa, L. C.; Ferraz, A.; Mastropietro, Vieri
2013-12-15
Coupled fermionic chains are usually described by an effective model written in terms of bonding and anti-bonding fermionic fields with linear dispersion in the vicinities of the respective Fermi points. We derive for the first time exact Ward Identities (WI) for this model, proving the existence of chiral anomalies which verify the Adler-Bardeen non-renormalization property. Such WI are expected to play a crucial role in the understanding of the thermodynamic properties of the system. Our results are non-perturbative and are obtained analyzing Grassmann functional integrals by means of constructive quantum field theory methods.
Fermion Monte Carlo Calculations on Liquid-3He
Kalos, M H; Colletti, L; Pederiva, F
2004-03-16
Methods and results for calculations of the ground state energy of the bulk system of {sup 3}He atoms are discussed. Results are encouraging: they believe that they demonstrate that their methods offer a solution of the ''fermion sign problem'' and the possibility of direct computation of many-fermion systems with no uncontrolled approximations. Nevertheless, the method is still rather inefficient compared with variational or fixed-node approximate methods. There appears to be a significant populations size effect. The situation is improved by the inclusion of ''Second Stage Importance Sampling'' and of ''Acceptance/Rejection'' adapted to their needs.
Residual entanglement of accelerated fermions is not nonlocal
Friis, Nicolai; Koehler, Philipp; Bertlmann, Reinhold A.; Martin-Martinez, Eduardo
2011-12-15
We analyze the operational meaning of the residual entanglement in noninertial fermionic systems in terms of the achievable violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality. We demonstrate that the quantum correlations of fermions, which were previously found to survive in the infinite acceleration limit, cannot be considered to be nonlocal. The entanglement shared by an inertial and an accelerated observer cannot be utilized for the violation of the CHSH inequality in case of high accelerations. Our results are shown to extend beyond the single-mode approximation commonly used in the literature.
COMPARISON OF OFF-LINE IR BUMP AND ACTION-ANGLE KICK MINIMIZATION.
LUO, Y.; PILAT, F.; PTITSYN, V.; TRBOJEVIC, D.; WEI, J.
2005-05-16
The interaction region bump (IR bump) nonlinear correction method has been used for the sextupole and octupole field error on-line corrections in the Relativistic Heavy Ion Collider (RHIC) . Some differences were found for the sextupole and octupole corrector strengths between the on-line IR bump correction and the predictions from the action-angle kick minimization. In this article, we compare the corrector strengths from these two methods based on the RHIC Blue ring lattice with the IR nonlinear modeling. The comparison confirms the differences between resulting corrector strengths. And the reason for the differences is found and discussed.
Study of {beta}-Decay in the Proton-Neutron Interacting Boson-Fermion Model
Zuffi, L.; Brant, S.; Yoshida, N.
2006-04-26
We study {beta}-decay in odd-A nuclei together with the energy levels and other properties in the proton-neutron interacting-boson-fermion model. We also report on the preliminary results in the odd-odd nuclei in the proton-neutron interacting boson-fermion-fermion model.
Perturbative quantum field theory in the framework of the fermionic projector
Finster, Felix
2014-04-15
We give a microscopic derivation of perturbative quantum field theory, taking causal fermion systems and the framework of the fermionic projector as the starting point. The resulting quantum field theory agrees with standard quantum field theory on the tree level and reproduces all bosonic loop diagrams. The fermion loops are described in a different formalism in which no ultraviolet divergences occur.
TaIrTe4: A ternary type-II Weyl semimetal
NASA Astrophysics Data System (ADS)
Koepernik, K.; Kasinathan, D.; Efremov, D. V.; Khim, Seunghyun; Borisenko, Sergey; Büchner, Bernd; van den Brink, Jeroen
2016-05-01
In metallic condensed matter systems two different types of Weyl fermions can in principle emerge, with either a vanishing (type-I) or with a finite (type-II) density of states at the Weyl node energy. So far only WTe2 and MoTe2 were predicted to be type-II Weyl semimetals. Here we identify TaIrTe4 as a third member of this family of topological semimetals. TaIrTe4 has the attractive feature that it hosts only four well-separated Weyl points, the minimum imposed by symmetry. Moreover, the resulting topological surface states—Fermi arcs connecting Weyl nodes of opposite chirality—extend to about 1/3 of the surface Brillouin zone. This large momentum-space separation is very favorable for detecting the Fermi arcs spectroscopically and in transport experiments.
Installation and first light of the BOOTES-IR near-IR camera
NASA Astrophysics Data System (ADS)
Cunniffe, R.; Castro-Tirado, A. J.; Kubánek, P.; Jelínek, M.; Vítek, S.; Gorosabel, J.; de Ugarte Postigo, A.; Riva, A.; Zerbi, F.; Claret, A.; Sánchez-Fernández, C.
2008-07-01
BIRCAM is a near-infrared (0.8-2.5um) cryogenic camera based on a 1Kx1K HgCdTe array. It was designed for - and is now mounted at - one of the Nasmyth foci of the fast-slewing 0.6 m BOOTES-IR telescope at the Sierra Nevada Observatory (OSN) in Spain. The primary science mission is prompt Gamma Ray-Burst afterglow research, with an implied demand for extremely time-efficient operation. We describe the challenges of installing a heavy camera on a small high-speed telescope, of integrating the dithering mechanism, the filterwheel, and the array itself into a high-efficiency instrument, the design of the software to meet the requirements.
Dealing confidently with IRS, Part I: Preparing for IRS audits.
Holub, S F; Walker, S R
1978-10-01
With the IRS apparently making health care institutions the focus of a nationwide audit emphasis, hospital administrators will want to prepare themselves for confident handling of audits. Four types of audit procedures are explained, suggestions are made for getting a hospital ready for an audit, and strategies are suggested for maintaining control over the audit's progress.
Detection of IR target by fusing multispectral IR data
NASA Astrophysics Data System (ADS)
Li, Liya; Qi, Meng; Gao, Xuhui
2011-08-01
Detection of the small target in clutter, usually regarded as singular points in the infrared image, is an important issue in infrared searching and tracking (IRST) system. Because of the far range of the target to the sensor, the stealth technology, the effects of inherent sensor noise and the phenomena of nature, the target is more difficult to be detected. Multispectral sensor system has been proved it could greatly improve detection of the small, hard-to-find targets by multispectral processing techniques (such as sensor or image fusion). Aiming at the problem of multispectral IR Target Detection, a kind method of the multispectral IR target detection is proposed, based on the existed detection systems. In this method, the image registration is done firstly to make the different sensors have a same scene. Then, a fusion rule, named as adaptive weighted voting theory, is developed to combine the target detection results from the different spectral sensors. The adaptive weighted voting theory can give the different weights, based on the different spectral IR characteristics, and these weights decide the detected target is identified as real target or background. The experimental results show that the proposed method can reduce the detection uncertainty and improve the detection performance. Compared with the single spectral detection results and the others fusion detection methods, it can decrease the lost alarm rate and the false alarm rate effectively. The proposed method has been employed in our IR surveillance system, and it is easy to be used in the various circumstances.
New IR detectors pig-tailed with IR fibers
NASA Astrophysics Data System (ADS)
Artiouchenko, Viatcheslav G.; Chekanova, Galina V.; Lartsev, Ivan Y.; Lobachev, Vladimir A.; Nikitine, Mikhail S.
2003-09-01
New generation of Mercury-Cadmium-Telluride (MCT) high performance infrared radiation (IR) detectors with IR-fiber input has been developed and fabricated. This new product is originated from 25 years experience in MCT detectors and IR fiber optics technologies. Range of products includes single- and multi-element detectors designed for registration of optical signals in spectral range from 2 to 18 μm. Detectors design is integrated or modular and includes package, sensitive element, cooling system, operating temperature sensor, optical components such as narrow band-pass filter and/or lens and/or different kind of optical window, optical connection unit and fiber pig-tail or fiber cable. Cooling system options include thermoelectric cooler, long-holding time dewar filled with liquid nitrogen, Joule-Thomson micro-liquidizer and Stirling-cycle cooler. Registered infrared radiation is delivered to sensitive area of detector through either Polycrystalline InfraRed (PIR-) Fiber (4 - 18 μm) or Chalcogenide IR-glass (CIR-) Fiber (2 - 6 μm). Unique feature intrinsic to Hg1-xCdxTe (MCT) alloys to form continuous series of alloy compositions "x" with proportionally changed energy gap Eg(x,T) allows to tune spectral responsivity of detector sensitive element with ordered spectral range and hence to use every time the highest sensitive detector.
Metz, D.
1982-01-01
The extreme pressures on the roof and walls of an earth-sheltered residential home are discussed and the need for careful planning is stressed. Pertinent terms are defined. Footings and wall structure (reinforced concrete walls and concrete block walls) are described. Roofing systems are discussed in detail and illustrated: (1) poured-in-place concrete roof slabs; (2) pre-cast concrete planks; and (3) heavy timber roofs. Insulation of earth-sheltered homes is reviewed in terms of using: (1) urethanes; (2) extruded polystyrene; and (3) expanded polystyrene. Advantages, disadvantages, R-factors, costs, and installation are discussed. (MJJ)
Robust collider limits on heavy-mediator Dark Matter
NASA Astrophysics Data System (ADS)
Racco, Davide; Wulzer, Andrea; Zwirner, Fabio
2015-05-01
We discuss how to consistently use Effective Field Theories (EFTs) to set universal bounds on heavy-mediator Dark Matter at colliders, without prejudice on the model underlying a given effective interaction. We illustrate the method for a Majorana fermion, universally coupled to the Standard Model quarks via a dimension-6 axial-axial four-fermion operator. We recast the ATLAS mono-jet analysis and show that a considerable fraction of the parameter space, seemingly excluded by a na¨ıve EFT interpretation, is actually still unexplored. Consistently set EFT limits can be reinterpreted in any specific underlying model. We provide two explicit examples for the chosen operator and compare the reach of our model-independent method with that obtainable by dedicated analyses.
Big Bounce and Inflation from Gravitational Four-Fermion Interaction
NASA Astrophysics Data System (ADS)
Khriplovich, I. B.
2013-11-01
The four-fermion gravitational interaction is induced by torsion. It gets dominating below the Planck scale. The regular, axial-axial part of this interaction by itself does not stop the gravitational compression. However, the anomalous, vector-vector interaction results in a natural way both in big bounce and in inflation.
B-Parameters of 4-Fermion Operators from Lattice QCD
Gupta, Rajan
1997-12-31
This talk summarizes the status of the calculations of B{sub K}, B{sub 7}, B{sub 8}, and B{sub s}, done in collaboration with T. Bhattacharya, C. Kilcup, and S. Sharpe. Results for staggered, Wilson, and Clover fermions are presented.
Bosonized noncommutative bi-fundamental fermion and S-duality
NASA Astrophysics Data System (ADS)
Blas, Harold
2005-06-01
We perform the path-integral bosonization of the recently proposed noncommutative massive Thirring model (NCMT1) [JHEP 0503 (2005) 037]. This model presents two types of current-current interaction terms related to the bi-fundamental representation of the group U(1). Firstly, we address the bosonization of a bi-fundamental free Dirac fermion defined on a noncommutative (NC) euclidean plane Bbb Rθ2. In this case we show that the fermion system is dual to two copies of the NC Wess-Zumino-Novikov-Witten model. Next, we apply the bosonization prescription to the NCMT1 model living on Bbb Rθ2 and show that this model is equivalent to two-copies of the WZNW model and a two-field potential defined for scalar fields corresponding to the global U(1) × U(1) symmetry plus additional bosonized terms for the four fermion interactions. The bosonic sector resembles to the one proposed by Lechtenfeld et al. [Nucl. Phys. B 705 (2005) 477] as the noncommutative sine-Gordon for a pair of scalar fields. The bosonic and fermionic couplings are related by a strong-weak duality. We show that the couplings of the both sectors for some representations satisfy similar relationships up to relevant re-scalings, thus the NC bi-fundamental couplings are two times the corresponding ones of the NC fundamental (anti-fundamental) and eight times the couplings of the ordinary massive Thirring and sine-Gordon models.
Effective field theories for QCD with rooted staggered fermions
Bernard, Claude; Golterman, Maarten; Shamir, Yigal
2008-04-01
Even highly improved variants of lattice QCD with staggered fermions show significant violations of taste symmetry at currently accessible lattice spacings. In addition, the 'rooting trick' is used in order to simulate with the correct number of light sea quarks, and this makes the lattice theory nonlocal, even though there is good reason to believe that the continuum limit is in the correct universality class. In order to understand scaling violations, it is thus necessary to extend the construction of the Symanzik effective theory to include rooted staggered fermions. We show how this can be done, starting from a generalization of the renormalization-group approach to rooted staggered fermions recently developed by one of us. We then explain how the chiral effective theory follows from the Symanzik action, and show that it leads to 'rooted' staggered chiral perturbation theory as the correct chiral theory for QCD with rooted staggered fermions. We thus establish a direct link between the renormalization-group based arguments for the correctness of the continuum limit and the success of rooted staggered chiral perturbation theory in fitting numerical results obtained with the rooting trick. In order to develop our argument, we need to assume the existence of a standard partially-quenched chiral effective theory for any local partially-quenched theory. Other technical, but standard, assumptions are also required.
Taste symmetry breaking with hypercubic-smeared staggered fermions
Bae, Taegil; Adams, David H.; Kim, Hyung-Jin; Kim, Jongjeong; Kim, Kwangwoo; Lee, Weonjong; Jung, Chulwoo; Sharpe, Stephen R.
2008-05-01
We study the impact of hypercubic (HYP) smearing on the size of taste-breaking for staggered fermions, comparing to unimproved and to asqtad-improved staggered fermions. As in previous studies, we find a substantial reduction in taste-breaking compared to unimproved staggered fermions (by a factor of 4-7 on lattices with spacing a{approx_equal}0.1 fm). In addition, we observe that discretization effects of next-to-leading order in the chiral expansion (O(a{sup 2}p{sup 2})) are markedly reduced by HYP smearing. Compared to asqtad valence fermions, we find that taste-breaking in the pion spectrum is reduced by a factor of 2.5-3, down to a level comparable to the expected size of generic O(a{sup 2}) effects. Our results suggest that, once one reaches a lattice spacing of a{approx_equal}0.09 fm, taste-breaking will be small enough after HYP smearing that one can use a modified power counting in which O(a{sup 2})<