Vortexlike excitations in the heavy-fermion superconductor CeIrIn5
Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; Thompson, J. D.
2016-05-01
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
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.
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.
Signatures of spin-glass behaviour in PrIr2B2 and heavy fermion behaviour in PrIr2B2C.
Anupam; Anand, V K; Hossain, Z; Adroja, D T; Geibel, C
2011-09-21
CEF-split singlet and the first excited state singlet is situated 15 K above the ground state. The Sommerfeld coefficient γ∼300 mJ mol(-1) K(-2) of PrIr(2)B(2)C is very high and reflects a heavy fermion behaviour in this compound. We believe that the heavy fermion state in PrIr(2)B(2)C has its origin in low lying crystal field excitations as has been observed in PrRh(2)B(2)C. PMID:21878715
Crystal Growth and Intergrowth Structure of the New Heavy Fermion Materials CeIrIn 5 and CeRhIn 5
NASA Astrophysics Data System (ADS)
Moshopoulou, E. G.; Fisk, Z.; Sarrao, J. L.; Thompson, J. D.
2001-04-01
The structures of the new heavy fermion materials CeIrIn5 and CeRhIn5 have been determined by single-crystal neutron (R(F)=0.051) and X-ray (R(F)=0.056) diffraction, respectively. Both compounds adopt tetragonal structure, space group P4/mmm (No. 123), Z=1, a=b=4.674(1) Å, and c=7.501(5) Å for CeIrIn5, and a=b=4.656(2) Å, and c=7.542(1) Å for CeRhIn5. The possible presence of antisite disorder, a long-standing question on this type of structure, was excluded by both electron and-neutron or X-ray diffraction. The compounds are built by monolayers of face-sharing distorted cuboctahedra [CeIn3] and monolayers of edge-sharing rectangular parallelepipeds [RhIn2] or [IrIn2], stacked alternatively in the [001] direction. Therefore, they are new members of the inhomogeneous linear homologous series MmTnT‧3m+2n. Because of their ordered intergrowth structure, the physical properties of the quasi-two-dimensional heavy electron systems CeIrIn5 and CeRhIn5 can be directly compared with the corresponding ones of their parent compound, the three-dimensional heavy fermion material CeIn3.
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.
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)
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.
The physics and chemistry of heavy fermions.
Fisk, Z; Sarrao, J L; Smith, J L; Thompson, J D
1995-01-01
The heavy fermions are a subset of the f-electron intermetallic compounds straddling the magnetic/nonmagnetic boundary. Their low-temperature properties are characterized by an electronic energy scale of order 1-10 K. Among the low-temperature ground states observed in heavy fermion compounds are exotic superconductors and magnets, as well as unusual semiconductors. We review here the current experimental and theoretical understanding of these systems. PMID:11607558
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 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
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.
Point contact spectroscopy of heavy fermions
NASA Astrophysics Data System (ADS)
Moser, M.; Wachter, P.; Franse, J. J. M.; Meisner, G. P.; Walker, E.
Point contact spectroscopy (PCS) has been performed on the heavy fermion systems CeAl3, CeCu6, UPt3, U6Co and U2PtC2. The dynamical resistance dU/dI is a function of the electronic density of states (EDS) at E/sub F/. The width of the EDS inferred from the PC measurements can be compared with the (GAMMA)-value of the specific heat.
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.
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
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.
Neutron scattering studies of heavy Fermions
NASA Astrophysics Data System (ADS)
Shapiro, S. M.
1985-08-01
Heavy Fermions are f electron materials characterized by a large linear term in the low temperature specific heat and a large magnetic susceptibility at low temperatures. This implies that there is a narrow peak in the f electron density of states at the Fermi energy. Typical examples are CeAl3, UBe13, CeCu2Si2, CeCu6, U2Zn17 and UPt3. Neutron scattering measurements can play an important role in understanding the magnetic interactions in these systems. Measurements of the form reveal details about the nature of the wave functions. Inelastic scattering studies gives information about the energy scale of the spin fluctuations and the narrow f-resonance. Such measurements on the above systems are reviewed with the goal of establishing systematics between the information obtained in neutron studies and that from bulk measurements.
Neutron scattering studies of the heavy Fermion superconductors
NASA Astrophysics Data System (ADS)
Goldman, A. I.
Recent neutron scattering measurements of the heavy Fermion superconductors are described. Those materials offer an exciting opportunity for neutron scattering since the f-electrons, which couple directly to magnetic scattering measurements, seem to be the same electrons which form the superconducting state below T sub c. In addition, studies of the magnetic fluctuations in these, and other heavy Fermion systems, by inelastic magnetic neutron scattering can provide information about the nature of the low temperature Fermi liquid character of these novel compounds.
Millikelvin cooling by heavy-fermion-based tunnel junctions
NASA Astrophysics Data System (ADS)
Prest, Martin; Min, Gao; Whall, Terry
2015-12-01
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.
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.
Magnetoelectric effects in heavy-fermion superconductors without inversion symmetry
NASA Astrophysics Data System (ADS)
Fujimoto, Satoshi
2005-07-01
We investigate the effects of strong electron correlation on magnetoelectric transport phenomena in noncentrosymmetric superconductors with particular emphasis on its application to the recently discovered heavy-fermion superconductor CePt3Si . Taking into account electron correlation effects in a formally exact way, we obtain the expression of the magnetoelectric coefficient for the Zeeman-field-induced paramagnetic supercurrent, the existence of which was predicted more than a decade ago. It is found that in contrast to the usual Meissner current, which is much reduced by the mass renormalization factor in the heavy-fermion state, the paramagnetic supercurrent is not affected by the Fermi liquid effect. This result implies that the experimental observation of the magnetoelectric effect is more feasible in heavy-fermion systems than that in conventional metals with moderate effective mass.
Heavy fermion nondecoupling effects in triple gauge boson vertices
NASA Astrophysics Data System (ADS)
Dedes, Athanasios; Suxho, Kristaq
2012-05-01
Within a spontaneously broken gauge group we carefully analyze and calculate triple gauge boson vertices dominated by triangle one-loop Feynman diagrams involving heavy fermions compared to external momenta and gauge boson masses. We perform our calculation strictly in four dimensions and derive a general formula for the off-shell, one-particle irreducible (1PI) effective vertex which satisfies the relevant Ward Identities and the Goldstone boson equivalence theorem. Our goal is to search for nondecoupling heavy fermion effects highlighting their synergy with gauge chiral anomalies. Particularly in the standard model, we find that when the arbitrary anomaly parameters are fixed by gauge invariance and/or Bose symmetry, the heavy fermion contribution cancels its anomaly contribution leaving behind anomaly and mass independent contributions from the light fermions. We apply these results in calculating the corresponding CP-invariant one-loop induced corrections to triple gauge boson vertices in the SM, minimal Z' models as well as their extensions with a fourth fermion generation, and compare with experimental data.
Photoelectron spectroscopy in heavy fermions: Inconsistencies with the Kondo model
Arko, A.J.; Joyce, J.J.; Blyth, R.R.; Canfield, P.C.; Thompson, J.D.; Bartlett, R.J.; Fisk, Z.; Lawrence, J.; Tang, J.; Riseborough, P.
1992-09-01
We have investigated a number of Ce and Yb heavy fermion compounds via photoelectron spectroscopy and compared the results to the predictions of the Imurity Anderson Hamiltonian within the Gunnarson-Schonhammer approach. For the low T{sub K} materials investigated we find little or no correlation with T{sub K}, the only parameter that can be determined independent of photoemission.
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 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.
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.
(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.
Heavy-fermion systems studied by {mu}SR technique
Amato, A.
1997-10-01
The author attempts to give a comprehensive discussion of studies performed with the positive-muon spin rotation and relaxation technique (also known as the {mu}SR technique) on heavy-fermion compounds. The subtle competition between the demagnetizing Kondo interaction and the intersite Ruderman-Kittel-Kasuya-Yosida exchange interaction is believed to be the primary ingredient for the wealth of different ground states observed for this class of rare-earth{endash} and actinide-containing intermetallic compounds. Due to its microscopic character, its sensitivity to extremely small internal fields, and its capacity to detect spatially inhomogeneous magnetic features, the {mu}SR technique has been extensively utilized to investigate the peculiar magnetic properties of these ground states and improve our knowledge of heavy-fermion phenomena. In addition to providing a short introduction to {mu}SR, where the intrinsic difficulties of the method are clearly stated, this article reviews the main results obtained by this technique on the best-known heavy-fermion compounds (superconductors, band magnets, local-moment magnets, non-Fermi-liquid systems, and Kondo insulators). Special emphasis is placed on the particular information obtainable by monitoring the implanted muon. {copyright} {ital 1997} {ital The American Physical Society}
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
Heavy fermions: From nodal metals to super-spins
NASA Astrophysics Data System (ADS)
Ramires Neves de Oliveira, Aline
Condensed matter physics is an area of research which lies at a sweet spot between two complementary perspectives: the atomistic point of view which takes into account all the details of the system of interest; and the framework of universality and emergent phenomena, which allows us to make drastic simplifications to the microscopic description of materials while still being able to explain much of the experimentally observed phenomena. This thesis addresses problems from both perspectives, focusing on heavy fermion systems. Heavy fermion systems are prototype materials for the study of strongly correlations and quantum criticality. Theoretical understanding of these systems is important for the design of new materials and for the fundamental understanding of quantum critical phenomena. This thesis is strongly motivated by recent experiments in an intrinsically quantum critical material, beta-YbAlB 4. This system shows anomalous critical exponents in transport and thermodynamics. In Chapter 2 we construct a phenomenological theory for the heavy fermion metal beta-YbAlB4 based on the Anderson model, taking into account the peculiarities of this specific material. We analyze the consequences of a non-trivial, momentum-dependent, hybridization matrix between f-electrons and conduction electrons, which gives rise to a nodal metal with unusual dispersion and singular thermodynamic properties, in accordance with experiments. In Chapter 3 we analyze the Electron Spin Resonance experiments in this same material and propose a theory including spin-orbit coupling, crystal electric fields and hyperfine coupling which can account for many of the features of the experimentally observed signal. Within a broader perspective on heavy fermion systems, the absence of a single unified theoretical description which can account for the plethora of phenomena observed in this class of materials also motivates us to consider new theoretical approaches. In Chapter 4 we generalize the
NASA Astrophysics Data System (ADS)
Heffner, R. H.
The interplay between magnetism and superconductivity in heavy fermion systems is discussed and the role of muon spin relaxation in elucidating these properties is emphasized. Relevant properties of all six heavy fermion superconductors are briefly surveyed and instances where superconductivity and magnetism compete, coexist, and couple with one another are pointed out. Current theoretical concepts underlying these phenomena are highlighted.
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.
Heffner, R.H.
1993-10-01
The interplay between magnetism and superconductivity in heavy fermion systems is discussed and the role of muon spin relaxation in elucidating these properties is emphasized. Relevant properties of all six heavy fermion superconductors are briefly surveyed and instances where superconductivity and magnetism compete, coexist and couple with one another are pointed out. Current theoretical concepts underlying these phenomena are highlighted.
Heavy fermion Ce3Co4Sn13 compound under pressure
NASA Astrophysics Data System (ADS)
Collave, J. R.; Borges, H. A.; Ramos, S. M.; Hering, E. N.; Fontes, M. B.; Baggio-Saitovitch, E.; Mendonça-Ferreira, L.; Bittar, E. M.; Pagliuso, P. G.
2015-05-01
The non-magnetic heavy fermion compound Ce3Co4Sn13 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 (TS), crystalline field effects (TCEF), and a low temperature maximum (Tmax), 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 TS and Tmax was constructed by mapping these features. Like for most Ce-based heavy fermion compounds, Tmax 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, TS, associated to a superlattice distortion and probably combined with a charge density wave transition, decreases as a function of pressure. However, differently from the Sr3-xCaxIr4Sn13 system, where a superlattice quantum phase transition is observed [L. E. Klintberg et al., Phys. Rev. Lett. 109, 237 008 (2012)], in Ce3Co4Sn13 TS ˜ 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 Tmax are observed, suggesting suppression of low temperature short range magnetic correlations.
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.
Heavy Fermion Scaling: Uranium versus Cerium and Ytterbium Compounds
Lawrence, J. M.; Wang, Cuihuan; Christianson, Andrew D; Bauer, E. D.
2011-01-01
In an effort to explore the differences between rare-earth-based and uranium-based heavy fermion (HF) compounds that reflect the underlying difference between local 4f moments and itinerant 5f moments we analyze scaling laws that relate the low temperature neutron spectra of the primary ('Kondo-esque') spin fluctuation to the specific heat and susceptibility. While the scaling appears to work very well for the rare earth intermediate valence (IV) compounds, for a number of key uranium compounds the scaling laws fail badly. There are two main reasons for this failure. First, the presence of antiferromagnetic (AF) fluctuations, which contribute significantly to the specific heat, alters the scaling ratios. Second, the scaling laws require knowledge of the high temperature moment degeneracy, which is often undetermined for itinerant 5f electrons. By making plausible corrections for both effects, better scaling ratios are obtained for some uranium compounds. We point out that, while both the uranium HF compounds and the rare earth IV compounds have spin fluctuation characteristic energies of order 5-25 meV, they differ in that the AF fluctuations that are usually seen in the uranium compounds are never seen in the rare earth IV compounds. This suggests that the 5f itineracy increases the f-f exchange relative to the rare earth case.
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.
Heavy-Fermion Superconductivity in URANIUM-PLATINUM(3)
NASA Astrophysics Data System (ADS)
Putikka, William Oliver
A phenomenological spin fluctuation model for superconductivity in the heavy-fermion metal UPt _3 is presented. The wavevector dependence of the interaction is assumed to be the same as the wavevector dependent magnetic susceptibility extracted from the neutron scattering experiments of Aeppli, et al. The other input for the calculation is the Fermi surface of UPt _3. Single particle band calculations done for UPt_3 give a Fermi surface which is very anisotropic. Despite the presence of strong correlations in UPt_3 the Fermi surface derived from band calculations is confirmed by the de Haas-van Alphen measurements of Taillefer, et al. However, the calculated band masses are smaller than the observed masses by a factor of 20. UPt_3 can thus be described at low temperatures in its normal state as a Fermi liquid, with very massive quasiparticles. The model considered here for the superconducting state is the pairing of the heavy quasiparticles by means of the spin fluctuation mediated interaction. A phase diagram is derived in terms of two dimensionless parameters giving the relative strength of the local repulsive part of the interaction and the in plane ferromagnetic interaction compared to the nearest neighbor antiferromagnetic interaction. s -, p- and d-wave phases are possible. The symmetry of the gap function favored by this model is the E_ {1g} representation of D_ {rm 6h}. To determine the symmetry of the gap function for this two dimensional representation the fourth order terms in the Ginzburg-Landau free energy are considered. The resulting gap function has a line of nodes in the basal plane and point nodes along the c -axis. A qualitative comparison of calculated properties for UPt_3 with this d-wave gap function to measured properties is given. Emphasis is on the observed power law temperature dependences for many low temperature properties and the difficulties in identifying the nodal structure due to impurity scattering. A discussion of the limitations
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
How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder.
Hamidian, Mohammad H; Schmidt, Andrew R; Firmo, Inês A; Allan, Milan P; Bradley, Phelim; Garrett, Jim D; Williams, Travis J; Luke, Graeme M; Dubi, Yonatan; Balatsky, Alexander V; Davis, J C
2011-11-01
Replacing a magnetic atom by a spinless atom in a heavy-fermion compound generates a quantum state often referred to as a "Kondo-hole". No experimental imaging has been achieved of the atomic-scale electronic structure of a Kondo-hole, or of their destructive impact [Lawrence JM, et al. (1996) Phys Rev B 53:12559-12562] [Bauer ED, et al. (2011) Proc Natl Acad Sci. 108:6857-6861] on the hybridization process between conduction and localized electrons which generates the heavy-fermion state. Here we report visualization of the electronic structure at Kondo-holes created by substituting spinless thorium atoms for magnetic uranium atoms in the heavy-fermion system URu(2)Si(2). At each thorium atom, an electronic bound state is observed. Moreover, surrounding each thorium atom we find the unusual modulations of hybridization strength recently predicted to occur at Kondo-holes [Figgins J, Morr DK (2011) Phys Rev Lett 107:066401]. Then, by introducing the "hybridization gapmap" technique to heavy-fermion studies, we discover intense nanoscale heterogeneity of hybridization due to a combination of the randomness of Kondo-hole sites and the long-range nature of the hybridization oscillations. These observations provide direct insight into both the microscopic processes of heavy-fermion forming hybridization and the macroscopic effects of Kondo-hole doping. PMID:22006302
How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder
Hamidian, Mohammad H.; Schmidt, Andrew R.; Firmo, Inês A.; Allan, Milan P.; Bradley, Phelim; Garrett, Jim D.; Williams, Travis J.; Luke, Graeme M.; Dubi, Yonatan; Balatsky, Alexander V.; Davis, J. C.
2011-01-01
Replacing a magnetic atom by a spinless atom in a heavy-fermion compound generates a quantum state often referred to as a “Kondo-hole”. No experimental imaging has been achieved of the atomic-scale electronic structure of a Kondo-hole, or of their destructive impact [Lawrence JM, et al. (1996) Phys Rev B 53:12559–12562] [Bauer ED, et al. (2011) Proc Natl Acad Sci. 108:6857–6861] on the hybridization process between conduction and localized electrons which generates the heavy-fermion state. Here we report visualization of the electronic structure at Kondo-holes created by substituting spinless thorium atoms for magnetic uranium atoms in the heavy-fermion system URu2Si2. At each thorium atom, an electronic bound state is observed. Moreover, surrounding each thorium atom we find the unusual modulations of hybridization strength recently predicted to occur at Kondo-holes [Figgins J, Morr DK (2011) Phys Rev Lett 107:066401]. Then, by introducing the “hybridization gapmap” technique to heavy-fermion studies, we discover intense nanoscale heterogeneity of hybridization due to a combination of the randomness of Kondo-hole sites and the long-range nature of the hybridization oscillations. These observations provide direct insight into both the microscopic processes of heavy-fermion forming hybridization and the macroscopic effects of Kondo-hole doping. PMID:22006302
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.
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
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.
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
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.
NASA Astrophysics Data System (ADS)
Pixley, Jedediah H.
Rare earth and actinide metal compounds have emerged as quintessential systems to experimentally and theoretically explore zero temperature quantum phase transitions. These so called heavy fermion metals provide a platform to systematically study physics on the edge of our understanding, where conventional approaches fail to describe the experimental observations. In this thesis, we are concerned with the theoretical description of the different types of quantum phases and phase transitions that are possible within heavy fermion metals. We first focus on understanding the unconventional quantum critical scaling properties observed in heavy fermion metals. Guided by the extended dynamical mean field theory (EDMFT) of the Kondo lattice, we study the physics of Kondo destruction in simplified quantum impurity models. Using the continuous time quantum Monte Carlo (CT-QMC), we show Kondo destroyed quantum critical points (QCPs) give rise to local correlation functions that obey frequency and magnetic field over temperature scaling, and have a linear in temperature relaxation rate. Our results are consistent with the experiments on the quantum critical heavy fermion metals YbRh2Si2, CeCu6- xAux, and beta-YbAlB4. Motivated by experiments on CeRhIn5 and related heavy fermion systems, we then focus on the superconducting properties of the Kondo destroyed QCPs. We introduce and solve an effective model that has both Kondo destruction and pairing correlations, using a combination of CTQMC and the numerical renormalization group (NRG) methods. We then solve the cluster EDMFT equations across the QCP for two and three dimensional magnetic fluctuations, using the CT-QMC as the cluster solver. In the two dimensional case, we find that the Kondo screening is driven critical at the antiferromagnetic QCP. In each case studied, we find that the pairing susceptibility is strongly enhanced in the vicinity of the QCP. Our results point to the exciting possibility of an unconventional
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.
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
Landau Renormalizations of Superfluid Density in the Heavy-Fermion Superconductor CeCoIn5
NASA Astrophysics Data System (ADS)
Shu, Lei; MacLaughlin, D. E.; Varma, C. M.; Bernal, O. O.; Ho, P.-C.; Fukuda, R. H.; Shen, X. P.; Maple, M. B.
2014-10-01
The formation of heavy-fermion bands can occur by means of the conversion of a periodic array of local moments into itinerant electrons via the Kondo effect and the huge consequent Fermi-liquid renormalizations. Leggett predicted for liquid He3 that Fermi-liquid renormalizations change in the superconducting state, leading to a temperature dependence of the London penetration depth Λ quite different from that in BCS theory. Using Leggett's theory, as modified for heavy fermions, it is possible to extract from the measured temperature dependence of Λ in high quality samples both Landau parameters F0s and F1s; this has never been accomplished before. A modification of the temperature dependence of the electronic specific heat Cel, related to that of Λ, is also expected. We have carefully determined the magnitude and temperature dependence of Λ in CeCoIn5 by muon spin relaxation rate measurements to obtain F0s=36±1 and F1s=1.2±0.3, and we find a consistent change in the temperature dependence of Cel. This, the first determination of F1s with a value ≪F0s in a heavy-fermion compound, tests the basic assumption of the theory of heavy fermions, that the frequency dependence of the self-energy is much more important than its momentum dependence.
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.
Heavy-fermion semiconductor behavior of the SU({ital N}{sub {ital d}}) Anderson lattice model
Hu, L.; Yang, F.; Sun, J. |; Lin, T. |
1995-08-15
The heavy-fermion semiconductor behavior of the SU({ital N}{sub {ital d}}) Anderson lattice model is examined by using the slave-boson technique within the framework of mean-field theory. The results show that the slave-boson mean-field theory of this model can present a heavy Fermi liquid or a heavy-fermion semiconductor ground state for different {ital n} values ({ital n} is the total number of the conduction and the on-site {ital f} electrons per lattice site), thus providing a unified description of the heavy Fermi liquid and the heavy-fermion semiconductor. The basic features of this theory are in qualitative agreement with the experimentally observed heavy-fermion semiconductor behavior of some rare-earth compounds.
Compact Multigluonic Scattering Amplitudes with Heavy Scalars and Fermions
Ferrario, Paola; Rodrigo, German; Talavera, Pere
2006-05-12
Combining the Berends-Giele and on-shell recursion relations we obtain an extremely compact expression for the scattering amplitude of a complex massive scalar-antiscalar pair and an arbitrary number of positive helicity gluons. This is one of the basic building blocks for constructing other helicity configurations from recursion relations. We also show explicitly that the scattering amplitude of massive fermions to gluons, all with positive helicity, is proportional to the scalar one, confirming in this way the recently advocated SUSY-like Ward identities relating both amplitudes.
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.
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.
Spin-orbit fluctuations in frustrated heavy-fermion metal LiV(2)O(4).
Tomiyasu, K; Iwasa, K; Ueda, H; Niitaka, S; Takagi, H; Ohira-Kawamura, S; Kikuchi, T; Inamura, Y; Nakajima, K; Yamada, K
2014-12-01
Spin fluctuations were studied over a wide momentum (ℏQ) and energy (E) space in the frustrated d-electron heavy-fermion metal LiV_{2}O_{4} by time-of-flight inelastic neutron scattering. We observed the overall Q-E evolutions near the characteristic Q=0.6 Å^{-1} peak and found another weak broad magnetic peak around 2.4 Å^{-1}. The data are described by a simple response function, a partially delocalized magnetic form factor, and antiferromagnetic short-range spatial correlations, indicating that heavy-fermion formation is attributable to spin-orbit fluctuations with orbital hybridization. PMID:25526141
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.
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
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.
NASA Astrophysics Data System (ADS)
Aynajian, Pegor; da Silva Neto, Eduardo H.; Zhou, Brian B.; Misra, Shashank; Baumbach, Ryan E.; Fisk, Zachary; Mydosh, John; Thompson, Joe D.; Bauer, Eric D.; Yazdani, Ali
2014-06-01
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 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 Ce- and U-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 in the Ce-based compounds to resolve their energy-momentum structure and to extract their mass enhancement, which develops with decreasing temperature. Finally, by extending these techniques to much lower temperatures, we investigate how superconductivity, with a nodal d-wave character, develops within a strongly correlated band of composite excitations.
Crossover Phase Diagram and Electronic State in the Heavy-Fermion Metamagnets UIr2Zn20 and UCo2Zn20
NASA Astrophysics Data System (ADS)
Hirose, Yusuke; Takeuchi, Tetsuya; Honda, Fuminori; Yoshiuchi, Shingo; Hagiwara, Masayuki; Yamamoto, Etsuji; Haga, Yoshinori; Settai, Rikio; Ōnuki, Yoshichika
2015-07-01
Crossover phase diagrams in the magnetic field versus temperature (H-T) plane of the nonmagnetic heavy-fermion metamagnets UT2Zn20 (T:Ir, Co) are studied by measuring the magnetic and electronic transport properties. The crossover phase diagrams of UIr2Zn20 and UCo2Zn20 are composed of a low-magnetic-field region (LFR) and a high-magnetic-field region (HFR), which are characterized by magnetic properties and the Hall effect, respectively. The LFR is found to form a closed area in the H-T plane, which is a quite different feature from the conventional uranium heavy-fermion compounds and the first observation in uranium compounds. From the drastic anomaly in the Hall effect at a metamagnetic field of UIr2Zn20, it is found that the metamagnetic behavior in UIr2Zn20 corresponds to a crossover from the heavy-fermion state to the field-induced ferromagnetic or polarized paramagnetic state accompanied by the reconstruction or topology change of Fermi surfaces. In UCo2Zn20, on the other hand, no sign of abrupt change in the electronic state at the metamagnetic field is observed. These contrastive crossover phase diagrams and the electronic state changes at the metamagnetic field are due to the different hybridization strengths between the 5f electrons of U atoms and the d electrons of Ir and Co atoms, leading to the differences in magnetic correlation and crystalline electric field ground state or the degree of itinerancy of 5f electrons.
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
Magnetic Field and Pressure Phase Diagrams of Uranium Heavy-Fermion Compound U2Zn17
NASA Astrophysics Data System (ADS)
Tateiwa, Naoyuki; Ikeda, Shugo; Haga, Yoshinori; Matsuda, Tatsuma D.; Yamamoto, Etsuji; Sugiyama, Kiyohiro; Hagiwara, Masayuki; Kindo, Koichi; Ōnuki, Yoshichika
2011-01-01
We have performed magnetization measurements at high magnetic fields of up to 53 T on single crystals of a uranium heavy-fermion compound U2Zn17 grown by the Bridgman method. In the antiferromagnetic state below the Néel temperature TN=9.7 K, a metamagnetic transition is found at Hc≃ 32 T for the field along the [11\\bar{2}0] direction (a-axis). The magnetic phase diagram for the field along the [11\\bar{2}0] direction is given. The magnetization curve shows a nonlinear increase at Hm≃ 35 T in the paramagnetic state above TN up to a characteristic temperature Tχmax where the magnetic susceptibility or electrical resistivity shows a maximum value. This metamagnetic behavior of the magnetization at Hm is discussed in comparison with the metamagnetic magnetism of the heavy-fermion super conductors UPt3, URu2Si2, and UPd2Al3. We have also carried out high-pressure resistivity measurement on U2Zn17 using a diamond anvil cell up to 8.7 GPa. Noble gas argon was used as a pressure-transmitting medium to ensure a good hydrostatic environment. The Néel temperature TN is almost pressure-independent up to 4.7 GPa and starts to increase in the higher-pressure region. The pressure dependences of the coefficient of the T2 term in the electrical resistivity A, the antiferromagnetic gap Δ, and the characteristic temperature Tρmax are discussed. It is found that the effect of pressure on the electronic states in U2Zn17 is weak compared with those in the other heavy fermion compounds.
Electronic structure and mass enhancement of the heavy fermion superconductor UPt 3
NASA Astrophysics Data System (ADS)
Wang, C. S.; Krakauer, H.; Pickett, W. E.
1985-12-01
The self-consistent general potential linearized augmented plane wave method has been applied to study the enegy bands of the heavy fermion superconductor UPt 3 within the local density approxination. We found 2.5 f-electrons per U atom and a f-band width of ≈1.9 eV pinned at the Fermi energy EF. An enhancement factor of 19 is deduced from the density of states at EF and the experimental linear coefficient of the specific heat. Possible sources of the renormalization are discussed based on available experimental information.
Unconventional flux dynamics in the heavy fermion superconductors UPt 3 and UBe 13
NASA Astrophysics Data System (ADS)
Amann, A.; Visani, P.; Aupke, K.; Mota, A. C.; Maple, M. B.; Dalichaouch, Y.; Armstrong, P. E.; Fisk, Z.; Mitin, A. V.
1994-12-01
We have investigated flux creep in single crystals of UPt 3 (Hc) and UBe 13 (Hc 4) in the temperature 5 mK < T < T c and for magnetic fields H < 0. The relaxation curves for both of these heavy fermion superconductors show novel behaviours, with decay lows which depend strongly on the applied field. At all temperatures, we observe contributions to the decays which seem to arise from different processes with different time dependences, namely logarithmic and stretched exponential.
A Phenomenological Theory of Metamagnetism in Ce-Based Heavy Fermion Compounds
NASA Astrophysics Data System (ADS)
Matsumoto, K.; Kosaka, S.; Murayama, S.
2016-04-01
A phenomenological theory is developed for the metamagnetism observed in heavy Fermion compounds by extension of the Landau theory for phase transitions. From simple analysis, the crossover behavior in high magnetic fields is indicated for the extended Landau-type free energy density. According to the finite temperature behavior of the extended Landau free energy density, theoretical magnetic phase diagrams that resemble those observed in CeRu2Si2 and Ce(Ru_{0.92}Rh_{0.08})2Si2 are obtained by using two sets of parameters, respectively.
Thermal Expansion and Magnetostriction of Heavy Fermion CeRu2Si2 at Millikelvin Temperatures
NASA Astrophysics Data System (ADS)
Inoue, Daiki; Kaido, Daisuke; Yoshikawa, Yuta; Minegishi, Mitsuyuki; Matsumoto, Koichi; Abe, Satoshi; Murayama, Shigeyuki
We have measured linear thermal expansion and magnetostriction of single crystal CeRu2Si2 that is well known as a heavy fermion metamagnetic compound. Thermal expansion and magnetostriction along the a-axis (B || a) and the c-axis (B || c) were measured by the capacitive dilatometer at temperatures down to 12 mK and in magnetic fields up to 9 T. We observed a strong anisotropy between a and c axis. In addition, negative deviations from Landau-Fermi liquid behavior for thermal expansion and magnetostriction coefficients were found below 50 mK and 0.4 T indicating non Fermi liquid behavior.
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.
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.
NASA Astrophysics Data System (ADS)
Pixley, J. H.; Yu, Rong; Si, Qimiao
2014-10-01
Considerable recent theoretical and experimental effort has been devoted to the study of quantum criticality and novel phases of antiferromagnetic heavy-fermion metals. In particular, quantum phase transitions have been discovered in heavy-fermion compounds with geometrical frustration. These developments have motivated us to study the competition between the Ruderman-Kittel-Kasuya-Yosida and Kondo interactions on the Shastry-Sutherland lattice. We determine the zero-temperature phase diagram as a function of magnetic frustration and Kondo coupling within a slave-fermion approach. Pertinent phases include the valence bond solid and heavy Fermi liquid. In the presence of antiferromagnetic order, our zero-temperature phase diagram is remarkably similar to the global phase diagram proposed earlier based on general grounds. We discuss the implications of our results for the experiments on Yb2Pt2Pb and related compounds.
NMR study of heavy fermion compound EuNi2P2
NASA Astrophysics Data System (ADS)
Magishi, K.; Watanabe, R.; Hisada, A.; Saito, T.; Koyama, K.; Fujiwara, T.
2015-03-01
We report the results of 31P-nuclear magnetic resonance (NMR) measurements on heavy fermion compound EuNi2P2 in order to investigate the magnetic properties at low temperatures from a microscopic view point. The Knight shift has a negative value in an entire temperature range, and the absolute value increases with decreasing temperature but exhibits a broad maximum around 40 K, which is similar to the behavior of the magnetic susceptibility. Also, the nuclear spin-lattice relaxation rate 1/T1 is almost constant at high temperatures above 200 K, which is reminiscent of the relaxation mechanism dominated by the interaction of the 31P nucleus with fluctuating Eu-4f moments. Below 200 K, 1/T1 gradually decreases on cooling due to the change of the valence in the Eu ion. At low temperatures, 1/T1 does not obey the Korringa relation, in contrast to typical heavy fermion compounds. The nuclear spin-spin relaxation rate 1/T2 shows the similar behavior as 1/T1 at high temperatures. But, below 50 K, 1/T2 increases upon cooling due to the development of the magnetic excitation.
Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickel oxypnictide
NASA Astrophysics Data System (ADS)
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.
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.
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
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.
Strong correlations in Kondo topological insulators: Two-dimensional heavy fermions, and beyond
NASA Astrophysics Data System (ADS)
Nikolic, Predrag
Samarium hexaboride (SmB6) is a candidate topological insulator with strong electron correlations. Empowered by the time-reversal (TR) symmetry and topology, the low-energy surface states of hybridized samarium's d and f orbitals can exhibit a rich two-dimensional heavy-fermion phenomenology. This talk will survey several interesting possibilities for correlated surface states, which depend on microscopic surface conditions. A pronounced participation of the f orbitals is expected to create a heavy-fermion Dirac metal, possibly unstable to spin density waves, superconductivity, or exotic Mott insulators (e.g. algebraic and non-Abelian spin liquids). The opposite limit of ``localized magnetic moments'' can produce a non-Fermi liquid of d electrons that exhibits two-dimensional quantum electrodynamics. Ultrathin films made from topological Kondo insulators can host lattices of SU(2) vortices, which need not break the TR symmetry. Landau-Ginzburg theory and numerical model calculations reveal the nature and stability of such vortex lattices, while field theory arguments predict that their quantum melting could yield novel incompressible quantum liquids with non-Abelian fractional excitations.
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.
An exploratory study of heavy domain wall fermions on the lattice
NASA Astrophysics Data System (ADS)
Boyle, P.; Jüttner, A.; Marinković, M. Krstić; Sanfilippo, F.; Spraggs, M.; Tsang, J. T.
2016-04-01
We report on an exploratory study of domain wall fermions (DWF) as a lattice regularisation for heavy quarks. Within the framework of quenched QCD with the tree-level improved Symanzik gauge action we identify the DWF parameters which minimise discretisation effects. We find the corresponding effective 4 d overlap operator to be exponentially local, independent of the quark mass. We determine a maximum bare heavy quark mass of am h ≈ 0 .4, below which the approximate chiral symmetry and O(a)-improvement of DWF are sustained. This threshold appears to be largely independent of the lattice spacing. Based on these findings, we carried out a detailed scaling study for the heavy-strange meson dispersion relation and decay constant on four ensembles with lattice spacings in the range 2 .0-5 .7 GeV. We observe very mild a 2 scaling towards the continuum limit. Our findings establish a sound basis for heavy DWF in dynamical simulations of lattice QCD with relevance to Standard Model phenomenology.
Probing the Nature of Superconductivity in the Heavy Fermion PuMGa5 and PuMIn5 (M =Co, Rh) Compounds
NASA Astrophysics Data System (ADS)
Bauer, Eric; Tobash, Paul; Mitchell, Jeremy; Thompson, Joe
2014-03-01
The discovery of superconductivity in PuCoGa5 with a Tc = 18.5 K has generated renewed interest in Pu-based compounds. PuCoGa5, and its superconducting cousin PuRhGa5 (Tc = 8.7 K), have the same crystal structure as the tetragonal CeMIn5 (T =Co, Rh, Ir) heavy fermion superconductors, suggesting that the structure plays a key role in generating superconductivity in these materials. While a variety of measurements have firmly established that the CeTIn5 compounds are unconventional d-wave superconductors, most probably mediated by antiferromagnetic spin fluctuations, it is less clear what drives the high transition temperature in PuCoGa5, which is an order of magnitude larger than all other know Ce- or U-based heavy fermion superconductors. The physical properties of two new members of this ``115'' family of superconductors, PuRhIn5 and PuCoIn5, indicate that they reside close to an antiferromagnetic quantum critical point, while the smaller effective masses and much smaller unit cell volumes of PuCoGa5 and PuRhGa5 suggest that they may be near a T =0 valence instability or that the Pu 5f electrons couple to conduction electrons in multiple channels to form ``composite'' superconducting pairs. The nature of superconductivity in these four Pu115 materials will be discussed. Work at Los Alamos was performed under the auspices of the US DOE.
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.
Pressure and field tuning in the heavy fermion ferromagnet CeAgSb2
NASA Astrophysics Data System (ADS)
Logg, Peter; Feng, Zhuo; Ebihara, Takao; Goh, Swee K.; Alireza, Patricia; Grosche, F. Malte
2012-12-01
The intermetallic compound CeAgSb2 is an unusual example of a ferromagnetically ordered heavy fermion system. Ferromagnetism sets in below the Curie temperature Tc=9.6 K at ambient pressure. We have investigated the magnetisation of CeAgSb2 under applied hydrostatic pressure of up to 45 kbar. Tc is suppressed rapidly, and at pressures > 35 kbar it is replaced by an unidentified ordered phase, possibly antiferromagnetism. The ordered magnetic moment in CeAgSb2 is aligned along the c-axis. We investigate the effect of transverse field tuning on Tc, and show that magnetic order at low temperature is suppressed by in-plane fields exceeding about 3 T.
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.
High-temperature signatures of quantum criticality in heavy-fermion systems.
Kroha, J; Klein, M; Nuber, A; Reinert, F; Stockert, O; v Löhneysen, H
2010-04-28
We propose a new criterion for distinguishing the Hertz-Millis (HM) and the local quantum critical (LQC) mechanism in heavy-fermion systems with a magnetic quantum phase transition (QPT). The criterion is based on our finding that the complete spin screening of Kondo ions can be suppressed by the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling to the surrounding magnetic ions even without magnetic ordering and that, consequently, the signature of this suppression can be observed in spectroscopic measurements above the magnetic ordering temperature. We apply the criterion to high-resolution photoemission measurements on CeCu(6 - x)Au(x) and conclude that the QPT in this system is dominated by the LQC scenario. PMID:21386409
Magnetic phase transitions in heavy-fermion compounds studied by thermal-expansion measurements
NASA Astrophysics Data System (ADS)
de Visser, A.; Lacerda, A.; Franse, J. J. M.; Flouquet, J.
1990-12-01
On alloying the heavy-fermion compounds CeRu 2Si 2 and UPt 3 with small amounts of La and Pd, respectively, long-range antiferromagnetic order develops with Néel temperatures in the order of a few kelvin. In order to study the volume effects that are involved with the evolution into the long-range ordered state, we have performed thermal-expansion measurements on the pure and doped systems. The results are compared with data on antiferromagnetic URu 2Si 2. Subsequently, we discuss thermal-expansion measurements in high-magnetic fields, in particular on CeRu 2Si 2, where a metamagnetic-like transition occurs as the intersite-correlations collapse in a field of 7.8 T. Most of the measurements have been performed on single-crystalline samples, revealing a pronounced anisotropy.
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
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.
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
NASA Astrophysics Data System (ADS)
Han, Siyuan
A new effect between a superconductor with superconducting transition temperature T(,cs) and a normal metal N (T(,cn)) (or another superconductor with T(,cn) < T(,cs)) has been experimentally observed and theoretically explained. That is when S and N are brought together to form a weak link the Josephson effect can occur in this SN system even in the temperature range T(,cn) < T < T(,cs), when the N side is in the normal state. This Josephson effect is believed to happen between the S and a region of proximity-induced super- conductivity in N near the contact with S. We call this effect the proximity-induced Josephson effect. The temperature dependence of the Josephson critical current I(,c)(T) of the SN point contact junc- tions have been studied experimentally. The experiments have been performed on Ta/Mo, Ta/UBe(,13) and Nb/Ta point contacts etc. The theoretical model is based on the linearized Gor'kov equation (or linearized Ginzburg-Landau equation) combined with de Gennes boundary conditions. This model is applicable only in the vicinity of the T(,c) of the SN system. Thus, we studied I(,c)(T) of the SN junctions near their T(,c). Good agreement between experimental data and theoretical result is obtained. Along with the recent discovery of the superconductivity in heavy fermion materials CeCu(,2)Si(,2), UBe(,13) and UPt(,3) the old question of p-wave pairing superconductivity is raised again (in case of the exist- ence of strong spin -orbit scattering, it should be called odd parity superconductivity, since in that case the wave function of Cooper pairs cannot be separated into spin part and orbit part). These rare -earth and actinide compounds exhibit properties which cannot be explained by the conventional isotropic s-wave pairing supercon- ductivity (or BCS superconductivity) but are consistent with the varieties of p-wave (or odd parity) superconductivity. Among these three heavy fermion superconductors UBe(,13) is thought to be the best candidate for
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
NASA Astrophysics Data System (ADS)
Prokleška, J.; Kratochvílová, M.; Uhlířová, K.; Sechovský, V.; Custers, J.
2015-10-01
The properties of the heavy-fermion superconductor Ce3PtIn11 are investigated by thermodynamic and transport measurements at ambient and under hydrostatic pressure. At ambient pressure the compound exhibits two successive magnetic transitions at T1≃2.2 K and TN≃2 K into antiferromagnetically ordered states and enters into a heavy-fermion superconducting phase below Tc≃0.32 K. The coexistence of long-range magnetic order and superconductivity is discussed in the context of the existence of the two crystallographically inequivalent Ce sites in the unit cell of Ce3PtIn11 . The experimental data allow us to construct the pressure-temperature phase diagram.
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 .
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.
Field-induced density wave in the heavy-fermion compound CeRhIn₅.
Moll, Philip J W; Zeng, Bin; Balicas, Luis; Galeski, Stanislaw; Balakirev, Fedor F; Bauer, Eric D; Ronning, Filip
2015-01-01
Strong electron correlations lead to a variety of distinct ground states, such as magnetism, charge order or superconductivity. Understanding the competitive or cooperative interplay between neighbouring phases is an outstanding challenge in physics. CeRhIn₅ is a prototypical example of a heavy-fermion superconductor: it orders anti-ferromagnetically below 3.8 K, and moderate hydrostatic pressure suppresses the anti-ferromagnetic order inducing unconventional superconductivity. Here we show evidence for a phase transition to a state akin to a density wave (DW) under high magnetic fields (>27 T) in high-quality single crystal microstructures of CeRhIn₅. The DW is signalled by a hysteretic anomaly in the in-plane resistivity accompanied by non-linear electrical transport, yet remarkably thermodynamic measurements suggest that the phase transition involves only small portions of the Fermi surface. Such a subtle order might be a common feature among correlated electron systems, reminiscent of the similarly subtle charge DW state in the cuprates. PMID:25798749
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
Possible Heavy Fermion State of the Caged Cubic Compound NdV2Al20
NASA Astrophysics Data System (ADS)
Namiki, Takahiro; Lei, Qiankun; Isikawa, Yosikazu; Nishimura, Katsuhiko
2016-07-01
The magnetic susceptibility M/H, the magnetization M, and the specific heat C were measured for the caged cubic compound NdV2Al20 single crystal at temperatures down to 0.5 K in magnetic fields H along the three principal crystallographic axes [001], [101], and [111]. The electrical resistivity ρ was measured in the temperature range of 1.9-300 K. A ferromagnetic phase transition was observed at a Curie temperature TC of 1.81 K. The easy direction of magnetization was the [001] direction at low fields, and changed to the [101] direction above 2 T. On cooling below 2 K at zero field, the specific heat divided by temperature, C/T, resulted in a large electronic specific heat coefficient γ of about 2 J/(K2 mol). A large C/T of more than 1 J/(K2 mol) remained at 9 T below 2 K. The temperature dependence of ρ showed the -ln T dependence at around 10 K. These behaviors possibly originate from a heavy fermion state.
Magnetic ordering of Ce in the heavy-fermion compound Ce3Al
NASA Astrophysics Data System (ADS)
Li, W.-H.; Peng, J. C.; Lin, Y.-C.; Lee, K. C.; Lynn, J. W.; Chen, Y. Y.
1998-06-01
Neutron diffraction and specific heat measurements have been performed to study the magnetic ordering of the Ce ions in the heavy-fermion compound Ce3Al. Detailed crystal structure analysis, determined using high resolution neutron diffraction patterns and Rietveld method, shows that the Ce ions may be grouped into two types: one in the Ce-Al chain, the other in the Ce-Ce chain. The specific-heat data reveal an anomaly at T≈2.2 K, but the calculated magnetic entropy is much smaller than the expected R ln 2 if all Ce spins ordered. Low temperature neutron diffraction measurements confirm that the transition at 2.2 K is magnetic and is associated with the ordering of the Ce spins. The magnetic unit cell is double the nuclear one along the a and c axes, and contains 48 Ce ions. Only the Ce ions in the Ce-Al chains participate in the ordering at 2.2 K, and they are coupled antiferromagnetically.
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
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.
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
2015-01-01
The interplay of structural, orbital, charge, and spin degrees of freedom is at the heart of many emergent phenomena, including superconductivity. 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 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. PMID:25675488
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.
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
Magnetic Properties of the Heavy Fermion System URANIUM-BERYLLIUM-13.
NASA Astrophysics Data System (ADS)
Ma, Yu Pei
1989-09-01
UBe_{13} is one of the heavy fermion superconductors with an unusually large electronic specific heat and an unconventional magnetic susceptibility. The magnetization in both the normal and mixed states of UBe_{13} has been measured in magnetic fields up to 19 Tesla and temperatures down to 50mK. For high fields and low temperatures, two types of capacitive DC magnetometers, a cantilever (CMAG) and a diaphragm (DMAG) magnetometer, have been developed. These are at present the only DC magnetometers which work simultaneously in a dilution refrigerator and a resistive Bitter magnet. In the normal state the magnetization at temperatures above T_{c} shows a slight deviation from simple linear behavior. Below T_{c }, however, the magnetization shows an unusual upturn at fields greater than 14T, which may be explained by field induced spin fluctuation or SDW transition. In the mixed state of UBe_{13}, a large and time-dependent hysteresis in the magnetization curve has been observed. This time dependence is well -described by an exponential decay, and the relaxation time is strongly dependent on temperature and magnetic field. Two different temporal responses corresponding to regimes above and below a crossover point in the hysteresis loops are found. This hysteresis has been shown to be due to anisotropic flux penetration. The magnetization curve in the superconducting mixed state is evidence of anisotropic superconductivity in UBe_{13}. The two regimes in the hysteresis loops support the suggestion that there exist two order parameters or two domain formations of the flux lattice in UBe_{13} . For comparison the time dependence of the magnetization of BiPb has been measured.
High pressure X-ray absorption spectroscopy studies of heavy-fermion cerium and uranium compounds
NASA Astrophysics Data System (ADS)
Antonio, Daniel
Investigations into f- electron heavy-fermion materials have revealed a wide range of novel behavior. Hydrostatic pressure is a valuable "clean" non-thermal parameter that can be used to systematically study them by tuning their ground state properties. The rare earth compound CeCu2Ge 2 shows an unusual two-domed region of unconventional superconductivity under pressure, similar to its isostructural counterpart CeCu2Si2. While the lower pressure dome at about 10 GPa is caused by a magnetic quantum critical point (QCP), the higher one at about 16 GPa is less well understood. Previous structural measurements have indicated that it may be caused by critical valence fluctuations, so in this study the valence of CeCu 2Ge2 is directly measured using X-ray Absorption Near Edge Spectroscopy (XANES) under pressure in a diamond anvil cell up to 20 GPa. An expected valence discontinuity is not seen, but comparisons to CeCu 2Si2 show interesting similarities. Uranium's 5f electrons are intermediate between localized and delocalized. Studying the degree of localization is vital to completely understand the properties of actinides. Performing XANES and Partial Florescence Yield (PFY) measurements in a diamond anvil cell to tune the distance between uranium atoms, I have measured the energy shift in the white line of UCu2Si2, U3Ni 5Al19, and UCd11 with pressure. A positive shift in energy indicated a delocalization of 5f electrons, a change in 5f configurations, or a combination of both.
Antiferromagnetism, valence fluctuation, and heavy-fermion behavior in EuCu2(Ge1-xSix)2
NASA Astrophysics Data System (ADS)
Hossain, Z.; Geibel, C.; Senthilkumaran, N.; Deppe, M.; Baenitz, M.; Schiller, F.; Molodtsov, S. L.
2004-01-01
We have investigated the magnetic, thermodynamic, transport, and electronic properties across the transition from the divalent antiferromagnetic state to the valence fluctuating state of Eu in the alloy EuCu2(Ge1-xSix)2. The antiferromagnetic state is very stable from x=0 up to x=0.6 and disappears rather abruptly at xc≈0.65. Near the crossover, we confirmed a pronounced Kondo-like behavior in the resistivity and in the thermopower. Further on, for x slightly larger than xc, we observe the formation of a heavy Fermi liquid at low temperatures, as evidenced by a large linear coefficient of the specific heat (γ=191 mJ/K2 mol for x=0.7), a large quadratic term in the resistivity and a strongly enhanced constant susceptibility χ0. This is a unique observation of heavy fermion behavior in a Eu compound. The photoemission spectra of the Eu 4f and 3d core levels indicate significant valence fluctuation even for x
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
Shubnikov-de Haas Oscillation in the cubic Γ3-based heavy fermion superconductor PrV2Al20
NASA Astrophysics Data System (ADS)
Shimura, Yasuyuki; Tsujimoto, Masaki; Sakai, Akito; Zeng, Bin; Balicas, Luis; Nakatsuji, Satoru
2015-03-01
PrV2Al20 is the cubic Γ3 doublet system that exhibits strong hybridization effects and heavy fermion superconductivity. We measured the magnetoresistance using a high quality single crystal of PrV2Al20 under the DC high magnetic field up to 35 T below ~ 0.4 K. We have succeeded in detecting the Shubnikov-de Haas (SdH) oscillation with a frequency of 250 T. Our analysis of this SdH oscillation yields the cyclotron effective mass (m*c/m0 ~ 5) and the mean-free path (l = 170 Å).
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)
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
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.
Non-Fermi Liquid Behaviour in the Heavy-Fermion Kondo Lattice Ce2Rh3Al9
NASA Astrophysics Data System (ADS)
Falkowski, M.; Strydom, A. M.
2014-04-01
In the heavy fermion class of strongly correlated electron systems, the Landau Fermi liquid description of metals has become a rather fragile basis on which to formulate an understanding of their ground state. The proximity to cooperative phenomena such as magnetic order and superconductivity and the amenability of Ce- and Yb-based compounds to be tuned into quantum criticality have been found to have extraordinary effects on the T→0 thermal scaling of electronic and magnetic properties. A collection of non-Fermi liquid scaling relations have thus far been proposed in the search for universality. Here we report on the physical properties of the heavy fermion Kondo lattice Ce2Rh3Al9. The low-temperature specific heat and electrical resistivity are best described by power laws in their temperature dependence, and we model these according to the expectation for a system close to a magnetic phase transition. We demonstrate how applied magnetic fields drive the transition from the Kondo coherent state, through a cross-over phase, and into Fermi-liquid behaviour at high fields and low temperatures.
NASA Astrophysics Data System (ADS)
Lan, Kenneth Ming-Der
^9Be nuclear magnetic resonance measurements are reported for the normal state of the actinide intermetallic compound UBe_{13} . The motivation for this work was to examine the enhancement effect of the heavy fermions in this material in terms of their effect on the dynamic and static parts of the local magnetic field provided by the heavy fermions. The NMR experiments were done over a wide range of temperature and magnetic field. In the normal state of UBe_{13}, measurements in the temperature range extending from 0.8 K to room temperature were carried out, while a magnetic field of up to 70 kOe was applied. The measured ^9Be Knight shift in the normal state of UBe_{13 } is large, strongly temperature dependent and highly anisotropic. Above the characteristic temperature T* ~ 10 K, the Knight shift is linearly proportional to the static susceptibility. However, it deviates from this behavior at low temperature. The average isotropic Knight shifts for T < 10 K are approximately -0.08(1) % and 0.09(1) % for Be_{rm I} and Be_{rm II}, respectively. These results indicate an enhancement by a factor of 26 over what is found in pure Be metal. The ^9Be spin-lattice relaxation rate in UBe_{13} shows that the noise power of ^9Be local -field fluctuation due to the presence of heavy electrons is three orders of magnitude larger than the value observed in the corresponding non-5f intermetallic compound ThBe _{13}. This enhancement of the relaxation rate is associated with the formation of a narrow state near the Fermi energy that has a large component of f-electron density. The magnetic field dependence of ^9 Be spin-lattice relaxation rate was also measured in the superconducting state to understand the role of undetermined paramagnetic impurities in the heavy fermion system. The relaxation is through nuclear spin diffusion to the paramagnetic center. The observed field dependence at low fields may arise from diffusion-limited relaxation. At high magnetic fields the spin
Muon Knight shift in d-electron heavy fermion compound Y0.95Sc0.05Mn2
NASA Astrophysics Data System (ADS)
Yamauchi, I.; Miyazaki, M.; Hiraishi, M.; Koda, A.; Kojima, K. M.; Kadono, R.; Nakamura, H.
2014-12-01
We report on the muon Knight shift in a polycrystalline sample of Y0.95Sc0.05Mn2 that is known as one of the d-electron heavy fermion compounds. Since the muon site is presumed to have a trigonal symmetry, it is expected that the Fourier-transformed (FT) spectrum line shape would exhibit a uni-axial powder pattern which has two edges determined by the parallel and perpendicular components of the Knight shift, K|| and K⊥, where K|| (K⊥) is proportional to the parallel (perpendicular) component of the spin susceptibility, χ|| (χ⊥). The observed FT spectrum at 2 K largely disagrees with the calculated line shape in isotropic (χ|| = χ⊥) and anisotropic (χ|| ≠ χ⊥) cases, suggesting that there must be field- induced staggered magnetization due to strong antiferromagnetic spin correlations.
Quasi-two-dimensional Fermi surfaces of the heavy-fermion superconductor Ce2PdIn8
NASA Astrophysics Data System (ADS)
Götze, K.; Klotz, J.; Gnida, D.; Harima, H.; Aoki, D.; Demuer, A.; Elgazzar, S.; Wosnitza, J.; Kaczorowski, D.; Sheikin, I.
2015-09-01
We report low-temperature de Haas-van Alphen (dHvA) effect measurements in magnetic fields up to 35 T of the heavy-fermion superconductor Ce2PdIn8 . The comparison of the experimental results with band-structure calculations implies that the 4 f electrons are itinerant rather than localized. The cyclotron masses estimated at high field are only moderately enhanced, 8 m0 and 14 m0 , but are substantially larger than the corresponding band masses. The observed angular dependence of the dHvA frequencies suggests quasi-two-dimensional Fermi surfaces in agreement with band-structure calculations. However, the deviation from ideal two-dimensionality is larger than in CeCoIn5, to which Ce2PdIn8 bears a lot of similarities. This subtle distinction accounts for the different superconducting critical temperatures of the two compounds.
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.
Cabrera-Baez, M; Ribeiro, R A; Avila, M A
2016-09-21
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 Yb(3+) 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. PMID:27419654
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.
Decoupling and nondecoupling of heavy fermions in theories with spontaneous symmetry breaking
Li, Ling-Fong . Dept. of Physics); Cheng, T.P. . Dept. of Physics Chinese Univ. of Hong Kong, Shatin . Dept. of Physics)
1991-01-01
The validity of the decoupling theorem is discussed in the context of gauge theories with spontaneous symmetry breaking. The presence of large Yukawa couplings which grow with heavy masses is responsible for the violation of decoupling theorem. 7 refs.
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)
Kaczorowski, D.; Pikul, A. P.; Gnida, D.; Tran, V. H.
2009-07-01
Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc=0.68K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN=10K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions.
Kaczorowski, D; Pikul, A P; Gnida, D; Tran, V H
2009-07-10
Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc=0.68 K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN=10 K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions. PMID:19659236
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
Multipolar phases and magnetically hidden order: review of the heavy-fermion compound Ce1-x La x B6.
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. PMID:27177075
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.
2015-11-01
YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of T*=0.7 K , fragile antiferromagnetic order below TN=0.4 K , a Kondo temperature of TK≈1 K , and crystalline-electric-field splitting on the order of E /kB=1 -10 K . 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 ×10-5Å , 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.
Heavy fermion bound states for diphoton excess at 750 GeV — collider and cosmological constraints
NASA Astrophysics Data System (ADS)
Han, Chengcheng; Ichikawa, Koji; Matsumoto, Shigeki; Nojiri, Mihoko M.; Takeuchi, Michihisa
2016-04-01
A colored heavy particle with sufficiently small width may form non-relativistic bound states when they are produced at the large hadron collider (LHC), and they can annihilate into a diphoton final state. The invariant mass of the diphoton would be around twice of the colored particle mass. In this paper, we study if such bound state can be responsible for the 750 GeV diphoton excess reported by ATLAS and CMS. We found that the best-fit signal cross section is obtained for the SU(2) L singlet colored fermion X with Y X = 4 /3. Having such an exotic hypercharge, the particle is expected to decay through some higher dimensional operators, consistent with the small width assumption. The decay of X may involve a stable particle χ, if both X and χ are odd under some conserved Z 2 symmetry. In that case, the particle X suffers from the constraints of jets + missing E T searches by ATLAS and CMS at 8 TeV and 13 TeV. We found that such a scenario still survives if the mass difference between X and χ is above ˜ 30 GeV for m X ˜ 375 GeV. Even assuming pair annihilation of χ is small, the relic density of χ is small enough if the mass difference between X and χ is smaller than ˜ 40 GeV.
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.
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
NASA Astrophysics Data System (ADS)
Custers, J.; Diviši, M.; Kratochvílová, M.
2016-02-01
We discuss the results of thermodynamic and transport measurements at ambient and under hydrostatic pressure of the recently discovered heavy fermion superconductor Ce3PtIn11. At p = 0 superconductivity emerges in the complex antiferromagnetic state below Tc = 0.32 K. Both phenomena coexist in a wide range of the p — T phase diagram. The critical pressure where TN → 0 and Tc is maximum equals pc = 1.3 GPa. Here, the resistivity follows ρ(T) α Tn with n = 0.90±0.05 suggesting a local moment-type of quantum critical point. The presence of a maximum structure in the susceptibility and the unusual pressure dependence of Tc hint to an understanding of properties of Ce3PtIn11 in the view of distinct different Kondo screened sublattices. Therefore, we analyze the magnetic entropy Smag within the spin-1/2 Kondo model while accounting for the fact that Ce3PtIn11 unit cell possesses two inequivalent Ce-sites, Ce1 and Ce2. We employ an extreme case scenario of non-interacting sublattices where the Ce1-sublattice is paramagnetic and only Ce2-sublattice orders magnetically and discussed its consequences.
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.
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.
NASA Astrophysics Data System (ADS)
Gelis, François; Tanji, Naoto
2016-02-01
We revisit the problem of quark production in high energy heavy ion collisions, at leading order in α s in the color glass condensate framework. In this first paper, we setup the formalism and express the quark spectrum in terms of a basis of solutions of the Dirac equation (the mode functions). We determine analytically their initial value in the Fock-Schwinger gauge on a proper time surface Q s τ 0 ≪ 1, in a basis that makes manifest the boost invariance properties of this problem. We also describe a statistical algorithm to perform the sampling of the mode functions.
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.
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
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.
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.
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.
Magnetism, f-electron localization and superconductivity in 122-type heavy-fermion metals.
Steglich, F; Arndt, J; Stockert, O; Friedemann, S; Brando, M; Klingner, C; Krellner, C; Geibel, C; Wirth, S; Kirchner, S; Si, Q
2012-07-25
Both CeCu2Si2 and YbRh2Si2 crystallize in the tetragonal ThCr2Si2 crystal structure. Recent neutron-scattering results on normal-state CeCu2Si2 reveal a slowing down of the quasielastic response which complies with the scaling expected for a quantum critical point (QCP) of itinerant, i.e., three-dimensional spin-density-wave (SDW), type. This interpretation is in full agreement with the non-Fermi-liquid behavior observed in transport and thermodynamic measurements. The momentum dependence of the magnetic excitation spectrum reveals two branches of an overdamped dispersive mode whose coupling to the heavy charge carriers is strongly retarded. These overdamped spin fluctuations are considered to be the driving force for superconductivity in CeCu2Si2 (Tc = 600 mK). The weak antiferromagnet YbRh2Si2 (TN = 70 mK) exhibits a magnetic-field-induced QCP at BN = 0.06 T (B⊥c). There is no indication of superconductivity down to T = 10 mK. The magnetic QCP appears to concur with a breakdown of the Kondo effect. Doping-induced variations of the average unit-cell volume result in a detachment of the magnetic and electronic instabilities. A comparison of the properties of these isostructural compounds suggests that 3D SDW QCPs are favorable for unconventional superconductivity. The question whether a Kondo-breakdown QCP may also give rise to superconductivity, however, remains to be clarified. PMID:22773300
Magnetism, f-electron localization and superconductivity in 122-type heavy-fermion metals
NASA Astrophysics Data System (ADS)
Steglich, F.; Arndt, J.; Stockert, O.; Friedemann, S.; Brando, M.; Klingner, C.; Krellner, C.; Geibel, C.; Wirth, S.; Kirchner, S.; Si, Q.
2012-07-01
Both CeCu2Si2 and YbRh2Si2 crystallize in the tetragonal ThCr2Si2 crystal structure. Recent neutron-scattering results on normal-state CeCu2Si2 reveal a slowing down of the quasielastic response which complies with the scaling expected for a quantum critical point (QCP) of itinerant, i.e., three-dimensional spin-density-wave (SDW), type. This interpretation is in full agreement with the non-Fermi-liquid behavior observed in transport and thermodynamic measurements. The momentum dependence of the magnetic excitation spectrum reveals two branches of an overdamped dispersive mode whose coupling to the heavy charge carriers is strongly retarded. These overdamped spin fluctuations are considered to be the driving force for superconductivity in CeCu2Si2 (Tc = 600 mK). The weak antiferromagnet YbRh2Si2 (TN = 70 mK) exhibits a magnetic-field-induced QCP at BN = 0.06 T (B⊥c). There is no indication of superconductivity down to T = 10 mK. The magnetic QCP appears to concur with a breakdown of the Kondo effect. Doping-induced variations of the average unit-cell volume result in a detachment of the magnetic and electronic instabilities. A comparison of the properties of these isostructural compounds suggests that 3D SDW QCPs are favorable for unconventional superconductivity. The question whether a Kondo-breakdown QCP may also give rise to superconductivity, however, remains to be clarified.
Macaluso, Robin T.; Millican, Jasmine N.; Nakatsuji, Satoru; Lee, Han-Oh; Carter, B.; Moreno, Nelson O.; Fisk, Zachary; Chan, Julia Y. . E-mail: jchan@lsu.edu
2005-11-15
Single crystals of Ce{sub 2}PdGa{sub 12} have been synthesized in Ga flux and characterized by X-ray diffraction. This compound crystallizes in the tetragonal P4/nbm space group, Z=2 with lattice parameters of a=6.1040(2)A and c=15.5490(6)A. It shows strongly anisotropic magnetism and orders antiferromagnetically at T{sub N}{approx}11K. A field-induced metamagnetic transition to the ferromagnetic state is observed below T{sub N}. Structure-property relationships with the related heavy-fermion antiferromagnet CePdGa{sub 6} are discussed.
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.
NASA Astrophysics Data System (ADS)
Tien, Cheng
Nuclear magnetic resonance (NMR) experiments have been carried out in two heavy fermion superconductors, CeCu(,2)Si(,2) and U(,1-x)Th(,x)Be(,13) (x = 0, 0.0331). The unusual normal-state and superconducting state behavior of CeCu(,2)SDi(,2) and UBe(,13) has recently been discovered. Both compounds exhibit enormous values of the normal-state low -temperature magnetic susceptibility (chi) and the linear specific heat coefficient (gamma). Standard analyses of (chi) and (gamma) result in a two order of magnitude enhancement of the conduction-electron mass, but the ratio (chi)/(gamma) retains a value appropriate to a free-electron gas. It is of interest to obtain as much microscopic information as possible. In one of our CeCu(,2)Si(,2) superconducting specimens, the observed temperature dependence of the spin-lattice relaxation rate 1/T(,1) (T) is consistent with a conventional quasiparticle excitation spectrum below the superconducting transition temperature T(,c). In the other superconducting CeCu(,2)Si(,2) sample, the nuclear spin-lattice relaxation rate decreases drastically just below T(,c) without the apparent enhancement observed in the first sample. This lack of enhancement in 1/T(,1) (T) suggests that the superconductivity in CeCu(,2)Si(,2) is not due to a conventional mechanism. Some unusual features in 1/T(,1) (T) between T(,c) and 1.2 K appear to signal a phase transition, possibly structural in nature. NQR measurements of the nonsuperconducting CeCu(,2)Si(,2) sample are consistent with extensive disorder in the Cu site occupation. The spin-lattice relaxation rate in UBe(,13) varies approximately as T('3) well below the transition temperature T(,c). This behavior is consistent with a class of anisotropic pairing models for which the superconducting gap vanishes along lines on the Fermi surface. Two phase transitions have been observed in the specific heat measurements of U(,0.9669)Th(,0.0331)Be(,13) at T(,c1) and T(,c2). For T(,c2) < T < T(,c1), 1/T(,1
NASA Astrophysics Data System (ADS)
Kang, Joonhee
Thin films of the heavy fermion superconductors, UBe_{13} and UPt _3 have been fabricated by dc sputtering. The growth of superconducting UBe_{13} films was easier than that of UPt_3 films because of much lower preparation temperature. Superconducting properties of UBe_{13} films were very similar to those of UBe_ {13} bulk material. Even though X-ray diffraction analysis showed that well ordered UPt _3 films had been prepared, the superconducting properties of the UPt_3 films were poor because of the presence of small concentrations of impurity phases. Impurity phase formation was difficult to deal with because temperatures as high as 1200 ^circC were required in the processing and because of the great sensitivity of UPt_3 to impurities. A difference between UBe _{13} films and bulk materials is the absence of the resistance peak at 2.4 K observed in bulk material in the films, a result which suggests that the resistance peak is unrelated to superconductivity. This is in contrast with a common view that it is. However the broad maximum in the normal state resistance found near 20 K was observed. The temperature dependence of the parallel and perpendicular critical magnetic fields of UBe_{13} films have been measured. The ratio of the critical fields, H _{{rm c2}parallel} /H_{{rm c2} |}, has been found to be at least 1.25 over the whole temperature range below T_ {rm c}, a value less than would be expected for s-wave pairing without surface pair-breaking, but greater than expected for any pairing configuration which is a pure angular momentum state with L not= 0. This observation suggests the existence of s-wave superconductivity in UBe_{13 } at least near its surfaces. A proximity effect experiment has been carried on UBe_ {13}/Al sandwiches. The measurement of critical fields of the Al layer suggests that there is no negative proximity effect between UBe_ {13} and Al, but rather positive proximity effect. This observation supports the view of the existence of s
NASA Astrophysics Data System (ADS)
Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques
2009-03-01
Valence instability and its critical fluctuations have attracted much attention recently in the heavy-electron systems. Valence fluctuations are essentially charge fluctuations, and it is highly non-trivial how the quantum critical point (QCP) as well as the critical end point is controlled by the magnetic field. To clarify this fundamental issue, we have studied the mechanism of how the critical points of the first-order valence transitions are controlled by the magnetic field [1]. We show that the critical temperature is suppressed to be the QCP by the magnetic field and unexpectedly the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be a cooperative phenomenon of Zeeman effect and Kondo effect, which creates a distinct energy scale from the Kondo temperature. This mechanism explains a peculiar magnetic response in CeIrIn5 and metamagnetic transition in YbXCu4 for X=In as well as a sharp contrast between X=Ag and Cd. We present the novel phenomena under the magnetic field to discuss significance of the proximity of the critical points of the first-order valence transition. [1] S. Watanabe et al. PRL100, (2008) 236401.
Tobash, Paul H.; Ronning, Filip; Thompson, J.D.; Bobev, Svilen; Bauer, Eric D.
2010-03-15
The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of single crystals are reported for the compound CePd{sub 1+x}Al{sub 6-x} (x=0.5) which crystallizes in the tetragonal SrAu{sub 2}Ga{sub 5}-type structure (space group P4/mmm). The compound was grown from an excess of molten Al flux from the respective elements and the crystal structure was established from single-crystal X-ray diffraction. Anomalies in the low temperature specific heat C{sub p}(T) and electrical resistivity rho(T) show that the compound undergoes ferromagnetic order at T{sub C}=2.8 K. In the ordered state, CePd{sub 1.5}Al{sub 5.5} displays heavy fermion behavior with a Sommerfeld coefficient of ca. 500 mJ/mol-K{sup 2}. - Graphical abstract: The compound CePd{sub 1+x}Al{sub 6-x} (x=0.5) has been synthesized and structurally characterized by single-crystal X-ray diffraction. The measured physical properties of temperature and field dependent magnetic susceptibility, specific heat, and electrical resistivity suggests that the compound undergoes ferromagnetic order at ca. 2.8 K and further exhibits relatively heavy fermion behavior with a Sommerfeld coefficient of 500 mJ/mol-K2.
Heavy fermions, metal-to-insulator transition, and quantum criticality in La y Cu3Ru x Ti4- x O12
NASA Astrophysics Data System (ADS)
Riegg, S.; Widmann, S.; Günther, A.; Meir, B.; Wehrmeister, S.; Sterz, S.; Kraetschmer, W.; Ebbinghaus, S. G.; Reller, A.; Büttgen, N.; Krug von Nidda, H.-A.; Loidl, A.
2015-07-01
In this work we investigate the solid-solution series La y Cu3Ru x Ti4- x O12. The titanate La2/3Cu3Ti4O12 ( x = 0) is an antiferromagnetic insulator exhibiting colossal dielectric constants, while the ruthenate LaCu3Ru4O12 ( x = 4) is known as a rare d-electron derived heavy-fermion compound. Detailed structural investigations, AC- and DC-magnetization measurements, resistivity, specific-heat, and magnetic-resonance investigations have been performed for all polycrystalline compounds prepared by solid-state synthesis. These experiments have been accompanied by band-structure calculations. Close to the Ru concentration x = 2 we identify a quantum-critical point coinciding with a metal-to-insulator transition. The quantum-critical point separates an insulating spin glass from a paramagnetic metal. Interestingly, there is no evidence for a divergence of the effective mass upon reaching the quantum-critical point from the metallic side. In the paramagnetic metal, Ru behaves like a canonical Kondo ion. While the Ru oxidation state remains stable at + 4 for the whole concentration regime, the Cu valence seems to decrease from + 2 in the insulating antiferromagnet with localized copper spins to a significantly lower value in the metallic heavy-fermion compounds.
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. PMID:25880601
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
2015-01-01
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
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
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}.
Logarithmic temperature dependence of samarium ion valence in the heavy-fermion S mxL a1 -xO s4S b12
NASA Astrophysics Data System (ADS)
Fushiya, Kengo; Miyazaki, Ryoichi; Higashinaka, Ryuji; Yamada, Akira; Mizumaki, Masaichiro; Tsutsui, Satoshi; Nitta, Kiyofumi; Uruga, Tomoya; Suemitsu, Bunya; Sato, Hideyuki; Aoki, Yuji
2015-08-01
We have measured x-ray absorption spectra at the Sm L3 edge to investigate the Sm-ion valence of (S mxL a1 -x) O s4S b12 , in which field-insensitive heavy-fermion behavior appears at low temperatures for x =1 . It has been found that the Sm-ion valance shifts to 2 + with La ion substitution; from v =+2.78 (x =1 ) to v =+2.73 (x =0.2 ) at 10 K. For all x investigated, its temperature dependence shows a logT behavior, indicating that the valence change is caused by "an unconventional Kondo effect" associated with Sm 4 f -electron charge degrees of freedom. Almost x independence of "the associated Kondo temperature" (T˜K=56 ±10 K ) indicates that the Kondo effect has a local nature, attributable to the cage structure of the filled skutterudite.
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.
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
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
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 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 Fe1xMxSi (x = 0; 0:02; 0:04; 0:1) was investigated with a combination of inelastic neutron scattering (INS), transport measurements, and rst-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 and increases electron-phonon coupling, leads to softened interatomic force-constantsmore » 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 rst-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. 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)
Zhao, Zuyu
1990-06-01
Two nonconventional superfluids, superfluid ^3He-B and the heavy fermion superconductor UPt_3 have been studied using different techniques: (1) A study of ^3He -B was performed in an acoustic sound cell with a path length of 381mum using the single-ended, c.w., acoustic impedance technique. The fundamental frequency of the x-cut quartz transducer employed in the experiments was 12.80 MHz. The following studies were performed: (a) A systematic measurement was made on the pair-breaking edge in zero magnetic field with ultrasonic frequencies of 64.3 MHz, 90.1 MHz, 141.6 MHz and 167.4 MHz, in the pressure range from 3 bar to 28 bar. The results of our measurements indirectly support the temperature scale of Greywall and the weak coupling plus (WCP) model of Rainer and Serene for the gap function. The pair-breaking edge was also measured in magnetic fields up to 1.36 kG perpendicular to the sound propagation direction and the predicted shift of the effective pair-breaking threshold (from 2 Delta(T) in zero field) by Omega = {gamma Hover 1+{1 over3}F_sp{o}{a}(2+Y) }(the renormalized Larmor frequency) has been observed. (b) The (imaginary) squashing mode was excited with sound frequencies of 141.6 MHz and 115.8 MHz. A doublet splitting (of about 0.3 MHz) of this mode was observed. This doublet splitting was found to be strongly pressure and frequency dependent, but independent of the magnetic field (at the low fields studied). Possible causes of this splitting include superfluid flow induced texture effects and finite wavevector (dispersion) effects. (c) Structure was observed with a sound frequency of 64.3 MHz in the vicinity of 2Delta(T) in a magnetic field of about 580 Gauss which is thought to be J_{z} = -1 component of the J = 1^- collective mode. (2) A surface impedance study of heavy Fermion superconductor UPt_3 was performed with an X-band microwave spectrometer (f ~eq 11.42 GHz) integrated with an Oxford 400 TLE dilution refrigerator so as to have top
NASA Astrophysics Data System (ADS)
Wu, Liang-Kai; Meng, Xiang-Fei
2014-11-01
The phase structure of QCD with imaginary chemical potential provides information on the phase diagram of QCD with real chemical potential. With imaginary chemical potential i μI=i π T , previous studies show that the Roberge-Weiss (RW) transition endpoints are triple points at both large and small quark masses, and second order transition points at intermediate quark masses. The triple and second order endpoints are separated by two tricritical ones. We present simulations with Nf=2 Wilson fermions to investigate the nature of RW transition endpoints. The simulations are carried out at 8 values of the hopping parameter κ ranging from 0.020 to 0.140 on different lattice volumes. The Binder cumulant, susceptibility, and reweighted distribution of the imaginary part of the Polyakov loop are employed to determine the nature of RW transition endpoints. The simulations show that the two tricritical points are within the ranges 0.070-0.080 and 0.120-0.140, respectively.
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
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)
Shimozawa, M.; Goh, S. K.; Endo, R.; Kobayashi, R.; Watashige, T.; Mizukami, Y.; Ikeda, H.; Shishido, H.; Yanase, Y.; Terashima, T.; Shibauchi, T.; Matsuda, Y.
2014-04-01
By using a molecular beam epitaxy technique, we fabricate a new type of superconducting superlattices with controlled atomic layer thicknesses of alternating blocks between the heavy-fermion superconductor CeCoIn5, which exhibits a strong Pauli pair-breaking effect, and nonmagnetic metal YbCoIn5. The introduction of the thickness modulation of YbCoIn5 block layers breaks the inversion symmetry centered at the superconducting block of CeCoIn5. This configuration leads to dramatic changes in the temperature and angular dependence of the upper critical field, which can be understood by considering the effect of the Rashba spin-orbit interaction arising from the inversion symmetry breaking and the associated weakening of the Pauli pair-breaking effect. Since the degree of thickness modulation is a design feature of this type of superlattices, the Rashba interaction and the nature of pair breaking are largely tunable in these modulated superlattices with strong spin-orbit coupling.
NASA Astrophysics Data System (ADS)
Ślebarski, A.; Goraus, J.; Witas, P.
2015-10-01
The effect of pressure on electrical resistivity of heavy-fermion compounds Ce3M4Sn13 , where M =Co , Rh, Ru, and the La3M4Sn13 counterparts is studied in the framework of the fully relativistic full potential local orbital method. The experiment shows that the electrical resistivity of Ce3Co4Sn13 and Ce3Rh4Sn13 increases with pressure, a similar pressure effect is obtained for isostructural La-based reference metals, while opposite behaviors under pressure are documented for Ce3Ru4Sn13 and La3Ru4Sn13 . The contrasting pressure dependent effects of Ce3Co4Sn13 and Ce3Ru4Sn13 are discussed. In order to clarify the various phenomena the band-structure calculations under applied pressure were performed. Here, we show that the resistivity increase with pressure arises from the formation of interband distances at the Fermi level in Ce3Co4Sn13 , this pseudo-gap-like effect is also pressure dependent, while in Ce3Ru4Sn13 the opposite change of resistivity results from the suppression of spin fluctuations under pressure.
NASA Astrophysics Data System (ADS)
Bossé, G.; Pan, LiDong; Li, Yize S.; Greene, L. H.; Eckstein, J.; Armitage, N. P.
2016-02-01
We present THz range optical conductivity data of a thin film of the near quantum critical heavy-fermion compound CeFe2Ge2 . Our complex conductivity measurements find a deviation from conventional Drude-like transport in a temperature range previously reported to exhibit unconventional behavior. We calculate the frequency-dependent effective mass and scattering rate using an extended Drude model analysis. We find the inelastic scattering rate can be described by a temperature-dependent power law ωn (T ), where n (T ) approaches ˜1.0 ±0.2 at 1.5 K. This is compared to the ρ ˜T1.5 behavior claimed in dc resistivity data and the ρ ˜T2 expected from Fermi-liquid theory. In addition to a low-temperature mass renormalization, we find an anomalous mass renormalization that persists to high temperature. We attribute this to a Hund's coupling in the Fe states in a manner similar to that recently proposed in the ferropnictides. CeFe2Ge2 appears to be a very interesting system where one may study the interplay between the usual 4 f lattice Kondo effect and this Hund's enhanced Kondo effect in the 3 d states.
NASA Astrophysics Data System (ADS)
Park, W. K.; Elenewski, J. E.; Aubin, H.; Greene, L. H.; Sarrao, J. L.; Thompson, J. D.
2003-03-01
We have built a cantilever-Andreev-tunneling (CAT) rig, designed to work in a 3He cryostat down to 300 mK. By combining a coarse approach based on a screw mechanism, and a fine approach using piezoelectric elements, we can control the tip-sample distance to sub-nm length-scales, as shown by our ability to reproducibly go from the tunneling to Andreev regimes on Nb films. Aluminum wire with a flat end surface coated with its natural oxide as the tunnel barrier is used as a tip, assuring a robust planar tunneling geometry instead of point contact or STM geometry. This technique has the advantages of enhancing the directionality of tunneling electrons' momenta and allowing temperature and field dependencies to be explored. Furthermore, this mechanically controlled planar junction technique is particularly suited for tunneling experiments with fragile superconductors, such as newly discovered heavy-Fermion superconductor CeCoIn5, which cannot be easily made into planar junctions. We will report our planar tunneling spectroscopy results on superconducting CeCoIn5 single crystals, and discuss the underlying pairing symmetry of this material.
NASA Astrophysics Data System (ADS)
Hattori, Kazumasa
2010-11-01
We investigate a two-orbital Anderson lattice model with Ising orbital intersite exchange interactions on the basis of a dynamical mean field theory combined with the static mean field approximation of intersite orbital interactions. Focusing on Ce-based heavy-fermion compounds, we examine the orbital crossover between two orbital states, when the total f-electron number per site nf is ˜1. We show that a “meta-orbital” transition, at which the occupancy of two orbitals changes steeply, occurs when the hybridization between the ground-state f-electron orbital and conduction electrons is smaller than that between the excited f-electron orbital and conduction electrons at low pressures. Near the meta-orbital critical end point, orbital fluctuations are enhanced and couple with charge fluctuations. A critical theory of meta-orbital fluctuations is also developed by applying the self-consistent renormalization theory of itinerant electron magnetism to orbital fluctuations. The critical end point, first-order transition, and crossover are described within Gaussian approximations of orbital fluctuations. We discuss the relevance of our results to CeAl2, CeCu2Si2, CeCu2Ge2, and related compounds, which all have low-lying crystalline-electric-field excited states.
Crystal Field Excitations in a Frustrated Heavy Fermion System, Pr_1.2Bi_0.8Ru_2O_7
NASA Astrophysics Data System (ADS)
van Duijn, Joost; Broholm, Collin; Adroja, Devashibhai; Perring, Toby; Adams, Mark; Hur, N.; Cheong, S.-W.
2004-03-01
Pr_1-xBi_xRu_2O7 is a recently pyrochlore oxide, with the Pr and Bi ions randomly distributed on octahedral sites. For x≈ 1 it is one of the few highly frustrated magnetic materials that is also metallic and it displays strongly renormalize low T properties. For x=1.2 the low temperature coefficient to the linear term of the specific heat (γ _S= 0.7 J/mole K^2) is for example more than 3 orders of magnitude larger than for a simple independent electron system. This material also fails to develop long-range magnetic ordering down to 2 K. Magnetic neutron scattering experiments have been carried out using the HET and IRIS spectrometers at the ISIS facility. Five Pr crystal field transitions in were found in the energy range from 10-120 meV. Analysis of the data indicates that the ground state is a doublet with a first excited singlet at 10 meV. The ground state doublet has a quasi-elastic response that is likely the origin of heavy fermion behavior in this system. This research was funded by the U.S. Department of Energy, under Grant No. DE-FG02-02ER45983, and by the National Science Foundation, under Grant No. NSF-DMR-0103858.
NASA Technical Reports Server (NTRS)
Strecker, Kevin; Truscott, Andrew; Partridge, Guthrie; Chen, Ying-Cheng
2003-01-01
Dual evaporation gives 50 million fermions at T = 0.1 T(sub F). Demonstrated suppression of interactions by coherent superposition - applicable to atomic clocks. Looking for evidence of Cooper pairing and superfluidity.
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.
NASA Astrophysics Data System (ADS)
Deppe, M.; Hartmann, S.; Macovei, M. E.; Oeschler, N.; Nicklas, M.; Geibel, C.
2008-09-01
We grew single crystals of Yb2Pt6Al15 and investigated the magnetic properties of this compound by means of susceptibility χ(T), specific heat C(T), resistivity ρ (T) and thermoelectric power S(T) measurements. While all properties follow in general the behavior typical for Kondo-lattice systems, χ(T) and C(T)/T present broad maxima in the T range 17 35 K, which matches nicely the prediction of the Coqblin Schrieffer model for J= 7/2. A large degeneracy of the local moment is also supported by a reduced Kadowaki Woods ratio. Thus, the analysis of all investigated properties evidences Yb2Pt6Al15 to be a paramagnetic Kondo-lattice system with the whole J= 7/2 multiplet involved in the formation of the Kondo state, a Kondo temperature of the order of 60 K, and a heavy Fermi-liquid ground state with a Sommerfeld coefficient γ 0 = 0.33 J (mol-Yb)-1 K-2 corresponding to a mass enhancement of the order of 30.
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.
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)
Wang, Zhijun; Alexandradinata, A.; Cava, Robert J.; Bernevig, B. Andrei
Spatial symmetries in crystals are distinguished by whether they preserve the spatial origin. We show how this basic geometric property gives rise to a new topology in band insulators. We study spatial symmetries that translate the origin by a fraction of the lattice period, and find that these nonsymmorphic symmetries protect a novel surface fermion whose dispersion is shaped like an hourglass; surface bands connect one hourglass to the next in an unbreakable zigzag pattern. These exotic fermions are materialized in the large-gap insulators: KHg X (X = As,Sb,Bi), which we propose as the first material class whose topology relies on nonsymmorphic symmetries. Beside the hourglass fermion, a different surface of KHg X manifests a 3D generalization of the quantum spin Hall effect. To describe the bulk topology of nonsymmorphic crystals, we propose a non-Abelian generalization of the geometric theory of polarization. Our nontrivial topology originates not from an inversion of the parity quantum numbers, but rather of the rotational quantum numbers, which we propose as a fruitful in the search for topological materials. Finally, KHg X uniquely exemplifies a cohomological insulator, a concept that we will introduce in a companion work.
Resistance minimum and heavy fermions.
Jun, Kondo
2006-12-01
The phenomenon of the resistance minimum in dilute magnetic alloys is explained in terms of the s-d interaction which takes account of scattering of the conduction electron off the magnetic impurities in metals. Some of the intermetallic compounds which involve rare earth elements or uranium show a very large electronic specific heat and remain non-magnetic even though they show a Curie-like susceptibility at higher temperatures. These phenomena are also explained based on the s-d interaction model. PMID:25792794
Resistance minimum and heavy fermions
Jun, Kondo
2006-01-01
The phenomenon of the resistance minimum in dilute magnetic alloys is explained in terms of the s-d interaction which takes account of scattering of the conduction electron off the magnetic impurities in metals. Some of the intermetallic compounds which involve rare earth elements or uranium show a very large electronic specific heat and remain non-magnetic even though they show a Curie-like susceptibility at higher temperatures. These phenomena are also explained based on the s-d interaction model. PMID:25792794
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
Kumar, Ravhi S.; Svane, Axel; Vaitheeswaran, Ganapathy; Kanchana, Venkatakrishnan; Antonio, Daniel; Cornelius, Andrew L.; Bauer, Eric D.; Xiao, Yuming; Chow, Paul
2015-10-19
The crystal structure and the Yb valence of the YbFe_{2}Ge_{2} heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. Furthermore, the measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr_{2}Si_{2}-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ~9 GPa, where at low temperature a pressure-induced quantum critical state was reported.
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}.
Kumar, Ravhi S; Svane, Axel; Vaitheeswaran, Ganapathy; Kanchana, Venkatakrishnan; Antonio, Daniel; Cornelius, Andrew L; Bauer, Eric D; Xiao, Yuming; Chow, Paul
2015-11-01
The crystal structure and the Yb valence of the YbFe2Ge2 heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. The measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr2Si2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ∼9 GPa, where at low temperature a pressure-induced quantum critical state was reported. PMID:26479903
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.
Chiral fermions in asymptotically safe quantum gravity
NASA Astrophysics Data System (ADS)
Meibohm, J.; Pawlowski, J. M.
2016-05-01
We study the consistency of dynamical fermionic matter with the asymptotic safety scenario of quantum gravity using the functional renormalisation group. Since this scenario suggests strongly coupled quantum gravity in the UV, one expects gravity-induced fermion self-interactions at energies of the Planck scale. These could lead to chiral symmetry breaking at very high energies and thus to large fermion masses in the IR. The present analysis which is based on the previous works (Christiansen et al., Phys Rev D 92:121501, 2015; Meibohm et al., Phys Rev D 93:084035, 2016), concludes that gravity-induced chiral symmetry breaking at the Planck scale is avoided for a general class of NJL-type models. We find strong evidence that this feature is independent of the number of fermion fields. This finding suggests that the phase diagram for these models is topologically stable under the influence of gravitational interactions.
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.
NASA Astrophysics Data System (ADS)
Takeda, Hikaru; Kato, Yusuke; Yoshimura, Masahiro; Shimizu, Yasuhiro; Itoh, Masayuki; Niitaka, Seiji; Takagi, Hidenori
2015-07-01
7Li and 51V NMR measurements up to 9.8 GPa have been made to elucidate local magnetic properties of a heavy-fermion spinel oxide LiV2O4 which undergoes a metal-insulator transition above ˜7 GPa. The temperature T and pressure P dependences of the 7Li and 51V Knight shifts and the nuclear spin-lattice relaxation rates 1 /T1 show that in the metallic phase, there is a crossover from a high-T region with weak ferromagnetic fluctuations to a low-T one with antiferromagnetic (AFM) fluctuations. The AFM fluctuations are enhanced below 20 K and 1.5 GPa, where a heavy Fermi-liquid state with the modified Korringa relation is formed. The evolution of the magnetic fluctuations is discussed from the aspect of the competition among several magnetic interactions. Above PMI˜6.7 GPa, we find the coexistence of metallic and insulating phases due to the first-order metal-insulator transition. The 7Li and 51V NMR spectra coming from the insulating phase have T -independent small Knight shifts and 7(1 /T1 ) with the thermally activated T dependence, indicating the formation of a spin-singlet cluster. We propose a model of a spin-singlet tetramer as discussed in geometrically frustrated materials.
Fermionization and Hubbard models
NASA Astrophysics Data System (ADS)
Dargis, P.; Maassarani, Z.
1998-12-01
We introduce a transformation which allows the fermionization of operators of any one-dimensional spin-chain. This fermionization procedure is independent of any eventual integrable structure and is compatible with it. We illustrate this method on various integrable and non-integrable chains, and deduce some general results. In particular, we fermionize XXC spin-chains and study their symmetries. Fermionic realizations of certain Lie algebras and superalgebras appear naturally as symmetries of some models. We also fermionize recently obtained Hubbard models, and obtain for the first time multispecies analogues of the Hubbard model, in their fermionic form. We comment on the conflict between symmetry enhancement and integrability of these models. Finally, the fermionic versions of the non-integrable spin-1 and spin- {3}/{2} Heisenberg chains are obtained.
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)
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, 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.
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.
Resonant pairing between fermions with unequal masses
Wu, Shin-Tza; Pao, C.-H.; Yip, S.-K.
2006-12-01
We study via mean-field theory the pairing between fermions of different masses, especially at the unitary limit. At equal populations, the thermodynamic properties are identical with the equal mass case provided an appropriate rescaling is made. At unequal populations, for sufficiently light majority species, the system does not phase separate. For sufficiently heavy majority species, the phase separated normal phase have a density larger than that of the superfluid. For atoms in harmonic traps, the density profiles for unequal mass fermions can be drastically different from their equal-mass counterparts.
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.
NMR evidence of anisotropic Kondo liquid behavior in CeIrIn5
NASA Astrophysics Data System (ADS)
Shockley, A. C.; Shirer, K. R.; Crocker, J.; Dioguardi, A. P.; Lin, C. H.; Nisson, D. M.; apRoberts-Warren, N.; Klavins, P.; Curro, N. J.
2015-08-01
We report detailed Knight-shift measurements of the two indium sites in the heavy-fermion compound CeIrIn5 as a function of temperature and field orientation. We find that the Knight-shift anomaly is orientation dependent, with a crossover temperature T* that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce 4 f states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity.
Superconductivity Induced by Surface Polishing in CeIrSi3
NASA Astrophysics Data System (ADS)
Iida, Hiroki; Sato, Masashi; Kimura, Noriaki
2016-07-01
We show that superconductivity observed in the antiferromagnetic state of CeIrSi3, a pressure-induced heavy fermion superconductor, is mainly due to a surface layer induced by mechanical polishing. The superconducting reduction of the electrical resistivity in the antiferromagnetic state strongly depends on the strength of the applied electrical current and dissipates after a heat treatment. These results indicate that mechanical polishing causes an inhomogeneous distortion on the surface of the sample and locally produces a high-pressure region in which the bulk superconductivity arises.
Entanglement in fermionic systems
Banuls, Mari-Carmen; Cirac, J. Ignacio; Wolf, Michael M.
2007-08-15
The anticommuting properties of fermionic operators, together with the presence of parity conservation, affect the concept of entanglement in a composite fermionic system. Hence different points of view can give rise to different reasonable definitions of separable and entangled states. Here we analyze these possibilities and the relationship between the different classes of separable states. The behavior of the various classes when taking multiple copies of a state is also studied, showing that some of the differences vanish in the asymptotic regime. In particular, in the case of only two fermionic modes all the classes become equivalent in this limit. We illustrate the differences and relations by providing a complete characterization of all the sets defined for systems of two fermionic modes. The results are applied to Gibbs states of infinite chains of fermions whose interaction corresponds to a XY Hamiltonian with transverse magnetic field.
NASA Astrophysics Data System (ADS)
Shimizu, Yusei; Kittaka, Shunichiro; Sakakibara, Toshiro; Tsutsumi, Yasumasa; Nomoto, Takuya; Ikeda, Hiroaki; Machida, Kazushige; Homma, Yoshiya; Aoki, Dai
2016-07-01
Quasiparticle excitations in UPd2 Al3 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 )∝H1 /2-like behavior at low temperatures for both two hexagonal crystal axes, i.e., H ∥[0001 ] (c axis) and H ∥[11 2 ¯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 ≲μ0H ≲2 T ). These behaviors in UPd2 Al3 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.
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
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
NASA Astrophysics Data System (ADS)
Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran
2016-03-01
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 C T . We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N . We also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.
Fermions from classical statistics
Wetterich, C.
2010-12-15
We describe fermions in terms of a classical statistical ensemble. The states {tau} of this ensemble are characterized by a sequence of values one or zero or a corresponding set of two-level observables. Every classical probability distribution can be associated to a quantum state for fermions. If the time evolution of the classical probabilities p{sub {tau}} amounts to a rotation of the wave function q{sub {tau}}(t)={+-}{radical}(p{sub {tau}}(t)), we infer the unitary time evolution of a quantum system of fermions according to a Schroedinger equation. We establish how such classical statistical ensembles can be mapped to Grassmann functional integrals. Quantum field theories for fermions arise for a suitable time evolution of classical probabilities for generalized Ising models.
NASA Astrophysics Data System (ADS)
Weiner, Richard M.
2010-05-01
It is conjectured that all known fermions are topological solitons. This could explain the non-observation of bosonic leptons and baryons and provide a physical mechanism for the Pauli exclusion principle.
Canonical gravity with fermions
Bojowald, Martin; Das, Rupam
2008-09-15
Canonical gravity in real Ashtekar-Barbero variables is generalized to allow for fermionic matter. The resulting torsion changes several expressions in Holst's original vacuum analysis, which are summarized here. This in turn requires adaptations to the known loop quantization of gravity coupled to fermions, which is discussed on the basis of the classical analysis. As a result, parity invariance is not manifestly realized in loop quantum gravity.
Inductive Measurements of Heavy Fermion Superconductors
NASA Astrophysics Data System (ADS)
Signore, Philippe Jean-Claude
Experimental results are presented on the temperature dependence of the penetration depth, lambda (T), in UPt_3, and on the upper critical field, B_{rm c2 }(T), of UBe_{13}. The objective of this work was to obtain a better understanding of the unusual superconductivity in these materials. The inductive response of eight UPt_3 samples obtained from seven different materials fabrication groups was measured from 50 to 700 mK at frequencies varying between 32 Hz and 33 MHz. The low frequency ( <=4.7 kHz) data suggest a linear temperature dependence of lambda(T/T _{rm c} <= 0.5) for the samples possessing a double feature near the superconducting transition temperature, T_{rm c}. We have verified that this double feature present in lambda(T) for some of the samples corresponds to the double jump observed in the specific heat. On the other hand, lambda (T/T_{rm c} <= 0.5) was found to have a quadratic temperature dependence for unannealed specimens which exhibit only a single transition at T_{rm c}. The linear temperature dependence in lambda(T) is consistent with the presence of line nodes in the basal plane, while the quadratic dependence found for other samples indicates that impurity scattering dominates in these specimens. The double transition in lambda(T) has been studied in magnetic fields up to 1.6 T for one of the specimens, and the resulting phase diagram is consistent with the one constructed from thermodynamical measurements. The high frequency ( >=3 MHz) data suggest lambda (T/T_{rm c} <= 0.5) ~ {rm T}^eta, where 2<=eta<=4. The possible origins of the frequency dependence of lambda(T) are discussed, as well as the effect of the surface quality on eta. Using sensitive mutual induction techniques, we have systematically measured B_{rm c2}(T) for three UBe_{13 } single crystals in fields up to 8 T oriented along the (100) and (110) directions, with particular emphasis on the region near the zero field critical temperature. In that low field regime and within our experimental uncertainties of 0.5 mK and 0.5 mT, no anisotropy in B_ {rm c2}(T) was observable for any of the samples. For one of these specimens, an anomaly in chi^'(B,T) was observed below the superconducting transition. The complete B_{rm c2}(T) phase diagrams are presented and compared to the results of other workers. The temperature dependence of the penetration depth down to 50 mK and in zero field is measured on two of the crystals.
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.
Grossman, Yuval; Harnik, Roni; Perez, Gilad; Schwartz, MatthewD.; Surujon, Ze'ev
2004-07-30
The observed flavor structure of the standard model arises naturally in ''split fermion'' models which localize fermions at different places in an extra dimension. It has, until now, been assumed that the bulk masses for such fermions can be chosen to be flavor diagonal simultaneously at every point in the extra dimension, with all the flavor violation coming from the Yukawa couplings to the Higgs. We consider the more natural possibility in which the bulk masses cannot be simultaneously diagonalized, that is, that they are twisted in flavor space. We show that, in general, this does not disturb the natural generation of hierarchies in the flavor parameters. Moreover, it is conceivable that all the flavor mixing and CP-violation in the standard model may come only from twisting, with the five-dimensional Yukawa couplings taken to be universal.
Grossman, Y
2004-07-24
The observed flavor structure of the standard model arises naturally in ''split fermion'' models which localize fermions at different places in an extra dimension. It has, until now, been assumed that the bulk masses for such fermions can be chosen to be flavor diagonal simultaneously at every point in the extra dimension, with all the flavor violation coming from the Yukawa couplings to the Higgs. We consider the more natural possibility in which the bulk masses cannot be simultaneously diagonalized, that is, that they are twisted in flavor space. We show that, in general, this does not disturb the natural generation of hierarchies in the flavor parameters. Moreover, it is conceivable that all the flavor mixing and CP-violation in the standard model may come only from twisting, with the five-dimensional Yukawa couplings taken to be universal.
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.
Scattering of universal fermionic clusters in the resonating group method
NASA Astrophysics Data System (ADS)
Naidon, Pascal; Endo, Shimpei; García-García, Antonio M.
2016-02-01
Mixtures of polarized fermions of two different masses can form weakly bound clusters, such as dimers and trimers, that are universally described by the scattering length between the heavy and light fermions. We use the resonating group method to investigate the low-energy scattering processes involving dimers or trimers. The method reproduces approximately the known particle–dimer and dimer–dimer scattering lengths. We use it to estimate the trimer–trimer scattering length, which is presently unknown, and find it to be positive.
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.
Probing the fermionic Higgs portal at lepton colliders
NASA Astrophysics Data System (ADS)
Fedderke, Michael A.; Lin, Tongyan; Wang, Lian-Tao
2016-04-01
We study the sensitivity of future electron-positron colliders to UV completions of the fermionic Higgs portal operator {H}^{dagger }{H}_{overline{χ}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 provide 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.
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.
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.
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.
Open fermionic quantum systems
Artacho, E.; Falicov, L.M. Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 )
1993-01-15
A method to treat a quantum system in interaction with a fermionic reservoir is presented. Its most important feature is that the dynamics of the exchange of particles between the system and the reservoir is explicitly included via an effective interaction term in the Hamiltonian. This feature gives rise to fluctuations in the total number of particles in the system. The system is to be considered in its full structure, whereas the reservoir is described only in an effective way, as a source of particles characterized by a small set of parameters. Possible applications include surfaces, molecular clusters, and defects in solids, in particular in highly correlated electronic materials. Four examples are presented: a tight-binding model for an adsorbate on the surface of a one-dimensional lattice, the Anderson model of a magnetic impurity in a metal, a two-orbital impurity with interorbital hybridization (intermediate-valence center), and a two-orbital impurity with interorbital repulsive interactions.
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.
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.
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.
NASA Technical Reports Server (NTRS)
Messerschmid, Ernst
1991-01-01
Charts and graphs relative to magnetoplasmadynamic (MPD) thruster technology are given. The research activities at the Institute of Space Transportation, University of Stuttgart, are summarized. Information is given on the Institute's Electric Propulsion and Plasma Wind Tunnel; thermal arcjet research; the nozzle-type thruster, DT-IRS; nozzle-type MPD thrusters; a hot anode thruster; the DT6 thruster; the ZT-1 thruster; the cylindrical MPD thruster; and a comparison of continuous and quasi-steady MPD.
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.
New chiral fermions, a new gauge interaction, Dirac neutrinos, and dark matter
NASA Astrophysics Data System (ADS)
de Gouvêa, André; Hernández, Daniel
2015-10-01
We propose that all light fermionic degrees of freedom, including the Standard Model (SM) fermions and all possible light beyond-the-standard-model fields, are chiral with respect to some spontaneously broken abelian gauge symmetry. Hypercharge, for example, plays this role for the SM fermions. We introduce a new symmetry, U(1) ν , for all new light fermionic states. Anomaly cancellations mandate the existence of several new fermion fields with nontrivial U(1) ν charges. We develop a concrete model of this type, for which we show that (i) some fermions remain massless after U(1) ν breaking — similar to SM neutrinos — and (ii) accidental global symmetries translate into stable massive particles — similar to SM protons. These ingredients provide a solution to the dark matter and neutrino mass puzzles assuming one also postulates the existence of heavy degrees of freedom that act as "mediators" between the two sectors. The neutrino mass mechanism described here leads to parametrically small Dirac neutrino masses, and the model also requires the existence of at least four Dirac sterile neutrinos. Finally, we describe a general technique to write down chiral-fermions-only models that are at least anomaly-free under a U(1) gauge symmetry.
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.
Fermionic influence on inflationary fluctuations
NASA Astrophysics Data System (ADS)
Boyanovsky, Daniel
2016-04-01
Motivated by apparent persistent large scale anomalies in the cosmic microwave background we study the influence of fermionic degrees of freedom on the dynamics of inflaton fluctuations as a possible source of violations of (nearly) scale invariance on cosmological scales. We obtain the nonequilibrium effective action of an inflaton-like scalar field with Yukawa interactions (YD ,M) to light fermionic degrees of freedom both for Dirac and Majorana fields in de Sitter space-time. The effective action leads to Langevin equations of motion for the fluctuations of the inflaton-like field, with self-energy corrections and a stochastic Gaussian noise. We solve the Langevin equation in the super-Hubble limit implementing a dynamical renormalization group resummation. For a nearly massless inflaton its power spectrum of super-Hubble fluctuations is enhanced, P (k ;η )=(H/2 π )2eγt[-k η ] with γt[-k η ]=1/6 π2 [∑i =1 NDYi,D 2+2 ∑j =1 NMYj,M 2]{ln2[-k η ]-2 ln [-k η ]ln [-k η0]} for ND Dirac and NM Majorana fermions, and η0 is the renormalization scale at which the inflaton mass vanishes. The full power spectrum is shown to be renormalization group invariant. These corrections to the super-Hubble power spectrum entail a violation of scale invariance as a consequence of the coupling to the fermionic fields. The effective action is argued to be exact in the limit of a large number of fermionic fields. A cancellation between the enhancement from fermionic degrees of freedom and suppression from light scalar degrees of freedom conformally coupled to gravity suggests the possibility of a finely tuned supersymmetry among these fields.
Fermionic composite models from complementarity
NASA Astrophysics Data System (ADS)
Bordi, F.; Casalbuoni, R.; Dominici, D.; Gatto, R.
1982-08-01
Composite models for (in principle massless) quarks and leptons without fundamental scalars are constructed with the aim of providing for fermionic realizations of models which include elementary bosons (by Abbott and Farhi, Casalbuoni and Gatto and Barbieri, Mohapatra and Masiero). The models use one confining unitary (subcolor) group (with left-handed fermions in the fundamental, in its conjugate, and either in the adjoint, or in the symmetric, or in the antisymmetric representation of subcolor) or two confining groups. Families may arise from discrete symmetries.
Searches for excited fermions in /ep collisions at HERA
NASA Astrophysics Data System (ADS)
ZEUS Collaboration; Chekanov, S.; Derrick, M.; Krakauer, D.; Magill, S.; Musgrave, B.; Pellegrino, A.; Repond, J.; Yoshida, R.; Mattingly, M. C. K.; Antonioli, P.; Bari, G.; Basile, M.; Bellagamba, L.; Boscherini, D.; Bruni, A.; Bruni, G.; Cara Romeo, G.; Cifarelli, L.; Cindolo, F.; Contin, A.; Corradi, M.; de Pasquale, S.; Giusti, P.; Iacobucci, G.; Levi, G.; Margotti, A.; Massam, T.; Nania, R.; Palmonari, F.; Pesci, A.; Sartorelli, G.; Zichichi, A.; Aghuzumtsyan, G.; Brock, I.; Goers, S.; Hartmann, H.; Hilger, E.; Irrgang, P.; Jakob, H.-P.; Kappes, A.; Katz, U. F.; Kerger, R.; Kind, O.; Paul, E.; Rautenberg, J.; Schnurbusch, H.; Stifutkin, A.; Tandler, J.; Voss, K. C.; Weber, A.; Wieber, H.; Bailey, D. S.; Brook, N. H.; Cole, J. E.; Foster, B.; Heath, G. P.; Heath, H. F.; Robins, S.; Rodrigues, E.; Scott, J.; Tapper, R. J.; Wing, M.; Capua, M.; Mastroberardino, A.; Schioppa, M.; Susinno, G.; Jeoung, H. Y.; Kim, J. Y.; Lee, J. H.; Lim, I. T.; Ma, K. J.; Pac, M. Y.; Caldwell, A.; Helbich, M.; Liu, X.; Mellado, B.; Paganis, S.; Schmidke, W. B.; Sciulli, F.; Chwastowski, J.; Eskreys, A.; Figiel, J.; Klimek, K.; Olkiewicz, K.; Przybycień, M. B.; Stopa, P.; Zawiejski, L.; Bednarek, B.; Grabowska-Bold, I.; Jeleń, K.; Kisielewska, D.; Kowal, A. M.; Kowal, M.; Kowalski, T.; Mindur, B.; Przybycień, M.; Rulikowska-Zarȩbska, E.; Suszycki, L.; Szuba, D.; Szuba, J.; Kotański, A.; Bauerdick, L. A. T.; Behrens, U.; Borras, K.; Chiochia, V.; Crittenden, J.; Dannheim, D.; Desler, K.; Drews, G.; Fox-Murphy, A.; Fricke, U.; Geiser, A.; Goebel, F.; Göttlicher, P.; Graciani, R.; Haas, T.; Hain, W.; Hartner, G. F.; Hebbel, K.; Hillert, S.; Kötz, U.; Kowalski, H.; Labes, H.; Löhr, B.; Mankel, R.; Martens, J.; Martínez, M.; Milite, M.; Moritz, M.; Notz, D.; Petrucci, M. C.; Polini, A.; Schneekloth, U.; Selonke, F.; Stonjek, S.; Surrow, B.; Whitmore, J. J.; Wichmann, R.; Wolf, G.; Youngman, C.; Zeuner, W.; Coldewey, C.; Lopez-Duran Viani, A.; Meyer, A.; Schlenstedt, S.; Barbagli, G.; Gallo, E.; Pelfer, P. G.; Bamberger, A.; Benen, A.; Coppola, N.; Markun, P.; Raach, H.; Wölfle, S.; Bell, M.; Bussey, P. J.; Doyle, A. T.; Glasman, C.; Lee, S. W.; Lupi, A.; McCance, G. J.; Saxon, D. H.; Skillicorn, I. O.; Bodmann, B.; Gendner, N.; Holm, U.; Salehi, H.; Wick, K.; Yildirim, A.; Ziegler, A.; Carli, T.; Garfagnini, A.; Gialas, I.; Lohrmann, E.; Foudas, C.; Gonçalo, R.; Long, K. R.; Metlica, F.; Miller, D. B.; Tapper, A. D.; Walker, R.; Cloth, P.; Filges, D.; Kuze, M.; Nagano, K.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Barakbaev, A. N.; Boos, E. G.; Pokrovskiy, N. S.; Zhautykov, B. O.; Ahn, S. H.; Lee, S. B.; Park, S. K.; Lim, H.; Son, D.; Barreiro, F.; García, G.; González, O.; Labarga, L.; del Peso, J.; Redondo, I.; Terrón, J.; Vázquez, M.; Barbi, M.; Bertolin, A.; Corriveau, F.; Ochs, A.; Padhi, S.; Stairs, D. G.; St-Laurent, M.; Tsurugai, T.; Antonov, A.; Bashkirov, V.; Danilov, P.; Dolgoshein, B. A.; Gladkov, D.; Sosnovtsev, V.; Suchkov, S.; Dementiev, R. K.; Ermolov, P. F.; Golubkov, Yu. A.; Katkov, I. I.; Khein, L. A.; Korotkova, N. A.; Korzhavina, I. A.; Kuzmin, V. A.; Levchenko, B. B.; Lukina, O. Yu.; Proskuryakov, A. S.; Shcheglova, L. M.; Solomin, A. N.; Vlasov, N. N.; Zotkin, S. A.; Bokel, C.; Engelen, J.; Grijpink, S.; Koffeman, E.; Kooijman, P.; Maddox, E.; Schagen, S.; Tassi, E.; Tiecke, H.; Tuning, N.; Velthuis, J. J.; Wiggers, L.; de Wolf, E.; Brümmer, N.; Bylsma, B.; Durkin, L. S.; Gilmore, J.; Ginsburg, C. M.; Kim, C. L.; Ling, T. Y.; Boogert, S.; Cooper-Sarkar, A. M.; Devenish, R. C. E.; Ferrando, J.; Große-Knetter, J.; Matsushita, T.; Rigby, M.; Ruske, O.; Sutton, M. R.; Walczak, R.; Brugnera, R.; Carlin, R.; dal Corso, F.; Dusini, S.; Limentani, S.; Longhin, A.; Parenti, A.; Posocco, M.; Stanco, L.; Turcato, M.; Adamczyk, L.; Iannotti, L.; Oh, B. Y.; Saull, P. R. B.; Toothacker, W. S.; Iga, Y.; D'Agostini, G.; Marini, G.; Nigro, A.; Cormack, C.; Hart, J. C.; McCubbin, N. A.; Heusch, C.; Park, I. H.; Pavel, N.; Abramowicz, H.; Dagan, S.; Gabareen, A.; Kananov, S.; Kreisel, A.; Levy, A.; Abe, T.; Fusayasu, T.; Kohno, T.; Umemori, K.; Yamashita, T.; Hamatsu, R.; Hirose, T.; Inuzuka, M.; Kitamura, S.; Matsuzawa, K.; Nishimura, T.; Arneodo, M.; Cartiglia, N.; Cirio, R.; Costa, M.; Ferrero, M. I.; Maselli, S.; Monaco, V.; Peroni, C.; Ruspa, M.; Sacchi, R.; Solano, A.; Staiano, A.; Bailey, D. C.; Fagerstroem, C.-P.; Galea, R.; Koop, T.; Levman, G. M.; Martin, J. F.; Mirea, A.; Sabetfakhri, A.; Butterworth, J. M.; Gwenlan, C.; Hall-Wilton, R.; Hayes, M. E.; Heaphy, E. A.; Jones, T. W.; Lane, J. B.; Lightwood, M. S.; West, B. J.; Ciborowski, J.; Ciesielski, R.; Grzelak, G.; Nowak, R. J.; Pawlak, J. M.; Smalska, B.; Tymieniecka, T.; Ukleja, A.; Ukleja, J.; Zakrzewski, J. A.; Żarnecki, A. F.; Adamus, M.; Plucinski, P.; Sztuk, J.; Eisenberg, Y.; Gladilin, L. K.; Hochman, D.; Karshon, U.; Breitweg, J.; Chapin, D.; Cross, R.; Kçira, D.; Lammers, S.; Reeder, D. D.; Savin, A. A.; Smith, W. H.; Deshpande, A.; Dhawan, S.; Hughes, V. W.; Straub, P. B.; Bhadra, S.; Catterall, C. D.; Frisken, W. R.; Khakzad, M.; Menary, S.
2002-11-01
Searches in /ep collisions for heavy excited fermions have been performed with the ZEUS detector at HERA. Excited states of electrons and quarks have been searched for in e+p collisions at a centre-of-mass energy of 300 GeV using an integrated luminosity of 47.7 pb-1. Excited electrons have been sought via the decays e*-->eγ, e*-->eZ and e*-->νW. Excited quarks have been sought via the decays q*-->qγ and q*-->qW. A search for excited neutrinos decaying via ν*-->νγ, ν*-->νZ and ν*-->eW is presented using e-p collisions at 318 GeV centre-of-mass energy, corresponding to an integrated luminosity of 16.7 pb-1. No evidence for any excited fermion is found, and limits on the characteristic couplings are derived for masses /<~250 GeV.
NASA Astrophysics Data System (ADS)
Colangeli, Matteo; Pezzotti, Federica; Pulvirenti, Mario
2015-05-01
We introduce a stochastic N-particle system and show that, as N → ∞, an effective description ruled by the homogeneous fermionic Uehling-Uhlenbeck equation is recovered. The particle model we consider is the same as the Kac model for the homogeneous Boltzmann equation with an additional exclusion constraint taking into account the Pauli Exclusion Principle.
The Gaussian entropy of fermionic systems
Prokopec, Tomislav; Schmidt, Michael G.; Weenink, Jan
2012-12-15
We consider the entropy and decoherence in fermionic quantum systems. By making a Gaussian Ansatz for the density operator of a collection of fermions we study statistical 2-point correlators and express the entropy of a system fermion in terms of these correlators. In a simple case when a set of N thermalised environmental fermionic oscillators interacts bi-linearly with the system fermion we can study its time dependent entropy, which also represents a quantitative measure for decoherence and classicalization. We then consider a relativistic fermionic quantum field theory and take a mass mixing term as a simple model for the Yukawa interaction. It turns out that even in this Gaussian approximation, the fermionic system decoheres quite effectively, such that in a large coupling and high temperature regime the system field approaches the temperature of the environmental fields. - Highlights: Black-Right-Pointing-Pointer We construct the Gaussian density operator for relativistic fermionic systems. Black-Right-Pointing-Pointer The Gaussian entropy of relativistic fermionic systems is described in terms of 2-point correlators. Black-Right-Pointing-Pointer We explicitly show the growth of entropy for fermionic fields mixing with a thermal fermionic environment.
Massive fermion model in 3d and higher spin currents
NASA Astrophysics Data System (ADS)
Bonora, L.; Cvitan, M.; Prester, P. Dominis; de Souza, B. Lima; Smolić, I.
2016-05-01
We analyze the 3d free massive fermion theory coupled to external sources. The presence of a mass explicitly breaks parity invariance. We calculate two- and three-point functions of a gauge current and the energy momentum tensor and, for instance, obtain the well-known result that in the IR limit (but also in the UV one) we reconstruct the relevant CS action. We then couple the model to higher spin currents and explicitly work out the spin 3 case. In the UV limit we obtain an effective action which was proposed many years ago as a possible generalization of spin 3 CS action. In the IR limit we derive a different higher spin action. This analysis can evidently be generalized to higher spins. We also discuss the conservation and properties of the correlators we obtain in the intermediate steps of our derivation.
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.
Domain wall fermion quenched spectroscopy
NASA Astrophysics Data System (ADS)
Malureanu, Catalin Ionut
We measure y and the hadron spectrum on quenched ensembles using the domain wall fermion formulation. For the first time a 1/mf behavior of y for small valence masses has been observed. Our measurements of y on two different volumes of 83 x 32 and 163 x 32 at β = 5.85 suggest the behavior goes away on large enough volumes. Extensive spectrum calculations were done on 8 3 x 32 lattices at β = 5.7 and 5.85 corresponding roughly to a box size of 1.6 fm and 1.0 fm respectively. We have investigated five values of the extent of the fifth dimension Ls = 10, 16, 24, 32 and 48 with valence masses in the range 0.02 to 0.2 for the β = 5.7 ensemble and two values of Ls = 10 and 16 with valence masses in the range 0.02 to 0.08 for the β = 5.85 ensemble. Our pion remains massive in the infinite Ls extrapolation. This may be a finite volume effect. The nucleon to rho mass ratio stays constant at 1.4(1). Scaling violations for domain wall fermions are smaller roughly by a factor of four compared to the scaling violations in similar calculations done with staggered fermions.
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.
Dephasing time of composite fermions
Lee, P.A.; Mucciolo, E.R.
1996-09-01
We study the dephasing of fermions interacting with a fluctuating transverse-gauge field. The divergence of the imaginary part of the fermion self-energy at finite temperatures is shown to result from a breakdown of Fermi{close_quote}s golden rule due to a faster than exponential decay in time. The strong dephasing affects experiments where phase coherence is probed. This result is used to describe the suppression of Shubnikov{endash}de Haas (SdH) oscillations of composite fermions (oscillations in the conductivity near the half-filled Landau level). We find that it is important to take into account both the effect of dephasing and the mass renormalization. We conclude that while it is possible to use the conventional theory to extract an effective mass from the temperature dependence of the SdH oscillations, the resulting effective mass differs from the {ital m}{sup {asterisk}} of the quasiparticle in Fermi-liquid theory. {copyright} {ital 1996 The American Physical Society.}
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.
Fermionic thermocoherent state: Efficiency of electron transport
NASA Astrophysics Data System (ADS)
Karmakar, Anirban; Gangopadhyay, Gautam
2016-02-01
On the basis of the fermionic coherent state of Cahill and Glauber [Phys. Rev. A 59, 1538 (1999)], 10.1103/PhysRevA.59.1538, we have introduced here the fermionic thermocoherent state in terms of the quasiprobability distribution which shows the appropriate thermal and coherent limits as in the bosonic case or the Glauber-Lachs state. It is shown that the fermionic thermocoherent state can be realized as a displaced thermal state of fermions. Its relation with the fermionic displaced number state and the fermion-added coherent state are explored in the spirit of the bosonic case. We have investigated the nature of the average current and the suppression of noise due to the thermocoherent character of the source. The theory is applied to the problem of electronic conduction. A modification of the Landauer conductance formula is suggested which reflects the role of nonzero coherence of the source in electron transport.
Cold collisions between boson or fermion molecules
Kajita, Masatoshi
2004-01-01
We theoretically investigate collisions between electrostatically trapped cold polar molecules and compare boson and fermion isotopes. Evaporative cooling seems possible for fermion molecules as the ratio of the collision loss cross section to the elastic collision cross section (R) gets smaller as the molecular temperature T lowers. With boson molecules, R gets larger as T lowers, which makes evaporative cooling difficult. The elastic collision cross section between fermion molecules can be larger than that for boson molecules with certain conditions.
Fermion back reaction and the sphaleron
Roberge, A. )
1994-02-15
Using a simple model, a new sphaleron solution which incorporates finite fermionic density effects is obtained. The main result is that the height of the potential barrier (sphaleron energy) decreases as the fermion density increases. This suggests that the rate of sphaleron-induced transitions increases when the fermionic density increases. However the rate increase is not expected to change significantly the predictions from the standard sphaleron-induced baryogenesis scenarios.
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.
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.
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.
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
Two Higgs doublets with fourth-generation fermions: Models for TeV-scale compositeness
Soni A.; Bar-Shalom, S.; Nandi, S.
2011-09-21
We construct a class of two Higgs doublets models with a 4th sequential generation of fermions that may effectively accommodate the low-energy characteristics and phenomenology of a dynamical electroweak symmetry breaking scenario which is triggered by the condensates of the 4th family fermions. In particular, we single out the heavy quarks by coupling the heavier Higgs doublet ({Phi}{sub h}) which possesses a much larger VEV only to them while the lighter doublet ({Phi}{sub {ell}) couples only to the light fermions. We study the constraints on these models from precision electroweak data as well as from flavor data. We also discuss some distinct new features that have direct consequences on the production and decays of the 4th family quarks and leptons in high-energy colliders; in particular, the conventional search strategies for t{prime} and b{prime} may need to be significantly revised.
Paired States of Composite Fermions
NASA Astrophysics Data System (ADS)
Bonesteel, N. E.
2002-03-01
There is compelling theoretical evidence(R. Morf, Phys. Rev. Lett. 80), 1505 (1998). that the ν=5/2 fractional quantum Hall state is a Moore-Read state(G. Moore and N. Read, Nucl. Phys. B 360), 362 (1991). -- a state which can be viewed as a spin-polarized p-wave `superconductor' of composite fermions. The question remains, how can one test this hypothesis experimentally? To address this we have developed a semi-phenomenological description of this state in which the Halperin-Lee-Read(B.I. Halperin, P.A. Lee, and N. Read, Phys. Rev. B 47), 7312 (1993). theory of the half-filled Landau level is modified by adding a p-wave pairing interaction between composite fermions by hand. The electromagnetic response functions for the resulting mean-field superconducting state are then calculated and used in an RPA calculation of the physical electronic response. For a clean enough sample, and for q << k_f, the transverse electromagnetic response function for composite fermions is governed by type-II coherence factors and shows a `Hebel-Slichter'-like peak as a function of temperature for low enough frequency. The possibility (and potential difficulties) of observing this peak indirectly in surface-acoustic-wave propagation experiments will be discussed. The observation of such a coherence peak would provide strong evidence of BCS pairing in the 5/2 state. Work supported by US DOE Grant No. DE-FG02-97ER45639. Work done in collaboration with K.C. Foster (FSU) and S.H. Simon (Lucent). note