Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M63: Heavy Fermions IIRecordings Available
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Sponsoring Units: DCMP Chair: John Singleton, NHMFL/ LANL Room: Hyatt Regency Hotel -Grant Park A |
Wednesday, March 16, 2022 8:00AM - 8:12AM |
M63.00001: Investigations on the thermoelectric properties of YbCo2-xNi xZn20 Jorge R Galeano-Cabral, Benny Schundelmier, Olatunde Oladehin, Juan Ordonez, Ryan Baumbach, Kaya Wei Thermoelectric devices are both solid-state heat pumps and energy generators. Having a reversible process without moving parts is of high importance for applications in remote locations or under extreme conditions. Yet most thermoelectric devices have a rather limited energy conversion efficiency due to the natural competition between high electrical conductivity and low thermal conductivity, both being essential conditions for achieving a high energy conversion efficiency. Heavy-fermion compounds YbTM2Zn20 (TM = Co, Rh, Ir) have been reported to be potential candidate materials for thermoelectric applications at low temperatures [1]. Motivated by this result, we applied doping studies on the transition metal sites in order to optimize the carrier concentration as well as to promote more efficient phonon scatterings. We will present the latest investigation on the Ni-doped specimens YbCo2-xNixZn20, of which an enhanced thermoelectric figure of merit values have been obtained. Additionally, we will discuss the effect of doping Ni on improving the Seebeck coefficient values. We will also present a thermal evaluation of potential thermoelectric devices composed of these new materials. |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M63.00002: Enhanced Thermoelectric Properties at Low Temperatures in Heavy Fermion Compounds CeaSmbEucYbdIr2Zn20 (a + b + c + d = 1) Benny c Schundelmier, Jorge R Galeano-Cabral, Keke Feng, Olatunde Oladehin, Ryan Baumbach, Kaya Wei Thermoelectricity provides a green approach for efficient energy conversion. Applying a temperature gradient across a thermoelectric device produces an electric voltage and vice versa. As previously reported, heavy fermion 1-2-20 compounds show favorable thermoelectric properties at low temperatures. [1] In a typical 1-2-20 compound, the heavy rare earth elements are encompassed by large cage-like structures which provides an avenue for achieving reduced lattice component of the thermal conductivity. In addition, the strongly hybridized f-electron states at the Fermi level result in large Seebeck coefficient values. By varying the ratio among different rare earth elements in CeaSmbEucYbdIr2Zn20 (a + b + c + d = 1), we are able to modify the hybridization strength of the f-electron states and improve the Seebeck coefficient values. This contributes to the overall enhanced thermoelectric properties of these compounds. Characterization of these materials through thermal transport, magnetometry, EDS, and XRD will be discussed in detail. |
Wednesday, March 16, 2022 8:24AM - 8:36AM Withdrawn |
M63.00003: nanocalorimeter spectroscopy of strongly correlated metals Arkady Shekhter Heat capacity measurements provide essential information about the full extent of low energy excitation in the strongly correlated systems. Nuclear schottky often obscure the physics in these systems. I will discuss a new calorimeter spectroscopy technique that -- coupled with ultrafast nanocalorimeters -- allows determination of electronic and nuclear components of heat capacity using time as a new experimental parameter. These measurements yield spin lattice relaxation time which provides information complementary to NMR. Calorimeter spectroscopy enables two independent determinations of electronic density of states in a strongly correlated system in a single measurement. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M63.00004: Effect of hybridization gap on the phononic and electronic excitations of CeCoIn5 Mai Ye, Hsiang-Hsi Kung, Priscila Rosa, Eric D Bauer, Girsh E Blumberg Heavy fermion metal CeCoIn5 has a coherence temperature T*=45K, below which individual Kondo singlets evolve into a coherent Kondo lattice [P. Coleman, Introduction to Many-Body Physics (Cambridge University Press, 2015)]. In this process, localized electrons acquire an effective intersite coupling mediated by conducting electrons, and gradually form a narrow band. The interaction between the narrow band and conduction band in turn opens up a hybridization gap. We study the phononic and electronic excitations of this compound by inelastic light scattering. Two optical phonon modes exhibit anomalies in their temperature dependence of frequency and linewidth below T*, indicating reduced electron-phonon scattering resulting from gap opening near the Fermi level. Moreover, below T* the continuum of electronic excitations in the XY scattering geometry is suppressed following cubic power law in frequency up to 50cm-1. Such cubic-power-law behavior is absent in other scattering geometries. These results support T* as the characteristic temperature marking the development of long-range coherence for individual Kondo singlets and the opening of hybridization gap. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M63.00005: Strange metal physics at high fields in “clean” CeOs4Sb12 John Singleton, Kathrin Gotze, Matthew J Pearce, Paul A Goddard, M Brian Maple, Pei-Chun Ho, Matthew J Coak The filled skutterudite CeOs4Sb12 has attracted attention because of its proposed topologically protected states and its very striking non-monotonic field (H) - temperature (T) phase boundary that is associated with a valence transition. In its high-H phase at low T, CeOs4Sb12 possesses a simple, almost spherical Fermi surface. Despite this apparently trivial situation, between fields of 20 T and 50 T, the T- and H-dependent magnetoresistance and Hall effect exhibit unusual behavior that is more characteristic of “strange metals” such as cuprate and pnictide superconductors. However, whereas such conduct is often associated with disorder in the latter systems, CeOs4Sb12 shows strong magnetic quantum oscillations signifying relative freedom from defects. We speculate that the strange metal physics is here associated with proximity to a quantum-critical point that also results in a H-dependent effective mass. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M63.00006: Examination of the hybridization gap in CeTX heavy-fermion compounds Thomas U Boehm, Rohit P Prasankumar, Yu Liu, Eric D Bauer, Filip Ronning The f-electrons of cerium hybridize with conduction electrons to produce coherent heavy bands at low |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M63.00007: Magnetoresistance and Torque Magnetization of YbB12 in Pulsed Magnetic Fields Christopher A Mizzi, Neil Harrison, William A Phelan, Lucas A Pressley, Tyrel M McQueen, Priscila Rosa, Mun K Chan The observation of magnetic quantum oscillations in nominally insulating SmB6 generated significant excitement due to its implications for the presence of topological surface states or a bulk neutral Fermi surface. More recently, similar oscillations have been reported in another Kondo insulator YbB12. There are currently numerous open questions regarding the nature of these oscillations including the relative contributions of the bulk, surfaces, and defects, as well as the presence of multiple oscillation frequencies. We present a pulsed magnetic field study of magnetoresistance and torque magnetization in YbB12. The angular and temperature dependences of these measurements provide important insights into the electronic structure of YbB12 and suggest a connection between the insulating phase oscillations and the field-induced insulator-metal transition. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M63.00008: NMR Study of Single Crystal CeVGe3 Cameron R Chaffey CeVGe3 is a heavy fermion antiferromagnet with TN ~ 6 K and a hexagonal unit cell. The small ratio of TN to the Curie-Weiss temperature in this material may point to a role for geometric frustration. We present nuclear magnetic resonance (NMR) of 51V in a single-crystal. Measurements of the Knight shift and spin-lattice relaxation rate (T1), performed at 11.7 Tesla both parallel to the c axis and in the a-b plane, highlight the antiferromagnetic transition and reveal a significant Knight shift anomaly. Broadening of the NMR spectra at low temperatures in the ordered phase suggest incommensurate magnetic ordering of the Ce. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M63.00009: NMR study on mixed valence insulator SmB6 Rong Cong, Erick Garcia, Wencong Liu, Arneil P Reyes, Suchitra Sebastian, Vesna F Mitrovic Owing to strong electronic correlations, SmB6 is a Kondo insulator that has been studied for several decades [1] and has more recently been proposed to be a topological Kondo insulator [2]. Recent magnetic torque measurements on pristine floating-zone grown single crystals of SmB6 found bulk quantum oscillations despite the bulk electrical insulating behavior [3], suggesting the surprising existence of a bulk Fermi surface in this unconventional insulator. We have conducted NMR measurements on the same high-quality floating zone grown single crystals of SmB6 below 1K and for magnetic fields up to 18T for two inequivalent boron sites B1 and B2. For all magnetic fields below 18T, the Knight shift remains constant, showing behavior akin to a bulk metal, despite the bulk electric insulating character of the material. The spin-lattice relaxation rate 1/T1 indicates the existence of localized fermion density of states at low fields. The anisotropy of the spin-lattice relaxation rate is suppressed with the increase of the magnetic field. The Korringa constant indicates the presence of ferromagnetic correlations up to 18T. We will discuss the implication of these results based on an in-gap state model [4] and the possibility of the existence of a neutral bulk Fermi surface. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative Agreement No. DMR-1644779 and the State of Florida. Work at Brown was supported in part by the National Science Foundation grant No. DMR-1905532. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M63.00010: Studying the Periodic Anderson Model using Functional Renormalization group Abhishek Som, Nahom K Yirga, David K Campbell The Periodic Anderson model(PAM) has been used to explain the physics of heavy fermion systems and describes localized impurity electrons with an on-site Coulomb repulsion interacting with delocalized conduction electrons via a hybridization term. Quantum critical points have been reported in the literature for heavy fermion systems with various hybridizations in place. In particular,in 2D systems, for local hybridization, the results show transition from an antiferromagnet to a Kondo insulator as a function of the hybridization (using the dynamic vertex approximation). We explore this transition for non-local hybridization treating the action for the system via the fRG(functional Renormalization Group). Doping the antiferromagnetic part of the phase diagram on small 2×2×2 clusters has also been shown previously to produce strong dx^2-y^2 superconducting correlations at lower temperatures. Taking this a step further, we study the impact of doping the conduction and impurity electrons on superconducting response in the system for large clusters, also using fRG. Finally, we also look at multiband systems with various degrees of interband hopping. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M63.00011: STM study of the atomic and electronic structure of a single-layer Kondo lattice CePt6/Pt(111) Koichiro Ienaga, Sunghun Kim, Toshio Miyamachi, Fumio Komori While bulk CePt5 shows antiferromagnetic order below 1 K, a multi-layered thin film of CePt5 grown on a Pt(111) substrate exhibits heavy-fermion behavior below 20 K[1]. However, the growth of single layer CePt5 has been controversial as summarized in Ref.[2] and spectroscopic studies for the electronic states of the single layer are still lacking. In this work, we study the structure and electronic states of 1 unit layer (u.l.) of a Ce-Pt intermetallic compound on Pt(111) using scanning tunneling microscopy/spectroscopy (STM/STS)[3]. By depositing Ce atoms onto Pt(111) and subsequent annealing, an ordered (2×2) structure was observed, which is reproduced by a structural model of 1 u.l. CePt6/Pt(111) consisting of a topmost Pt4 layer and an underneath CePt2 layer. By measuring STS spectra and quasiparticle interference, we found that an onset energy of the surface state observed on Pt(111) shifts downward on the surface Pt4 layer of the 1 u.l. CePt6 due to charge transfer from the CePt2 layer. We discuss possible two-dimensional coherent Kondo effect with the observed STS spectra on the 1 u.l. CePt6. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M63.00012: A DFT + DMFT study of the two-channel quadrupolar Kondo effect in PrV2Al20 Marvin Lenk, Fei Gao, Johann Kroha, Andriy H Nevidomskyy Praseodymium-based cubic 1-2-20 materials like PrV2Al20 exhibit a strong coupling between Pr 4f states and conduction electrons. They experimentally show traces of a two-channel quadrupolar Kondo effect in competition with quadrupolar ordering and superconductivity [1]. Valence fluctuations on the Pr atom occur between the magnetic quadrupole 4f2 Γ3 doublet and the excited 4f1 configuration with a dipole Kramers-doublet Γ7. This specific setup leads to an exotic two-channel quadrupolar Kondo effect, where the channel degree of freedom carries a dipole moment and the Kondo degree of freedom a quadrupolar moment. A quadrupolar analog to the famous Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction principally allows for quadrupolar ordering in competition with the Kondo singlet formation. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M63.00013: Ultrafast, coherent time evolution of terahertz-pumped heavy-fermion systems Francisco Meirinhos, Johann Kroha The characterisation of new quantum phases of matter has recently been intensified by the application of terahertz (THz) spectroscopy in the time domain to heavy-fermion (HF) systems [1-3]. It was experimentally shown that a single-cycle THz pulse disrupts the strongly correlated Kondo ground state in HF compounds such as CeCu6−xAux, and that it recovers after a characteristic delay time, the Kondo coherence time τ*K= ħ / (kBTK), accompanied by the emission of a temporally confined THz echo pulse. In this way, time-domain THz spectroscopy provides direct, background-free access to both the quasi-particle spectral weight and the characteristic time/energy scales, across a HF quantum phase transition [1-2]. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M63.00014: Electronic Structure Study of a Kondo Lattice System CeCuSb2 Sawani Datta, Ram Prakash Pandeya, Arka Bikash Dey, Christoph Schlueter, Andrei Gloskovskii, Thiago Peixoto, Arumugam Thamizhavel, Kalobaran Maiti Investigating the electronic structure of a rare-earth-based system has various complexity due to the correlation of f electrons [1]. In the rare earth series, Ce has some unique properties due to the higher radial expansion of f orbital. We have studied the electronic structure of CeCuSb2, which is an antiferromagnetic Kondo lattice system [2] and forms in layered tetragonal structure. We performed high-resolution hard x-ray photoemission spectroscopy of a CeCuSb2 single crystal by varying photon energy and temperature. We observed that the surface termination affects the hybridization of Ce atoms. Though the bulk studies show Kondo behavior, the Ce 3d core-level spectra do not show the temperature dependence of the features expected in a Kondo lattice system. Sb spectra at different photon energies show significant differences with the change in surface sensitivity manifesting surface-bulk difference in the electronic structure. Sb(2) is found to be relatively more strongly bonded to Ce than Sb(1); the differences reduce at higher temperatures. These results provide an interesting scenario of the evolution of complex hybridization physics and their surface-bulk differences. |
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