Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T64: Heavy Fermions IIIRecordings Available
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Sponsoring Units: DCMP Chair: Daniel Silevitch, Caltech Room: Hyatt Regency Hotel -Grant Park B |
Thursday, March 17, 2022 11:30AM - 11:42AM |
T64.00001: Pseudospin-triplet superconductivity in CeRh2As2 Daniel F Agterberg, David C Cavanagh, Philip Brydon, TATSUYA SHISHIDOU, Michael Weinert Recent measurements suggest that CeRh2As2 has field induced odd-parity superconductivity [1]. Here, after an overview of recent experimental developments, I will discuss how the underlying crystal structure links closely to superconductivity in this material. Specifically, we argue that the local inversion symmetry breaking of Ce atomic sites lead to a pseudospin Kramer’s band degeneracy that behaves differently from more usual spin ½ degeneracies. The consequences of this on odd-parity superconductivity in CeRh2As2 will be highlighted [2]. |
Thursday, March 17, 2022 11:42AM - 11:54AM |
T64.00002: Psuedospin in CeRh2As2 TATSUYA SHISHIDOU, David C Cavanagh, Philip Brydon, Daniel F Agterberg, Michael Weinert A field-induced novel phase transition, from even- to odd-parity superconducting pairing state, has recently been observed in CeRh2As2 [1]. The question why this is the case in CeRh2As2 and not in other materials remains to be answered. In this talk, based on DFT calculations and supporting symmetry arguments, we address question through an examination of the normal state properties, including the Fermi surface arising from renormalized 4f bands and electron spin polarization near the chemical potential of CeRh2As2 [2]. |
Thursday, March 17, 2022 11:54AM - 12:06PM |
T64.00003: Critical currents across grain boundaries in polycrystalline CeCoIn5 Sanu Mishra, Sean Thomas, Rodney J Mccabe, Shizeng Lin, Eric D Bauer, Filip Ronning The study of grain boundaries (GB) in superconductors has both fundamental and applied interests. In high temperature cuprate superconductors studies of the critical currents across GBs have provided important information on the symmetry of the order parameter and are critical for the observation of spontaneously generated half-flux magnetic quanta [1]. Similar to cuprate superconductors, heavy fermion superconductors (HFS) host rich physics in the form of unconventional superconducting phases with nodal quasiparticles. However, there have been relatively few phase sensitive measurements of the order parameter thereby emphasizing the need for investigations of critical currents across GBs in HFS. |
Thursday, March 17, 2022 12:06PM - 12:18PM |
T64.00004: Ground state of Ce3Bi4Pd3 unraveled by hydrostatic pressure Ajeesh Mukkattu Omanakuttan, Sean Thomas, Satya K Kushwaha, Eric D Bauer, Filip Ronning, Joe D Thompson, Neil Harrison, Priscila F. S. Rosa Noncentrosymmetric Ce3Bi4Pd3 has recently attracted tremendous attention as a strongly correlated topological semimetal candidate [1]. Conflicting experimental results, however, argue for either a Weyl Kondo semimetallic or a narrow-gap Kondo insulating ground state [2-4]. Using electrical transport measurements under hydrostatic pressure, we find that Ce3Bi4Pd3 becomes progressively more insulating with increasing pressure, a behavior typical of Ce-based Kondo insulators such as Ce3Bi4Pt3. Moreover, the hybridization gap shows a quadratic increase with pressure akin to the effect of Pt substitution observed in Ce3Bi4(Pt1-xPdx)3 series [2]. The pressure dependence of the carrier density, obtained from Hall resistivity measurements on a microstructure device of Ce3Bi4Pd3, is in excellent agreement with the enhancement of the insulating gap under pressure. Our results suggest that the Kondo coupling prevails as the primary tuning parameter in this class of materials and Ce3Bi4Pd3 has a narrow-gap Kondo insulating ground state. |
Thursday, March 17, 2022 12:18PM - 12:30PM |
T64.00005: Electron-Phonon Coupling-Induced Breakdown of Raman Selection Rules in C-type Eu2O3 John E Slimak, Alexandra N Cote, S. Lance Cooper, Greg MacDougall The energetic proximity of phonons and crystal-electric-field (CEF) levels in rare earth materials is conducive to strong electron-phonon coupling that can give rise to interesting phenomena and novel material properties, including Davydov splittings, cooperative Jahn-Teller effects, and hybrid vibronic exctiations. To explore the role that CEF-phonon coupling plays in governing the physical properties of one class of rare earth materials, the rare earth sesquioxides, we present Raman spectroscopic measurements of C-type Eu2O3 as a function of temperature. It has been previously reported that near room temperature, energy transfer can readily occur between two symmetry inequivalent Eu3+ ions in Eu2O3 [1] mediated by electron-phonon interactions. Our Raman spectra reveal features with strongly temperature-dependent intensities that energetically coincide with Raman-forbidden Tu phonons predicted by lattice dynamics calculations [2] and the energy differences between excited states of the C2 and S6 Eu3+ ions of Eu2O3 [1]. We propose that the Raman selection rules for these excitations are relaxed by the strong electron-phonon coupling present in Eu2O3. |
Thursday, March 17, 2022 12:30PM - 12:42PM |
T64.00006: Anomalous hall effect in a ferromagnetic kondo system Hasan Siddiquee, Christopher Broyles, Sheng Ran Topology and strong electronic correlations are essential components to observe emergent phenomena in novel quantum materials, although their intersection in experimental systems has not been extensively studied yet. Recently theoretical calculations predicted that strong electronic correlations incorporated with crystalline symmetry could lead to topological gapless states. Here we study a ferromagnetic Kondo lattice system with nonsymmorphic crystal structure, which is designed to observe topological gapless states in the presence of strong electronic correlations. We observed anomalous hall effect, with a sign change of anomalous hall conductivity upon cooling the system. The change of sign of anomalous hall conductivity cannot be attributed to skew scattering as the direction of the magnetic order is not changed. Instead, scaling analysis indicates that the anomalous Hall conductivity at low temperatures is dominated by the non-trivial Berry curvature. The possible topological state in ferromagnetic Kondo lattice system provides a unique opportunity to explore the effect of topology in strongly correlated systems. |
Thursday, March 17, 2022 12:42PM - 12:54PM |
T64.00007: Exploring DFT+U parameter space with a Bayesian calibration assisted by Markov chain Monte Carlo sampling Pedram Tavadze, Reese Boucher, Guillermo Avandaño-Franco, Keenan X Kocan, Sobhit Singh, Viviana Dovale-Farelo, Wilfredo Wilfredo Ibarra-Hernández, Matthew B Johnson, David S Mebane, Aldo H Romero Density-functional theory has gained popularity because of its ability to predict properties of a large group of materials a priori. However, this triumphant ability stops short for strongly correlated materials where the non-universality of the exchange-correlation functionals becomes substantial. One solution to this problem is to introduce a Hubbard correction for the treatment of the strongly correlated electronic states at the mean-field level, used in the so-called DFT+U approaches. Unfortunately, this U correction turns the theory into a semiempirical method as the exact values of the correction parameters U and J are unknown and their parameterization can vary considerably from one material to another composed of the same strongly correlated atoms. In this study, we select a group of iron-based compounds to explore the space of the U and J correction parameters that simultaneously improve the prediction results for all the studied materials. We perform this exploration using a Bayesian calibration assisted by Markov chain Monte Carlo sampling to determine the distribution of the correction parameters. The following are the main findings of this study: LDA requires a significantly larger U parameter compared with the GGA functionals. The U and J obtained for PBE are the most transferable to other iron-based compounds. The Dudarev approximation can result in a closer prediction to the Lichtenstein approach in PBE compared to that of in LDA and PBEsol. Lastly, PBE predicts lattice parameters reasonably well without the Hubbard correction for iron-based compounds. |
Thursday, March 17, 2022 12:54PM - 1:06PM |
T64.00008: Role of pressure induced c-f hybridization on the valence transition in EuPd2Si2 Young-Joon Song, Susanne Schulz, Kristin Kliemt, Cornelius Krellner, Roser Valenti Tetragonal EuPd2Si2 is well-known to show a valence transition from divalent (Eu2+) to trivalent (Eu3+) states by a change in temperature or pressure. However, its mechanism has not been completely studied yet. In this presentation, we will address the microscopic origin of the valence transition in tetragonal EuPd2Si2 under pressure using a combination of ab initio calculations and photoemission measurements. Our results indicate that an enhanced c-f hybridization between localized Eu 4f states and itinerant conduction states ( Eu 5d, Pd 4d, and Si 3p ) plays a vital role for the valence transition to happen. Lastly, the effects of Au doping on the valence states of EuPd2Si2 will be also discussed. |
Thursday, March 17, 2022 1:06PM - 1:18PM |
T64.00009: Exotic heavy fermion superconductivity in atomically thin CeCoIn5 films Tomoya Asaba, Lang Peng, Masahiro Naritsuka, Satoru Akutagawa, Shota Suetsugu, Masahiro Haze, Yuichi Kasahara, Takahito Terashima, Robert Peters, Yuji Matsuda Previous studies on topological superconductivity have been mainly focused on s-wave superconductors, where fine-tuning of the Fermi energy is required. In contrast, in two-dimensional (2D) d-wave superconductors with strong spin-orbit interaction, topological superconductivity can emerge without fine-tuning the band structure due to the parity-mixed d+p wave state. Here we report an in-situ scanning tunneling microscopy study of atomically thin films of CeCoIn5, a d-wave heavy-fermion superconductor. Both hybridization and superconducting gaps are clearly resolved even in monolayer CeCoIn5, providing direct evidence of 2D superconductivity of heavy quasiparticles. More remarkably, in these atomically thin films, while the superconducting transition temperature is suppressed to nearly half of the bulk, the out-of-plane upper critical field is significantly enhanced and by far exceeds the Pauli and bulk orbital limits. The results reveal the emergence of exotic superconductivity such as the d+p wave state, providing a new playground for exploring topological superconductivity. |
Thursday, March 17, 2022 1:18PM - 1:30PM |
T64.00010: Observation of Kondo lattice behavior in antiferromagnetic metal FeTe Younsik Kim, Minsoo Kim, Cheng-Maw Cheng, Joonyoung Choi, Saegyeol Jung, Donghui Lu, Jong Hyuk Kim, Soohyun Cho, Dongjoon Song, Dongjin Oh, Li Yu, Young Jai Choi, Hyeong-Do Kim, Younjung Jo, Soonsang Huh, Changyoung Kim Finding d-electron heavy fermion (HF) states has been an important topic as the diversity in d-electron materials can lead to many exotic Kondo effect-related phenomena or new states of matter such as topological Kondo insulator. Yet, obtaining direct spectroscopic evidence for a d-electron HF system has been elusive to date. Here, we report the observation of Kondo lattice behavior in an antiferromagnetic metal, FeTe, via angle-resolved photoemission spectroscopy (ARPES) and transport properties measurements. The Kondo lattice behavior is represented by the emergence of a sharp quasiparticle at low temperatures. The transport property measurements confirm the low-temperature Fermi liquid behavior and reveal successive coherent-incoherent crossover upon increasing temperature. It is also found that the low-temperature coherent state of the Kondo lattice is facilitated by a long-range magnetism. We interpret the Kondo lattice behavior as a result of hybridization between localized Fe 3dxy and itinerant Te 5pz orbitals. Our observations suggest unusual cooperation of Kondo lattice behavior and long-range magnetism. |
Thursday, March 17, 2022 1:30PM - 1:42PM |
T64.00011: Heavy quasiparticles in CeRh2As2: Renormalized bands, Fermi surfaces, and electronic instabilities Gertrud Zwicknagl, Evrard-Ouicem Eljaouhari We present calculations of the heavy quasiparticles in the heavy-fermion compoundCeRh2As2. The narrow 4f-derived bands are calculated by means of the Renormalized Band (RB) method. The RB scheme provides a framework for a realistic description of the coherent low-energy excitations in a Fermi liquid which combines material-specific ab-initio methods and phenomenological considerations in the spirit of the Landau theory of Fermi liquids. The central focus of the present study are the role played by the non-symmorphic lattice structure and the consequences of the Crystalline Electric Field (CEF) which removes the orbital degeneracy of the Ce 4f states. We conjecture that the quasi-quartet CEF ground state in combination with pronounced nesting features of the Fermi surface may give rise to a quadrupole density wave. |
Thursday, March 17, 2022 1:42PM - 1:54PM |
T64.00012: Interplay between multigap superconductivity and multipolar order in PrTi2Al20 Akito Sakai, Yosuke Matsumoto, Mingxuan Fu, Masaki Tsujimoto, Eoin O’Farrell, Satoru Nakatsuji Unconventional superconductivity (SC) is one of the most astonishing yet hardest problems in condensed matter physics. While exotic SCs often appear near the border of magnetic order, a new route to realize unconventional SC is orbital instability found in iron-based compounds. However, it is difficult to directly explore the orbital instability effect experimentally since the orbital degree of freedom is always accompanied by the spin degree of freedom in d-electron materials. |
Thursday, March 17, 2022 1:54PM - 2:06PM |
T64.00013: Kondo-stabilized spin-liquid phase of 2 impurities Krzysztof P Wójcik, Johann Kroha The phase diagram of the conventional 2-impurity Kondo model and its relevance to correlated lattice models have been a subject of a long debate. It it features Jones-Varma quantum phase transition (QPT) between the Kondo and the RKKY phase, which is unstable against particle-hole asymmetry. I will present results obtained for a modified 2-impurity model, where each of the impurities is coupled to a different host, and the hosts (not impurities) are directly coupled by spin-spin exchange. The model exhibits Jones-Varma QPT even away from the particle-hole symmetry point. Even more importantly, a second QPT occurs upon tuning the same inter-host coupling to even higher values, where the system forms 2-impurity version of a spin-liquid, defined as a state with large, but not complete spin-spin correlations and non-universal impurity spectral density. I will discuss the possibilities for realization of this scenario in quantum-dot structures and heavy-fermion materials. |
Thursday, March 17, 2022 2:06PM - 2:18PM |
T64.00014: AC elastocaloric investigation of the antiferroquadrupolar order in DyB2C2 Linda Ye, Matthias S Ikeda, Thanapat Worasaran, Maja D Bachmann, Matthew E Sorensen, Ian R Fisher Elastic strain applied in situ has emerged in recent years as a versatile tuning parameter for quantum materials. To address the key question of how strain perturbs various strongly correlated electronic phases, a thermodynamic probe that can be implemented under strained conditions is highly desirable. Our group has developed an AC elastocaloric (EC) technique that measures adiabatic temperature oscillations induced by a modulating strain, with the simultaneous application of a DC bias strain as the tuning parameter [1]. Here we use this new technique to investigate the response of DyB2C2, a prototypical rare earth system hosting an antiferroquadrupole order [2]. In addition to unraveling a strain-tuning of the underlying quadrupolar and magnetic phase transitions, we have also uncovered an unusual enhancement of entropy with strain in the antiferroquadrupole phase. Our findings suggest that strain can serve as an incisive probe of antiferroquadrupolar systems, and, more broadly, demonstrate the rich prospects that may be accessed by EC measurements. |
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