Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P07: Topological Electronic States in Kondo insulators and other f-electron materials |
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Sponsoring Units: DCMP Chair: Piers Coleman, Rutgers University, New Brunswick Room: BCEC 109B |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P07.00001: Neutral Fermi surfaces in Mixed Valent Kondo Insulators: Majorana Hubbard Operators Piers Coleman The development of slave particle approaches provides a way to explore different patterns of operator fractionalization in strongly correlated systems. The recent observation of quantum oscillations in mixed valent SmB2 has raised the possibility of neutral Fermi surfaces in this material[1-4]. This motivates a search for a representation of the Hubbard operator in terms of Majorana, rather than Dirac fermions. In this talk I will describe how this can be achieved and using the method, discuss the prospects for a two-phase description of SmB6, in terms of a competition between a fully gapped strong topological insulator and a strange dielectric. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P07.00002: The role of f-p hybridization in the bulk f-electronic structure of SmB6 Jonathan Denlinger, Dae-Jeong Kim, Zachary Fisk The topological origin of in-gap surface states of mixed-valent SmB6, a candidate topological Kondo insulator, is currently being debated. In addition, there exist distinct discrepancies in the bulk electronic structure between DFT-based theory, ARPES, recent NIXS determination of the unoccupied f-hole symmetry [1], and the existence of low temperature dHvA oscillations [2,3]. Here we explore the role of f-p hybridization in assisting f-d hybridization in the formation of an insulating gap in its f-electronic structure. In a five-band model, the relative phase of f-d and f-p hybridizations allows tuning of the f-band structure between DFT-like and ARPES-like solutions, and hybridization amplitude tuning allows selection of the unoccupied X-point f-hole character. Also theoretically enabled is prediction of a distinct ARPES-measured 3D bulk f-hole-like dispersion at the “H”-point between adjacent X-point d-electron pockets. The H-point f-dispersion then naturally leads to exploration of the Landau level sharp DOS-discontinuity model [4] to quantitatively explain the size and shape of the dominant dHvA orbits. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P07.00003: Effect of reduced sample dimensions on the insulating state of SmB6 Joonbum Park, Mun Chan, Priscila Rosa, Neil Harrison The putative topological Kondo insulator SmB6 has shown compelling evidence of robust conductive surface states, however less attention has been paid to the insulating bulk states which lies beneath. Here, we present the electrical transport measurements of the insulating state of SmB6 down to T ~ 250 mK. We observed that the temperature dependence of resistivity shows additional power law-like dependence with temperature. These features develop below T < 1.5 K with reduction of sample dimensions, typically below 150 μm. We discuss whether the origin of these features are from dominant surface conduction over bulk conduction or due to impurities. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P07.00004: Search for charge neutral majorana fermions in SmB6 under uniaxial strain Brian Casas, Laisi Chen, Zachary Fisk, Jing Xia The existence of a charge neutral fermi surface as evidenced from measurements of a large three dimensional fermi surface has motivated renewed interest in the bulk of samarium hexaboride. Thermal transport measurements have been performed using both flux and floating grown zone crystals, each resulting in different conclusions regarding a fermionic contribution suggestive of these charge neutral majorana fermions. Uniaxial strain has been shown to tune the mixed valence physics in the bulk and as such may be critical in understanding the underlying behavior of SmB6. Here we report our progress on thermal transport on SmB6 under uniaxial strain |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P07.00005: Ionic liquid gating on Al-flux grown SmB6 using Hall bar geometry Alexa Rakoski, Dmitri Mihaliov, Cagliyan Kurdak, Priscila Rosa, Zachary Fisk Samarium hexaboride (SmB6) is a correlated material in which strong f-d interactions lead to the opening of a small hybridization gap below 100 K at the Fermi energy. Below 4 K, the plateau in resistivity which was a long standing mystery in SmB6 has been proposed to arise from a crossover to surface conduction due to topological effects. We investigate how this plateau, as well as the corresponding plateau in the Hall coefficient, can be tuned by gating with the ionic liquid DEME-TFSI. Results are obtained on an Al-flux grown sample in Hall bar geometry prepared by finely polishing on all sides. The sample is suspended in the ionic liquid to ensure that all surfaces contributing to transport are gated. We find that resistivity can be changed by over 15% in the range of accessible voltages in the liquid, and that the Hall coefficient demonstrates a much larger effect of up to 33% change over the same range. We also present a model based on measured parameters of the 2D Fermi surface in SmB6 to explore these changes. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P07.00006: Itinerate states in rare-earth hexaborides observed via resonant inelastic x-ray scattering Donal Sheets, Jian-Xin Zhu, Maxim Dzero, Diego M Casa, Jungho Kim, Priscila Rosa, Zachary Fisk, Ignace Jarrige, Jason Hancock We present X-ray resonant inelastic x-ray scattering (RIXS) data collected at the L edges of divalent hexaborides YbB6 and EuB6. At an incident energy corresponding to the divalent resonance, we observe strong RIXS signal which appears to be well-described by the unoccupied 5d density of states calculated from density functional theory. In addition, we observe a second set of RIXS excitations at higher incident energy which does not correspond to any observable feature in absorption. This anomalous scattering persists to low incident energy and therefore induces excited states which are relevant to material behavior. The two classes of excitation show distinct polarizationdependence and we propose a process which describes the origin of this RIXS intensity. Our results suggest far-reaching utility of L-edge RIXS in characterizing itinerant states of f-filling materials at a microscopic level. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P07.00007: Charge neutral fermions and quantum oscillations in a topological Kondo insulator YbB12 Yuki Sato, Ziji Xiang, Yuichi Kasahara, Tomoya Taniguchi, Shigeru Kasahara, Lu Chen, Tomoya Asaba, Colin Tinsman, Hinako Murayama, Ohei Tanaka, Yuta Mizukami, Takasada Shibauchi, Fumitoshi Iga, John Singleton, Lu Li, Yuji Matsuda Recent observations of quantum oscillations (QOs) in transport and thermodynamic parameters at high magnetic fields in a Kondo insulator YbB12 have been a big surprise since it seems to host a Fermi surface, which is a defining character of a metal. In this talk, I will present low-temperature heat-transport measurements to discuss low energy excitations in the ground state of YbB12. At zero field, despite the resistivity ρxx being far larger than that of conventional metals, a sizeable T-linear dependent term in the thermal conductivity in the zero-temperature limit, κ0xx/T is clearly resolved, leading to a spectacular violation of the Wiedemann-Franz law: the Lorenz ratio L = κxxρxx/T is 104-105 times larger than that expected in conventional metals. These data indicate that YbB12 is a charge insulator but a thermal metal, suggesting the presence of itinerant neutral fermions. Remarkably, more insulating crystals with larger activation energies exhibit larger amplitudes of the resistive QOs as well as a larger κ0xx/T, in stark contrast to conventional metals. Moreover, we find that these fermions couple to magnetic field, despite their charge neutrality. Our findings expose novel gapless and highly itinerant, charge-neutral quasi-particles in this unconventional quantum state. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P07.00008: Enhanced quantum oscillations in Kondo Insulators Yen-Wen Lu, Chung-Hou Chung, Chung-Yu Mou We investigate quantum oscillations resulting from the Kondo screening due to Landau levels in Kondo insulators. It is shown that |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P07.00009: Anomalous symmetry-breaking response in proposed type-II Weyl semimetal Halyna Hodovanets, Chris Eckberg, Daniel Campbell, Daniel J Kraft, Sean A Winters, Hyunsoo Kim, Johnpierre Paglione We present details of flux growth and physical properties of noncentrosymmetric magnetic RAlGe (where R = Rare Earth) single crystals. The RAlGe family has been proposed, based on systematic first-principles band structure calculations, to host key elements of Weyl semimetals and as such offers a playground for new and exciting physics. We will discuss the effects of different rare earth species on the ground state magnetic order, magnetic anisotropy and correlation of the magnetotransport and crystal symmetry in the ordered state. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P07.00010: Many-body dynamics and Kondo coherence collapse in an ultrafast driven Kondo insulator Wei Zhu, Alexis Chacon, Jian-Xin Zhu Intense ultrafast pulse-driven electronics have provided systematic insights into the dynamics of electrons in condensed matter systems, which opens up prospects for quantum control of solids and all-optical band structure reconstruction. So far the studies have been carried out in solids where ‘bare’ electronic excitations dominate quantum dynamics. However, the underlying many-body dynamics due to correlations and couplings with other degrees of freedom such as lattice, spin or orbitals, has remained out of reach. Here, we introduce an ultrafast laser to optically pump and probe a Kondo lattice, in which conducting electrons strongly couple with magnetically local moments. The laser field excites collective doublon-hole pairs and drives a transient Kondo insulator melting, which are documented through the time-, frequency-, and momentum-dependent influence on the electronic structure. After photo-excitation, doublon-hole re-collision results in high-frequency photon emission. The information that we demonstrate as being accessible with time- and angle-resolved photo-electron spectroscopy and high-harmonic generation spectra, will stimulates the investigation of non-equilibrium dynamics and non-linear phenomenon in heavy-fermion systems. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P07.00011: Exploring the valence transition in CeOs4Sb12 in high magnetic fields Kathrin Goetze, Matthew J. Pearce, Paul Goddard, Alix McCollam, Thomas Khouri, Marcelo Jaime, M Brian Maple, Kalyan Sasmal, Tatsuya Yanagisawa, John Singleton, Pei-Chun Ho We present measurements of resistivity, magnetostriction, and PDO conductivity on the skutterudite CeOs4Sb12 in static and pulsed magnetic fields up to 30/60 T, respectively. The temperature and field dependencies allow us to map out the boundaries of the low temperature phase (L phase) in the H-T-phase diagram which - contrary to previous results - shows an unusual dome-like appearance extending to 45 T. The L phase is characterized by semiconducting behaviour with a small Fermi surface whereas the metallic high-temperature, high-field H phase exhibits a large Fermi surface. Magnetostriction results suggest that the L to H transition is accompanied by a valence transition. Additional features in transport and PDO within the L phase point towards further alteration of the band structure with applied field. We discuss the phase diagram of CeOs4Sb12 in the context of hybridization of 4f electrons and compare it to other skutterudites. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P07.00012: Transport and magnetic properties of correlated Ce3Bi4Pd3 at high magnetic fields Satya K. Kushwaha, Mun Keat Chan, Priscila Rosa, Eric Bauer, Joe D Thompson, Jian-Xin Zhu, Chao Cao, Filip Ronning, Neil Harrison High magnetic fields are capable of destroying the Kondo effect, hence pro- viding an experimental tool to tune the ground state of f-electron systems.1 Ce3Bi4Pd3 is a narrow gap Kondo insulator recently predicted to be a strongly correlated Weyl semimetal.2 Here we present transport and mag- netization measurements in Ce3Bi4Pd3 under pulsed magnetic fields to 60 Tesla, the results are significantly different from Ce3Bi4Pt3. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P07.00013: Bulk topological Fermi arcs in heavy fermion systems Yuki Nagai, Yang Qi, Hiroki Isobe, Vladyslav Kozii, Liang Fu We find that heavy fermion systems can have bulk ``Fermi arcs''. In an interacting electron system, we can define the effective Hamiltonian Heff = H+Σ, where the many-body Hamiltonian is Hermitian, but the one-body quasiparticle Hamiltonian is non-Hermitian due to the finite quasiparticle lifetime. By introducing a topological theory of finite-lifetime quasiparticles, we can find that the low-energy dispersion of the Dirac material is reshaped and a topologically protected bulk Fermi arc appears[1,2]. Finite quasiparticle lifetime is a generic property of quantum many body systems, resulting from scatterings. The exceptional points of the non-Hermitian quasiparticle Hamiltonian matrix play a crucial role. With the use of the dynamical mean field theory (DMFT) calculation, we confirm our statement in Kondo insulators with a momentum-dependent hybridization in two-dimensions. We show that the concept of the exceptional points in the non-Hermitian quasiparticle Hamiltonian is one of powerful tools to predict new phenomena in strongly correlated electron systems. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P07.00014: Exploration of large anomalous Hall effect and topological Berry curvature in strongly correlated d- and f-electron magnets Eric Bauer, T. Asaba, Nakheon Sung, M. M. Piva, M. Curtis, Sean Thomas, Priscila Rosa, Joe D Thompson, Filip Ronning The discovery of new topological states of matter and the effects of topology on the bulk properties of materials has attracted widespread attention [1], as these states are promising candidates for future technological applications such as quantum computing, memory storage, and sensors. While much of the research has focused on the exploration of topological states in materials without strong electronic correlations, these correlations open up new routes to generating novel topological states. For example, competing interactions among the magnetic moments of d- or f-electrons lead to magnetic frustration and often give rise to non-collinear or non-coplanar spin structures. Mobile conduction electrons feel the effects of a large (fictitious) magnetic field when they move in the topological spin texture of these non-collinear and non-coplanar magnets, which gives rise to a large anomalous Hall effect in compounds such as Mn3Sn [2,3]. In this talk, I discuss our recent work on the exploration of the anomalous Hall effect and topological Berry curvature in a variety of strongly correlated d- and f-electron magnets. |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P07.00015: Possible observation of topological surface states in a d-electron Kondo Insulator with angle-resolved photoemission spectroscopy Kejun Xu, Yu He, Sudi Chen, Makoto Hashimoto, Donghui Lu, Sung-Kwan Mo, Zhixun Shen We use angle-resolved photoemission to probe the low energy bands of a d-electron Kondo Insulator exhibiting many similar properties as the prototypical f-electron topological kondo insulator candidate SmB6. We find a set of fermi surface features that disperse across Ef, despite the bulk being insulating. Photon energy dependence shows the 2D nature of these bands. We discuss similarity and differences to SmB6 and open questions that challenges the current understanding of strongly correlated topological insulators. |
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