Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K41: Topological Kondo Semimetals and Low Carrier SystemsInvited
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Sponsoring Units: DCMP DMP Chair: Piers Coleman, Rutgers Univ Room: LACC 502A |
Wednesday, March 7, 2018 8:00AM - 8:36AM |
K41.00001: Experimental Evidence for Weyl Semimetal Behavior in Kondo Systems Invited Speaker: Silke Buehler-Paschen The quest for topologically nontrivial phases in strongly correlated electron systems has recently led to the notion of Weyl-Kondo semimetals [1]. We have observed direct thermodynamic evidence for the corresponding linear electronic dispersion, with strongly renormalized velocity, in the new non-centrosymmetric cubic material Ce3Bi4Pd3 [2]. Its isostructural sister compound Ce3Bi4Pt3 is a canonical Kondo insulator. Our study of the substitution series Ce3Bi4(Pt1-xPdx)3 showed that, while the replacement of the 5d element Pt by the much lighter 4d element Pd strongly reduces the conduction electron spin-orbit coupling, it is isostructural, isoelectronic, and isosize [2]. This indicates that the Weyl semimetal state may develop near a (non-centrosymmetric) Kondo insulator in the presence of reduced spin-orbit coupling. Also other candidate materials, in particular tetragonal CeRu4Sn6 [3-5] and orthorhombic CeNiSn [6], will be discussed. |
Wednesday, March 7, 2018 8:36AM - 9:12AM |
K41.00002: Weyl-Kondo Semimetal in Heavy Fermion Systems Invited Speaker: Hsin-Hua Lai The study of strongly correlated and topologically nontrivial insulators goes back in decades to quantum Hall systems. By contrast, topological conductors with strong correlations have yet to be identified. Heavy fermion semimetals are a prototype of strongly correlated systems and, given their inherently strong spin-orbit coupling, present a natural setting to make progress. We have advanced a Weyl-Kondo semimetal phase [1] within a well-defined three-dimensional lattice model that breaks the inversion symmetry. The quasiparticles near the Weyl nodes develop out of the Kondo effect, as do the surface states that feature Fermi arcs. This has allowed us to propose a key thermodynamic signature of the Weyl-Kondo semimetal phase, viz. the specific heat C going as T cubed with a prefactor enhanced by as much as 9 orders of magnitude compared to the expected value for weakly correlated systems. This thermodynamic signature has been realized in the recently discovered heavy fermion semimetal Ce3Bi4Pd3 [2]. Our findings provide the much-needed theoretical foundation for the experimental search of topological conductors with strong correlations, and open up a way for systematic studies of such quantum phases that naturally entangle multiple degrees of freedom. |
Wednesday, March 7, 2018 9:12AM - 9:48AM |
K41.00003: Evidence for topological Kondo semimetals Invited Speaker: Huiqiu Yuan In this presentation, we will report our recent progress studying the topological properties of the correlated semimetals RX (R = Ce, Pr, Sm; X=Sb, Bi) and YbPtBi. |
Wednesday, March 7, 2018 9:48AM - 10:24AM |
K41.00004: New aspects in topological heavy fermion systems Invited Speaker: Po-Yao Chang Heavy fermion materials provide a playground to extend our current understanding of topological phases of matter. This talk will present two new types of topological Kondo systems that go beyond the standard models. Firstly, when topology meets nonsymmorphic crystal symmetries, a Z4 topological insulating phase emerges with Mobius twisted surface states. The heavy fermion semimetal CeNiSn is one candidate ”Mobius Kondo Insulators”[1]. Secondly, heavy Weyl semimetals can emerge from topological Kondo insulators drive by the formation of a parity-violating hybridization between d- and f-electrons [2]. We show the renormalization effect induced by hybridization and the development of the surface Kondo breakdown, which gives rise to a temperature-dependent of re-configuration of Fermi arcs which will be visible in quantum oscillation experiments.
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Wednesday, March 7, 2018 10:24AM - 11:00AM |
K41.00005: ARPES investigations of proposed topological low carrier density Ce and Yb compounds Invited Speaker: Jonathan Denlinger In the search for new strongly correlated topological materials, going beyond the initial candidate material SmB6, a number of issues arise in the angle-resolved photoemission (ARPES) interpretations of observed Dirac-like band dispersions and two-dimensionality. In particular the example of YbB6, a divalent small-gap semiconductor at ambient pressure, misinterpreted as a topological Kondo insulator, highlights issues of surface termination, polarity and band-bending, V-shaped non-parabolicity of band dispersions arising from small gaps, degrees of two-dimensionality, interpretation of circular dichroism, and use of theoretical band-gap correction methods. With such lessons in mind, we focus attention on three low carrier density heavy fermion systems of (i) YbPtBi, an ultra-heavy-fermion half-Heusler semimetal, (ii) CeSb and related fcc monopnictide semimetals, and (iii) CeRhSb, a Kondo insulator with predicted Mobius-type surface state dispersion. We critically assess the ARPES evidence for their proposed topological properties and highlight the tool of surface alkali-dosing to help distinguish surface state scenarios. In addition, we report progress in the understanding of their various bulk properties including CEF splittings, temperature-dependence of f-states and magnetic ground states. |
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