Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K23: Novel Surface and Bulk States in Topological Kondo InsulatorsInvited

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Sponsoring Units: DCMP Chair: James Analytis, University of California, Berkeley Room: New Orleans Theater B 
Wednesday, March 15, 2017 8:00AM  8:36AM 
K23.00001: Bulk Fermi surface of chargeneutral excitations in SmB$_{\mathrm{6}}$ or not: A heattransport study Invited Speaker: Shiyan Li Recently, there have been increasingly hot debates on whether a bulk Fermi surface of chargeneutral excitations exists in the topological Kondo insulator SmB$_{\mathrm{6}}$. To unambiguously resolve this issue, we perform the lowtemperature thermal conductivity measurements of a highquality SmB$_{\mathrm{6}}$ single crystal down to 0.1 K and up to 14.5 T. Our experiments show that the residual linear term of thermal conductivity at the zero field is \textit{zero}, within the experimental accuracy. Furthermore, the thermal conductivity is insensitive to the magnetic field up to 14.5 T. These results demonstrate the absence of fermionic chargeneutral excitations in bulk SmB$_{\mathrm{6}}$, such as scalar Majorana fermions or spinons and, thus, exclude the existence of a bulk Fermi surface suggested by a recent quantum oscillation study of SmB$_{\mathrm{6}}$. This puts a strong constraint on the explanation of the quantum oscillations observed in SmB$_{\mathrm{6}}$. [1] Y. Xu, S. Cui, J. K. Dong, D. Zhao, T. Wu, X. H. Chen, Kai Sun, Hong Yao, and S. Y. Li, Phys. Rev. Lett. 116, 246403 (2016). [Preview Abstract] 
Wednesday, March 15, 2017 8:36AM  9:12AM 
K23.00002: Unconventional Fermi surface associated with novel quasiparticles in the Kondo insulator SmB$_{\mathrm{6}}$ Invited Speaker: Suchitra Sebastian The search for a Fermi surface in the absence of a Fermi liquid has endured for decades. We present evidence for the realisation of such a state in the Kondo Insulator SmB$_{\mathrm{6}}$, which is an extreme example of Fermi liquid breakdown. Experimental results are presented from complementary techniques including quantum oscillations, specific heat capacity, thermal conductivity, and oscillatory entropy down to low temperatures. An experimental comparison is made with alternative theoretical models that associate novel quasiparticles with the unconventional Fermi surface we uncover in SmB$_{\mathrm{6}}$. A new paradigm for the realisation of a Fermi surface in the absence of conventional quasiparticles is proposed in the vicinity of a Kondo insulator transition. \newline *This work was performed in collaboration with M. Hartstein, W. H. Toews, Y.T. Hsu, B. Zeng, X. Chen, M. Ciomaga Hatnean, Q. R. Zhang, S. Nakamura, A. S. Padgett, G. RodwayGant, J. Berk, M. K. Kingston, G. H. Zhang, M. K. Chan, S. Yamashita, T. Sakakibara, Y. Takano, J. H. Park, L. Balicas, N. Harrison, N. Shitsevalova, G. Balakrishnan, G. G. Lonzarich, R. W. Hill, and M. Sutherland [Preview Abstract] 
Wednesday, March 15, 2017 9:12AM  9:48AM 
K23.00003: Modelling SmB$_6$: Distinct topological crystalline phases, surface states, and surface reconstruction Invited Speaker: Matthias Vojta SmB$_6$ has been proposed to be both a strong topological insulator and a topological crystalline insulator. For this and related cubic topological Kondo insulators, we discuss a set of tightbinding bandstructure models. We prove the existence of four different topological phases, distinguished by the sign of mirror Chern numbers. For all phases, we compute the properties of topological surface states on generic $(lmn)$ surfaces. We highlight the possibility of transitions between different topological states and explore their signatures. Finally, we investigate a $2\times1$ surface reconstruction and its effect on surface quasiparticleinterference (QPI) spectra. [Preview Abstract] 
Wednesday, March 15, 2017 9:48AM  10:24AM 
K23.00004: Chiral edge transport induced by Diracelectronmediated ferromagnetic domain walls in topological Kondo insulator SmB$_6$ Invited Speaker: Yasuyuki Nakajima Topological Kondo insulators provide a novel quantum state of matter with a nontrivial metallic surface robust against perturbations with time reversal symmetry in the bulk energy gap driven by strong electron correlations. One of the most promising candidates of the correlated topological insulator is Kondo compound SmB$_6$ [1]. Identified by extensive study including nonlocal transport [2] and anguleresolved photoemission spectroscopy [3], metallic surface states exist in the Kondo insulating gap formed by the hybridization between itinerant conduction electrons and localized felectrons at low temperatures. However, the observations of polaritydriven surface states [4] and three dimensional Fermi surface in insulating states [5], together with lack of direct evidence of the chiral nature of surface conduction, have brought into question the topological nature in this material. Here, we report detailed study on very lowtemperature magnetoresistance, revealing unusual ferromagnetic hysteresis with a sign reversal stemming from chiral edge conduction channels between the Dirac electron mediated ferromagnetic domains on the surfaces. Combined with suppression of the weak antilocalization and observation of anomalous Hall effect in the surface conduction, the unusual hysteresis provides strong evidence for the presence of topologically nontrivial surface states in SmB$_6$ [6].\\ \\$[1]$ A. Menth et al., Phys. Rev. Lett. 22, 295 (1969). \newline [2] S. Wolgast et al., Phys. Rev. B 88, 180405 (2013). \newline [3] M. Neupane et al., Nat. Commun. 4, 2991 (2013). \newline [4] Z.H. Zhu et al., Phys. Rev. Lett. 111, 216402 (2013). \newline [5] B.S. Tan et al., Science 349, 287 (2015). \newline [6] Y. Nakajima et al., Nat. Phys. 12, 213 (2016). [Preview Abstract] 
Wednesday, March 15, 2017 10:24AM  11:00AM 
K23.00005: Unconventional electronic properties of conventional Kondo insulator Invited Speaker: Maxim Dzero The physics of samarium hexaboride  a narrow gap strongly correlated semiconductor discovered almost 50 years ago  continues to inspire experimental and theoretical research. Much of the recent experimental work seeks to test the theoretical proposal that samarium hexaboride could be a prototypical example of the first correlated Z$_{\mathrm{2}}$ topological Kondo insulator. In this talk I will first outline the main ideas which lead to realization that samarium hexaboride becomes a topological Kondo insulator below a certain temperature. I will discuss recent theoretical works which propose several experiments helping to prove that the metallic surface states in samarium hexaboride are indeed topological. Finally, I will review most recent experiments which challenge our current understanding of physics of this fascinating material. [Preview Abstract] 
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