Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H44: Topological Insulators Including SmB6 |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Luis Balicas, Natl High Magnetic Field Lab Room: LACC 504 |
Tuesday, March 6, 2018 2:30PM - 2:42PM |
H44.00001: Weyl-Kondo semimetal and proximate phases in heavy fermion systems Sarah Grefe, Hsin-Hua Lai, Silke Buehler-Paschen, Qimiao Si Recently we have introduced a periodic Anderson model on a noncentrosymmetric lattice and demonstrated a Weyl-Kondo semimetal (WKSM) [1], a strongly correlated topological semimetal phase. It features Weyl nodes developing out of the Kondo effect, with strongly reduced effective electron velocity, corresponding to a narrow band. Our proposed key experimental signatures have been realized in the recently discovered noncentrosymmetric heavy fermion semimetal Ce3Bi4Pd3 [2]. In this work, we address the role of space group symmetry on the WKSM phase, and study the overall phase diagram by analyzing transitions from WKSM to nearby phases. Furthermore, amid the rapidly expanding experimental results, we explore the thermodynamic signatures of these phases. |
Tuesday, March 6, 2018 2:42PM - 2:54PM |
H44.00002: Critical Examination of Quantum Oscillations in SmB$_6$: Magnetic Breakthrough. Peter Riseborough, Zachary Fisk We critically review the results of magnetic torque measurements on SmB$_6$ that show quantum oscillations. Similar studies have been given two different interpretations. One interpretation is based on the existence of metallic surface states, while the second interpretation is in terms of a three-dimensional Fermi-surface involving neutral fermionic excitations. We argue that the range of fields used spans the critical field at which magnetic breakthrough occurs. The phenomenon of magnetic breakthrough involves the formation of Landau orbits which produces a directional-dependent suppression of Bragg scattering. We conclude that the measurements performed under higher field conditions are fully consistent with expectations based on a three-dimensional semiconducting state with magnetic breakthrough |
Tuesday, March 6, 2018 2:54PM - 3:06PM |
H44.00003: Fermi Surfaces in Kondo Insulators Hsu Liu, Mate Hartstein, William Toews, Yu-Te Hsu, Bin Zeng, Xiaoye Chen, Monica Ciomaga Hatnean, Michelle Johannes, Qiu Run Zhang, Shota Nakamura, Andrew padgett, Gilles Rodway-Gant, Mun Chan, Satoshi Yamashita, Toshio Sakakibara, Yasumasa Takano, Ju-Hyun Park, Luis Balicas, Neil Harrison, Natalya Shitsevalova, Geetha Balakrishnan, Gilbert Lonzarich, Robert Hill, Michael Sutherland, Suchitra Sebastian We report experimental signatures signifying the existence of bulk Fermi surfaces in the Kondo insulator family and compare these with theoretical models. We have observed quantum oscillations, traditionally considered a hallmark of Fermi liquids, in magnetization in the Kondo insulator SmB6 [Hartstein et al., nphys4295]. The quantum oscillations, taken together with measured finite specific heat coefficient at low temperatures, finite quantum oscillatory entropy, and magnetic field enhancement of thermal conductivity, suggest the existence of bulk Fermi surfaces that originate from novel quasiparticles that couple to magnetic fields but not DC electric fields. Since our experimental observation, a number of innovative theories have been proposed to explain how a Fermi surface could arise in charge gapped Kondo insulators. Here, we explore experimental signatures in light of these theoretical proposals. |
Tuesday, March 6, 2018 3:06PM - 3:18PM |
H44.00004: Bulk Rotational Symmetry Breaking in Kondo Insulator SmB6 Ziji Xiang, Benjamin Lawson, Tomoya Asaba, Colin Tinsman, Lu Chen, Chao Shang, Xianhui Chen, Lu Li In Kondo insulators the insulating behavior is introduced by the interaction between localized and conduction electrons at low temperature. Theories predicted that Kondo insulator is a promising candidate of strongly electron correlated topological insulator. The de Haas-van Alphen (dHvA) effect, i.e., oscillation in magnetization generated by the energy quantization of conduction electrons in magnetic field, has been observed in the insulating phase of samarium hexaboride (SmB6), a typical Kondo insulator. Intense debate has been put on the origin of the dHvA oscillations. We measured the dHvA signal using torque magnetometry in SmB6 single crystals. Besides the 2D-like angular dependence of dHvA oscillation frequencies, the angle-dependent amplitude breaks the 4-fold rotational symmetry of the cubic crystal structure. The angular and temperature dependence of dHvA amplitudes are both consistent with the behavior of a 2D Fermi liquid system down to 40 mK and up to 45 T [1]. Our results demonstrate the existence of 2D electronic states with light quasiparticle mass in SmB6, which are consistent with the interpretation of topologically protected surface states. |
Tuesday, March 6, 2018 3:18PM - 3:30PM |
H44.00005: High temperature bulk transport on floating-zone and Al-flux grown SmB6 using Hall bar geometry Alexa Rakoski, Yun Suk Eo, Kai Sun, Cagliyan Kurdak, Priscila Rosa, Zachary Fisk, Monica Ciomaga Hatnean, Geetha Balakrishnan, Boyoun Kang, Myung-suk Song, Beongki Cho Samarium hexaboride is a correlated topological insulator in which strong interactions between f and d electrons lead to the opening of a small hybridization gap at the Fermi energy below about 100 K. At higher temperatures, at which the gap has not formed, the f-d interactions instead lead to strong skew scattering in the presence of a magnetic field. In addition, the bulk of SmB6 is interesting in light of recent quantum oscillation results suggesting an unconventional bulk Fermi surface. We investigate the bulk of SmB6 and the role of f-d interactions in its electronic properties via Hall coefficient and resistivity measurements from 4-400 K using a standard Hall bar geometry. Data are presented for a variety of samples, including pure SmB6 grown by both the aluminum flux method and the floating zone method, as well as SmB6 intentionally grown with Sm deficiencies. We find a dramatic variation in the transport properties of these samples, most notably in the sign of the Hall coefficient above 60 K, even among pure samples grown by different methods, and we are continuing to investigate the origin of these variations. |
Tuesday, March 6, 2018 3:30PM - 3:42PM |
H44.00006: Low temperature residual bulk resistivity in floating zone SmB6 using the inverted resistance measurement Yun Suk Eo, Juniar Lucien, Alexa Rakoski, Dmitri Mihaliov, Cagliyan Kurdak, Monica Ciomaga Hatnean, Geetha Balakrishnan Samarium hexaboride (SmB6) is a fascinating heavy-fermion system which appears to be the first correlated topological insulator with robust surface conduction and truly insulating bulk. We studied the low-temperature bulk transport of SmB6 motivated by the magnetotorque report suggesting that the material might have an unconventional bulk Fermi surface. The bulk Fermi surface has been reported in SmB6 crystals grown by the floating zone method. In electrical transport below ~4 K, there is a well-known resistance plateau that originates from the surface conduction. We found some of our SmB6 crystals grown by the floating zone method show an absence of this resistance plateau, but instead a moderate resistance change. This resistance change is weak enough that it can be interpreted as the surface resistance plateau with a large temperature dependence. However, by using the inverted resistance technique, we clearly show that it originates from the bulk. The samples are being characterized using X-ray diffraction, Auger, high-resolution TEM, and energy dispersive X-Ray spectroscopy measurements with the goal of identifying differences between SmB6 crystals grown by Al-flux and floating-zone methods. |
Tuesday, March 6, 2018 3:42PM - 3:54PM |
H44.00007: Overcoming Kondo insulating behavior via disorder, a possible connection of the SmB6 puzzle Sudeshna Sen, Eduardo Miranda, N S Vidhyadhiraja, Wei Ku, Vladimir Dobrosavljevic Experimental reports of certain low-temperature metallic features for the proposed topological Kondo insulator SmB6 has recently led to serious controversy in the field. Here we address this issue by exploring the effects of disorder in a generic Kondo insulator, by examining an appropriate Anderson lattice model within dynamical mean-field theory. We find that even a moderate strength of disorder produces a very broad distribution of local Kondo scales, which proves sufficient to overcome the typical Kondo insulating behavior, and giving rise to a poor conductor with anomalous properties. Physically, the local regions with very low Kondo temperatures correspond to a locally reduced Kondo gap, thus producing significant disorder-induced in-gap states. Our results offer a possible resolution of the current debate on SmB6. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H44.00008: Screened Moments in a Kondo insulator: extrinsic origin of in-gap states in SmB6 Wesley Fuhrman, Juan Chamorro, Pavel Alekseev, Jean-Michel Mignot, Thomas Keller, Jose Rodriguez, Yiming Qiu, Predrag Nikolic, Tyrel McQueen, Collin Broholm
|
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H44.00009: Evolution of the low energy electronic states in SmxLa(1-x)B6 studied by ARPES Marta Zonno, Matteo Michiardi, Fabio Boschini, Eduardo Da Silva Neto, Elia Razzoli, Berend Zwartsenberg, Ryan Day, Pascal Nigge, Michael Schneider, Giorgio Levy, Priscila Rosa, Zachary Fisk, Ilya Elfimov, George Sawatzky, Andrea Damascelli In the recent years, the interplay between topological orders and electronic correlations has attracted the attention of the scientific community. Theoretical works propose SmB6 as a Topological Kondo Insulator in which topologically protected surface states lie within the bulk band gap stemming from the hybridization of localized f-electrons with conduction electrons [1, 2]. However, experimental evidences of the bulk origin of the in gap states have been reported; in particular Z.-H. Zhu et al. observed non-topological surface states originating from B-2p dangling bonds on a polar surface [3]. In order to overcome the complexity in the theoretical interpretations of the ground state of SmB6, we use ARPES to study a wide range of SmxLa(1-x)B6 samples. LaB6 has the same crystal structure of SmB6 and presents qualitatively the same features in the electronic structure, but the lack of f-electrons leads to a metallic ground state. Here we report on the evolution of the low energy electronic states in SmB6 as a function of electronic correlations by gradually varying the stoichiometry of SmxLa(1-x)B6 compounds. |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H44.00010: Mixed-valence insulators with neutral Fermi-surfaces Senthil Todadri, Debanjan Chowdhury, Inti Sodemann Samarium hexaboride is a classic three-dimensional mixed valence system with a high-temperature metallic phase that evolves into a paramagnetic charge insulator below 40 kelvin. A number of recent experiments have suggested the possibility that the low-temperature insulating bulk hosts electrically neutral gapless fermionic excitations. In this work we describe a new phase of matter---composite exciton Fermi liquid--- a mixed valence insulator with a three dimensional fermi-surface of a neutral fermion, that we name the "composite exciton". We describe the mechanism responsible for the formation of such excitons, discuss the phenomenology of the composite exciton Fermi-liquids and make comparison to experiments in SmB6. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H44.00011: Quantum Oscillations in Insulators with Neutral Fermi Surfaces Inti Sodemann, Debanjan Chowdhury, Senthil Todadri We describe a theory of quantum oscillations in insulators with a fermi sea of neutral fermions minimally coupled to an emergent U(1) gauge field. In the presence of a physical magnetic field the emergent magnetic field develops a non-zero value leading to Landau quantization for the neutral fermions. We will describe the temperature and magnetic field dependence of oscillations in magnetization and in electrical resistivity and discuss suitable experimental conditions for the observation of these effects in the composite exciton fermi liquid state proposed in mixed valence insulators as well as in the spinon fermi surface state proposed in triangular organic materials. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H44.00012: Spectroscopic nature of the topological Kondo insulator SmB6 Wan Kyu Park, Shu Liu, Laura Greene, D.J. Kim, Zachary Fisk Samarium hexaboride (SmB6), a well-known Kondo insulator, has recently received great deal of attention due to the possibility of being a correlated topological insulator. Despite numerous experimental findings supportive of this possibility, its detailed spectroscopic properties remain to be elucidated. Our recent tunneling spectroscopy based on planar junctions on SmB6 [1, 2] has not only found evidence for the existence of multiple surface Dirac fermions, in agreement with a quantum oscillation study as well as theoretical predictions, but also revealed their intriguing topological nature affected by the interaction with bulk excitations, called spin excitons [3]. We will present tunneling conductance spectra for two different surface orientations as a function of temperature and magnetic field and discuss the implications of our results. In particular, we will focus on some of the outstanding open questions in relation to our findings. [1] W. K. Park et al., Proc. Natl. Acad. Sci. U. S. A. 113, 6599 (2016); [2] L. Sun et al., Phys. Rev. B 95, 195129 (2017); [3] G. A. Kapilevich et al., Phys. Rev. B 92, 085133 (2015). |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H44.00013: Optical Pump-Probe and Transient Grating Study of SmB6 Peter Kissin, Monica Ciomaga Hatnean, Guangwu Duan, Xin Zhang, Geetha Balakrishnan, Richard Averitt We study ultrafast quasiparticle (QP) relaxation and diffusion dynamics in Al flux-grown SmB6 single crystals using optical pump-probe (OPPS) and transient grating (TGS) spectroscopies. OPPS is sensitive to small gaps in the density of states near the Fermi energy due to the relaxation bottleneck effect. TGS, a variant of OPPS in which two pump pulses are interfered on the sample surface to create a spatially periodic excitation, yields additional information, including the optical phases and diffusion constants associated with photoexcited QPs. SmB6 is a mixed valence compound that becomes a Kondo Insulator when a hybridization gap opens near 50 K. At low temperatures, anomalous behavior is observed with a variety of experimental techniques. Past OPPS results on SmB6 show changes in the QP relaxation dynamics in the low temperature phase1,2. Using TGS, we measure relaxation and diffusion dynamics of QPs as a function of pump excitation density, crystal surface, and probe wavelength, from room temperature to 3.3 K, in an attempt to clarify the origin of the anomalous low temperature OPP signal reported in previous studies. |
Tuesday, March 6, 2018 5:06PM - 5:18PM |
H44.00014: Ultrafast electronic dynamics in a strongly correlated insulator SmB$_{6}$ Kejun Xu, Alexandre Gauthier, Heike Pfau, Jonathan Sobota, Jing Xia, Patrick Kirchmann, Zhi-Xun Shen SmB$_{6}$ is a strongly correlated Kondo insulator that forms a gap at the Fermi level due to hybridization between Sm 4f and 5d states. Such a gap can support interaction-driven excitons protected by strongly renormalized bands as discussed in inelastic neutron scattering and Raman spectroscopy studies. We excite SmB$_{6}$ with an ultrafast laser pulse, and study the resulting dynamics using time- and angle-resolved photoemission spectroscopy. We discover a coherent oscillatory response of the electronic states near the Gamma point, which we characterize as function of excitation density and temperature. We discuss possible origins for the observed mode. |
Tuesday, March 6, 2018 5:18PM - 5:30PM |
H44.00015: Laser-irradiated Kondo insulators: Controlling the Kondo effect and topological phases Kazuaki Takasan, Masaya Nakagawa, Norio Kawakami We investigate theoretically the nature of laser-irradiated Kondo insulators. Using Floquet theory and the slave-boson approach, we study a periodic Anderson model and derive an effective model that describes laser-irradiated Kondo insulators. In this model, we find two generic effects induced by laser light. One is dynamical localization, which suppresses hopping and hybridization. The other is laser-induced hopping and hybridization, which can be interpreted as synthetic spin-orbit coupling or a magnetic field. The first effect drastically changes the behavior of the Kondo effect. The second effect triggers topological phase transitions.Our results make it possible to dynamically control the Kondo effect and topological phases in heavy-fermion systems. We also discuss experimental setups to detect the signatures. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700