Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S37b: SmB6 and Correlated Topological Materials |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Wan Kyu Park, National High Magnetic Field Laboratory: Florida State University Room: 384 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S37b.00001: Thermoelectric Measurements and Angle-Resolved Magnetic Torque in Kondo Insulator SmB$_6$ Ziji Xiang, Colin Tinsman, Tomoya Asaba, Benjamin Lawson, Gang Li, Fan Yu, Lu Chen, Hongwoo Baek, Chao Shang, Xianhui Chen, Lu Li Kondo insulator samarium hexaboride (SmB$_6$) has attracted much attention in recent years as a potential candidate of an interaction-driven topological insulator. One of the most puzzling phenomena observed in SmB$_6$ is the clear quantum oscillations appearing in magnetic torque at a low temperature even though the overall resistance curve is insulating. The origin of quantum oscillation is, however, still under debate with indications of both two-dimensional Fermi surfaces and three-dimensional bulk nature. We use two different approaches to study this phenomenon in detail. We carried out angle-resolved torque magnetometry measurements in a magnetic field up to 45 T and a temperature range down to 40 mK. The quantum oscillation amplitudes show almost no temperature dependence below 500 mK. The strongest oscillation branch shows a four-fold symmetry with magnetic field rotated in (010) plane. The angular dependence of its amplitude is consistent with a two-dimensional electron system in which the carrier mobility is suppressed by the in-plane magnetic field. We will also discuss the result of our low-temperature Seebeck effect and Nernst effect measurements in SmB$_6$ under strong magnetic field. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S37b.00002: Kondo insulator SmB6 under strain: surface dominated conduction near room temperature Alex Stern, Maxim Dzero, Victor Galitski, Zach Fisk, Jing Xia SmB6 is a strongly correlated mixed-valence Kondo insulator with a newly discovered surface state, proposed to be of non-trivial topological origin. However, the surface state dominates electrical conduction only below T*$=$4 K limiting its scientific investigation and device application. Here, we report the enhancement of T* in SmB6 under the application of tensile strain. With 0.7{\%} tensile strain we report surface dominated conduction at up to a temperature of 240 K, persisting even after the strain has been removed. This can be explained in the framework of strain-tuned temporal and spatial fluctuations of f-electron configurations, which might be generally applied to other mixed-valence materials. We note that this amount of strain can be induced in epitaxial SmB6 films via substrate in potential device applications. [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S37b.00003: Anomalous 3D bulk AC conduction within the Kondo gap of SmB$_6$ single crystals N. J. Laurita, C. M. Morris, S. M. Koohpayeh, P. F. S. Rosa, W. A. Phelan, Z. Fisk, T. M. McQueen, N. P. Armitage The Kondo insulator SmB$_6$ displays anomalous transport behavior at low temperatures which has recently been proposed to originate from in-gap topological surface states. Here, we investigate the low energy optical conductivity within the hybridization gap of single crystals of SmB$_6$ via time domain terahertz spectroscopy. Samples grown by both optical floating zone and aluminum flux methods are investigated and are found to display significant 3D bulk conduction originating within the Kondo gap that is many orders of magnitude larger than any known impurity band conduction. The nature of these in-gap states and their coupling with the low energy spin excitons of SmB$_6$ is discussed. Additionally, we show that any surface states, which lie below our detection threshold if present, must have a sheet resistance of R $\ge$ 1 k$\Omega$. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S37b.00004: Study of bulk resistivity of SmB$_6$ below the bulk to surface crossover temperature using non-local Corbino transport. Yun Suk Eo, Juniar Lucien, Kai Sun, Cagliyan Kurdak, Priscila Ferrari S. Rosa, Zachary Fisk There is growing evidence that samarium hexaboride (SmB$_6$) is a unique material that has a truly insulating bulk and topologically protected metallic surface states. It has a well-known resistance plateau below $\sim$4 K due to the crossover from bulk to surface conduction. Below this crossover temperature, conventional transport measurements can only detect surface properties, because there is little current flowing through the bulk. Because of this, questions remain about whether the bulk behavior above and below the crossover is identical, or whether exotic bulk states are present, as some experiments have suggested. Here, we introduce a non-local measurement technique that employs Corbino structures on the surface to detect bulk behavior below $\sim$4 K. We use two types of structures, a Corbino with two additional rings, or two sets of coaxially aligned Corbinos on the top and bottom surfaces. Using these structures, we measured bulk conductivity at temperatures down to $\sim$2 K, where surface conductivity dominates transport by many orders of magnitude. We find that the bulk behavior is identical above and below the crossover temperature, and that the activation energy is 3.3 meV. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S37b.00005: Understanding temperature-dependent bulk transport in samarium hexaboride without relying on in-gap states Alexa Rakoski, Yun Suk Eo, Kai Sun, Cagliyan Kurdak We present a new model to explain the difference between the transport and spectroscopy gaps in samarium hexaboride (SmB$_{6}$), which has been a mystery for some time. We propose that SmB$_{6}$ can be modeled as an intrinsic semiconductor with a screening length that diverges at cryogenic temperatures. In this model, we find a self-consistent solution to Poisson's equation in the bulk, with boundary conditions based on Fermi energy pinning due to surface charges. The solution yields band banding in the bulk; this explains the difference between the two gaps because spectroscopic methods measure the gap near the surface, while transport measures the average over the bulk. We also connect the model to transport parameters, including the Hall coefficient and thermopower, using semiclassical transport theory. The divergence of the screening length additionally explains the 10-12 K feature in data for these parameters, demonstrating a crossover from bulk dominated transport above this temperature to surface-dominated transport below this temperature. We find good agreement between our model and a collection of transport data from 4-40 K. This model can also be generalized to materials with similar band structure. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S37b.00006: Characterization of bulk and surface conduction of alloys of SmB6 using a coaxially aligned double-sided Corbino structure Juniar Lucien, Yun Suk Eo, Dmitri Mihaliov, Cagliyan Kurdak, Boyoun Kang, Beongki Cho, Priscila F. S. Rosa, Zachary Fisk It is well-known that the transport properties of topological Kondo insulator SmB$_{6}$ can be altered by introducing either vacancies or substitutional atoms in the Sm site. Previous studies have reported that SmB$_{6}$ would still exhibit an activated behavior as well as a robust low-temperature resistance plateau in the dilute doping limit, whereas it may have a metallic bulk in the high limit. In some cases, the resistance plateau value is a few orders of magnitude lower than that of pure SmB$_{6}$. This is difficult to explain within the topological insulator framework because increased disorder would normally result in lower mobility and therefore higher resistance. To resolve this issue, we studied samples with either vacancies or La substitution using a coaxially aligned double-sided Corbino geometry, which allowed us to extract temperature-dependent surface and bulk conductivities from a single sample. In a sample with 25\% La, we found the material to be a bulk conductor. On the other hand, for a sample with 25\% vacancy in the Sm site, we found the bulk to be truly insulating and the surface conductivity to be similar to that of pure SmB$_{6}$, which is inconsistent with previous reports. We will discuss the possible origins of these inconsistencies. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S37b.00007: Is SmB6 a failed superconductor?â€”Part I: long-wave length action Onur Erten, Po-Yao Chang, Piers Coleman, Alexei Tsvelik The theory of superfluids and superconductors is founded on London's idea of ``wavefunction rigidity", in which gradients of the condensate phase carry a persistent superflow. However, the theory of neutral superfluids reveals that a stable superflow also requires the topological quantization of circulation: when this is absent, as in the case of $^3$He-A, the superflow is unstable. Motivated with the controversial experimental results on SmB$_6$, we generalize this idea to charged superfluids, in which a higher dimensional order parameter manifold topologically destabilizes vortices, causing the rapid decay of supercurrents into a novel diamagnetic insulator. I will present a Ginzburg-Landau type long wavelength action of a `failed' superconductor and discuss how supercurrents decay through formation of space-time skyrmions. This work is done in collaboration with Po-Yao Chang, Piers Coleman and Alexei M. Tsvelik. [Preview Abstract] |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S37b.00008: Is SmB$_6$ a failed superconductor? --- Part II: a microscopic model Po-Yao Chang, Onur Erten, Piers Coleman, Alexei Tsvelik Heavy fermion materials provide a natural playground for extending our current understanding of topological phases of matter in the presence of strong correlations. In this talk, we would like to present a microscopic model of failed superconductivity in heavy fermion systems and its application to SmB$_6$. The essential part of the microscopic model is a Majorana representation of impurities in the Kondo lattices. We demonstrate a composite order parameter in this model cannot sustain stable supercurrent. In the mean-field level, we show a gapless Majorana Fermi sea emerges and is decoupled from impurities. We observe mirror symmetry protected surface states coexist with a bulk gapless Majorana Fermi sea. We establish the existence of a gapless Majorana Fermi sea may potentially resolve mysterious issues of quantum oscillation measurements in SmB$_6$. This work is done in collaboration with Onur Erten, Piers Coleman and Alexei M. Tsvelik. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S37b.00009: Is SmB6 a failed superconductor? Part III: Experimental Consequences Piers Coleman, Onur Erten, Po-Yao Chang, Alexei Tsvelik I will discuss how the idea of {\sl failed superconductivity} can be applied to the anomalous bulk properties of SmB$_{6}$, focusing on experimental consequences of this idea. While transport and ARPES measurements provide evidence of metallic surface states with an insulating bulk, specific heat, thermal/optical transport and quantum oscillations suggest the bulk {\sl hosts gapless neutral excitations.} We argue that these paradoxes can be understood as a result of a broken gauge invariance, restored at long distances by the macroscopic failure of the superconducting state. In particular, I shall discuss how the observation of a linear-in-field thermal conductivity[1] can be understood as the result of a skyrmion fluid within a failed superconductor[2,3,4], and provide various predictions for the low field physics and spectroscopy that can be used to test this idea. \\ \noindent [1] S. Sebastian et al, SCES 2016, Hangzhou. \\ \noindent [2] P. Coleman, E. Miranda and A. Tsvelik, Physica B: Cond. Matt., 186-188, 362 (1993). \\ \noindent [3] G. Baskaran, arXiv 1507.03477 \\ \noindent [4] O. Erten, P.-Y. Chang, P. Coleman, A. Tsvelik, preprint (2016) [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S37b.00010: Visualizing the Topologically Induced States of Strongly Correlated Electrons in SmB$_6$ Harris Pirie, Jennifer E. Hoffman, Yang He, Michael M. Yee, Anjan Soumyanarayanan, Dae-Jeong Kim, Zachary Fisk, Dirk Morr, Mohammad Hamidian The synergy between strong correlations and a topological invariant is predicted to generate exotic topological order, fractional quasiparticles and new platforms for quantum computation. SmB$_6$ is a promising candidate in which interactions generate an insulating state whose gap arises from heavy fermion hybridization of low lying $f$-states with a Fermi sea. We used spectroscopic imaging scanning tunneling microscopy to visualize the hybridization of distinct crystal-field-split $f$-levels and the temperature-dependent evolution of an insulating gap spanning the chemical potential. Here, armed with a clear description of the bulk bands, we look within the insulating gap and directly image two dispersing surface states converging to a Dirac point close to the chemical potential. We show that these measurements are consistent with Dirac cones centered at the $X$ and $\Gamma$ points in the surface Brillouin zone corresponding to a strong topological invariant. The observation of topological states induced from strong correlations establishes SmB$_6$ as an exciting playground for exotic physics. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S37b.00011: Heavy Weyl fermion state in CeRu$_4$Sn$_6$ Yuanfeng Xu, Changming Yue, Hongming Weng, Xi Dai We have found a new type of topological state, heavy Weyl fermion state, in the strongly correlated system CeRu$_4$Sn$_6$. Based on LDA+Gutzwiller calculation, which can treat the strong correlation effects effectively, both type-I and type-II Weyl fermion state can be formed in the quasi-particle band structure and the numbers of Weyl points are sensitive to the valence of Cerium. The surface calculations indicate that the topologically protected Fermi arc states exist on the (010) but not on the (001) surfaces. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S37b.00012: High field exploration beyond the quantum limit in three-dimensional metals Ross McDonald, Brad Ramshaw, Zengwei Zhu, Kim Putkonen, Arkady Shehter, Neil Harrison, Fedor Balakerev, Eric Bauer, Filip Ronning, Jon Betts Bandstructure topology is expected to have a profound influence upon the properties of metals at magnetic fields beyond the quantum limit, where all electrons occupy a single Landau level. In 2D electronic systems indexing Landau depopulation with field probes the Berry phase and provides the definitive identification of Dirac like dispersion. For multiband systems, in particular 3D metals, the connection between the Landau level depopulation and band topology is less trivial owing to mobility of charge between bands. Furthermore, in comparison to artificial 2D electron systems, very few 3D metals exist with sufficiently low carrier densities to access the quantum limit in even the highest available magnetic fields. Increased degeneracy at low Landau level occupation enhances the influence of electronic correlations -- famously manifest as the occurrence of the Fractional Quantum Hall Effect in trivial 2D electron systems. In 3D semimetals the band topology dictates a subtle balance between these correlations and depopulation effects due to the absence (or occurrence) of a band crossing. This talk presents recent magneto transport studies of 3D low carrier density semimetals revealing novel phenomena at extreme magnetic fields. These include the valley polarizing effect of tilted magnetic fields in the quantum limit of Bismuth, the observation of field induced excitonic insulating phases in the quantum limit of Graphite and a novel field induced phase beyond the quantum limit of the Weyl semimetal TaAs. [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S37b.00013: Negative longitudinal magnetoresistance in ErSb Nirmal Ghimire, Junfeng He, Hong Zheng, Stephan Rosenkranz, Z.-X. Shen, John Mitchell Recently, NaCl-type rare earth monopnictides have attracted much attention due to the indication of topological band properties both in theoretical calculations and spectroscopic and transport property measurements. Non-magnetic TX (T $=$ Y, La) and X $=$ (Sb, Bi) show extremely large transverse magnetoresistance, and Shubnikov-de Haas oscillations in the magnetotransport measurements. There are claims of surface state in LaBi and LaSb, but isostructural YSb with similar transport properties as those of the former two lacks a spectroscopic evidence of a non-trivial surface state. The magnetic counterparts CeSb, CeBi and NdSb show Dirac or Dirac-like dispersion in ARPES measurements. These spectroscopic features in these compounds are robust against the magnetic ordering. In order to further understand the interplay between magnetism and the electronic character, we have studied another rare earth antimonide ErSb that shows an antiferromagnetic ordering below 3.7 K. We will present the magnetic, transport and electronic properties of this compound and discuss on the longitudinal magnetoresistance, which is positive in the antiferromagnetic state and becomes negative above the T$_{N\, }$up to more than a decade in temperature. [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S37b.00014: Coherent spin-wave excitations in antiferromagnetic Weyl semimetal candidates Mn$_3$(Sn,Ge) Guy Marcus, Jonas Kindervater, Muhammad Ikhlas, Naoki Kiyohara, Agustinus A. Nugroho, Satoru Nakatsuji, Minoru Soda, Takatsugu Masuda, Matthew B. Stone, Collin L. Broholm Multiple theoretical proposals have identified Mn$_3$X (with X=Sn,Ge) as type-II Weyl semimetals (WSMs). While strong experimental evidence also exists for other WSMs, information regarding magnetic excitations in any of these materials remains lacking. To this end, we present high-resolution neutron scattering measurements of coherent spinwaves in the metallic Mn$_3$X. Linearly dispersive modes present with bandwidths exceeding 80~meV, approaching the scale of electronic excitations. They are gapped as much as 5~meV, also an important temperature scale ($\sim$50~K) in transport measurements. Mn$_3$Sn is distinguished by branches arising from incommensurate Bragg locations. The small transverse width of the observed modes is typically associated with localized magnetic moments, contrary to both the itineracy indicated by transport measurements and our generic understanding of d-band magnetism. In an attempt to make sense of this discrepancy and as a first step towards identifying any anomalous magnetic scattering, we compare our results to first principle calculations and linear spinwave theory. [Preview Abstract] |
Thursday, March 16, 2017 2:03PM - 2:15PM |
S37b.00015: Transport and thermodynamic properties of Dirac antiferromagnetic CuMnAs single crystals Ni Ni, Eve Emmanouilidou, Huibo Cao, Bing Shen, Jie Xing, Aoshuang Shi Although much research effort has been made on nonmagnetic topological semimetals, such as Dirac semimetals Cd3As2, Na3Bi, and Weyl semimetals TaAs family, the study of magnetic topological semimetals is less explored. Recently CuMnAs has been proposed to an antiferromagnetic Dirac semimetal with both time-reversal and inversion symmetry breaking. In this talk, we will present the growth, transport and thermodynamic properties of Dirac antiferromagnetic CuMnAs single crystals. [Preview Abstract] |
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. |
© 2020 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
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700