Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F05: Topological Superconductivity: 3D MaterialsFocus
|
Hide Abstracts |
Sponsoring Units: DMP Room: BCEC 108 |
Tuesday, March 5, 2019 11:15AM - 11:51AM |
F05.00001: Observation of Topological Surface State in High Temperature Superconductor MgB2 Invited Speaker: Xiaoqing Zhou Most topological superconductors known-to-date suffer from low transition temperatures (Tc) and/or high fragility to disorder and dopant levels, which greatly hamper the progress in this promising field. In this work, we suggest BCS superconductor MgB2 as a superior candidate: not only is its superconducting Tc=39K nearly triple the current record of all candidate topological superconductors, but it also has topological Dirac nodal line states which are highly tolerant against disorder and inadvertent doping variations. Our density functional theory (DFT) calculation and Angle-resolved Photoemission Spectroscopy (ARPES) measurements locate the topological Dirac Nodal Lines and their corresponding topological surface states on the [010] faces of MgB2, which could host topological superconductivity via the proximity effect to the bulk. |
Tuesday, March 5, 2019 11:51AM - 12:03PM |
F05.00002: Termination-dependent Superconducting Topological Surface States in Non-centrosymmetric PbTaSe2 Tien-Ming Chuang, Syu-You Guan, Peng-Jen Chen, Ming-Wen Chu, Raman Sankar, Fangcheng Chou, Horng-Tay Jeng, Chia-Seng Chang TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface or edge states. Within each vortex core of TSCs, there exist the zero energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. So far, PbTaSe2 is the only stoichiometric bulk material exhibits the required topological surface states at EF combined with fully gapped bulk superconductivity [1]. Interestingly, two distinct and stable cleaved surfaces have been identified to be Pb- and Se-termination by using spectroscopic imaging-scanning tunneling microscope. Two terminations exhibit striking difference in both atomic and electronic structures above Tc. In the superconducting state, both exhibit a full superconducting gap and zero energy bound state in the superconducting vortex cores. Our results show PbTaSe2 is a great platform for the study of 2D TSC. |
Tuesday, March 5, 2019 12:03PM - 12:15PM |
F05.00003: Topological superconductors in the Pb-Sn-In-Te system Genda Gu, Ruidan Zhong, John A. Schneeloch, Yangmu Li, Qiang Li, Tonica Valla, John Tranquada The discovery of 3D topological insulator materials and topological superconductor open up a new research field in the condensed matter physics. In order to search for the new topological superconductor, we have grown a large number of the single crystals of Pb-system ( Pb-Sn-In-Te) topological crystalline insulator and their topological superconductor . We have measured the physical properties on these single crystals by various techniques. We have studied the effect of crystal growth condition, impurity and composition on the bulk electrical conductivity of these single crystals. We try to find out which composition and crystal growth condition is the best for the best topological superconductor. We have got the bulk topological superconductor with Tc=4.8K. |
Tuesday, March 5, 2019 12:15PM - 12:27PM |
F05.00004: Approaching the type 2 Dirac point in Co-doped PdTe2 Wenkai Zheng, Rico Schoenemann, Gregory T. McCandless, Greta Chappell, Shirin Mozaffari, Yu-Che Chiu, Julia Y. Chan, Ryan Baumbach, Luis Balicas Topological states of quantum matter have been investigated intensively in recent few years. A combination of superconductivity and topological order is considered to be a potential platform for realizing Majorana fermions. PdTe2 was classified as a type 2 Dirac semimetal where the Dirac points are located 0.5 eV below the Fermi level. Furthermore, PdTe2 is a superconductor with Tc below 2K. In order to preserve the Dirac points and lower the Fermi level we substituted up to 50% of Pd with Co. While the magnetoresistance is strongly reduced compared to the pure Pd compound, our Co doped samples still show superconductivity with a Tc of 0.22 K at a Co concentration of 50%. So far however, all evidences still point towards PdCoTe2 being a conventional superconductor. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F05.00005: Effects of point-like disorder on electronic properties of PdTe2 superconductor Erik Timmons, Makariy Tanatar, Kyuil Cho, Serafim Teknowijoyo, Na Hyun Jo, Sergey Budko, Paul Canfield, Ruslan Prozorov, Marcin Konczykowski Electric and thermal conductivities were measured before and after the introduction of a controlled point-like disorder in single crystals of PdTe2 by 2.5 MeV electron irradiation. Superconducting transition temperature is suppressed, but not strong enough that together with the exponential variation of the low-temperature London penetration depth indicates nodeless superconductivity. The normal state resistivity perfectly follows the Matthiessen's rule as seen in a parallel upwards shift after irradiation. Its temperature variation can be fitted well by the Bloch-Grüneisen formula with Debye temperature determined from the specific heat. Thermal conductivity measurements show a good agreement with the Wiedemann-Franz law. |
Tuesday, March 5, 2019 12:39PM - 12:51PM |
F05.00006: Enhanced Correlation Effects in Nodal-line Semimetal ZrSiSe Yinming Shao, Alexander N. Rudenko, Jin Hu, Yanglin Zhu, Alexander I. Lichtenstein, Zhiqiang Mao, Mikhail Katsnelson, Dimitri Basov Three-dimensional (3D) Dirac fermions with highly-dispersive linear bands are usually considered weakly correlated, due to relatively large bandwidths (W) compared to Coulomb interactions (U). With the discovery of nodal-line semimetals, the Dirac dispersion has been extended to lines and loops, with reduced kinetic energy along the line [1]. However, experimental evidence for the predicted enhanced correlations in nodal-line semimetals has been rare. Here we show in ZrSiSe enhanced correlation effects through a combination of optical/magneto-optical spectroscopy and density-functional-theory (DFT) calculations. Near 40% kinetic energy reduction compared to DFT has been observed in ZrSiSe and the averaged Fermi velocity is also renormalized. ZrSiSe is therefore a novel candidate to study correlation-driven physics in Dirac systems as well as strong Berry curvature effects associated with spin-orbit-coupling. |
Tuesday, March 5, 2019 12:51PM - 1:03PM |
F05.00007: Possible valence skipping superconductivity in doped Dirac metal Teppei Ueno, Takanori Wakita, Tetsuya Furukawa, Tetsuaki Itou, Takayoshi Yokoya, Jun Akimitsu, Kaya Kobayashi We studied the superconductivity in NaCl-type structured AgSnSe2 (Tc~3-6 K). The material is perceived as Ag-doped to imaginary NaCl-type SnSe, a Dirac metal. By varying the ratio of Ag/Sn, i.e., changing the ratio of Sn valence states, 2+ and 4+, we found that the Sn 2+ state is crucial for the realization of superconductivity along with the lattice constant. This finding is supported by the XPS, showing the clear coexistence of Sn 2+ and Sn 4+ in the superconducting Ag-Sn-Se compounds, but not in non-superconducting Sn-Se. The NMR experiments on the same superconducting compounds, however, indicated the Sn state is almost 3+, as is expected from the neutrality. The disagreement on these experiments may come from the electronic states in the compound’s unique superconductivity. |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F05.00008: Superconductivity and Nontrivial Band Topology in NbN Polytypes Kunchala Ramesh Babu, Guang-Yu Guo Niobium nitride is a good superconductor in its cubic structure (d-NbN) with Tc = 17 K [1]. Recent experiments on hexagonal NbN (e-NbN) revealed the existence of superconductivity with a Tc of 12 K [2]. WC-type NbN possesses topological properties with three fold band crossings [3]. Here we study the electronic band structure and superconductivity in these NbN polytypes by performing density functional calculations. Interestingly, our results reveal that all three NbN polytypes are topological metals. Specifically, d-NbN and e -NbN are, respectively, type-II and type-I Dirac metals, while WC-NbN is a topological metal with triply degenerate nodes. Our results also show that the electron-phonon coupling in d-NbN is much stronger than in e-NbN and WC-NbN. This results in a much higher superconducting transition temperature (Tc = 18 K) than in e-NbN and WC-NbN. Our findings thus suggest that the NbN polytypes would provide valuable opportunities for studying exotic phenomena arising from the interplay between superconductivity and band topology. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F05.00009: Spontaneously polarized half-gapped superconductivity in UTe2 Sheng Ran, Chris Eckberg, Qing-Ping Ding, Yuji Furukawa, Tristin E Metz, Shanta Saha, I-Lin Liu, Mark Zic, Johnpierre Paglione, Nicholas Butch We discovered novel nonunitary spin-triplet superconductivity in UTe2, with the highest Tc and Hc2 among all candidates. Superconducting state closely resembles that of ferromagnetic superconductors, but the normal state is paramagnetic and shows no indication of magnetic ordering. UTe2 exhibits an extremely large, anisotropic upper critical field Hc2, temperature independent NMR Knight shift in the superconducting state, and a large residual normal electronic density of states indicating that half of the electrons remain ungapped. All these results strongly indicate that the superconductivity in UTe2 is carried by nonunitary spin-triplet pairs. This discovery yields a new platform for encoding information using topological excitations and for manipulation of spin-polarized currents. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F05.00010: Fermi-arc superconductivity in Dirac Semimetal Cd3As2 Ce Huang, Tong Zhou, Kam Tuen Law, Faxian Xiu Cd3As2 is a three-dimensional Dirac semimetal with separated Dirac points in momentum space which are connected by Fermi arcs. In spite of their extensive studies via transport and spectroscopic approaches, the coupling of Fermi-arc states to superconductivity remains elusive. Here, we report the observation of proximity-induced Fermi-arc superconductivity in SC/Cd3As2 hybrid structures. The proximity gap in Fermi arcs is comparable to the parent superconductor which exhibits a flat conductance plateau in differential conductance spectra. The proximity-induced pairing gap on bulk states, however, is small and manifests itself as a zero-bias broad peak (ZBBP). Corroborated with theory, we further unveil a systematic suppression of the ZBBP and an appearance of conductance plateau when the Fermi-arc states become gradually dominant. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F05.00011: The spectral fingerprint of the enhanced surface superconducting gap in β–Bi2Pd Jianyu Guan, Lingyuan Kong, Tian Qian, Yujie Sun, Hong Ding Topological superconductors are attracting a majority of attentions and inspired community to investigate the candidate materials. The recent discovery of enhanced surface superconducting gap and zero bias conductance peak in β-Bi2Pd thin film by STM [1] provides a possibility to get higher Tc topological superconductor. But the driving force behind the enhanced superconductivity is still under debate. We grown the β-Bi2Pd thin film by MBE system and detect using in-situ angle resolved photoemission spectroscopy. We observed quantum well bands due to the high quality of the grown thin film. More importantly, we clearly distinguished the bulk band and surface band in momentum space. In the surface band, we detected the spectral fingerprint of the enhance superconducting gap. |
Tuesday, March 5, 2019 1:51PM - 2:03PM |
F05.00012: Topologically nontrivial phases in superconducting transition metal carbides Richard Zhan, Xuan Luo Topological superconductors have shown great potential in the search for unique quasiparticles such as Majorana fermions. Combining nontrivial band topology and superconductivity can lead to topological superconductivity due to the proximity effect. In this work, we used first principle calculations to predict that rocksalt phases of VC and CrC are superconducting with topologically nontrivial states. The phonon dispersions of these transition metal carbides displayed no imaginary frequencies, which suggests dynamic stability. Therefore, these transition metal carbides are practical candidates for studying topological superconductors and their associated Majorana bound states. |
Tuesday, March 5, 2019 2:03PM - 2:15PM |
F05.00013: Topological character of A15 superconductors Minsung Kim, Cai-Zhuang Wang, Kai-Ming Ho A15 superconductors are type-II s-wave BCS superconductors that have been known for decades. However, the topological aspects of their electronic structures remain unnoticed so far. In this study, we perform first-principles band structure calculations to show that the band topology of the A15 superconductors Ta3Sb, Ta3Sn, and Ta3Pb is nontrivial. We also find that there appear topological surface states in accordance with the bulk-boundary correspondence. Due to the bulk superconductivity and the proximity effect, topological superconductivity will be induced at the surface, which can host Majorana zero modes at vortices. Our results show that the A15 superconductors are promising candidate materials to realize the px + i py type topological superconductivity and the Majorana mode. |
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