Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R45: Exotic Topological SuperconductorsFocus
|
Hide Abstracts |
Sponsoring Units: DMP Room: 392 |
Thursday, March 16, 2017 8:00AM - 8:36AM |
R45.00001: Topological Edge States in High-Temperature Superconductor FeSe/SrTiO3(001) Film Invited Speaker: feng liu Superconducting and topological states are two most intriguing quantum phenomena in solid materials. The entanglement of these two states, the topological superconducting state, will give rise to even more exotic quantum phenomena. While many materials are found to be either a superconductor or a topological insulator, it is very rare that both states exist in one material. In this talk, I will present recent studies based on first-principles theory as well as scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy experiments, demonstrating that the recently discovered ``two-dimensional (2D) superconductor'' of single-layer FeSe also exhibits 1D topological edge states within an energy gap of \textasciitilde 40 meV at M point below the Fermi level. It is the first 2D material that supports both superconducting and topological states, offering an exciting opportunity to study 2D topological superconductors through proximity effect. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R45.00002: Tip-induced superconductivity in the topological crystalline insulator Pb$_{0.6}$Sn$_{0.4}$Te Shekhar Das, Leena Aggarwal, Subhajit Roychowdhury, Mohammad Aslam, Sirshendu Gayen, Kanishka Biswas, Goutam Sheet Materials exhibiting nontrivial topological properties are in the focus of contemporary condensed matter physics and the emergence of exotic phases of matter from these materials is an outstanding issue. Pb$_{0.6}$Sn$_{0.4}$Te was recently known to be a topological crystalline insulator. In this talk, I will show that by forming a mesoscopic point-contact between a normal, non-superconducting elemental metal as a tip and Pb$_{0.6}$Sn$_{0.4}$Te as a sample, a superconducting phase is induced locally in a confined region under the point-contact. Interestingly, neither the tip nor the sample is a superconductor, but a prominent superconducting phase appears only under the point-contact at a high transition temperature $T_c$ that falls in a range between 3.7 K and 6.5 K. From experiments under different conditions with tips made up of different materials, both magnetic and non-magnetic, I will also discuss the nature of superconductivity. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R45.00003: Experimental realization of a Superconductor-Topological Insulator (HfTe3/HfTe5) layered heterostructure Yeliang WANG, Yuqi Wang, Xu Wu, Yan Shao, Shi-Yu Zhu, Hong-Jun Gao We fabricated a superconductor--topological insulator--normal metal heterostructure with a layered configuration of HfTe3/HfTe5/Hf for the first time. This heterostructure can indeed form spontaneously by tuning the experimental parameters. The atomic structure of the heterostructure has been determined by in situ STM and XPS. STS measurements directly reveal a bandgap as large as 60 meV in HfTe5 film and a superconducting spectrum in HfTe3/HfTe5 film. Unlike the artificial film lift-transfer-stacking technique, our current method of making desired heterostructures is based on a spontaneous formation process of surface reaction and epitaxial growth and significantly simplifies the fabrication process. This method may offer new routes for the development of other related functional heterostructures and nanodevices. The generated hybrid structure HfTe3/HfTe5/Hf has potential applications in both quantum-spin Hall effect-based and Majorana-based devices for novel technological applications like high-efficiency quantum computation. [Adv. Mater. 28, 5013 (2016).] [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R45.00004: Majorana zero modes in Dirac semimetal Josephson junctions Chuan Li, Jorrit de Boer, Bob de Ronde, Yingkai Huang, Mark Golden, Alexander Brinkman We have realized proximity-induced superconductivity in a Dirac semimetal and revealed the topological nature of the superconductivity by the observation of Majorana zero modes. As a Dirac semimetal, Bi$_{0.97}$Sb$_{0.03}$ is used, where a three-dimensional Dirac cone exists in the bulk due to an accidental touching between conduction and valence bands. Electronic transport measurements on Hall-bars fabricated out of Bi$_{0.97}$Sb$_{0.03}$ flakes consistently show negative magnetoresistance for magnetic fields parallel to the current, which is associated with the chiral anomaly. In perpendicular magnetic fields, we see Shubnikov-de Haas oscillations that indicate very low carrier densities. The low Fermi energy and protection against backscattering in our Dirac semimetal Josephson junctions provide favorable conditions for a large contribution of Majorana zero modes to the supercurrent. In radiofrequency irradiation experiments, we indeed observe these Majorana zero modes in Nb-Bi$_{0.97}$Sb$_{0.03}$-Nb Josephson junctions as a 4$\pi$ periodic contribution to the current-phase relation. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R45.00005: Proving nontrivial topology of pure bismuth by quantum confinement Suguru Ito, Bao-jie Feng, Masashi Arita, Akari Takayama, Ro-Ya Liu, Takashi Someya, Wei-Chuan Chen, Takushi Iimori, Hirofumi Namatame, Masaki Taniguchi, Cheng-Maw Cheng, Shu-Jung Tang, Fumio Komori, Katsuyoshi Kobayashi, Tai-Chang Chiang, Iwao Matsuda The topology of pure bismuth (Bi) has been controversial due to its extreme electronic structures [1,2]. The three-dimensional Dirac-like dispersion is so sharp against a momentum resolution expected in usual angle-resolved photoelectron spectroscopy (ARPES) that the bulk bands have never been clearly observed [1]. This is a serious problem because the band gap of Bi is very small (~10 meV [2]) and a slight energy shift in bulk bands can easily transform a topologically nontrivial case into a trivial case. In the present study, we overcame these difficulties by performing high-resolution ARPES measurements on Bi(111) films with thicknesses increasing from 14 to 202 bilayers. Detailed analyses on the phase shift of the confined wave functions precisely determined the surface and bulk electronic structures, which unambiguously show nontrivial topology. [1] Y. Ohtsubo \textit{et al}., New J. Phys. 15, 033041 (2013). [2] L. Aguilera \textit{et al}., PRB 91, 125129 (2015). [3] S. Ito \textit{et al}., PRL in press, arXiv1605.03531. [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R45.00006: Studies on Bi/Ni bilayer superconductivity Sung Po Chao, Shiue-Cheng Lu, Jin-Han Lin, Pok-Man Chiu, Wan-Ju Li, Peng-Jen Chen, Yung Liou, Ting-Kuo Lee Motivated by the recent observations[1] of possible p-wave in Bi/Ni bilayer, we study this system with similar growth methods. Due to higher temperature in the substrate during our sample growth compared with [1], we find clear evidences of forming alloys in both Bi/Ni and Ni/Bi bilayers, both showing superconductivity with maximal critical temperature around 4K. The critical temperature also has similar thickness dependence as seen in Ref.[1]. The formation of alloys indicates the Bi/Ni superconductivity found in our samples could be of phonon mediated type II superconductivity. Further point contact Andreev reflection measurements or other surface probes are needed to see if we could also observe the p-wave like signature in our samples as in Ref.[1]. From the theory side, we propose a simple model, similar to the proximity induced p-wave by Sau et al.[2], to explain why in our sample the p-wave like Andreev signals is likely to be observed, assuming the strong spin-orbit coupled surface states of Bi thin film are not completely destroyed by the formation of alloys.\\ References:\\ [1]Gong Xin-Xin et al , Chinese Phys. Lett. 32 067402 (2015).\\ [2]J. D. Sau et al , Phys.Rev. Lett. 104, 040502 (2010) . [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R45.00007: Theory of spontaneous time-reversal symmetry breaking in superconducting Bi/Ni epitaxial bilayers Mehdi Kargarian, Victor M. Yakovenko, Victor M. Galitski We develop a theory to understand the superconducting Bi/Ni epitaxial bilayers that breaks the time-reversal symmetry spontaneously. In order to explain this experimental observation [1], we adopt a model incorporating the exchange coupling between magnetic moments of nickel (Ni) and itinerant electron states of bismuth (Bi). Due to strong spin-orbit coupling, the surface states of Bi(110) are basically described by nondegenerate Fermi pockets with the largest one centered around the center of the surface Brillouin zone. The spin and momentum are strongly locked on the Fermi surface as in the surface states of 3D topological insulators. We showed that the spin-orbit coupling in Bi and magnetic fluctuations arising from Ni cooperatively induce pairing channels classified by definite total angular momentum $J_z$. The superconducting order parameter breaks the time-reversal symmetry selecting either $J_z =+2$ or $J_z =- 2$, corresponding to $d_{xy}+id_{x^2-y^2}$ and $d_{xy}-id_{x^2-y^2}$ pairings, respectively, which can be controlled by a weak training magnetic field. [1] X. Gong, M. Kargarian, A. Stern, D. Yue, H. Zhou, X. Jin, V. M. Galitski, V. M. Yakovenko, J. Xia, "Time-Reversal-Symmetry-Breaking Superconductivity in Epitaxial Bismuth/Nickel Bilayers", arXiv:1609.08538 [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R45.00008: Topological Weyl singularity in the Andreev spectrum of multi-terminal Josephson junction Tomohiro Yokoyama, Yuli Nazarov We theoretically investigate a multi-terminal Josephson junction. Such junctions can be realized, for instance, with crossed InSb nanowires. N superconductors can define N-1 independent superconducting phase differences. The spectrum of Andreev bound states in the junction is $2\pi$ periodic in all the phase differences. By regarding the phase differences as ``quasimomenta'' for crystal, the Andreev spectrum can be proposed as ``an energy band structure in artificial material.'' We exhibit a topological Weyl singularity in the Andreev spectrum. \footnote{T.\ Yokoyama and Yu.\ V.\ Nazarov, Phys.\ Rev.\ B {\bf 92}, 155437 (2015).} We examine a model using scattering matrix based on a Beenakker's determinant equation to calculate the Andreev levels. The Weyl singularity requires more than three superconducting terminals. In a 3D space of the phase differences, the Weyl points come always in groups of four. They are present even in the absence of SO interaction, thus even for doubly degenerate spectrum. The SO interaction splits the conical spectrum of the Weyl points, however does not vanish the points. The Weyl points can be removed by the pair annihilation when one tunes the scattering matrix. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R45.00009: Majorana surface modes of topological septet pairing in spin-$3/2$ semi-metals Wang Yang, Congjun Wu Multi-component electronic systems exhibit richer structures of topological superconductivity beyond the conventional scenarios of spin singlet and triplet pairings in spin-$1/2$ systems. Examples include the half-Heusler compounds RPtBi series (R for rare earth), whose electronic structures are described by effective spin-$3/2$ particles due to strong spin-orbit coupling. Recent experiments provide evidence to unconventional superconductivity in these materials with nodal spin septet pairing. We systematically study topological pairing structures in spin-$3/2$ systems and calculate surface spectrum, which exhibit zero energy flat band and cubic dispersion. These unusual features of surface states can be tested in future spectroscopy experiments. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R45.00010: Characterization of Topological Superconductivity in Weyl Semimetals Yi Li Novel topological superconducting pairing symmetry has been proposed in doped time-reversal breaking Weyl semimetals, where the Berry phase of Cooper pairing states between two Fermi surfaces with opposite Chern numbers gives rise to new pairing symmetry characterized by monopole harmonics. By comparing this novel pairing symmetry with familiar examples of unconventional superconductivity, we reveal exotic properties originating from topologically-protected nodal structures of its gap function, and propose possible detections of this novel superconducting pairing symmetry. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R45.00011: Superconductivity in the doped antiperovskite oxide Sr$_{3-x}$SnO Shingo Yonezawa, Mohamed Oudah, Atsutoshi Ikeda, Jan Niklas Hausmann, Toshiyuki Fukumoto, Shingo Kobayashi, Masatoshi Sato, Yoshiteru Maeno In the antiperovskite oxide $A_3B$O, oxygen atoms occupy the center of the ordinary perovskite structure and the $A$ metal octahedrally coordinate the oxygen. More interestingly, the $B$ metal exhibits a negative valence state, which is unusual for metallic ions. Because of such structural and electrical uniqueness, the antiperovskite oxides attracts much attention these days. In particular, the prediction of Dirac semimetal states in Ca$_3$PbO and its related compounds triggered extensive investigation [1]. Here, we report discovery of superconductivity in Sr$_{3-x}$SnO, based on the observation of zero resistivity and Meissner screening [2]. To the best of our knowledge, this compound is the first superconductor among the known antiperovskite oxides. In addition, this compound may host topological superconductivity, because of the strong orbital mixing of the underlying electronic state.\newline [1] T. Kariyado and M. Ogata, J. Phys. Soc. Jpn. \textbf{80}, 083704 (2011).\newline [2] M. Oudah \textit{et al.}, Nature Comm. \textbf{7}, 13617 (2016). [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R45.00012: Self-forming superconducting microstructures from Weyl semimetals Maja D. Bachmann, Nityan Nair, Felix Flicker, Roni Ilan, Nirmal J. Ghimire, Eric D. Bauer, Filip Ronning, James G. Analytis, Philip J.W. Moll Topological semi-metals host protected electronic states on their surface where the topology of the bulk bands is broken. By coupling them to a superconducting gap, exotic electronic excitations such as zero-energy Majorana modes can appear on the surface. In non-superconducting topological materials a gap can be induced via the proximity effect. A traditional path towards proximity-induced superconductivity involves growing a superconducting film on the non-superconducting topological material. We present a new way of fabricating superconducting microstructures from the non-superconducting Weyl-semimetal NbAs under Ga ion irradiation from a focused ion beam (FIB). Thereby As is preferentially removed from the surface, while the Nb-rich layer left behind shows robust type-II superconductivity with $T_c \sim$ 3K and $H_{c2} \sim$ 7T. In this approach the superconducting film self-forms on a single crystal, which may strongly influence the interface and coupling properties. Using this approach, we present a route towards fabricating superconducting topological nanowires. [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. |
© 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