Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L45: Superconducting Topological InsulatorFocus

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Sponsoring Units: DMP Chair: Johnpierre Paglione, University of Maryland Room: 392 
Wednesday, March 15, 2017 11:15AM  11:51AM 
L45.00001: tbd Invited Speaker: J. F. Jia tbd [Preview Abstract] 
Wednesday, March 15, 2017 11:51AM  12:03PM 
L45.00002: The Superconductivity of the Topologically Protected Surface States of Bi${}_2$Se${}_3$: Theory Nicholas Sedlmayr, Ian Dayton, Alex Levchenko, Stuart Tessmer The superconducting proximity effect induced in materials in close contact with a superconductor is well known. Similarly the topologically protected surface states recently found on the surfaces of special crystals can leak into appropriate adjoining materials. We bring these two effects into proximity and study how superconductivity and topologically protected surface states interact with each other, a situation of interest in the search for Majorana bound states. We look at the scanning tunneling microscopy of a large topological insulator with superconducting islands deposited on the surface, and analyze theoretical models which capture the hybridization between the topological surface states and the superconducting states. The density of states of both the topological insulator and the superconductor turn out to exhibit interesting proximity effects. [Preview Abstract] 
Wednesday, March 15, 2017 12:03PM  12:15PM 
L45.00003: MagneticFieldEnhanced Superconducting Proximity Effect in Bi$_{\mathrm{\mathbf{2}}}$\textbf{Se}$_{\mathrm{\mathbf{3}}}$\textbf{ nanowire Josephson Junctions and their anomalous Shapiro steps} Feng Junya, Song Zhijun, Zhang Hao, Ji Zhongqing, Lu Li The superconducting proximity effect between swave superconductors and materials with strong spinorbit coupling is an interesting issue. In this work, we have investigated the magnetic field dependence of the critical supercurrent of Al/Pd(Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ nanowires)Al/Pd proximity effect Josephson junctions. We find that the critical supercurrent of the devices is anomalously enhanced in magnetic field. We have also studied the effect of microwave irradiation on the devices, and found anomalous fractional Shapiro steps. We will discuss the implications of the phenomena observed. [Preview Abstract] 
Wednesday, March 15, 2017 12:15PM  12:27PM 
L45.00004: Mapping visiblelight direct optical excitations of a topological insulator via trARPES Hadas Soifer, J. A. Sobota, A. V. Gauthier, S.L. Yang, H. Xiong, H. Pfau, C. Rotundo, P. S. Kirchmann, Z. X. Shen Topological insulators have been in the focus of condensedmatter research in recent years. In particular, much effort was dedicated to optically manipulate the spintextured electrons in the topological surface states. In this work we use time and angleresolved photoemission spectroscopy (trARPES) to induce and probe direct optical transitions to unoccupied states of the topological insulator Bi$_2$Se$_3$. We tuned the excitation wavelength in the visible regime, and studied the ultrafast dynamics of the electronic excitation and decay. The detailed timeresolved data allowed us to clearly resolve different contributions to the excited population. We used a timemapping procedure to identify the initial states, and observed processes involving topological surface states as either the initial or excited state. Our results reveal the intricacies of photoexcitations of topological surface states, and establish pumptuning in the visible regime as a tool for optical control of topological insulators. [Preview Abstract] 
Wednesday, March 15, 2017 12:27PM  12:39PM 
L45.00005: Comparison of the Fermi Surfaces of Bi$_{2}$Se$_{3}$, Cu$_{x}$Bi$_{2}$Se$_{3}$, and Nb$_{x}$Bi$_{2}$Se$_{3}$ Benjamin Lawson, Paul Corbae, Gang Li, Fan Yu, Tomoya Asaba, Colin Tinsman, Y. Qiu, J. E. Medvedeva, Y.S. Hor, Lu Li Topological insulator Bi$_{2}$Se$_{3}$ is made superconducting with Cu and Nb doping. These have been the leading candidates to realize topological superconductivity. To understand the new physics showcased in these system, a detailed knowledge of the electronic structure is needed. We present a comparison of the quantum oscillations in the magnetization and transport of undoped, Cudoped, and Nbdoped Bi$_{2}$Se$_{3}$. Whereas Cu dopants in Bi$_{2}$Se$_{3}$ simply raise the chemical potential indicated by a larger Fermi pocket, Nbdoped Bi$_{2}$Se$_{3}$ has two distinct oscillation frequencies. The multiple frequencies observed in the quantum oscillations indicate that the doping changes the band structure of Nbdoped Bi$_{2}$Se$_{3}$ with interesting implications for its topological nature. [Preview Abstract] 
Wednesday, March 15, 2017 12:39PM  12:51PM 
L45.00006: Evidence of nodes in the order parameter of the superconducting doped topological insulator Nb$_{\mathrm{x}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ via penetration depth measurements M. P. Smylie, H. Claus, U. Welp, W.K. Kwok, Y. Qiu, Y. S. Hor, A. Snezhko The lowtemperature variation of the London penetration depth $\lambda $(T) in the candidate topological superconductor Nb$_{\mathrm{x}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ (x$=$0.25) is reported for several crystals. The measurements were carried out by means of a tunneldiode oscillator technique in both field orientations (H$_{\mathrm{rf}}$ // c and H$_{\mathrm{rf}}$ // ab planes). All samples exhibited quadratic temperature dependence at low temperatures clearly indicating the presence of point nodes in the superconducting order parameter. The results presented here are not consistent with a complete superconducting gap. We interpret our data on Nb$_{\mathrm{x}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3\thinspace }}$in terms of a nematic oddparity spintriplet pairing state with E$_{\mathrm{u}}$ symmetry. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Contract No. DEAC0206CH11357. MPS thanks ND Energy for supporting his research and professional development through the ND Energy Postdoctoral Fellowship Program. YSH acknowledges support from National Science Foundation grant number DMR1255607. [Preview Abstract] 
Wednesday, March 15, 2017 12:51PM  1:03PM 
L45.00007: Rotational Symmetry Breaking in a Trigonal superconductor Nbdoped Bi$_{2}$Se$_{3}$ Tomoya Asaba, Benjamin Lawson, Colin Tinsman, Lu Chen, Paul Corbae, Gang Li, Yunsheng Qiu, Yew San Hor, Liang Fu, Lu Li Topological superconductors (TSC) have been attracting huge interest due to their potential applications to topological quantum computation. While it has been challenging to confirm TSC, recently it has been predicted that superconducting doped Bi$_2$Se$_3$ shows a nematic order in the TSC state. In this study we probed the rotational symmetry of a TSC candidate Nbdoped Bi$_2$Se$_3$ in both normal and superconducting states by torque magnetometry. The magnetic field was applied inplane and the symmetry of magnetic anisotropic susceptibility as well as hysteresis loop was measured. While $\sin 6\phi$ dependence was observed in the normal state, $\sin 2\phi$ and $\sin 4\phi$ components become dominant instead of vanishing $\sin 6\phi$ component in the superconducting state. This indicates rotational symmetry breaking in the superconducting state, suggesting nematic order as predicted. [Preview Abstract] 
Wednesday, March 15, 2017 1:03PM  1:15PM 
L45.00008: Magnetism in a Promising Topological Superconductor Nb$_{\mathrm{0.25}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ Seng Huat Lee, Yunsheng Qiu, Eric William Bohannan, Yew San Hor Nb$_{\mathrm{x}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ was found to be a promising candidate of topological superconductor [1]. In addition to its superconductivity, Nb$_{\mathrm{x}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ also depicts paramagnetism. Not only do the magnetism and superconductivity coexist but they also mutually assist each other to give rise to a state which could be well described as a symbiosis of the two phases. The emergent of the symbiotic state can have exotic phenomenon[1,2]. We will report the magnetic and the transport properties for this promising topological superconductor in this presentation. [1] Y. Qiu \textit{et. al.}, arXiv: 1512.03519. [2] F. Q. Noah, W.Y. He, and K. T. Law, arXiv: 1608.05825. [Preview Abstract] 
Wednesday, March 15, 2017 1:15PM  1:27PM 
L45.00009: Theoretical study on the Nbdoped topological insulator Bi2Se3 Kong Xiangru, Liu Xiongjun Recently, Nbdoped Bi$_2$Se$_3$ (Nb$_{0.25}$Bi$_2$Se$_3$) was reported to be typeII superconductor with gapless edge states being preserved. Interestingly, a macroscopic magnetic ordering also appears below the superconducting critical temperature. Coexistence of a magnetism and superconductivity in a topological insulator may lead to topological superconductor which could realize Majorana fermions in condensed matter physics. Here, we propose to study the underlying mechanism of the emergent magnetism, and find the possibilities to realize topological superconductors. [Preview Abstract] 
Wednesday, March 15, 2017 1:27PM  1:39PM 
L45.00010: The effect of disorder on the superconducting state of the candidate topological superconductor Nb$_x$Bi$_2$Se$_3$ Kristin Willa, M. P. Smylie, H. Claus, U. Welp, A. Snezhko, W.K. Kwok, Y. Qiu, Y. S. Hor, P. Niraula, E. Bokari, A. Kayani The effects of disorder and electron scattering in topological superconductors are largely unknown. Aiming at eliminating this deficiency we study the influence of proton irradiation on the candidate topological superconductor Nb$_x$Bi$_2$Se$_3$. As the irradiationdeposited defect density increases we observe a rapid suppression of $T_c$ and a strong increase in residual resistivity in both magnetization and transport measurements. These results are inconsistent with a fully gaped superconductor; they rather suggest a nodal order parameter, in agreement with penetration depth measurements [1]. We interpret our data in terms of a nematic superconducting state with $E_u$ symmetry. [1] M. P. Smylie {\it et al.}, arXiv:1608.08164. [Preview Abstract] 
Wednesday, March 15, 2017 1:39PM  1:51PM 
L45.00011: Antipeak profile of the nuclear magnetic relaxation rate in a superconducting topological insulator Yuki Nagai, Yukihiro Ota, Masahiko Machida We theoretically reveal that 3D multiorbital topological superconductivity can be identified by a bulk measurement, i.e., the temperature dependence of nuclear magnetic relaxation (NMR) rates [1]. Superconducting topological insulators such as CuxBi2Se3, are the candidates of the bulk 3D topological superconductors [2]. We claim that the bulk measurements of NMR rates detect a 3D oddparity fully gapped topological superconducting state in timereversalinvariant multiorbital systems. Below a critical temperature Tc, the NMR rate in the topological state exhibits an antipeak profile, which is opposite to the conventional swave state. This inversion coherence effect comes from a twist of order parameters with respect to orbital and spin degrees of freedom. Our calculations in the model for candidates of the topological superconductors prove that this inverse effect appears as a concave temperature dependence of the NMR rates. We propose that a timereversalinvariant orbitalsinglet spintriplet topological superconductivity is characterized by the temperature dependence of the NMR rate. [1] YN, Y. Ota and M. Machida, PRB92, 180502R (2015),YN and Y. Ota, arXiv:1605.08154, to be published in PRB. [2] S. Sasaki, et al., Phys. Rev. Lett. 107, 217001 (2011). [Preview Abstract] 
Wednesday, March 15, 2017 1:51PM  2:03PM 
L45.00012: The Superconductivity of the Topologically Protected Surface States of Bi${}_2$Se${}_3$: Experiment Ian Dayton, Nicholas Sedlmayr, Can Zhang, Eric Huemiller, Thomas Chasapis, Alex Levchenko, Mercouri Kanatzidis, Dale Van Harlingen, Stuart Tessmer Placing a 3D topological insulator (TI) in proximity to an swave superconductor (S) is predicted to induce 2D pwave superconductivity into the topologicallyprotected surface state (TSS). The details of the TI/S interface are critical for the search for Majorana bound states in these systems. In this talk, we will present cryogenic scanning tunneling microscopy measurements of Bi${}_2$Se${}_3$ with nanometer scale islands of Nb and PbBi deposited on the surface. Local density of states measurements are consistent with superconductivity in the top quintuple layer, with a coherence length of about 500 nm. Moreover, we find clear evidence of a reverse proximity effect for which the TSS from the TI leaks back into the local density of states measured on the superconducting islands. [Preview Abstract] 
Wednesday, March 15, 2017 2:03PM  2:15PM 
L45.00013: Indium substitution effect on the topological crystalline insulator (Pb,Sn)Te Ruidan Zhong, John Schneeloch, John Tranquada, Genda Gu Topological crystalline insulator has been of great interest in the area of condensed matter physics. We investigated the indue substitution effect on the crystal structure, transport properties in the topological crystalline insulators (Pb,Sn)InTe. By introducing different amount of indium, the system shows quite divergent resistivity behaviors at low temperatures. As the doping level increases, the system changes from weakly metallic to truly bulkinsulating, and then become superconducting with a transition temperature Tc positively correlated to the indium concentration. We address this issue from the view of bulk electronic structure. The current work summarizes the indium substitution effect on the (Pb,Sn)Te compound, and discusses those effects from two aspects of topological and superconducting properties. [Preview Abstract] 
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