Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R05: Topological Superconductivity: Bi2Se3, SrRuO4, and Other MaterialsFocus
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Sponsoring Units: DMP Chair: Madhab Neupane, University of Central Florida Room: BCEC 108 |
Thursday, March 7, 2019 8:00AM - 8:36AM |
R05.00001: Topological superconductivity revealed by scanning tunneling spectroscopy Invited Speaker: Donglai Feng CuxBi2Se3 hosts both topological surface states and bulk superconductivity. It has been identified recently as a topological superconductor (TSC) with an extraordinary nematic, i. e. C2-symmetric, superconducting state and odd-parity pairing. Using scanning tunneling microscopy (STM), we directly examine the response of the superconductivity of CuxBi2Se3 to magnetic field. Under out-of-plane fields, we discover elongated magnetic vortices hosting a zero-bias conductance peak (ZBCP) consistent with the Majorana zero mode (MZM) expected in a TSC. Under in-plane fields (B//), the average superconducting gap exhibits two-fold symmetry with field orientation, the long C2 symmetry axes are pinned to the dihedral mirror planes under B//=0.5 T but slightly rotate under B//=1.0 T. Moreover, a nodeless Δ4x gap structure is semi-quantitatively determined for the first time. Our data paint a microscopic picture of the nematic superconductivity in CuxBi2Se3 and pose strong constraints on theory. [1] |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R05.00002: Superconductivity in zerovalent copper intercalated Bi2Se3 crystals Min-Nan Ou, Shih-Hsun Yu, Mitch M. C. Chou, Yang-Yuan Chen In order to understanding of the role of Cu atoms to the formation of superconducting quasiparticles. A series of CuxBi2Se3 (x= 0~ 0.3) crystals prepared with Bridgman method followed by an electrochemical technique (EC method) at room temperature. The existence of copper confirmed by means of XRD, SEM and TEM EDS mapping as well. Where the obvious increasing on lattice c confirm the intercalating of copper atoms rather than the substitution. The further study on temperature dependent electrical resistance and magnetic susceptibility revealed a superconducting transition at about TC = 3 ~ 3.5 K. As an illustration, optimized 10 at% of Cu, a clear superconducting transition at TC = 3.4 K with large shielding fraction (volume susceptibility) of ~ 95% is observed. The characteristic peaks of the zerovalent chemical state of copper confirmed by x-ray photoelectron spectra (XPS) and Auger electron spectra (AES). By the electron energy loss spectroscopy (EELS), near-edge fine structure revealed the absence of Cu1+ and Cu2+ characterization peaks, which confirmed the zerovalent of intercalated copper atom. The results of this work suggested that the formation of superconducting quasiparticles do not relate to the charge transfer of copper. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R05.00003: Reproducible Growth of Superconducting Sr2RuO4 Films by Molecular-Beam Epitaxy Nathaniel Schreiber, Hari Nair, Jacob P Ruf, Ludi Miao, Yingfei Li, Morgan Grandon, David Baek, Berit Goodge, Lena Fitting Kourkoutis, Kyle M Shen, Darrell G. Schlom The unconventional, likely chiral p-wave, superconductivity in Sr2RuO4 has been studied extensively in bulk single crystals since its discovery over 20 years ago. The superconducting state in Sr2RuO4 is extremely sensitive to defects and non-magnetic impurities, and therefore superconductivity has only been observed in very pure crystals with a midpoint Tc of up to ~1.5 K [1]. Thin films of Sr2RuO4 have only recently been realized, and this advancement is important for both the study of the unconventional superconducting properties and for the implementation of Sr2RuO4 in any future practical applications. In this talk, we report a thermodynamic growth window, in which we can reproducibly grow superconducting Sr2RuO4 thin films by molecular-beam epitaxy with transition temperatures of up to 1.8 K on (110) NdGaO3 substrates [2]. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R05.00004: Effects of deep superconducting gap minima and disorder on thermal transport in Sr2RuO4 Zhiqiang Wang, John Dodaro, Catherine Kallin Recent thermal conductivity measurements on Sr2RuO4 were interpreted as favoring a pairing gap function with vertical line nodes while conflicting with chiral p-wave pairing. Motivated by this work we study the effects of deep superconducting gap minima on impurity induced quasiparticle thermal transport in chiral p-wave models of Sr2RuO4. Combining a self-consistent T-matrix analysis and self-consistent Bogoliubov-de-Gennes calculations, we show that the dependence of the residual thermal conductivity on the normal state impurity scattering rate can be quite similar to the d-wave pairing state that was shown to fit the thermal conductivity measurements, provided the normal state impurity scattering rate is large compared with the deep gap minima. Consequently, thermal conductivity measurements on Sr2RuO4 can be reconciled with a chiral p-wave pairing state with deep gap minima. However, the data impose serious constraints on such models and these constraints are examined in the context of several different chiral p-wave models. |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R05.00005: Superconducting Symmetries of Sr2RuO4 from Spin- and Charge-fluctuations Olivier Gingras, Reza Nourafkan, Andre-Marie Tremblay, Michel Cote Although the normal state of Sr2RuO4 is well understood, its pairing symmetry is still debated [1]. From its correlated multi-orbital normal state, we construct the spin- and charge-fluctuation pairing interactions. These interactions depend on the proximity to an instability and on the size of the screened Hund's coupling. We present the leading gap function symmetries obtained by solving the frequency dependent linearized Eliashberg equation [2]. Close to magnetic instabilities, we find spin-singlet d-wave pairing. Away, where charge-fluctuations increase, we observe the emergence of two even-parity spin-triplet states: an odd in frequency s-wave and two degenerate momentum-independent states that pair electrons on different orbitals and are odd in orbial indices. We will explain by what means spin- and charge-fluctuations mediated pairing favors such symmetries, how to understand them from specific features of the correlated electronic structure and compare their gap value with experiments. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R05.00006: STM study of impurity states in topological superconducting candidates Li(Fe,Co)As and PbTaSe2 Songtian Sonia Zhang, Jiaxin Yin, Genfu Chen, Guoqing Chang, Tay-Rong Chang, Kun Jiang, Changqing Jin, Hsin Lin, Ziqiang Wang, Raman Sankar, Zahid Hasan Introducing impurities, both magnetic and nonmagnetic, into superconducting systems via surface or bulk chemical substitution can both provide a wealth of information about the underlying system, as well as manipulate some of its crucial properties. Here, we use low temperature scanning tunnelling microscopy to study vortex core and impurity states in topological superconductor candidates Li(Fe,Co)As and PbTaSe2 at 0.4K. We perform a systematic study in the Li(Fe,Co)As system of eight Co concentrations, spanning its entire superconducting phase diagram. Using a superconducting tip, we explore the impurity effects on the topological surface states as well as bulk superconductivity in PbTaSe2. Our results not only provides strong constraints on their superconducting order parameters, but also sheds light on the interplay of magnetism and topological superconductivity. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R05.00007: Rotational symmetry breaking in the upper critical field of topological superconductor candidate CaSn3 Yasuyuki Nakajima, K A M Hasan Siddiquee, Riffat Munir, Charuni Dissanayake, Priyanka Vaidya, Cameron Nickle, Enrique Del Barco, Derrick VanGennep, James Hamlin Electronic nematicity is a quantum analogue to liquid crystals, breaking the rotational symmetry, but preserving the translational symmetry. The electronic nematic states emerge not only in strongly correlated systems, including quantum Hall liquids, high temperature cuprate and iron-based superconductors, and heavy fermion compounds [1], but also in weakly correlated systems, such as the superconducting states in doped-topological insulators known as nematic superconductivity [2]. Closely correlated with the topological nature, the nematic superconductivity in topological materials has attracted great interest. Here, we report systematic studies of the upper critical field of topological superconductor candidate CaSn3, forming a cubic structure with point group Oh. We reveal two-fold symmetry in the anisotropy of upper critical field, breaking the underlying lattice structure. Similar to doped-topological insulator MxBi2Se3 (M=Sr, Cu and Nb), the rotational symmetry breaking indicates the realization of nematic superconductivity in CaSn3. We will discuss the possible superconducting pairing state stabilized in this system. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R05.00008: WITHDRAWN ABSTRACT
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Thursday, March 7, 2019 10:00AM - 10:12AM |
R05.00009: Topological superconductivity in full shell proximitized nanowires Roman Lutchyn, Georg W. Winkler, Bernard Van Heck, Torsten Karzig, Karsten Flensberg, Leonid Glazman, Chetan Nayak We consider a new model system supporting Majorana zero modes based on semiconductor nanowires with a full superconducting shell. We demonstrate that, in the presence of spin-orbit coupling in the semiconductor induced by a radial electric field, the winding of the superconducting order parameter leads to a topological phase supporting Majorana zero modes. The topological phase persists over a large range of chemical potentials and can be induced by a predictable and weak magnetic field piercing the cylinder. The system can be readily realized in semiconductor nanowires covered by a full superconducting shell, opening a pathway for realizing topological quantum computing proposals. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R05.00010: Topological superconductivity in full-shell nanowires: numerical results and phase diagrams Roman Lutchyn, Georg W. Winkler, Bernard Van Heck, Torsten Karzig, Karsten Flensberg, Leonid Glazman, Chetan Nayak We investigate numerically the Majorana topological phase appearing in semiconductor nanowires with a full superconducting shell. We consider both toy models and more realistic models where the electrostatic profile in the semiconducting core is computed self-consistently and the semiconductor and superconductor are treated on equal footing in the strong coupling regime. The topological phase diagram is computed for different core radii. This talk is a continuation of the previous talk on the same topic by R.M. Lutchyn. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R05.00011: Josephson junctions with weak links of topological crystalline insulator nanowires Christie J Trimble, Pengzi Liu, Judy Cha, James R Williams Incorporating superconductivity in topological states of matter offers potential routes to novel excitations with properties essential to topological quantum computation. Topological crystalline insulators (TCIs) are topological states of matter protected by crystalline symmetry, in contrast to the more commonly used time-reversal invariant topological insulators. In this talk, we report on the fabrication of Josephson junctions using nanowires of SnTe, a TCI, as the weak link material. We show the divergence of our devices from standard Josephson junction behavior using DC techniques, highlighting intriguing novel behavior in the magnetic diffraction pattern, and discuss the origin of this behavior in terms of pi phase difference across the junction. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R05.00012: Is a quantum dot a good tool to detect the topological properties of a proximitized Rasba nanowire? Denis Chevallier, Olesia Dmytruk, Daniel Loss, Jelena Klinovaja Recent experiments in developing Majorana qubits have focused on semiconductor-superconductor Rashba nanowire junctions. A quantum dot is located in the non-superconducting section of the nanowire and is used to probe its topological properties. Various phenomena can be understood with the transport measurement through the quantum dot such as the renormalization of the g-factor [1] as well as the flipping of the bulk band resulting from the topological transition [2,3]. However, the presence of such quantum dot can also mimic the zero-bias peak feature [4], questioning the presence of the topological phase and, as a consequence, temporarily blocking the road towards topological quantum computation. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R05.00013: Andreev bound states and Fabry-Perot interference in InAsSb nanowires Fanming Qu, Jiangbo He, Jianghua Ying, Guangtong Liu, Jie Fan, Zhongqing Ji, Dong Pan, Jianhua Zhao, Li Lu Andreev bound states (ABSs) are electronic analogues of Fabry-Perot interference. Signatures of Majorana zero modes have been demonstrated as merging of electron and hole ABSs as well as zero bias conductance peaks. We take the bottom-up route to study the ABSs and Fabry-Perot interference in InAsSb nanowires. The superconductor-InAsSb-superconductor device shows induced hard superconducting gap in the quantum dot regime. The g factor is extracted consistently from the evolution of both the excited states and the Kondo effect in magnetic field. Moreover, the device can be driven to the Fabry-Perot interference regime where ABSs are observed. |
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