Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session X03: Topological Superconductors and SuperfluidsFocus
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Sponsoring Units: DCMP Room: BCEC 107B |
Friday, March 8, 2019 8:00AM - 8:12AM |
X03.00001: Symmetry-protected line nodes and Majorana flat bands in nodal crystalline superconductors Shingo Kobayashi, Shuntaro Sumita, Youichi Yanase, Masatoshi Sato Over the last few years, the study on node structures in SCs has received renewed interest due to the fact that they are a kind of topological objects. In this context, a line node in time-reversal (TR) invariant SCs is protected by a one-dimensional (1D) topological number and induces a Majorana flat band (MFB) in a surface. The MFBs exhibit a zero-bias conductance peak through the tunneling measurement for TR invariant SCs such as high-Tc SCs and non-centrosymmetric SCs, which gives a conclusive evidence for the bulk topological line nodes. |
Friday, March 8, 2019 8:12AM - 8:24AM |
X03.00002: Full proximity approach to induced gap in topological superconductor junctions Fnu Setiawan, Chien-Te Wu, Kathryn Levin Recently, a Josephson junction formed from a two-dimensional electron gas (2DEG) proximitized by two superconductors subjected to an in-plane magnetic field has emerged as a viable platform to realize topological superconductivity [1-3]. In this talk, we address the proximity-induced superconductivity in this setup by studying the full proximity model of a superconductor-insulator-superconductor junction in contact with a spin-orbit-coupled substrate. To this end, we numerically solve the Bogoliubov-de Gennes Hamiltonian of this model and study the effect of spin-orbit coupling and thickness of the substrate on the induced pairing amplitude and energy dispersion. Finally, we will discuss the topological phase diagram of multiband topological Josephson junctions for a thick substrate. |
Friday, March 8, 2019 8:24AM - 8:36AM |
X03.00003: Hot electron magnetotransport in the high mobility GaAs/AlGaAs two dimensional electron system below 1K C.Rasadi Munasinghe, Binuka Gunawardana, Rasanga Samaraweera, Tharanga Nanayakkara, U. Kushan Wijewardena, Sajith Withanage, Annika Kriisa, Christian Reichl, Werner Wegscheider, Ramesh Mani Non-equilibrium hot electron phenomena play a major role in semiconductor transport when, for example, the heat applied directly to the electronic system becomes substantial. The carrier temperature can differ from the lattice temperature, and the carrier temperature results, in the steady state, from a balance between energy gain from the heating source, and energy loss to the lattice from electron-phonon scattering. In this experimental study, we examine heating induced by the small ac-bias current utilized in the low-frequency lock-in based four terminal transport measurements. Since at small bias current, the carrier heating is expected to be small, we have utilized an effect that is associated with a small energy scale to follow the heating effect, namely the spin splitting in the Shubnikov-de Haas effect. The development of fields such as spintronics and spin-based quantum computing have encouraged further studies, such as this one, of the parameters affecting the behavior of electron spin in low dimensional electron systems. Thus, magneto-transport measurements have been carried out below 1K to observe the ac current effect on the characteristic features of the GaAs/AlGaAs system. In this report, we show evidence for a carrier heating effect due to the small ac bias. |
Friday, March 8, 2019 8:36AM - 8:48AM |
X03.00004: Topological Phases in Nodeless Tetragonal Superconductors Santiago Varona, Laura Ortiz, Oscar Viyuela, Miguel Angel Martin-Delgado We compute the topological phase diagram of 2D tetragonal superconductors for the only possible nodeless pairing channels compatible with that crystal symmetry. Subject to a Zeeman field and spin-orbit coupling, we demonstrate that these superconductors show surprising topological features: non-trivial high Chern numbers, massive edge states, and zero-energy modes out of high symmetry points, even though the edge states remain topologically protected. Interestingly, one of these pairing symmetries, d+id, has been proposed to describe materials such as water-intercalated sodium cobaltates, bilayer silicene or highly doped monolayer graphene. |
Friday, March 8, 2019 8:48AM - 9:00AM |
X03.00005: Fractional Josephson Vortices and Braiding of Majorana Zero Modes in Planar Superconductor-Semiconductor-Superconductor Josephson junctions Ady Stern, Erez Berg We consider the one-dimensional (1D) topological superconductor that may form in a planar superconductor-metal-superconductor Josephson junction in which the metal is is subjected to spin orbit coupling and to an in-plane magnetic field. This 1D topological superconductor has been the subject of recent theoretical and experimental attention. We examine the effect of perpendicular magnetic field and a supercurrent driven across the junction on the position and structure of the Majorana zero modes that are associated with the topological superconductor. In particular, we show that under certain conditions the Josephson vortices fractionalize to half-vortices, each carrying half of the superconducting flux quantum and a single Majorana zero mode. Furthemore, we show that the system allows for a current-controlled braiding of Majorana zero modes. |
Friday, March 8, 2019 9:00AM - 9:12AM |
X03.00006: An Exactly Solvable Interacting Edge Theory for a Weak 2D Topological Superconductor. Joseph Sullivan, Meng Cheng We study interacting edge states of a 2D weak topological superconductor protected by time-reversal symmetry. Such a system can be viewed as a stack of Marjorana/Kitaev chains (class BDI), possessing translation symmetry in the transverse direction. Interestingly, in this model, time-reversal symmetry forbids terms quadratic in fermionic degrees of freedom on the edge, so any edge dynamics must be inherently interacting. We proposed an exactly solvable model for the edge and worked out its phase diagram. It is shown that the edge is either symmetry breaking or gapless as expected from the bulk-boundary correspondence of a topological phase. We then construct a low energy field theory for the model in the gapless phase. We propose that the same field theory describes the edge of an intrinsically interacting fermionic symmetry-protected phase with Z_4 x Z_2^T symmetry. |
Friday, March 8, 2019 9:12AM - 9:24AM |
X03.00007: Majorana corner states in D class Xin Liu, Xiao-Hong Pan, Kai-Jie Yang Majorana corner states (MCSs) in D class can naturally form a topological qubit. In this talk, we show that how to realize MCSs in two-dimensional topological insulators in the presence of both superconductivity and magnet. It is noted that there is only one MCS at each corner which is allowed due to the time-reversal symmetry broken. An edge theory is performed to clearly demonstrate the physics behind these results. At last, we study the spin property of MCSs and propose to use spin-resolved scanning tunneling microscope to detect their existence. |
Friday, March 8, 2019 9:24AM - 9:36AM |
X03.00008: Generalized Aubry-André-Harper model with p-wave superconducting pairing Qi-Bo Zeng, Shu Chen, Rong Lü We investigate a generalized Aubry-André-Harper (AAH) model with p-wave superconducting pairing. Both the hopping amplitudes between the nearest-neighboring lattice sites and the on-site potentials in this system are modulated by a cosine function with a periodicity of 1/α. In the incommensurate case [α = (√5 - 1)/2], due to the modulations on the hopping amplitudes, the critical region of this quasiperiodic system is significantly reduced and the system becomes easier to be turned from extended states to localized states. In the commensurate case (α = 1/2), we find that this model shows three different phases when we tune the system parameters: Su-Schrieffer-Heeger (SSH)-like trivial, SSH-like topological, and Kitaev-like topological phases. The phase diagrams and the topological quantum numbers for these phases are presented in this work. This generalized AAH model combined with superconducting pairing provides us with a useful test field for studying the phase transitions from extended states to Anderson localized states and the transitions between different topological phases. |
Friday, March 8, 2019 9:36AM - 9:48AM |
X03.00009: Conformal phase transition in topological superconductors Flavio Nogueira, Jeroen Van den Brink, Asle Sudbo A conformal phase transition (CPT) is a phase transition defining a critical point with a non-power law diverging |
Friday, March 8, 2019 9:48AM - 10:00AM |
X03.00010: Superconformal Cardy states and entanglement structure of 1D quantum critical points with emergent supersymmetry Chun Chen, Joseph Maciejko Condensed matter systems with quantum critical points exhibiting emergent spacetime supersymmetry in the long-wavelength, low-energy limit have attracted much attention recently. In particular, several elements of the N=1 series of superconformal minimal models originally discovered by Friedan, Qiu, and Shenker in 1985 have been realized recently in a variety of 1D quantum lattice models ranging from anyonic spin chains to interacting Majorana chains and boson-fermion mixtures. To better understand the entanglement structure of these exotic quantum critical points, we revisit the problem of the construction of boundary states for the superconformal minimal models and find a new set of Cardy states not previously discussed. As an application of this formalism we present and discuss numerical DMRG results for the entanglement spectrum of the Grover--Sheng--Vishwanath model as a lattice realization of the tricritical Ising universality class. |
Friday, March 8, 2019 10:00AM - 10:12AM |
X03.00011: Majorana Corner Modes in a High-Temperature Platform Zhongbo Yan, Fei Song, Zhong Wang We introduce two-dimensional topological insulators in proximity to high-temperature cuprate or iron based superconductors as high-temperature platforms of Majorana Kramers pairs of zero modes. The proximity-induced pairing at the helical edge state of the topological insulator serves as a Dirac mass, whose sign changes at the sample corner because of the pairing symmetry of high-Tc superconductors. This sign changing naturally creates at each corner a pair of Majorana zero modes protected by time-reversal symmetry. Conceptually, this is a topologically trivial superconductor-based approach for Majorana zero modes. We provide quantitative criteria and suggest candidate materials for this proposal.[Reference: Phys. Rev. Lett. 121, 096803 (2018)] |
Friday, March 8, 2019 10:12AM - 10:24AM |
X03.00012: Zero-energy Andreev bound states from quantum dots in proximitized Rashba nanowires Christopher Reeg, Olesia Dmytruk, Denis Chevallier, Daniel Loss, Jelena Klinovaja We study an analytical model of a Rashba nanowire that is partially covered by and coupled to a thin superconducting layer, where the uncovered region of the nanowire forms a quantum dot. We find that, even if there is no topological phase possible, there is a trivial Andreev bound state that becomes pinned exponentially close to zero energy as a function of magnetic field strength when the length of the dot is tuned with respect to its spin-orbit length such that a resonance condition of Fabry-Perot type is satisfied. In this case, we find that the Andreev bound state remains pinned near zero energy for Zeeman energies that exceed the characteristic spacing between Andreev levels but that are smaller than the spin-orbit energy of the dot. Importantly, as the pinning of the Andreev bound state depends only on properties of the dot, we conclude that this behavior is unrelated to topological superconductivity. To support our analytical model, we also perform a numerical simulation of a hybrid system that explicitly incorporates a thin superconducting layer, showing that all qualitative features of our analytical model are present in the numerical results. |
Friday, March 8, 2019 10:24AM - 10:36AM |
X03.00013: The survival of topological signatures in the presence of average symmetries Yingyi Huang, Ching-Kai Chiu The robust properties in topological states of matter under the effect of disorders is of great theoretical as well as experimental interests. One focus is on the disorders breaking either spatial symmetry or non-spatial symmetry (e.g., time-reversal, particle-hole and chiral symmetry) but restoring it on average. In this work, we consider a quasi-one-dimensional topological superconductor in the presence of disorders preserving average time-reversal symmetry or mirror symmetry. By calculating the transport signatures of multi-chain Kitaev and Majorana models, we show that the survival of the edge modes depends on the form of the disorders. |
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