Bulletin of the American Physical Society
2014 Annual Meeting of the Mid-Atlantic Section of the APS
Volume 59, Number 9
Friday–Sunday, October 3–5, 2014; University Park, Pennsylvania
Session C2: Topology in Condensed Matter |
Hide Abstracts |
Chair: Jay Kikkawa, University of Pennyslvania Room: Life Sciences Building 004 |
Saturday, October 4, 2014 10:30AM - 11:06AM |
C2.00001: Detection and utilization of topological superconductors in solid state systems Invited Speaker: Jay Sau Majorana modes are fermion-like excitations that were originally proposed in particle physics by Ettore Majorana and are characterized as being their own anti-particle. In condensed matter systems Majorana modes occur as fractionalized excitations with topologically protected degeneracy associated with such excitations. In this talk, I will start by reviewing a recent set of proposals for realizing Majorana modes in a large class of spin-orbit coupled, time-reversal symmetry broken superconducting systems. I will then discuss the possibility of confirming topological superconductivity using the fractional Josephson effect. Finally, I will discuss the possibility of using such Majorana modes for topological quantum computation. [Preview Abstract] |
Saturday, October 4, 2014 11:06AM - 11:18AM |
C2.00002: Numerical studies on magnetoconductance of the topological insulator nanotubes Hsiu-Chuan Hsu, Ajit Coimbatore Balram, Jainendra Jain, Chaoxing Liu It has been shown that the conductance oscillates as a function of the parallel magnetic flux with a period of $\phi_0$ ($\phi_0=h/e$, one flux quantum)in topological insulator(TI) nanowires. A pair of gapless helical modes arise on the cylindrical surface of a TI nanowire when a magnetic flux of half-integer of $\phi_0$ threads through it. This conductance oscillation has been a direct evidence of the transport of the surface helical modes of TI. Nonetheless, consider a TI nanotube, there are two cylindrical surfaces giving rise to two oscillation periods in terms of magnetic field. In an effort to study the magnetoconductance oscillation of TI nanotubes, we calculated the conductance within the Landauer formalism in clean and disordered limit. We found an unambiguous oscillation feature and discuss the origin of the magnetoconductance oscillation. This feature demonstrates a transport signature of the helical surface modes of the TI nanotube. [Preview Abstract] |
Saturday, October 4, 2014 11:18AM - 11:30AM |
C2.00003: Interaction effect of a topological semimetal Na3Bi in magnetic fields Ruixing Zhang, Jimmy Hutasoit, Chaoxing Liu We study the interaction induced instability of a topological semimetal Na$_3$Bi in magnetic field based on the mean field theory. The phase diagram can be classified by two sets of order parameters, which break chiral symmetry and thus gap the system. In certain interaction parameter regions, we find these two order parameters can co-exist. To understand this phase co-existence and phase transitions in the phase diagram, we analytically solve the minimum problem of free energy perturbatively. The possible experimental consequence is also studied. [Preview Abstract] |
Saturday, October 4, 2014 11:30AM - 11:42AM |
C2.00004: Spin Texture and Mirror Chern number in Hg-Based Chalcogenides Chaoxing Liu, Qingze Wang, Shu-chun Wu, Claudia Felser, Binghai Yan The unique feature of surface states in topological insulators is the so-called ``spin-momentum locking,'' which means that electron spin is oriented along a fixed direction for a given momentum and forms a texture in the momentum space. In this work, we study spin textures of two typical topological insulators in Hg-Based Chalcogenides, namely HgTe and HgS, based on both the first principles calculation and the eight band Kane model. We find opposite helicities of spin textures between these two materials, originating from the opposite signs of spin-orbit couplings. Furthermore, we reveal that different mirror Chern numbers between HgTe and HgS characterize different topological natures of the systems with opposite spin textures and guarantee the existence of gapless interface states. [Preview Abstract] |
Saturday, October 4, 2014 11:42AM - 11:54AM |
C2.00005: Giant anisotropic magneto-resistance in the magnetic topological insulator Cr$_x$(Bi,Sb)$_{2-x}$Te$_3$ Abhinav Kandala, Anthony Richardella, Chaoxing Liu, Nitin Samarth We report the observation of a giant anisotropic magneto-resistance (GAMR) effect in the magnetic topological insulator Cr$_x$(Bi,Sb)$_{2-x}$Te$_3$ as an external field (and the magnetization $M$) is rotated from out-of-plane (azimuthal angle $\theta = 0^{\circ}$) to in-plane ($\theta = 0^{\circ}$)). While the rotation of a magnetic field in-plane produces a weak, conventional anisotropic magnetoresistance (AMR) that follows the standard angular dependence (AMR $\sim \cos^2\phi$, where $\phi$ is the angle between $M$ and the current density $J$), the GAMR is much larger in magnitude and deviates from the standard $\cos^2\theta$, dependence. We explain the observed GAMR through a quantum magnetic phase transition from an ``imperfect'' quantum anomalous Hall (QAH) insulator to a trivial ferromagnetic semiconductor as the magnetization is tilted from out-of-plane to in-plane. We expect the GAMR to become stronger in the ideal QAH regime where edge state conduction dominates over bulk conduction, thus providing a route toward proof-of-concept ferromagnetic topological insulator transistors and magnetic field sensors. Funded by DARPA. [Preview Abstract] |
Saturday, October 4, 2014 11:54AM - 12:06PM |
C2.00006: Composite-fermion trions in the fractional quantum Hall effect Ajit Coimbatore Balram, Ursula Wurstbauer, Arkadiusz Wojs, Aron Pinczuk, Jainendra Jain Resonant inelastic light scattering experiments of the ``fractional quantum Hall'' state have indicated the existence of excitations below the Zeeman energy in the vicinity of the lowest Landau level filling $\nu =$1/3. We investigate this observation in terms of composite fermions, the emergent particles of the fractional quantum Hall state that are bound states of electrons and two flux quanta. We identify the low energy excitations with positively or negatively charged composite-fermion(CF) trions, created when a photo-excited CF particle-hole pair forms a bound state with an existing CF particle ($\nu $ \textgreater 1/3) or CF hole ($\nu $ \textless 1/3). These are the smallest realizations of ``skyrmions'' in the fractional quantum Hall state. This identification is well supportedby an excellent agreement between the calculated and the measured binding energies, and by the fact that the mode disappears for $\nu $ \textgreater 1/3 when a transition to a fully spin-polarized state occurs. The spectroscopy of trion bound states serves as an extremely sensitive tool for investigating the interaction between composite fermions, which is relevant to the formation of exotic fractional quantum Hall states in this filling factor region, including those at $\nu =$4/11 and 5/13. [Preview Abstract] |
Saturday, October 4, 2014 12:06PM - 12:18PM |
C2.00007: Robustness of Topological Superconductivity in Proximity-Coupled Topological Insulator Nanoribbons Piyapong Sitthison, Tudor Stanescu A numerical study of low-energy physics of topological insulator(TI) nanoribbon proximity-coupled to s-wave superconductors(SCs) shows that induced gap is strongly band-dependent and collapses for low amplitude bands at the interface. The surface-type bands have most of their weight near the top or the bottom surface of the nanoribbon. It suggests that single interface TI-SC could experience a collapse of the induced gap. On the other hand, the nanoribbons sandwiched between two superconductors are capable of realizing the full potential of TI-based structures to harbor robust topological superconducting phases. [Preview Abstract] |
Saturday, October 4, 2014 12:18PM - 12:30PM |
C2.00008: Quantum Interference Control of Currents in Bi$_{2}$Se$_{3}$ Topological Insulators Derek Bas Quantum interference control of photocurrents are investigated in Bi$_{2}$Se$_{3}$ films ranging from 6 to 40 quintuple layers in thickness. The samples are grown with a two-step method on sapphire substrates and protected with an MgF$_{2}$ capping layer that prevents oxidation. Co-polarized harmonically related pulses excite carriers through interference of single- and two-photon absorption pathways, which have a polar distribution in momentum space leading to a ballistic photocurrent. The current is measured using time-domain terahertz spectroscopy. Dependences of the relative phase between the two pulses and intensity of each pulse show the correct signatures confirming the third-order nonlinear quantum interference control. Azimuthal angle dependence allows the injection current to be separated from a relative-phase independent shift current generated by the fundamental pulses alone. The shift current is a second-order nonlinear optical process arising from the surface states, while the injection current arises from surface-to-surface transitions at an energy of 1.6 eV. A thickness dependence of the injection current in the Bi$_{2}$Se$_{3}$ film is dominated by the product of the linear and nonlinear absorption. The two-photon absorption coefficient is explored as a function of film thickness for the first time. [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. |
© 2019 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
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700