Mesoscale And Nanoscale Physics
Effect of chiral anomaly on the circular dichroism and Hall angle in doped and tilted Weyl semimetals (1903.03072v1)
Ashutosh Singh, J. P. Carbotte
From the Kubo formula for transport in a tilted Weyl semimetal we calculate the absorptive part of the dynamic conductivity for both right and left handed circular polarized light. These depend on the real part of the longitudinal conductivity and the imaginary part of the transverse (Hall) conductivity. We include the effect of the chiral anomaly which pumps charge from negative to positive chirality node when the ususal term is included in the electrodynamics and obtain analytic expressions. To calculate the Hall angle we further provide expressions for the imaginary part of longitudinal and real part of the transverse conductivity and compare results with and without the pumping term. We also consider the case of a non centro symmetric Weyl semimetal in which the chiral nodes are displaced in energy by an amount . This leads to modification in dichroism and Hall angle which parallel the pumping case.
Nanoscale Thermal Imaging of VO via Poole-Frenkel Conduction (1903.03062v1)
Alyson Spitzig, Adam Pivonka, Harry Mickalide, Alex Frenzel, Jeehoon Kim, Changhyun Ko, You Zhou, Kevin O'Connor, Eric Hudson, Shriram Ramanathan, Jennifer E. Hoffman, Jason Hoffman
We present a new method for nanoscale thermal imaging of insulating thin films using atomic force microscopy (AFM). By sweeping the voltage applied to a conducting AFM tip in contact mode, we measure the local current through a VO film. We fit the resultant current-voltage curves to a Poole-Frenkel conduction model to extract the local temperature of the film using fundamental constants and known film properties. As the local voltage is further increased, the nanoscale region of VO undergoes an insulator-to-metal transition. Immediately preceding the transition, we find the average electric field to be 32 MV/m, and the average local temperature to be at least 335 K, close to the bulk transition temperature of 341 K, indicating that Joule heating contributes to the transition. Our thermometry technique enables local temperature measurement of any film dominated by the Poole-Frenkel conduction mechanism, and provides the opportunity to extend our technique to materials that display other conduction mechanisms.
M. Marganska, D. R. Schmid, A. Dirnaichner, P. L. Stiller, Ch. Strunk, M. Grifoni, A. K. Hüttel
A magnetic field, through its vector potential, usually causes measurable changes in the electron wave function only in the direction transverse to the field. Here we demonstrate experimentally and theoretically that in carbon nanotube quantum dots, combining cylindrical topology and bipartite hexagonal lattice, a magnetic field along the nanotube axis impacts also the longitudinal profile of the electronic states. With the high (up to 17T) magnetic fields in our experiment the wave functions can be tuned all the way from "half-wave resonator" shape, with nodes at both ends, to "quarter-wave resonator" shape, with an antinode at one end. This in turn causes a distinct dependence of the conductance on the magnetic field. Our results demonstrate a new strategy for the control of wave functions using magnetic fields in quantum systems with nontrivial lattice and topology.
A. F. Croxall, F. Sfigakis, J. Waldie, I. Farrer, D. A. Ritchie
We present observations of an anisotropic resistance state at Landau level filling factor in a two-dimensional hole system (2DHS), which occurs for certain values of hole density and average out-of-plane electric field . The 2DHS is induced by electric field effect in an undoped GaAs/AlGaAs quantum well, where front and back gates allow independent tuning of and , and hence the symmetry of the confining potential. For ~cm and ~V/m, the magnetoresistance along greatly exceeds that along , suggesting the formation of a quantum Hall nematic or `stripe' phase. Reversing the sign of rotates the stripes by . We suggest this behavior may arise from mixing of the hole Landau levels and a combination of the Rashba and Dresselhaus spin-orbit coupling effects.
Yang Peng, Yong Xu
We propose a realization of chiral Majorana modes propagating on the hinges of a 3D antiferromagnetic topological insulator, which was recently theoretically predicted and experimentally confirmed in the tetradymite-type -related ternary chalgogenides. These materials consist of ferromagnetically ordered 2D layers, whose magnetization direction alternates between neighboring layers, forming an antiferromagnetic order. Besides surfaces with a magnetic gap, there also exsist gapless surfaces with a single Dirac cone, which can be gapped out when proximity coupled to an -wave superconductor. On the sharing edges between the two types of gapped surfaces, the chiral Majorana modes emerge. We further propose experimental signatures of these Majoana hinge modes in terms of two-terminal conductance measurements.
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