THz Measures of Axion Electrodynamics and Exotic Superconducting Interfaces in Topological Insulator Films and Their Heterostructures
Abstract
Major Goals: Two principle areas of investigation have been planned for this project. Both use the technique of THz spectroscopy. The first goal has been already been met. We have searched for the predicted regime of ÒaxionÓ electrodynamics in TI thin films. Here it is predicted that when time-reversal symmetry is broken at their surfaces they will exhibit a quantized magnetoelectric response (e.g. an electric polarization created by a magnetic field and a magnetization created by an electric field). This quantized response is expected to manifest itself as quantized Faraday rotation (e.g. the rotation of the plane of linearly polarized light), the scale of which is set by the fine-structure constant. This mimics the electrodynamic response of the proposed exotic ÒaxionÓ elementary particle. The quantized response is a 3D TI version of the quantized Hall conductance that is found in the 2D quantum Hall effect. The observation of a quantized magnetoelectric response is the definitive measure of these materials as distinct states of matter. The second aspect of this project is now getting started. We will investigate the THz response of heterostuctures of TI films with superconductors. The interest here is in the induced proximity effect in the TI surface states. Because of the non-trivial spin momentum locking in the TI band-structure, a novel nodeless p-wave like superconducting state is expected to be induced even if the fundamental interactions are intrinsically s-wave. This superconducting state is expected to have a host of interesting properties as a consequence of this exotic symmetry, including the presence of Majorana fermion excitations residing in vortex cores. The solid-state realization of Majorana fermions are believed to be useful for quantum computation schemes and their realization on a 2D surface would be a major advance.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 04, 2018
- Source ID
- W911NF1510560
Entities
People
- Peter Armitage
Organizations
- Army Contracting Command
- Johns Hopkins University
- United States Army