Electromagnetic absorption of semiconductor 2D Majorana nanowires

Abstract

We calculate the cross section for the electromagnetic absorption of planar 2D Majorana nanowires. The electromagnetic field is described in the dipole approximation. We discuss the signatures on the cross section of a near-zero-energy mode. A low energy peak for transverse polarization, absent in the longitudinal one, reveals the presence of the Majorana-like state. This peak is relatively robust against the thermal smearing of the level occupations. We consider the influence of optical masks hiding parts of the nanowire from the radiation.

Electromagnetic absorption of quasi‐1D Majorana nanowires

“…The differences between x and y polarization in presence of a Majorana state were already suggested in Ref. [13]. However, in that work the number of eigenstates was truncated to lower values and thus the absorption for higher energies was less converged than in this work.…”

“…2. We notice here that dipole transitions between the two states of a given pair are fobidden because of particle-hole symmetry [13].…”

“…[13] by focussing on the quasi-1D limit of very long and narrow nanowires. We use a mixed grid-basis approach, discretizing the longitudinal x coordinate in a grid and describing the transverse y degree of freedom in a basis of square well eigenstates ( Fig.…”

Circular dichroism of chiral Majorana states

“…2 ). We explain this selection rule noticing the following restrictions for transitions from the negative n -th state to the positive m -th state ( −n → m ): (a) Transitions between conjugate states −n → n are forbidden by particle–hole symmetry [ 25 ], and (b) n even to m odd transitions (or vice versa) are forbidden because of destructive interference along the nanostructure perimeter with the excitation operator. This rule is far less obvious than rule (a) and results from the approximately 1D character of the chiral edge modes and the interference induced by the propagation through corners.…”

“…We want to investigate how this behavior is actually realized by explicit calculations of the optical aborption. In previous works we analyzed the optical absorption of localized Majorana states in nanowires [ 25 – 26 ]. In those systems the CD vanishes and the presence of the Majorana state is signaled by a plateau with lower absorption, starting at mid-gap energy, of the y -polarized signal with respect to the x -polarized signal.…”