Nonlocal Orbital-Angular-Momentum Dichroism of Vortex Light in Strained Crystals

Abstract

Vortex light carries orbital angular momentum (OAM) in its transverse phase, unlike spin, which is encoded in polarization. We show that this phase cannot produce OAM dichroism in any continuously translation-invariant system, even when optical nonlocality and multipole light--matter coupling are included. Nonuniform strain in a two-dimensional Dirac material bypasses this no-go condition by supplying transverse momentum transfer through a long-wavelength pseudo-gauge field, so that the OAM dichroism factorizes into a nonlocal elasto-optic tensor and the overlap of the vortex transverse phase current with the strain field. For a micron-scale Gaussian bubble, the resonant OAM-odd conductivity reaches \(\sim10^{-3}e^2/\hbar\), within reach of differential optical measurements.