An Anomalous Circular Photogalvanic Effect in the Weyl Semimetal TaAs

TL;DR

This paper reports the observation of an anomalous circular photogalvanic effect in the Weyl semimetal TaAs, revealing helicity-dependent photocurrents linked to asymmetric optical excitation of Weyl cones.

Contribution

It demonstrates the first experimental observation of CPGE in TaAs and attributes it to asymmetric carrier excitation in Weyl cones due to optical spin selection rules.

Findings

CPGE voltage depends on light helicity

Reverses with polarization change

Periodical oscillation with optical polarization

Abstract

Weyl semimetal (WSM) is expected to be an ideal spintronic material owing to its spin currents carried by the bulk and surface states with spin-momentum locking. A photocurrent generation in noncentrosymmetric WSM was also predicted owing to its broken inversion symmetry and linear energy dispersion which are unique to Weyl systems. In our recent measurements, the circular photogalvanic effect (CPGE) has been demonstrated in WSM of TaAs. The CPGE voltage is proportional to the helicity of the incident light and reverses its direction on changing the radiation helicity from left handed to right handed, a periodical oscillation therefore appears following with the alteration of optical polarization. We herein attribute the CPGE to the asymmetric optical excitation of the Weyl cone, which could result in an asymmetric distribution of photoexcited carriers in momentum space according to an optical spin selection rule.