Spin-current version of solar cells in non-centrosymmetric magnetic insulators

TL;DR

This paper proposes a theory for generating a bulk photovoltaic spin current in non-centrosymmetric magnetic insulators using electromagnetic waves, revealing a new spin-current solar cell concept with stable, impurity-resistant properties.

Contribution

It introduces a novel theory for producing DC spin currents in magnetic insulators via electromagnetic waves, extending the photovoltaic effect to magnetic excitations.

Findings

Nonlinear spin conductivity is nonzero in various noncentrosymmetric magnets.

The photon-driven spin current is of shift current type, stable against impurities.

The phenomenon is a bulk effect, distinct from interface spin pumping.

Abstract

Photovoltaic effect, e.g., solar cells, converts light into DC electric current. This phenomenon takes place in various setups such as in noncentrosymmetric crystals and semiconductor pn junctions. Recently, we proposed a theory for producing DC spin current in magnets using electromagnetic waves, i.e., the spin-current counterpart of the solar cells. Our calculation shows that the nonlinear conductivity for the spin current is nonzero in a variety of noncentrosymmetric magnets, implying that the phenomenon is ubiquitous in inversion-asymmetric materials with magnetic excitations. Intuitively, this phenomenon is a bulk photovoltaic effect of magnetic excitations, where electrons and holes, visible light, and inversion-asymmetric semiconductors are replaced with magnons or spinons, THz or GHz waves, and asymmetric magnetic insulators, respectively. We also show that the photon-driven spin current is shift current type, and as a result, the current is stable against impurity scattering. This bulk photovoltaic spin current is in sharp contrast to that of well-known spin pumping that takes place at the interface between a magnet and a metal.