Pure bulk orbital and spin photocurrent in two-dimensional ferroelectric materials

We elucidate a bias-free light-induced orbital and spin current through nonlinear response theory, generalizing the bulk photovoltaic effect (BPV) in inversion-symmetry-broken materials from charge to spin and orbital degrees of freedom. Using first-principles calculations for two-dimensional nonmagnetic ferroelectrics (e.g., GeS and analogs), which have vertical mirror and time-reversal symmetries but lack inversion symmetry, we reveal that beyond the conventional photocurrent parallel to the mirror plane under linearly polarized light, the symmetry-forbidden transverse charge photocurrent actually hides counter-propagating electron flows that carry opposite angular momenta. This yields a pure orbital-moment current with zero net charge current. Spin–orbit coupling converts this orbital current into a pure spin current. We propose a four-terminal device to simultaneously detect photo-induced charge, orbital, and spin currents. All these currents couple to ferroelectric polarization, allowing amplitude and direction control via ferroelectric phase transitions, providing a route from photo-induced electronics to orbitronics and spintronics in nanoscale devices.

Xingchi Mu, Yiming Pan, Jian Zhou