Antiparallel Spin Polarization and Spin Current Induced by Thermal Current and Locally Broken Inversion Symmetry in a Double‐Quantum Well Structure

Abstract

Generating a nonequilibrium spin polarization with a driving force is first realized by the electric current in a system with broken inversion symmetry and extended to that induced by the thermal current and that appearing in an inversion‐symmetric system with locally broken inversion symmetry. This article theoretically explores the spin polarization generated by the thermal current and the locally broken inversion symmetry in a symmetric double‐quantum well structure (DQWS). This thermally induced spin polarization (TISP) appears in the antiparallel configuration with the TISP of two wells in opposite directions. The calculation using the Boltzmann equation in the relaxation‐time approximation under the condition of zero charge current shows that the local TISP exhibits the maximum at a finite Rashba spin–orbit interaction when the electron density is fixed. This is because the local TISP in the DQWS is enhanced at the chemical potential near the bottom of the first‐excited sub‐band. This enhancement also occurs in a single quantum well with globally broken inversion symmetry. Another finding is that the maximum of the local TISP appears at a nonzero interwell coupling. The spin current by the diffusion of the local TISP into an adjacent electrode is also calculated.