Current selects the helicity of a chiral phonon

Abstract The emergence of spin-polarized electrons from nonmagnetic chiral molecules and crystals is called Chirality-induced spin selectivity (CISS). A chiral phonon of definite wavevector q can strongly enhance it, but near equilibrium the two helicities +q and −q are equally populated: they are time-reversal partners and their contributions cancel. We show that in a biased chiral conductor the current causes the phonon of one helicity to damp less than the other. The damping asymmetry is odd in the current, odd under q → −q, invariant under a mirror that reverses the structural handedness, and equal, mode for mode, to the current-induced nonconservative Berry force on the phonon coordinate. Closing the phonon kinetics with a rate equation turns the asymmetry into a net lattice helicity: at any finite bias one helicity is preferentially populated, with no threshold, growing linearly with the current as V → 0; above a threshold that helicity becomes a self-sustained coherent travelling wave. We demonstrate this effect in elemental tellurium, treated as an open quantum system (electronic Hamiltonian, phonon bath, and electron–phonon coupling) within a quasi-ab initio framework. The electronic Hamiltonian is supplied by a vertex-corrected quasipar-ticle self-consistent GW (QSGˆWQSGˆ QSGˆW) potential with spin–orbit coupling; nuclear displacements are modeled with a machine-learned interatomic potential, which yields chiral phonon modes at finite ±q z on the Γ–A line. The perturbation to the electronic Hamiltonian from a nuclear displacement is approximated by a frozen-phonon deformation potential. In tellurium the damping asymmetry grows linearly with the current, the resulting lattice helicity persists from low temperature to room temperature, and the coherent regime appears below about 20 K at 0.2 V and 40 K at 0.4 V. No optical pump is needed: a bias alone drives the current and selects the phonon helicity; reversing the current reverses the selection.