Chirality-induced spin-selective Peierls transition

Chirality, referring to the absence of mirror and inversion symmetries, is a ubiquitous concept in nature. In condensed matter physics, vigorous research has clarified how chiral materials harbour unconventional electronic and vibrational responses. In parallel, recent studies have demonstrated that chiral structures can be engineered or tuned from achiral precursors. Despite these complementary advances, an integrated understanding of electronic and phononic dynamics, self-organized chiral structures, and their interplay is still lacking. Such an integrated framework is crucial both for elucidating the spontaneous formation and stabilization of chiral structures and for advancing the electronic functionalities of chiral materials. Here, we predict novel spontaneous structural phase transitions unique to chiral crystals with screw symmetry. In quasi-one-dimensional chiral crystals, the phonon frequency renormalized by the electron-phonon coupling depends on the handedness of circular polarization. Consequently, the soft mode encoding the intrinsic phonon angular momentum induces spin-selective Peierls gaps in the electronic band, entailing a helical spin density wave and chiral lattice distortion. We also elucidate the chiral signature of collective modes. Our findings offer new avenues for advanced spintronics applications and crucial insights into the elusive mechanisms underlying the formation process of chirality in nature.

💡 Research Summary

This paper theoretically predicts a novel spontaneous phase transition in chiral crystals, termed the “chirality-induced spin-selective Peierls transition (CISSPT)”. The work bridges the concepts of structural chirality, chiral phonon dynamics, and electron-phonon cooperative phenomena.

The study focuses on quasi-one-dimensional chiral conductors with screw symmetry (e.g., three-fold screw axis). In such systems, transverse acoustic (TA) phonons propagating along the chiral axis possess intrinsic angular momentum, manifesting as left- or right-handed circular polarization. The authors derive the electron-phonon coupling (EPC) Hamiltonian under this screw symmetry, which reveals a selection rule: coupling to these chiral TA phonons connects electronic states with different spins (spin-flip process), unlike conventional coupling to longitudinal acoustic (LA) phonons.

A central result is the “handedness-dependent Kohn anomaly.” The phonon frequency renormalized by electrons depends on the phonon’s angular momentum handedness. Consequently, the chiral phonon mode with the lower frequency softens at the nesting vector Q = 2kF. Crucially, which mode softens first is tied to the handedness of the parent chiral crystal. This leads to different transition temperatures for left- and right-handed crystals.

When this soft chiral phonon condenses, it induces a unique electronic order via the EPC selection rule. The order parameter couples electrons with opposite spins connected by the wavevector Q, opening a “spin-selective Peierls gap” in the electronic band structure. This results in the formation of a helical spin-density wave (SDW) in the itinerant electrons. Simultaneously, the finite expectation value of the phonon field induces a chiral lattice distortion with the same periodicity. Thus, CISSPT jointly produces a helical SDW and a chiral structural modulation, with the helicity (handedness of the spiral) inherited from the parent crystal.

The paper further analyzes the collective excitations of this state. The phase mode (phason) exhibits sliding dynamics similar to conventional charge density waves. A distinctive prediction is that applying an electric field to drive this sliding motion will, due to the chiral nature of the underlying order, result in a net transport of mechanical angular momentum, suggesting a novel chiral mechanical response.

Finally, the authors discuss experimental signatures for identifying CISSPT in future materials, including handedness-dependent phonon softening, a characteristic reduction in electrical conductivity, and detection of the helical SDW via techniques like neutron scattering. This work provides a new integrated framework for understanding how chirality can actively drive cooperative electronic and structural orders, offering fresh avenues for spintronics and for elucidating the emergence of chirality in condensed matter systems.