Abstract
Chiral phonons are the ones with nonzero polarization and can be observed only via a selective coupling with valley electrons and circularly polarized photons. In such process, a new physical quantity, i.e., pseudo-angular momentum (PAM), is required to meet the selection rule. However, phonon PAM was thought to be quantized and can be only defined in the symmorphic systems. In this work, we generalized the definition of PAM to three-dimensional non-symmorphic systems, which show distinct different properties compared with the one in symmorphic systems, e.g., PAM can be non-quantized and q-dependent but still be an observable quantity by experiments. Such new definitions and discoveries can help us to obtain chiral phonons in a broader class of systems with a nonzero group velocity and to convey information like chirality and angular momentum in solids as expected. Materials are also offered to understand the new definition and for further experimental detection.
Highlights
Chiral phonons and pseudoangular momentum in nonsymmorphic systemsWe generalized the definition of PAM to systems with screw rotation symmetry, i.e., nonsymmorphic systems, which show distinct properties compared with the one in symmorphic systems: (i) PAM can be nonintegers and q dependent but still be an observable quantity by experiments; (ii) phonon PAM and phonon angular momentum are not equal due the special Wyckoff position in the real space, in contrast to the previous works where most of the atoms are at rotation-invariant Wyckoff positions
Chirality has been widely studied in fundamental physics since it reveals symmetry breaking ofparticles and governs many unconventional phenomena, such as chiral anomaly [1–3], unconventional Landau spectrum [4,5], Klein tunneling [6], nontrivial surface states [7–17], and so on
The phase difference between sublattices under screw rotation symmetry leads to a noninteger value of lo. (ii) We only need to consider the atomic position components along the screw rotation axis when calculating lo, which means that the atomic positions in plane will make no influence on lo. (iii) Case II which we propose is the only possibility for nonsymmorphic systems with screw rotation symmetry
Summary
We generalized the definition of PAM to systems with screw rotation symmetry, i.e., nonsymmorphic systems, which show distinct properties compared with the one in symmorphic systems: (i) PAM can be nonintegers and q dependent but still be an observable quantity by experiments; (ii) phonon PAM and phonon angular momentum are not equal due the special Wyckoff position in the real space, in contrast to the previous works where most of the atoms are at rotation-invariant Wyckoff positions. Materials are offered to understand the new definition and for further experimental detection
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