KEK連携コロキウム(永長直人氏)

概要

When the system lacks both parity and mirror symmetries, it is called "chiral" and can be classified into right-handed and left-handed. Chirality is one of the most fundamental issue in many branches of sciences [1]. In biology, the chirality of DNA is the same for all the living creatures on earth. In chemistry, to synthesize the molecules of one chirality selectively is an important issue. In physics, the parity violation is a striking feature of weak interaction. Here we focus on the chirality appearing in dynamics. It appears trivial that the flow of particles are different between right and left directions when the system is chiral. However, this is not the case as seen from the simplest problem of a single particle scattering problem by one-dimensional asymmetric potential. Namely, the unitary nature of the quantum mechanical time evolution put the constraint on the S-matrix, and the transmission/reflection probabilities are the same for right and left incident waves. Dissipation breaks the unitary nature of the time evolution, and hence the friction, which brings the classical nature of the dynamics, plays an important role for the directional (nonreciprocal) responses of the system. The time-reversal symmetry of the microscopic Hamiltonian also plays an essential role in the nonreciprocal responses of the system. In this talk, I will discuss that the most fundamental principles in physics manifest themselves in the nonreciprocal responses of chiral systems, i.e., the symmetries, dissipation, quantum-classical crossover/transition, quantal Berry phase and topology, and many-body correlation effects. The concrete examples to discuss include magnetochiral anisotropy of semiconductors [2], Weyl semimetals [3], and superconductors [4], nonlinear spin current generation in Rashba-Dresselhaus systems, and shift currents under photo-excitations [5]. The collaborators of these works are T. Morimoto, K.W. Kim, R. Wakatsuki, K. Hamamoto, M. Ezawa, H. Ishizuka, S. Hoshino, S.Koshikawa, S.Shimizu, Y.Kaneko Y. Saito, T. Ideue, Y. Iwasa, and Y. Tokura.

[1] M. Gardner, The Ambidextrous Universe. Left, Right and the Fall of Parity (1964)

[2] T. Ideue et al., Nature Physics 13, 578-583 (2017).

[3] T. Morimoto and N. Nagaosa, Phys. Rev. Lett. 117, 146603 (2016).

[4] R. Wakatsuki et al., Science Advances 3, e1602390 (2017)

[5] T. Morimoto and N. Nagaosa, Science Advances 2, e1501524 (2016).