Time: 10:00am, Nov. 4th (Friday), 2022
Place: Rm M830, IOP-CAS
Online Link: https://voovmeeting.com/dm/uVDNdwHmqe1G
Speaker: Prof. Sun, Zhiyuan 孙志远 (Department of Physics, Tsinghua University)
An emerging subject in nonequilibrium physics is “order parameter steering” where experimentally controllable perturbations (e.g., light pulses) may drive the order parameters of symmetry broken phases to evolve in time. I will theoretically demonstrate this phenomenon in two cases: mean field steering and fluctuation steering. In the first case, we show that in excitonic insulators with s-wave electron-hole pairing, an applied light pulse can induce a p-wave component to the order parameter, and further drive it to rotate in the s+ip plane. In one dimension, each cycle of rotation pumps exactly two electrons across the sample while higher dimensional systems are similar, realizing a Thouless charge pump as a collective manybody effect. In the second case, we study the dynamics of a competing order system which is rapidly heated up by a pump and then cooled down due to electron-lattice heat transfer. In the cooling process, exponentially growing thermal fluctuations lead the system into the phase associated with the faster-relaxing order parameter, which is not necessarily the ground state. This theory offers a natural explanation for the widespread experimental observation that metastable states may be induced by laser pulses.
PRL 126, 027601 (2021), PRX 10, 021028 (2020)