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An emerging subject in nonequilibrium dynamics is “order parameter steering” where experimentally controllable perturbations (such as light) can drive the order parameter of symmetry broken phases to evolve. We theoretically demonstrate this phenomenon in two scenarios: mean field steering and fluctuation steering. In the first scenario, we show that in excitonic insulators with s-wave electron-hole pairing in the ground state, an applied electric field (either pulsed or static) 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 many body effect. In the second scenario, we study the dynamics of a competing order system which is rapidly heated up by a pump and then cools down to its equilibrium temperature. 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 induced collapse of a dominant order.
References:
Z. Sun and A. J. Millis, Phys. Rev. Lett. 126, 027601 (2021)
Z. Sun and A. J. Millis, Phys. Rev. X 10, 021028 (2020)
Dr. Zhiyuan Sun graduated from University of Science and Technology of China in 2012 and obtained his PhD at UC San Diego with Prof. Michael Fogler in 2018. Since then, he has been working as a postdoc at Columbia University. His research interest covers collective excitations in nano (2D) materials, electron hydrodynamics, and nonequilibrium dynamics of novel states of matter.