Seminar: Dr. Yafei Ren | University of Delaware
In-Person PHYS 401
Location
Physics : 401
Date & Time
November 19, 2025, 11:00 am – 12:00 pm
Description
TITLE: "Nonadiabatic Wave-Packet Dynamics in Quantum Materials: Geometry, Berry Phases, and Analogue Gravity”
ABSTRACT: The motion of electrons in crystalline materials lies at the heart of modern condensed matter physics and underpins technologies ranging from semiconductors to emerging quantum devices. A powerful and intuitive way to describe this motion is through wave packets, which advanced profound concepts such as topological insulators, anomalous transport, and modern theory of polarization and magnetization.
ABSTRACT: The motion of electrons in crystalline materials lies at the heart of modern condensed matter physics and underpins technologies ranging from semiconductors to emerging quantum devices. A powerful and intuitive way to describe this motion is through wave packets, which advanced profound concepts such as topological insulators, anomalous transport, and modern theory of polarization and magnetization.
In this talk, after introducing the adiabatic wave-packet framework and illustrating how Berry phases naturally emerge and influence electron dynamics, I will present our recent work extending this framework to the nonadiabatic regime, where inter-band transitions are driven by rapid motion of the wave-packet center and/or varying spatiotemporal perturbations. This generalized theory reveals three key new ingredients: 1) A nonadiabatic metric tensor in phase space that provides a geometric description of electron motion analogous to how gravity guides particles in general relativity; 2) Corrections to Berry phases that generate emergent electromagnetic fields from time-dependent potentials or coherent lattice or spin dynamics; 3) Higher-order energy corrections.
These results establish a unified framework for exploring nonlinear transport and low-frequency driven quantum materials, opening new pathways to control electronic, magnetic, and lattice properties that remain to be understood.
Biosketch:
Dr. Yafei Ren received his B.S. and Ph.D. degrees from the University of Science and Technology of China in 2013 and 2019, respectively, during which time he was a visiting scholar at California State University, Northridge. He then carried out postdoctoral research at the University of Texas at Austin and the University of Washington. In 2023 he joined the Department of Physics and Astronomy at the University of Delaware. His research focuses on the influence of geometric phases on the electronic, lattice, and spin degrees of freedom, their mutual interactions, and nonequilibrium dynamics.
