Special Colloquium
Department of Physics, NCU
Toward solid-state devices exploiting the Berry curvature effects with non-adiabatic dynamics
Speaker
Dr. 涂維元 (Wei-Yuan Tu)
Department of Physics, National Cheng Kung University, Taiwan
Date 2021.2.25 (Thu)
Time 10:00am
Place S4-625
Abstract
In this talk, we will depict a possible route toward conceiving device blueprints that exploit Berry phase effects in solid-state electronics. In contrast to the typical impression of the Berry curvature effects, usually introduced via adiabatic dynamics, we are particularly interested in the non-adiabatic aspects. On one hand, this is because the Berry curvature (which is inversely proportional to the square of the gap) is most pronounced at band anti-crossings with small gaps where the non-adiabatic dynamics is anticipated. On the other hand, for device applications, the externally applied fields are expected to steer the dynamics so that they shall be of finite magnitudes, other than infinitesimal (as required by the adiabatic limit), and are able to evoke non-adiabatic dynamics. As an initiative, we explore the non-adiabatic aspect of Hall effect at Berry curvature hotspots. We show that there exists a general connection between the field induced electron-hole coherence and intrinsic Hall velocity. In coherent evolution, the electron-hole coherence can manifest as a sizable ac Hall velocity. When environmental noise is taken into account, its joint action with the electric field favors a form of electron-hole coherence that is a function of wavevector and field only, leading to a dc non-linear Hall effect. The Hall current has all odd order terms in the field, and still retains the intrinsic role of the Berry curvature. Despite this initiative, a number of challenges await for turning quantum materials with interesting Berry phase properties into functional quantum devices. These include non-equilibrium dynamics, decoherence and non-Abelian gauge structures, etc. In pointing to the future research possibilities, we shall also outline some tangible strategies that help to exploit Berry curvature physics for device functionalities.