Berry phase jumps and giant nonreciprocity in Dirac quantum dots

Dirac electrons in 2D materials exhibit a Berry phase, an unusual feature induced by the pseudospin which causes the wave function to acquire a measurable phase when system parameters cycle around a closed path. Observing manifestations of the Berry phase via coherent control of quantum state trajectories is experimentally challenging in solid-state systems. In this talk, I will discuss our theoretical proposal to exploit confined Dirac electrons inside circular quantum dots to control and measure the Berry phase of electron orbital states[1]. In particular, we show that weak magnetic fields can be used to control the behavior of electron trajectories and induce a giant non-reciprocal effect driven by the Berry phase. Non-reciprocity is manifest in anomalously large field-induced splittings of quantum dot resonances which are degenerate at B=0 due to time-reversal symmetry. The effect, which is strongest for gapless Dirac particles, overwhelms the magnetic-field-induced orbital and Zeeman splittings. This exotic behavior is unique to quantum dots in Dirac materials and is absent in conventional quantum dots. The non-reciprocity, predicted for a large family of two-dimensional Dirac materials, has recently been observed in scanning tunneling spectroscopy measurements in graphene[2]. The effect is shown to be robust against perturbations of the circular confining potential and, as such, can be exploited in a variety of switchable optoelectronic applications.

References:
[1] JFRN, L.S. Levitov, PRB 94, 235406 (2016).
[2] F. Ghahari, et al, Science 356, 845 (2017).