Condensed Matter Seminar Series

Peter P. Orth

Iowa State University

Ultrafast control of symmetry and topology using coherent light

Symmetry plays a key role in both conventional and topological phases of matter, making the ability to optically drive symmetry changes a critical step in developing future technologies that rely on such control.
Topological materials, like the newly discovered topological semimetals, are particularly sensitive to a breaking or restoring of time-reversal and crystalline symmetries, which affect both bulk and surface electronic states. Here, we discuss two examples of ultrafast symmetry control in topological systems. First, we show results of a recent experiment that uses photocurrent generation to break time-reversal and spatial symmetries in the prototypical type-I Weyl semimetal TaAs [1]. Symmetry changes are revealed via a detailed theoretical analysis of second-harmonic generation spectroscopy results. We demonstrate that the degree of symmetry breaking can be controlled by the light polarization. Second, we show that bicircular light (BCL) offers, which consists of a superposition of two circular light beams with integer frequency ratios, offers enhanced tunability of magnetic symmetry breaking compared to single-frequency light. We discuss implications for controlling surface state properties and driving topological phase transitions in strained and unstrained Cd3As2.
 
[1] N. Sirica et al., Photocurrent-driven transient symmetry breaking in the Weyl semimetal TaAs, arXiv:2005.10308 (2020).