120th CEMS Colloquium

Title

Dynamical Control of Quantum Materials by Light

Abstract

Optical manipulation of quantum systems has gained a growing interest over decades. With the recent development of ultrafast advanced light sources, the concept is now being applicable to complex condensed matter systems. In particular, ultrafast laser spectroscopy techniques have enabled the dynamical control of quantum materials, demonstrating the capability of disentangling the intertwined order, inducing symmetry broken ordered states and revealing hidden phases which are inaccessible by static perturbations to equilibrium phases. The concept is not limited to the light-control of symmetry-broken states, but also extended to the manipulation of topological state of matter in a nonequilibrium manner, dubbed as Floquet engineering.

In this colloquium, I will introduce two striking examples along this context: 1) light-induced superconductivity in high-T_c cuprate superconductors, and 2) Floquet engineering in three-dimensional(3D) Dirac electron systems. In the first part, I will report our recent observation of light-induced Josephson plasma edge in La-based cuprate superconductors, suggesting Cooper pair formation far above T_c. In the second part, I will report on the Floquet engineering of 3D Dirac electrons in a thin film of bismuth. The emergence of Weyl states at one photon resonance of Dirac bands is indicated through the time-resolved observation of anomalous Hall effect. The results reveal that the Floquet-Weyl state is universally induced at the one photon resonance when time-reversal symmetry breaking, circularly polarized light is irradiated onto materials with large spin-orbit interactions.