Thermalization in Quantum Materials:
Two-Photon Photoelectron Spectroscopy of a-RuCl3

 
The idea of “quantum materials” might sound redundant but it is motivated by profound recent discoveries of topological phases in materials that had been once thought to be very simple [1]. At present, focus on identification of new quantum materials is driven by hopes of future quantum information technologies that will require careful control of quantum states. An important challenge is that information stored in the quantum state of a solid may be degraded as the solid evolves toward a thermal state, i.e. one characterized by an “effective” temperature. We need to ask: If we drive a quantum system, how rapidly does it thermalize? In this talk, I will present an overview of quantum materials and modern ideas about thermalization in many body systems. I’ll then report on our latest two photon photoelectron (2PPE) spectroscopy experiments on a-RuCl3 that indicate very rapid (<100 fs) thermalization of excited states. a-RuCl3 is a correlated spin-orbit coupled material that has been suggested as a candidate for unique spin liquid phases due to anisotropic exchange interactions [2]. Our experiments on the ultrafast electron dynamics in this system provide insights into its quantum phases and information loss.

[1] Editorial, Nature 12, 105 (2016).
[2] Bannerjee et al., Science 356, 1055 (2017).