A time-domain phase diagram of metastable quantum states

Our collaborators at the Jozef Stefan Institute – the leading author, Jan Ravnik, is now a PSI Fellow at LMN – report a ‘dynamical’ phase diagram of metastable quantum states generated via photoexcitation of the prototypical dichalcogenide material 1T-TaS₂.

Conventionally, phase diagrams are thought of as static without temporal evolution. However, many functional properties of materials arise as a result of complex temporal changes which occur on different timescales. Presenting the phase diagram of metastable states introduces a time axis, requiring measurements on different timescales. The study of Jan Ravnik and collaborators, published in Nature Communications, reports such a ‘dynamical’ phase diagram spanning time over fifteen orders of magnitude, as established using femtosecond spectroscopy and scanning tunnelling microscopy.

The study focuses on the prototypical quasi-two-dimensional transition metal dichalcogenide material 1T-TaS₂, which was earlier shown to display multiple metastable electronic and structural ordering phenomena. Besides the conceptual novelty, the current results highlight how the phase boundaries between the various quantum states evolve with time, and how excitation conditions influence long-term metastability. Thereby, the study also paves the way towards understanding other related metastable quantum states. Since the electronically ordered states of 1T-TaS₂ can be generated via optical excitation and also electric current injection in devices, the material presents a playground for future research of the metastable states and nanofabricated switching devices.

The experiments were conducted in the group of Prof. Dragan D. Mihailović at the Jozef Stefan Institute in Ljubljana, Slovenia, with which LMN has established a collaboration on transition metal chalcogenides aiming to investigate the materials at PSI's accelerator-based photon sources and fabricate efficient ultrafast memory devices.