Scientists capture first-ever view of a hidden quantum phase in a 2D crystal
This illustration represents the light-induced collapse of the nanoscale charge order in a 2D crystal of tantalum disulfide (star-shapes) and the generation of a hidden metastable metallic state (spheres). Credit: Frank Yi Gao

Harold "Doc" Edgerton, a professor at MIT, developed high-speed strobe- flash photography in the 1960s that allowed us to see events too quickly for the eye.

Scientists at MIT and the University of Texas at Austin have for the first time captured snapshots of a light-caused metastable phase hidden from the equilibrium universe. They were able to see the transition in real-time by using single-shot techniques on a 2D crystal.

The work shows the birth and evolution of a hidden quantum phase caused by an ultra short laser pulse.

"Usually, shining lasers on materials is the same as heating them, but not in this case," says the co-lead author of the book. The irradiation of the crystal rearranges the electronic order, creating a new phase different from the high- temperature one.

The paper on this research was published today. The project was coordinated by two professors, one at MIT and one at UT-Austin.

There is a laser show.

Nelson says that it's important to understand the origin of the metastable quantum phases.

Baldini says that the key to this result was the development of a state-of-the-art laser method that could make movies with a time resolution of 100 femtoseconds.

The material is made up of layers of tantalum and sulfur atoms that are bound together. An unconventional distribution of electrons known as a "charge density wave" can be found below a critical temperature.

A single intense light pulse pushes the material into a metastable hidden metal even though it is an insulator. Baldini says that it is a quantum state. People have observed this light-generated hidden phase before, but the ultrafast quantum processes behind its creation were still unknown.

Nelson says that observing an ultrafast transformation from one electronic order to another that may persist indefinitely is not practical with time-resolved techniques.

There are a lot of pulse's of insight.

A unique method was developed by the researchers that involved splitting a single probe laser pulse into several hundred different probes that all arrived at the sample at different times before and after the switch. By measuring changes in each probe pulse after they were reflected from or transmitted through the sample and then stringing the measurement results together like individual frames, they could construct a movie that provides insight into the mechanisms through which transformation occur.

The authors used a single-shot measurement to show that the melting of the charge density wave leads to the formation of a hidden state. The interpretation was confirmed by theoretical calculations.

The same methodology can now be used to study other exotic phenomena in quantum materials. The development of optoelectronic devices with on-demand photoresponses could be helped by this discovery.

More information: Frank Y. Gao et al, Snapshots of a light-induced metastable hidden phase driven by the collapse of charge order, Science Advances (2022). DOI: 10.1126/sciadv.abp9076 Journal information: Science Advances

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