The development of high-speed flash photography in the 1960s by the late MIT professor Harold “Doc” Edgerton allowed us to visualize events that were too fast for the eye to see — a bullet piercing an apple, or a drop that meets a pool of milk.
Now, for the first time, scientists from MIT and the University of Texas at Austin have captured snapshots of a light-induced metastable using a suite of advanced spectroscopic tools phase hidden from the equilibrium universe. By using single-shot spectroscopy techniques on a 2D crystal with nanoscale modulations of the electron density, they were able to observe this transition in real time.
“With this work, we show the birth and evolution of a hidden quantum phase that is induced by an ultra-short laser pulse in an electronically modulated crystal,” says Frank Gao Ph.D. ’22, co-lead author of an article on the work, who is currently a postdoc at UT Austin.
“Usually, lasing materials is the same as heating them, but not in this case,” adds Zhuquan Zhang, co-lead author and current MIT chemistry student. “Here, irradiating the crystal rearranges the electronic order and creates an entirely new phase, distinct from the high-temperature phase.”
An article about this research was published today in scientific advances. The project was coordinated jointly by Keith A. Nelson, Haslam and Dewey Professor of Chemistry at MIT, and Edoardo Baldini, Assistant Professor of Physics at UT-Austin.
“Understanding the origin of such metastable quantum phases is important in order to answer longstanding fundamental questions in non-equilibrium thermodynamics,” says Nelson.
“The key to this result was the development of a state-of-the-art laser process that can film irreversible processes quantum materials with a temporal resolution of 100 femtoseconds,” adds Baldini.
The material tantalum disulfide consists of covalently bonded layers of tantalum and sulfur atoms loosely stacked on top of each other. below a critical temperatureThe material’s atoms and electrons form nanoscale “Star of David” structures – an unconventional distribution of electrons known as a “charge density wave”.
The formation of this new phase makes the material an insulator, but the glow of a single, intense pulse of light pushes the material into a metastable burial metal. “It’s a transient quantum state frozen in time,” says Baldini. “People have observed this light-induced latent phase before, but the ultrafast quantum processes behind its formation were still unknown.”
Nelson adds: “One of the major challenges is that observing an ultrafast transformation from an electronic order to one that can exist indefinitely is impractical using traditional time-resolved techniques.”
impulses of insight
Researchers developed a unique method in which a single probe laser pulse was split into several hundred different probe pulses, all arriving at the sample at different times, before and after switching was initiated by a separate, ultrafast excitation pulse. By measuring changes in each of these probe pulses after they are reflected from or transmitted through the sample, and then stringing the measurement results together like individual images, they could construct a movie that offers microscopic insights into the mechanisms by which transformations take place.
By capturing the dynamics of this complex phase transition in a single-shot measurement, the authors showed that the melting and rearrangement of the charge density wave leads to the formation of the hidden state. Theoretical calculations by Zhiyuan Sun, a Harvard Quantum Institute postdoc, confirmed this interpretation.
While this study was conducted with one specific material, the researchers say the same methodology can now be used to study other exotic phenomena in quantum materials. This discovery may also help in the development of optoelectronic devices with on-demand light response.
Frank Y. Gao et al, Snapshots of a light-induced metastable hidden phase driven by charge-order collapse, scientific advances (2022). DOI: 10.1126/sciadv.abp9076
Massachusetts Institute of Technology
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Citation: Scientists capture first ever view of a Hidden Quantum Phase in a 2D Crystal (2022, July 25), retrieved July 26, 2022 from https://phys.org/news/2022-07-scientists-capture-first- ever-view -hidden.html
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