Lasers make quantum materials reveal their hidden properties

In the realm of scientific discovery, researchers continually seek methods to illuminate the hidden properties of materials.

This pursuit has led to a significant breakthrough at the University of California San Diego, where a team of researchers has employed advanced optical techniques to shed light on the enigmatic qualities of a quantum material known as Ta2NiSe5 (TNS).

The team’s research marks a pivotal step in understanding quantum materials.

Illuminating the quantum world

Materials typically react to external stimuli like temperature or pressure changes. Yet, the research team at UC San Diego has harnessed the unmatched speed of light to elicit rapid responses from materials, thereby revealing properties that would otherwise remain concealed.

“In essence, we shine a laser on a material and it’s like stop-action photography where we can incrementally follow a certain property of that material,” said Professor of Physics Richard Averitt, who led the research and is one of the paper’s authors.

“By looking at how constituent particles move around in that system, we can tease out these properties that are really tricky to find otherwise.”

Quest to unveil hidden quantum properties

The innovative experiment was spearheaded by Sheikh Rubaiat Ul Haque, a recent UC San Diego graduate and now a postdoctoral scholar at Stanford University.

Collaborating with Yuan Zhang, another graduate student from Averitt’s lab, Haque refined a technique known as terahertz time-domain spectroscopy.

This enhancement enabled the team to explore a material’s properties across a wider frequency range, pushing the boundaries of their research.

Underpinning their experimental work is a theory by Professor Eugene Demler of ETH Zürich, another author of the paper.

Demler, along with his graduate student Marios Michael, hypothesized that when quantum materials like TNS are excited by light, they might transform into a medium that amplifies terahertz frequency light.

This hypothesis provided a crucial framework for Haque and his colleagues to investigate TNS’s optical properties more closely.

Understanding excitons and condensates

A core concept in their research is the formation of excitons — bound states of an electron and a hole created when an electron is elevated to a higher energy level by a photon.

These excitons can condense, behaving as a single entity. Utilizing Demler’s theory, along with density functional calculations from Angel Rubio’s group at the Max Planck Institute for the Structure and Dynamics of Matter, the team observed anomalous terahertz light amplification.

This observation was pivotal in uncovering some of the elusive properties of the TNS exciton condensate.

The implications of this discovery are far-reaching. Condensates represent a well-defined quantum state, and this spectroscopic technique could enable the imprinting of their quantum properties onto light.

Future applications for hidden properties

This advancement holds promise for applications in the burgeoning field of entangled light sources, which leverage the interconnected properties of multiple light sources using quantum materials.

Looking ahead, Haque optimistically remarks, “I think it’s a wide-open area,” stated Haque. “Demler’s theory can be applied to a suite of other materials with nonlinear optical properties. With this technique, we can discover new light-induced phenomena that haven’t been explored before.”

This sentiment captures the essence of their work — a bold stride into uncharted scientific territory, promising a deeper understanding and potential new applications of quantum materials.

The full study was published in the journal Nature Materials.

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