Certain materials have desirable properties that are hidden, and like shining a flashlight in the dark, scientists can use light to reveal these properties. Researchers have developed an advanced optical technique that uses light to reveal the hidden properties of the quantum material Ta2NiSe5 (TNS). By using terahertz time-domain spectroscopy, the team observed unusual terahertz light amplification, indicating the presence of exciton condensates. This discovery opens up new possibilities for using quantum materials for entangled light sources and other applications in quantum physics.
UC San Diego researchers have used an advanced optical technique to learn more about a quantum material called Ta2NiSe5 (TNS). Their research results were published in the journal Nature Materials.
Materials can be perturbed by different external stimuli, usually changes in temperature or pressure; however, since light is the fastest thing in the universe, materials respond very quickly to light stimuli, revealing otherwise hidden properties.
Advanced optical technologies in quantum materials
"Essentially, we shine a laser on a material, which is like stop-motion photography, and we can follow a certain property of the material step by step," said Richard Avitt, a professor of physics who led the study and was one of the paper's authors. "By observing how the constituent particles move through this system, we can identify these properties that would otherwise be difficult to detect."
The experiment was conducted by first author Sheikh Rubaiat Ul Haque, who graduated from UC San Diego in 2023 and is now a postdoctoral scholar at Stanford University. Together with Yuan Zhang, another graduate student in the Everett lab, he refined a technique called terahertz time-domain spectroscopy. This technique allows scientists to measure the properties of materials within a certain frequency range, and Haack's improvements allow them to access a wider frequency range.
Quantum states and light amplification
The work is based on a theory put forward by another author of the paper, Eugene Demler, a professor at ETH Zurich. Demler and his graduate student Marios Michael proposed the idea that when certain quantum materials are excited by light, they might become a medium that amplifies light at terahertz frequencies. This prompted Haack and colleagues to take a closer look at the optical properties of TNS.
When an electron is excited to a higher level by a photon, a hole is left behind. If electrons and holes combine, excitons are produced. Excitons may also form condensates - a state that occurs when particles come together and behave as a single entity.
With the support of Demler's theory and using density functional calculations by Angel Rubio's group at the Max Planck Institute for the Structure and Dynamics of Matter, the research team was able to observe the anomalous terahertz light amplification phenomenon, thus revealing some hidden properties of the TNS exciton condensed state.
Condensates are well-defined quantum states, and some of their quantum properties can be imprinted onto light using this spectroscopic technique. This could have implications for the emerging field of entangled light sources (multiple light sources with interrelated properties) that exploit quantum materials.
"I think this is a broad field," Haack said. "Demler's theory can be applied to a range of other materials with nonlinear optical properties. With this technology, we can discover new light-induced phenomena that have never been explored before."
Compiled source: ScitechDaily