Researchers at the University of California San Diego, led by Professor Richard Averitt, have used an advanced optical technique to uncover hidden properties of a quantum material called Ta2NiSe5. The experiment was conducted by Sheikh Rubaiat Ul Haque, a postdoctoral scholar at Stanford University, and Yuan Zhang. They improved upon a technique called terahertz time-domain spectroscopy, based on a theory by Professor Eugene Demler at ETH Zürich.
The team observed anomalous terahertz light amplification, revealing hidden properties of the material. This could have implications in the field of entangled light sources utilizing quantum materials. Funding was provided by various organizations including DARPA and the Swiss National Science Foundation.
Unveiling Hidden Properties of Quantum Materials with Light
Researchers at the University of California San Diego have utilized an advanced optical technique to uncover hidden properties of a quantum material known as Ta2NiSe5 (TNS). The study, led by Professor of Physics Richard Averitt, was published in Nature Materials. The team used light as a stimulus, which is the fastest thing in the universe, to prompt a quick response from the material, revealing properties that would otherwise remain concealed.
Averitt explains the process as akin to stop-action photography, where a laser is shone on a material, allowing the team to incrementally follow a certain property of that material. By observing how constituent particles move within the system, the team can identify properties that are otherwise difficult to detect.
The Role of Terahertz Time-Domain Spectroscopy
The experiment was spearheaded by Sheikh Rubaiat Ul Haque, a graduate of UC San Diego and currently a postdoctoral scholar at Stanford University. Haque, along with Yuan Zhang, another graduate student in Averitt’s lab, enhanced a technique known as terahertz time-domain spectroscopy. This method enables scientists to measure a material’s properties over a range of frequencies. The improvements made by Haque and Zhang allowed them to access a broader range of frequencies.
Theoretical Basis and Practical Application
The research was grounded in a theory proposed by Eugene Demler, a professor at ETH Zürich, and his graduate student Marios Michael. They suggested that when certain quantum materials are excited by light, they may transform into a medium that amplifies terahertz frequency light. This theory guided Haque and his colleagues to investigate the optical properties of TNS.
When a photon excites an electron to a higher level, it leaves behind a hole. If the electron and hole are bound, an exciton is formed. Excitons can also form a condensate, a state that occurs when particles unite and behave as a single entity.
Uncovering the Hidden Properties of TNS Exciton Condensate
Using Haque’s technique, supported by Demler’s theory and density functional calculations by Angel Rubio’s group at the Max Planck Institute for the Structure and Dynamics of Matter, the team was able to observe anomalous terahertz light amplification. This observation revealed some of the hidden properties of the TNS exciton condensate.
Condensates are a well-defined quantum state, and using this spectroscopic technique could allow some of their quantum properties to be imprinted onto light. This could have implications in the emerging field of entangled light sources, where multiple light sources have interconnected properties.
Future Implications and Funding
Haque believes that this is a wide-open area of research. Demler’s theory can be applied to a range of other materials with nonlinear optical properties. With this technique, new light-induced phenomena that haven’t been explored before can be discovered.
The research was funded by several organizations, including the DARPA DRINQS Program, the Swiss National Science Foundation, the Army Research Office, the European Research Council, the Cluster of Excellence ‘Advanced Imaging of Matter’, Grupos Consolidados, Deutsche Forschungsgemeinschaft, and the Flatiron Institute.
