Optical Thermal Measurements of Thermal Diffusivity in 1T-TaS2

Thermal response of electronic materials can detect phase transitions and transport processes. Moreover, micron-scale measurements avoid sample imperfections such as dislocations, grain boundaries, and other defects, and allow for proper averaging on macroscopic samples. We use a photo-thermal microscope for high resolution thermal diffusivity and optical reflectivity measurements. A laser beam is focused at the surface of the targeted sample; the laser power is modulated to create a periodic, point-like heat source. A nearby laser measures the local reflectivity. In this talk we focus on 1T-TaS₂, a quasi-2D Mott insulator with various competing charge density wave (CDW) orders and a proposed quantum spin liquid phase at low temperature [1]. We study the nature of the phase transitions through anomalies in differential reflectivity (dR/dT) and the transport behavior though measurements of thermal diffusivity (D_Q). In particular, anomalies in dR/dT at the 180K- and 345K- CDW transitions are discussed in terms of the nature of the phase transitions and D_Q is discussed in terms of its implications on transport mechanisms.

[1] 10.1103/PhysRevLett.121.046401