Pressure dependent thermoreflectance spectroscopy induced by interband transitions in metallic nano-film

Utilizing high-pressure tomodulate optical properties, such as thermoreflectance (dR/dT), over a wide range has received much attention. Nevertheless, how the pressure exerts on the complex dielectric constant and finally on dR/dT remains elusive. Here, we perform a thoroughly experimental and theoretical investigation on dR/dT of Al nano-film from 0 to 25 GPa. The dR/dT values exhibit a sinelike pressure-dependence, with the zero-crossing appearing at around 6 GPa. These special phenomena are well explained from electron transition viewpoints. The first-principles calculations show that the energy difference of parallel bands is enlarged from 1.45 to 2 eV, thereby increasing the threshold for electron transitions. The lifted threshold changes the optical absorption rates of Al and the density of states of the electrons involving interband transitions; finally, the resulting dR/dT exhibits such a pressure-dependent behavior. Our findings provide a deep insight on pressure-induced electronic transitions and photon-electron interactions in metals.

Automated summary

Utilizing high pressure to modulate the optical properties of Al nano-film, this study found that the dR/dT values exhibit a sine-like pressure dependence, with the zero-crossing occurring at around 6 GPa, which can be explained from the perspective of electron transitions.