Ultrafast Spectroscopy of Dirac Semimetal Cd3As2 under Pressure

TL;DR

This study uses ultrafast spectroscopy to investigate how applying pressure affects the electronic states and phase transitions of the Dirac semimetal Cd3As2, revealing new relaxation dynamics and phase behavior.

Contribution

It introduces an experimental setup for pressure-dependent ultrafast spectroscopy of Cd3As2 and provides theoretical insights into pressure-induced phase transitions and electronic relaxation processes.

Findings

Significant changes in relaxation processes at ~3 GPa and ~9 GPa

Emergence of sub-picosecond relaxation dynamics beyond 9 GPa

Pressure-dependent behavior explained by quadratic band opening

Abstract

Topological properties of a three-dimensional Dirac semimetal Cd3As2, protected by crystal rotation and time-reversal symmetry, can be tuned with the application of pressure. Ultrafast spectroscopy is a unique tool to investigate the character and time evolution of electronic states, emphasizing the signatures of transition. We designed an experimental setup for in-situ pressure-dependent ultrafast optical pump optical probe spectroscopy of Cd3As2 using a symmetric diamond anvil cell. The fast relaxation processes show significant changes across pressure-induced phase transitions at PC1, approximately 3 GPa, and PC2, approximately 9 GPa. A new sub-picosecond time scale relaxation dynamics emerges beyond PC2. Theoretical calculations of differential reflectivity for both interband and intraband processes indicate that the negative (positive) differential reflectivity (Delta R/R) results from the interband (intraband) processes. The pressure-dependent behavior of relaxation dynamics amplitudes beyond PC1 emphasized the necessity of incorporating quadratic band opening in the calculations, explaining the transition of Cd3As2 from a Dirac semimetal to a semiconducting phase. The time evolution of differential reflectivity is calculated using the electronic temperature as a function of time, as provided by the two-temperature model, which fits the experimental data.