Pressure-Induced Reversible Local Structural Disorder in Superconducting AuAgTe4

Here, we report results of the investigation of the lattice dynamics of the sylvanite mineral AuAgTe4 in a wide temperature and pressure range by Raman spectroscopy, together with the first-principle calculations. At ambient pressure, the experimental spectrum agrees well with the calculation data. The temperature behavior of the phonon self-energies (frequencies and linewidths) are described by an anharmonic mechanism and imply negligible contributions of electron-phonon interaction at low temperatures. A structural phase transition was recorded in the pressure range of 4-6 GPa, which is in accordance with theoretical predictions. At higher pressures, evidence of local structural disorder was found that made it possible to experimentally observe the spectrum of the density of vibrational states of AuAgTe4, which becomes superconducting under pressure.