Coherent soft-mode phonon generation and detection in ultrathin SrTiO3 grown directly on silicon

TL;DR

This study demonstrates the generation and detection of coherent soft-mode phonons in ultrathin SrTiO3 films grown on silicon, revealing insights into phonon dynamics at nanoscale thicknesses.

Contribution

It presents the first direct observation of coherent soft-mode phonons in SrTiO3 films as thin as 2 nm on silicon using time-resolved spectroscopy.

Findings

Detection of 0.2 THz soft mode in ultrathin films

Observation of relaxational hopping of Ti ions

Polarization dependence helps identify phonon modes

Abstract

Time-resolved two color pump-probe polarization spectroscopy was performed at room temperature on SrTiO3 films grown directly on Si with film thickness varying from 2 nm to 7.8 nm. The E soft mode with a characteristic frequency of 0.2 THz is impulsively generated and measured in these coherently strained tetragonal phase SrTiO3 thin films. Another over-damped signal observed indicates the possible relaxational hopping of Ti ion between double potential wells. The dependence of the coherent phonon signal on pump and probe laser polarization helps to identify the phonon modes.