Suppression of atomic displacive excitation in photo-induced A$_{\mathrm{1g}}$ phonon mode of bismuth unveiled by low-temperature time-resolved x-ray diffraction

TL;DR

This study used low-temperature time-resolved x-ray diffraction to observe ultrafast atomic motions in bismuth, revealing that atomic displacement in the A₁g phonon mode is suppressed at low temperatures, indicating suppressed displacive excitation.

Contribution

It demonstrates the suppression of displacive excitation of the A₁g phonon mode in bismuth at low temperatures using advanced x-ray diffraction techniques.

Findings

Atomic displacement in A₁g phonon mode is suppressed at low temperatures.

Displacive excitation process is suppressed as temperature decreases.

Time-resolved x-ray diffraction effectively captures ultrafast atomic motions.

Abstract

An ultrafast atomic motion of a photo-induced coherent phonon of bismuth at low temperatures was directly observed with time-resolved x-ray diffraction. A cryostat with a window that is transparent to both optical lasers and x-rays enabled versatile diffraction measurements in a wide temperature range including below 10 K. It is found that an atomic displacement in a fully symmetric A$_{\mathrm{1g}}$ phonon mode is suppressed at low temperatures. This result indicates the displacive excitation process is suppressed in the phonon generation with decreasing temperature.