Study of temperature dependent atomic correlations in MgB$_{2}$

TL;DR

This study investigates how atomic correlations in MgB$_{2}$ evolve with temperature using neutron diffraction, revealing mostly decoupled B and Mg vibrations with temperature-independent small positive correlations.

Contribution

It provides the first detailed temperature-dependent analysis of atomic pair correlations in MgB$_{2}$ using PDF measurements and compares experimental results with theoretical predictions.

Findings

B and Mg vibrations are mostly decoupled.

Small positive correlation factors are temperature independent.

Experimental correlations differ from theoretical calculations.

Abstract

We have studied the evolution with temperature of the local as well as the average crystal structure of MgB$_2$ using the real-space atomic pair distribution function (PDF) measured by high resolution neutron powder diffraction. We have investigated the correlations of the B-B and B-Mg nearest neighbor pair motion by comparing, in the wide temperature range from T=10 K up to T=600 K, the mean-square displacements (MSD) of single atoms with the mean-square relative displacements (MSRD) obtained from the PDF peak linewidths. The results show that the single atom B and Mg vibrations are mostly decoupled from each other, with a small predominance of positive (in phase) correlation factor for both the B-B and B-Mg pairs. The small positive correlation is almost temperature independent, in contrast with our theoretical calculations; this can be a direct consequence of the strong decay processes of the $E_{2g}$ anharmonic phonons.