Pressure Effects and Large Polarons in Layered MgB_2 Superconductor

TL;DR

This paper models how pressure influences the superconducting critical temperature of MgB_2 by considering large polarons affecting its band structure, providing theoretical estimates consistent with experimental data.

Contribution

It introduces a polaron-based model to explain pressure dependence of T_c in MgB_2, linking polaron effects to band shifts and superconductivity.

Findings

dT_c/dp estimated as -α(5.2±0.9) K/GPa

Estimated Froehlich coupling constant α between 0.15 and 0.45

Model aligns with experimental pressure dependence data

Abstract

We consider the dependence of the MgB_2 superconducting critical temperature on the pressure. Our model exploits the influence of the large polarons on the band structure of the layered MgB_2 superconductor. Namely, the hole Pekar-Froehlich polarons form quasi two-dimensional potential wells in the boron plane which shift the positions of the sigma- and pi-bands. This energy shift depends on the pressure and the Cooper pairing of the correlated sigma-electrons happens inside polaron wells. The results obtained are as follows: dT_c/dp = -\alpha (5.2 \pm 0.9) K/GPa or dT_c/dp = -\alpha (6.9\pm 1.1) K/GPa for a different choice of the Grueneisen parameter. Being compared with known experimental data they give us a resonable interval for the value of the Froehlich electron-phonon coupling constant: \alpha = 0.15 - 0.45.