Carbon Doping in MgB_2 : Role of Boron and Carbon p_x(y) Bands

TL;DR

This study investigates how carbon doping affects the electronic structure and superconducting transition temperature of MgB2 alloys, revealing that increased carbon content shifts the Fermi energy and reduces specific p states, aligning with experimental T_c trends.

Contribution

The paper introduces a density-functional approach combined with disorder modeling to analyze electronic and superconducting changes in MgB2 alloys with carbon doping.

Findings

Fermi energy shifts outward with increasing carbon content.

Small effects of disorder in the boron plane.

Sharp decline in B and C p_{x(y)} states at high doping levels.

Abstract

We have studied the changes in the electronic structure and the superconducting transition temperature T_c of Mg(B_{1-x}C_{x})_{2} alloys as a function of x with 0\leq x\leq 0.3. Our density-functional-based approach uses coherent-potential approximation to describe the effects of disorder, Gaspari-Gyorffy formalism to estimate the electron-phonon matrix elements and Allen-Dynes equation to calculate T_c in these alloys. We find that the changes in the electronic structure of Mg(B_{1-x}C_{x})_{2} alloys, especially near the Fermi energy E_F, come mainly from the outward movement of E_F with increasing x, and the effects of disorder in the B plane are small. In particular, our results show a sharp decline in both B and C p_{x(y)} states for 0.2\leq x\leq 0.3. Our calculated variation in T_{c} of Mg(B_{1-x}C_{x})_{2} alloys is in qualitative agreement with the experiments.