Electronic structure of superconducting ${MgB}_{2}$ and related binary and ternary borides

Authors:

First-principles full potential linear muffin-tin orbital–generalized gradient approximation electronic structure calculations of the new medium-

T_{C}

superconductor (MTSC)

{MgB}_{2}

and related diborides indicate that superconductivity in these compounds is related to the existence of

p_{x, y}

-band holes at the

Γ

point. Based on these calculations, we explain the absence of medium-

T_{C}

superconductivity for

{BeB}_{2},

{AlB}_{2},

{ScB}_{2}

, and

{YB}_{2} .

The simulation of a number of

{MgB}_{2}

-based ternary systems using a supercell approach demonstrates that (i) the electron doping of

{MgB}_{2}

(i.e.,

{MgB}_{2 - y} X_{y}

with

X = Be,

C, N, O) and the creation of defects in the boron sublattice (nonstoichiometric

{MgB}_{2 - y})

are not favorable for superconductivity, and (ii) a possible way of searching for similar or higher MTSC should be via hole doping of

{MgB}_{2}

({CaB}_{2})

or isoelectronic substitution of Mg (i.e.,

{Mg}_{1 - x} M_{x} B_{2}

with

M = Be,

Ca, Li, Na, Cu, Zn) or creating layered superstructures of the

{MgB}_{2} / {CaB}_{2}

type.

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Electronic structure of superconductingMgB2and related binary and ternary borides