Raising the diboride superconductor transition temperature using quantum interference effects

Abstract

The model of two ( σ and π) channel superconductivity known to be necessary to explain the superconductivity in MgB 2 has been applied to the Al 1-x Mg x B 2 diborides by tuning x from MgB 2 to AlMgB 4 . The evolution of the interband coupling parameter (probing the strength of the interchannel pairing due to quantum interference effects) and the two gaps in the σ and π channel as a function of x have been calculated. While in MgB 2 the quantum interference effects give an amplification of T c by a factor of 1.5 in comparison with the dominant intra σ band single channel pairing, in AlMgB 4 the amplification is about 100, in comparison with the dominant intra π band single channel pairing.

Anomalous Thermal Expansion in Superconducting Mg1− x Al x B2 System

“…It has been shown [21] that the interband pairing term shows a broad resonance as expected for a superconducting Feshbach shape resonance. Experimental evidence for the 2D-3D topology cross-over in the band is indicated a frequency hardening and a line-width narrowing of the Raman E 2g mode indicating a strong reduction of the electron-phonon interaction going from 2D regime to the 3D regime through the ETT point [29,30].…”

“…The two gaps but a single T c show directly the key role of interband pairing (IP) and there is now a wide scientific agreement that IP in MgB 2 increases T c by about a factor two. The theoretical interest is now focusing in understanding the physics of interband pairing by tuning the chemical potential in the proximity to the 2D-3D topology cross-over in the band (the 2D-3D ETT) [21][22][23][24][25][26]. The chemical potential can be tuned experimentally toward the 2D-3D ETT by chemical substitutions of aluminum or scandium for magnesium [28][29][30] or carbon for boron [31].…”

Feshbach Shape Resonance in Multiband Superconductivity in Heterostructures

“…The increase of the critical temperature determined by the Feshbach shape resonance [125,162,180] of the interband pairing is given by ∆T c T F = (T c (exp) − T c (BCS)) T F that is plotted in Fig. 7 as a function of Lifshitz parameter z.…”

From the Pion Cloud of Tomonaga to the Electron Pairs of Schrieffer: Many Body Wave Functions from Nuclear Physics to Condensed Matter Physics

“…Today in the field of high temperature superconductivity [14,15,16,17,18] and in the quantum condensation of fermionic ultracold gases [19,20,21,22] there is high interest in superconductivity in strongly interacting fermionic systems where quantum condensation takes place in a regime of intermediate coupling between the BCS and the BEC regime, called BCS-BEC crossover.…”