Is MgB₂a BCS-like charged superfluid?

Abstract

Two complementary mechanisms have been proposed for relatively high temperature superconductor MgB 2 . While the first is the electron-phonon mechanism of BCS theory, advocated strongly by Pickett and co-workers, the second, by Bianconi et al., invokes Feshbach shape resonances. While we cannot presently discount the second mechanism, and while both proposals exploit the multiband nature of the electronic structure of MgB 2 , we show here that five body-centred cubic (bcc) transition metals, whose superconducting transition temperature correlate intimately with elastic constants and therefore are plainly BCS-like in character, lie on a curve which has MgB 2 at the high T c end. Any alternative mechanism to electron-phonon interaction in MgB 2 will need to account quantitatively for this circumstance.Keywords: Electron-phonon mechanism; Superfluid MgB 2 In a recent study [1], we have related the superconducting transition temperature T c of five body-centred cubic (bcc) transition metals to elastic constants and especially to the so-called Cauchy deviation (see figure 1). Here, we want to relate such results for these BCS-like transition metals to recent work on MgB 2 , with a relatively high transition temperatureTo do this, we show in figure 2, for comparison with figure 1, the five bcc metals on a conventional BCS plot in which the transition temperature T c is scaled with the Debye temperature  D [3]. Unlike figure 1, where the five bcc metals are ordered via the elastic constants precisely with their transition temperatures, figure 2 has a less simple ordering, even though these five metals lie on a (scaled) BCS-like plot.