Transverse field μSR investigation of the flux lattice in Mg1−xAlxB2

Effect of Two Gaps on the Flux-Lattice Internal Field Distribution: Evidence of Two Length Scales inMg1−xAlxServenti1, Allodi2, Renzi3 et al. 2004Phys. Rev. Lett.Self Cite562391View full textAdd to dashboardCite

“…Early SR results [17] on the pure sample revealed a large field variation of the second moment 2 of the muon line, proportional to the inverse squared of the penetration depth , attributed to low field pinning effects. Subsequent studies [18,19] detected a reduction of in Al and C substituted powders, consistent with filling of the band. Recent measurements [20] extended the field range to 5 T and attributed H to a field dependence of .…”

“…In extreme type II materials σ µ would be proportional to the inverse squared London penetration depth. Subsequent studies [18,19] detected a reduction of σ µ in Al and C substituted powders, consistent with filling of the σ band. Recent measurements [20] extended the field range to 5 T and attributed σ µ (H) to a field dependence of the coherence length.…”

“…It is apparent that increasing values of x lead to a reduction of σ µ , i.e. to an increase [18,19] of the penetration depth λ(x). This is not surprising since λ −2 is proportional to an effective superconducting carrier density n, in analogy with the simple London model.…”

Small Fermi energy, zero-point fluctuations, and nonadiabaticity inMgB2

“…4 Estimates of the Fermi energy can be inferred also from penetration depth measurements giving E F = 3200 K in MgB 2 , 5 and even less in Al and C doped compounds. 5,6 In previous studies we have analyzed some of the effects related to a small Fermi energy E σ F on different electronic and vibrational properties of MgB 2 . One of these effects is the breakdown of Migdal's theorem, and consequently of the Migdal-Eliashberg diagrammatic theory, which occurs when the Fermi energy E σ F and the phonon energy ω ph are comparable (ω ph /E σ F < ∼ 1).…”