Identical superconducting gap on different Fermi surfaces ofCa(Al0.5Si0.5)2with theAlB2structure

Abstract

Angle-resolved photoemission spectroscopy of Ca(Al 0 . 5 Si 0 . 5 ) 2 (CaAISi), which is a superconductor (transition temperature is 7.7 K) with the AlB 2 structure, revealed that superconducting gaps on two Fermi surfaces (FSs) with three-dimensional character around Γ(A) and M(L) in the Brillouin zone provide essentially the same superconducting gap value (∼1.2 meV′0.2 meV). This is in contrast to the case of MgB 2 , in which different FSs exhibit different gap values. The reduced gap value 2Δ(0)/k B T c of ∼4.2′0.2 classifies CaAlSi as a moderately strong-coupling superconductor.