Identical superconducting gap on different Fermi surfaces of Ca(Al_0.5Si_0.5)₂ with the AlB₂ structure

Angle-resolved photoemission spectroscopy of Ca(Al_0.5Si_0.5)₂ (CaAlSi), which is a superconductor (transition temperature is 7.7 K) with the AlB₂ 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 (∼1.2meV±0.2meV). This is in contrast to the case of MgB₂, in which different FSs exhibit different gap values. The reduced gap value 2Δ(0)/k_BT_c of ∼4.2±0.2 classifies CaAlSi as a moderately strong-coupling superconductor.