Quantum normal-to-inhomogeneous superconductor phase transition in nearly two-dimensional metals

Abstract

In multiband systems, electrons from different orbitals coexist at the Fermi surface. An attractive interaction among these quasiparticles gives rise to interband or hybrid pairs which eventually condense in a superconducting state. These quasiparticles have a natural mismatch of their Fermi wave vectors, δkF, which depends on the strength of the hybridization between their orbitals. The existence of this natural scale suggests the possibility of inhomogeneous superconducting ground states in these systems, even in the absence of an applied magnetic field. Furthermore, since hybridization V depends on pressure, this provides an external parameter to control the wave vectors’ mismatch at the Fermi surface. In this work, we study the phase diagram of a two-dimensional, two-band metal with interband pairing. We show that as the mismatch between the Fermi wave vectors of the two hybrid bands is reduced, the system presents a normal-to-inhomogeneous superconductor quantum phase transition at a critical value of the hybridization Vc=Δ0. The superconducting ground state for V<Vc is characterized by a wave vector with magnitude |qc|=qc=2Δ0/v¯f. Here Δ0 is the superconducting gap in the homogeneous state and v¯f the average Fermi velocity. We discuss the nature of the quantum critical point at Vc and obtain the associated quantum critical exponents.

Similar papers