Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors

Abstract

We show that in multiband superconductors even small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vortices by producing long-range intervortex attraction. This type of vortex interaction results in unusual response to low magnetic fields leading to phase separation into domains of a two-component Meissner states and vortex droplets.

Microscopic theory of type-1.5 superconductivity in multiband systems

“…(11) are shown by blue dashed and dash-dotted lines correspondingly. In the case (i) near the critical temperature the angles are approximately equal, which provides for this regime a microscopic verification for of the results obtained using phenomenological GL theories 10,11 . At lower temperatures the discrepancy is considerable and grows with the increasing interband coupling.…”

“…Therefore the type-1.5 magnetic response can arise even infinitesimally far away from T c from the interplay of two density modes which originate from the underlying two-gap physics. This behaviour was demonstrated in the framework of phenomenological two-component U (1) GL models 10,11 . Here we develop a theory of type-1.5 superconductivity based on a microscopic theory without involving a GL expansion.…”

“…However, in contrast to type-I case, these vortices have repulsive interaction at short ranges. 6,[10][11][12] . This kind of non-monotonic vortex interaction results in the appearance of the additional "semi-Meissner" phase in low magnetic fields.…”

Experimentally observable signatures of odd-frequency pairing in multiband superconductors

“…the exchange of whole Cooper pairs between bands. [21][22][23][24][25][26] However, conceptually much simpler is single-quasiparticle scattering, or tunneling, between the superconducting bands. The origin of interband quasiparticle scattering can be impurity scattering, but a common intrinsic source is superconductivity associated with specific orbitals, which subsequently hybridize to form the low-energy bands around the Fermi surface.…”

Vortex dynamics for low-κtype-II superconductors

“…10 . The intermediate-mixed state has been explained by the appearance of a long-range vortex attraction that causes an S-shape (unstable) magnetization curve from which the equilibrium states are obtained by a Maxwell construction 11,[14][15][16][17][18] . The observations of bubble-like or stripelike or other irregular vortex domains indeed show the existence of the inter-vortex attraction for low-κ type-II superconductors, but the presence of long-range order between vortex domains means that the long-range interaction between vortices should be repulsive rather than attractive.…”