Distinct magnetic signatures of fractional vortex configurations in multiband superconductors

Abstract

Vortices carrying fractions of a flux quantum are predicted to exist in multiband superconductors, where vortex core can split between multiple band-specific components of the superconducting condensate. Using the two-component Ginzburg-Landau model, we examine such vortex configurations in a two-band superconducting slab in parallel magnetic field. The fractional vortices appear due to the band-selective vortex penetration caused by different thresholds for vortex entry within each band-condensate, and stabilize near the edges of the sample. We show that the resulting fractional vortex configurations leave distinct fingerprints in the static measurements of the magnetization, as well as in ac dynamic measurements of the magnetic susceptibility, both of which can be readily used for the detection of these fascinating vortex states in several existing multiband superconductors. PACS numbers: 74.25Ha, 74.25Uv, 74.70Xa, 74.70Ad Multiband superconductors [1, 2] present a variety of intriguing properties that are not found in their singlecomponent counterparts. Theoretical predictions have added more striking properties to that list and challenge experiments to prove them. One of such properties is the appearance of fractional vortices in multiband materials [3], seemingly violating flux quantization. This is only possible for different winding numbers of different order parameters in a system of coexisting weakly interacting condensates, and is facilitated for significantly different length scales of the condensates -especially under mesoscopic confinement [4][5][6][7][8][9]. Weakly coupled multiband materials [10] and superconducting multilayers [11] as their artificial analogue are readily available, hence clever experiments should be devised for detecting and manipulating fractional vortices (see e.g. Ref. 12). In addition, dynamic dissociation of vortices is predicted in the flux flow regime [13], as well as the stationary vortex splitting [14,15] stemming from phase frustration in superconductors with three or more bands [16,17], but neither of those vortex fractionalizations has been realized to date.In this Letter we explore the effect of a surface in stabilizing the fractional vortices in multiband superconductors [18], and propose static (dc) and dynamic (ac) measurements to directly detect them. We consider a twoband superconducting slab in parallel magnetic field H, with width much larger than the field penetration depth in order to prevent strong confinement effects. For our numerical experiments, we have used the two-component Ginzburg-Landau (TCGL) model, where by cautiously setting temperature T close to the critical temperature T c , we ensure the qualitative and quantitative validity of our results (for comparison with other available theoretical models, see e.g. . In the TCGL framework, as given in Ref. 22, eight independent material parameters are needed for a system with both interband and magnetic coupling, namely, the Fermi velocity of the first band v 1 , the square of the ratio of the Ferm...

Phase shifter based on an ultrathin superconducting bilayer with a through-hole for a superconducting device

“…Finally, the plausibility of the formation of a fractional quantum in view of the previous theories are discussed. Several theories exist to predict a fractional flux quantum and a fractional vortex in the bilayer and multicomponent superconductors with a finite quadratic Josephson interaction between two components [7,[30][31][32][33][34][35][36][37][38][39][40][41][42]. Although these theories have not been experimentally confirmed (in other words, the situations discussed in these theories…”

Current-induced massless mode of the interband phase difference in two-band superconductors

“…The detection of a fractionally quantized magnetic flux is one way to confirm the presence of the i-soliton [12,13,21,31,32,34,35,[39][40][41][42][43][44][45]. For this detection, we may slightly modify the circuit shown in Fig.…”

Gradient flow in the Ginzburg-Landau model of superconductivity

“…Multiband superconductors [46][47][48] can exhibit new physics and vortex configurations not found in single band superconductors.…”