Low-energy quasiparticle states at superconductor/charge-density-wave interfaces

Spectra and spin structures of Andreev interface states and the Josephson current are investigated theoretically in junctions between clean superconductors (SC) with ordered interlayers. The Josephson current through the ferromagnetinsulator-ferromagnet interlayer can exhibit a nonmonotonic dependence on the misorientation angle. The characteristic behavior takes place if the π state is the equilibrium state of the junction in the particular case of parallel magnetizations. We find a novel channel of quasiparticle reflection (Q reflection) from the simplest two-sublattice antiferromagnet (AF) on a bipartite lattice. As a combined effect of Andreev and Q reflections, Andreev states arise at the AF/SC interface. When the Q reflection dominates the specular one, Andreev bound states have almost zero energy on AF/ s-wave SC interfaces, whereas they lie near the edge of the continuous spectrum for AF/d-wave SC boundaries. For an s-wave SC/AF/s-wave SC junction, the bound states are found to split and carry the supercurrent. Our analytical results are based on a novel quasiclassical approach, which applies to interfaces involving itinerant antiferromagnets. Similar effects can take place on interfaces of superconductors with charge density wave materials (CDW), including the possible d-density wave state (DDW) of the cuprates.

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“…Similar effects for CDW/SC interfaces have been studied recently in [3]. Subgap Andreev states arise at CDW/dSC and DDW/sSC interfaces.…”

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confidence: 74%

Superconducting Junctions with Ferromagnetic, Antiferromagnetic or Charge-Density-Wave Interlayers

Barash¹,

Bobkova²,

Andersen³

et al. 2006

AIP Conference Proceedings

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“…( 7) of Ref. 35 and can be obtained from there simply by substituting the magnetic m and s-wave ∆ s order parameters for the charge density wave W s and d-wave ∆ d order parameters respectively. As follows from Eq.…”

Section: Quasiparticle States At Sc/af Interfacesmentioning

confidence: 99%

Bound states at the interface between antiferromagnets and superconductors

et al. 2005

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We present a detailed theoretical investigation of interfaces and junctions involving itinerant antiferromagnets. By solving the Bogoliubov-de Gennes equations with a tight-binding model on a square lattice, we study both the self-consistent order parameter fields proximate to interfaces between antiferromagnets (AF) and s-wave (sSC) or d-wave (dSC) superconductors, the dispersion of quasiparticle subgap states at interfaces and interlayers, and the local density of states (LDOS) as a function of distance from the interface. In addition, we present the quasiclassical approach to interfaces and junctions involving itinerant antiferromagnets developed in an earlier paper. Analytical results are in excellent agreement with what we obtain numerically. Strong effects of pair breaking in the presence of low-energy interface Andreev states are found in particular for AF/sSC interfaces when interface potentials are not too high. Potential barriers induce additional extrema in the dispersive quasiparticle spectra with corresponding peaks in the LDOS. Discrete quasiparticle dispersive levels in AF -normal metal (N) -AF systems are found to strongly depend on the misorientation angle of the magnetizations in the two antiferromagnets.

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“…Some authors have also considered F/S heterostructures where the impurity scattering rate was disregarded or assumed to be small, corresponding to the ballistic regime. 20,21,22,23,24,25,26,27 Although the agreement between theory and experiment in this research area has proven to be satisfactory in many cases, there are still discrepancies to be accounted for. For instance, the Usadel equation has failed to account quantitatively for the critical temperature in F/S/F spin-valves.…”

Section: Introductionmentioning

confidence: 99%

Proximity effect in ferromagnet/superconductor hybrids: From diffusive to ballistic motion

2009

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We present an analytical study of the proximity effect in ferromagnet/superconductor (F/S) heterostructures, allowing for an arbitrary magnetic exchange energy as well as arbitrary impurity and spin-flip scattering rates within a quasiclassical approach. While previous studies mainly have focused on the clean or dirty limits, our results grant access to the regime of intermediate impurity concentrations, thus allowing us to probe the crossover from the clean to dirty limit. We find that in the crossover regime, all possible symmetry correlations of the proximity-induced anomalous Green's function are induced in the ferromagnet. We also point out that the local density of states oscillates spatially, not only for an F/S bilayer, but also for a normal/superconductor (N/S) bilayer in the diffusive limit, a fact which appears to have gone unnoticed in the literature. Within the weak-proximity effect regime, we present compact analytical expressions valid for arbitrary exchange fields and impurity scattering rates for i) the local density of states in an F/S bilayer, ii) the Josephson current in an S/F/S junction, and iii) the critical temperature in an F/S/F multilayer. For all cases, we study in particular the crossover regime between diffusive and ballistic motion. Our results may be useful for analyzing experimental data in cases when the dirty limit is not fully reached, thus invalidating the use of the Usadel equation.

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Low-energy quasiparticle states at superconductor/charge-density-wave interfaces

Cited by 5 publications

References 22 publications

Superconducting Junctions with Ferromagnetic, Antiferromagnetic or Charge-Density-Wave Interlayers

Superconducting Junctions with Ferromagnetic, Antiferromagnetic or Charge-Density-Wave Interlayers

Bound states at the interface between antiferromagnets and superconductors

Proximity effect in ferromagnet/superconductor hybrids: From diffusive to ballistic motion

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