Spontaneous generation of fractional vortex-antivortex pairs at single edges of high-Tc superconductors

Holmvall, Patric; Löfwander, Tomas; Fogelström, Mikael

doi:10.1088/1742-6596/969/1/012037

Cited by 9 publications

(10 citation statements)

References 35 publications

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“…As we argued in refs. 26,27 within the scenario with spontaneous loop currents, the split of the Andreev band might be difficult to resolve in a tunneling experiment because of the broken translational symmetry along the edge and associated variations in the superflow field. This leads to a smearing effect for tunnel contacts with an area larger than the coherence length and an expected wide, largely temperature-independent, peak centered at zero energy.…”

Section: Discussionmentioning

confidence: 99%

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Broken translational symmetry at edges of high-temperature superconductors

et al. 2018

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Flat bands of zero-energy states at the edges of quantum materials have a topological origin. However, their presence is energetically unfavorable. If there is a mechanism to shift the band to finite energies, a phase transition can occur. Here we study high-temperature superconductors hosting flat bands of midgap Andreev surface states. In a second-order phase transition at roughly a fifth of the superconducting transition temperature, time-reversal symmetry and continuous translational symmetry along the edge are spontaneously broken. In an external magnetic field, only translational symmetry is broken. We identify the order parameter as the superfluid momentum ps, that forms a planar vector field with defects, including edge sources and sinks. The critical points of the vector field satisfy a generalized Poincaré-Hopf theorem, relating the sum of Poincaré indices to the Euler characteristic of the system.

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Section: Discussionmentioning

confidence: 99%

“…In this paper, we consider a peculiar scenario 26,27 where spontaneous supercurrents also break translational symmetry along the edge. This scenario too does not rely on any additional interaction term in the Hamiltonian.…”

Section: Introductionmentioning

confidence: 99%

Broken translational symmetry at edges of high-temperature superconductors

et al. 2018

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“…In the present work, we have assumed that the spontaneous surface current J(r) depends only on the coordinate perpendicular to the surface. This assumption excludes the possibility of a spontaneously-induced vortex chain structure, which has recently been predicted to appear along the surface of the high-T c cuprates [13][14][15] . The surface phase transition temperature to the vortex chain state was reported to be higher than that for the surface state considered here.…”

Section: Discussionmentioning

confidence: 96%

Influence of diffuse surface scattering on the stability of superconducting phases with spontaneous surface current generated by Andreev bound states

Miyawaki

Higashitani

2018

Phys. Rev. B

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We report a theoretical study on the phase transition between superconducting states with and without spontaneous surface current. The phase transition takes place due to the formation of surface Andreev bound states in unconventional superconductors. Based on the quasiclassical theory of superconductivity, we examine the influence of atomic-scale surface roughness on the surface phase transition temperature Ts. To describe the surface effect, the boundary condition for the quasiclassical Green's function is parameterized in terms of specularity (the specular reflection probability in the normal state at the Fermi level). This boundary condition allows systematic study of the surface effect ranging from the specular limit to the diffuse limit. We show that diffuse quasiparticle scattering at a rough surface causes substantial reduction of Ts in the d-wave pairing state of high-Tc cuprate superconductors. We also consider a p-wave pairing state in which Andreev bound states similar to those in the d-wave state are generated. In contrast to the d-wave case, Ts in the p-wave state is insensitive to the specularity. This is because the Andreev bound states in the p-wave superconductor are robust against diffuse scattering, as implied from symmetry consideration for odd-frequency Cooper pairs induced at the surface; the p-wave state has odd-frequency pairs with s-wave symmetry, while the d-wave state does not.

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“…The goal of this paper has been to provide a more complete picture of spontaneous symmetry-breaking tied to zero-energy Andreev states, and discuss experimental conditions where such phases can be observed. As an example, we have considered a particular phase with a spontaneous superfluid momentum due to pair-breaking interfaces in unconventional d-wave superconductors [23][24][25] . However, the results and the analysis presented in this paper can be extended to other phases and systems that host surface Andreev states, e.g.…”

Section: Discussionmentioning

confidence: 99%

Spontaneous symmetry breaking at surfaces of d -wave superconductors: Influence of geometry and surface ruggedness

et al. 2019

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Surfaces of d-wave superconductors may host a substantial density of zero-energy Andreev states. The zero-energy flat band appears due to a topological constraint, but comes with a cost in free energy. We have recently found that an adjustment of the surface states can drive a phase transition into a phase with finite superflow that breaks time-reversal symmetry and translational symmetry along the surface. The associated Doppler shifts of Andreev states to finite energies lower the free energy. Direct experimental verification of such a phase is still technically difficult and controversial, however. To aid further experimental efforts, we use the quasiclassical theory of superconductivity to investigate how the realization and the observability of such a phase are influenced by sample geometry and surface ruggedness. Phase diagrams are produced for relevant geometric parameters. In particular, critical sizes and shapes are identified, providing quantitative guidelines for sample fabrication in the experimental hunt for symmetry-breaking phases. arXiv:1902.07530v1 [cond-mat.supr-con]

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Spontaneous generation of fractional vortex-antivortex pairs at single edges of high-Tc superconductors

Cited by 9 publications

References 35 publications

Broken translational symmetry at edges of high-temperature superconductors

Broken translational symmetry at edges of high-temperature superconductors

Influence of diffuse surface scattering on the stability of superconducting phases with spontaneous surface current generated by Andreev bound states

Spontaneous symmetry breaking at surfaces of d -wave superconductors: Influence of geometry and surface ruggedness

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