Sensitivity of superconducting states to the impurity location in layered materials

Zinkl, Bastian; Ramires, Aline

doi:10.1103/physrevb.106.014515

Cited by 5 publications

(2 citation statements)

References 47 publications

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“…The gap is measured in units of the topological gap for the topological pristine system T . In particular, it is observed that the location of the impurity strongly impacts the gap of the system [90]. The resulting gap of the defective system can range from the pristine value, observed for impurities at the exchange maximum, to nearly zero, observed for impurities away from the exchange maximum [Fig.…”

Section: Strong Impurities In Topological Moiré Superconductorsmentioning

confidence: 99%

Impurity-induced excitations in a topological two-dimensional ferromagnet/superconductor van der Waals moiré heterostructure

Khosravian

Lado

2022

Phys. Rev. Materials

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The emergence of a topological superconducting state in van der Waals heterostructures provides a new platform for exploring novel strategies to control topological superconductors. In particular, impurities in van der Waals heterostructures, generically featuring a moiré pattern, can potentially lead to the unique interplay between atomic and moiré length scales, a feature absent in generic topological superconductors. Here we address the impact of nonmagnetic impurities on a topological moiré superconductor, both in the weak and strong regime, considering both periodic arrays and single impurities in otherwise pristine infinite moiré systems. We demonstrate a fine interplay between impurity-induced modes and the moiré length, leading to radically different spectral and topological properties depending on the relative impurity location and moiré lengths. Our results highlight the key role of impurities in van der Waals heterostructures featuring moiré patterns, revealing the key interplay between length and energy scales in artificial moiré systems.

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Section: Strong Impurities In Topological Moiré Superconductorsmentioning

confidence: 99%

Impurity-induced excitations in a topological two-dimensional ferromagnet/superconductor van der Waals moiré heterostructure

Khosravian

Lado

2022

Phys. Rev. Materials

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“…In this class of materials, despite the threefold rotational symmetry of the lattice, bulk superconducting (SC) properties consistently show peculiar twofold symmetry [3][4][5][6][7][8][9] that points to the realization of an odd-parity gap function with E u symmetry. Although this gap function is unconventional and strongly anisotropic, the superconductivity is nonetheless protected from disorder due to the generalized Anderson's theorem, thanks to the additional orbital degrees of freedom and layered structure [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Rotation of gap nodes in the topological superconductor Cux(PbSe)5(Bi2Se3)6

Bagchi,

Brede,

Ramires

et al. 2024

Phys. Rev. B

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Among the family of odd-parity topological superconductors derived from Bi 2 Se 3 , Cu x (PbSe) 5 (Bi 2 Se 3 ) 6 (CPSBS) has been elucidated to have gap nodes. Although the nodal gap structure has been established by specific-heat and thermal-conductivity measurements, there has been no direct observation of the superconducting gap of CPSBS using scanning tunneling spectroscopy (STS). Here we report the first STS experiments on CPSBS down to 0.35 K, which found that the vortices generated by out-of-plane magnetic fields have an elliptical shape, reflecting the anisotropic gap structure. The orientation of the gap minima is found to be aligned with the bulk direction when the surface lattice image shows twofold symmetry, but, surprisingly, it is rotated by 30 • when twofold symmetry is absent. In addition, the superconducting gap spectra in zero magnetic field suggest that the gap nodes are most likely lifted. We argue that only an emergent symmetry at the surface, allowing for a linear superposition of gap functions with different symmetries in the bulk, can lead to the rotation of the gap nodes. The absence of inversion symmetry at the surface additionally lifts the nodes. This result establishes the subtle but crucial role of crystalline symmetry in topological superconductivity.

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Topological nodal line in superfluid 3He and the Anderson theorem

Kamppinen,

Rysti,

Volard

et al. 2023

Nat Commun

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Superconductivity and superfluidity with anisotropic pairing—such as d-wave in cuprates and p-wave in superfluid 3He—are strongly suppressed by impurities. Meanwhile, for applications, the robustness of Cooper pairs to disorder is highly desired. Recently, it has been suggested that unconventional systems become robust if the impurity scattering mixes quasiparticle states only within individual subsystems obeying the Anderson theorem that protects conventional superconductivity. Here, we experimentally verify this conjecture by measuring the temperature dependence of the energy gap in the polar phase of superfluid 3He. We show that oriented columnar non-magnetic defects do not essentially modify the energy spectrum, which has a Dirac nodal line. Although the scattering is strong, it preserves the momentum along the length of the columns and forms robust subsystems according to the conjecture. This finding may stimulate future experiments on the protection of topological superconductivity against disorder and on the nature of topological fermionic flat bands.

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Sensitivity of superconducting states to the impurity location in layered materials

Cited by 5 publications

References 47 publications

Impurity-induced excitations in a topological two-dimensional ferromagnet/superconductor van der Waals moiré heterostructure

Impurity-induced excitations in a topological two-dimensional ferromagnet/superconductor van der Waals moiré heterostructure

Rotation of gap nodes in the topological superconductor Cux(PbSe)5(Bi2Se3)6

Topological nodal line in superfluid 3He and the Anderson theorem

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