Proximity-Induced Odd-Frequency Superconductivity in a Topological Insulator

Abstract

At an interface between a topological insulator (TI) and a conventional superconductor (SC), superconductivity has been predicted to change dramatically and exhibit novel correlations. In particular, the induced superconductivity by an s-wave SC in a TI can develop an order parameter with a p-wave component. Here we present experimental evidence for an unexpected proximity-induced novel superconducting state in a thin layer of the prototypical TI, Bi 2 Se 3 proximity coupled to Nb. From depthresolved magnetic field measurements below the superconducting transition temperature of Nb, we observe a local enhancement of the magnetic field in Bi 2 Se 3 that exceeds the externally applied field, thus supporting the existence of an intrinsic paramagnetic Meissner effect arising from an odd-frequency superconducting state. Our experimental results are complemented by theoretical calculations supporting the appearance of such a component at the interface which extends into the TI. This state is topologically distinct from the conventional Bardeen-Cooper-Schrieffer state it originates from. To the best of our knowledge, these findings present a first observation of bulk odd-frequency superconductivity in a TI. We thus reaffirm the potential of the TI-SC interface as a versatile platform to produce novel superconducting states.

Time-reversal invariant and fully gapped unconventional superconducting state in the bulk of the topological compound Nb0.25Bi2Se3

“…Finally, the observation of the paramagnetic shift in the SC state of Nb 0.25 Bi 2 Se 3 , instead of the expected diamagnetic shift imposed by the SC state, deserves some attention. In general, the paramagnetic shift can have few possible causes: field-induced magnetism [60,61], vortex disorder [62], oddfrequency superconducting state [63], and by the suppression of the negative Knight shift below T c due to singlet pairing. Considering the absence of any trace of magnetism in Nb 0.25 Bi 2 Se 3 and the symmetric line shape from TF-μSR, magnetism and disorder effects can be excluded as being the origin of the observed paramagnetic shift.…”

Probing the superconducting gap structure in the noncentrosymmetric topological superconductor ZrRuAs

“…The physics of topological superconductors (TSCs) has attracted considerable attention [1][2][3][4][5][6][7][8]. However, despite tremendous research activity, only a few materials with the potential to act as bulk topological superconductors, including Sr 2 RuO 4 [9], the Weyl semimetal T d -MoTe 2 [10], Cu/Sr/Nbdoped Bi 2 Se 3 [11][12][13][14][15][16], and PdTe 2 [17], have been identified.…”

Odd-frequency superconductivity in dilute magnetic superconductors

“…Despite this, the detection of odd-ω pairing has remained a theoretical chimera and only very recently has its experimental realization apparently been confirmed. One recent study has reported odd-ω superconductivity at the interface of a topological insulator with a conventional superconductor [29]. In another recent development, which builds upon earlier theoretical work [30,31], the presence of an odd-ω component in scanning tunneling spectroscopy (STS) has finally been reported in a system of a magnetic impurity in contact with a conventional superconductor [32].…”