Two-band induced superconductivity in single-layer graphene and topological insulator bismuth selenide

Abstract

Proximity-induced superconductivity in single-layer graphene (SLG) and in topological insulators represent almost ideal examples of superconductivity in two dimensions. Fundamental mechanisms governing superconductivity in the 2D limit are of central interest for modern condensed-matter physics. To deduce fundamental parameters of superconductor/ graphene/superconductor and superconductor/bismuth selenide/superconductor junctions we investigate the self-field critical currents in these devices using the formalism of the Ambegaokar-Baratoff model. Our central finding is that the induced superconducting state in SLG and bismuth selenide each exhibits gapping on two superconducting bands. Based on recent results obtained on ultra-thin films of natural superconductors, including single-atomic layer of iron selenide, double and triple atomic layers of gallium, and several atomic layer tantalum disulphide, we conclude that a two-band induced superconducting state in SLG and bismuth selenide is part of a wider, more general multiple-band phenomenology of currently unknown origin.

Classifying Induced Superconductivity in Atomically Thin Dirac-Cone Materials

“…Despite a fact that authors [61] did not mention the presence of these two upturns in raw experimental Bc2(T) data and more detailed measurements of Bc2(T) requires to reveal more accurately Gor'kov two-band fit Band 1 Band 2 temperature (K) T c2 the position and parameters for the third band, there is already enough experimental evidences that Sn/SLG/Sn array exhibits at least two-superconducting bands gapping, and thus, the report of Han et al [61] supports our primary idea that atomically thin films exhibits multiple-band superconducting gapping phenomenon [50,52].…”

“…In Fig. 5 we show temperature-dependent self-field critical currents, Ic(sf,T), in Nb/(Bi0.06Sb0.94)2Te3nanoribbon/Nb reported by Schüffelgen et al [58], where TI nanoribbon has thickness of 2b = 10 nm, and, thus, the condition of 2b < (0) [50,52] was satisfied.…”

“…Here we need to stress, that identical Ic(sf,T) enhancement (or, in another words, Ic(sf,T) upturn [12]) at approximately the same reduced temperature of T≤0.25·Tc in atomically-thin S/N/S junction was first reported by Calado et al [12] in MoRe/SLG/MoRe junction in 2015. One years later, less prominent Ic(sf,T) enhancement (however, which is still very clearly visible in raw experimental data [50]), in nominally the same MoRe/SLG/MoRe junctions at T≤0.25·Tc was reported by Borzenets et al [15]. Based on this, it will be incorrect to attribute the Ic(sf,T) enhancement at low reduced temperatures in Nb/BiSbTeSe2-nanoribon/Nb [48] to unique property of S/TI/S junctions.…”

“…In Ref. 50 we showed that S/SLG/S and S/Bi2Se3/S junctions exhibit two-decoupled band superconducting state, for which, for general case of multiple-decoupled bands, temperaturedependent self-field critical current, Ic(sf,T), can be described by the equation:…”

DC Self-Field Critical Current in Superconductor/Dirac-Cone Material/Superconductor Junctions and The Request for Ballistic Model Reexamination

“…The primary task for this work is to show that Ic(sf,T) in a variety of S/DCM/S junctions in the ballistic regime cannot be described by KO-based model. To prove this, experimental Ic(sf,T) datasets in S/DCM/S junctions were analyzed by two models: modified Ambegaokar-Baratoff model [51] and ballistic Titov-Beenakker model [52]. property of superconductor/topological insulator/superconductor (S/TI/S) junctions, but one is rather the demonstration of general feature of S/DCM/S devices and atomically thin superconducting systems.…”