Fulde-Ferrell states in inverse proximity-coupled magnetically doped topological heterostructures

Abstract

We study the superconducting properties of the thin film BCS superconductor proximity coupled to a magnetically doped topological insulator(TI). Using the mean field theory, we show that Fulde-Ferrell(FF) pairing can be induced in the conventional superconductor by having inverse proximity effect(IPE). This occurs when the IPE of the TI to the superconductor is large enough that the normal band of the superconductor possesses a proximity induced spin-orbit coupling and magnetization. We find that the energetics of the different pairings are dependent on the coupling strength between the TI and the BCS superconductor and the thickness of the superconductor film. As the thickness of the superconductor film is increased, we find a crossover from the FF pairing to the BCS pairing phase. This is a consequence of the increased number of the superconducting bands, which favor the BCS pairing, implying that the FF phase can only be observed in the thin-film limit. In addition, we also propose transport experiments that show distinct signatures of the FF phase.arXiv:1702.07383v1 [cond-mat.supr-con]

Proximity-Induced Superconducting States of Magnetically Doped 3D Topological Insulators with High Bulk Insulation

“…In three-dimensional (3D) TI-based junctions, although the origins of zero-bias conduction peaks are still controversial due to the existing bulk carriers [17], such signals are considered to also represent the p-wave superconductivity states [18,19]. Furthermore, the 3D TI-based junctions potentially induce further unconventional superconductivity states, which provide another possible way to access Majorana fermions; the proximity-induced superconductive states depend on the strength and direction of the applied magnetic fields and moments [20][21][22][23].…”

Finite momentum Cooper pairing in three-dimensional topological insulator Josephson junctions

“…The agreement between the simulation and the experimentally observed pattern indicates that the formation of the side branches is a result of the transfer of superconducting intensity due to the additional phase modulation generated by B y . This feature is known to be a key signature of finite momentum pairing and distinguishes the system from typical BCS superconductivity 16 , 28 , 29 .…”

“…This is predicted to stabilize an FFLO superconducting state: the spin–orbit coupling lifts the degeneracy in the Fermi surfaces of the material and introduces an anisotropy to the surfaces that makes it more amenable to a finite momentum phase 13 – 15 . In particular, time-reversal invariant topological insulators (TIs), whose surface states are massless Dirac fermions, are proposed to be an attractive candidate for unconventional superconductivity that carries finite momentum pairing 16 . To the best of our knowledge, experimental signatures of finite momentum Cooper pairs in TIs have mainly been sought after in the electron-doped regime of the two-dimensional (2D) TI HgTe quantum wells 17 , but the surface states of three-dimensional (3D) TIs also provide unique advantages to engineering finite momentum pairing.…”

“…The Dirac cones on the surfaces are non-degenerate and have spin-momentum locking. As a consequence, the Fermi surface of the Dirac cone shifts uni-directionally under the application of an in-plane magnetic field to the surface, which can lead to an FFLO state 13 , 16 . Even though transport measurements in normal 3D TIs are often complicated by the presence of bulk carriers, there is experimental consensus that the metallic surface state dominates transport in a proximity-coupled TI even when the bulk is not depleted 18 – 22 .…”

Pressure-induced topological superconductivity in the spin–orbit Mott insulator GaTa4Se8

“…One can also make use of the pairing symmetry in this material which results in the unconventional magnetic oscillation pattern [52][53][54][55][56] . Figure 3d shows the schematic setup of the Josephson corner junction which is constructed on the corner of the lacunar spinel crystal.…”