Superconductivity of Topological Surface States and Strong Proximity Effect in Sn_1–xPb_xTe‐Pb Heterostructures

Abstract

Superconducting topological crystalline insulators are expected to form a new type of topological superconductors to host Majorana zero modes under the protection of lattice symmetries. The bulk superconductivity of topological crystalline insulators has been induced through chemical doping and proximity effect. However, only conventional full gaps are observed, so the existence of topological superconductivity in topological crystalline insulators is still controversial. Here, we report the successful fabrication of atomically flat lateral and vertical Sn 1-x Pb x Te-Pb heterostructures by molecular beam epitaxy. The superconductivity of the Sn 1-x Pb x Te-Pb heterostructures can be directly investigated by scanning tunneling spectroscopy. Unconventional peak-dip-hump gap features and fourfold symmetric quasiparticle interference patterns taken at the zero energy support the presence of the topological superconductivity in superconducting Sn 1-x Pb x Te. Strong superconducting proximity effect and easy preparation of various constructions between Sn 1-x Pb x Te and Pb make the heterostructures to be a promising candidate for topological superconducting devices to detect and manipulate Majorana zero modes in the future.A topological superconductor (TSC) is characterized by having a pairing gap in the bulk and gapless Andreev bound states at its boundary, which is topologically distinct from a conventional superconductor (SC). [1,2] TSCs contain Majorana zero modes (MZMs) which obey non-Abelian statistics, [3][4][5] thus exhibiting great potential applications in fault-tolerant topological quantum computing. [6][7][8] After the realization of topological insulators (TIs), [1,9,10] the search for TSCs in real materials has already been a very hot topic in condensed matter physics. Natural TSCs are rarely found, but topological superconductivity can be induced in TIs through chemical doping and superconducting proximity effect. Bulk superconductivity of doped TIs such as Cu, [11,12] Sr, [13,14] Nb [15,16] doped Bi 2 Se 3 have been discovered. The superconducting doped TI is considered as TSC, [17,18] but scanning tunneling microscopy and spectroscopy (STM/STS) experiments show conventional full BCS-like s-wave gaps without any in-gap states. [19,20] Further calculation suggests that the U-shaped STS spectrum in Cu x Bi 2 Se 3 is related to the cylindrical shape of the Fermi surface. [21,22] For proximity induced superconductivity in TIs, it has been theoretically proposed that combining a conventional s-

Hybrid Symmetry Epitaxy of the Superconducting Fe(Te,Se) Film on a Topological Insulator

“…3 Superconductor (SC)/topological insulator (TI) heterostructure has been intensively investigated since it is considered one of the most promising approaches to implement topological superconductor (TSC) via proximity effect. [1][2][3][4][5][6][7][8][9][10] In particular, the proximity-induced TSC provides a number of advantages over the chemical doping method [11][12][13] in terms of controllability, both theoretically and experimentally. The simplest approach to construct SC/TI heterostructure would be to combine elemental superconductors such as Al, Nb and Pb with the TI layer.…”

“…The simplest approach to construct SC/TI heterostructure would be to combine elemental superconductors such as Al, Nb and Pb with the TI layer. 5,[14][15][16][17][18] However, considering that elemental superconductors can easily react with the TI layer and form an interfacial dead layer, 19 a compound superconductor sharing the same anion with the TI layer would be a much better candidate for the SC/TI heterostructure.…”

Hybridization mechanism of the dual proximity effect in superconductor-topological insulator interfaces

“…Perhaps the most heavily studied proximitized TI materials to date are Bi 2 Se 3 , Bi 2 Te 3 and HgTe, while interestingly doping the parent compound by either Cu or Nb reveals native topological superconductivity in Bi 2 Se 3 [42,43]. The coexistence of superconducting and topological orders in the regime of the proximity effect has been further tested [44][45][46], including junctions of TI and unconventional -wave superconductors [47], and a large volume of transport data is available, especially on tunneling conductance and Andreev reflection [48][49][50][51]. The key signature of MZMs in S-TI-S junctions, namely 4 periodic Josephson current, ( ) ∝ sin( ∕2), has not been so far unambiguously detected.…”

Anomalous superconducting proximity effect of planar Pb–RhPb2 heterojunctions in the clean limit

“…If the proximitized materials are magnetic, topologically nontrivial or exhibit strong spin-orbit interaction [4][5][6][7][8][9][10][11][12] , the long-sought Majorana bound states can emerge as non-Abelian anyons, potentially useful as the building blocks for fault-tolerant quantum computation 13 . In principle, the leakage of Cooper pairs induces subgap structures and profoundly modifies the local density of states (DOS) in the proximitized materials over a certain distance d from the heterointerfaces [14][15][16] , which has been widely explored with spatially resolved scanning tunneling microscopy/spectroscopy (STM/STS) techniques [17][18][19][20][21][22][23][24][25] . However, most of these studies are limited to vertically stacked superconducting heterojunctions [17][18][19][20][21][22] , complicated by the interface strain control and discrete spatial variation.…”