Robust Fabry–Perot interference in dual-gated Bi2Se3 devices

Abstract

We study Fabry-Perot interference in hybrid devices, each consisting of a mesoscopic superconducting disk deposited on the surface of a three-dimensional topological insulator. Such structures are hypothesized to contain protected zero modes known as Majorana fermions bound to vortices. The interference manifests as periodic conductance oscillations of magnitude ∼ 0.1 e 2 /h. These oscillations show no strong dependence on bulk carrier density or sample thickness, suggesting that they result from phase coherent transport in surface states. However, the Fabry-Perot interference can be tuned by both top and back gates, implying strong electrostatic coupling between the top and bottom surfaces of topological insulator.The wave-like nature of electrons can manifest in mesoscopic devices through interference effects. For example, if electrons traverse through a sufficiently clean sample between two leads with a finite probability of reflection at the sample-lead interface, then periodic conductance oscillations can occur as incident electrons interfere constructively or destructively with reflected carriers. Such Fabry-Perot interference has been observed in carbon nanotubes [1], semiconducting nanowires [2], and graphene [3]. In all cases, special care during sample preparation must be taken to ensure quasi-ballistic transport.Phase coherent transport in topological insulators (TIs) attracts attention for two reasons. First, at the surface of a TI there are gapless states that behave as helical Dirac electrons [4], with the electron spin constrained to be perpendicular to momentum. This spin-momentum locking generates a nontrivial Berry phase of π as an electron moves in a complete circle around the Brillouin zone, which suppresses backscattering and protects the surface states from nonmagnetic disorder. Second, if superconductivity is induced in the surface states of TIs, the resulting system will resemble a spinless p x + ip y superconductor, with protected zero energy modes known as Majorana fermions bound to vortices [5]. These Majorana fermions possess non-Abelian exchange statistics [6,7] and can be detected through interferometry [8][9][10]. The complex geometry of the proposed interferometers as well as possible complications from bulk states encourage further studies of phase coherent transport in hybrid TIsuperconductor devices.Here, we report on transport studies of dual gated hybrid devices consisting of a superconducting disk deposited on the surface of a 3D TI. We find clear signatures of gate-tuned Fabry-Perot oscillations. The magnitude of the oscillations is essentially the same for lightly-and heavily-doped devices, implying that they originate from surface states of the TI rather than the bulk. However, the oscillations can be tuned by applying a bias either to the top or back gate, suggesting the Fermi levels of the top and bottom surfaces are locked. The resilience of the Fabry-Perot oscillations after multiple fabrication steps and over lengths of at least 800 nm as well as the option of using ...

Phase diagram of the interacting Majorana chain model

“…Such Josephson vortices carry MZMs and their spacing can be conveniently controlled by the magnetic field amplitude. Evidence suggestive of MZMs in such devices has recently been reported [57].…”

Conduction spectroscopy of a proximity induced superconducting topological insulator

“…> 10 µm, so this is highly unlikely. Note, that the resonances in S-TI-S junctions by Finck et al [44,45] are in fact attributed to Fabry-Perot resonances in the TI, but there the interlayer thickness is a lot shorter. Furthermore, if the resonances were to occur in our flake, they should also be present in the nonlocal signal.…”

Scanning tunneling microscopy of superconducting topological surface states inBi2Se3

“…This coexistence of topological and trivial surface states leads to certain complications in the context of the proximity effect. In particular, phase coherent transport measurements [20,27,28] suggest that the superconducting proximity effect of trivial states is in the diffusion dominated transport regime, whereas topological states display transport peculiarities that are specific to the ballistic domain of transport.…”

“…[6][7][8][9][10][11], and a multitude of experimental efforts. The latter span from angleresolved photoemission spectroscopy, scanning tunneling microscopy, point contact, and differential conductance measurements [12][13][14][15][16], through to observations of supercurrents and unusual Josephson Fraunhofer patterns [17][18][19][20][21][22][23][24][25]; experiments on phase coherent transport including multiple Andreev reflections, Fabry-Perot interferometry and Aharonov-Bohm oscillations [26][27][28][29].…”