Conduction spectroscopy of a proximity induced superconducting topological insulator

Abstract

The combination of superconductivity and the helical spin-momentum locking at the surface state of a topological insulator (TI) has been predicted to give rise to p-wave superconductivity and Majorana bound states. The superconductivity can be induced by the proximity effect of a an s-wave superconductor (S) into the TI. To probe the superconducting correlations inside the TI, dI/dV spectroscopy has been performed across such S-TI interfaces. Both the alloyed Bi${}_{1.5}$Sb${}_{0.5}$Te${}_{1.7}$Se${}_{1.3}$ and the stoichiometric BiSbTeSe${}_2$ have been used as three dimensional TI. In the case of Bi${}_{1.5}$Sb${}_{0.5}$Te${}_{1.7}$Se${}_{1.3}$, the presence of disorder induced electron-electron interactions can give rise to an additional zero-bias resistance peak. For the stoichiometric BiSbTeSe${}_2$ with less disorder, tunnel barriers were employed in order to enhance the signal from the interface. The general observations in the spectra of a large variety of samples are conductance dips at the induced gap voltage, combined with an increased sub-gap conductance, consistent with p-wave predictions. The induced gap voltage is typically smaller than the gap of the Nb superconducting electrode, especially in the presence of an intentional tunnel barrier. Additional uncovered spectroscopic features are oscillations that are linearly spaced in energy, as well as a possible second order parameter component.

Semiconductor Science and Technology; Special Issue on Hybrid Quantum Materials and Devices

References in corpus (9)

• Non-Abelian Anyons and Topological Quantum Computation
• Superconducting proximity effect and Majorana fermions at the surface of a topological insulator
• Evidence of Majorana fermions in an Al - InAs nanowire topological superconductor
• Electrically detected interferometry of Majorana fermions in a topological insulator
• Observation of topological surface state quantum Hall effect in an intrinsic three-dimensional topological insulator
• Observation of Dirac Holes and Electrons in a Topological Insulator
• Majorana Fermions and Odd-frequency Cooper Pairs in a Nano Wire
• Transport signatures of superconducting hybrids with mixed singlet and chiral triplet states
• Proximity effects at the interface of a superconductor and a topological insulator in NbN - Bi_2Se_3 thin film bilayers

Cited by in corpus (1)

• Signatures of Topological Superconductivity in Bulk Insulating Topological Insulator BiSbTe${}_{1.25}$Se${}_{1.75}$ in Proximity with Superconducting NbSe${}_2$