Josephson Effect in Pb/I/NbSe₂ Scanning Tunneling Microscope Junctions

Abstract

We have developed a method for the reproducible fabrication of superconducting scanning tunneling microscope (STM) tips. We use these tips to form superconductor/insulator/superconductor tunnel junctions with the STM tip as one of the electrodes. We show that such junctions exhibit fluctuation dominated Josephson effects, and describe how the Josephson product IcRN can be inferred from the junctions' tunneling characteristics in this regime. This is first demonstrated for tunneling into Pb films, and then applied in studies of single crystals of NbSe2. We find that in NbSe2, IcRN is lower than expected, which could be attributed to the interplay between superconductivity and the coexisting charge density wave in this material.

Josephson scanning tunneling microscopy: A local and direct probe of the superconducting order parameter

“…11 Josephson studies using a superconducting STM on conventional superconductors have shown good agreement between the measured I C R N and BCS predictions. 12,13 For high-T C superconductors, on the other hand, there is no established theory to relate I C R N with ⌬ derived from the quasiparticle excitation spectrum. There can be at least two additional issues not present for conventional superconductors.…”

Friedel oscillations and Majorana zero modes in inhomogeneous superconductors

“…As a promising experimental tool to detect the spatial textures of competing superconducting order parameters and of MBS wave functions, we discuss JSTM [38][39][40][41][42][43] compute the expected signatures in the Jospheson current. We extend previous theoretical work (see, in particular, Ref.…”

“…Potential 28,29 . In addition, we show a JSTM [38][39][40][41][42][43] tip that allows to probe the spatial texture of the order parameter and of the MBS wave function as we discuss in this paper.…”

Scanning Josephson Tunneling Microscopy of Single-CrystalBi2Sr2CaCu2O8+δwith a Conventional Superconducting Tip

“…The operation of this SC-STM has been demonstrated with the observation of Josephson tunneling between the tip and both SC Pb films [9] and SC NbSe 2 [10]. The signature Josephson response of the SC-STM differs from that of typical low R N planar S/I/S devices.…”

“…Furthermore, this parameter is directly linked to both the SC order parameter amplitude and the energy gaps BCS of the materials through the BCS relationship. Josephson studies using a SC-STM on conventional superconductors were validated by the good agreement between the measured I C R N and BCS theory [9,10]. For HTSCs, on the other hand, there is no estab-lished theory to relate I C R N with derived from the QP excitation spectrum.…”