Point contact tunneling spectroscopy apparatus for large scale mapping of surface superconducting properties

Abstract

We describe the design and testing of a point contact tunneling spectroscopy device that can measure material surface superconducting properties (i.e., the superconducting gap Δ and the critical temperature T(C)) and density of states over large surface areas with size up to mm(2). The tip lateral (X,Y) motion, mounted on a (X,Y,Z) piezo-stage, was calibrated on a patterned substrate consisting of Nb lines sputtered on a gold film using both normal (Al) and superconducting (PbSn) tips at 1.5 K. The tip vertical (Z) motion control enables some adjustment of the tip-sample junction resistance that can be measured over 7 orders of magnitudes from a quasi-ohmic regime (few hundred Ω) to the tunnel regime (from tens of kΩ up to few GΩ). The low noise electronic and LabVIEW program interface are also presented. The point contact regime and the large-scale motion capabilities are of particular interest for mapping and testing the superconducting properties of macroscopic scale superconductor-based devices.

A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities

“…PCT is a powerful technique that measures the surface density of states (DOS) and the related superconducting properties: the superconducting gap ∆, the critical temperature T c and the phenomenological inelastic scattering parameter Γ using the native oxide layer as tunnel barrier [29]. These parameters play a crucial role in the SRF cavity performances; at low external magnetic field 0.00E+00 5.00E-08 intensities (neglecting vortices dynamic) R S depends on the DOS at the fermi level ν(E f ) that in turn depends on ∆, Γ and the temperature for a superconductor.…”

Analysis of Nb3Sn surface layers for superconducting radio frequency cavity applications

“…In our setup, the junctions are made by approaching the sample surface with a PtIr tip, creating a SIN (superconductor-insulator-normal) junction where an oxide layer serves as the insulator. The sample is mounted on a X-Y-Z piezo stage that control both the tip-sample separation and the lateral positioning, thus enabling large scale mapping of the surface density of states 17 . Typical normalized conductance spectra as shown in Fig.…”

A modular point contact spectroscopy probe for sub-Kelvin applications

“…A measurement probe for a He4 cooled system, which goes down to 1.4 K 4,26 and where exchange gas plays an important role to cool down the sample space, is quite easy to fabricate and handle. However, designing a probe for a He3 system, which goes down to sub-Kelvin temperature is a quite a challenging job as the sample probe needs to be transferred into a chamber maintained at high vacuum.…”

“…Point contact spectroscopy (PCS) [1][2][3][4] is a tool utilised to study the energy dependent differential conductance (and its higher orders) of a mesoscopic confined region and relies on the fact that I-V characteristics of a mesoscopic point contact between metals, show deviation from linear ohmic characteristics due to the interaction of the electrons with elementary excitation. This involves formation of mesoscopic point contacts between two materials and then studying the I-V characteristics of the contact region to obtain energy, momentum and spin resolved information about the Fermi surface.…”