Superconductivity in epitaxial PtSb(0001) thin films

TL;DR

This work reports superconductivity in epitaxial PtSb(0001) thin films grown on SrF2(111) and characterized by comprehensive structural and transport measurements. Using anisotropic Ginzburg–Landau theory, the authors extract the upper critical fields and coherence lengths, finding $T_c = 1.72\ \mathrm{K}$, $ξ_{ab} \approx 55\ \mathrm{nm}$, and $ξ_c \approx 14\ \mathrm{nm}$ for the thickest film, with a pronounced field-induced transition broadening indicating type-II behavior. A substantial critical current density of $J_c \approx 6\times 10^4\ \mathrm{A/cm^2}$ at $0.5\ \mathrm{K}$ demonstrates viable supercurrents in lithographic PtSb devices. The results position PtSb within the NiAs-type superconductors as a lattice-matched platform for proximity heterostructures, including potential superconductor/altermagnet architectures, enabling controlled interfaces for superconducting spintronics applications.

Abstract

We report superconductivity in epitaxial PtSb(0001) thin films grown on SrF2(111). Electrical transport measurements reveal a superconducting transition at $T_{\mathrm c}=1.72$ K. The field-induced broadening of the transition and the presence of finite upper critical fields are consistent with type-II superconductivity. We determine the resistively defined upper critical fields for magnetic fields applied perpendicular and parallel to the film plane and parameterize their temperature dependence using an anisotropic Ginzburg-Landau approach. For the thickest film ($d=50$ nm), this yields coherence lengths of $ξ_{ab}\approx 55$ nm and $ξ_c\approx 14$ nm. Current-voltage characteristics show sizeable critical currents, with a critical current density reaching $J_{\mathrm c}\approx 6e4$ A/cm$^2$ at 0.5 K. These results establish epitaxial PtSb as a superconducting thin-film platform compatible with lattice-matched heterostructures in the NiAs-type materials family.

Figures (4)

• Figure 1: Structural characterization of epitaxial PtSb(0001) thin films on SrF2(111). (a) Symmetric XRD radial scan of a 15nm PtSb(0001) film showing only PtSb 000$\ell$ reflections together with the substrate peaks marked by a star; Laue thickness fringes indicate uniform thickness and high crystalline coherence. An inset shows the unit cell structure of PtSb Momma2011. (b) Tapping-mode AFM topography of a 30nm PtSb(0001) film, revealing $\sim$10--100nm terraces separated by bi-atomic steps. (c) Cross-sectional HAADF-STEM image along the $[01\bar{1}0]$ zone axis, resolving the layered stacking of Pt and Sb atomic planes.
• Figure 2: Superconducting transition in PtSb thin films. (a) Resistivity $\rho(T)$ at zero magnetic field for a 30nm thick PtSb epitaxial film. An inset shows an optical microscope image of the used device structure. (b) Superconducting transitions in the normalized resistivity for films with thicknesses of 15nm, 30nm and 50nm (the 30nm and 50nm traces largely overlap). (c) Normalized resistivity $\rho(T)/\rho_{\mathrm n}$ of a 50nm film at various magnetic fields applied perpendicular to the film plane, where $\rho_{\mathrm n}$ denotes the normal-state resistivity (see main text).
• Figure 3: Upper critical fields for magnetic fields applied perpendicular and parallel to the film plane. (a) Perpendicular upper critical field $\mu_0H_{\mathrm c2}^{\perp}$ versus temperature measured in a 50nm thick PtSb epitaxial film; the solid line is a fit using Eq. (\ref{['eq:perpcriticalfields']}). (b) Parallel upper critical field $\mu_0H_{\mathrm c2}^{\parallel}$ versus temperature measured in a 30nm thick film; the solid line is a fit using Eq. (\ref{['eq:parallelcriticalfields']}) to the data points shown in blue. The inset shows the same data plotted versus $\sqrt{1-T/T_{\mathrm c}}$, emphasizing the approximately linear behavior close to $T_{\mathrm c}$.
• Figure 4: Current-driven transport in PtSb. (a) Differential resistance $\mathrm{d}V/\mathrm{d}I$, obtained by numerical differentiation of measured $V(I)$ characteristics, shown as a function of current for a 50nm thick PtSb film at temperatures from 0.5K to 1.9K in 0.2K steps. Here $\mathrm{d}V/\mathrm{d}I$ is converted to a differential sheet resistance (in $\Omega/\square$) to normalize out the Hall-bar geometry. (b) Color map of $\mathrm{d}V/\mathrm{d}I$ as a function of current density $J$ and temperature. The critical current density $J_{\mathrm c}$ is extracted from the position of the maximum in $\mathrm{d}V/\mathrm{d}I$ (see text) and reaches $\approx 60kA/cm^2$ at 0.5K.