INVITED TALK ABSTRACT

Surface superconductivity and magnetic field modulation in the topological Weyl semimetal t-PtBi₂

Yanina Fasano ^1,2,3,4, Sebastian Schimmel ^4,5, Joaquín Puig ^1,2,3,4, A. Cruz García ^1,2, J. Zabala ¹, V. F. Correa ^1,3, P. Pedrazzini ¹, Julia Besproswanny ^4,5, Grigory Shipunov ⁴, Saicharan Aswartham ⁴, Bernd Büchner ^4,6 & Christian Hess ^4,5

1. Low Temperatures Lab, Centro Atómico Bariloche, Argentina.
2. Instituto de Nanociencia y Nanotecnología and Instituto Balseiro, CNEA –CONICET, Centro Atómico Bariloche, Bariloche, Argentina.
3. Instituto Balseiro, CNEA and and Universidad Nacional de Cuyo, Bariloche, Argentina
4. Leibniz-Institute for Solid State and Materials Research (IFW-Dresden), Dresden, Germany.
5. Fakultät für Mathematik und Naturwissenschaften, Bergische Universität Wuppertal, Wuppertal, Germany.
6. Institute of Solid State and Materials Physics and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, Dresden, Germany.

Topological superconductivity is a promising concept for generating fault-tolerant qubits. Early experimental studies looked at hybrid systems and doped intrinsic topological or superconducting materials at very low temperatures. However, higher critical temperatures are indispensable for technological exploitation. Angle-resolved photoemission spectroscopy results have revealed that superconductivity in the type-I Weyl semimetal—trigonal PtBi₂ (t-PtBi₂)—is located at the Fermi-arc surface states, which renders the material a potential candidate for intrinsic topological superconductivity.[1] Aso, using scanning tunnelling microscopy and spectroscopy, we show that t-PtBi₂ presents surface superconductivity at elevated temperatures (5 K).[2] The gap magnitude is elusive: it is spatially inhomogeneous and spans from 0 to 20 meV. In particular, the large gap value and the shape of the quasiparticle excitation spectrum resemble the phenomenology of high-Tc superconductors. Moreover, we show that the superconducting state at 5 K persists in magnetic fields up to 12 T, but we were not able to resolve vortices with STM.[2] Here we will show that the magnetic field is modulated at the surface of t-PtBi₂ by means of magnetic decoration imaging at 2K, but we ascertain that the modulation pattern does not look like the typical vortex structure of quantized vortices in type-II superconductors.

[1] Kuibarov, A., Suvorov, O., Vocaturo, R. et al. Evidence of superconducting Fermi arcs. Nature 626, 294–299 (2024).

^[2] S. Schimmel, Y. Fasano et al., Nature Communications 15, 9895 (2024).