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TT: Fachverband Tiefe Temperaturen

TT 68: Superconductivity: Properties and Electronic Structure

TT 68.10: Talk

Thursday, March 21, 2024, 12:00–12:15, H 3010

Visualizing delocalized quasiparticles in the vortex state of NbSe₂ — •Jian-Feng Ge^{1, 2}, Koen Bastiaans³, Jiasen Niu², Tjerk Benschop², Maialen Larrazabal⁴, and Milan Allan² — ¹Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany — ²Leiden Institute of Physics, Leiden University, 2333 CA Leiden, The Netherlands — ³Department of Quantum Nanoscience, Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft, The Netherlands — ⁴Debye Institute for Nanomaterials Science, Utrecht University, 3508 TA Utrecht, The Netherlands

Bogoliubov quasiparticles play a crucial role in understanding the behavior of a superconductor at the nanoscale, particularly in a vortex lattice where they are thought to be confined to the vortex cores. Here, we use scanning tunneling noise microscopy, which can locally quantify quasiparticles by measuring the effective charge, to observe and image delocalized quasiparticles around vortices in NbSe₂ for the first time. Our data reveals a strong spatial variation of the quasiparticle concentration when tunneling into the vortex state. We find that quasiparticle poisoning dominates when vortices are less than four times the coherence length apart. Our results set a new length scale for quasiparticle poisoning in vortex-based Majorana qubits and yield information on the effect of vortices in quantum circuits. Finally, we can describe our findings within the Ginzburg-Landau framework, but the microscopic origin of the far-extending quasiparticles is yet to be understood.

Keywords: Superconducting vortex; quasiparticle poisoning; delocalization; Majorana qubit; shot noise