Visualizing delocalized quasiparticles in the vortex state of NbSe

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 NbSe 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.

Read the article on arXiv.