Bound states in superconductors and interfaces

Workshop Report

The focused workshop Bound States in Superconductors and Interfaces took place
from 8-th till 10-th April 2019, and hosted 66 participants from 20 different
countries. Its main purpose was to exchange information on the current realizations,
challenges and future perspectives of electronic bound states inside the superconductor
energy gap at impurities, interfaces with superconducting reservoirs and various
hybrid nanostructures. The associated quasiparticles are presently of considerable
importance because they enable unique phenomena, such as e.g. long-lived qubits,
evolution of discrete sub-gap states into topologically non-trivial bands hosting
Majorana-type endmodes, and allow for experimentally controllable spectroscopy
of correlated many-body states.

The workshop brought together the leading experts, both in experimental and theoretical
studies in this field. The talks discussed realizations of the subgap states in various
materials and devices, their detection in hybrid quantum dots and/or artificial quantum
impurities embedded in the Josephson- and Andreev-type junctions, spectroscopy of the bound
states in semiconducting nanowires, carbon nanotubes, hybrid superconductor-semiconductor
quantum dots, gate-tunable studies of the subgap Kondo regime and many other related issues.
Theoretical lectures have addressed the correlation effects, nonlocal processes, dynamic
phenomena and properties of exotic mutations of the bound states in topological materials.

A comprehensive overview of the phenomena related to existence of defects/impurities
in superconductors has been delivered by Alexander V. Balatsky (NORDITA), emphasizing
the recently discovered Dirac materials and exotic types of electron pairing with
an odd symmetry. His colloquium has been attended not only by participants of the
workshop but also by members of the Max Planck Institute and other neighboring
research institutions. Invited lectures have been given by internationally recognized
experts of the experimental and theoretical studies. Several younger scientists have
contributed their brief talks on important problems related to the bound states.
During the first day of the workshop there has been organized a poster session
with 30 presentations. Individual discussions between participants gave an
opportunity to exchange ideas and might stimulate the ongoing and establish
new collaboration projects, leading to development of this research field.
Overall, the workshop provided a pleasant atmosphere with lively discussions.