Zero-bias anomaly in a nanowire quantum dot coupled to superconductors Journal Article

Author(s): Lee, Eduardo J; Jiang, Xiaocheng; Aguado, Ramón; Katsaros, Georgios; Lieber, Charles M; De Franceschi, Silvano
Article Title: Zero-bias anomaly in a nanowire quantum dot coupled to superconductors
Abstract: We studied the low-energy states of spin-1/2 quantum dots defined in InAs/InP nanowires and coupled to aluminum superconducting leads. By varying the superconducting gap Δ with a magnetic field B we investigated the transition from strong coupling Δ≪T K to weak-coupling Δ≫T K, where T K is the Kondo temperature. Below the critical field, we observe a persisting zero-bias Kondo resonance that vanishes only for low B or higher temperatures, leaving the room to more robust subgap structures at bias voltages between Δ and 2Δ. For strong and approximately symmetric tunnel couplings, a Josephson supercurrent is observed in addition to the Kondo peak. We ascribe the coexistence of a Kondo resonance and a superconducting gap to a significant density of intragap quasiparticle states, and the finite-bias subgap structures to tunneling through Shiba states. Our results, supported by numerical calculations, own relevance also in relation to tunnel-spectroscopy experiments aiming at the observation of Majorana fermions in hybrid nanostructures.
Keywords: Superconductivity; Josephson; Strong coupling; Semiconductor quantum dots; Critical fields; Hybrid nanostructures; InAs/InP; Kondo resonances; Kondo temperatures; Low-energy state; Majorana; Numerical calculation; Quasi-particle state; Superconducting gaps; Superconducting lead; Supercurrents; Tunnel coupling; Weak couplings; Zero-bias; Zero-bias anomaly; Aluminium; Nanowires
Journal Title: Physical Review Letters
Volume: 109
Issue 18
ISSN: 1079-7114
Publisher: American Physical Society  
Date Published: 2012-10-31
Start Page: Article number 186802
Sponsor: This work was supported by the EU Marie Curie program and by the Agence Nationale de la Recherche. R. A. acknowledges support from the Spanish Ministry of Science and Innovation through Grant No. FIS2009-08744
DOI: 10.1103/PhysRevLett.109.186802
Open access: yes (repository)