akhuettel's andreev [5 articles]

Abstract

We study Andreev transport through double quantum dots coupled to normal and superconducting (SC) leads, using the numerical renormalization group. The ground state of this system shows a crossover between a local Cooper-pairing singlet state and a Kondo singlet state, which is caused by the competition between the Coulomb interaction and the SC proximity. We show that the ground-state properties reflect this crossover especially for small values of the inter-dot coupling $t$, while in the opposite case, for large $t$, another singlet with an inter-dot character becomes dominant. ...

Abstract

We study carbon nanotubes (CNTs) connected to Nb superconducting electrodes through a thin (less than 5 nm) Pd layer. We show that the carbon nanotubes form nanoscale point contacts detecting superconducting proximity effect via Andreev reflection, where an electron injected from the nanotube is reflected as a hole at the Pd/Nb interface and a Cooper pair forms in the Nb. Our data cannot be quantitatively explained by a single interface model, where only one interface between the CNT and a superconducting ...

Abstract

We have contacted single wall carbon nanotubes (SWCNTs) grown by chemical vapour deposition to superconducting Ti/Al/Ti electrodes. The device we here report on is in the Kondo regime exhibiting a fourfold shell structure, where a clear signature of the superconducting electrodes is observed below the critical temperature. Multiple Andreev reflections are revealed by sub-gap structure and a narrow peak in the differential conductance around zero bias is seen depending on the shell filling. We interpret the peak as a proximity induced ...

Abstract

We have measured the current (I)-voltage (V) characteristics of a single-wall carbon nanotube quantum dot coupled to superconducting source and drain contacts in the intermediate coupling regime. Whereas the enhanced differential conductance dI/dV due to the Kondo resonance is observed in the normal state, this feature around zero-bias voltage is absent in the superconducting state. Nonetheless, a pronounced even-odd effect appears at finite bias in the dI/dV subgap structure caused by Andreev reflection. The first-order Andreev peak appearing around V=/e is ...

Abstract

We report measurements of the nonlinear conductance of InAs nanowire quantum dots coupled to superconducting leads. We observe a clear alternation between odd and even occupation of the dot, with subgap peaks at |Vsd|=/e markedly stronger (weaker) than the quasiparticle tunneling peaks at |Vsd|=2/e for odd (even) occupation. We attribute the enhanced peak to an interplay between Kondo correlations and Andreev tunneling in dots with an odd number of spins, and we substantiate this interpretation by a poor man's scaling analysis. ...