arXiv subjects

Alžběta Kadlecová

Publications and source records attributed to Alžběta Kadlecová.

2 recordsLinked to original sources

arXiv2020

Practical Guide to Quantum Phase Transitions in Quantum-Dot-Based Tunable Josephson Junctions

Quantum dots attached to BCS superconducting leads exhibit a $0-π$ impurity quantum phase transition, which can be experimentally controlled either by the gate voltage or by the superconducting phase difference. For the pertinent superconducting single-impurity Anderson model, we newly present two simple analytical formulae describing the position of the phase boundary in parameter space for the weakly correlated and Kondo regime, respectively. Furthermore, we show that the two-level approximation provides an excellent description of the low temperature physics of superconducting quantum dots near the phase transition. We discuss reliability and mutual agreement of available finite temperature numerical methods (Numerical Renormalization Group and Quantum Monte Carlo) and suggest a novel approach for efficient determination of the quantum phase boundary from measured finite temperature data. Our results enable fast and efficient, yet reliable characterization and design of such nanoscopic tunable Josephson junction devices.

cond-mat.mes-hall↗

arXiv2017

Quantum dot attached to superconducting leads: Relation between symmetric and asymmetric coupling

We study the Anderson single-level quantum dot attached to two BCS superconducting leads with the same gap size. We reveal that a system with asymmetric tunnel coupling to the leads ($Γ_{L}\neqΓ_{R}$) can be related to the symmetric system with the same net coupling strength $Γ=Γ_{L}+Γ_{R}$. Surprisingly, it is the symmetric case which is the most general, meaning that all physical quantities in case of asymmetric coupling are fully determined by the symmetric ones. We give ready-to-use conversion formulas for the $0-π$ phase transition boundary, on-dot quantities, and the Josephson current, and illustrate them on the NRG results of Oguri, Tanaka and Bauer [Phys. Rev. B 87, 075432 (2013)] for the three-terminal setup. We apply our theory to the recent $0-π$ transition measurement of Delagrange et al. [Phys. Rev. B 93, 196437 (2016)] and determine the asymmetry of the experimental setup from the measured transition width. Finally, we establish that the widely assumed Kondo "universality" of physical quantities depending only on the ratio of the Kondo temperature and the superconducting gap $T_{K}/Δ$ cannot hold for asymmetric junctions.

cond-mat.mes-hall↗