Subgap features due to quasiparticle tunneling in quantum dots coupled to superconducting leads

Pfaller, Sebastian; Donarini, Andrea; Grifoni, Milena

doi:10.1103/physrevb.87.155439

Cited by 26 publications

(47 citation statements)

References 38 publications

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“…1(d), we observe two Coulomb triangles that do not close on the V b ¼ 0 line but at eV b ∼ AEΔ, and that are shifted along the V g axis. These features are typical of a N-dot-S structure and are due to the gap and BCS peaks in the density of states of the S contact [67][68][69]. The conductance resonances corresponding to an alignment between the dot level and the BCS peaks display negative differential resistance areas [68] [see red areas in Fig.…”

Section: Negative Photon Damping By a N-dot-s Bijunctionmentioning

confidence: 99%

Cavity Photons as a Probe for Charge Relaxation Resistance and Photon Emission in a Quantum Dot Coupled to Normal and Superconducting Continua

et al. 2016

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Microwave cavities have been widely used to investigate the behavior of closed few-level systems. Here, we show that they also represent a powerful probe for the dynamics of charge transfer between a discrete electronic level and fermionic continua. We have combined experiment and theory for a carbon nanotube quantum dot coupled to normal metal and superconducting contacts. In equilibrium conditions, where our device behaves as an effective quantum dot-normal metal junction, we approach a universal photon dissipation regime governed by a quantum charge relaxation effect. We observe how photon dissipation is modified when the dot admittance turns from capacitive to inductive. When the fermionic reservoirs are voltage biased, the dot can even cause photon emission due to inelastic tunneling to/from a BardeenCooper-Schrieffer peak in the density of states of the superconducting contact. We can model these numerous effects quantitatively in terms of the charge susceptibility of the quantum dot circuit. This validates an approach that could be used to study a wide class of mesoscopic QED devices.

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Section: Negative Photon Damping By a N-dot-s Bijunctionmentioning

confidence: 99%

Cavity Photons as a Probe for Charge Relaxation Resistance and Photon Emission in a Quantum Dot Coupled to Normal and Superconducting Continua

et al. 2016

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“…At high temperature, transport becomes possible both at low bias and in parts of the Coulomb blockade region due to quasiparticles excited across the superconducting energy gap. 13 This is illustrated in Fig. 1(c), showing the product (black solid line) of the quasiparticle density of states (blue dash-dotted line) and the Fermi function (red dotted line).…”

mentioning

confidence: 99%

“…13 The theory is generalized here to include also the shell and orbital degrees of freedom of the CNT. Specifically, the quantum dot is modeled by the Hamiltonian…”

mentioning

confidence: 99%

“…This suggests that, as explained below, the observed sub-gap features are not due to Andreev reflections but rather to thermal excitation of quasiparticles across the gap, as predicted recently by some of us. 13 We perform a systematic analysis of the temperature dependence of the observed features. A good agreement between experimental data and theoretical predictions in the linear as well as in the nonlinear regime is obtained.…”

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confidence: 99%

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Subgap spectroscopy of thermally excited quasiparticles in a Nb-contacted carbon nanotube quantum dot

et al. 2014

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We present electronic transport measurements of a single wall carbon nanotube quantum dot coupled to Nb superconducting contacts. For temperatures comparable to the superconducting gap peculiar transport features are observed inside the Coulomb blockade and superconducting energy gap regions. The observed temperature dependence can be explained in terms of sequential tunneling processes involving thermally excited quasiparticles. In particular, these new channels give rise to two unusual conductance peaks at zero bias in the vicinity of the charge degeneracy point and allow to determine the degeneracy of the ground states involved in transport. The measurements are in good agreement with model calculations.

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“…We emphasize that if we had not considered the infinite-gap approximation for the superconducting lead, it would have been necessary in Eq. (7) to consider the effect of coupling to the superconducting lead by introducing its corresponding Lindblad superoperator 47 . We also note that the above formalism best describes the coupled DQD-resonator system when the coupling between DQD and resonator is weak.…”

Section: B Master Equation Descriptionmentioning

confidence: 99%

Lasing in a coupled hybrid double quantum dot-resonator system

Tabatabaei

Jahangiri

2020

Phys. Rev. B

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We theoretically investigate the possibility of lasing in an electromagnetic resonator coupled to a voltage-biased hybrid-double-quantum-dot comprised of a double-quantum-dot tunnel coupled simultaneously to a normal metal and a superconducting lead. Using a unitary transformation, we derive a resonator-double-quantum-dot interaction Hamiltonian in the rotating wave approximation which reveals the fact that lasing in this system is mediated by electron transitions between Andreev energy levels in the system's density of states. Moreover, by employing a markovian master equation incorporating dissipation effects for the electronic and photonic degrees of freedom, we numerically calculate the steady-state reduced density-matrix of the system from which we determine the average photon number and its statistics in the resonator in various parameter regimes. We find that at some appropriate parameter configurations, lasing can be considerably enhanced due to the possiblity of electron tansitions between multiple Andreev levels in the system.

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Subgap features due to quasiparticle tunneling in quantum dots coupled to superconducting leads

Cited by 26 publications

References 38 publications

Cavity Photons as a Probe for Charge Relaxation Resistance and Photon Emission in a Quantum Dot Coupled to Normal and Superconducting Continua

Cavity Photons as a Probe for Charge Relaxation Resistance and Photon Emission in a Quantum Dot Coupled to Normal and Superconducting Continua

Subgap spectroscopy of thermally excited quasiparticles in a Nb-contacted carbon nanotube quantum dot

Lasing in a coupled hybrid double quantum dot-resonator system

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