arXiv subjects

G. Koblmueller

Publications and source records attributed to G. Koblmueller.

6 recordsLinked to original sources

arXiv2026

Thermal bottleneck in a freely suspended superconducting island on InAs nanowire

We investigate the heat balance in superconducting islands (S-islands) formed in epitaxial Al/InAs nanowires (NWs) freely suspended above the substrate. We employ a Joule spectroscopy approach, which traces the superconductor-normal transition in the S-island mediated by heating of the neighboring InAs NW segments via transport current. The temperature of the surrounding 3He bath is varied with nearby mesoscopic heaters and controlled with the NW Johnson noise thermometry. The experiment reveals a substantial thermal relaxation bottleneck associated with the cooling via surrounding 3He, which gives rise to phonon heating in the S-island. Our results uncover the role of environmental cooling in non-equilibrium experiments in S-islands in NW devices.

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arXiv2025

Superconducting bistability in floating Al islands of hybrid Al/InAs nanowires

We investigate a non-equilibrium aspect of the current-driven superconducting-normal phase transition in floating Al islands of epitaxial full-shell Al/InAs nanowires. Within a transition region discontinuous voltage jumps and hysteretic behaviour of the I-V characteristics are observed, associated with the destruction and recovery of the superconducting order parameter in the island. The strength of the two features varies strongly in different devices in a mutually correlated way and can be suppressed by a small magnetic field. Numerical calculation explains this behaviour in terms of a tiny non-equilibrium correction to the electronic energy distribution at low energies. The experiment demonstrates a critical failure of a two-temperature non-equilibrium model of the superconductor-normal transition in floating islands of hybrid nanowire devices.

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arXiv2024

Fate of the superconducting state in floating islands of hybrid nanowire devices

We investigate the impact of transport current on the superconducting order parameter in superconducting islands in full-shell epitaxial Al-InAs nanowires. Depending on a device layout, the suppression of superconductivity occurs in three fundamentally different ways -- by a critical current in the case of superconducting reservoirs and by a critical voltage or by a critical Joule power in the case of normal reservoirs. In the latter case, the collapse of the superconducting state depends on the ratio of the dwell time and the electron-phonon relaxation time of quasiparticles in the island. For low resistive and high resistive coupling to the reservoirs, respectively, the relaxation-free regime and the strong electron-phonon relaxation regime are realized. Our results shed light on potential shortcomings of finite-bias transport spectroscopy in floating islands.

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arXiv2022

Heat-mode excitation in a proximity superconductor

Mesoscopic superconductivity deals with various quasiparticle excitation modes, only one of them -- the charge-mode -- being directly accessible for conductance measurements due to the imbalance in populations of quasi-electron and quasihole excitation branches. Other modes carrying heat or even spin, valley etc. currents populate the branches equally and are charge-neutral, which makes them much harder to control. This noticeable gap in the experimental studies of mesoscopic non-equilibrium superconductivity can be filled by going beyond the conventional DC transport measurements and exploiting spontaneous current fluctuations. Here, we perform such an experiment and investigate the transport of heat in an open hybrid device based on a superconductor proximitized InAs nanowire. Using shot noise measurements, we investigate sub-gap Andreev heat guiding along the superconducting interface and fully characterize it in terms of the thermal conductance on the order of $G_\mathrm{th}\sim e^2/h$, tunable by a back gate voltage. Understanding of the heat-mode also uncovers its implicit signatures in the non-local charge transport. Our experiments open a direct pathway to probe generic charge-neutral excitations in superconducting hybrids.

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arXiv2021

Charge-neutral nonlocal response in superconductor-InAs nanowire hybrid devices

Nonlocal quasiparticle transport in normal-superconductor-normal (NSN) hybrid structures probes sub-gap states in the proximity region and is especially attractive in the context of Majorana research. Conductance measurement provides only partial information about nonlocal response composed from both electron-like and hole-like quasiparticle excitations. In this work, we show how a nonlocal shot noise measurement delivers a missing puzzle piece in NSN InAs nanowire-based devices. We demonstrate that in a trivial superconducting phase quasiparticle response is practically charge-neutral, dominated by the heat transport component with a thermal conductance being on the order of conductance quantum. This is qualitatively explained by numerous Andreev reflections of a diffusing quasiparticle, that makes its charge completely uncertain. Consistently, strong fluctuations and sign reversal are observed in the sub-gap nonlocal conductance, including occasional Andreev rectification signals. Our results prove conductance and noise as complementary measurements to characterize quasiparticle transport in superconducting proximity devices.

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arXiv2018

Noise insights into electronic transport

Typical experimental measurement is set up as a study of the system's response to a stationary external excitation. This approach considers any random fluctuation of the signal as spurious contribution which is to be eliminated via time-averaging or, equivalently, bandwidth reduction. Beyond that lies a conceptually different paradigm -- the measurement of the system's spontaneous fluctuations. The goal of this overview article is to demonstrate how current noise measurements bring insight into hidden features of electronic transport in various mesoscopic conductors, ranging from 2D topological insulators to individual carbon nanotubes.

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