6 research outputs found
Photon-assisted tunneling at the atomic scale: Probing resonant Andreev reflections from Yu-Shiba-Rusinov states
Tunneling across superconducting junctions proceeds by a rich variety of
processes, which transfer single electrons, Cooper pairs, or even larger
numbers of electrons by multiple Andreev reflections. Photon-assisted tunneling
combined with the venerable Tien-Gordon model has long been a powerful tool to
identify tunneling processes between superconductors. Here, we probe
superconducting tunnel junctions including an impurity-induced Yu-Shiba-Rusinov
(YSR) state by exposing a scanning tunneling microscope with a superconducting
tip to microwave radiation. We find that a simple Tien-Gordon description
describes tunneling of single electrons and Cooper pairs into the bare
substrate, but breaks down for tunneling via YSR states by resonant Andreev
reflections. We develop an improved theoretical description which is in
excellent agreement with the data. Our results establish photon-assisted
tunneling as a powerful tool to analyze tunneling processes at the atomic scale
which should be particularly informative for unconventional and topological
superconductors
Diode effect in Josephson junctions with a single magnetic atom
Current flow in electronic devices can be asymmetric with bias direction, a phenomenon underlying the utility of diodes1 and known as non-reciprocal charge transport2. The promise of dissipationless electronics has recently stimulated the quest for superconducting diodes, and non-reciprocal superconducting devices have been realized in various non-centrosymmetric systems3,4,5,6,7,8,9,10. Here we investigate the ultimate limits of miniaturization by creating atomic-scale Pb–Pb Josephson junctions in a scanning tunnelling microscope. Pristine junctions stabilized by a single Pb atom exhibit hysteretic behaviour, confirming the high quality of the junctions, but no asymmetry between the bias directions. Non-reciprocal supercurrents emerge when inserting a single magnetic atom into the junction, with the preferred direction depending on the atomic species. Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle currents flowing by means of electron–hole asymmetric Yu–Shiba–Rusinov states inside the superconducting energy gap and identify a new mechanism for diode behaviour in Josephson junctions. Our results open new avenues for creating atomic-scale Josephson diodes and tuning their properties through single-atom manipulation
Diode effect in Josephson junctions with a single magnetic atom
Current flow in electronic devices can be asymmetric with bias direction, a
phenomenon underlying the utility of diodes and known as non-reciprocal charge
transport. The promise of dissipationless electronics has recently stimulated
the quest for superconducting diodes, and non-reciprocal superconducting
devices have been realized in various non-centrosymmetric systems. Probing the
ultimate limits of miniaturization, we have created atomic-scale Pb--Pb
Josephson junctions in a scanning tunneling microscope. Pristine junctions
stabilized by a single Pb atom exhibit hysteretic behavior, confirming the high
quality of the junctions, but no asymmetry between the bias directions.
Non-reciprocal supercurrents emerge when inserting a single magnetic atom into
the junction, with the preferred direction depending on the atomic species.
Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle
currents flowing via Yu-Shiba-Rusinov (YSR) states inside the superconducting
energy gap. Our results open new avenues for creating atomic-scale Josephson
diodes and tuning their properties through single-atom manipulation
Photon-assisted resonant Andreev reflections:Yu-Shiba-Rusinov and Majorana states
Photon-assisted tunneling frequently provides detailed information on the
underlying charge-transfer process. In particular, the Tien-Gordon approach and
its extensions predict that the sideband spacing in bias voltage is a direct
fingerprint of the number of electrons transferred in a single tunneling event.
Here, we analyze photon-assisted tunneling into subgap states in
superconductors in the limit of small temperatures and bias voltages where
tunneling is dominated by resonant Andreev processes and does not conform to
the predictions of simple Tien-Gordon theory. Our analysis is based on a
systematic Keldysh calculation of the subgap conductance and provides a
detailed analytical understanding of photon-assisted tunneling into subgap
states, in excellent agreement with a recent experiment. We focus on tunneling
from superconducting electrodes and into Yu-Shiba-Rusinov states associated
with magnetic impurities or adatoms, but we also explicitly extend our results
to include normal-metal electrodes or other types of subgap states in
superconductors. In particular, we argue that photon-assisted Andreev
reflections provide a high-accuracy method to measure small, but nonzero
energies of subgap states which can be important for distinguishing
conventional subgap states from Majorana bound states.Comment: 20 pages, 8 figure
Manuskript-Titel: "Photon-assisted tunneling at the atomic scale: Probing resonant Andreev reflections from Yu-Shiba-Rusinov states"
Tunnelling across superconducting junctions proceeds by a rich variety of processes, which transfer single electrons, Cooper pairs or even larger numbers of electrons by multiple Andreev reflections. Photon-assisted tunnelling combined with the venerable Tien–Gordon model has long been a powerful tool to identify tunnelling processes between superconductors. Here, we probe superconducting tunnel junctions including an impurity-induced Yu–Shiba–Rusinov (YSR) state by exposing a scanning tunnelling microscope with a superconducting tip to microwave radiation. We find that a simple Tien–Gordon description describes tunnelling of single electrons and Cooper pairs into the bare substrate, but breaks down for tunnelling via YSR states by resonant Andreev reflections. We develop an improved theoretical description that is in excellent agreement with the data. Our results establish photon-assisted tunnelling as a powerful tool to analyse tunnelling processes at the atomic scale, which should be particularly informative for unconventional and topological superconductors
Original experimental data and code for the Paper "Diode effect in Josephson junctions with a single magnetic atom"
Current flow in electronic devices can be asymmetric with bias direction, a phenomenon underlying the utility of diodes and known as non-reciprocal charge transport. The promise of dissipationless electronics has recently stimulated the quest for superconducting diodes, and non-reciprocal superconducting devices have been realized in various non-centrosymmetric systems. Here, we probe the ultimate limits of miniaturization by creating atomic-scale Pb--Pb Josephson junctions in a scanning tunneling microscope. Pristine junctions stabilized by a single Pb atom exhibit hysteretic behavior, confirming the high quality of the junctions, but no asymmetry between the bias directions.
Non-reciprocal supercurrents emerge when inserting a single magnetic atom into the junction, with the preferred direction depending on the atomic species. Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle currents flowing via electron-hole asymmetric Yu-Shiba-Rusinov (YSR) states inside the superconducting energy gap and identify a new mechanism for diode behavior in Josephson junctions. Our results open new avenues for creating atomic-scale Josephson diodes and tuning their properties through single-atom manipulation