Implementation of a High-Frequency Circuit into a Scanning Tunneling Microscope

Tunneling across superconducting junctions is associated with a variety of different processes that transfer single electrons, Cooper pairs, or even larger amounts of electrons by multiple Andreev reflections. Resonances inside the superconducting energy gap, like e.g. induced by magnetic adatoms, add resonant Andreev reflections to the variety of tunneling processes. We have successfully established two spectroscopic methods to study the nature of tunneling processes in superconductors. In the first approach, we complement the capabilities of a scanning tunneling microscope by introducing high-frequencies (HF) up to 40 GHz into the tunnel junction. The charge carriers involved in the tunneling process can exchange energy with the radiated HF field which leads to photon-assisted tunneling. Based on the theory of Tien und Gordon it is predicted that the sideband spacing in the bias voltage is a direct fingerprint of the number of electrons transferred in a single tunneling event. Here we have used photon-assisted tunneling to study superconducting tunnel junctions that exhibit Yu-Shiba-Rusinov states (YSR) induced by magnetic Mn adatoms on Pb(111). By exploiting the tunability of the junction conductivity we could specifically obtain insights into the contributions of single-electron tunneling and resonant Andreev processes to the YSR states. While the simple Tien-Gordon description is sufficient to describe single-electron tunneling and Cooper pair tunneling into the pure substrate, we show that the description breaks down for resonant Andreev reflections. We developed an improved theoretical model based on rate equations and the ac modulation of the bias voltage. Our model is in excellent agreement with our data. In a second spectroscopic approach, we investigate Cooper pair tunneling in current-biased Josephson junctions. We show that the critical current is strongly reduced by magnetic impurities, which reflects a reduced superconducting order parameter in the vicinity of the magnetic adatom. Our results of photon-assisted tunneling and Josephson spectroscopy show that we have established two powerful methods for the investigation of superconducting tunneling processes at the atomic scale. These methods could be particularly informative for the investigation of unconventional and topological superconductors

No stain, no pain – A multidisciplinary review of factors underlying domestic laundering

Today\u27s washing appliances are much more efficient than those of a decade ago, but the environmental benefits of this efficiency are counteracted by shifts in consumer behavior. Initiatives to reverse these shifts have often proven futile, indicating a basic lack of clarity on why we clean our clothes. This article is an explorative review with the aim of identifying dominant factors that shape how we do our laundry. The results can be used both as an introduction to laundry research in general, as well as a baseline for future interdisciplinary research. Three guiding principles are presented that describe the most influential factors underlying laundering: (1) technology changes conventions, while social context dictates technology acceptance; (2) technological solutions are often suggested to influence consumers, but individual concerns seem to override the effect of such interventions; (3) consumers are guided by social conventions, rooted in underlying psychological dynamics (e.g. moral dimensions of cleanliness). Looking at these principles it is understandable why interventions for sustainability are failing. Many interventions address only a part of a principle while disregarding other parts. For example, consumers are often informed of the importance of sustainability (e.g. “washing at lower temperature is good for the environment”), while questions of social belonging are left out (e.g. “many of your neighbors and friends wash at lower temperature”). To increase the possibility of a lasting change, it would be beneficial if instead all of the three principles could be addressed given the specific consumer group of interest

Mind the (reporting) gap—a scoping study comparing measured laundry decisions with self-reported laundry behaviour

Purpose: Many environmental assessments of consumer products and household services rely on self-reported data. Life cycle assessments of domestic laundering are no exception. However, potential discrepancies between self-reported behaviour and actual everyday decisions are seldom investigated due to practical challenges in collecting relevant data. This means that environmental impacts relying on such self-reported data are much more uncertain than previously acknowledged. Method: Laundering data was collected at the Chalmers’ HSB Living lab (CHSBLL), a combined multi-family house and research facility in Gothenburg. The collection was both done passively (through the washing machines) as well as actively (through surveys to the tenants). RFID-readers were also installed in the machines and a number of clothing items tagged, allowing for identification. The site-specific data was later supplemented with a large statistical representative study for domestic laundering of Swedish households. This unique data quality allowed the comparison of passively collected data with survey data from tenants in a real-life setup, while validating the results from a national perspective. Result and conclusions: The results suggest that consumers have trouble remembering personal choices regarding domestic laundering, meaning that self-reported data are more uncertain than previously thought. In general, the participants overestimated the amount of laundry they washed and underestimated their frequency of washing. Additionally, many participants showed an interest in changing to alternative wash programs although this change failed to materialize when they were presented with this option in real-life. The findings have potential consequences for environmental assessments and implicate those previous estimations underestimate emissions per kg laundry washed

Quantum Phase Transition and Transport

The exchange scattering at magnetic adsorbates on superconductors gives rise to Yu-Shiba-Rusinov (YSR) bound states. Depending on the strength of the exchange coupling, the magnetic moment perturbs the Cooper pair condensate only weakly, resulting in a free-spin ground state, or binds a quasiparticle in its vicinity, leading to a (partially) screened spin state. Here, we use the flexibility of Fe-porphin (FeP) molecules adsorbed on a Pb(111) surface to reversibly and continuously tune between these distinct ground states. We find that the FeP moment is screened in the pristine adsorption state. Approaching the tip of a scanning tunneling microscope, we exert a sufficiently strong attractive force to tune the molecule through the quantum phase transition into the free-spin state. We ascertain and characterize the transition by investigating the transport processes as function of tip-molecule distance, exciting the YSR states by single-electron tunneling as well as (multiple) Andreev reflections

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 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

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

Infection of the Central Nervous System, Sepsis and Amyotrophic Lateral Sclerosis

Severe infections may lead to chronic inflammation in the central nervous system (CNS) which may in turn play a role in the etiopathogenesis of amyotrophic lateral sclerosis (ALS). The relentless progression and invasive supportive treatments of ALS may on the other hand induce severe infections among ALS patients.The present study included 4,004 ALS patients identified from the Swedish Patient Register during 1991-2007 and 20,020 age and sex matched general population controls. Conditional logistic regression was used to estimate the odds ratios (ORs) of ALS given a previous hospitalization for CNS infection or sepsis. Cox models were used to estimate the hazard ratios (HRs) of hospitalization for CNS infection or sepsis after ALS diagnosis. Overall, previous CNS infection (OR: 1.3, 95% confidence interval [CI]: 0.8, 2.4) or sepsis (OR: 1.2, 95% CI: 0.9, 1.6) was not associated with ALS risk. However, compared to ALS free individuals, ALS cases were more likely to be hospitalized for sepsis after diagnosis (HR: 2.6, 95% CI: 1.9, 3.5). We did not observe a higher risk of CNS infection after ALS diagnosis.Our results suggest that acute and severe infections unlikely contribute to the development of ALS; however, ALS patients are at a higher risk of sepsis after diagnosis, compared to ALS free individuals