Researchers bring the theory of thermoelectricity in superconductors and experiment into agreement.
We present an analysis of wave mixing in the recently developed Josephson traveling-wave parametric amplifier (JTWPA). Circuit simulations performed using WRSPICE show the full behavior of the JTWPA, allowing propagation of all tones. The coupled mode equations (CMEs) containing only pump, signal, and idler propagation are shown to be insufficient to completely capture complex mixing behavior in the JTWPA. Extension of the CMEs through additional state vectors in the analytic solutions allows closer agreement with WRSPICE. We consider an ordered framework for the systematic inclusion of extended eigenmodes and make a comparison with WRSPICE at each step. The agreement between the two methods validates both approaches and provides insight into the operation of the JTWPA.
This paper investigates the feasibility of using weak link nanobridges as Josephson junction elements for the purpose of creating Josephson circuits. We demonstrate the development of a single-step electron beam lithography procedure to fabricate niobium nanobridges with dimensions down to . The single-step process facilitates fabrication that is scalable to complex circuits that require many junctions. We measure the IV-characteristics (IVC) of the nanobridges between temperatures of and and find agreement with numerical simulations and the analytical resistively shunted junction (RSJ) model. Furthermore, we investigate the behaviour of the nanobridges under rf irradiation and observe the characteristic microwave-induced Shapiro steps. Our simulated IVC under rf irradiation using both the RSJ model and circuit simulator are in agreement with the experimental data. As a potential use of nanobridges in circuits requiring many junctions, we investigate the theoretical performance of a nanobridge-based Josephson comparator circuit using .
In this work we present detection and susceptibility measurement experiments on a single superparamagnetic Dynal bead with a diameter of 1 lm and a magnetic moment of _ 4 _ 108lB. Accurate bead positioning was achieved via non-invasive AFM nanomanipulation.The detection and magnetic characterization of the bead were performed using ultra-sensitive InSb Hall devices. Single bead detection was demonstrated using a step-wise change of the dc magnetic field; measurements were performed using only the in-phase component of the total ac Hall voltage. Very clear evidence of the bead presence is demonstrated simultaneously with explicit separation of parasitic inductive signals.Additional experiments performed using a sweeping change of the dc field allowed susceptibility measurements of a single Dynal bead. The numerical outcomes of both sweeping and stepping experiments are in a very good agreement. The method presented here opens up new possibilities for the reliable and accurate detection of small magnetic moments, which is of high importance for metrological applications as well as highly sensitive biological, medical, and environmental detectors.
Quantitative trap and long range transportation of micro-particles by using phase controllable acoustic waveWe present a phase-sensitive ac-dc Hall magnetometry method which allows a clear and reliable separation of real and parasitic magnetic signals of a very small magnitude. High-sensitivity semiconductor-based Hall crosses are generally accepted as a preferential solution for non-invasive detection of superparamagnetic nanobeads used in molecular biology, nanomedicine, and nanochemistry. However, detection of such small beads is often hindered by inductive pick-up and other spurious signals. The present work demonstrates an unambiguous experimental route for detection of small magnetic moments and provides a simple theoretical background for it. The reliability of the method has been tested for a variety of InSb Hall sensors in the range 600 nm-5 m. Complete characterization of empty devices, involving Hall coefficients and noise measurements, has been performed and detection of a single FePt bead with diameter of 140 nm and magnetic moment of Ϸ 10 8 B has been achieved with a 600 nm-wide sensor.
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