Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMesoscopic cross-film cryotrons: Vortex trapping and dc-Josephson-like oscillations of the critical current
90
0
0.0
(
0
)
Added by
Alexei Yu. Aladyshkin
Publication date
2011
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We investigate theoretically and experimentally the transport properties of a plain Al superconducting strip in the presence of a single straight current-carrying wire, oriented perpendicular to the superconducting strip. It is well known that the critical current of the superconducting strip, Ic, in such cryotron--like system can be tuned by changing the current in the control wire, Iw. We demonstrated that the discrete change in the number of the pinned vortices/antivortices inside the narrow and long strip nearby the current-carrying wire results in a peculiar oscillatory dependence of Ic on Iw.
rate research
Read More
The transport through a metal-superconductor interface is governed by a special charge conversion process, the Andreev reflection, where each incident electron drags another electron with itself to form a Cooper pair. At the normal side a hole is left behind dressed by superconducting correlations. For a low transparency interface the simultaneous transfer of two charges is strongly suppressed leading to a reduced conductance. Here we demonstrate that this reduced conductance can be turned to an infinite one by tuning the nanoscale geometry. Creating variable size nanojunctions between a thin metallic film and a superconducting tip we study how multiple phase-coherent scatterings enhance the superconducting correlations at the normal side. By increasing the coherent volume of carriers initially the transmission through the interface is continuously enhanced. However, as the phase-coherent volume reaches the opposite surface of the thin film a resonator is formed, and a robust transition is induced due to Cooper pair condensation.
We calculate the phase, the temperature and the junction length dependence of the supercurrent for ballistic graphene Josephson-junctions. For low temperatures we find non-sinusoidal dependence of the supercurrent on the superconductor phase difference for both short and long junctions. The skewness, which characterizes the deviation of the current-phase relation from a simple sinusoidal one, shows a linear dependence on the critical current for small currents. We discuss the similarities and differences with respect to the classical theory of Josephson junctions, where the weak link is formed by a diffusive or ballistic metal. The relation to other recent theoretical results on graphene Josephson junctions is pointed out and the possible experimental relevance of our work is considered as well.
Josephson junctions with ferromagnetic layers are vital elements in a new class of cryogenic memory devices. One style of memory device contains a spin valve with one hard magnetic layer and one soft layer. To achieve low switching fields, it is advantageous for the soft layer to have low magnetization and low magnetocrystalline anisotropy. A candidate class of materials that fulfills these criteria is the Pd$_{1-x}$Fe$_{x}$ alloy system with low Fe concentrations. We present studies of micron-scale elliptically-shaped Josephson junctions containing Pd$_{97}$Fe$_{3}$ layers of varying thickness. By applying an external magnetic field, the critical current of the junctions are found to follow characteristic Fraunhofer patterns. The maximum value of the critical current, extracted from the Fraunhofer patterns, oscillates as a function of the ferromagnetic barrier thickness, indicating transitions in the phase difference across the junction between values of zero and $pi$.
We study the dynamics of current-biased Josephson-junction arrays with a magnetic penetration depth smaller than the lattice spacing. We compare the dynamics imaged by low-temperature scanning electron microscopy to the vortex dynamics obtained from model calculations based on the resistively-shunted junction model, in combination with Maxwells equations. We find three bias current regions with fundamentally different array dynamics. The first region is the subcritical region, i.e. below the array critical current I_c. The second, for currents I above I_c, is a vortex region, in which the response is determined by the vortex degrees of freedom. In this region, the dynamics is characterized by spatial domains where vortices and antivortices move across the array in opposite directions in adjacent rows and by transverse voltage fluctuations. In the third, for still higher currents, the dynamics is dominated by coherent-phase motion, and the current-voltage characteristics are linear.
We present low-temperature measurements of the low-frequency $1/f$ noise arising from an ensemble of two-level fluctuators in the oxide barrier of Al/AlO$_{x}$/Al Josephson junctions. The fractional noise power spectrum of the critical-current and normal-state resistance have similar magnitudes and scale linearly with temperature, implying an equivalence between the two. Compiling our results and published data, we deduce the area and temperature scaling of the noise for AlO$_{x}$ barrier junctions. We find that the density of two-level fluctuators in the junction barrier is similar to the typical value in glassy systems. We discuss the implications and consistency with recent qubit experiments.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
