97 research outputs found
Supercurrent in Nb/InAs-Nanowire/Nb Josephson junctions
We report on the fabrication and measurements of planar mesoscopic Josephson
junctions formed by InAs nanowires coupled to superconducting Nb terminals. The
use of Si-doped InAs-nanowires with different bulk carrier concentrations
allowed to tune the properties of the junctions. We have studied the junction
characteristics as a function of temperature, gate voltage, and magnetic field.
In junctions with high doping concentrations in the nanowire Josephson
supercurrent values up to 100\,nA are found. Owing to the use of Nb as
superconductor the Josephson coupling persists at temperatures up to 4K. In all
junctions the critical current monotonously decreased with the magnetic field,
which can be explained by a recently developed theoretical model for the
proximity effect in ultra-small Josephson junctions. For the low-doped
Josephson junctions a control of the critical current by varying the gate
voltage has been demonstrated. We have studied conductance fluctuations in
nanowires coupled to superconducting and normal metal terminals. The
conductance fluctuation amplitude is found to be about 6 times larger in
superconducting contacted nanowires. The enhancement of the conductance
fluctuations is attributed to phase-coherent Andreev reflection as well as to
the large number of phase-coherent channels due to the large superconducting
gap of the Nb electrodes.Comment: 5 Figure, submitted to Journal of Applied Physic
Scaling behaviour of relaxation dependencies in metaloxide superconductors
Superconducting glass state has been investigated in different types of metaloxide ceramics, Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O, Ba-Pb-Bi-O, using the highly sensitive SQUID magnetometer. The analysis of long-time relaxation processes of thermoremanent magnetization m(sup trm) (+) = M(sub o) - Slnt displayed scaling dependence of the decay rate S = -dM/dlnt on quantity of trapped magnetic flux M(sub o): 1gs = 31g M(sub o) - observed universal dependence S is approximately M(sup 3) (sub o) seems to one of the features of superconducting glass state in metaloxide ceramics
Nonlinear Seebeck Effect in a Model Granular Superconductor
The change of the Josephson supercurrent density of a weakly-connected
granular superconductor in response to externally applied arbitrary thermal
gradient dT/dx (nonlinear Seebeck effect) is considered within a model of 3D
Josephson junction arrays. For dT/dx>(dT/dx)_c, where (dT/dx)_c is estimated to
be of the order of 10^4 K/m for YBCO ceramics with an average grain's size of
10 microns, the weak-links-dominated thermopower S (Seebeck coefficient) is
predicted to become strongly dT/dx-dependent.Comment: REVTEX, no figure
Electric field dependence of thermal conductivity of a granular superconductor: Giant field-induced effects predicted
The temperature and electric field dependence of electronic contribution to
the thermal conductivity (TC) of a granular superconductor is considered within
a 3D model of inductive Josephson junction arrays. In addition to a
low-temperature maximum of zero-field TC K(T,0) (controlled by mutual
inductance L_0 and normal state resistivity R_n), the model predicts two major
effects in applied electric field: (i) decrease of the linear TC, and (ii)
giant enhancement of the nonlinear (i.e., grad T-dependent) TC with
[K(T,E)-K(T,0)]/K(T,0) reaching 500% for parallel electric fields E=E_T
(E_T=S_0|grad T| is an "intrinsic" thermoelectric field). A possiblity of
experimental observation of the predicted effects in granular superconductors
is discussed.Comment: 5 LaTeX pages (jetpl.sty included), 2 EPS figures. To be published in
JETP Letter
Разработка способов десульфуризации трансформаторных масел
We report on combined dc and microwave electronic measurements of magnetic flux transport in micron and submicron-patterned high-T-c films. In a given temperature regime below the superconducting transition temperature T-c, the current-driven flux transport is restricted to flux motion guided by the submicron patterns. Via frequency-dependent measurements of the forward transmission coefficient S-21 it is demonstrated that the mechanism of the guided flux transport depends on the microwave frequency and the geometrical size of the superconducting structures. At low frequencies, flux is transported via Abrikosov vortices leading to additional microwave losses. Above a geometrically defined frequency, a different mechanism seems to be responsible for flux transport that does not contribute to the microwave losses and most likely represents a phase-slip type mechanism. The limiting vortex velocity obtained from the frequency dependence of the microwave properties agrees with the Larking-Ovchinnikov critical vortex velocity that is determined via dc pulse measurements. In spite of the change of mechanism, guidance of flux persists in these nanopatterns up to high frequencies of several GHz
General Relativistic Thermoelectric Effects in Superconductors
We discuss the general-relativistic contributions to occur in the
electromagnetic properties of a superconductor with a heat flow. The appearance
of general-relativistic contribution to the magnetic flux through a
superconducting thermoelectric bimetallic circuit is shown. A response of the
Josephson junctions to a heat flow is investigated in the general-relativistic
framework. Some gravitothermoelectric effects which are observable in the
superconducting state in the Earth's gravitational field are considered.Comment: 13 pages, 2 figure
Effect of repetitive transmitter signals on SQUID response
Results of SQUID application in geophysical time domain transient electromagnetic (TEM) measurements are presented, We analyze peculiarities of SQUID TEM recordings, comparing them to data of commonly used induction coil. Two significant effects have been observed with the SQUID TEM system which are less pronounced or not observed in corresponding reference coil data, We consider a model for SQUID TEM measurements, taking into account the effect of repetitive transmitter signals which gives a possible explanation for these effects
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