295 research outputs found
Superconductor-insulator transition in capacitively coupled superconducting nanowires
We investigate superconductor–insulator quantum phase transitions in ultrathin capacitively coupled superconducting nanowires with proliferating quantum phase slips. We derive a set of coupled Berezinskii–Kosterlitz–Thouless-like renormalization group equations demonstrating that interaction between quantum phase slips in one of the wires gets modified due to the effect of plasma modes propagating in another wire. As a result, the superconductor–insulator phase transition in each of the wires is controlled not only by its own parameters but also by those of the neighboring wire as well as by mutual capacitance. We argue that superconducting nanowires with properly chosen parameters may turn insulating once they are brought sufficiently close to each other
Plasma modes in capacitively coupled superconducting nanowires
We investigate plasma oscillations in long electromagnetically coupled superconducting nanowires. We demonstrate that in the presence of inter-wire coupling plasma modes in each of the wires get split into two “new” modes propagating with different velocities across the system. These plasma modes form an effective dissipative quantum environment interacting with electrons inside both wires and causing a number of significant implications for the low-temperature behavior of the systems under consideration
Giant microwave-induced -periodic magnetoresistance oscillations in a two-dimensional electron gas with a bridged-gate tunnel point contact
We have studied the magnetoresistance of the quantum point contact fabricated
on the high mobility two-dimensional electron gas (2DEG) exposed to microwave
irradiation. The resistance reveals giant -periodic oscillations with the
relative amplitude of up to \% resulting from the propagation
and interference of the edge magnetoplasmons (EMPs) in the sample. This giant
photoconductance is attributed to the considerably large local electron density
modulation in the vicinity of the point contact. We have also analyzed the
oscillation periods of the resistance oscillations and, comparing
the data with the EMP theory, extracted the EMP interference length . We
have found that the length substantially exceeds the distance between the
contact leads but rather corresponds to the distance between metallic contact
pads measured along the edge of the 2DEG. This resolves existing controversy in
the literature and should help to properly design highly sensitive microwave
and terahertz spectrometers based on the discussed effect.Comment: 5 pages, 5 figure
Strong Effects of Weak Localization in Charge Density Wave/Normal Metal Hybrids
Collective transport through a multichannel disordered conductor in contact
with charge-density-wave electrodes is theoretically investigated. The
statistical distribution function of the threshold potential for charge-density
wave sliding is calculated by random matrix theory. In the diffusive regime
weak localization has a strong effect on the sliding motion.Comment: To be published in Physical Review
Dynamic structure selection and instabilities of driven Josephson lattice in high-temperature superconductors
We investigate the dynamics of the Josephson vortex lattice in layered
high-T superconductors at high magnetic fields. Starting from coupled
equations for superconducting phases and magnetic field we derive equations for
the relative displacements [phase shifts] between the planar Josephson arrays
in the layers. These equations reveal two families of steady-state solutions:
lattices with constant phase shifts between neighboring layers, starting from
zero for a rectangular configuration to for a triangular configuration,
and double-periodic lattices. We find that the excess Josephson current is
resonantly enhanced when the Josephson frequency matches the frequency of the
plasma mode at the wave vector selected by the lattice structure. The regular
lattices exhibit several kinds of instabilities. We find stability regions of
the moving lattice in the plane lattice structure - Josephson frequency. A
specific lattice structure at given velocity is selected uniquely by boundary
conditions, which are determined by the reflection properties of
electromagnetic waves generated by the moving lattice. With increase of
velocity the moving configuration experiences several qualitative
transformations. At small velocities the regular lattice is stable and the
phase shift between neighboring layers smoothly decreases with increase of
velocity, starting from for a static lattice. At the critical velocity
the lattice becomes unstable. At even higher velocity a regular lattice is
restored again with the phase shift smaller than . With increase of
velocity, the structure evolves towards a rectangular configuration.Comment: 28 pages, 12 figures, submitted to Phys. Rev.
Experimental Evidence for Coulomb Charging Effects in the Submicron Bi-2212 Stacks
We developed the focused ion beam (FIB) and ion milling techniques for a
fabrication of the Bi_2Sr_2CaCu_2O_{8+\delta} (Bi-2212) stacked junctions with
in-plane size L_{ab} from several microns down to the submicron scale without
degradation of T_c. We found that behaviour of submicron junctions (L_{ab} < 1
{\mu}m) is quite different from the bigger ones. The critical current density
is considerably suppressed, the hysteresis and multibranched structure of the
IV characteristics are eliminated, the periodic structure of current peaks
reproducibly appears on the IV curves at low temperatures. A period of the
structure, {\Delta}V, is consistent with the Coulomb charging energy of a
single pair, {\Delta}V = e/C with C the effective capacitance of the stack. We
consider this behaviour to originate from the Coulomb blockade of the intrinsic
Josephson tunneling in submicron Bi-2212 stacks.Comment: 13 pp, incl. 1 table and 4 fig
Resonances, instabilities, and structure selection of driven Josephson lattice in layered superconductors
We investigate dynamics of Josephson vortex lattice in layered high T
superconductors at high magnetic fields. It is shown that the average electric
current depends on the lattice structure and is resonantly enhanced when the
Josephson frequency matches the frequency of the plasma mode. We find the
stability regions of moving lattice. It is shown that a specific lattice
structure at given velocity is uniquely selected by the boundary conditions: at
small velocities periodic triangular lattice is stable and looses its stability
at some critical velocity. At even higher velocities a structure close to a
rectangular lattice is restored.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Current-Induced Step Bending Instability on Vicinal Surfaces
We model an apparent instability seen in recent experiments on current
induced step bunching on Si(111) surfaces using a generalized 2D BCF model,
where adatoms have a diffusion bias parallel to the step edges and there is an
attachment barrier at the step edge. We find a new linear instability with
novel step patterns. Monte Carlo simulations on a solid-on-solid model are used
to study the instability beyond the linear regime.Comment: 4 pages, 4 figure
High-Field Quasiparticle Tunneling in Bi_2Sr_2CaCu_2O_8+delta: Negative Magnetoresistance in the Superconducting State
We report on the c-axis resistivity rho_c(H) in Bi_2Sr_2CaCu_2O_{8+\delta}
that peaks in quasi-static magnetic fields up to 60 T. By suppressing the
Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity
\sigma_c (H), we find that the negative slope of \rho_c(H) above the peak is
due to quasiparticle tunneling conductivity \sigma_q(H) across the CuO_2 layers
below H_{c2}. At high fields (a) \sigma_q(H) grows linearly with H, and (b)
\rho_c(T) tends to saturate (sigma_c \neq 0) as T->0, consistent with the
scattering at the nodes of the d-gap. A superlinear sigma_q(H) marks the normal
state above T_c.Comment: 4p., 5 fig. (.eps), will be published in Phys. Rev. Let
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