Search results for "Persistent current"
showing 8 items of 18 documents
Large diamagnetic persistent currents
2007
In multichannel rings, evanescent modes will always co-exist with propagating modes. The evanescent modes can carry a very large diamagnetic persistent current that can oscillate with energy and are very sensitive to impurity scattering. This provides a natural explanation for the large diamagnetic persistent currents observed in experiments.
Current-spin-density-functional study of persistent currents in quantum rings
2000
We present a numerical study of persistent currents in quantum rings using current spin density functional theory (CSDFT). This formalism allows for a systematic study of the joint effects of both spin, interactions and impurities for realistic systems. It is illustrated that CSDFT is suitable for describing the physical effects related to Aharonov-Bohm phases by comparing energy spectra of impurity-free rings to existing exact diagonalization and experimental results. Further, we examine the effects of a symmetry-breaking impurity potential on the density and current characteristics of the system and propose that narrowing the confining potential at fixed impurity potential will suppress t…
Aharonov–Bohm/Casher effect in a Kondo ring
2000
The in#uence of a magnetic impurity or ultrasmall quantum dot on the spin and charge persistent currents of a mesoscopic ring is investigated. The system consists of electrons in a one-dimensional ring threaded by spin-dependent Aharonov}Bohm/Casher #uxes, and coupled via an antiferromagnetic exchange interaction to a localized electron. The problem is mapped onto a Kondo model for the even-parity channel plus free electrons in the odd-parity channel. The twisted boundary conditions representing the #uxes couple states of opposite parity unless the twist angles / a satisfy / a "f a p, where f a are integers, with spin index a"C, B. For these special values of / a , the model is solvable by …
Superconductivity in one dimension
2008
Superconducting properties of metallic nanowires can be entirely different from those of bulk superconductors because of the dominating role played by thermal and quantum fluctuations of the order parameter. For superconducting wires with diameters below $ \sim 50$ nm quantum phase slippage is an important process which can yield a non-vanishing wire resistance down to very low temperatures. Further decrease of the wire diameter, for typical material parameters down to $\sim 10$ nm, results in proliferation of quantum phase slips causing a sharp crossover from superconducting to normal behavior even at T=0. A number of interesting phenomena associated both with quantum phase slips and with …
Microscopic model for multiple flux transitions in mesoscopic superconducting loops
2006
A microscopic model is constructed which is able to describe multiple magnetic flux transitions as observed in recent ultra-low temperature tunnel experiments on an aluminum superconducting ring with normal metal - insulator - superconductor junctions [Phys. Rev. B \textbf{70}, 064514 (2004)]. The unusual multiple flux quantum transitions are explained by the formation of metastable states with large vorticity. Essential in our description is the modification of the pairing potential and the superconducting density of states by a sub-critical value of the persistent current which modulates the measured tunnel current. We also speculate on the importance of the injected non-equilibrium quasi…
Macroscopic persistent currents in laser ablated YBa2Cu3O7-x films
2011
AbstractThin films of YBa2Cu3O7-x have been produced in situ by laser ablation. As the condensation of the superconducting film is done onto hot substrates (600 - 780°C) at high oxygen pressures (~ 1 mbar), this techniques does not require any special postannealing step. Thus the total process time amounts to less than 10 min. Films were found to be polycrystalline with the c-axis preferentially oriented normal to the substrate plane on single crystalline (001) SrTiO3 and (random) ZrO2, as measured by ion channeling (Xmin = 5.5 % on SrTiO3), x-ray scattering and TEM. Complete superconducting transitions above 90 K with transition widths of about 1 K have been observed even on YSZ substrates…
Coherent superposition of current flows in an atomtronic quantum interference device
2015
We consider a correlated Bose gas tightly confined into a ring shaped lattice, in the presence of an artificial gauge potential inducing a persistent current through it. A weak link painted on the ring acts as a source of coherent back-scattering for the propagating gas, interfering with the forward scattered current. This system defines an atomic counterpart of the rf-SQUID: the atomtronics quantum interference device (AQUID). The goal of the present study is to corroborate the emergence of an effective two-level system in such a setup and to assess its quality, in terms of its inner resolution and its separation from the rest of the many-body spectrum, across the different physical regime…
Macroscopic persistent currents in YBa2Cu3O7
1988
Persistent currents in polycrystalline YBa2Cu3O7 rings have been investigated by measuring the spatial distribution of the magnetic flux trapped in field-cooled samples. The results unambiguously show that macroscopic persistent ring currents exist. The critical current density depends very sensitively on the sample quality, reachingj c ≈250 A/cm2 at 77 K for our best samples.