1,318 research outputs found
Effect of morphology on the superconductor-insulator transition in one-dimensional nanowires
Journal ArticleWe study the effect of morphology on the low-temperature behavior of superconducting nanowires which vary in length from 86 nm to 188 nm. A well-defined superconductor-insulator transition is observed only in the family of homogeneous wires, in which case the transition occurs when the normal resistance is close to h/4e2. Inhomogeneous wires, on the other hand, exhibit a mixed behavior, such that signatures of the superconducting and insulating regimes can be observed in the same sample. The resistance versus temperature curves of inhomogeneous wires show multiple steps, each corresponding to a weak link constriction (WLC) present in the wire. Similarly, each WLC generates a differential resistance peak when the bias current reaches the critical current of the WLC. Due to the presence of WLC's an inhomogeneous wire splits into a sequence of weakly interacting segments where each segment can act as a superconductor or as an insulator. Thus the entire wire then shows a mixed behavior
Dichotomy in short superconducting nanowires: thermal phase slippage vs. Coulomb blockade
ManuscriptQuasi-one-dimensional superconductors or nanowires exhibit a transition into a nonsuperconducting regime, as their diameter shrinks. We present measurements on ultrashort nanowires (∼40-190 nm long) in the vicinity of this quantum transition. Properties of all wires in the superconducting phase, even those close to the transition, can be explained in terms of thermally activated phase slips. The behavior of nanowires in the nonsuperconducting phase agrees with the theories of the Coulomb blockade of coherent transport through mesoscopic normal metal conductors. Thus it is concluded that the quantum transition occurs between two phases: a "true superconducting phase" and an "insulating phase". No intermediate, "metallic" phase was found
Determination of the Superconductor-Insulator Phase Diagram for One-Dimensional Wires
We establish the superconductor-insulator phase diagram for quasi-one
dimensional wires by measuring a large set of MoGe nanowires. This diagram is
consistent with the Chakravarty-Schmid-Bulgadaev phase boundary, namely with
the critical resistance being equal to R_Q = h/4e^2. We find that transport
properties of insulating nanowires exhibit a weak Coulomb blockade behavior.Comment: 5 pages, 4 figure
Determination of the superconductor-insulator phase diagram for one-dimensional wires
Journal ArticleWe establish the superconductor-insulator phase diagram for quasi-one-dimensional wires by measuring a large set of MoGe nanowires. This diagram is roughly consistent with the Chakravarty-Schmid-Bulgadaev phase boundary, namely, with the critical resistance being equal to RQ ¼ h=4e2. Deviations from this boundary for a small fraction of the samples prompt us to suggest an alternative phase diagram, which matches the data exactly. Transport properties of wires in the superconducting phase are dominated by phase slips, whereas insulating nanowires exhibit a weak Coulomb blockade behavior
Influence of high magnetic fields on the superconducting transition of one-dimensional Nb and MoGe nanowires
Journal ArticleThe effects of a strong magnetic field on superconducting Nb and MoGe nanowires with diameter ~10 nm have been studied. We have found that the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory of thermally activated phase slips is applicable in a wide range of magnetic fields and describes well the temperature dependence of the wire resistance, over 11 orders of magnitude. The field dependence of the critical temperature, Tc, extracted from the LAMH fits is in good quantitative agreement with the theory of pair-breaking perturbations that takes into account both spin and orbital contributions. The extracted spin-orbit scattering time agrees with an estimate τs.o. ~ τ (hc/Ze2)4, where τ is the elastic scattering time and Z is the atomic number
Influence of high magnetic fields on superconducting transition of one-dimensional Nb and MoGe nanowires
The effects of strong magnetic field on superconducting Nb and MoGe nanowires
with diameter nm have been studied. We have found that the
Langer-Ambegaokar-McCumber-Halperin (LAMH) theory of thermally activated phase
slips is applicable in a wide range of magnetic fields and describes well the
temperature dependence of the wire resistance, over eleven orders of magnitude.
The field dependence of the critical temperature, , extracted from the
LAMH fits is in good quantitative agreement with the theory of pair-breaking
perturbations that takes into account both spin and orbital contributions. The
extracted spin-orbit scattering time agrees with an estimate , where is the elastic scattering time and
is the atomic number.Comment: accepted for publication in Physical Review Letter
Magnetic field enhancement of superconductivity in ultra-narrow wires
We study the effect of an applied magnetic field on sub-10nm wide MoGe and Nb
superconducting wires. We find that magnetic fields can enhance the critical
supercurrent at low temperatures, and does so more strongly for narrower wires.
We conjecture that magnetic moments are present, but their pair-breaking
effect, active at lower magnetic fields, is suppressed by higher fields. The
corresponding microscopic theory, which we have developed, quantitatively
explains all experimental observations, and suggests that magnetic moments have
formed on the wire surfaces.Comment: 4 pages, 3 figures, 1 tabl
Carbon fibre tips for scanning probe microscopy based on quartz tuning fork force sensors
We report the fabrication and the characterization of carbon fibre tips for
their use in combined scanning tunnelling and force microscopy based on
piezoelectric quartz tuning fork force sensors. We find that the use of carbon
fibre tips results in a minimum impact on the dynamics of quartz tuning fork
force sensors yielding a high quality factor and consequently a high force
gradient sensitivity. This high force sensitivity in combination with high
electrical conductivity and oxidation resistance of carbon fibre tips make them
very convenient for combined and simultaneous scanning tunnelling microscopy
and atomic force microscopy measurements. Interestingly, these tips are quite
robust against occasionally occurring tip crashes. An electrochemical
fabrication procedure to etch the tips is presented that produces a sub-100 nm
apex radius in a reproducible way which can yield high resolution images.Comment: 14 pages, 10 figure
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