293 research outputs found
Superconducting Nanowires as Nonlinear Inductive Elements for Qubits
We report microwave transmission measurements of superconducting Fabry-Perot
resonators (SFPR), having a superconducting nanowire placed at a supercurrent
antinode. As the plasma oscillation is excited, the supercurrent is forced to
flow through the nanowire. The microwave transmission of the resonator-nanowire
device shows a nonlinear resonance behavior, significantly dependent on the
amplitude of the supercurrent oscillation. We show that such
amplitude-dependent response is due to the nonlinearity of the current-phase
relationship (CPR) of the nanowire. The results are explained within a
nonlinear oscillator model of the Duffing oscillator, in which the nanowire
acts as a purely inductive element, in the limit of low temperatures and low
amplitudes. The low quality factor sample exhibits a "crater" at the resonance
peak at higher driving power, which is due to dissipation. We observe a
hysteretic bifurcation behavior of the transmission response to frequency sweep
in a sample with a higher quality factor. The Duffing model is used to explain
the Duffing bistability diagram. We also propose a concept of a nanowire-based
qubit that relies on the current dependence of the kinetic inductance of a
superconducting nanowire.Comment: 28 pages, 7 figure
Quantitative analysis of quantum phase slips in superconducting MoGe nanowires revealed by switching-current statistics
We measure quantum and thermal phase-slip rates using the standard deviation
of the switching current in superconducting nanowires at high bias current. Our
rigorous quantitative analysis provides firm evidence for the presence of
quantum phase slips (QPS) in homogeneous nanowires. We observe that as
temperature is lowered, thermal fluctuations freeze at a characteristic
crossover temperature Tq, below which the dispersion of the switching current
saturates to a constant value, indicating the presence of QPS. The scaling of
the crossover temperature Tq with the critical temperature Tc is linear, which
is consistent with the theory of macroscopic quantum tunneling. We can convert
the wires from the initial amorphous phase to a single crystal phase, in situ,
by applying calibrated voltage pulses. This technique allows us to probe
directly the effects of the wire resistance, critical temperature and
morphology on thermal and quantum phase slips.Comment: 7 pages, 7 figures, 1 tabl
Superconducting properties of polycrystalline Nb nanowires templated by carbon nanotubes
Journal ArticleContinuous Nb wires, 7-15 nm in diameter, have been fabricated by sputter-coating single fluorinated carbon nanotubes. Transmission electron microscopy revealed that the wires are polycrystalline, having grain sizes of about 5 nm. The critical current of wires thicker than ~12 nm is very high (107 A/cm2) and comparable to the expected depairing current. The resistance versus temperature curves measured down to 0.3 K are well described by the Langer-Ambegaokar-McCumber-Halperin theory of thermally activated phase slips. Quantum phase slips are suppressed
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
Electronic mean free path in as-produced and purified single-wall carbon nanotubes
The effect of purification on room temperature electronic transport
properties of single-wall carbon nanotubes (SWNT) was studied by submerging
samples into liquid mercury. The conductance plots of purified SWNTs showed
plateaus, indicating weak dependence of the electrical resistance on the length
of the tube connecting the electrodes, providing evidence of quasi-ballistic
conduction in SWNTs. The electronic mean free path of the purified SWNTs
reached a few microns, which is longer than that of the as-produced SWNTs, and
which is consistent with the calculation based on the scattering by acoustic
phonons
Superconductor-insulator transition in nanowires and nanowire arrays
Superconducting nanowires are the dual elements to Josephson junctions, with
quantum phase-slip processes replacing the tunneling of Cooper pairs. When the
quantum phase-slip amplitude ES is much smaller than the inductive energy EL,
the nanowire responds as a superconducting inductor. When the inductive energy
is small, the response is capacitive. The crossover at low temperatures as a
function of ES/EL is discussed and compared with earlier experimental results.
For one-dimensional and two-dimensional arrays of nanowires quantum phase
transitions are expected as a function of ES/EL. They can be tuned by a
homogeneous magnetic frustration.Comment: 15 pages, 10 figure
Reply on the comment on the paper "Superconducting transition in Nb nanowires fabricated using focused ion beam"
In this communication we present our response to the recent comment of A.
Engel regarding our paper on FIB- fabricated Nb nanowires (see Vol. 20 (2009)
Pag. 465302). After further analysis and additional experimental evidence, we
conclude that our interpretation of the experimental results in light of QPS
theory is still valid when compared with the alternative proximity-based model
as proposed by A. Engel.Comment: 3 pages, 1 figure, accepted by Nanotechnolog
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