1,732 research outputs found
Quantum Phase Transitions and Vortex Dynamics in Superconducting Networks
Josephson junction arrays are ideal model systems where a variety of
phenomena, phase transitions, frustration effects, vortex dynamics, chaos, to
mention a few of them, can be studied in a controlled way. In this review we
focus on the quantum dynamical properties of low capacitance Josephson junction
arrays. The two characteristic energy scales in these systems are the Josephson
energy, associated to the tunneling of Cooper pairs between neighboring
islands, and the charging energy, which is the energy cost to add an extra
electron charge to a neutral island. The phenomena described in this review
stem from the competition between single electron effects with the Josephson
effect. One example is the (quantum) Superconductor-Insulator phase transition
which occurs by varying the ratio between the coupling constants and/or by
means of external magnetic/electric fields. We will describe how the phase
diagram depends on the various control paramters and the transport properties
close to the quantum critical point. The relevant topological excitations on
the superconducting side of the phase diagram are vortices. In low capacitance
junction arrays vortices behave as massive underdamped particles that can
exhibit quantum behaviour. We will report on the various experiments and
theoretical treatments on quantum vortex dynamics.Comment: To be published in Physics Reports. Better quality figures can be
obtained upon reques
Efficient readout of micromechanical resonator arrays in ambient conditions
We present a method for efficient spectral readout of mechanical resonator
arrays in dissipative environments. Magnetomotive drive and detection is used
to drive double clamped resonators in the nonlinear regime. Resonators with
almost identical resonance frequencies can be tracked individually by sweeping
the drive power. Measurements are performed at room temperature and atmospheric
pressure. These conditions enable application in high throughput resonant
sensor arrays.Comment: 4 pages, 4 figure
On Mean-Field Theory of Quantum Phase Transition in Granular Superconductors
In previous work on quantum phase transition in granular superconductors,
where mean-field theory was used, an assumption was made that the order
parameter as a function of the mean field is a convex up function. Though this
is not always the case in phase transitions, this assumption must be verified,
what is done in this article
Strongly coupled modes in a weakly driven micromechanical resonator
We demonstrate strong coupling between the flexural vibration modes of a
clamped-clamped micromechanical resonator vibrating at low amplitudes. This
coupling enables the direct measurement of the frequency response via
amplitude- and phase modulation schemes using the fundamental mode as a
mechanical detector. In the linear regime, a frequency shift of
is observed for a mode with a line width of
in vacuum. The measured response is well-described by the
analytical model based on the Euler-Bernoulli beam including tension.
Calculations predict an upper limit for the room-temperature Q-factor of
for our top-down fabricated micromechanical beam
resonators.Comment: 9 pages, 2 figure
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