687 research outputs found
Topology effects on the heat capacity of mesoscopic superconducting disks
Phase transitions in superconducting mesoscopic disks have been studied over
the H-T phase diagram through heat capacity measurement of an array of
independent aluminium disks. These disks exhibit non periodic modulations
versus H of the height of the heat capacity jump at the superconducting to
normal transition. This behaviour is attributed to giant vortex states
characterized by their vorticity L. A crossover from a bulk-like to a
mesoscopic behaviour is demonstrated. versus H plots exhibit
cascades of phase transitions as L increases or decreases by one unity, with a
strong hysteresis. Phase diagrams of giant vortex states inside the
superconducting region are drawn in the vortex penetration and expulsion
regimes and phase transitions driven by temperature between vortex states are
thus predicted in the zero field cooled regime before being experimentally
evidenced
Measurement of thermal conductance of silicon nanowires at low temperature
We have performed thermal conductance measurements on individual single
crystalline silicon suspended nanowires. The nanowires (130 nm thick and 200 nm
wide) are fabricated by e-beam lithography and suspended between two separated
pads on Silicon On Insulator (SOI) substrate. We measure the thermal
conductance of the phonon wave guide by the 3 method. The cross-section
of the nanowire approaches the dominant phonon wavelength in silicon which is
of the order of 100 nm at 1K. Above 1.3K the conductance behaves as T3, but a
deviation is measured at the lowest temperature which can be attributed to the
reduced geometry
Non-linear Frequency Transduction of Nano-mechanical Brownian Motion
We report on experiments addressing the non-linear interaction between a
nano-mechanical mode and position fluctuations. The Duffing non-linearity
transduces the Brownian motion of the mode, and of other non-linearly coupled
ones, into frequency noise. This mechanism, ubiquitous to all weakly-nonlinear
resonators thermalized to a bath, results in a phase diffusion process altering
the motion: two limit behaviors appear, analogous to motional narrowing and
inhomogeneous broadening in NMR. Their crossover is found to depend
non-trivially on the ratio of the frequency noise correlation time to its
magnitude. Our measurements obtained over an unprecedented range covering the
two limits match the theory of Y. Zhang and M. I. Dykman, Phys. Rev. B 92,
165419 (2015), with no free parameters. We finally discuss the fundamental
bound on frequency resolution set by this mechanism, which is not marginal for
bottom-up nanostructures.Comment: Article plus Supplementary Materia
Nanocalorimetry
International audience1. Definition Calorimetry is the part of thermodynamics which aims to measure any quantity of heat (enthalpy, specific heat, heat release) stored, released or brought into play in any state of matter, in a reaction, or in phase transitions [Lavoisier1780]. More precisely, the terminology of "Nanocalorimetry" may cover different concepts depending on the area of science where it is used. It concerns any calorimetric method in which either the samples to be studied have a size in the range of the nanometer scale or the measured energies involved are of the order of the nanojoule or below
Thermal signatures of Little-Parks effect in the heat capacity of mesoscopic superconducting rings
We present the first measurements of thermal signatures of the Little-Parks
effect using a highly sensitive nanocalorimeter. Small variations of the heat
capacity of 2.5 millions of non interacting micrometer-sized
superconducting rings threaded by a magnetic flux have been measured by
attojoule calorimetry. This non-invasive method allows the measurement of
thermodynamic properties -- and hence the probing of the energy levels -- of
nanosystems without perturbing them electrically. It is observed that is
strongly influenced by the fluxoid quantization (Little-Parks effect) near the
critical temperature . The jump of at the superconducting phase
transition is an oscillating function of with a period ,
the magnetic flux quantum, which is in agreement with the Ginzburg-Landau
theory of superconductivity.Comment: To be published in Physical Review B, Rapid Communication
Enlargement of the active rift during glaciations
During the last glaciation, an ice sheet covered Iceland approximately 1000 m thick. A reconstruction of the ice flow lines shows that the ice sheet was partly drained through fast-flowing streams. The major drainage routes correlate with locations of geothermal anomalies, suggesting that ice stream activity was favoured by water produced in regions of high geothermal heat flux. A widening of active rift zone was also deduced revealing a coupling between deep and surface processes
Quantum criticality at the superconductor to insulator transition revealed by specific heat measurements
The superconductor-insulator transition (SIT) is considered an excellent
example of a quantum phase transition which is driven by quantum fluctuations
at zero temperature. The quantum critical point is characterized by a diverging
correlation length and a vanishing energy scale. Low energy fluctuations near
quantum criticality may be experimentally detected by specific heat, , measurements. Here, we use a unique highly sensitive experiment to measure
of two-dimensional granular Pb films through the SIT. The specific
heat shows the usual jump at the mean field superconducting transition
temperature marking the onset of Cooper pairs formation.
As the film thickness is tuned toward the SIT, is
relatively unchanged, while the magnitude of the jump and low temperature
specific heat increase significantly. This behaviour is taken as the
thermodynamic fingerprint of quantum criticality in the vicinity of a quantum
phase transition.Comment: 9 pages, 5 figures, 1 tabl
Classical decoherence in a nanomechanical resonator
SI not providedInternational audienceDecoherence is an essential mechanism that defines the boundary between classical and quantum behaviours, while imposing technological bounds for quantum devices. Little is known about quantum coherence of mechanical systems, as opposed to electromagnetic degrees of freedom. But decoherence can also be thought of in a purely classical context, as the loss of phase coherence in the classical phase space. Indeed the bridge between quantum and classical physics is under intense investigation, using classical nanomechanical analogues of quantum phenomena. In the present work, by separating pure dephasing from dissipation, we quantitatively model the classical decoherence of a mechanical resonator: through the experimental control of frequency fluctuations, we engineer artificial dephasing. We report on the methods available to define pure dephasing in these systems, which are prerequisite in the understanding of decoherence processes in mechanical devices, both classical and quantum
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