214 research outputs found
Non-invasive thermometer based on proximity superconductor for ultra-sensitive calorimetry
We present radio-frequency thermometry based on a tunnel junction between a
superconductor and proximitized normal metal. It allows operation in a wide
range of biasing conditions. We demonstrate that the standard finite-bias
quasiparticle tunneling thermometer suffers from large dissipation and loss of
sensitivity at low temperatures, whereas thermometry based on zero bias anomaly
avoids both these problems. For these reasons the latter method is suitable
down to lower temperatures, here to about 25 mK. Both thermometers are shown to
measure the same local temperature of the electrons in the normal metal in the
range of their applicability
Violation of the fluctuation-dissipation theorem in time-dependent mesoscopic heat transport
We have analyzed the spectral density of fluctuations of the energy flux
through a mesoscopic constriction between two equilibrium reservoirs. It is
shown that at finite frequencies, the fluctuating energy flux is not related to
the thermal conductance of the constriction by the standard
fluctuation-dissipation theorem, but contains additional noise. The main
physical consequence of this extra noise is that the fluctuations do not vanish
at zero temperature together with the vanishing thermal conductance.Comment: 5 pages, 1 figur
Violation of the Wiedemann-Franz Law in a Single-Electron Transistor
We study the influence of Coulomb interaction on the thermoelectric transport
coefficients for a metallic single-electron transistor. By performing a
perturbation expansion up to second order in the tunnel-barrier conductance, we
include sequential and cotunneling processes as well as quantum fluctuations
that renormalize the charging energy and the tunnel conductance. We find that
Coulomb interaction leads to a strong violation of the Wiedemann-Franz law: the
Lorenz ratio becomes gate-voltage dependent for sequential tunneling, and is
increased by a factor 9/5 in the cotunneling regime. Finally, we suggest a
measurement scheme for an experimental realization.Comment: published version, minor changes; 4 pages, 3 figure
Micrometre-scale refrigerators
A superconductor with a gap in the density of states or a quantum dot with
discrete energy levels is a central building block in realizing an electronic
on-chip cooler. They can work as energy filters, allowing only hot
quasiparticles to tunnel out from the electrode to be cooled. This principle
has been employed experimentally since the early 1990s in investigations and
demonstrations of micrometre-scale coolers at sub-kelvin temperatures. In this
paper, we review the basic experimental conditions in realizing the coolers and
the main practical issues that are known to limit their performance. We give an
update of experiments performed on cryogenic micrometre-scale coolers in the
past five years
A superconducting antenna-coupled hot-spot microbolometer
We report the electrical properties of an antenna-coupled niobium vacuum-bridge bolometer, operated at a temperature of 4.2 K, in which the thermal isolation is maximized by the vacuum gap between the bridge and the underlying silicon substrate. The device is voltage-biased, which results in a formation of a normal state region in the middle of the bridge. The device shows a current responsivity of −1430 A/W and an amplifier limited electrical noise equivalent power of 1.4×10−14 W/√Hz.Peer reviewe
Heat due to system-reservoir correlations in thermal equilibrium
The heat flow between a quantum system and its reservoir is analyzed when initially both are in a separable thermal state and asymptotically approach a correlated equilibrium. General findings are illustrated for specific systems and various classes of non-Markovian reservoirs relevant for solid state realizations. System-bath correlations are shown to be substantial at low temperatures even in the weak coupling regime. As a consequence, predictions of work and heat for actual experiments obtained within conventional perturbative approaches may often be questionable. Correlations induce characteristic imprints in heat capacities which opens a proposal to measure them in solid state devices.Peer reviewe
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