Search results for "Quasiparticle"
showing 10 items of 280 documents
Spatially resolved measurement of nonequilibrium quasiparticle relaxation in superconducting Al
2011
Spatially resolved relaxation of nonequilibrium quasiparticles in a superconductor at ultralow temperatures was experimentally studied. It was found that the quasiparticle injection through a tunnel junction results in the modification of the shape of the I-V characteristic of a remote ``detector'' junction. The effect depends on the temperature, injection current, and proximity to the injector. The phenomena can be understood in terms of the creation of quasiparticle charge and energy disequilibrium characterized by two different length scales ${\ensuremath{\Lambda}}_{{Q}^{*}}~5$ and ${\ensuremath{\Lambda}}_{{T}^{*}}~40$ $\ensuremath{\mu}$m. The findings are in good agreement with existing…
Experimental evidence of an incomplete thermalization of the energy in an x-ray microcalorimeter with a TaAu absorber.
2008
We have conducted an experimental test at our XACT facility using an x-ray microcalorimeter with Ta∕Au absorber and neutron transmutation doped germanium thermal sensor. The test was aimed at measuring the percentage of energy effectively thermalized after absorption of x-ray photons in superconducting tantalum. Moreover, in general, possible formation of long living quasiparticles implies that by using a superconducting absorber, a fraction of the deposited energy could not be thermalized on the useful time scale of the thermal sensor. To investigate this scenario, we exploited an absorber made of gold, where no energy trapping is expected, with a small piece of superconducting tantalum at…
Low-Frequency Imaginary Impedance at the Superconducting Transition of 2H - NbSe2
2020
The superconducting transition leads to a sharp resistance drop in a temperature interval that can be a small fraction of the critical temperature ${T}_{c}$. A superconductor exactly at ${T}_{c}$ is thus very sensitive to all kinds of thermal perturbation, including the heat dissipated by the measurement current. We show that the interaction between electrical and thermal currents leads to a sizable imaginary impedance at frequencies of the order of tens of hertz at the resistive transition of single crystals of the layered material $2H$-${\mathrm{Nb}\mathrm{Se}}_{2}$. We explain the result using models developed for transition-edge sensors. By measuring under magnetic fields and at high cu…
Evidence for eight node mixed-symmetry superconductivity in a correlated organic metal
2015
We report a combined theoretical and experimental investigation of the superconducting state in the quasi-two-dimensional organic superconductor $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br. Applying spin-fluctuation theory to a low-energy material-specific Hamiltonian derived from ab initio density functional theory we calculate the quasiparticle density of states in the superconducting state. We find a distinct three-peak structure that results from a strongly anisotropic mixed-symmetry superconducting gap with eight nodes and twofold rotational symmetry. This theoretical prediction is supported by low-temperature scanning tunneling spectroscopy on in situ cleaved single crystals of $\kappa$-(ET)$_2$…
Field-induced suppression of the pi-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB_2 at temperatures near …
2009
We report on the magnetic-field-induced variations of the microwave surface resistance, R_s, in a polycrystalline MgB_2 sample, at different values of temperature. We have detected a magnetic hysteresis in R_s, which exhibits an unexpected plateau on decreasing the DC magnetic field below a certain value. In particular, at temperatures near T_c the hysteresis manifests itself only through the presence of the plateau. Although we do not quantitatively justify the anomalous shape of the magnetic hysteresis, we show that the results obtained in the reversible region of the R_s(H) curve can be quite well accounted for by supposing that, in this range of magnetic field, the pi-gap is almost supp…
Unified description of 2+_1 states within the deformed quasiparticle random-phase approximation
2013
We describe low-lying collective states in deformed even-even nuclei within a deformed quasiparticle random-phase approximation (dQRPA) by using a single-particle basis with good angular momentum. The statistical factors, accounting for the level occupancy, appear in the dQRPA in a natural way as rotation coefficients that take the intrinsic system to the laboratory system. We have used our model by performing a systematic analysis of E2 transitions from the first ${2}^{+}$ state to the ground state for all superfluid nuclei in the range $50lZ\ensuremath{\le}100$ by using a common charge polarization parameter $\ensuremath{\chi}=0.2$. In spite of its similarity to the QRPA, this method is a…
Spatial development of multiple-gap states in nonequilibrium superconductors
1985
We have studied the gap instability in a superconductor under tunneling injection at high voltages by probing the spatial distribution of the phonon emission. A high sensitivity was achieved by using the fountain pressure of superfluid helium for detecting the phonons. Spatial structures were observed at gap depressions as small as 2%. From their spatial development we find that the quasiparticles diffuse into regions where their density is higher.
Integrated plasmonic waveguides: A mode solver based on density of states formulation
2009
International audience; We express the density of states (DOS) near guided resonances of plasmonic waveguides by using multiple-scattering theory. In direct analogy with the case of localized electronic defect states in condensed matter, we demonstrate that optical DOS variations follow a lorentzian profile near guided modes resonances. The lorentzian shape gives quantitative information on the guided modes (effective index, propagation length, and polarization state). We numerically investigate both leaky and bound (lossy) modes supported by dielectric-loaded surface-plasmon-polariton waveguides.
Collective excitations of 3He clusters
1991
Collective excitations of3He clusters are studied by treating the cluster as a quantum liquid drop. We have used the Random-Phase Approximation sum rules technique within a Density Functional Formalism. Results forL=2 to 10 surface modes and theL=0 volume mode are presented.
Excitons in few-layer hexagonal boron nitride: Davydov splitting and surface localization
2018
Hexagonal boron nitride (hBN) has been attracting great attention because of its strong excitonic effects. Taking into account few-layer systems, we investigate theoretically the effects of the number of layers on quasiparticle energies, absorption spectra, and excitonic states, placing particular focus on the Davydov splitting of the lowest bound excitons. We describe how the inter-layer interaction as well as the variation in electronic screening as a function of layer number $N$ affects the electronic and optical properties. Using both \textit{ab initio} simulations and a tight-binding model for an effective Hamiltonian describing the excitons, we characterize in detail the symmetry of t…