Search results for "CONDUCTIVITY"
showing 10 items of 1988 documents
Shot noise for resonant Cooper pair tunneling
2001
We study intrinsic noise of current in a superconducting single-electron transistor, taking into account both coherence effects and Coulomb interaction near a Cooper-pair resonance. Due to this interplay, the statistics of tunneling events deviates from the Poisson distribution and, more important, it shows even-odd asymmetry in the transmitted charge. The zero-frequency noise is suppressed significantly when the quasiparticle tunneling rates are comparable to the coherent oscillation frequency of Cooper pairs.
Superconductivity in one dimension
2008
Superconducting properties of metallic nanowires can be entirely different from those of bulk superconductors because of the dominating role played by thermal and quantum fluctuations of the order parameter. For superconducting wires with diameters below $ \sim 50$ nm quantum phase slippage is an important process which can yield a non-vanishing wire resistance down to very low temperatures. Further decrease of the wire diameter, for typical material parameters down to $\sim 10$ nm, results in proliferation of quantum phase slips causing a sharp crossover from superconducting to normal behavior even at T=0. A number of interesting phenomena associated both with quantum phase slips and with …
Temperature and angular dependence of the upper critical field of UPd2Al3 thin films
1997
Abstract Temperature and angular resolved measurements of the upper critical field Bc2 of UPd2Al3 thin films are presented and compared with new theoretical calculations for weak-coupling s- and d-wave superconductors in the clean limit. In order to take account of the observed anisotropy of the initial slopes near T c , B′ c 2 = −4.9 T/K for B ‖ c and B′ c 2 = −5.8 T/K for B ⊥ c , and the crossing of the phase boundaries in the temperature dependence of Bc2 near T ∗ ≈ 0.75 T/T c , the calculations include anisotropic orbital and paramagnetic pair breaking. Recent speculations upon the occurence of a non-uniform superconducting “Fulde-Ferrell-Larkin-Ovchinnikov”-state are also considered an…
Direct observation of the quasiparticle relaxation in YBa2Cu3O7
1999
Abstract The real and imaginary parts of the optical conductivity ( σ 1 + iσ 2 ) in the superconducting state of YBa 2 Cu 3 O 7−δ thin films have been obtained by submillimeter spectroscopy for frequencies from 3 to 35 cm −1 . The quasiparticle relaxation can be directly observed in this frequency range. A Drude-type analysis allows to extract the temperature dependence of the scattering rate. The collapse of the relaxation rates provides clear experimental evidence that the spin fluctuations become gapped below T C .
Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors
2018
In multiband systems, such as iron-based superconductors, the superconducting states with locking and antilocking of the interband phase differences are usually considered as mutually exclusive. Fo ...
Flux-flow instability and its anisotropy inBi2Sr2CaCu2O8+δsuperconducting films
1999
We report measurements on voltage instability at high flux-flow velocities in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ superconducting films. Current-voltage $(I\ensuremath{-}V)$ characteristics have been measured as a function of temperature, magnetic field, and angle between the field and the c axis of the sample. Voltage jumps were observed in $I\ensuremath{-}V$ characteristics taken in all magnetic-field directions and in extended temperature and field ranges. An analysis of the experimental data, based on a theory for viscous flux-flow instability with a finite heat-removal rate from the sample, yielded the inelastic scatterin…
Microwave spectroscopy on heavy-fermion systems: probing the dynamics of charges and magnetic moments
2013
Investigating solids with light gives direct access to charge dynamics, electronic and magnetic excitations. For heavy fermions, one has to adjust the frequency of the probing light to the small characteristic energy scales, leading to spectroscopy with microwaves. We review general concepts of the frequency-dependent conductivity of heavy fermions, including the slow Drude relaxation and the transition to a superconducting state, which we also demonstrate with experimental data taken on UPd2Al3. We discuss the optical response of a Fermi liquid and how it might be observed in heavy fermions. Microwave studies with focus on quantum criticality in heavy fermions concern the charge response, …
Pressure-Induced Collapse of the Charge Density Wave and Higgs Mode Visibility in 2H−TaS2
2019
The pressure evolution of the Raman active electronic excitations of the transition metal dichalcogenides $2H\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ is followed through the pressure phase diagram embedding incommensurate charge-density-wave and superconducting states. At high pressure, the charge-density wave is found to collapse at 8.5 GPa. In the coexisting charge-density-wave and superconducting orders, we unravel a strong in-gap superconducting mode, attributed to a Higgs mode, coexisting with the expected incoherent Cooper-pair breaking signature. The latter remains in the pure superconducting state reached above 8.5 GPa. Our report constitutes a new observation of such Raman active H…
Thermalization efficiency of superconducting absorbers for thermal X-ray microcalorimeters
2004
The persistence of long living quasiparticles created in the energy thermalization process can affect the performances of a thermal X-ray microcalorimeter with superconducting absorber. Numerical simulations indicate that in an ab- sorber made of high-purity Sn, operated at temperatures lower than 100 mK, up to 60% of the deposited energy can remain trapped in the quasiparticle system for a time much longer than the time scale of the thermal sensor response, producing a reduction of the SNR of the detector. Other pure superconductors can present the same problem and therefore a microscopic analysis of the physical properties can be useful to identify suitable absorbing materials and optimiz…
Orbital character variation of the Fermi surface and doping dependent changes of the dimensionality inBaFe2−xCoxAs2from angle-resolved photoemission …
2010
From a combination of high resolution angle-resolved photoemission spectroscopy and density functional calculations, we derive information on the dimensionality and the orbital character of the electronic states of ${\text{BaFe}}_{2\ensuremath{-}x}{\text{Co}}_{x}{\text{As}}_{2}$. Upon increasing Co doping, the electronic states in the vicinity of the Fermi level take on increasingly three-dimensional character. Both the orbital variation with ${k}_{z}$ and the more three-dimensional nature of the doped compounds have important consequences for the nesting conditions and thus possibly also for the appearance of antiferromagnetic and superconducting phases.