Search results for "SIP"
showing 10 items of 1280 documents
Nature of Heavy Quasiparticles in Magnetically Ordered Heavy FermionsUPd2Al3andUPt3
2002
The optical conductivity of the heavy fermions $\mathrm{UPd}{}_{2}{\mathrm{Al}}_{3}$ and $\mathrm{UPt}{}_{3}$ has been measured in the energy range from 0.04 to 5 meV. In both compounds a well pronounced pseudogap of less than 1 meV develops in the optical response at low temperatures; we relate this to the antiferromagnetic ordering. From the energy dependence of the effective mass and scattering rate we conclude that the enhancement of the mass mainly occurs below the energy which is related to magnetic correlations between the local magnetic moments and the itinerant electrons. This implies that the magnetic order in these compounds is the prerequisite to the formation of the heavy quasi…
Microscopic model for multiple flux transitions in mesoscopic superconducting loops
2006
A microscopic model is constructed which is able to describe multiple magnetic flux transitions as observed in recent ultra-low temperature tunnel experiments on an aluminum superconducting ring with normal metal - insulator - superconductor junctions [Phys. Rev. B \textbf{70}, 064514 (2004)]. The unusual multiple flux quantum transitions are explained by the formation of metastable states with large vorticity. Essential in our description is the modification of the pairing potential and the superconducting density of states by a sub-critical value of the persistent current which modulates the measured tunnel current. We also speculate on the importance of the injected non-equilibrium quasi…
Spectral broadening by quasiparticle pile-up in X-ray microcalorimeters with superconducting absorbers
2004
Long-living quasiparticles can pile-up in a superconducting absorber of an X-ray microcalorimeter when photons are detected at high count rate. These quasiparticles can give a non-negligible contribution to the total heat capacity of the detector thus affecting the pulse height spectrum of detected photons. We investigated this effect with numerical simulations and evaluated the resulting spectral broadening as a function of the photon absorption rate, and the heat capacity of the detector for a NTD germanium microcalorimeter with pure Sn absorber.
Test of x-ray microcalorimeters with bilayer absorbers
2008
Superconducting absorbers for thermal X-ray microcalorimeters should convert into thermalized phonons and transfer to the thermal sensor most of the energy deposited by single photons, on a time scale as short as a few tens of microseconds. Since deposition of X-ray energy in a superconductor produces quasiparticles by breaking up of Cooper pairs, the thermalization efficiency depends on the time scale on which they survive within the absorber volume, trapping part of the absorbed energy. According to the predicted values of their microscopic parameters, in many standard type-I superconducting metals the quasiparticle life time at very low temperatures results too long to allow for recombin…
Characterisation of Cooper Pair Boxes for Quantum Bits
2001
We have fabricated and measured single Cooper pair boxes (SCB) using superconducting single electron transistors (SET) as electrometers. The box storage performance for Cooper pairs was measured by observing the changes in the SCB island potential. We are also fabricating niobium structures, which are expected to have less problems with quasiparticle contamination than similar aluminium based devices because of the high critical temperature. The use of niobium may also reduce decoherence and thereby increase the time available for quantum logic operations.
Negative magnetoresistance of ultra-narrow superconducting nanowires in the resistive state
2008
We present a phenomenological model qualitatively explaining negative magnetoresistance in quasi-one-dimensional superconducting channels in the resistive state. The model is based on the assumption that fluctuations of the order parameter (phase slips) are responsible for the finite effective resistance of a narrow superconducting wire sufficiently close to the critical temperature. Each fluctuation is accompanied by an instant formation of a quasi-normal region of the order of the non-equilibrium quasiparticle relaxation length 'pinned' to the core of the phase slip. The effective time-averaged voltage measured in experiment is a sum of two terms. First one is the conventional contributio…
Elementary excitations in superfluidH3e-H4emixtures
2010
We have studied the dynamic structure function of superfluid $^{3}\text{H}\text{e-}^{4}\text{H}\text{e}$ mixtures at zero temperature as a function of pressure and $^{3}\text{H}\text{e}$ concentration. Results obtained in the full random-phase approximation (RPA) plus density-functional theory and in a generalized Landau-Pomeranchuk approach are presented and compared with experiment. Analytic expressions for several sum rules of the dynamic structure functions have been determined, and have been used to obtain average energies of the collective excitations. In the RPA approach, the dispersion relation of the collective modes shows typical features of level repulsion between zero-soundlike …
Dissipative terms of thermal nature in the theory of an ideal monoatomic superfluid
1996
A dissipative model of helium II was built up in previous works, using a 13-field extended thermodynamic theory formulated by Liu and Muller. In this work a generalization of such model is presented, where an extended thermodynamics with 14 fields due to Kremer is used. It is shown that the fourteenth field is able to account for the experimental data concerning the second sound attenuation. Further, the proposed theory is able to explain the Osborne experiment. Finally, a comparison with the two-fluid model is performed, emphasizing the different ways in which the dissipative phenomena are explained by the two theories.
Probing spectral properties of the QGP with real-time lattice simulations
2018
We present a new method to obtain spectral properties of a non-Abelian gauge theory in the region where occupation numbers are high. The method to measure the (single-particle) spectral function is based on linear response theory and classical-statistical lattice simulations. Although we apply it to a system far from equilibrium in a self-similar regime, the extracted spectral function can be understood within the hard thermal loop (HTL) formalism and can thus be connected to thermal equilibrium at high temperatures. This allows us to obtain quantities like the lifetime of quasiparticles that are beyond the leading order and difficult to compute within HTL. The approach has the potential to…
Microscopic description of dissipative dynamics of a level-crossing transition
2011
We analyze the effect of a dissipative bosonic environment on the Landau-Zener-Stuckelberg-Majorana (LZSM) level crossing model by using a microscopic approach to derive the relevant master equation. For an environment at zero temperature and weak dissipation our microscopic approach confirms the independence of the survival probability on the decay rate that has been predicted earlier by the simple phenomenological LZSM model. For strong decay the microscopic approach predicts a notable increase of the survival probability, which signals dynamical decoupling of the initial state. Unlike the phenomenological model our approach makes it possible to study the dependence of the system dynamics…