Search results for "Condensed Matter::Superconductivity"
showing 10 items of 632 documents
Electron–phonon coupling in degenerate silicon-on-insulator film probed using superconducting Schottky junctions
2002
Abstract Energy flow rate in degenerate n-type silicon-on-insulator (SOI) film is studied at low temperatures. The electrons are heated above the lattice temperature by electric field and the electron temperature is measured via semiconductor–superconductor quasiparticle tunneling. The energy flow rate in the system is found to be proportional to T 5 , indicating that electron–phonon relaxation rate and electron–phonon phase breaking rate are proportional to T 3 . The electron–phonon system in the SOI film is in the “dirty limit” where the electron mean free path is smaller than the inverse of the thermal phonon wave vector.
Superconductivity in palladium-based Heusler compounds
2009
This work reports on four more Heusler superconductors: ${\text{Pd}}_{2}\text{ZrAl}$, ${\text{Pd}}_{2}\text{HfAl}$, ${\text{Pd}}_{2}\text{ZrIn}$, and ${\text{Pd}}_{2}\text{HfIn}$. These compounds exhibit superconducting transition temperatures ranging from 2.4--3.8 K as determined by resistivity measurements. According to their behavior in an external magnetic field, all compounds are type II bulk superconductors. The occurrence of superconductivity was predicted for these compounds using electronic structure calculations. The electronic structures exhibit van Hove singularities (saddle points) at the $L$ point. These lead to a maximum in the corresponding density of states and superconduct…
Strong-coupling effects in the heavy-fermion superconductor UPd2Al3
2000
Abstract Recent results of superconducting tunneling spectroscopy on epitaxial thin films of the antiferromagnetic heavy-fermion superconductor UPd 2 Al 3 are presented. Strong-coupling effects in the tunneling density of states are analyzed within the framework of the anisotropic Eliashberg theory for a pair-coupling mechanism based on the exchange of antiferromagnetic spin excitations. The multi-sheeted Fermi surface of UPd 2 Al 3 is taken into account.
Change of the vortex core structure in two-band superconductors at the impurity-scattering-driven s±/s++ crossover
2017
We report a nontrivial transition in the core structure of vortices in two-band superconductors as a function of interband impurity scattering. We demonstrate that, in addition to singular zeros of the order parameter, the vortices there can acquire a circular nodal line around the singular point in one of the superconducting components. It results in the formation of the peculiar ``moat''-like profile in one of the superconducting gaps. The moat-core vortices occur generically in the vicinity of the impurity-induced crossover between ${s}_{\ifmmode\pm\else\textpm\fi{}}$ and ${s}_{++}$ states.
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…
Energy dependence of the electron-boson coupling strength in the electron-doped cuprate superconductor Pr1.85Ce0.15CuO4−δ
2017
In the conventional theory of superconductivity the critical temperature Tc is determined by the electron-phonon coupling constant and the phonon cut-off frequency. The hallmark experiments of McMillan and Rowell demonstrated that bosons (phonons) responsible for pairing can be observed through the frequency dependence of the gap parameter. Determination of the electron-boson coupling strength in high-${T}_{c}$ cuprates is, however, not an easy task. One of the promising ways is to measure the energy relaxation rate of photoexcited carriers by using femtosecond real-time techniques. Here, considering the electron relaxation process within the conduction band, it is commonly assumed that the…
Flat Bands as a Route to High-Temperature Superconductivity in Graphite
2016
Superconductivity is traditionally viewed as a low-temperature phenomenon. Within the BCS theory this is understood to result from the fact that the pairing of electrons takes place only close to the usually two-dimensional Fermi surface residing at a finite chemical potential. Because of this, the critical temperature is exponentially suppressed compared to the microscopic energy scales. On the other hand, pairing electrons around a dispersionless (flat) energy band leads to very strong superconductivity, with a mean-field critical temperature linearly proportional to the microscopic coupling constant. The prize to be paid is that flat bands can probably be generated only on surfaces and i…
Irreversibility of the threshold field for dendritic flux avalanches in superconductors
2010
Hysteretic effects are seen in the upper and lower threshold fields for the appearance of dendritic flux instabilities, first explained in Yurchenko et al. [Phys. Rev. B 76 (2007) 092504], in NbN-films. We have measured the threshold fields at increasing and decreasing applied fields at different temperatures and proposed a mechanism explaining how the hysteresis arises by analyzing the field profiles inside the sample.
History dependence of the magnetization of thin HTSC films: an explanation for distorted SQUID signals
1997
Abstract The magnetizations of thin film disk-shaped type-II superconductors in perpendicular magnetic fields are considered by aid of Mikheenko's critical state model which has been corrected by Zhu for the case of a time-varying periodic field. This paper presents the application of this scheme to an arbitrary nonperiodic time dependence H ( t ). We calculate the influence of field inhomogeneities in a magnetometer on the current density distribution of a disk-shaped type-II superconductor. The resulting SQUID pickup signals and magnetic moments are compared to measurements performed on a 200 nm thick YBa 2 Cu 3 O 7 film in the irreversible regime of the phase diagram. Theory and experime…
Superconductor-Diamond Hybrid Quantum System
2016
This chapter describes recent progress on research into superconducting flux qubit, NV diamond, and superconductor-diamond hybrid quantum systems. First, we describe important physical properties of superconducting macroscopic artificial atoms i.e., the tunability of the qubit energy level spacing, the coherence property, an example of strong coupling to another quantum system such as an LC harmonic oscillator, and qubit state readout through a Josephson bifurcation amplifier. We then introduce the NV center in diamond as an intriguing candidate for quantum information processing, which offers excellent multiple accessibility via visible light, microwaves and magnetic fields. Finally, we de…