Search results for "Conductor"

Static and dynamic interaction betweenπanddelectrons in organic superconductorβ″-(BEDT-TTF)4[(H3O)Fe(C2O4)3]·C6H5Brstudied byC13NMR spectroscopy

2016

We present the results of $^{13}\mathrm{C}$ NMR experiments in an organic superconductor with localized Fe spins ${\ensuremath{\beta}}^{\ensuremath{''}}\ensuremath{-}{(\text{BEDT-}\mathrm{TTF})}_{4}[({\mathrm{H}}_{3}\mathrm{O})\mathrm{Fe}{({\mathrm{C}}_{2}{\mathrm{O}}_{4})}_{3}]\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{C}}_{6}{\mathrm{H}}_{5}\mathrm{Br}$. We reveal the antiferromagnetic coupling between Fe $d$ spins and $\ensuremath{\pi}$ spins, which creates an exchange field antiparallel to the external field direction at the $\ensuremath{\pi}$ electrons. In addition to the static effects of Fe spins, we show from the nuclear spin-lattice relaxation rate measurement that the magn…

Nonlocal pure spin current injection via quantum pumping and crossed Andreev reflection

2005

A pure spin current injector is proposed based on adiabatic pumping and crossed normal/Andreev reflection. The device consists of a three-terminal ferromagnet-superconductor-semiconductor system in which the injection of a pure spin current is into the semiconductor which is coupled to the superconductor within a coherence length away from the ferromagnet enabling the phenomena of crossed normal /Andreev reflection to operate. Quantum pumping is induced by adiabatically modulating two independent parameters of the ferromagnetic lead, namely the magnetization strength and the strength of coupling between the ferromagnet and the superconductor. The competition between the normal/Andreev refle…

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)$_2$…

Microwave second-harmonic response of ceramic MgB2 samples

2005

Nonlinear microwave response of different ceramic MgB2 samples has been investigated by the technique of second-harmonic emission. The second-harmonic signal has been investigated as a function of temperature, DC magnetic field and input microwave power. The attention has mainly been devoted to the response at low magnetic fields, where nonlinear processes arising from motion of Abrikosov fluxons are ineffective. The results show that different mechanisms are responsible for the nonlinear response in the different ranges of temperature. At low temperatures, the nonlinear response is due to processes involving weak links. At temperatures close to Tc, a further contribution to the harmonic em…

Skyrmion formation due to unconventional magnetic modes in anisotropic multiband superconductors

2018

Multiband superconductors have a sufficient number of degrees of freedom to allow topological excitations characterized by Skyrmionic topological invariants. In the most common, clean s-wave multiband, systems the interband magnetic coupling favours composite vortex solutions, without a Skyrmionic topological charge. It was discussed recently that certain kinds of anisotropies lead to hybridisation of the interband phase difference (Leggett) mode with magnetic modes, dramatically changing the hydromagnetostatics of the system. Here we report this effect for a range of parameters that substantially alter the nature of the topological excitations, leading to solutions characterized by a nontr…

Electronic and structural properties of palladium-based Heusler superconductors

2008

Abstract This work reports on superconductivity in the Heusler compounds Pd2ZrAl and Pd2HfAl. Magnetisation and resistance measurements were carried out to verify their superconducting states. The compounds exhibit transition temperatures of 3.2 K (Zr) and 3.4 K (Hf). From their behaviour in external magnetic fields, it was determined that both compounds are type II superconductors. Similar to the half-metallic ferromagnets, the superconducting Heusler compounds follow an electron counting scheme based on theoretical considerations. As found from ab initio calculations, the superconductivity can be explained by a valence instability at the L -point, that has been used as design criterion.

Observable Variables in Thermoelectric Phenomena

2002

New transport equations for the thermoelectric phenomena have been deduced. All of the variables in this formulation are observable quantities. The limitations of the usual formulations, which work with nonobservable quantities, have been overcome. The electric potential can be measured by using auxiliary probes which connect the electronic conductor to a potentiometer. This observable electric potential depends on the nature of the probes but not on the room temperature where the potentiometer is placed. Also, we emphasize that absolute values for the thermoelectric power are in contradiction with the thermodynamic limitation of measuring electric potential differences in these systems. Th…

Magnetic hysteresis in the microwave surface resistance of Nb samples in the critical state

2006

We discuss the hysteretic behavior of the field-induced variations of the microwave surface resistance in superconductors in the critical state. Measurements have been performed in a bulk sample of Nb and a powdered one at different values of the temperature. We discuss a model, based on the Coffey and Clem theory, in which we take into account the flux distribution inside the sample, due to the critical state. The experimental results are justified quantitatively in the framework of our model. We show that by fitting the experimental data it is possible to determine the value of the critical current density and its field dependence.

Microwave Surface Resistance of High-Tc Superconductors near Liquid Nitrogen Temperature

2011

Effect of carrier transfer on the PL intensity in self-assembled In (Ga) As/GaAs quantum rings

2006

We present results concerning the carrier transfer between In(Ga)As quantum rings in a stacked multilayer structure, which is characterised by a bimodal size distribution. This transfer of carriers explains the observed temperature behaviour of diode lasers based on that kind of stacked layer structures. The inter-ring carrier transfer can be possible by phonon assisted tunnelling from the ground state of the smallring family towards the big-ring family of the bimodal size distribution. This process is thermally activated in the range 40–80 K.