Search results for " electrons"
showing 10 items of 1168 documents
Microwave Properties of Nb/PdNi/Nb Trilayers
2012
We combine wideband (1-20 GHz) Corbino disk and dielectric resonator (8.2 GHz) techniques to study the microwave properties in Nb/PdNi/Nb trilayers, grown by UHV dc magnetron sputtering, composed by Nb layers of nominal thickness $d_S$=15 nm, and a ferromagnetic PdNi layer of thickness $d_F$= 1, 2, 8 and 9 nm. We focus on the vortex state. Magnetic fields up to $H_{c2}$ were applied. The microwave resistivity at fixed $H/H_{c2}$ increases with $d_F$, eventually exceeding the Bardeen Stephen flux flow value.
The role of correlations in the high-pressure phase of FeSe
2011
This study addresses the structural and electronic properties of the NiAs- and MnP-type phases dominating in FeSe at high pressures. The analysis is performed using first-principle band structure calculations within the framework of the B3LYP hybrid exchange-correlation functional. Based on the volume-pressure relation deduced from the available experimental data, we optimize the form and internal coordinates of the unit cell, which agree reasonably well with experiment. In particular, the present calculations resolve the structural NiAs-MnP phase transition which occurs at about 10 GPa. Both structures are found to be semiconducting at low pressures and metallizing at about 80-90 GPa. Usin…
Multiple band crossings and Fermi surface topology: Role of double nonsymmorphic symmetries in MnP-type crystal structures
2019
We use relativistic ab-initio methods combined with model Hamiltonian approaches to analyze the normal-phase electronic and structural properties of the recently discovered WP superconductor. Remarkably, the outcomes of such study can be employed to set fundamental connections among WP and the CrAs and MnP superconductors belonging to the same space group. One of the key features of the resulting electronic structure is represented by the occurrence of multiple band crossings along specific high symmetry lines of the Brilloiun zone. In particular, we demonstrate that the eight-fold band degeneracy obtained along the SR path at (kx,ky)=(Pi,Pi) is due to inversion-time reversal invariance and…
Superconductivity with broken time-reversal symmetry inside a superconducting s-wave state
2018
In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors, in which superconductivity may coexist with magnetism, and only a few examples are known, when superconductivity itself induces spontaneous magnetism. The most known compounds are Sr$_2$RuO$_4$ and some noncentrosymmetric superconductors. Here, we report the finding of a narrow dome of a novel $s+is'$ superconducting (SC) phase with broken time-reversal symmetry (BTRS) inside the broad $s$-wave SC region of the centrosymmetric multiband superconductor Ba$_{\rm 1-x}$K$_{\rm x}$Fe$_2$As$_2$ ($0.7 \lesssim x \lesssim 0.85$). We observe spontaneous magnetic fields …
Proximity-induced Josephson-quasiparticle process in a single-electron transistor
1998
We have performed the first experiments in a superconductor - normal metal - superconductor single electron transistor in which there is an extra superconducting strip partially overlapping the normal metal island in good metal-to-metal contact. Superconducting proximity effect gives rise to current peaks at voltages below the quasiparticle threshold. We interpret these peaks in terms of the Josephson-quasiparticle process and discuss their connection with the proximity induced energy gap in the normal metal island.
Electronic Properties, Band Structure, and Fermi Surface Instabilities ofNi1+/Ni2+NickelateLa3Ni2O6, Isoelectronic with Superconducting Cuprates
2009
Electronic structure calculations were performed for the mixed-valent Ni(1+)/Ni(2+) nickelate La3Ni2O6, which exhibits electronic instabilities of the Fermi surface similar to that of the isostructural superconducting La2CaCu2O6 cuprate. La3Ni2O6 shows activated hopping, which fits to Mott's variable-range-hopping model with localized states near the Fermi level. However, a simple local spin density approximation calculation leads to a metallic ground state. The calculations including local density approximation+Hubbard U and hybrid functionals indicate a multiply degenerate magnetic ground state. For electron-doped La2ZrNi2O6, which is isoelectronic with La2CaCu2O6, an antiferromagnetic in…
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.
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…