Search results for "conductivity"

Structure and electrical resistivity of mixed-valent EuNi2P2 at high pressure.

2014

The structural properties and electrical resistivity of homogeneous mixed-valent EuNi2P2 are studied at pressures up to 45 GPa. No structural phase transition is observed in the whole pressure range and the overall pressure behavior of the structural parameters is similar to that of related compounds in the collapsed tetragonal ThCr2Si2-type structure. Electrical resistivity measured up to 31 GPa at temperatures between 4 and 300 K exhibits continuous changes from the behavior typical for a mixed-valent Eu system to that of a normal metallic system at pressures above 20 GPa, indicating a transition of the strongly mixed-valent Eu atoms with a valence ~2.5 towards a pure trivalent state. No …

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…

Enhanced superconductivity in atomically thin TaS2

2016

The ability to exfoliate layered materials down to the single layer limit has presented the opportunity to understand how a gradual reduction in dimensionality affects the properties of bulk materials. Here we use this top–down approach to address the problem of superconductivity in the two-dimensional limit. The transport properties of electronic devices based on 2H tantalum disulfide flakes of different thicknesses are presented. We observe that superconductivity persists down to the thinnest layer investigated (3.5 nm), and interestingly, we find a pronounced enhancement in the critical temperature from 0.5 to 2.2 K as the layers are thinned down. In addition, we propose a tight-binding …

Investigation of Many‐Body Effects in the Quasi‐Two‐Dimensional Electronic System of Organic Charge‐Transfer Salts

2019

Intercalation chemistry of superconducting zirconium and hafnium nitride halides

2001

Abstract Lithium intercalation in MNX (M=Zr, Hf; X=Cl, Br) may lead to superconducting compounds with critical temperatures up to 24 K. Electrochemical lithiation experiments agree with the results obtained with chemical methods, as samples with larger capacity on discharge are also those having larger lithium contents after chemical lithiation. Variations exist in the electrochemical profiles of different batches for these compounds indicating differences in the intercalation reaction pathway. High-resolution electron microscopy images confirm the structural model isotypic to SmSI for β-MNX phases. The major part of crystals from ZrNX as well as from the HfNCl samples showing a high lithiu…

Polymer solution processing of (Bi, Pb)SrCaCuO

1991

Abstract A simple polymer processing route to the 110 K phase (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+δ superconductor has been developed. The influence of the polymer to metal starting ratio, as well as the sintering temperature and time on the quality of the resulting superconducting powders has been studied by XRD, a.c. susceptibility and resistivity measurements. Microstructure of ceramic compacts has been studied by SEM, and qualitatively analysed by EDS for compositional homogeneity. The results indicate that the polymer synthesis route described here may offer a good alternative to the conventional solid state preparation methods towards attaining homogeneous 110 K superconductor powder withi…

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.

Coherent coupling between vortex bound states and magnetic impurities in 2D layered superconductors

2021

Bound states in superconductors are expected to exhibit a spatially resolved electron-hole asymmetry which is the hallmark of their quantum nature. This asymmetry manifests as oscillations at the Fermi wavelength, which is usually tiny and thus washed out by thermal broadening or by scattering at defects. Here we demonstrate theoretically and confirm experimentally that, when coupled to magnetic impurities, bound states in a vortex core exhibit an emergent axial electron-hole asymmetry on a much longer scale, set by the coherence length. We study vortices in 2H-NbSe2 and in 2H-NbSe1.8S0.2 with magnetic impurities, characterizing these with detailed Hubbard-corrected density functional calcu…

Vector Potential at High School: A Way to Introduce Superconductivity and to Review Electromagnetism

2014

Superconductivity is a rich and complex topic that generates great interest and curiosity in high school students. Most of the presentations of superconductivity give a great importance to magnetism. But typically in these presentations the physical role is played by the magnetic field B while the magnetic vector potential A is never mentioned. Moreover the explanation of the quantum phenomena at the base of the superconductivity are often not enough developed and generally given only at a popular level. We think that the key point for a meaningful presentation at high school is the vector potential. In this paper we present a teaching path on the vector potential and a pilot experimentatio…