Search results for "ELECTRICAL RESISTIVITY"
showing 10 items of 357 documents
Possibility of unconventional superconductivity of SrTiO3−δ
2003
Abstract SrTiO3−δ can show metallic behavior and superconductivity at T It is demonstrated that by variation of the annealing temperature in vacuum the transport properties of SrTiO3−δ can be tuned continuously from semiconducting to metallic. We present measurements of the upper critical field Bc2(T) which show near Tc a positive curvature. This unusual temperature dependence is consistent with a model of weakly interacting charged bosons which condense in the superconducting state (local pairing). However, measurements of current–voltage curves reveal only small critical currents of our samples. This observation is discussed in the framework of doping inhomogeneities.
Superconductivity in Nb21S8, a Phase with Metal Cluster Chains
1998
Phase pure samples of Nb21S8 are obtained by chemical transport and molten flux reactions in sealed niobium containers at 850−950 °C. In the temperature range from 5 to 290 K the electrical conductivity is found to be moderate metallic with a specific resistivity of 3.90 mΩ cm at 273 K. Magnetic susceptibility measurements give weak, almost temperature independent paramagnetism above ∼40 K. These metallic properties are compared with the structure of Nb21S8, which contains linear single and double chains of fused body centered niobium cubes, separated by S and additional Nb atoms. Both physical measurements consistently show a transition into the superconducting state below 4.1(5) and 3.7(2…
Coexistence of superconductivity and magnetism by chemical design.
2010
Although the coexistence of superconductivity and ferromagnetism in one compound is rare, some examples of such materials are known to exist. Methods to physically prepare hybrid structures with both competing phases are also known, which rely on the nanofabrication of alternating conducting layers. Chemical methods of building up hybrid materials with organic molecules (superconducting layers) and metal complexes (magnetic layers) have provided examples of superconductivity with some magnetic properties, but not fully ordered. Now, we report a chemical design strategy that uses the self assembly in solution of macromolecular nanosheet building blocks to engineer the coexistence of supercon…
New magnetic conductors and superconductors based on BEDT-TTF and BEDS-TTF
2005
Abstract Here we present our last results in the search for multifunctionality in conducting molecular materials obtained by combining paramagnetic molecular complexes with organic donors to produce paramagnetic molecular metals and superconductors. The structural and physical characterization of two new molecular paramagnetic superconductors ET 4 [H 3 OM(C 2 O 4 ) 3 ].PhBr (M III = Cr and Fe) are presented (ET = BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene). These salts present a superconductor transition at T c = 1.5 and 4.0 K, respectively and very anisotropic critical fields H c2a ≈ H c2b ≈0.5 T and H C2C ≈ 8 T for the Fe derivative. We will also present the structural and physica…
Preparation and characterization of (Hg0.7Mo0.3)Sr2(Ca0.7Y0.3)Cu2Ox and (Hg0.9Re0.1)Ba2CaCu2Oy superconducting films by laser ablation
2000
Abstract Oriented (Hg 0.7 Mo 0.3 )Sr 2 (Ca 0.7 Y 0.3 )Cu 2 O x and (Hg 0.9 Re 0.1 )Ba 2 CaCu 2 O y superconducting films were prepared on SrTiO 3 substrates using laser ablation and post-Hg-vapor annealing. Due to the stability of Mo 0.3 Sr 2 (Ca 0.7 Y 0.3 )Cu 2 O x and Re 0.1 Ba 2 CaCu 2 O y in air, no special handling was needed during the grinding, mixing and pressing of the precursor targets. The superconductivity of the films was characterized with the temperature dependence of the ac susceptibility ( χ - T ) and the resistance ( R - T ) while the crystallography was probed with x-ray diffraction (XRD) and scanning electron microscopy (SEM).
Effect of film thickness on the transport properties of MgB2 synthesized by spray pyrolysis
2011
Abstract Polycrystalline MgB2 films of different thickness have been prepared by employing spray pyrolysis technique on MgO (1 0 0) substrate. The MgB2 and other phases have been confirmed using X-ray diffraction technique and no trace of impurities phases have been found. The resistivity behavior shows that the superconducting transition temperature lies in the range of 37–39 K with narrow transition width. The transport critical current density vary with films thickness and achieved highest value ∼1.2 × 106 A/cm2 at 20 K for 2.0 μm thick film and its values increase as thickness increases.
Complex conductivity in high-Tc single crystal superconductors
1994
The electromagnetic surface impedance of single crystal high-T c superconductors has been examined within the framework of the two-fluid model and the hypothesis that the em field modulates the partial concentrations of both normal and condensate fluids. A comparison with experimental data is reported
Resistivity and irreversibility line of (Hg0.9Re0.1)Ba2CaCu2O6+δ HTS thin films
2003
Abstract High-quality epitaxial (Hg 0.9 Re 0.1 )Ba 2 CaCu 2 O 6+ δ HTS thin films were successfully prepared by pulsed laser deposition (PLD) of Hg-free precursor material on (1 0 0)-oriented SrTiO 3 substrates with subsequent Hg vapour annealing. (Hg 0.9 Re 0.1 )Ba 2 CaCu 2 O 6+ δ HTS thin films exhibit sharp superconducting transitions at T c ≈122 K. The electrical resistance for c -axis oriented HgRe-1212 films has been studied as a function of temperature and dc magnetic fields up to 10 T parallel to the crystallographic c -axis. The irreversibility line for the HgRe-1212 has been deduced from the data and investigated as a function of reduced temperature T / T c . The result of the irr…
Effect of pressure on superconductivity in NaAlSi
2012
The ternary superconductor NaAlSi, isostructural with LiFeAs, the ``111'' iron pnictide superconductor, is investigated under pressure. The structure remains stable up to 15 GPa. Resistivity and susceptibility measurements show an increase of ${T}_{c}$ up to 2 GPa, followed by a decrease until superconductivity disappears at 4.8 GPa. Band structure calculations show that pressure should have a negligible effect on the electronic structure and the Fermi surface and thus the disappearance of superconductivity under pressure must have a different origin. We compare the electronic structure of NaAlSi under pressure with that of nonsuperconducting isostructural NaAlGe.
Normal and mixed state Hall effect in (Hg0.9Re0.1)Ba2CaCu2O6+δ fully textured HTSC thin films
2004
Abstract Temperature and magnetic field dependence of the Hall effect in the normal and mixed state of fully textured (Hg0.9Re0.1)Ba2CaCu2O6+δ (HgRe-1212) HTSC thin films prepared by laser ablation deposition have been studied. The longitudinal resistivity ρxx and Hall resistivity ρyx of HgRe-1212 superconductor thin films were measured for a wide range of magnetic fields from 125 mT to 12 T with the field perpendicular to the ab plane and the current in the ab plane. A sign change of the Hall resistivity is observed in fields below 3 T in the region close to the superconducting onset temperature. The temperature dependencies ρxx ∝ T and ρyx ∝ 1/T have been observed for HgRe-1212 thin films…