Search results for "conductivity"
showing 10 items of 1988 documents
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)$_2$…
Phase separation in superconducting and antiferromagneticRb0.8Fe1.6Se2probed by Mössbauer spectroscopy
2011
${}^{57}$Fe-M\"ossbauer studies of superconducting Rb${}_{0.8}$Fe${}_{1.6}$Se${}_{2.0}$ with ${T}_{C}$ $=$ 32.4 K were performed on single-crystalline and polycrystalline samples in the temperature range 4.2--295 K. They reveal the presence of 88% magnetic and 12% nonmagnetic Fe${}^{2+}$ species with the same polarization dependence of their hyperfine spectra. The magnetic species are attributed to the 16$i$ sites of the $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}\ifmmode\times\else\texttimes\fi{}1$ superstructure and the nonmagnetic Fe species to a nanosized phase observed in recent structural studies of superconducting K${}_{x}$Fe${}_{2\ensuremath{-}}$${}_{y}$Se${}_{2}$ systems ra…
Collective amplitude mode fluctuations in a flat band superconductor formed at a semimetal surface
2016
We study the fluctuations of the amplitude (i.e., the Higgs-Anderson) mode in a superconducting system of coupled Dirac particles proposed as a model for possible surface or interface superconductivity in rhombohedral graphite. This system also serves as a generic model of a topological semimetal with an interaction-driven transition on its surface. We show that the absence of Fermi energy and vanishing of the excitation gap of the collective amplitude mode in the model leads to a large fluctuation contribution to thermodynamic quantities, such as the heat capacity. As a consequence, the mean-field theory becomes inaccurate, indicating that the interactions lead to a strongly correlated sta…
Comment on “Nonlocal In-Plane Resistance due to Vortex-Antivortex Dynamics in High-TcSuperconducting Films”
1999
A Comment on the Letter by Y. Kopelevich et al., Phys. Rev. Lett. 80, 4048 (1998). The authors of the Letter offer a Reply.
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…
Josephson junctions and superconducting field effect transistors based on epitaxial Bi2Sr2Can-1CunO2(n+2) thin films
1998
Abstract Josephson junctions based on thin films of the Bi2Sr2Ca2Cu3O10+δ compound show IcRn products compatible with YBa2Cu3O7−δ samples. Using quasiparticle tunneling experiments we found evidence for a superconductor–insulator–superconductor tunneling process via localized states in the barrier. The Bi2Sr2CaCu2O8+δ compound is investigated regarding possible applications in superconducting field effect devices. We present thin films of four unit cells thickness that are superconducting at 58 K. An inverted metal–insulator–superconductor structure was prepared. From the modulation of the normal state resistance we estimate a carrier density of 7×1019 cm−3 for a superconducting sample. The…
Growth characteristics of sputter-deposited thin films
1996
Thin films of the heavy-fermion superconductor were deposited on various substrate materials in various orientations by means of a quasi-multilayer sputter process. Strongly (0001)-textured growth of the hexagonal compound was found for a uranium content in the range of 23% to 28% on sapphire and with perfect in-plane order on the latter substrate material. Atomic force microscopy and scanning electron microscopy revealed a Vollmer - Weber-like growth mode resulting in the development of large compressive strain in films on . As a result the electronic transport properties - in particular the temperature dependence of the resistivity - were strongly renormalized. Strong deviations from the …
Broadband infrared conductivity in an YBa2Cu3O6.7 thin film
2001
Infrared reflectivity of an oxygen reduced YBa2Cu3O6.7 thin film was measured in the frequency range 30 cm-1 < v < 7000 cm-1 and for temperatures 5 K < T < 300 K. At lower frequencies, 3 cm-1 < v < 40 cm-1, the complex conductivity σ*=σ1+iσ2 was measured directly using a transmission technique. Both data sets were combined to obtain the reflectivity in a broad frequency range and thus to improve substantially the quality of the Kramers-Kronig analysis at low frequencies. The analysis of the conductivity spectra reveals that the low-frequency spectral weight strongly depends on temperature directly above TC but saturates for T ≥ 150 K.
Superconductivity in high‐quality (Hg 0.9 Re 0.1 )Ba 2 CaCu 2 O 6+ δ HTSC thin films
2004
High-quality epitaxial (Hg0.9Re0.1)Ba2CaCu2O6+δ (HgRe-1212) HTS thin films were successfully prepared using pulsed laser deposition (PLD) of the Re0.1Ba2CaCu2O6+δ precursor and subsequent Hg vapor annealing. The thin films exhibit a sharp superconducting transition at Tc ≈ 120 K. The resistive transitions have been investigated in magnetic fields up to 6 T parallel and perpendicular to the c-axis. We have determined the activation energy of thermally activated flux-motion for both magnetic field orientations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)