Preparation of Tl-Ba-Ca-Cu-O thin films by diffusion of Tl into laser evaporated Ba2Ca2Cu3Ox films

Preparation of superconducting Tl-Ba-Ca-Cu-O thin films by diffusion of Tl into laser evaporated Ba₂Ca₂Cu₃O_x thin films is reported. From a sintered Ba₂Ca₂Cu₃O_x bulk sample we prepared using a pulsed Nd:YAG laser, Ba-Ca-Cu-O thin films on sapphire and SrTiO₃ single-crystal substrates. Subsequently the films were loaded with Tl by simultaneously annealing the films together with a sintered Tl₂Ba₂Ca₂Cu₃O₁₀ sample both enclosed in a small stainless steel box; in our procedure Tl contamination was reduced to a minimum. T_c values near 100 K and critical currents of 5·10³ A/cm² at 77 K were obtained.     

Transverse Thermoelectricity in a Tilted Metallic Multilayer Structure

Thermoelectricity is investigated in a material designed to show anisotropic transport properties: Copper/constantan/copper multilayer structures were prepared by sintering of a compressed stack of alternating foils of these materials and are described by effective in-plane properties and for the Seebeck-coefficient and the thermal conductivity along the layers, and out-of-plane-properties and along the stack axis. Samples in form of thin slabs prepared by cutting the stack obliquely to the stack axis showed thermoelectric fields transverse to temperature gradients across the slab due to off-diagonal elements in the Seebeck-tensor, and may be used as devices for detection of laser radiation.     

Step-like growth of Bi2Sr2CaCu2O8 films on off axis oriented (001) SrTiO3

High-quality Bi₂Sr₂CaCu₂O₈ (BSCCO) films were grown by means of pulsed-laser deposition on 10° off-axis oriented (001) SrTiO₃ substrates. The films exhibit a step-like morphology and they are properly oriented along the (001) direction. Their normal-state resistivity measured along the tilt (off-axis (100) direction of the substrate) was, typically, 260 times higher than that along the (010) direction. Such films reveal a transverse Seebeck-effect which significantly exceeds that observed with YBa₂Cu₃O₇ (YBCO).     

Far-infrared laser spectroscopy of phonon difference band absorption in TlCl

Far-infrared laser radiation is used to study the lattice absorption of a TlCl crystal over a large temperature range. We found a strong absorption band caused by phonon difference processes where longitudinal and transverse acoustic phonons with wave vectors at the Brillouin zone boundary are involved.     

Far infrared reflectance of a mixed phase Y-Ba-Cu-O superconductor

We have studied the far infrared reflectance of the mixed phase superconductor Y_1.2Ba_0.8CuO_4–y. The reflectance spectrum shows sharp phonon resonances and an electronic contribution that we attribute to reflection at a mesh-like structure of the conducting phase embedded in nonconducting material; in comparison, the reflectance of single phase superconducting material is mainly determined by the dynamical electronic conductivity.     

Homogeneously broadened far-infrared absorption line due to the E → 2A transition of excited chromium ions in ruby

By use of far-infrared laser spectroscopy, we have found that for a high-quality ruby crystal at low temperature, the absorption line due to the electronic transition between the excited states $\text{E}\text{(}{}^2\text{E)}$ and $\text{2}\text{A}\text{(}{}^2\text{E) of Cr}{}^{\mathrm{3+}}$ ions is homogeneously broadened. From the linewidth (0.011 cm^-1) the lifetime of the 2ā level against emission of 29 cm^-1 phonons is obtained.     

Nernst effect in Tl-Ba-Ca-Cu-O superconducting films due to infrared laser heating

A Nernst effect has been observed in a high temperature superconductor for the first time. Irradiating superconducting Tl–Ba–Ca–Cu–O thin films by short pulses of a TEA-CO₂ laser, a photovoltaic signal is detected perpendicular to a magnetic field applied parallel to the film surface. The signal is attributed to magnetic flux line depinning and flux line transport driven by the laser induced temperature gradient. The results are described by thermal flux line activation leading to a calculated distribution of pinning energies from 100 K to 4000 K.     

Far-infrared reflectivity of sintered YBa2Cu3O7 in the normal and superconducting state

We report on a study of the far-infrared reflection for a sintered YBa₂Cu₃O₇ sample that contained a large portion of preferentially oriented crystallites with thea–b plane parallel to the surface and that showed extraordinary high far-infrared reflectivity. From experimental reflection data we determined, by Kramers-Kronig analysis, the dynamical conductivity and extracted the contributions due to free charge carriers and phonons, respectively. We find evidence for an anomalous behavior of the dynamical conductivity at temperatures aboveT _c ; the dynamical conductivity increases strongly for temperatures approachingT _c and is strongly frequency dependent. By use of the Mattis-Bardeen theory we obtain an estimate for the superconducting energy gap of 2/kT _c 4.6 (forTT _c ). We find that the lowest frequency infrared-active phonon mode is less damped in the superconducting state than in the normal state.     

Far infrared response of thin film Bi2Sr2CaCu2O8 using a free electron laser

The far infrared response of granular thin-film Bi₂Sr₂CaCu₂O₈ superconductor has been investigated using long (5 s) but sharply truncated free electron laser pulses in the frequency range between 50 cm^–1 and 125 cm^–1. Under constant current bias, a fast response and a slow bolometric signal component could be identified in this energy range, which is below the BCS energy gap ( 200 cm^–1). Measurements of the power dependences of the signal voltages showed that both the fast and the thermal responses are consistent with the predictions of the resistively shunted Josephson junction model.