Superconducting Tl-Ca-Ba-Cu-O thin films prepared by diffusion of Tl into an excimer laser ablated Ca2Ba2Cu3Ox film

In this paper we present a description of the Nernst electric field E generated by forced flux tube motion due to a temperature gradient backward differenceT. Depending on the value of backward differenceT with respect to a critical gradient backward differenceTcrit, we find for backward differenceT/backward differenceTcritmuch less-than 1 a regime E ∝ backward differenceT, in close analogy to the regime of thermally activated flux flow in transport current measurements (characterized by an electric field proportional to the transport current). The theory for backward differenceT<backward differenceTcrit is applied to an analysis of experimental results obtained for polycrystalline Tl2Ba2CaCu2Ox films. From the temperature dependence of the Nernst field we derive activation energies for flux depinning

Thermoelectric Effect in Normal-State YBa2Cu3O7-δ Films

Signal pulses of several 100 volts and currents of several amperes have been obtained at lateral surface contacts on normal-state YBa2Cu3O7-δ films in response to pulsed laser irradiation. The signals are shown to be of thermoelectric origin. Thermoelectric fields transverse to the laser-induced temperature gradient are due to the anisotropy of the thermopower in YBa2Cu3O7-δ giving rise to non-zero off-diagonal elements Sij propto α of the Seebeck tensor for films prepared with a tilt angle α between the film c-axis and the film surface normal. Large-tilt-angle films (up to α = 20°) could be grown on specially cut substrates and may be useful as almost wavelength-independent room temperature radiation detectors

Heat propagation in high Tc films investigated by optical response measurements

The optical response of granular Tl‐Ba‐Ca‐Cu‐O films has been used to investigate thermal properties of the films. An analysis of the response using a heat transfer model yields a thermal diffusivity D=10−3 cm2/s at 150 K which rises to 6×10−3 cm2/s at a temperature of 30 K and allows for an estimation of the boundary resistance Rbd≊10−3 K cm2/W between film and substrate. The dependence of the response time on film thickness obtained from the heat transfer model is compared with published data indicating that in many experiments the observed response is mainly bolometric in origin

Characterization of YBCO films by torque magnetometry

We report on the observation of a thermopile effect caused by laser radiation heating in thin films of high-Tc material. The thermopile effect is due to a transverse Seebeck effect. The transverse Seebeck effect is observable first because of the anisotropy of YBa2Cu3O7−δ, and secondly because it is possible to grow off-axis epitaxial films. The thermopile effect can be used for developing detectors for laser radiation

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

Normal state YBa2Cu3Ox films: A new fast thermal detector for far infrared laser radiation with a uniform wavelength response

Room temperature YBa2Cu3Ox films, epitaxially grown on oriented substrates, are shown to be effective detectors of far infrared laser pulses. The photovoltage arises due to an anisotropic material thermopower subject to the thermal gradient arising from the radiation heating. For a 40 nm thick film we have measured a responsivity of (5±2)×10−7 V/W, independent of frequency in the range from 20 to 110 cm−1. The response time is limited by thermal diffusion, giving a 200 MHz detector bandwidth and a noise equivalent power of 3.6×10−3 W(Hz)−1/2 for this film thickness. Due to their large area (1 cm2) and uniform spectral response, such films may be useful replacements for pyroelectric power/energy meters