Thermoelectric Effect in Normal-State YBa ₂ Cu ₃ O _7-δ Films

Abstract

Abstract. -Signal pulses of several 100 volts and currents of several amperes have been obtained at lateral surface contacts on normal-state YBa2Cu307_^ 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 YB2^Cuz01_i giving rise to non-zero off-diagonal elements a a of the Seebeck tensor for films prepared with a tilt angle a between the film c-axis and the film surface normal. Large-tilt-angle films (up to a = 20°) could be grown on specially cut substrates and may be useful as almost wavelength-independent room temperature radiation detectors. In this letter experiments are reported which proof that the voltaic signals are purely of thermoelectric origin. A comparison of signals induced by laser irradiation, or, alternatively, by a thermal heat source, shows that the signal strength is solely related to the flow of thermal energy through the film. Furthermore, it is shown that the voltaic signals are proportional to the tilt angle a between the crystallographic film c-axis and the film surface normal, in accordance with the tensorial Seebeck effect.The thermoelectric field due to the Seebeck effect is given by where S is the Seebeck tensor and VT the temperature gradient. With respect to the coordinate system defined in fig. 1, the Seebeck tensor for YBa2Cu307_4> depending on the tilt angle a, and taking into account the values of main anisotropy of the thermopower Sc along the crystallographic c-axis and Sab in the (a, 6)-plane [7], is of the form

Anisotropy of the In-Plane and Out-of-Plane Resistivity and the Hall Effect in the Normal State of Vicinal-Grown YBa2Cu3O7−δ Thin Films

“…Several conditions are essential for reliable measurements of vicinal films. The required high level of crystallinity and epitaxial growth of the films sets an upper limit for the vicinal angle in YBCO [ 5 ]. Conversely, should not be too small to allow for an adequate sensitivity of the measurements.…”

“…A subsequently deposited YBCO films replicates the surface steps and grows epitaxially in a self-organized roof-tile manner. For tilt angles , a regular vicinal growth of the YBCO film and an approximately linear increase of the thermoelectric signal with has been reported [ 5 ].…”

Development of a transverse thermoelectric voltage effect in artificial SrTiO3/SrTi1−xNbxO3 epitaxial multilayer films with incline-oriented sublayers

“…The transverse thermoelectric (TTE) voltage effect was first found and demonstrated in a high T c superconductor YBa 2 Cu 3 O 7−δ thin film grown on miscut substrates, in which an unusually large transverse voltage was generated when laser was illuminated on the surface of this film. 1 And then, it was proved that the unique TTE voltage effect is a special TE phenomenon which utilized the non-vanishing components in the off-diagonal term of the Seebeck tensor S. 2,3 This effect has great potential versatile applications such as fast self-powered room temperature detectors, 4 waste heat recovery devices and laser power meters. [5][6][7][8] The pioneering researchers clarified that materials exhibiting the TTE voltage effect must have three essential factors: (i) specific crystallographic orientation (inclined crystal orientation), i.e.…”

“…1(a) for details], (ii) anisotropy of the Seebeck coefficient ΔS = S ab − S c ≠ 0 (here treated as a scalar), and (iii) establishment of the temperature gradient ∇ z T along the out-of-plane (z-axis) direction. Based on the above description, Lengfellner et al derived the TTE voltage U y along the transverse (y-direction) direction in the xy plane of the film, 3 which is given by…”