Manipulating vortex motion by thermal and Lorentz force in high temperature superconductors

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By using thermal and Lorentz force, the vortex motion is successfully manipulated in the mixed state of underdoped La₂ ₋ ₓSrₓCuO₄ single crystals and optimally doped YBa₂Cu₃O₇ ₋ δ thin films. A conclusion is drawn that the strong Nernst signal above Tc is induced by vortex motion. In the normal state, in order to reduce the dissipative contribution from the quasiparticle scattering and enhance the signal due to the possible vortex motion, a new measurement configuration is proposed. It is found that the in-plane Nernst signal (H | | c) can be measurable up to a high temperature in the pseudogap region, while the Abrikosov flux flow dissipation can only be measured up to Tc. This may point to different vortices below and above Tc if we attribute the strong Nernst signal in the pseudogap region to the vortex motion. Below Tc the dissipation is induced by the motion of the Abrikosov vortices. Above Tc the dissipation may be caused by the motion of the spontaneously generated unbinded vortex-antivortex pairs.