Sign reversal of hall coefficients near T_c in high-T_c YBa₂Cu₃O_y films

Hall coefficients and resistivities of YBa₂Cu₃O_y films in super-conducting mixed state have been measured at T near T_c. A sign reversal of Hall coefficients in superconducting mixed state is accounted for in terms of the induced electric field, E_ind = B × v_L/c. Eind occurs as a result of the motion of the flux-vortex; B the magnetic induction; v_L the resultant velocity of the flux vortex; and c the speed of light. The normal carriers were driven to one side of the sample by the transverse component E_ind,y (perpendicular to the transport current j_s). In a steady state, an electric field E_acc, yx would be developed by the accumulated charge carriers and the direction of the E_acc, yx is opposite to that of the Hall electric field in the normal state. A sign reversal of Hall coefficient would occur if E_acc, yx dominates in the transverse electric fields. This picture explains both p-type and n-type superconductors.