Singularity in the positive Hall coeffcient near pre‐onset temperatures in high‐Tc superconductors

Hall measurements using continuous extremely slow cooling and reheating rates as well as employing eqiulibrium point‐by‐point conventional techniques reveals a clear anomally in RH at pre‐onset temperatures near Tc in polycrystalline samples Y1Ba2Cu3O7 and Bi2Sr2Ca2Cu3O10. The anomaly has the appearance of a singularity of Dirac‐delta function which parallels earlier work on La1−xSrxCuO4. Recent single crystal work on the Bi‐containing high‐Tc superconductor is in accord with a clearcut anomaly. The singularity is tentatively interpreted to be associated (upon cooling) with initially the removal of positive holes from the hopping conduction system of the normal state such as from the increased concentration of bound virtual excitons due to increased exciton and hole lifetimes at low temperature. Subsequently the formation of Cooper pairs by mediation from these centers (bound‐holes) and/or bound excitons) may cause an ionization of these bound virtual excitons thereby re‐introducing holes and electrons in...