Field-enhanced diamagnetism in intense magnetic field in the pseudogap state of the cuprate $\rm Bi_2Sr_2CaCu_2O_{8+δ}

Abstract

In hole-doped cuprates, Nernst experiments imply that the superconducting state is destroyed by spontaneous creation of vortices which destroy phase coherence. Using torque magnetometry on $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{r}}_2\mathrm{CaC}{\mathrm{u}}_2{\mathrm{O}}_{8+\delta }$, we uncover a field-enhanced diamagnetic signal $M$ above the transition temperature $T_c$ that increases with applied field to 32 Tesla and scales just like the Nernst signal. The magnetization results above $T_c$ distinguish $M$ from conventional amplitude fluctuations, and strongly support the vortex scenario for the loss of phase coherence at $T_c$.

4 pages, 4 figures. Added 1 new figure panel (Fig. 1b). Extended discussion of susceptibility anisotropy and pseudogap state. 6 new new Refs. Deleted 5 old ones. Phys. Rev. Lett., in press