Strongly nonlinear magnetization above $T_c$ in $\rm Bi_2Sr_2CaCu_2O_{8+\delta}$

TL;DR

This study reveals that in Bi2Sr2CaCu2O8+δ, magnetization above Tc exhibits strong non-linearity and divergence in susceptibility, indicating the persistence of pair condensates and London rigidity in the pseudogap regime.

Contribution

The paper provides detailed high-resolution magnetometry evidence of nonlinear magnetization and diverging susceptibility above Tc, supporting the existence of a surviving pair condensate in cuprate superconductors.

Findings

Magnetization above Tc is strongly nonlinear in magnetic field.

Susceptibility diverges as temperature approaches Tc from above.

Magnetization follows a non-analytic H^{1/δ} form with temperature-dependent δ.

Abstract

Using high-resolution magnetometry we have investigated in detail the magnetization $M$ above the critical temperature $T_c$ in $\rm Bi_2Sr_2CaCu_2O_{8+\delta}$. In a broad range of temperature $T$ above $T_c$, we find that $M(T,H)$ is strongly non-linear in the field $H$. We show that as $T\to T_c$, the susceptibility $\chi(T,H)$ diverges to very large values ($\chi \to$ -1) if measured in weak $H$. In addition, $M(H)$ displays an anomalous non-analytic form $M\sim H^{1/\delta}$ in weak fields with a strongly $T$-dependent exponent $\delta(T)$. These features strongly support the proposal that, above $T_c$, the pair condensate survives to support significant London rigidity.