Thermal Variations of Magnetic Excitation Spectrum in Slightly Overdoped Bi2.1Sr1.9CaCu2O8+δ

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We measured the inelastic neutron scattering of slightly overdoped high-$T_{\text{c}}$ superconductor Bi2.1Sr1.9CaCu2O8+δ (Bi2212: $T_{\text{c}}=86.2 \pm 3.5$ K). We observed the enhancement of a commensurate peak at $(1/2,1/2,-14)$ and $\omega\sim 34$ meV in the superconducting state, which is similar to the previously reported resonance peak in the YBa2Cu3O6+x (YBCO) and Bi2212 systems. However, the temperature dependence above $T_{\text{c}}$ is different: substantial resonance spectral weight remains above $T_{\text{c}}$, and shows a sharp drop at $T\sim 200$ K, which roughly agrees with the onset of the pseudogap ($T^{*}$). We propose that the different thermal variations of the magnetic excitations in high-$T_{\text{c}}$ superconductors can be understood in terms of the pseudogap phase and redistribution of the magnetic spectral weight across $T_{\text{c}}$ and $T^{*}$.
2009-07-15