YBa_2Cu_3O_(7-δ)超导体的低温X射线衍射研究

Low Temperature X-Ray Diffraction Study of YBa_2Cu_3O_(7-δ) Superconductor

测量了氧含量最佳掺杂的YBa2Cu3O7-δ(YBCO)超导体的低温X射线衍射。对于最佳掺杂样品,高精度的X衍射可以发现其(013),(103),(113)和(020)等衍射峰的d值的温度关系在Tc=91K附近有细微的异常,同时(103)、(013)和(113)等衍射峰积分强度均在Tc附近出现明显的反常变化。例如,(103)和(013)的峰强度先有所下降,然后又增加,而在Tc处形成一个极小值。衍射峰强度的变化通过Debye-Waller因子反映出晶格振动频率等变化,在此基础上探讨了与CuO2平面有关的声子频率的可能变化。结果说明,即使在非传统的d-波超导体中,晶格振动在Tc附近也可能存在可观测的变化,声子在高温超导机制中究竟起了什么作用值得深究。

The measurement of low temperature X-ray diffraction was performed on the optimally doped YBa2Cu3O7-δ. Very tiny anomalies can be observed in the temperature dependence of the d values of the （103）, （013）, （113） and （020） reflection peaks, and clear anomalous changes in the integrated intensities （I.I.） of the （013） plus （103）, and （113） reflection peaks were observed around Tc of 91 K. For example, the I.I. of the （103） and （013） peaks first decreases just above Tc, and then decreases to show a minimum around Tc. The change of the I.I. reflects the change in the phonon frequency through a Debye-Waller factor. The possible change of the phonon frequency was discussed based on our observations. Our results indicate that there could be observable changes in the lattice dynamics at Tc even for the non-conventional d-wave pairing superconductors. The role of phonons in the high-Tc superconducting mechanism should be taken into account.