铜氧化物超导体两能隙问题的电子拉曼散射理论研究

Theoretical research on two gaps in cuprate superconductors: an electronic Raman scattering study

电子拉曼实验表明在空穴型掺杂的铜氧化物超导体中存在两能隙行为,即在欠掺杂区,随着掺杂浓度的降低,一个能隙逐渐增大而且在超导转变温度以上仍然存在,而另一个能隙逐渐减小且在DDW态依然存在.解释两能隙行为非常重要因为它与赝能隙的机理密切相关.本文计算了超导序和d-density-wave(DDW)序竞争机理下相图上不同区域的电子拉曼谱,发现欠掺杂区能隙表现出两能隙行为,与实验一致.特别地,本文发现B1g峰对应能量由超导和DDW序共同决定,且随着掺杂浓度的降低而增大,在DDW态依然存在.而B2g峰只对超导序敏感,所以在正常态消失(即使存在DDW序).B1g和B2g两个通道拉曼峰与掺杂浓度和温度的依赖关系也与最近的实验相符.这些结果对赝能隙的竞争序机理是一个有力的支持.

Electronic Raman experiments have shown the presence of two types of gaps in hole-doped cuprate superconductors： one is the gap that increases with underdoping and survives in the pseudogap normal state and the other is the gap that traces the superconducting dome and disappears above the transition temperature. This two-gap behavior is important in that it is related to the mechanism of the pseudogap. By calculating the electronic Raman spectra we show that this behavior is consistent with the picture in which the d-wave superconducting （SC） order and d-density-wave （DDW） order compete in the phase diagram. In particular,the energy of the B1g peak is determined by both the SC and the DDW orders, increases with underdoping and survives in the DDW normal state. On the other hand,the B2g peak is shown to be sensitive to the SC order alone,and thus vanishes in the normal state （even if in the presence of the DDW order）. The doping dependence and the temperature dependence of the peak energies in the two channels accord nicely with recent experimental results,which strongly supports the competing-order point of view for the superconducting and pseudogap phases.