Tunneling Spectroscopy Study on the Origin of Coherence of Election-Pans m High-Tc Superconductor

在本研究中，Bi2212的隧道光谱测量证实，小赝隙(SPG)开始在d波超导体的平均场临界温度附近生长，并顺利地连接到超导(SC)态的能隙。在Bi2212上的ARPES测量表明，在T~T_c，SPG的发展使费米线变成以(π/2，π/2)为中心的所谓的节点费米弧。在高T_c铜酸盐中，节点费米弧上的移动空穴具有很高的面内迁移率，当它们开始形成对时，有望驱动SPG区的超导电性。这是因为具有高面内迁移率的移动载流子的配对将在导致超导的过程中起到关键作用。事实上，本研究表明，在只有节点费米弧上的空穴与超导电性有关的条件下，可以定量地解释La214的SPG区U(0)的显著降低。这与实验结果一致，即隧道谱和ARPES谱的相干峰在SPG区相当模糊，反映了费米线反节点处准粒子的性质。通过扫描隧道显微镜和光谱(STM/STS)在Bi2212上的测量，我们还排除了没有相分离导致U(0)显著抑制的可能性，至少在感兴趣的SPG区域是这样。因此，我们得出结论，节点费米弧上的移动空穴导致了SPG区的超导。

In the present study, it was confirmed in the tunneling spectroscopy measurements on Bi2212 that the small pseudogap (SPG) starts to grow around the mean-field critical temperature of d-wave superconductors, and connects smoothly to the energy gap of the superconducting (SC) state. The development of SPG reduces the Fermi line into the so-called nodal Fermi arc centered near (π/2,π/2) at T〜T_c, as was revealed by ARPES measurements on Bi2212. In high T_c-cuprates, mobile holes on the nodal Fermi arcs have high in-plane mobility, and are expected to drive the superconductivity in the SPG regime when they start to form pairs. This is because the pairing of mobile carriers with high in-plane mobility will play a crucial role in causing the superconductivity. In fact, it was demonstrated in the present study that the remarkable reduction of U(0) in the SPG regime of La214 can be explained quantitatively on condition that only holes on the nodal Fermi arcs will be associated with the superconducutivity. This is consistent with the experimental result that the coherence peaks of both tunneling and ARPES spectra, reflecting the nature of quasi-particles over the antinodal parts of the Fermi line, are rather smeared in the SPG regime. By scanning tunneling microscopy and spectroscopy (STM/STS) measurements on Bi2212, we also ruled out the possibility that no phase separation causes the remarkable suppression of U(0), at least, in the SPG regime of interest. Thus, we concluded that mobile holes on the nodal Fermi arcs cause the superconductivity in the SPG regime.