Development of high-energy resolution photoemission spectrometer and study of the electronic structure near the Fermi level

我们在东北大学建造了一台高能量分辨率光电发射光谱仪，它具有直径300 mm的半球形电子能量分析器和高亮度放电灯。光谱仪的基准压力小于2x 10 ^<-11>Torr。使用闭合循环He低温恒温器将样品冷却至8 K。我们已经实现了约12 meV的能量分辨率，这是在同一水平的世界纪录。利用这种光电发射光谱仪，我们研究了各种有趣的材料和现象，如下所示。1. Bi_2Sr_2CaCu_2O_8高温超导体超导能隙及其各向异性的直接观测和dx^2-y^2对称性的确定2.在非铜氧化物层状钙钛矿超导体Sr_2RuO_4中观察到扩展的VHS，它与在铜氧化物高温超导体中观察到的扩展的VHS十分相似。3.第一次直接观察到由于CeB_6.4晶体场分裂而产生的卫星结构。稀土氧化物铈的磁相变研究。首次直接观察到了CeSb的费米面拓扑结构随磁相变的变化。5. UPd_2Al_3.6中E_F附近定域和巡游5 f态的直接识别及其温度变化准一维有机导体DCNQI-Cu的Peierls能隙的观测和E_F.7附近电子态的Tomonaga-Luttinger特征的确定.第一次直接观察到磁铁矿Fe_3O_4中Verwey跃迁引起的能隙。

We have constructed a high-energy resolution photoemission spectrometer at Tohoku University, which has a 300-mm-in-diameter hemispherical electron energy analyzer and a highly bright discharging lamp. The base pressure of the spectrometer is less than 2x10^<-11> Torr. The sample is cooled down to 8 K using a closed-cycle He cryostat. We have achieved the energy-resolution of about 12 meV,which is on the same level of the world record. With this photoemission spectrometer, we have investigated various interesting materials and phenomena as shown in the following. 1. Direct observation of superconducing gap and its anisotropy in Bi_2Sr_2CaCu_2O_8 high-Tc superconductor and identification of the dx^2-y^2 symmetry. 2. Observation of an extended van-Hove sigularity (VHS) in a non-cuprate layred perovskite superconductor Sr_2RuO_4, which is quite similar to the extended VHSs observed in cuprate high-Tc superconductors. 3. First direct observation of a satellite structure due to the crystal-field splitting in CeB_6.4. Study of the magnetic phase transition of cerium monopnictides. The first direct observation of the change of the Fermi surface topology of CeSb accompanied by the magnetic phase transition. 5. Direct identification of localized and itinerant 5f states near E_F and its temperature variation in UPd_2Al_3.6. Observation of a Peierls gap of a quasi-1D organic conductor DCNQI-Cu and identification of the Tomonaga-Luttinger character of the electronic states near E_F.7. First direct observation of an energy gap in magnetite Fe_3O_4 due to the Verwey transition.