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

点击翻译按钮获取中文摘要

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.