Center for Correlated Electron Systems

Seminar

Two-dimensional-ARPES by momentum microscopy (M.M.) and soft X-ray resonance inelastic scattering (SXRIXS) in solids

September 16, 2015l Hit 1095
Date : October 20, 2015 16:00 ~ 17:00
Speaker : Prof. Shigemasa SUGA(Osaka University)
Location : Bldg. 19, Rm. 210

Spectroscopy in h=0.006-10 keV is now in a new phase. In the case of ARPES, almost two orders of magnitude higher detection efficiency is realized by use of a momentum microscope (M.M.) composed of a PEEM type input lens and an aberration-suppressed S-like tandem hemispherical deflection analyzers (HDAs). High resolutions can be achieved for kx, ky and EB. High detection efficiency is based on the possible full 2 steradian acceptance of photoelectrons and simultaneous (kx,ky) detections at 100100 to 200200 (kx,ky) points up to 2nd, 3rd Brillouin zones (BZs). Owing to PEEM, ARPES in m region is feasible.
Relative intensities at all (kx,ky) points are uniquely determined in contrast to the conventional 2D ARPES by a single HDA, where the sample must be rotated to cover a wide (kx,ky) region. Experimental results can directly be compared with calculated results of advanced theories up to the details including faint ARPES structures. Several typical results are discussed. In addition, the present status of extremely powerful spin-resolved 2D-ARPES by Spin-M.M. with 106 times higher spin detection efficiency than Mott detector will be briefly introduced.      
In contrast to rather surface sensitive ARPES for metals and semi-conductors, studies of electronic structures of insulators are much behind. Photon spectroscopy is well known to be applicable to insulators, providing bulk information. Various external perturbations such as magnetic field can also be applied. We have recently performed SXRIXS on various transition metal oxides. Studies of M-I-T (metal to  insulator-transition) can be an interesting subject of SXRIXS as demonstrated for V oxides. In the case of a CrO2 thin film, which is a ferromagnetic half metal covered by AF insulator Cr2O3 surface layer, ARPES could not reveal reliable electronic structures. We could, however, reveal bulk SXRIXS spectrum of CrO2 by comparing the results with that of bulk Cr2O3. We further observed clear circular dichroism in SXRIXS of CrO2 in an external magnetic field. Since the h resolution will be much improved in the SX region down to 10 meV in the near future, SXRIXS studies of H, E, as well as uniaxial stress effects will be very promising.