Ayumi Harasawa

A new compact electron spin polarimeter with a high efficiency

We have developed a new compact retarding-potential Mott spin polarimeter and achieved an efficiency of 1.9×10−4 for gold target operating in 25 keV. A novel design of the retarding field electron optics with 0.59 sr collection solid angle for scattered electrons was adopted based on Monte Carlo calculations for the spin-dependent electron scattering process and electron beam ray-tracing calculations. We have combined the new spin polarimeter with an angle-resolved photoelectron spectrometer and measured the spin- and angle-resolved photoelectron spectra and studied the spin-dependent electronic structure of Ni(110) along the ΓS line of its surface Brilluoin zone.

A new spin-polarized photoemission spectrometer with very high efficiency and energy resolution

A new spin- and angle-resolved photoemission spectrometer was developed adopting the very-low-energy-electron-diffraction (VLEED)-type spin polarimeter. The Fe(001)p(1x1)-O film grown on MgO(001) crystal for the VLEED target yields significantly high spin-resolving power, the effective Sherman function of 0.40+/-0.02, with long lifetime and stability compared to the conventional Fe(001) target. Under the favor of high resolving power, approximately 100 times higher efficiency than that of conventional Mott-type spin polarimeter, the figure of merit of 1.9+/-0.2x10(-2) was achieved. Owing to this high efficiency, high-energy resolution can be realized with this new spin-polarized photoemission spectrometer. The simplified ways of target preparation and revitalization make the VLEED spin polarimeter much more convenient and feasible for the spin-polarized photoemission spectroscopy.

VARIED LINE-SPACING PLANE GRATING MONOCHROMATOR FOR UNDULATOR BEAMLINE

A varied line‐spacing plane grating monochromator is installed at an undulator beamline BL‐19B of the Photon Factory. Small contribution of aberrations to image sizes at a focal plane of the varied line‐spacing plane grating is calculated with use of an optical path function. The largest resolving power obtained from a ray tracing is estimated to be 4600 at a photon energy of 1239.85 eV and 10 000 at 91.2 eV. Gas absorption spectra show the similar extent of resolution obtained by the ray tracing. A high brightness with a high resolution may be realized in this monochromator.

New soft X-ray beamline BL07LSU at SPring-8

The design and performance of a new soft X-ray beamline BL07LSU at SPring-8 are described. The combination of a novel segmented cross undulator and beamline monochromator has achieved high energy resolution (E/ΔE > 10000) and high photon flux [>1012 photons s−1 (0.01% bandwidth)−1] in the photon energy range 250–2000 eV with fully controllable polarization.

Valley spin polarization by using the extraordinary Rashba effect on silicon

The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. So far, however, such devices have not been realized due to the difficulty to polarize the valleys, which is an indispensable step to activate this degree of freedom. Here we show the formation of 100% spin-polarized valleys by a simple and easy way using the Rashba effect on a system with C3 symmetry. This polarization, which is much higher than those in ordinary Rashba systems, results in the valleys acting as filters that can suppress the backscattering of spin-charge. The present system is formed on a silicon substrate, and therefore opens a new avenue towards the realization of silicon spintronic devices with high efficiency.

Development of soft x-ray time-resolved photoemission spectroscopy system with a two-dimensional angle-resolved time-of-flight analyzer at SPring-8 BL07LSU

We have developed a soft x-ray time-resolved photoemission spectroscopy system using synchrotron radiation (SR) at SPring-8 BL07LSU and an ultrashort pulse laser system. Two-dimensional angle-resolved measurements were performed with a time-of-flight-type analyzer. The photoemission spectroscopy system is synchronized to light pulses of SR and laser using a time control unit. The performance of the instrument is demonstrated by mapping the band structure of a Si(111) crystal over the surface Brillouin zones and observing relaxation of the surface photo-voltage effect using the pump (laser) and probe (SR) method.

Element specific imaging by scanning tunneling microscopy combined with synchrotron radiation light

Microscopic surface images showing a distribution of a designated element was obtained by scanning tunneling microscopy combined with synchrotron radiation light. A tip current induced by photoirradiation is found to increase when the photon energy is just above the absorption edge of a sample element. From the photoinduced current measured during the tip scanning over the surface, element specific images were obtained. An estimated spatial resolution of the chemical imaging is less than 20nm, better than that achieved by photoemission electron microscopy.

Development and trial measurement of synchrotron-radiation-light- illuminated scanning tunneling microscope

Scanning tunneling microscope (STM) study is performed under synchrotron-radiation-light illumination. The equipment is designed so as to achieve atomic resolution even under rather noisy conditions in the synchrotron radiation facility. By measuring photoexcited electron current by the STM tip together with the conventional STM tunneling current, Si 2p soft-x-ray absorption spectra are successfully obtained from a small area of Si(111) surface. The results are a first step toward realizing a new element-specific microscope.

Spin texture in type-II Weyl semimetal WTe 2

We determine the band structure and spin texture of

Large out-of-plane spin polarization in a spin-splitting one-dimensional metallic surface state on Si(557)-Au

{\mathrm{WTe}}_{2}