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The spin texture of the spin-split surface states on Bi(111) has been comprehensively investigated by high energy and angular resolution spin- and angle-resolved photoelectron spectroscopy. A large out-of-plane spin component that alternately changes its sign is clearly observed. There is no evidence for peculiar polarization oscillation of the in-plane spin component, which was suggested to be due to breaking of the time-reversal symmetry in a previous report [A. Takayama et al., Phys. Rev. Lett. 106, 166401 (2011)]. The observed band structure and spin polarization are well reproduced by the $kp$ model Hamiltonian considering the ${C}_{3v}$ crystal symmetry, and the in-plane polarization variation at the different $k$ points can be understood by the photoemission final-state effect.

We use bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy and investigate bulk electronic structures of Ce monopnictides (CeX; X=P, As, Sb and Bi). By exploiting a paradigmatic study of the band structures as a function of their spin-orbit coupling (SOC), we draw the topological phase diagram of CeX and unambiguously reveal the topological phase transition from a trivial to a nontrivial regime in going from CeP to CeBi induced by the band inversion. The underlying mechanism of the topological phase transition is elucidated in terms of SOC in concert with their semimetallic band structures. Our comprehensive observations provide a new insight into the band topology hidden in the bulk of solid states., Comment: 5 pages, 4 figures

We report simple preparation of viscoelastic gels induced by multiple intermolecular interactions using low-molecular-weight aromatic sulfonates and alkylammoniums in water. The flow properties of ...

We report an angle-resolved photoemission (ARPES) study of $\beta$-YbAlB$_4$, which is known to harbor unconventional quantum criticality (QC) without any tuning. We directly observe a quasiparticle peak (QP), emerging from hybridization, characterized by a binding energy and an onset of coherence both at about 4 meV. This value conforms with a previously observed reduced Kondo scale at about 40 K. Consistency with an earlier study of carriers in $\beta$-YbAlB$_4$ via the Hall effect strongly suggests that this QP is responsible for the QC in $\beta$-YbAlB$_4$. A comparison with the sister polymorph $\alpha$-YbAlB$_4$, which is not quantum critical at ambient pressure, further supports this result. Indeed, within the limitation of our instrumental resolution, our ARPES measurements do not show tangible sign of hybridization in this locally isomorphic system, while the conduction band we observe is essentially the same as in $\beta$-YbAlB$_4$. We therefore claim that we identified by ARPES the carriers responsible for the QC in $\beta$-YbAlB$_4$. The observed dispersion and the underlying hybridization of this QP are discussed in the context of existing theoretical models., Comment: 12 pages including Supplemental Materials, with 5 figures and 3 supplemental figures

Spin-resolved band structures of $L$-gap surface states on Ag(111) and Cu(111) are investigated by spin- and angle-resolved photoelectron spectroscopy (SARPES) with a vacuum-ultraviolet laser. The observed spin textures of the Ag(111) and Cu(111) surface states agree with that expected by the conventional Rashba effect. The Rashba parameter of the Ag(111) surface state is estimated quantitatively and is $80%$ of that of Cu(111). The surface-state wave function is found to be predominantly of even mirror symmetry with negligible odd contribution by SARPES using a linearly polarized light. The results are consistent with our theoretical calculations for the orbital-resolved surface state.

We theoretically show that a single free electron in circular motion radiates an electromagnetic wave possessing helical phase structure, which is closely related to orbital angular momentum carried by it. We experimentally demonstrate it by interference and double-slit diffraction experiments on radiation from relativistic electrons in spiral motion. Our results indicate that photons carrying orbital angular momentum should be created naturally by cyclotron/synchrotron radiations or Compton scatterings in various situations in cosmic space. We propose promising laboratory vortex photon sources in various wavelengths ranging from radio wave to gamma-rays.

Spin states of photoelectrons excited from spin-polarized surface states of Bi(111) surfaces are theoretically studied. The electronic states with a mirror symmetry are focused on in particular. We present a method for calculating spin expectation values of photoelectrons using results of density-functional methods in the plane-wave basis. We show that the free-electron approximation for final states is not sufficient for explaining an experimental result obtained in spin- and angle-resolved photoelectron spectroscopy. We point out two effects of the time-reversal symmetry in photoelectron emission. One is that the out-of-plane component of spin orientation is reversed to that of the time-reversed state. This property may be used for distinguishing the orientation of samples by shedding light with polarizations that break the mirror symmetry. Another is the asymmetry in photoemission intensity between an initial state and its time-reversed state due to the breaking of the time-reversal symmetry intrinsic in the photoemission process.

The Dirac-cone surface states of topological insulators are characterized by a chiral spin texture in k-space with the electron spin locked to its parallel momentum. Mid-infrared pump pulses can induce spin-polarized photocurrents in such a topological surface state by optical transitions between the occupied and unoccupied part of the Dirac cone. We monitor the ultrafast dynamics of the corresponding asymmetric electron population in momentum space directly by time- and angle-resolved two-photon photoemission (2PPE). The elastic scattering times of 2.5 ps deduced for Sb2Te3 corresponds to a mean-fee path of 0.75 μm in real space.

We present energy-momentum mapping of surface Dirac photocurrent in the topological insulator Sb$_2$Te$_3$ by means of time- and angle-resolved two-photon photoemission spectroscopy combined with polarization-variable mid-infrared pulse laser. It is demonstrated that the direct optical transition from the occupied to the unoccupied part of the surface Dirac-cone permits the linear and circular photogalvanic effect which thereby enables us to coherently control the surface electric-current by laser polarization. Moreover, the surface current mapping directly visualizes ultrafast current dynamics in the Dirac cone in the time domain. We unravel the ultrafast intraband relaxation dynamics of the inelastic scattering and momentum scattering separately. Our observations pave the pathway for coherent optical control over surface Dirac electrons in topological insulators.

UTokyo Research掲載「バレートロニクス材料の提案」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/a-proposed-valleytronics-material/, UTokyo Research "A proposed valleytronics material" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/a-proposed-valleytronics-material/

We use spin- and angle-resolved photoemission spectroscopy (SARPES) combined with polarization-variable laser and investigate the spin-orbit coupling effect under interband hybridization of Rashba spin-split states for the surface alloys Bi/Ag(111) and Bi/Cu(111). In addition to the conventional band mapping of photoemission for Rashba spin-splitting, the different orbital and spin parts of the surface wavefucntion are directly imaged into energy-momentum space. It is unambiguously revealed that the interband spin-orbit coupling modifies the spin and orbital character of the Rashba surface states leading to the enriched spin-orbital entanglement and the pronounced momentum dependence of the spin-polarization. The hybridization thus strongly deviates the spin and orbital characters from the standard Rashba model. The complex spin texture under interband spin-orbit hybridyzation proposed by first-principles calculation is experimentally unraveled by SARPES with a combination of p- and s-polarized light., 6 pages, 4 figures

We investigate the surface electronic structures of polar 1T'-MoTe2, the Weyl semimetal candidate realized through the nonpolar-polar structural phase transition, by utilizing the laser angle-resolved photoemission spectroscopy (ARPES) combined with first-principles calculations. Two kinds of domains with different surface band dispersions are observed from a single-crystalline sample. The spin-resolved measurements further reveal that the spin polarizations of the surface and the bulk-derived states show the different domain-dependences, indicating the opposite bulk polarity. For both domains, some segment-like band features resembling the Fermi arcs are clearly observed. The patterns of the arcs present the marked contrast between the two domains, respectively agreeing well with the slab calculation of (0 0 1) and (0 0 -1) surfaces. The present result strongly suggests that the Fermi arc connects the identical pair of Weyl nodes on one side of the polar crystal surface, whereas it connects between the different pairs of Weyl nodes on the other side., 13 pages, 4 figures

Interference of spin-up and spin-down eigenstates depicts spin rotation of electrons, which is a fundamental concept of quantum mechanics and presents technological challenges for the electrical spin manipulation. Here, we visualize this coherent spin physics through laser spin- and angle-resolved photoemission spectroscopy on a spin-orbital entangled surface state of a topological insulator. It is revealed that the linearly polarized laser can simultaneously excite spin-up and spin-down states, and these quantum-spin bases are coherently superposed in photoelectron states. The superposition and the resulting spin rotation is manipulated by the direction of the laser field. Moreover, the full observation of the spin rotation displays the phase of the quantum states. This presents a new facet of laser-photoemission technique for investigation of quantum-spin physics, opening new possibilities in the field of quantum spintronic applications.

Photoemission established KHgSb as a nonsymmorphic topological insulator, which hosts hourglass-shaped surface states., Topological insulators (TIs) host novel states of quantum matter characterized by nontrivial conducting boundary states connecting valence and conduction bulk bands. All TIs discovered experimentally so far rely on either time-reversal or mirror crystal symmorphic symmetry to protect massless Dirac-like boundary states. Several materials were recently proposed to be TIs with nonsymmorphic symmetry, where a glide mirror protects exotic surface fermions with hourglass-shaped dispersion. However, an experimental confirmation of this new fermion is missing. Using angle-resolved photoemission spectroscopy, we provide experimental evidence of hourglass fermions on the (010) surface of crystalline KHgSb, whereas the (001) surface has no boundary state, in agreement with first-principles calculations. Our study will stimulate further research activities of topological properties of nonsymmorphic materials.

The measured electronic structure of Nd${}_{2}$Ir${}_{2}$O${}_{7}$ through its metal-insulator transition indicates an unusual Slater to Mott crossover with reducing temperature. This constrains theoretical models which suggest this material has topologically protected magnetic states.

We combine tunable midinfrared (mid-IR) pump pulses with time- and angle-resolved two-photon photoemission to study ultrafast photoexcitation of the topological surface state (TSS) of Sb_{2}Te_{3}. It is revealed that mid-IR pulses permit a direct excitation from the occupied to the unoccupied part of the TSS across the Dirac point. The novel optical coupling induces asymmetric transient populations of the TSS at ±k_{∥}, which reflects a macroscopic photoexcited electric surface current. By observing the decay of the asymmetric population, we directly investigate the dynamics of the long-lived photocurrent in the time domain. Our discovery promises important advantages of photoexcitation by mid-IR pulses for spintronic applications.

Spin polarized surface states of Bi(111) film fabricated on Si(111) surface have been investigated by means of high-resolution spin-resolved photoemission spectroscopy. In contrast to the Rashba-type spin-split ideal two-dimensional electron gas in which the spin orientation is locked in-plane and tangential to the electron momentum, significant out-of-plane spin polarization has been observed in the surface states which are forming the hole pocket. The out-of-plane spin polarization is anti-symmetric with respect to Γ-M line and vanishes at the line suggesting that the out-of-plane polarization is derived from the three-fold symmetry of the Bi crystal. The magnitude of the out-of-plane spin components depends on the condition of Bi film fabrication, which is consistent with the recent x-ray diffraction results suggesting the existence of double domains rotating 180° each other on the Bi(111) film grown on Si(111) surface. [DOI: 10.1380/ejssnt.2012.153]

A monolithic lens-window-prism (LWP) device, made of lithium fluoride (LiF) or magnesium fluoride (MgF2), was proposed. When either of the devices was fixed onto one end of a gas cell filled with Xe, it becomes a “wedge-crystal”-like device and was used to convert a 1 MHz femtosecond 347 nm laser to its third harmonic radiation at 10.7 eV. This led to an improved beam profile and a more compact and less lossy configuration. A stable output power of ∼11 μW was demonstrated for 2 h using LiF-LWP. In addition, MgF2-LWP was also verified for its practicability at 10.7 eV.

We determine the band structure and spin texture of WTe2 by spin- and angle-resolved photoemission spectroscopy (SARPES). With the support of first-principles calculations, we reveal the existence of spin polarization of both the Fermi arc surface states and bulk Fermi pockets. Our results support WTe2 to be a type-II Weyl semimetal candidate and provide important information to understand its extremely large and nonsaturating magnetoresistance., Comment: Published version

We describe a spin- and angle-resolved photoelectron spectroscopy (SARPES) apparatus with a vacuum-ultraviolet (VUV) laser ($h\nu$= 6.994 eV) developed at the Laser and Synchrotron Research Center at the Institute for Solid State Physics, The University of Tokyo. The spectrometer consists of a hemispherical photoelectron analyzer equipped with an electron deflector function and twin very-low-energy-electron-diffraction-type spin detectors, which allows us to analyze the spin vector of a photoelectron three-dimensionally with both high energy and angular resolutions. The combination of the high-performance spectrometer and the high-photon-flux VUV laser can achieve an energy resolution of 1.7 meV for SARPES. We demonstrate that the present laser-SARPES machine realizes a quick SARPES on the spin-split band structure of a Bi(111) film even with 7 meV energy and 0.7$^\circ$ angular resolutions along the entrance-slit direction. This laser-SARPES machine is applicable to the investigation of spin-dependent electronic states on an energy scale of a few meV., Comment: 15 pages, 5 figures

A Weyl semimetal is a new state of matter that host Weyl fermions as quasiparticle excitations. The Weyl fermions at zero energy correspond to points of bulk band degeneracy, Weyl nodes, which are separated in momentum space and are connected only through the crystal's boundary by an exotic Fermi arc surface state. We experimentally measure the spin polarization of the Fermi arcs in the first experimentally discovered Weyl semimetal TaAs. Our spin data, for the first time, reveal that the Fermi arcs' spin polarization magnitude is as large as 80% and possesses a spin texture that is completely in-plane. Moreover, we demonstrate that the chirality of the Weyl nodes in TaAs cannot be inferred by the spin texture of the Fermi arcs. The observed non-degenerate property of the Fermi arcs is important for the establishment of its exact topological nature, which reveal that spins on the arc form a novel type of 2D matter. Additionally, the nearly full spin polarization we observed (~80%) may be useful in spintronic applications., 4 figures, 15 pages

Topological insulators (TIs) are a new quantum state of matter. Their surfaces and interfaces act as a topological boundary to generate massless Dirac fermions with spin-helical textures. Investigation of fermion dynamics near the Dirac point is crucial for the future development of spintronic devices incorporating topological insulators. However, research so far has been unsatisfactory because of a substantial overlap with the bulk valence band and a lack of a completely unoccupied Dirac point (DP). Here, we explore the surface Dirac fermion dynamics in the TI Sb$_2$Te$_3$ by time- and angle-resolved photoemission spectroscopy (TrARPES). Sb$_2$Te$_3$ has a DP located completely above the Fermi energy ($E_F$) with an in-gap DP. The excited electrons in the upper Dirac cone stay longer than those below the Dirac point to form an inverted population. This was attributed to a reduced density of states (DOS) near the DP ., Comment: 10 pages, 3 figures. Accepted for publication (submission date: March 11, 2015)

We report the electric transport study of the three-dimensional topological insulator ${\text{TlBiSe}}_{2}$. We propose an analysis procedure which determines the two-carrier transport properties in precision. Magnetotransport properties reveal a multicarrier conduction of high- and low-mobility electrons in the bulk, which is in qualitative agreement with angle-resolved photoemission results [K. Kuroda et al., Phys. Rev. Lett. 105, 146801 (2010)]. The temperature dependence of the Hall mobility is explained well with the conventional Bloch-Gr\"uneisen formula and yields the Debye temperature ${\mathrm{\ensuremath{\Theta}}}_{\mathrm{D}}=113\ifmmode\pm\else\textpm\fi{}14$ K. The results indicate that the scattering of bulk electrons is dominated by acoustic phonons.

The surfaces of three-dimensional topological insulators (TIs) characterized by a spin-helical Dirac fermion provide a fertile ground for realizing exotic phenomena as well as having potential for wide-ranging applications. To realize most of their special properties, the Dirac point (DP) is required to be located near the Fermi energy with a bulk insulating property while it is hardly achieved in most of the discovered TIs. It has been recently found that TlBiSe2 features an in-gap DP, where upper and lower parts of surface Dirac cone are both utilized. Nevertheless, investigations of the surface transport properties of this material are limited due to the lack of bulk insulating characteristics. Here, we present the first realization of bulk insulating property by tuning the composition of Tl1-xBi1+xSe2-d without introducing guest atoms that can bring the novel properties into the reality. This result promises to shed light on new exotic topological phenomena on the surface.

We report the observation of two-dimensional Shubnikov-de Hass (SdH) oscillations in the topological insulator Tl$_{1-x}$Bi$_{1+x}$Se$_2$. Hall effect measurements exhibited electron-hole inversion in samples with bulk insulating properties. The SdH oscillations accompanying the hole conduction yielded a large surface carrier density of $n_{\rm{s}}=5.1 \times10^{12}$/cm$^2$, with the Landau-level fan diagram exhibiting the $\pi$ Berry phase. These results showed the electron-hole reversibility around the in-gap Dirac point and the hole conduction on the surface Dirac cone without involving the bulk metallic conduction.

Time- and angle-resolved two-photon photoemission (2PPE) was used to study the electronic structure and ultrafast electron dynamics of the $p$-doped topological insulator ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ and its derivative ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{2}\mathrm{S}$. Our 2PPE experiments directly reveal that the massless Dirac-cone like energy dispersion of topological surface states is realized above the Fermi energy in both materials. The observed bulk conduction bands of ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{2}\mathrm{S}$ are found to be shifted to higher energies as compared to ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$. This shift has, however, surprisingly almost no influence on the electron dynamics in the topological surface state, which proceed on a picosecond time scale.

The surface termination of the promising topological insulator TlBiSe${}_{2}$ has been studied by surface- and bulk-sensitive probes. Our scanning tunneling microscopy has unmasked for the first time the unusual surface morphology of TlBiSe${}_{2}$ obtained by cleaving, where islands are formed by residual atoms on the cleaved plane. The chemical condition of these islands was identified using core-level spectroscopy. We observed thallium core-level spectra that are strongly deformed by a surface component in sharp contrast to the other elements. We propose a simple explanation for this behavior by assuming that the sample cleaving breaks the bonding between thallium and selenium atoms, leaving the thallium layer partially covering the selenium layer. These findings will assist the interpretation of future experimental and theoretical studies of this surface.

We report an effective and a quantitative analysis method for one of pharmaceuticals, sulpiride, in river water by online solid phase extraction (SPE) connected with liquid chromatography–mass spectrometry (LC–MS) using a molecularly imprinted polymer as a preconcentration medium. The polymer prepared with a pseudo template molecule showed the selective retention ability based on the interval recognition of functional groups in sulpiride. Also, the imprinted polymer provided an effective concentration of a trace level of sulpiride in offline SPE with dual washing processes using water and acetonitrile, although another imprinted polymer prepared by an authentic method using sulpiride and methacrylic acid as a template and a functional monomer, respectively, showed the selective adsorption only in organic solvents. Furthermore, we employed the imprinted polymer as the preconcentration column of online SPE-LC–MS and the results supposed that the proposed system allowed the quantitative analysis of sulpiride with high sensitivity and recovery (10 ng/L at 96%). Additionally, the determination of sulpiride in real river water without an additional spiking was effectively achieved by the system.

A topological surface state that is protected physically under the Bi2Te3-like five-layer block has been revealed on the Pb-based topological insulator (TI) PbBi4Te7 by bulk sensitive angle-resolved photoelectron spectroscopy (ARPES). Furthermore, conservation of the spin polarization of the hidden topological surface states is directly confirmed by bulk-sensitive spin ARPES observation. This finding paves the way to realize the real spintronics devices by TIs that are operable in the real environment.

Bias voltage dependent scattering of the topological surface state is studied by scanning tunneling microscopy/spectroscopy for a clean surface of the topological insulator Bi${}_{2}$Te${}_{2}$Se. A strong warping of constant energy contours in the unoccupied part of the spectrum is found to lead to a spin-selective scattering. The topological surface state persists to higher energies in the unoccupied range far beyond the Dirac point, where it coexists with the bulk conduction band. This finding sheds light on the spin and charge dynamics over a wide energy range and opens a way to designing optospintronic devices.

We have found a perpendicular magnetic anisotropy of iron adatoms on a surface of the prototypical three-dimensional topological insulator Bi2Se3 by using x-ray magnetic circular dichroism measurements. The orbital magnetic moment of Fe is strongly enhanced at lower coverage, where angle-resolved photoemission spectroscopy shows coexistence of non-trivial topological states at the surface.

Spin polarization of a topological surface state for GeBi${}_{2}$Te${}_{4}$, the newly discovered three-dimensional topological insulator, has been studied by means of state-of-the-art spin- and angle-resolved photoemission spectroscopy. It has been revealed that the disorder in the crystal has a minor effect on the surface-state spin polarization, which is $70%$ near the Dirac point in the bulk energy gap region ($\ensuremath{\sim}$180 meV). This finding promises not only to realize a highly spin-polarized surface-isolated transport but also to add functionality to its thermoelectric and thermomagnetic properties.

Helical spin textures with marked spin polarizations of topological surface states have been unveiled for the first time by state-of-the-art spin- and angle-resolved photoemission spectroscopy for two promising topological insulators, Bi(2)Te(2)Se and Bi(2)Se(2)Te. Their highly spin-polarized natures are found to be persistent across the Dirac point in both compounds. This novel finding paves a pathway to extending the utilization of topological surface states of these compounds for future spintronic applications.

Quasiparticle interference induced by cobalt adatoms on the surface of the topological insulator Bi${}_{2}$Se${}_{3}$ is studied by scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and x-ray magnetic circular dichroism. It is found that Co atoms are selectively adsorbed on top of Se sites and act as strong scatterers at the surface, generating anisotropic standing waves. A long-range magnetic order is found to be absent, and the surface state Dirac cone remains gapless. The anisotropy of the standing wave is ascribed to the heavily warped iso-energy contour of unoccupied states, where the scattering is allowed due to a nonzero out-of-plane spin.

The experimental evidence is presented of the topological insulator state in PbBi2Te4. A single surface Dirac cone is observed by angle-resolved photoemission spectroscopy with synchrotron radiation. Topological invariants Z2 are calculated from the ab initio band structure to be 1;(111). The observed two-dimensional isoenergy contours in the bulk energy gap are found to be the largest among the known three-dimensional topological insulators. This opens a pathway to achieving a sufficiently large spin current density in future spintronic devices.

4 páginas, 4 figuras.-- PACS numbers: 73.20.-r, 72.20.Dp, 72.25.-b.-- et al., We have performed scanning tunneling microscopy and differential tunneling conductance (dI/dV) mapping for the surface of the three-dimensional topological insulator Bi2Se3. The fast Fourier transformation applied to the dI/dV image shows an electron interference pattern near Dirac node despite the general belief that the backscattering is well suppressed in the bulk energy gap region. The comparison of the present experimental result with theoretical surface and bulk band structures shows that the electron interference occurs through the scattering between the surface states near the Dirac node and the bulk continuum states., This work was financially supported by the JSPS Grant-in-Aid for Scientific Research (B) 20340092.

4 páginas, 3 figuras.-- PACS numbers: 73.20.-r, 79.60.-i.-- et al., A hexagonal deformation of the Fermi surface of Bi2Se3 has been for the first time observed by angle-resolved photoemission spectroscopy. This is in contrast to the general belief that Bi2Se3 possesses an ideal Dirac cone. The hexagonal shape is found to disappear near the Dirac node, which would protect the surface state electrons from backscattering. It is also demonstrated that the Fermi energy of naturally electron-doped Bi2Se3 can be tuned by 1% Mg doping in order to realize the quantum topological transport., This work was financially supported by the JSPS Grant-in-Aid for Scientific Research (B) No. 20340092.

4 páginas, 4 figuras.-- PACS numbers: 73.20.-r, 79.60.-i.-- et al., We report the first observation of a topological surface state on the (111) surface of the ternary chalcogenide TlBiSe2 by angle-resolved photoemission spectroscopy. By tuning the synchrotron radiation energy we reveal that it features an almost ideal Dirac cone with the Dirac point well isolated from bulk continuum states. This suggests that TlBiSe2 is a promising material for realizing quantum topological transport., This work was financially supported by the JSPS Grant-in-Aid for Scientific Research (B) 20340092.

Undoped and slightly Eu-doped SmB6 show the opening of a gap with decreasing temperature below ~150 K. The spectral shapes near the Fermi level (EF) at 15 K have shown strong increase in intensity of a peak at a binding energy (EB) of around 12 meV with decreasing the photon energy (hn) from 17 eV down to 7 eV. Angle resolved spectra of SmB6 measured at hn = 35 eV just after the in-situ cleavage showed clear dispersions of several bands in the EB region from EF to 4 eV. Spin-polarized photoelectron spectra were then measured at 12 K and light incidence angle of ~50 deg. In contrast to the lack of spin polarization for the linearly polarized light excitation, clear spin polarization was observed in the case of circularly polarized light excitation. The two prominent peaks at EB~12 and ~150 meV have shown opposite signs of spin polarization which are reversed when the helicity of the light is reversed. The sign and the magnitude of spin- polarization are consistent with a theoretical prediction for the 6H5/2 and 6H7/2 states., Comment: all correspondence should be addressed to ssmsuga@gmail.com

Highly efficient spin- and angle-resolved photoelectron spectrometer named ESPRESSO (Efficient SPin REsolved SpectroScopy Observation) machine has been developed at the beamline BL-9B in Hiroshima Synchrotron Radiation Center. Combination of high-resolution hemispherical electron analyzer and the high-efficient spin detector based on very low energy electron diffraction by the ferromagnetic target makes the high-energy resolution and angular resolution compatible with spin- and angle-resolved photoemission (SARPES) measurement. 7.5 meV in energy and ±0.18° in angular resolution have been achieved with spin resolution. The ESPRESSO machine, combination of quick energy-band dispersion measurement and Fermi surface mapping by two-dimensional electron detector for the spin integrated ARPES and the high-efficient spin analysis by the efficient spin detector realizes the comprehensive investigation of spin electronic structure of materials.