High-resolution three-dimensional spin- and angle-resolved photoelectron spectrometer using vacuum ultraviolet laser light

Yaji, Koichiro; Harasawa, Ayumi; Kuroda, Kenta; Toyohisa, Sogen; Nakayama, M.; Ishida, Y.; Fukushima, Akiko; Watanabe, S.; Chen, Chuangtian; Komori, Fumio; Shin, Shik

doi:10.1063/1.4948738

Cited by 81 publications

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References 31 publications

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“…Laser-SARPES experiments were performed at home-built laser-SARPES machine implemented by a high-flux 6.994-eV laser source [24]. The laser-SARPES machine is equipped with two high efficient VLEED (Very-Low Energy Electron Diffraction) spin detectors and a hemispherical analyzer with a photoelectron reflector function (SCIENTA-OMICRON DA30L).…”

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Coherent control over three-dimensional spin polarization for the spin-orbit coupled surface state of Bi2Se3

et al. 2016

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Interference of spin-up and spin-down eigenstates depicts spin rotation of electrons, which is a fundamental concept of quantum mechanics and accepts 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 unambiguously revealed that the linearly polarized laser can simultaneously excite spin-up and spin-down states and these quantum spin-basis are coherently superposed in photoelectron states. The superposition and the resulting spin rotation is arbitrary 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.PACS numbers: 73.20. At, Coherent manipulation of electron spin offers many potential applications in spintronic devices [1] and spinbased quantum information science [2,3]. The key is to take control over the superposition of spin-up and spindown states resulting in interference. Spin-orbit coupling (SOC) mediates electric field and electron spin; thus electric/optical control of spins may become possible. Up to now, the coherent spin manipulation through electric fields is demonstrated in a few systems, such as quantum qubits [3,4] and semiconductor-heterostructure interfaces [5]. Optical control of spins utilizing the superimposed states in diamond is also demonstrated [6]. In this Letter we introduce a great methodology which is capable of directly accessing this scheme in photoelectron spin, based on a combination of polarization-variable laser with spin-and angle-resolved photoemission spectroscopy (laser-SARPES).We use the technique for a well-understood model system, a spin-polarized surface state of a topological insulator (TI), Bi 2 Se 3 . The TI has been discovered as a new class of matter, which is characterized by a metallic topological surface-state (TSS) intersecting the bulk bandgap [7,8]. The TSS forms spin-polarized Dirac-cone-like energy dispersion [9][10][11][12][13][14]. In particular, as a consequence of the strong SOC, different spins and orbitals are mixed in the TSS wavefunction, which generates a spin-orbital entangled texture [15][16][17]. Since the electric field of light couples to the orbitals, polarized light can, in princi- * These two authors contributed equally. † kuroken224@issp.u-tokyo.ac.jp ‡ komori@issp.u-tokyo.ac.jp ple, selectively excite the fully spin-polarized electrons with either spin-up or spin-down from the spin-orbital entanglement. The spin-selective excitation in the TSS by polarized light was theoretically studied [18,19] and demonstrated in previous SARPES experiments [20][21][22][23]. The entangled spin-orbital texture of the TSS is therefore suitable for the coherent spin control as a novel source of spin...

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Coherent control over three-dimensional spin polarization for the spin-orbit coupled surface state of Bi2Se3

et al. 2016

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“…The full spin information is experimentally unraveled only by a combination of p-and s-polarized light in accordance with a view of the SO entanglement. cron DA30L photoelectron analyzer [26]. The experimental configuration is shown in Fig.…”

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Direct mapping of spin and orbital entangled wave functions under interband spin-orbit coupling of giant Rashba spin-split surface states

et al. 2017

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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. PACS numbers:A realization of functional capabilities to generate spinsplitting of electronic states without any external magnetic field is a key subject in the research of spintronics [1]. A promising strategy exploits the influence of spin-orbit (SO) interaction that can give rise to the lifting of spin degeneracy under broken space inversion symmetry, the so-called Rashba effect [2]. In the conventional Rashba model, an eigenstate of the SO-induced spin-splitting is treated with an assumption of a pure spin state fully chiral spin-polarized which protects electrons from backscattering [2][3][4][5]. However, in real materials, the assumption can be usually broken because the SO coupling mixes different states with different orbitals and orthogonal spinors in a quasiparticle eigenstate [6][7][8]. The SO entanglement can permit the spin-flip electron backscattering [9] and moreover orbital mixing in the eigenstate can play a significant role in an emergence of the large spin-splitting [10][11][12][13][14]. Therefore, it is essentially important to experimentally explore the SO coupling not only in the lifting spin degeneracy but also in the spin and orbital wavefunction as eigenstates.Beyond the conventional Rashba model, a well-ordered surface alloy BiAg 2 grown on Ag(111) provides an ideal case to study the SO entanglement in Rashba surface states. In the surface alloy, an occupied sp z -like band and a mostly unoccupied p xy -like band show significant Rashba spin splitting [15,16] and cross each other at the specific k || [17][18][19] as shown in Fig. 1 (b). In particular, density functional theory (DFT) calculations showed the strong SO entanglement [8,9] and predicted the complex spin texture that is significantly different from the conventional Rashba model; the sp z band switches spinpolarization at the crossing through SO-induced interband hybridization [19] which is in contrast to the similar system BiCu 2 /Cu(111) as shown in Fig. 1 (b) [14,20,21]. While the presence of the spin-polarized electronic bands ...

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“…analyzer mounted with two sets of very-low-energy electron diffraction spin detectors were used at the Institute of Solid State Physics (ISSP), The University of Tokyo [29]. The total energy resolution was set to 30 and 3 meV, respectively.…”

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Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoTe2

et al. 2017

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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 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. Weyl nodes) at the Fermi level (EF). The bulk electronic structure of Weyl semimetals is characterized by the spin-polarized Weyl cone dispersions formed through the breaking of either time-reversal or space-inversion symmetry [1][2][3][4]. At the surface, on the other hand, the chiral charge associated with the Weyl nodes warrants the existence of the gapless surface states, socalled Fermi arcs that connect the two-dimensionally (2D) projected Weyl nodes. Due to these unusual bulk and surface electronic states, a variety of new magnetoelectric phenomena have been predicted [4][5][6][7][8][9]. Until now, several experimental verifications of realistic Weyl semimetal compounds have been raised (eg. the TaAs family [10][11][12] The single-crystalline 1T'-MoTe2 was synthesized as reported elsewhere [19,20].ARPES at 25 K was performed using the He-discharge lamp (21.2 eV) and the fourth harmonic generation of Ti:sapphire laser (6.43 eV, s-polarized light) [28], with a VG-Scienta R4000WALanalyzer. The total energy resolution was set to 10 and 3 meV, respectively. For the laser-SARPES at 25 K and the ARPES at 100 K, a 6.99 eV laser (s-polarized light) and a ScientaOmicron DA30Lanalyzer mounted with two sets of very-low-energy electron diffraction spin detectors were used at the Institute of Solid State Physics (ISSP), The University of Tokyo [29]. The total energy resolution was set to 30 and 3 meV, respectively. Samples were cleaved in situ at room temperature. All measurements were performed in ultrahigh vacuum better than 1×10 -10 Torr.Electronic structure calculations were performed within the context of density functional theory (DFT) using the Perdew-Burke-Ernzerhof exchange-correlation functional as implemented in the VASP program [30,31]. Relativistic effects were fully included. The structure parameters in Ref.[14] were used, and the corresponding Brillouin zone was sampled by a 20 × 10 × 5 k-mesh. To focus on the near-EF electronic structure, the ARPES images...

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High-resolution three-dimensional spin- and angle-resolved photoelectron spectrometer using vacuum ultraviolet laser light

Cited by 81 publications

References 31 publications

Coherent control over three-dimensional spin polarization for the spin-orbit coupled surface state of Bi2Se3

Coherent control over three-dimensional spin polarization for the spin-orbit coupled surface state of Bi2Se3

Direct mapping of spin and orbital entangled wave functions under interband spin-orbit coupling of giant Rashba spin-split surface states

Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoTe2

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