Name: experimental methods for spin- and angle-resolved photoemission spectroscopy combined with polarization-variable laser
Uploaded: 2018-06-28T13:00:00
Description: Watch this Scientific Journal Video about Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser at JoVE.com

We thank M. Nakayama, S. Toyohisa, A. Fukushima and Y. Ishida for supports to the experimental setup. We gratefully acknowledge funding from the JSPS Grantin-Aid for Scientific Research (B) through Project No. 26287061 and for Young Scientists (B) through Project No. 15K17675. This work was also supported by MEXT of Japan (Innovative Area &#34;Topological Materials Science,&#34; Grant No. 16H00979) and JSPS KAKENHI (Grant No. 16H02209)

1. Sample Mount and Installation
<ol>
	<li>Cut single-crystal samples of Bi2Se313 in an approximate size of 1 &#215; 1 &#215; 0.5 mm3 and use sliver-based epoxy to glue the sample to the sample holder.</li>
	<li>Paste the scotch tape on the sample surface. 
	NOTE: The scotch tape is used to cleave the sample in ultrahigh vacuum (UHV) chamber to obtain an atomically clean surface.</li>
	<li>Install the sample into the sample magazine in the load lock, and sta...

<ol>
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Electron Spectrosc. 124 (2), 263-279 (2002).</li><li>Souma, S., Takayama, S., Sugawara, K., Sato, T., Takahashi, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrahigh-resolution+spin-resolved+photoemission+spectrometer+with+a+mini+Mott+detector.">Ultrahigh-resolution spin-resolved photoemission spectrometer with a mini Mott detector.</a> Rev. Sci. Instrum. 81 (9), 096101 (2010).</li><li>Okuda, T., Kimura, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spin-+and+angle-resolved+photoemission+of+strongly+spin-orbit+coupled+systems.">Spin- and angle-resolved photoemission of strongly spin-orbit coupled systems.</a> J. Phys. Soc. 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Instrum. 87 (5), 053111 (2016).</li><li>Shimojima, T., Okazaki, K., Shin, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-temperature+and+high-energy-resolution+laser+photoemission+spectroscopy.">Low-temperature and high-energy-resolution laser photoemission spectroscopy.</a> J. Phys. Soc. Jpn. 84 (7), 072001 (2015).</li><li>Augustine, S., Mathai, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth,+morphology,+and+microindentation+analysis+of+Bi2Se3,+Bi1.8In0.2Se3,+and+Bi2Se2.8Te0.2+single+crystals.">Growth, morphology, and microindentation analysis of Bi2Se3, Bi1.8In0.2Se3, and Bi2Se2.8Te0.2 single crystals.</a> Mater. Res. Bull. 36 (13), 2251-2261 (2001).</li><li>Hasan, M. Z., Kane, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Colloquium:+Topological+insulators.">Colloquium: Topological insulators.</a> Rev. Mod. Phys. 82 (4), 3045-3067 (2010).</li><li>Ando, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Topological+insulator+materials.">Topological insulator materials.</a> J. Phys. Soc. Jpn. 82 (10), 102011 (2013).</li><li>Zhang, H., Liu, C. -. X., Qi, X. -. L., Dai, X., Fang, Z., Zhang, S. -. 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C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spin-orbital+texture+in+topological+insulators.">Spin-orbital texture in topological insulators.</a> Phys. Rev. Lett. 111 (6), 066801 (2013).</li><li>Kuroda, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=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.</a> Phys. Rev. B. 94 (16), 165162 (2016).</li><li>Meier, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interference+of+spin+states+in+photoemission+from+Sb/Ag(111)+surface+alloys.">Interference of spin states in photoemission from Sb/Ag(111) surface alloys.</a> J Phys-Condens Mat. 23 (7), 072207 (2011).</li><li>Dil, J. H., Meier, F., Osterwalder, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rashba-type+spin+splitting+and+spin+interference+of+the+Cu(111)+surface+state+at+room+temperature.">Rashba-type spin splitting and spin interference of the Cu(111) surface state at room temperature.</a> J Electron Spectrosc. 201, 42-46 (2015).</li><li>Yaji, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spin-dependent+quantum+interference+in+photoemission+process+from+spin-orbit+coupled+states.">Spin-dependent quantum interference in photoemission process from spin-orbit coupled states.</a> Nature Commun. 8, 14588 (2017).</li><li>Noguchi, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+mapping+of+spin+and+orbital+entangled+wave+functions+under+interband+spin-orbit+coupling+of+giant+Rashba+spin-split+surface+states.">Direct mapping of spin and orbital entangled wave functions under interband spin-orbit coupling of giant Rashba spin-split surface states.</a> Phys. Rev. B. 95 (6), 04111(R) (2017).</li></ol>

ARPES and SARPES techniques have been commonly used for studying electronic band structures through the band mapping and spin-detection1,2. In addition to these general advantages shown above, laser-SARPES based on orbital selection rule in optical dipole excitation can be employed as a novel technique for visualizing the spin-orbital coupling effect in the wavefunction and quantum spin interference. As demonstrated in Figure 9<stron...

Angle-resolved photoemission spectroscopy (ARPES) technique has developed into one of the most powerful tool to investigate quasiparticle band structures in solid states1. The most of attractive feature of ARPES is the capability for band mapping to characterize electronic states in energy and momentum space. Spin-resolved ARPES (SARPES), which is here equipped with spin-detectors, e.g. Mott detector2,3, further enables us to resolve the spin character of the observed band structures4. Since the Mott detector can measure the spin with two axes (x and z, or y and z), the combination of the two Mott detectors further allows one to obtain the spin orientation in three dimension4,5. For several decades, however, the SARPES experiments were suffered from their low efficiency (typically 1/10000 compared to that for spin-integrated ARPES measurement)3,4,5,6,7, which had limited the energy and angular-resolutions. Recently, the energy resolution of SARPES has been increased with a high-efficient spin detector based on exchange scattering, the so-called very-low-energy electron-diffraction (VLEED) detector7,8,9,10. With this detector, the data quality has been significantly improved and the data acquisition time has been shortened. Recently, SARPES has succeeded greatly to address spin-polarized electronic states and particularly spin-orbit coupling effect resulting in the spin texture of the surface bands7.
Here, we employ SARPES measurements with a polarization-variable vacuum ultraviolet laser light (laser-SARPES) and demonstrate the great advantages of this combined technique. Through the investigation on the spin-orbit coupled surface states in Bi2Se3, we present two capabilities of laser-SARPES. Firstly, due to the orbital selection rule of linearly polarized lasers in dipole transition regime, p- and s-polarized lights selectively excite a part of eigen-wavefunctions with different orbital symmetry. Such an orbital selective excitation is thereby available in SARPES, namely, orbital-selective SARPES. Secondly, three-dimensional (3D) spin-detection in SARPES shows the direction of the spin quantum axis and directly displays full information of the light-polarization dependence. In this protocol, we briefly describe a methodology to perform this state-of-the-art laser-SARPES technique to study the strong spin-orbit coupling effects.
Our laser-SARPES system is located at The Institute for Solid State Physics, The University of Tokyo11. The schematic drawing of our laser-SAPRES machine is shown in Figure 1. The polarization-variable 7-eV laser light12 illuminates the sample surface and the photoelectrons are emitted from the sample. The polarization of laser is automatically controlled by MgF2-based &#955;/2- and &#955;/4-waveplates to selectively use linear and circular polarizations. A hemispherical electron analyzer corrects the photoelectrons, and analyzes their kinetic energy (Ekin) and emission angle (&#952;x and &#952;y). The photoelectron intensities are mapped on the Ekin-&#952;x screen monitored by a CCD camera. This image is directly transformed into the energy band structure in reciprocal space.
For SARPES measurement, the photoelectrons with a specific emission angle and kinetic energy analyzed by the electron analyzer are&#160;guided to two VLEED-type spin detectors with a 90-degree photoelectron deflector and the photoelectron beams are focused onto two different targets of Fe(001)-p(1&#215;1) films terminated by oxygen. The photoelectrons reflected by the targets are detected in single channel detection by using a channeltron placed in each spin detector. The VLEED targets can be magnetized with Helmholtz-type electric coils which are arranged with orthogonal geometry with respect to each other. The magnetization direction is controlled by the bipolar condenser bank. The double VLEED spin detectors thereby enable us to analyze the spin-polarization vector of the photoelectron in three dimensions.

<table>
	<tbody>
		<tr>
			<td>DA30-L hemispherical analyzer</td>
			<td>ScientaOmicron</td>
			<td></td>
			<td>http://www.scientaomicron.com/en/products/353/1170</td>
		</tr>
		<tr>
			<td>Silver-based epoxy</td>
			<td>Epoxy Technology</td>
			<td>H20E</td>
			<td></td>
		</tr>
		<tr>
			<td>Sctoch tape</td>
			<td>3M</td>
			<td>801-1-18C</td>
			<td></td>
		</tr>
		<tr>
			<td>UHV valve</td>
			<td>VAT</td>
			<td>01034-KE01</td>
			<td></td>
		</tr>
		<tr>
			<td>linear/rotary feedthrough</td>
			<td>Ferrovac</td>
			<td>MD40</td>
			<td></td>
		</tr>
		<tr>
			<td>transfer rod</td>
			<td>UHV design</td>
			<td>PP series</td>
			<td></td>
		</tr>
		<tr>
			<td>wobble stick</td>
			<td>Ferrovac</td>
			<td>WM40</td>
			<td></td>
		</tr>
		<tr>
			<td>Paladin compact 355</td>
			<td>Coherent</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>half waveplate</td>
			<td>Kogakugiken</td>
			<td></td>
			<td>order made</td>
		</tr>
		<tr>
			<td>Bipolar condenser bank</td>
			<td>Tsuji electronics</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

experimental methods for spin- and angle-resolved photoemission spectroscopy combined with polarization-variable laser

The goal of this protocol is to present how to perform spin- and angle-resolved photoemission spectroscopy combined with polarization-variable 7-eV laser (laser-SARPES), and demonstrate a power of this technique for studying solid state physics. Laser-SARPES achieves two great capabilities. Firstly, by examining orbital selection rule of linearly polarized lasers, orbital selective excitation can be carried out in SAPRES experiment. Secondly, the technique can show full information of a variation of the spin quantum axis as a function of the light polarization. To demonstrate the power of the collaboration of these capabilities in laser-SARPES, we apply this technique for the investigations of spin-orbit coupled surface states of Bi2Se3. This technique affords to decompose spin and orbital components from the spin-orbit coupled wavefunctions. Moreover, as a representative advantage of using the direct spin detection collaborated with the polarization-variable laser, the technique unambiguously visualizes the light polarization dependence of the spin quantum axis in three-dimension. Laser-SARPES dramatically increases a capability of photoemission technique.

Before starting SARPES experiments, k positions need to be accurately determined for taking spin-resolved spectrum by using high statistic spin-integrated ARPES results with high energy- and angular-resolutions (protocol 5.1-5.5). This is demonstrated in Figure 7 where the ARPES results for a Bi2Se3 single crystal are presented. This material is known as a prototypical topological insulator with a spin-polarized surface states<s...

Watch this Scientific Journal Video about Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser at JoVE.com

Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser

Here, we combine polarization-variable 7-eV laser with spin- and angle-resolved photoemission technique to visualize the spin-orbital coupling effect in solid states.

The goal of this protocol is to present how to perform spin- and angle-resolved photoemission spectroscopy combined with polarization-variable 7-eV laser ...

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