Development of bulk-sensitive spin-resolved ultrahigh-resolution
photoemission spectrometer
S. Souma1, A. Takayama2, K. Sugawara2, T. Sato2 and T. Takahashi1,2,3
1
WPI-AIMR, Tohoku University, Sendai 980-8578, Japan2
Department of Physics, Tohoku University, Sendai 980-8578, Japan
3
Japan Science and Technology Agency, CREST, Kawaguchi 332-0012, Japan
Angle-resolved
photoemission
spectroscopy(ARPES) is known as a powerful technique toinvestigate the fine electronic structure relevant to theintriguing physical phenomena in solids such as
superconductivity, heavy fermions, metal-insulatortransition, and so on. This technique, yet, has sufferedfrom two inherent problems originating in theprinciple of PES itself, namely, (1) the high surface
sensitivity, and (2) the difficulty in resolving the spinpolarization of electrons. To overcome thoseproblems, we have constructed an ultrahigh resolution
photoemission spectrometer equipped with a newly
developed xenon-plasma discharge lamp and amini-Mott detector.
Figure 1 shows the xenon plasma discharge lampthat provides several intense resonance lines fromxenon plasma in the energy range of 8-11 eV, whichis enough to achieve high bulk-sensitivity.[1] Theenergy width of radiation from the lamp isintrinsically very narrow owing to small Doppler
broadening due to the high mass of the xenon atom,and low pressure operation of the discharging plasma
reducing the self absorption effect. Combined with alarge hemispherical energy analyzer and a sphericalconcaved grating, we achieved high energy resolution
less than 1 meV as a total system in thespin-integrated mode. The photoelectron intensity
excited by the xenon lamp is bigger than that of theordinary helium lamps by 1-2 order of magnitude.
This is quite useful to compensate the low efficiency
in the case of spin-resolved photoemission.
We have developed a compact Mott spin detector
operating at 25 kV and adapted it to the large
hemispherical electron energy analyzer through anelectron deflector lens. We have redesigned theanalyzer and mounted the entrance of the deflector
lens at a location close to the 40mm microchannel
plate (MCP). This enables the observation of electronenergy and momentum by the MCP with comparable
quality to modern electron analyzers, simultaneously
to the electron spin measurement by the Mottdetector.
Figure 2 shows spin-resolved ARPES spectra of
the Shockley state of the Sb(111) surface, which is
known as a typical case where the spin of the electronband is polarized along the plane due to the surface
Rashba effect.[2] The spectra are recorded by fourchanneltrons in the Mott detector to measure theelectron spin polarization of two orthogonal

directions, that is, in-plane and out-of plane to the(111) surface. As clearly seen, a pronounced peak at
0.1 eV in the up-spin spectrum of the in-plane
direction is considerably reduced in the down-spin
spectrum, in sharp contrast to the perfectsuperimposing of the up- and down-spin spectra of
the out-of-plane direction. This result is in good
agreement with the surface Rashba effect andunambiguously shows the spin-resolving performanceof the developed photoemission system.

Fig. 1.

Fig. 2.

Xenon-plasma discharge lamp

Spin-resolved ARPES spectra of Sb(111)[1] S. Souma et al., RSI, 78 (2007) 123104.
[2] K. Sugawara et al., PRL, 96 (2006) 046411.