Spin Polarization of the Photoelectrons and Photon Polarization of X-Ray Absorption: Spectroscopy and Magnetometry

We introduce here how to perform spectroscopies that are sensitive to the spin polarization of the electron states, via the direct measure of the P vector of a (photo)electron beam in a suitable experimental set-up and how to perform photoemission/photoab

  • PDF / 1,998,834 Bytes
  • 32 Pages / 439.37 x 666.142 pts Page_size
  • 18 Downloads / 167 Views

DOWNLOAD

REPORT


Spin Polarization of the Photoelectrons and Photon Polarization of X-Ray Absorption: Spectroscopy and Magnetometry Giorgio Rossi

Abstract We introduce here how to perform spectroscopies that are sensitive to the spin polarization of the electron states, via the direct measure of the P vector of a (photo)electron beam in a suitable experimental set-up and how to perform photoemission/photoabsorption experiments that, by exploiting the polarization of the exciting photon beam, are directly sensitive to the spin order in the initial state revealing, for example, the magnetization state of solids and surfaces or the effects of spin-orbit interaction in the surface electronic structure.

20.1 Introduction The energy E, momentum k and spin s structure of solids and surfaces in the reciprocal space reflect the phenomena that we describe as “correlation effects”: magnetism, orbital ordering, superconductivity, in short the whole low-energy properties of condensed matter. Angularly Resolved Photo-Electron Spectroscopy (ARPES) [1] can be “completed” by measuring the spin-polarization, P, of the photoelectrons; in such case it is called SP-ARPES or S-ARPES meaning “spin-polarized angularly resolved photoelectron spectroscopy” [2–6]. Within the dipole approximation S = 0, robust data analysis methods allow to approximate the initial electron quantum state [1, 2, 7]. The measure of the spin polarization vector P is accomplished by electron scattering experiments [8]: it is performed on photoelectron beams that are pre-selected in energy and in momentum and then accelerated to collide with a heavy-atom solid target. The spin detection is therefore performed “downstream” of G. Rossi (B) Dipartimento di Fisica dell’Università degli studi di Milano, via Celoria 16, 20133 Milano, Italy e-mail: [email protected] Advanced Photoelectric-Effect Experiments (APE) and Nano Foundries and Fine Analysis (NFFA) collaborations, Istituto Officina dei Materiali-CNR, 34149 Basovizza, TS, Italy S. Mobilio et al. (eds.), Synchrotron Radiation, DOI: 10.1007/978-3-642-55315-8_20, © Springer-Verlag Berlin Heidelberg 2015

539

540

G. Rossi

the ARPES analyser without loss of information as far as the ARPES selection is done with purely electrostatic fields (no magnetic fields in the photoelectron path) not to perturb the spin of the photoelectron beam. Spin polarization measurements can be accomplished, for example, in the Mott detector where the spin-orbit interaction of a 10–150 keV electron diffused by the central field of a heavy nucleus modifies the purely charge scattering trajectories in such way that a right-left scattering asymmetry is measured in a plane perpendicular to the spin quantization axis [8]. In fact spin-orbit interaction (SOI) is ubiquitous being one of the basic interactions that determines the spin band structure of solids, being dominant in the final state spectroscopy of initially closed core electron shells, being the coupling vehicle between photon polarization and spin structures in the photoexcited matter system