A New Spin on Photoemission Spectroscopy

Abstract

Professor Alessandra Lanzara, ChairThe electronic spin degree of freedom is of general fundamental importance to all matter.Understanding its complex roles and behavior in the solid state, particularly in highly correlated and magnetic materials, has grown increasingly desirable as technology demands advanced devices and materials based on ever stricter comprehension and control of the electron spin. However, direct and efficient spin dependent probes of electronic structure are currently lacking.Angle Resolved Photoemission Spectroscopy (ARPES) has become one of the most successful experimental tools for elucidating solid state electronic structures, bolstered by continual breakthroughs in efficient instrumentation. In contrast, spin-resolved photoemission spectroscopy has lagged behind due to a lack of similar instrumental advances. The power of photoemission spectroscopy and the pertinence of electronic spin in the current research climate combine to make breakthroughs in Spin and Angle Resolved Photoemission Spectroscopy (SARPES) a high priority .This thesis details the development of a unique instrument for efficient SARPES and represents a radical departure from conventional methods. A custom designed spin polarimeter based on low energy exchange scattering is developed, with projected efficiency gains of two orders of magnitude over current state-of-the-art polarimeters. For energy analysis, the 1 popular hemispherical analyzer is eschewed for a custom Time-of-Flight (TOF) analyzer offering an additional order of magnitude gain in efficiency. The combined instrument signifies the breakthrough needed to perform the high resolution SARPES experiments necessary for untangling the complex spin-dependent electronic structures central to today's condensed matter physics.

A high-efficiency spin-resolved photoemission spectrometer combining time-of-flight spectroscopy with exchange-scattering polarimetry

“…The electron optics of the TOF-EEA can be tuned to provide a fairly 'square' transmission envelope, however measured spectra should be corrected for variations in the transmission function. 55 For all M2 spectra presented in the present paper, this has been performed by normalizing the recorded spectra by experimentally measured transmission functions. These were obtained by recording spectra with identical TOF-EEA settings, but with higher photon energies to place known flat regions of the resulting photoemission spectrum within the bandpass.…”

“…To make use of the large combined efficiency gains of this arrangement, we have developed a spin-resolved, TOFbased spectrometer (spin-TOF) with this approach. 55…”

Reply to “Comment on ‘Spin–Orbit Coupling Induced Gap in Graphene on Pt(111) with Intercalated Pb Monolayer’”

“…The resulting error is calculated as Therefore, the averaging procedure decreases the error of measurements. The statistical error in spin polarization measurements is given by , where A is the asymmetry and I = I L + I R .…”