J. A. Knapp

Angle-resolved photoemission and valence band dispersions for GaAs: Direct vs indirect models

Abstract Angle-resolved photoemission measurements for GaAs(110) have been extended to h v = 100 eV. These results show that dominant emission peaks are due to direct transitions. Weaker one-dimensional density of states features sometimes observed are due to surface umklapp/secondary cone and lifetime effects. Accurate band dispersions for all four valence bands GaAs along the [110] direction are given using simple normal emission and off-normal emission methods. Electron and hole lifetimes are directly determined.

Experimental band dispersions Ekalong three main symmetry lines of LaB6 using angle-resolved photoemission from one crystal surface

Abstract Accurate valence band dispersions E k of LaB6 have been determined along three main symmetry lines ΓM, ΓX, and XM using one single crystal (001) surface by a simple new photoemission technique of general utility. Using direct interband transitions, E k dispersions are mapped out by suitably scanning polar emission angle and the photon energy. Detailed results agree well with recent Xα-APW energy band calculations.

Experimental energy band dispersions and magnetic exchange splittings for Fe, Co and Ni☆

Abstract A long-standing goal has been the determination of accurate exchange-split band dispersions for the itinerant ferromagnets Fe, Co and Ni. As often noted, magnetic exchange splittings and band dispersions E ( k ) are fundamental for understanding various physical properties involving d-band electronic structure, collective itinerant-electron ferromagnetism, transition metal surfaces, etc. Using polarization-dependent angle-resolved photoemission and synchroton radiation, we have recently determined the temperature-dependent exchange splitting and band dispersions for Ni [1, 2], Fe [3] and Co [3]. We have shown that direct transitions are of primary importance for normal photoemission from Ni(111), Fe(111) and Co(0001) and determine accurate exchange-split band dispersions E ( k ) for fcc Ni along the Γ symmetry line, for bcc Fe along the ΓPH symmetry line and for hcp Co along the ΓAΓ line. These results together with experimental E ( k ) dispersions for Cu [4] permit systematic comparison with state-of-the-art ab-initio band calculations [5]. This comparison shows that the ratio of the theoretical-to-experimental occupied d-band width is about 1.1, 1.2, 1.45 and 1.1 for Fe, Co, Ni and Cu, respectively, while the ratio of the theoretical-to- experimental exchange splitting δ E ex is about 1.0, 1.2 and 2.2 for Fe, Co and Ni, respectively. General conclusions are as follows: (1) Fe, Co and Ni can all be described by a Stoner-Wohlfarth-Slater (SWS) spin-split band model, and (2) state-of-the-art ab-initio one-electron band calculations quantitatively described Fe and Cu quite accurately, Co less well and Ni rather poorly. This behavior is consistent with electron-electron correlation effects for unfilled d-shells which increase in importance on going from Fe to Co to Ni.

Abstract: Electronic and magnetic properties of nickel as described using experimental spin‐split energy band dispersions

Angle‐resolved photoemission studies of Ni (111) and Ni (100) crystals, used to determine energy‐vs‐momentum s‐ and d‐band dispersions, show that ferromagnetic nickel can be described by a spin‐split itinerant band model with an exchange splitting. An experimental one‐electron energy band model for Ni gives a consistent description of various electronic and magnetic properties including Fermi surface radii, spin‐polarized field emission and photoemission data, Bohr magneton number and optical properties. (AIP)