[en] The temperature dependence of angle-resolved photoemission from quantum-well states in ultrathin films of Ag on V(100) has been examined for films from 1--8 ML thickness within the temperature range 45--600 K. Contrary to bulk solids, the photoemission peaks shift to higher binding energy as the temperature is increased. The temperature dependence of the peak widths is linear, consistent with the expected behavior for electron-phonon coupling, but the coupling parameter λ is found to show a strong oscillatory dependence on film thickness, with some values many times larger than those found for bulk silver. The observations are explained in terms of the influence on both the initial and final states in the photoemission process of the static and dynamic movements of the surface-vacuum interface barrier induced by temperature changes

[en] The self-energy of the photohole in 2H-TaSe₂ is measured by angle-resolved photoemission spectroscopy as a function of binding energy and temperature. In the charge-density wave (CDW) state, a structure in the self-energy is detected at ∼65 meV that cannot be explained by electron-phonon scattering. A reduction in the scattering rates below this energy indicates the collapse of a major scattering channel with the formation of the CDW state accompanying the appearance of a bosonic ''mode'' in the excitation spectrum of the system

[en] High-resolution photoemission is used to study the electronic structure of the cuprate superconductor, Bi₂Sr ₂CaCu₂O_8+δ , as a function of hole doping and temperature. A kink observed in the band dispersion in the nodal line in the superconducting state is associated with coupling to a resonant mode observed in neutron scattering. From the measured real part of the self-energy it is possible to extract a coupling constant which is largest in the underdoped regime, then decreasing continuously into the overdoped regime

[en] By examining thermally excited states above the Fermi level in angle resolved photoemission spectroscopy, we show that the disconnected Fermi arcs observed in the pseudogap state of the cuprate phase diagram are actually components of fully enclosed hole pockets. The spectral weight of these pockets is vanishingly small at the Luttinger surface, coincident with the antiferromagnetic zone-boundary formed by the underlying spin lattice, creating the illusion of the Fermi arcs. The area of the pockets as measured in this study is consistent with the doping level, and hence the carrier density, of the samples measured. Furthermore, the shape and area of the pockets is well reproduced by phenomenological models of the pseudogap phase that reflect its proximity to a Mott insulator

[en] A comprehensive optical design for a high-resolution, high-flux, wide-energy range, micro-focused beamline working in the vacuum ultraviolet and soft x-ray photon energy range is proposed. The beamline is to provide monochromatic radiation to three photoelectron microscopes: a full-field x-ray photoelectron emission microscope and two scanning instruments, one dedicated to angle resolved photoemission spectroscopy (μ-ARPES) and one for ambient pressure x-ray photoelectron spectroscopy and scanning photoelectron microscopy (AP-XPS/SPEM). Microfocusing is achieved with state of the art elliptical cylinders, obtaining a spot size of 1 μm for ARPES and 0.5 μm for AP-XPS/SPEM. A detailed ray tracing analysis quantitatively evaluates the overall beamline performances.

[en] For optimally doped Bi₂Sr ₂CaCu₂O_8+δ , scattering rates in the normal state are found to have a linear temperature dependence over most of the Fermi surface. In the immediate vicinity of the (π, 0) point, the scattering rates are nearly constant in the normal state, consistent with models in which scattering at this point determines the c -axis transport. In the superconducting state, the scattering rates away from the nodal direction appear to level off and become temperature independent. (c) 2000 The American Physical Society

[en] We demonstrate angle-resolved, tunable, two-photon photoemission (2PPE) to map a bulk unoccupied band, viz. the Cu sp band 0 to 1 eV below the vacuum level, in the vicinity of the L point. This short-lived bulk band is seen due to the strong optical pump rate, and the observed transition energies and their dispersion with photon energy (ℎ/2π)ω, are in excellent agreement with tight-binding band-structure calculations. The variation of the final-state energy with (ℎ/2π)ω has a measured slope of ∼1.64 in contrast to values of 1 or 2 observed for 2PPE from two-dimensional states. This unique variation illustrates the significant role of the perpendicular momentum (ℎ/2π)k_{perpendicular} in 2PPE.