Angle-Resolved Photoemission Spectroscopy (ARPES) maps the dispersion of electronic bands near the Fermi level and, in particular, the Fermi surface itself by exciting the bound electrons in a sample with a given photon energy. The momentum parallel to the surface is fully conserved, thus making the method suitable for layered low-dimensional materials. The three-dimensional momentum distribution is also reflected in the photoelectron features thus making the spectroscopy applicable to metallic single crystals, provided that a well-defined clean surface can be prepared in ultra-high vacuum. The minimum samples size is 500 x 500 μm2 given by the light spot (50 x 50 μm2) and the sphere of confusion of the sample goniometer.
Angle resolved photoemission (ARPES) is the most direct probe of the electronic band dispersion in crystalline solids. It has played a key role in elucidating the properties of many frontier materials such as the high-temperature superconductors and continues to make a vast impact in correlated electron physics and surface/nano-science. The development of high resolution UV-beamlines at third generation synchrotrons and the advent of electron spectrometers with massive parallel detection have improved the relevant figure of merit in ARPES, which is given by the product of energy/momentum resolution and count rate, by at least 5 decades over the past 15 years. This has helped transforming ARPES from a niche spectroscopy into one of the most important techniques in experimental condensed matter physics.
ARPES has a wide range of applications that include:
Carbon based materials
Graphene, molecular electronics (HR-ARPES), carbon nanotubes, BN nanostructure (nano-ARPES);
Transition metal oxides
Quantitative analysis of electron interactions, Fermi surfaces, renormalisation, energy gaps;
Ultra small bandwidth dispersions;
ARPES as soon as single crystals are grown, nano-ARPES from inclusions and samples that are difficult to cleave;
Surfaces & interfaces
Molecular adsorbates, ultrathin films, stepped surfaces, epitaxially grown nano-wires, topological insulators.
Topological insulators, Dirac semimetals and investigation of the Weyl fermions.
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