SRC Users' Meeting - Synchrotron Radiation Center - University of ...

THE FERMI SURFACES OF THIN Sb(111) FILMS
Hartmut Höchst and Christian R. Ast
Synchrotron Radiation Center, University of Wisconsin-Madison
3731 Schneider Drive, Stoughton, WI, 53589
The unique electronic properties of the group-V elements Sb and Bi, their small
Fermi energy combined with highly anisotropic electron and hole masses and carrier
concentrations several orders of magnitude lower than in normal metals makes them
prime candidates for potential thermoelectric converters. Devices based on nano-scale
structures of Sb and Bi or alloys thereof are among those with the highest conversion
efficiency.[1,2]
The rhombohedral (A7) crystal structure of the group V-elements causes a
negative band gap. The conduction band minimum at the L-point is lower than the
valence band maxima, which occur at the H-point for Sb and at the T-point for Bi. As a
result, the Fermi surfaces (FS) consist of six pockets centered at the H-points or of two
half-pockets centered at the T-points. Band structure calculations using different
theoretical approaches agree in some basic overall Fermi surface features.[3-6].The
calculated dimensions of the Fermi surface however have been far from experimental
results based on magnetotransport and resonance measurements. These data were
historically the most accurate even though indirect sources to judge the quality of the
various theoretical approaches. More recently, photoemission spectroscopy (PES) was
recognized to be a potentially useful additional tool to investigate the electronic
properties near the FS. Compared to the classical FS measurements, PES has the
advantage that information can be gathered from very small samples, at elevated
temperatures and from materials, which exhibit strong impurity, compositional or
structurally related scattering effects otherwise detrimental to most classical resonance
based FS measurements.
We report the first photoemission based FS data of Sb. Combining ARPES with
the tuneability of synchrotron radiation allows determining the parallel components of the
Fermi momentum k x and k y . Using a simple final state model provides also access to the
perpendicular component k enables us to separate the three dimensional hole- pocket
typical for bulk Sb from additional FS features which are of 2D-nature and most likely
related to the presence of a Sb bilayer on the (111)-surface. Compared to Bi[7-9], which
has extremely small bulk hole-pockets, preventing a detailed k-mapping due to
experimental limitations in the momentum resolution, the carrier concentration in Sb is
~200 times larger and thus opening up the possibility of tracing the contours of the bulk
hole-FS. The location and cross section of the hole pocket in the mirror plane compares
well with theoretical predictions based upon pseudopotential calculations by Falicov and
Lin [3] while other more recent and advanced model calculations [4-6] seem not to
comply with our data.
Acknowledgements
The Synchrotron Radiation Center (SRC) is funded by the National Science Foundation
(NSF) under Grant No. DMR-0884402.