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Abstract:
All conventional metals are known to possess a three-dimensional Fermi
surface, which is the locus in reciprocal space of the long-lived
electronic excitations that govern their electronic properties at low
temperatures. These excitations should have well-defined momenta with
components in all three dimensions. The high-transition-temperature
(high-T-c) copper oxide superconductors have unusual, highly
two-dimensional properties above the superconducting transition(1).
This, coupled with a lack of unambiguous evidence for a
three-dimensional Fermi surface, has led to many new and exotic models
for the underlying electronic ground state(2). Here we report the
observation of polar angular magnetoresistance oscillations(3) in the
overdoped superconductor Tl2Ba2CuO6+delta in high magnetic fields, which
firmly establishes the existence of a coherent three-dimensional Fermi
surface. Analysis of the oscillations reveals that at certain symmetry
points, however, this surface is strictly two-dimensional. This striking
form of the Fermi surface topography, long-predicted by electronic band
structure calculations(4), provides a natural explanation for a wide
range of anisotropic properties both in the normal(5,6) and
superconducting states(7-9). Our data reveal that, despite their extreme
electrical anisotropy, the high-T-c materials at high doping levels can
be understood within a framework of conventional three-dimensional metal
physics.
