L.V. Gasparov, P.Lemmens, N.N. Kolesnikov,
G. Guntherodt.
Electronic Raman scattering in Tl2Ba2CuO6+d
:
Symmetry of the order parameter, oxygen doping effects, and normal-state
scattering.
Abstract:
Single crystals of the optimally doped, moderately and strongly overdoped
high-temperature superconductor Tl2Ba2CuO6+d
(Tl-2201) with Tc= 80, 56, and 30 K, respectively,
have been investigated by polarized Raman scattering. By taking the peak
position of the B1g component of electronic
Raman scattering as 2D0
we
found that the reduced gap value (2D0/kBTc
) strongly decreases with increasing doping. The behavior
of the low-frequency scattering for the B1g
and B2g scattering components is similar for optimally
doped and overdoped crystals and can be described by a w3
and w law, respectively, which is consistent
with a d-wave symmetry of the order parameter. In contrast
to the optimally doped Tl-2201 in both moderately and strongly overdoped
Tl-2201, the relative (compared to the B1g) intensity
of the A1g scattering component is suppressed.
We suggest that the van Hove singularity is responsible for the observed
changes of Raman intensity and reduced gap value with doping. Electronic
Raman scattering in the normal state is discussed in the context of the
scattering from impurities and compared to the existing infrared data.
The scattering rate evaluated from the Raman measurements is smaller for
the overdoped samples, compared to the moderately overdoped samples.