Research Nuggets
This page will be filled regularly with our latest results:
Effects of doping in the s± gap
(Jan. 14, 2014)
One liner: The s± nature of the
superconducting gap in BaFe2As2 is such
that in-plane doping by cobalt atoms depletes superconductivity,
whereas out-of-plane potassium doping preserves the
superconducting stiffness.
More details: Opposite to conventional materials,
in an s± superconductor non magnetic impurity
scattering mixes electron and hole states with opposing phases
and, hence, is pair-breaking. The superconducting state optical
conductivity (see figure) of Co doped BaFe2As2
shows a very large residual conductivity below the gap energy
(hatched area). This is the signature of unpaired quasiparticles.
Conversely, in the K doped material, a full gap (vanishingly small optical
conductivity) is present. In the former compound, Co atoms go
into the FeAs planes and, hence, act as diffusion centers. In the
latter, K atoms enter the structure outside the plane and
do not mix the bands at the Fermi level. The strong residual
conductivity in the Co material opposed to the zero valued sub-gap
optical conductivity in the K doped compound strongly supports
a s± symmetry superconductor where impurity
is pair-breaking.
Publication: Optical conductivity of Ba0.6K0.4Fe2As2:
The effect of in-plane and out-of-plane doping the superconducting gap.,
Y.M. Dai, B. Xu, B. Shen, H.H. Wen, X.G. Qiu, and R.P.S.M. Lobo,
EPL 104, 47006 (2013)
[EPL page]
Linear scattering rate in Ba0.6K0.4Fe2As2
(Sep. 30, 2013)
One liner: The curvature observed in the temperature
dependence of the resistivity of Ba0.6K0.4Fe2As2
comes from an incoherent band with a flat lifetime and a
coherent band T-linear scattering rate, which we associate to
quantum critical point fluctuations.
More details: The temperature dependence of the resistivity
of Ba0.6K0.4Fe2As2
has a negative curvature (top panel). We show that this can
be explained by a multiband contribution to transport where one
band has an incoherent-like large, temperature independent,
scattering rate and another band has a sharp Drude peak with
a scattering rate evolving linearly with temperature (bottom
panel). The low temperature resistivity is dominated by the
narrow peak whereas a crossover to the flat incoherent band
takes over above ~170 K. The linear, hidden, scattering rate
seems to originate from spin fluctuations close to an
antiferromagnetic quantum critical point.
Publication: Hidden T-linear scattering rate in
Ba0.6K0.4Fe2As2
revealed by optical spectroscopy, Y.M. Dai, B. Xu,
B. Shen, X. Xiao, H.H. Wen, X.G. Qiu, C.C. Homes, and
R.P.S.M. Lobo, Phys. Rev. Letters 111,
117001 (2013)
[PRL page]