5 research outputs found
Quantum corrections to the conductivity of fermion - gauge field models: Application to half filled Landau level and high- superconductors
We calculate the Altshuler-Aronov type quantum correction to the conductivity
of charge carriers in a random potential (or random magnetic field)
coupled to a transverse gauge field. The gauge fields considered simulate the
effect of the Coulomb interaction for the fractional quantum Hall state at half
filling and for the model of high- superconducting compounds. We
find an unusually large quantum correction varying linearly or quadratically
with the logarithm of temperature, in different temperature regimes.Comment: 12 pages REVTEX, 1 figure. The figure is added and minor misprints
are correcte
Linear Field Dependence of the Normal-State In-Plane Magnetoresistance of Sr2RuO4
The transverse and longitudinal in-plane magnetoresistances in the normal
state of superconducting Sr2RuO4 single crystals have been measured. At low
temperatures, both of them were found to be positive with a linear
magnetic-field dependence above a threshold field, a result not expected from
electronic band theory. We argue that such behavior is a manifestation of a
novel coherent state characterized by a spin pseudo gap in the quasi-particle
excitation spectrum in Sr2RuO4.Comment: 4 pages + 5 figure
Kondo effect in underdoped n-type superconductors
We present high-field magnetotransport properties of high-quality
single-crystalline thin films of heavily underdoped nonsuperconducting
(La,Ce)2CuO4, (Pr,Ce)2CuO4, and (Nd,Ce)2CuO4. All three materials show
identical behavior. They are metallic at high temperatures and show an
insulating upturn at low temperatures. The insulating upturn has a log T
dependence, but saturates toward the lowest temperatures. Notably, the
insulating upturn tends to be suppressed by applying magnetic fields. This
negative magnetoresistance has a log B dependence, and its anisotropy shows non
simple behavior. We discuss these findings from the viewpoints of Kondo
scattering and also two-dimensional weak localization, and demonstrate Kondo
scattering as a more plausible explanation. The Kondo scatters are identified
as Cu2+ spins in the CuO2 planes.Comment: 17 pages, 6 figures, submitted to Phys. Rev. Let
Negative in-plane and out-of-plane magnetoresistivities in optimally doped Bi2Sr2Ca0.8Y0.2Cu2O8+d single crystal
Both the in-plane and out-of-plane magnetoresistivities have been measured in
the normal state of an optimally doped Bi2Sr2Ca0.8Y0.2Cu2O8+d single crystal
with a magnetic field applied parallel and perpendicular to the CuO2 planes.
Whatever the magnetic field and the current directions are, a negative
magnetoresistivity is obtained over a wide range of temperature above the
critical temperature Tc. For the in-plane and out-of-plane measurements, the
non-dominant orbital contribution to magnetoresistivity suggests the
substantial role played by the spin degrees of freedom.Comment: 4 pages, 3 figures accepted for publication in Physical Revue