948 research outputs found
Optical response of high- cuprates: possible role of scattering rate saturation and in-plane anisotropy
We present a generalized Drude analysis of the in-plane optical conductivity
(,) in cuprates taking into account the effects of
in-plane anisotropy. A simple ansatz for the scattering rate
(,), that includes anisotropy, a quadratic frequency
dependence and saturation at the Mott-Ioffe-Regel limit, is able to reproduce
recent normal state data on an optimally doped cuprate over a wide frequency
range. We highlight the potential importance of including anisotropy in the
full expression for (,) and challenge previous
determinations of () in which anisotropy was neglected and
() was indicated to be strictly linear in frequency over a wide
frequency range. Possible implications of our findings for understanding
thermodynamic properties and self-energy effects in high- cuprates will
also be discussed.Comment: 8 pages, 7 figures. To be published in Physical Review
Destruction of chain-superconductivity in YBa_2Cu_4O_8 in a weak magnetic field
We report measurements of the temperature dependent components of the
magnetic penetration depth {\lambda}(T) in single crystal samples of
YBa_2Cu_4O_8 using a radio frequency tunnel diode oscillator technique. We
observe a downturn in {\lambda}(T) at low temperatures for currents flowing
along the b and c axes but not along the a axis. The downturn in {\lambda}_b is
suppressed by a small dc field of ~0.25 T. This and the zero field anisotropy
of {\lambda}(T) likely result from proximity induced superconducting on the CuO
chains, however we also discuss the possibility that a significant part of the
anisotropy might originate from the CuO2 planes.Comment: 5 page
Violation of the isotropic- approximation in overdoped La_{2-x}Sr_xCuO_4
Magnetotransport measurements on the overdoped cuprate La_{1.7}Sr_{0.3}CuO_4
are fitted using the Ong construction and band parameters inferred from
angle-resolved photoemission. Within a band picture, the low temperature Hall
data can only be fitted satisfactorily by invoking strong basal-plane
anisotropy in the mean-free-path . This violation of the isotropic-
approximation supports a picture of dominant small-angle elastic scattering in
cuprates due to out-of-plane substitutional disorder. We show that both band
anisotropy and anisotropy in the elastic scattering channel strongly
renormalize the Hall coefficient in overdoped La_{2-x}Sr_xCuO_4 over a wide
doping and temperature range.Comment: 4 pages, 4 figure
A Tale of Two Metals: contrasting criticalities in the pnictides and hole-doped cuprates
The iron-based high temperature superconductors share a number of
similarities with their copper-based counterparts, such as reduced
dimensionality, proximity to states of competing order, and a critical role for
3d electron orbitals. Their respective temperature-doping phase diagrams also
contain certain commonalities that have led to claims that the metallic and
superconducting properties of both families are governed by their proximity to
a quantum critical point (QCP) located inside the superconducting dome. In this
review, we critically examine these claims and highlight significant
differences in the bulk physical properties of both systems. While there is now
a large body of evidence supporting the presence of a (magnetic) QCP in the
iron pnictides, the situation in the cuprates is much less apparent, at least
for the end point of the pseudogap phase. We argue that the opening of the
normal state pseudogap in cuprates, so often tied to a putative QCP, arises
from a momentum-dependent breakdown of quasiparticle coherence that sets in at
much higher doping levels but which is driven by the proximity to the Mott
insulating state at half filling. Finally, we present a new scenario for the
cuprates in which this loss of quasiparticle integrity and its evolution with
momentum, temperature and doping plays a key role in shaping the resultant
phase diagram.Comment: This key issues review is dedicated to the memory of Dr. John Loram
whose pioneering measurements, analysis and ideas inspired much of its
conten
Temperature Dependence of Interlayer Magnetoresistance in Anisotropic Layered Metals
Studies of interlayer transport in layered metals have generally made use of
zero temperature conductivity expressions to analyze angle-dependent
magnetoresistance oscillations (AMRO). However, recent high temperature AMRO
experiments have been performed in a regime where the inclusion of finite
temperature effects may be required for a quantitative description of the
resistivity. We calculate the interlayer conductivity in a layered metal with
anisotropic Fermi surface properties allowing for finite temperature effects.
We find that resistance maxima are modified by thermal effects much more
strongly than resistance minima. We also use our expressions to calculate the
interlayer resistivity appropriate to recent AMRO experiments in an overdoped
cuprate which led to the conclusion that there is an anisotropic, linear in
temperature contribution to the scattering rate and find that this conclusion
is robust.Comment: 8 pages, 4 figure
Linear magnetoresistance in a quasi-free two dimensional electron gas in an ultra-high mobility GaAs quantum well
We report a magnetotransport study of an ultra-high mobility
(\,cm\,V\,s) -type GaAs
quantum well up to 33 T. A strong linear magnetoresistance (LMR) of the order
of 10 % is observed in a wide temperature range between 0.3 K and 60 K. The
simplicity of our material system with a single sub-band occupation and free
electron dispersion rules out most complicated mechanisms that could give rise
to the observed LMR. At low temperature, quantum oscillations are superimposed
onto the LMR. Both, the featureless LMR at high and the quantum
oscillations at low follow the empirical resistance rule which states that
the longitudinal conductance is directly related to the derivative of the
transversal (Hall) conductance multiplied by the magnetic field and a constant
factor that remains unchanged over the entire temperature range. Only
at low temperatures, small deviations from this resistance rule are observed
beyond that likely originate from a different transport mechanism for
the composite fermions
Dimensionality-driven spin-flop transition in quasi-one-dimensional PrBa2Cu4O8
In the quasi-one-dimensional cuprate PrBaCuO, the Pr cations
order antiferromagnetically at 17 K in zero field. Through a combination of
magnetic susceptibility, torque magnetometry, specific heat and interchain
transport measurements, the anisotropic temperature-magnetic field phase
diagram associated with this ordering has been mapped out. A low-temperature
spin-flop transition in the Pr sub-lattice is found to occur at the same
magnetic field strength and orientation as a dimensional crossover in the
ground state of the metallic CuO chains. This coincidence suggests that the
spin reorientation is driven by a change in the anisotropic
Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction induced by a corresponding
change in effective dimensionality of the conduction electrons.Comment: 8 pages, 8 figure
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