8 research outputs found
Nearly isotropic upper critical fields in a SrFeCoAs single crystal
We study temperature dependent upper critical field of a
SrFeCoAs single crystal (\textit{T}=20.2 K) along
\textit{ab}-plane and \textit{c}-axis through resistivity measurements up to 50
T. For the both crystalline directions, becomes nearly isotropic
at zero temperature limit, reaching 48 T. The temperature dependence of
the curves is explained by interplay between orbital and Pauli
limiting behaviors combined with the two band effects.Comment: Proceedings of M2S-IX, Tokyo 200
Magnetotransport near a quantum critical point in a simple metal
We use geometric considerations to study transport properties, such as the
conductivity and Hall coefficient, near the onset of a nesting-driven spin
density wave in a simple metal. In particular, motivated by recent experiments
on vanadium-doped chromium, we study the variation of transport coefficients
with the onset of magnetism within a mean-field treatment of a model that
contains nearly nested electron and hole Fermi surfaces. We show that most
transport coefficients display a leading dependence that is linear in the
energy gap. The coefficient of the linear term, though, can be small. In
particular, we find that the Hall conductivity is essentially
unchanged, due to electron-hole compensation, as the system goes through the
quantum critical point. This conclusion extends a similar observation we made
earlier for the case of completely flat Fermi surfaces to the immediate
vicinity of the quantum critical point where nesting is present but not
perfect.Comment: 11 pages revtex, 4 figure
Impurity and strain effects on the magnetotransport of La1.85Sr0.15Cu(1-y)Zn(y)O4 films
The influence of zinc doping and strain related effects on the normal state
transport properties(the resistivity, the Hall angle and the orbital magneto-
resistance(OMR) is studied in a series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with
values of y between 0 and 0.12 and various degrees of strain induced by the
mismatch between the films and the substrate. The zinc doping affects only the
constant term in the temperature dependence of cotangent theta but the strain
affects both the slope and the constant term, while their ratio remains
constant.OMR is decreased by zinc doping but is unaffected by strain. The ratio
delta rho/(rho*tan^2 theta) is T-independent but decreases with impurity
doping. These results put strong constraints on theories of the normal state of
high- temperature superconductors
Magnetotransport in the Normal State of La1.85Sr0.15Cu(1-y)Zn(y)O4 Films
We have studied the magnetotransport properties in the normal state for a
series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with values of y, between 0 and
0.12. A variable degree of compressive or tensile strain results from the
lattice mismatch between the substrate and the film, and affects the transport
properties differently from the influence of the zinc impurities. In
particular, the orbital magnetoresistance (OMR) varies with y but is
strain-independent. The relations for the resistivity and the Hall angle and
the proportionality between the OMR and tan^2 theta are followed about 70 K. We
have been able to separate the strain and impurity effects by rewriting the
above relations, where each term is strain-independent and depends on y only.
We also find that changes in the lattice constants give rise to closely the
same fractional changes in other terms of the equation.The OMR is more strongly
supressed by the addition of impurities than tan^2 theta. We conclude that the
relaxation ratethat governs Hall effect is not the same as for the
magnetoresistance. We also suggest a correspondence between the transport
properties and the opening of the pseudogap at a temperature which changes when
the La-sr ratio changes, but does not change with the addition of the zinc
impurities
Intrinsic anisotropy versus effective pinning anisotropy in YBa2Cu3O7 thin films and nanocomposites
The intrinsic and effective anisotropies, both in the liquid and solid vortex regimes, of
YB
a
2
C
u
3
O
7
(YBCO) pristine and nanocomposite thin films have been investigated. Angular resistivity measurements under varying fields and temperatures were performed to characterize the intrinsic vs effective anisotropy of samples in the regime of long-range vortex displacements. The effective anisotropy
γ
eff
was determined from the scaling of the irreversibility line, applying the Blatter approach developed for uniaxial anisotropic superconductors. Resistive measurements in flux flow were utilized, in addition to
H
c
2
measurements in ultrahigh-fields, to determine the intrinsic anisotropy mass γ, enabling the study of a large number of samples with varied nanoparticle compositions. In order to access the intrinsic anisotropy in the vortex solid phase, complex impedance measurements at high microwave frequencies were performed, allowing us to access the flux-flow intrinsic anisotropy in the regime of very short vortex oscillations within the pinning potential wells. Results show that while the effective anisotropy
γ
eff
decays as the nanoparticles-induced nanostrain in the YBCO films increases, the intrinsic anisotropy γ (determined both in dc and at microwave frequency) remains unaltered.Peer reviewe