364 research outputs found
Dynamics of the Local Moment Induced by Nonmagnetic Defects in Cuprates
We present a study of the spin dynamics of magnetic defects induced by Li
substitution of the plane Cu in the normal state of YBaCuO. The
fluctuations of the coupled Cu magnetic moments in the vicinity of Li are
probed by near-neighbour Y {\it and} Li NMR spin lattice relaxation.
The data indicates that the magnetic perturbation fluctuates as a single entity
with a correlation time which scales with the local static
susceptibility. This behaviour is reminiscent of the low Kondo state of
magnetic impurities in conventional metals. Surprisingly it extends well above
the ``Kondo'' temperature for the underdoped pseudogapped case.Comment: 4 pages, 5 figures (same), major modifications to text, accepted in
PR
Non-magnetic impurities in two- and three- dimensional Heisenberg antiferromagnets
In this paper we study in a large-S expansion effects of substituting spins
by non-magnetic impurities in two- and three- dimensional Heisenberg
antiferromagnets in a weak magnetic field. In particular, we demonstrate a
novel mechanism where magnetic moments are induced around non-magnetic
impurities when magnetic field is present. As a result, Curie-type behaviour in
magnetic susceptibility can be observed well below the Neel temperature, in
agreement with what is being observed in and
compounds.Comment: Latex fil
Phase segregation in NaxCoO2 for large Na contents
We have investigated a set of sodium cobaltates (NaxCoO2) samples with
various sodium content (0.67 \le x \le 0.75) using Nuclear Quadrupole Resonance
(NQR). The four different stable phases and an intermediate one have been
recognized. The NQR spectra of 59Co allowed us to clearly differentiate the
pure phase samples which could be easily distinguished from multi-phase
samples. Moreover, we have found that keeping samples at room temperature in
contact with humid air leads to destruction of the phase purity and loss of
sodium content. The high sodium content sample evolves progressively into a
mixture of the detected stable phases until it reaches the x=2/3 composition
which appears to be the most stable phase in this part of phase diagram.Comment: 5 pages, 4 figure
Universal sheet resistance and revised phase diagram of the cuprate high-temperature superconductors
Upon introducing charge carriers into the copper-oxygen sheets of the
enigmatic lamellar cuprates the ground state evolves from an insulator into a
superconductor, and eventually into a seemingly conventional metal (a Fermi
liquid). Much has remained elusive about the nature of this evolution and about
the peculiar metallic state at intermediate hole-carrier concentrations (p).
The planar resistivity of this unconventional metal exhibits a linear
temperature dependence (\rho T) that is disrupted upon cooling toward
the superconducting state by the opening of a partial gap (the pseudogap) on
the Fermi surface. Here we first demonstrate for the quintessential compound
HgBaCuO a dramatic switch from linear to purely quadratic
(Fermi-liquid-like, \rho T) resistive behavior in the pseudogap
regime. Despite the considerable variation in crystal structures and disorder
among different compounds, our result together with prior work gives new
insight into the p-T phase diagram and reveals the fundamental resistance per
copper-oxygen sheet in both linear (\rho_S = A_{1S} T) and quadratic (\rho_S =
A_{2S} T) regimes, with A_{1S} A_{2S} 1/p. Theoretical
models can now be benchmarked against this remarkably simple universal
behavior. Deviations from this underlying behavior can be expected to lead to
new insights into the non-universal features exhibited by certain compounds
Muon-spin-rotation study of the effect of Zn substitution on magnetism in YBa2Cu3Ox
The magnetic properties of YBa2(Cu0.96Zn0.04)3Ox were studied in detail by means of muon spin rotation and relaxation for 6.0≤x≤6.92. The complete magnetic phase diagram was mapped out and a disordered magnetic state was found to persist between x=6.4 and x≃6.7 (metallic transition), in contrast with pure YBa2Cu3Ox. The appearance of this magnetic state is attributed to the effect of Zn on the doped hole dynamics and might be associated with the freezing of local moments due to Zn (6.43≤x≤6.88), which were also detected here, in the paramagnetic state
Zn-doping effect on the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals
We report the magnetotransport properties of
Bi_{2}Sr_{2-x}La_{x}Cu_{1-z}Zn_{z}O_{6+\delta} (Zn-doped BSLCO) single crystals
with z of up to 2.2%. Besides the typical Zn-doping effects on the in-plane
resistivity and the Hall angle, we demonstrate that the nature of the
low-temperature normal state in the Zn-doped samples is significantly altered
from that in the pristine samples under high magnetic fields. In particular, we
observe nearly-isotropic negative magnetoresistance as well as an increase in
the Hall coefficient at very low temperatures in non-superconducting Zn-doped
samples, which we propose to be caused by the Kondo scattering from the local
moments induced by Zn impurities.Comment: 4 pages, 4 figures, final version (one reference added), published in
Phys. Rev.
Charge Localization from Local Destruction of Antiferromagnetic Correlation in Zn-doped YBa2Cu3O7-d
The in-plane normal-state resistivity of Zn-doped YBa2Cu3O7-d single crystals
is measured down to low temperatures by suppressing superconductivity with
magnetic fields up to 18 T. Substitution of Cu with Zn in the CuO2 planes is
found to induce carrier localization at low temperatures in "clean" samples
with kF l > 5, where the mean free path l is larger than the electron wave
length and thus localization is not normally expected. The destruction of the
local antiferromagnetic correlation among Cu spins by Zn is discussed to be the
possible origin of this unusual charge localization.Comment: 4 pages of LaTeX (revtex and epsf) including 4 postscript figure
Detection by NMR of a "local spin-gap" in quenched CsC60
We present a 13C and 133Cs NMR investigation of the CsC60 cubic quenched
phase. Previous ESR measurements suggest that this phase is metallic, but NMR
reveals contrasting electronic behavior on the local scale. The 13C
spin-lattice relaxation time (T1) exhibits a typical metallic behavior down to
50 K, but indicates that a partial spin-gap opens for T<50 K. Unexpectedly,
133Cs NMR shows that there are two inequivalent Cs sites. For one of these
sites, the NMR shift and (T1T)^{-1} follow an activated law, confirming the
existence of a spin-gap. We ascribe this spin-gap to the occurrence of
localized spin-singlets on a small fraction of the C60 molecules.Comment: 4 figure
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