8 research outputs found
Detection of the Unusual Magnetic Orders in the Pseudogap Region of a High-Temperature Superconducting YBa2Cu3O6.6 Crystal by Muon-Spin Relaxation
We present muon spin relaxation (muSR) measurements on a large YBa2Cu3O6.6
single crystal in which two kinds of unusual magnetic order have been detected
in the pseudogap region by neutron scattering. A comparison is made to
measurements on smaller, higher quality YBa2Cu3Oy single crystals. One type of
magnetic order is observed in all samples, but does not evolve significantly
with hole doping. A second type of unusual magnetic order is observed only in
the YBa2Cu3O6.6 single crystal. This magnetism has an ordered magnetic moment
that is quantitatively consistent with the neutron experiments, but is confined
to just a small volume of the sample (~ 3%). Our findings do not support
theories that ascribe the pseudogap to a state characterized by loop-current
order, but instead indicate that dilute impurity phases are the source of the
unusual magnetic orders in YBa2Cu3Oy.Comment: 4 pages, 4 figure
Inhomogeneous Magnetic-Field Response of YBa2Cu3Oy and La2-xSrxCuO4 Persisting above the Bulk Superconducting Transition Temperature
We report that in YBa2Cu3Oy and La2-xSrxCuO4 there is a spatially
inhomogeneous response to magnetic field for temperatures T extending well
above the bulk superconducting transition temperature Tc. An inhomogeneous
magnetic response is observed above Tc even in ortho-II YBa2Cu3O6.50, which has
highly ordered doping. The degree of the field inhomogeneity above Tc tracks
the hole doping dependences of both Tc and the density of the superconducting
carriers below Tc, and therefore is apparently coupled to superconductivity.Comment: Modified discussio
Hole doping dependences of the magnetic penetration depth and vortex core size in YBa2Cu3Oy: Evidence for stripe correlations near 1/8 hole doping
We report on muon spin rotation measurements of the internal magnetic field
distribution n(B) in the vortex solid phase of YBa2Cu3Oy (YBCO) single
crystals, from which we have simultaneously determined the hole doping
dependences of the in-plane Ginzburg-Landau (GL) length scales in the
underdoped regime. We find that Tc has a sublinear dependence on
1/lambda_{ab}^2, where lambda_{ab} is the in-plane magnetic penetration depth
in the extrapolated limits T -> 0 and H -> 0. The power coefficient of the
sublinear dependence is close to that determined in severely underdoped YBCO
thin films, indicating that the same relationship between Tc and the superfluid
density is maintained throughout the underdoped regime. The in-plane GL
coherence length (vortex core size) is found to increase with decreasing hole
doping concentration, and exhibit a field dependence that is explained by
proximity-induced superconductivity on the CuO chains. Both the magnetic
penetration depth and the vortex core size are enhanced near 1/8 hole doping,
supporting the belief by some that stripe correlations are a universal property
of high-Tc cuprates.Comment: 12 pages, 13 figure
Spin-glass state of vortices in YBa2Cu3Oy and La2-xSrxCuO4 below the metal-to-insulator crossover
Highly disordered magnetism confined to individual weakly interacting
vortices is detected by muon spin rotation in two different families of
high-transition-temperature superconductors, but only in samples on the
low-doping side of the low-temperature normal state metal-to-insulator
crossover (MIC). The results support an extended quantum phase transition (QPT)
theory of competing magnetic and superconducting orders that incorporates the
coupling between CuO2 planes. Contrary to what has been inferred from previous
experiments, the static magnetism that coexists with superconductivity near the
field-induced QPT is not ordered. Our findings unravel the mystery of the MIC
and establish that the normal state of high-temperature superconductors is
ubiquitously governed by a magnetic quantum critical point in the
superconducting phase.Comment: 9 pages, 9 figure
Direct Search for a Ferromagnetic Phase in a Heavily Overdoped Nonsuperconducting Copper Oxide
The doping of charge carriers into the CuO2 planes of copper oxide Mott
insulators causes a gradual destruction of antiferromagnetism and the emergence
of high-temperature superconductivity. Optimal superconductivity is achieved at
a doping concentration p beyond which further increases in doping cause a
weakening and eventual disappearance of superconductivity. A potential
explanation for this demise is that ferromagnetic fluctuations compete with
superconductivity in the overdoped regime. In this case a ferromagnetic phase
at very low temperatures is predicted to exist beyond the doping concentration
at which superconductivity disappears. Here we report on a direct examination
of this scenario in overdoped La2-xSrxCuO4 using the technique of muon spin
relaxation. We detect the onset of static magnetic moments of electronic origin
at low temperature in the heavily overdoped nonsuperconducting region. However,
the magnetism does not exist in a commensurate long-range ordered state.
Instead it appears as a dilute concentration of static magnetic moments. This
finding places severe restrictions on the form of ferromagnetism that may exist
in the overdoped regime. Although an extrinsic impurity cannot be absolutely
ruled out as the source of the magnetism that does occur, the results presented
here lend support to electronic band calculations that predict the occurrence
of weak localized ferromagnetism at high doping.Comment: 13 pages, 5 figure