623 research outputs found
Systematic Study of Short Range Antiferromagnetic Order and The Spin-Glass State in Lightly Doped La2-xSrxCuO4
Systematic measurements of the magnetic susceptibility were performed on
single crystals of lightly doped La2-xSrxCuO4 (x=0.03, 0.04 and 0.05). For all
samples the temperature dependence of the in-plane magnetic susceptibility
shows typical spin-glass features with spin-glass transition temperatures Tg of
6.3K, 5.5K and 5.0K for x=0.03, 0.04 and 0.05, respectively. The canonical
spin-glass order parameter extracted from the in-plane susceptibility of all
the samples follows a universal scaling curve. On the other hand, the
out-of-plane magnetic susceptibility deviates from Curie law below a
temperature Tdv, higher than Tg. Comparing with previous neutron scattering
results with an instrumental energy resolution of 0.25 meV from Wakimoto et
al., the x-dependence of Tdv is qualitatively the same as that of Tel, the
temperature below which the elastic magnetic scattering develops around (pi,
pi). Thus, a revised magnetic phase diagram in the lightly doped region of
La2-xSrxCuO4 is proposed. The Curie constants calculated from the in-plane
susceptibility are independent of the Sr concentration. On the basis of the
cluster spin-glass model, this fact might reflect an inhomogeneous distribution
of doped holes in the CuO2 plane, such as in a stripe structure.Comment: 7 pages, 6 figure
Resonant inelastic X-ray scattering study of overdoped LaSrCuO
Resonant inelastic x-ray scattering (RIXS) at the copper K absorption edge
has been performed for heavily overdoped samples of LaSrCuO
with and 0.30. We have observed the charge transfer and
molecular-orbital excitations which exhibit resonances at incident energies of
and 8.998 keV, respectively. From a comparison with previous
results on undoped and optimally-doped samples, we determine that the
charge-transfer excitation energy increases monotonically as doping increases.
In addition, the -dependences of the RIXS spectral weight and absorption
spectrum exhibit no clear peak at keV in contrast to results in
the underdoped samples. The low-energy ( eV) continuum excitation
intensity has been studied utilizing the high energy resolution of 0.13 eV
(FWHM). A comparison of the RIXS profiles at and
indicates that the continuum intensity exists even at in the
overdoped samples, whereas it has been reported only at and
for the sample. Furthermore, we also found an additional excitation on
top of the continuum intensity at the and positions.Comment: 7 pages, 7 figure
Charge-transfer exciton in La2CuO4 probed with resonant inelastic x-ray scattering
We report a high-resolution resonant inelastic x-ray scattering study of
La2CuO4. A number of spectral features are identified that were not clearly
visible in earlier lower-resolution data. The momentum dependence of the
spectral weight and the dispersion of the lowest energy excitation across the
insulating gap have been measured in detail. The temperature dependence of the
spectral features was also examined. The observed charge transfer edge shift,
along with the low dispersion of the first charge transfer excitation are
attributed to the lattice motion being coupled to the electronic system. In
addition, we observe a dispersionless feature at 1.8 eV, which is associated
with a d-d crystal field excitation.Comment: 5 pages, 4 figure
Pre-travel consultations quality criteria: a Delphi consensus
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Diagonal static spin correlation in the low temperature orthorhombic Pccn phase of La1.55Nd0.4Sr0.05CuO4
Elastic neutron scattering measurements have been performed on Nd, Sr
co-doped La1.55Nd0.4Sr0.05CuO4, which exhibits a structural phase transition at
Ts ~ 60K from the low temperature orthorhombic Bmab phase (labelled LTO1) to
the low temperature orthorhombic Pccn phase (labelled LTO2). At low
temperatures, well below Ts, elastic magnetic peaks are observed at the
``diagonal'' incommensurate (IC) positions (0, 1+/-0.055, 0), with modulation
direction only along the orthorhombic b-axis just as in Nd-free
La1.95Sr0.05CuO4. In the present study, the one-dimensionality of the IC
modulation, which is naturally explained by a stripe model, is clearly
demonstrated with our "single-domain" crystal. The temperature dependence of
the IC peak intensity suggests a substantial contribution from the Nd3+ spins
below ~3K. Consistent with this, the L dependence of the magnetic scattering is
accurately accounted for by a model in which the contribution of the Nd3+ spins
is explicitly included.Comment: 8 pages, 8 figure
Direct relation between the low-energy spin excitations and superconductivity of overdoped high- superconductors
The dynamic spin susceptibility, , has been measured over the
energy range of meV for overdoped
LaSrCuO. Incommensurate (IC) spin excitations are observed
at 8 K for all superconducting samples for with
peaking at meV. The IC peaks at 6 meV become smaller in
intensity with increasing and, finally, become unobservable for a sample
with which has no bulk superconductivity. The maximum
decreases linearly with (onset) in the overdoped region, implying a direct
cooperative relation between the spin fluctuations and the superconductivity.Comment: 4 pages, 4 figure
Neutron scattering study of soft phonons and diffuse scattering in insulating LaSrCuO
Soft phonons and diffuse scattering in insulating LaSrCuO
() have been studied by the neutron scattering technique. The X-point
phonon softens from high temperature towards the structural transition
temperature K, and the Z-point phonon softens again below 200 K.
The Z-point phonon softening persists to low temperature, in contrast to the
behavior observed in the superconducting compound, in which the
Z-point phonon hardens below . The diffuse scattering associated with the
structural phase transition at 410 K appears at commensurate positions. These
results highlight interesting differences between superconducting and
insulating samples.Comment: 5 pages, 5 figure
Striped superconductors in the extended Hubbard model
We present a minimal model of a doped Mott insulator that simultaneously
supports antiferromagnetic stripes and d-wave superconductivity. We explore the
implications for the global phase diagram of the superconducting cuprates. At
the unrestricted mean-field level, the various phases of the cuprates,
including weak and strong pseudogap phases, and two different types of
superconductivity in the underdoped and the overdoped regimes, find a natural
interpretation. We argue that on the underdoped side, the superconductor is
intrinsically inhomogeneous -- striped coexistence of of superconductivity and
magnetism -- and global phase coherence is achieved through Josephson-like
coupling of the superconducting stripes. On the overdoped side, the state is
overall homogeneous and the superconductivity is of the classical BCS type.Comment: 5 pages, 3 eps figures. Effect of t' on stripe filling + new
references are adde
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