Showing papers by "Marc Kastner published in 1999"
TL;DR: In this article, the spin-density wave order of a single crystal of a stage-4 superconducting state with a high temperature of 42 K was investigated and it was shown that the spin direction in the copper-oxide plane is similar to that in the undoped antiferromagnetic insulator.
Abstract: We report neutron-scattering measurements of spin-density wave order within the superconducting state of a single crystal of predominately stage-4 ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4+y}$ with a ${T}_{c}$ (onset) of 42 K. The low-temperature elastic magnetic scattering is incommensurate with the lattice and is characterized by long-range order in the copper-oxide plane with the spin direction identical to that in the insulator. Between neighboring planes, the spins exhibit short-range correlations with a stacking arrangement reminiscent of that in the undoped antiferromagnetic insulator. The elastic magnetic peak intensity appears at the same temperature within the errors as the superconductivity, suggesting that the two phenomena are strongly correlated. These observations directly reveal the persistent influence of the antiferromagnetic order as the doping level increases from the insulator to the superconductor. In addition, our results confirm that spin-density wave order for incommensurabilities near $1/8$ is a robust feature of the ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$-based superconductors.
185 citations
TL;DR: In this paper, the authors performed neutron-scattering measurements to search for possible elastic incommensurate magnetic peaks in superconducting materials and found that the peak intensity first appears at the onset of superconductivity.
Abstract: Neutron-scattering measurements have been performed to search for possible elastic incommensurate magnetic peaks in superconducting ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ with $x=0.10,$ 0.12, and 0.15. The most dramatic effects are found for $x=0.12;$ in this case, the peak intensity first appears at the onset of superconductivity ${T}_{c}(=31 \mathrm{K}).$ The resolution-limited peak width indicates that the static magnetic correlation length exceeds 200 \AA{} isotropically in the ${\mathrm{CuO}}_{2}$ planes. Weak elastic peaks are also observed at low temperatures for $x=0.10$ while for $x=0.15$ any incommensurate elastic scattering is below the limit of detectability. Elastic peaks are observed in Zn-substituted nonsuperconducting ${\mathrm{La}}_{1.88}{\mathrm{Sr}}_{0.12}{\mathrm{Cu}}_{0.97}{\mathrm{Zn}}_{0.03}{0}_{4}.$ However, in this case, the Zn substitution degrades the magnetic order; the peak appears at lower temperature (17 K) and the correlation length is shorter (80 \AA{}) than that in the Zn-free $x=0.12$ sample.
169 citations
TL;DR: In this paper, Neutron-scattering experiments have been performed on lightly doped La{sub 2{minus}x}Sr{sub x}CuO{sub 4} single crystals in both the insulating (x=0.03,0.04, 0.06) and superconducting (x = 0.05) regions.
Abstract: Neutron-scattering experiments have been performed on lightly doped La{sub 2{minus}x}Sr{sub x}CuO{sub 4} single crystals in both the insulating (x=0.03,0.04,0.05) and superconducting (x=0.06) regions. Elastic magnetic peaks are observed at low temperatures in all samples with the maximum peak linewidth occurring at the critical concentration x{sub c}=0.05. Incommensurate peaks are observed only at x=0.05, the positions of which are rotated by 45{degree} in reciprocal space about ({pi},{pi}) from those observed for x{ge}0.06 in the superconducting phase. {copyright} {ital 1999} {ital The American Physical Society}
132 citations
TL;DR: In this article, Neutron-scattering experiments have been performed on lightly-doped La(2-x)Sr(x)CuO4 single crystals in both the insulating (x=0.03, 0.04,0.05) and superconducting (x = 0.06) regions.
Abstract: Neutron-scattering experiments have been performed on lightly-doped La(2-x)Sr(x)CuO4 single crystals in both the insulating (x=0.03,0.04,0.05) and superconducting (x=0.06) regions. Elastic magnetic peaks are observed at low temperatures in all samples with the maximum peak linewidth occuring at the critical concentration x_c=0.05. New incommensurate peaks are observed only at x=0.05, the positions of which are rotated by 45 degrees in reciprocal space about (pi,pi) from those observed for x>=0.06 in the superconducting phase.
125 citations
TL;DR: In this article, the Coulomb blockade peak positions of a quantum dot were studied in the regime of GaAs/AlxGa12xAs, and the quantum dot was defined by patterning the two-dimensional electron gas of a silicon metal-oxide-semiconductor field effect transistor structure using stacked gates.
Abstract: We present an experimental study of the fluctuations of Coulomb-blockade peak positions of a quantum dot. The dot is defined by patterning the two-dimensional electron gas of a silicon metal-oxide-semiconductor field-effect transistor structure using stacked gates. This permits variation of the number of electrons on the quantum dot without significant shape distortion. The ratio of charging energy to single-particle energy is considerably larger than in comparable GaAs/AlxGa12xAs quantum dots. The statistical distribution of the conductance peak spacings in the Coulomb-blockade regime was found to be unimodal and does not follow the Wigner surmise. The fluctuations of the spacings are much larger than the typical single-particle level spacing and thus clearly contradict the expectation of constant interaction‐random matrix theory. @S0163-1829~99!50916-8#
68 citations
TL;DR: In this paper, the instantaneous spin-spin correlations in La{sub 2}CuO{sub 4} (T{sub N}=325 K) over the temperature range 337{endash}824 K have been carried out.
Abstract: We have carried out a neutron-scattering study of the instantaneous spin-spin correlations in La{sub 2}CuO{sub 4} (T{sub N}=325 K) over the temperature range 337{endash}824 K. Incident neutron energies varying from 14.7{endash}115 meV have been employed in order to guarantee that the energy integration is carried out properly. The results so obtained for the spin-correlation length as a function of temperature when expressed in reduced units agree quantitatively both with previous results for the two-dimensional (2D) tetragonal material Sr{sub 2}CuO{sub 2}Cl{sub 2} and with quantum Monte Carlo results for the nearest-neighbor square lattice S= (1) /(2) Heisenberg model. All of the experimental and numerical results for the correlation length are well described without any adjustable parameters by the behavior predicted for the quantum nonlinear sigma model in the low-temperature renormalized classical regime. The amplitude, on the other hand, deviates subtly from the predicted low-temperature behavior. These results are discussed in the context of recent theory for the 2D quantum Heisenberg model. {copyright} {ital 1999} {ital The American Physical Society}
50 citations
TL;DR: In this paper, it was shown that quantum fluctuations cause a two dimensional Ising ordering of the Cu{sub II } subsystems, lifting the degeneracy and a dramatic increase of the out-of-plane spin-wave gap, unique for {ital order out of disorder}.
Abstract: Sr{sub 2}Cu {sub 3}O{sub 4}Cl{sub 2} has Cu{sub I } and Cu{sub II } subsystems, forming interpenetrating S=1/2 square lattice Heisenberg antiferromagnets. The classical ground state is degenerate, due to frustration of the intersubsystem interactions. Magnetic neutron scattering experiments show that quantum fluctuations cause a two dimensional Ising ordering of the Cu{sub II } `s, lifting the degeneracy, and a dramatic increase of the Cu{sub I } out-of-plane spin-wave gap, unique for {ital order out of disorder}. The spin-wave energies are quantitatively predicted by calculations which include quantum fluctuations. {copyright} {ital 1999} {ital The American Physical Society }
41 citations
TL;DR: In this article, a synchrotron x-ray-scattering study of magnetoresistive manganite was conducted and it was shown that the photoinduced structural change is a common property of the charge-ordered perovskite manganites.
Abstract: We report a synchrotron x-ray-scattering study of the magnetoresistive manganite ${\mathrm{La}}_{0.875}{\mathrm{Sr}}_{0.125}{\mathrm{MnO}}_{3}.$ At low temperatures, this material undergoes an x-ray-induced structural transition at which charge ordering of ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ ions characteristic to the low-temperature state of this compound is destroyed. The transition is persistent but the charge-ordered state can be restored by heating above the charge-ordering transition temperature and subsequently cooling. The charge-ordering diffraction peaks, which are broadened at all temperatures, broaden more upon x-ray irradiation, indicating the finite correlation length of the charge-ordered state. Together with the recent reports on x-ray-induced transitions in ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3},$ our results demonstrate that the photoinduced structural change is a common property of the charge-ordered perovskite manganites.
38 citations
TL;DR: In this article, the dependence of the magnetization on field, temperature, and crystallographic orientation for the superconductivity of the CuO{sub 2} network was studied.
Abstract: The Cu{sub 3}O{sub 4} layer in Sr{sub 2}Cu{sub 3}O{sub 4}Cl{sub 2} is a variant of the square CuO{sub 2} lattice of the high-temperature superconductors, in which the center of every second plaquette contains an extra Cu{sup 2+} ion. The ions that make up the conventional CuO{sub 2} network, called CuI, have CuI-CuI exchange energy {approx}130thinspmeV, and order antiferromagnetically at about 380 K; the CuII-CuII exchange is only {approx}10thinspmeV, and the CuII{close_quote}s order at {approx}40thinspK. A study is reported here of the dependence of the magnetization on field, temperature, and crystallographic orientation for this interesting system. We show that the small permanent ferromagnetic moment, that appears when the CuI spins order, and the unusual spin rotation transitions seen most clearly for one particular direction of the magnetic field, are the result of several small bond-dependent anisotropic terms in the spin Hamiltonian that are revealed because of the frustration of the isotropic Heisenberg interaction between CuI and CuII spins. These include a term which favors collinearity of the CuI and CuII spins, which originates from quantum fluctuations, and also the pseudodipolar interaction. Some of these small interactions also come into play in other lamellar cuprates, connected with the high-T{sub c} superconductivity materials,more » and in many spin-chain and spin-ladder compounds. {copyright} {ital 1999} {ital The American Physical Society}« less
14 citations
TL;DR: In this article, a quantum Monte Carlo study of the thermodynamic properties of arrays of spin ladders with various widths (n), coupled via a weak interladder exchange coupling {alpha}J, where {ital J} is the intraladder coupling both along and between the chains.
Abstract: We report a quantum Monte Carlo study of the thermodynamic properties of arrays of spin ladders with various widths (n), coupled via a weak interladder exchange coupling {alpha}J, where {ital J} is the intraladder coupling both along and between the chains. This coupled ladder system serves as a simplified model for the magnetism of presumed ordered spin and charge stripes in the two-dimensional CuO{sub 2} planes of hole-doped copper oxides. Our results for n=3 with weak interladder coupling {alpha}=0.05, estimated from the t-t{sup {prime}}-t{sup {double_prime}}-J model, show good agreement with the ordering temperature of the recently observed spin-density-wave condensation in La{sub 2}CuO{sub 4+y}. We show that there exists a quantum critical point at {alpha}{sub c}{approx_equal}0.07 for n=4, and determine the phase diagram. Our data at this quantum critical point agree quantitatively with the universal scaling predicted by the quantum nonlinear {sigma} model. We also report results on random mixtures of n=2 and n=3 ladders, which correspond to the doping region near but above 1/8. Our study of the magnetic static structure factor reveals a saturation of the incommensurability of the spin correlations around 1/8, while the incommensurability of the charge stripes grows linearly with hole concentration. The implications of thismore » result for the interpretation of neutron-scattering experiments on the dynamic spin fluctuations in La{sub 2{minus}x}Sr{sub x}CuO{sub 4} are discussed. {copyright} {ital 1999} {ital The American Physical Society}« less
7 citations
TL;DR: In this article, the IC peak in superconducting LSCO of x = 0.12 was found to appear around 31 K, which is very close to T c. The line width reaches almost resolution limit, which indicates that the static magnetic correlation length exceeds 200 A −1 isotropically in the CuO 2 planes.
TL;DR: In this article, the elastic magnetic peaks appear at low temperatures in both insulating ( x = 0.02-0.05) and superconducting (x =0.06) samples, and the integrated intensity drastically changes across the low temperature insulator-superconductor boundary.
TL;DR: In this paper, the Coulomb energy of the initial electron-hole pair was investigated in three-dimensional close-packed solids of colloidal CdSe quantum dots and it was shown that surface ligands that promote initial separation of the electron and hole reduce the electric field required for the onset of the photocurrent.
Abstract: We demonstrate photoconductivity and conductivity in three-dimensional close-packed solids of colloidal CdSe quantum dots. We observe quantum dot size and surface passivation dependent photoconductivity that can be qualitatively understood by considering the energy required in order to overcome the Coulomb energy of the initial electron-hole pair. Our results suggest that surface ligands that promote initial separation of the electron and hole reduce the electric field required for the onset of the photocurrent. The dark conductance is much smaller than the photoconductance. Hysteretic behaviour and extremely long-lived current transients are observed in the dark current that are suggestive of Coulomb-glass behaviour.
01 Jan 1999
TL;DR: In this article, a review of dynamical spin correlations in high-Tc superconductor studied by neutron scattering is presented based on a recent work on hole-doped La2Cu04.
Abstract: Static, dynamical spin correlations in high-Tc superconductor studied by neutron scattering are reviewed based on our recent work on hole-doped La2Cu04. Spin correlation in the superconducting phase exhibits a long period spatial modulation. The doping, temperature, energy dependences of the spin fluctuations revealed a concordant relation between the incommensurate dynamical spin correlation, superconductivity. No-well defined spin correlation exists beyond the upper critical doping of the superconducting phase. Below Tc, a well-defined energy-gap of ~7meV opens in the dynamical spin susceptibility for the optimally doped or slightly overdoped phases. In contrast, no well-defined energy-gap opens for the underdoped samples. In addition to the dynamical spin fluctuations, a long range incommensurate static magnetic order is observed around 1/8-doping in the superconducting states. For x=0.12, the onset temperature of the magnetic order is highest, corresponds to Tc.