R. J. Birgeneau

Neutron-scattering study of spin-density wave order in the superconducting state of excess-oxygen-doped La{sub 2}CuO{sub 4+y}

We report neutron-scattering measurements of spin-density wave order within the superconducting state of a single crystal of predominately stage-4 La{sub 2}CuO{sub 4+y} with a T{sub 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 La{sub 2}CuO{sub 4}-based superconductors. {copyright} {ital 1999} {ital The American Physical Society}

Ferroelectric ordering in the relaxor Pb(Mg1/3Nb2/3)O-3 as evidenced by low-temperature phonon anomalies

Neutron scattering measurements of the lowest-energy TO phonons in the relaxor Pb(Mg 1 / 3 Nb 2 / 3 )O 3 (PMN) are reported for 10≤T7≤50 K. The soft mode, which is overdamped by the polar nanoregions below the Burns temperature T d =620 K, surprisingly recovers below 220 K. The square of the soft-mode energy (∞ω 0 ) 2 increases linearly with decreasing temperature and is consistent with the behavior of a ferroelectric soft mode. At 10 K, ∞ω 0 reaches II meV, the same value observed in ferroelectric Pb(Zn 1 / 3 Nb 2 / 3 )O 3 at low T. An unusual broadening of the TA phonon starts at T d and disappears at 220 K, coincident with the recovery of the TO mode. These dynamics suggest that a well-developed ferroelectric state is established below 220 K.

From incommensurate to dispersive spin-fluctuations : The high-energy inelastic spectrum in superconducting YBa2Cu3O6.5

We have investigated the spin-fluctuations at energy transfers up to

Transition probabilities for ƒ-electron J-multiplets in cubic crystal fields

\ensuremath{\sim}110\phantom{\rule{0.3em}{0ex}}\mathrm{meV}

Electronic phase separation in lightly doped La 2 − x Sr x Cu O 4

, well above the resonance energy

Phase transitions in diluted magnets: Critical behavior, percolation, and random fields

(33\phantom{\rule{0.3em}{0ex}}\mathrm{meV})

Neutron scattering study of the lattice dynamical phase transitions in KMnF3

in the

Photoelectron spin-flipping and texture manipulation in a topological insulator

\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}

Mean field theory, the Ginzburg criterion, and marginal dimensionality of phase transitions

ortho-II superconductor using neutron time-of-flight and triple-axis techniques. The spectrum at high energies differs from the low-energy incommensurate modulations previously reported where the incommensurate wave vector is largely independent of energy. Well above the resonance the peak of the spin response lies at wave vectors that increase with energy. Within error the excitations at all energies above the resonance are best described by a ring around the

Enhancement of long-range magnetic order by magnetic field in superconducting La 2 CuO 4 + y

(\ensuremath{\pi},\ensuremath{\pi})