arXiv subjects

H. Woo

Publications and source records attributed to H. Woo.

5 recordsLinked to original sources

arXiv2006

High Energy Spin Excitations in Electron-Doped Superconducting Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-δ}$ with $T_c=21$ K

We use high-resolution inelastic neutron scattering to study the low-temperature magnetic excitations of electron-doped superconducting Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-δ}$ ($T_c=21\pm 1$ K) over a wide energy range (4 meV$\le\hbarω\le 330$ meV). The effect of electron-doping is to cause a wave vector ($Q$) broadening in the low-energy ($\hbarω\le 80$ meV) commensurate spin fluctuations at ($π$,$π$) and to suppress the intensity of spin-wave-like excitations at high energies ($\hbarω\ge 100$ meV). This leads to a substantial redistribution in the spectrum of the local dynamical spin susceptibility $χ^{\prime\prime}(ω)$, and reveals a new energy scale similar to that of the lightly hole-doped YB$_2$Cu$_3$O$_{6.353}$ ($T_c=18$ K).

cond-mat.supr-con↗

arXiv2004

Universal magnetic excitation spectrum in cuprates

We have recently used inelastic neutron scattering to measure the magnetic excitation spectrum of La(1.875)Ba(0.125)CuO(4) up to 200 meV. This particular cuprate is of interest because it exhibits static charge and spin stripe order. The observed spectrum is remarkably similar to that found in superconducting YBa(2)Cu(3)O(6+x) and La(2-x)Sr(x)CuO(4); the main differences are associated with the spin gap. We suggest that essentially all observed features of the magnetic scattering from cuprate superconductors can be described by a universal magnetic excitation spectrum multiplied by a spin gap function with a material-dependent spin-gap energy.

cond-mat.supr-con↗

arXiv2004

Quantum Magnetic Excitations from Stripes in Copper-Oxide Superconductors

In the copper-oxide parent compounds of the high-transition-temperature superconductors, the valence electrons are localized, one per copper site, due to strong intraatomic Coulomb repulsion. A symptom of the localization is antiferromagnetism, where the spins of localized electrons alternate between up and down. The superconductivity appears when mobile 'holes' are doped into this insulating state, and it coexists with antiferromagnetic fluctuations. In one approach to the coexistence, the holes are believed to self-organize into 'stripes' that alternate with antiferromagnetic (insulating) regions within copper-oxide planes. Such an unusual electronic state would necessitate an unconventional mechanism of superconductivity. There is an apparent problem with this picture, however: measurements of magnetic excitations in superconducting YBa(2)Cu(3)O(6+x) near optimum doping are incompatible with the naive expectations for a material with stripes. Here we report neutron scattering measurements on stripe-ordered La(1.875)Ba(0.125)CuO(4). We show that the measured excitations are, surprisingly, quite similar to those in YBa(2)Cu(3)O(6+x) (i.e., the predicted spectrum of magnetic excitations is wrong). We find instead that the observed spectrum can be understood within a stripe model by taking account of quantum excitations. Our results support the concept that stripe correlations are essential to high-transition-temperature superconductivity.

cond-mat.supr-con↗

arXiv2003

Spinons in the strongly correlated copper oxide chains in SrCuO2

We have investigated the spin dynamics in the strongly correlated chain copper oxide SrCuO$_2$ for energies up to $\gtrsim 0.6$ eV using inelastic neutron scattering. We observe an acoustic band of magnetic excitations which is well described by the "Muller-ansatz" for the two-spinon continuum in the S=1/2 antiferromagnetic Heisenberg spin chain. The lower boundary of the continuum extends up to $\approx 360$ meV, which corresponds to an exchange constant $J = 226(12)$ meV. Our finding that an effective Heisenberg spin Hamlitonian adequately describes the spin sector of this 1D electron system, even though its energy scale is comparable to that of charge excitations, provides compelling experimental evidence for spin-charge separation.

cond-mat.str-el↗

arXiv2003

Spin excitations in stripe-ordered La2-xSrxNiO4 (x=0.275 and 1/3)

We report neutron scattering measurements of the spectrum of magnetic excitations in the stripe-ordered phase of La2-xSrxNiO4 (x=0.275 and 1/3). The propagating spin excitations follow a similar dispersion relation for the two compositions, but the line widths are broader for x=0.275 than for x=1/3.

cond-mat.str-el↗