On the Magnetic Excitation Spectra of High Tc Cu Oxides up to the Energies far above the Resonance Energy

TL;DR

This paper investigates the magnetic excitation spectra of high-Tc cuprates, extending measurements to energies well above the resonance energy, and analyzes the data using a phenomenological susceptibility model, revealing insights into spectral features and stripe effects.

Contribution

It demonstrates that a generalized susceptibility model can explain spectral features above the resonance energy and highlights the need to consider stripe phenomena in La214 systems.

Findings

Model reproduces rotation of incommensurate peaks above resonance energy.

Agreement with experimental data is good for YBCO, less so for La214.

Stripe effects are important for understanding La214 spectra.

Abstract

Magnetic excitation spectra c"(q,w) of YBa2Cu3Oy and La214 systems have been studied. For La1.88Sr0.12CuO4, c"(q,w) have been measured up to ~30 meV and existing data have been analyzed up to the energy w~150 meV by using the phenomenological expression of the generalized magnetic susceptibility c(q,w)=c0(q,w)/{1+J(q)c0(q,w)}, where c0(q,w) is the susceptibility of the electrons without the exchange coupling J(q) among them. In the relatively low energy region up to slightly above the resonance energy Er, it has been reported by the authors' group that the expression can explain characteristics of the q- and w-dependence of the spectra of YBa2Cu3Oy (YBCO or YBCOy). Here, it is also pointed out that the expression can reproduce the rotation of four incommensurate peaks of c"(q,w) within the a*-b* plane about (p/a, p/a) {or so-called (p, p)} point by 45 degree, which occurs as w goes to the energy region far above Er from E below Er. For La2-xSrxCuO4 and La2-xBaxCuO4, agreements between the observed results and the calculations are less satisfactory than for YBCO, indicating that we have to take account of the existence of the "stripes" to consistently explain the observed c"(q,w) of La214 system especially near x=1/8.