Energy Spectrum of Spin Fluctuations in Superconducting La2-xSrxCuO4 (0.10 < x < 0.25)

TL;DR

This study investigates the energy spectrum of spin fluctuations in La2-xSrxCuO4 superconductors, revealing a gap and enhancement features in optimally doped samples, but not in underdoped or overdoped ones, using inelastic neutron scattering.

Contribution

It provides detailed insights into the doping-dependent spin excitation spectrum and identifies a gap-like feature and enhancement around 7meV in optimally doped samples.

Findings

Energy gap observed in optimally doped samples

Enhancement of spin susceptibility around 7meV in certain doping levels

No clear gap or enhancement in underdoped and heavily overdoped samples

Abstract

The energy spectrum of incommensurate spin fluctuations in superconducting Sr-doped La2CuO4 has been studied by inelastic neutron scattering experiments. An energy gap in the spin excitation spectrum is observed in the superconducting state of optimally doped (x=0.15) and slightly overdoped (x=0.18) samples. At temperatures well below Tc, the incommensurate peaks diminish rapidly in intensity with decreasing energy below ~8meV and merge into the background below ~3.5meV for x=0.15 and ~4.5meV for x=0.18. For both samples, the energy spectrum of the q-integrated spin susceptibility, x"(w), exhibits an enhancement around 7meV, which is caused by a broadening in the momentum width of the incommensurate peaks. The gap-like structure in the energy spectrum and the enhancement of x"(w) survive at Tc. On the other hand, for both underdoped (x=0.10) and heavily overdoped (x=0.25) samples there is neither a clear energy gap nor an enhancement of x"(w) below Tc.