Incommensurate Spin Ordering and Fluctuations in underdoped La_{2-x}Ba_{x}CuO_{4}

TL;DR

This study uses neutron scattering to investigate incommensurate spin order and low-energy spin dynamics in underdoped La_{2-x}Ba_{x}CuO_{4}, revealing magnetic order unaffected by superconductivity or magnetic fields, with weak doping dependence of incommensurability.

Contribution

It provides new insights into the magnetic behavior of underdoped La_{2-x}Ba_{x}CuO_{4} and shows that magnetic field effects differ from related cuprates, highlighting non-universality.

Findings

Static incommensurate magnetic order appears below T_N=39.5 K.

Magnetic order is unaffected by superconductivity or magnetic fields up to 7 Tesla.

Incommensurability δ is weakly dependent on doping.

Abstract

Using neutron scattering techniques, we have studied incommensurate spin ordering as well as low energy spin dynamics in single crystal underdoped \LBCO with x$\sim$0.095 and 0.08; high temperature superconductors with T$_C \sim$ 27 K and 29 K respectively. Static two dimensional incommensurate magnetic order appears below T$_N$=39.5 $\pm$ 0.3 K in \LBCO (x=0.095) and a similar temperature for x=0.08 within the low temperature tetragonal phase. The spin order is unaffected by either the onset of superconductivity or the application of magnetic fields of up to 7 Tesla applied along the c-axis in the x=0.095 sample. Such magnetic field {\it independent} behaviour is in marked contrast with the field induced enhancement of the staggered magnetisation observed in the related \LSCO system, indicating this phenomenon is not a universal property of cuprate superconductors. Surprisingly, we find that incommensurability $\delta $ is only weakly dependent on doping relative to \LSCO. Dispersive excitations in \LBCO (x=0.095) at the same incommensurate wavevector persist up to at least 60 K. The dynamical spin susceptibility of the low energy spin excitations saturates below \tc, in a similar manner to that seen in the superconducting state of La$_2$CuO$_{4+y}$.