Andrew Boothroyd

Abstract:

We report the results of a muon-spin relaxation ( μ SR ) investigation of La 2 − x Sr x CoO 4 , an antiferromagnetic insulating series which has been shown to support charge ordered and magnetic stripe phases and an hourglass magnetic excitation spectrum. We present a revised magnetic phase diagram, which shows that the suppression of the magnetic ordering temperature is highly sensitive to small concentrations of holes. Distinct behavior within an intermediate x range ( 0.2 ≤ x ≲ 0.6 ) suggests that the putative stripe ordered phase extends to lower x than previously thought. Further charge doping ( 0.67 ≤ x ≤ 0.9 ) prevents magnetic ordering for T ≳ 1.5 K .

Abstract:

Recent experiments indicate that static stripe-like charge order is generic to the hole-doped copper oxide superconductors and competes with superconductivity. Here we show that a similar type of charge order is present in La5/3Sr1/3CoO4, an insulating analogue of the copper oxide superconductors containing cobalt in place of copper. The stripe phase we have detected is accompanied by short-range, quasi-one-dimensional, antiferromagnetic order, and provides a natural explanation for the distinctive hourglass shape of the magnetic spectrum previously observed in neutron-scattering measurements of La2−xSrxCoO4 and many hole-doped copper oxide superconductors. The results establish a solid empirical basis for theories of the hourglass spectrum built on short-range, quasi-static, stripe correlations.