Cooperative coupling of static magnetism and bulk superconductivity in the stripe phase of La2−xBaxCuO4 : Pressure- and doping-dependent studies

Static spin-stripe order and superconductivity were systematically studied in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_x{\mathrm{CuO}}₄$ $(0.11\ensuremath{\le}x\ensuremath{\le}0.17)$ at ambient pressure by means of magnetization and $\ensuremath{\mu}\mathrm{SR}$ experiments. We find that all the investigated ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_x{\mathrm{CuO}}₄$ samples exhibit static spin-stripe order and that the quasi-two-dimensional superconducting (SC) transition temperature ${T}_{\mathrm{c}1}$ and the static spin-stripe order temperature ${T}_{\mathrm{so}}$ have very similar values throughout the phase diagram. Moreover, the magnetic and the SC properties of the $x=0.155$ (LBCO-0.155) and $x=0.17$ (LBCO-0.17) samples were studied under hydrostatic pressure. As a remarkable result, in these bulk cuprate superconductors, the three-dimensional SC transition temperature ${T}_{\mathrm{c}}$ and ${T}_{\mathrm{so}}$ nearly coincide $[{T}_{\mathrm{c}}(p)\phantom{\rule{4pt}{0ex}}\ensuremath{\simeq}\phantom{\rule{4pt}{0ex}}{T}_{\mathrm{so}}(p)]$ at all pressure investigated $(0\ensuremath{\le}p\ensuremath{\le}2.3$ GPa). We also observed a pressure induced transition from long-range spin stripe order to a disordered magnetic state at ${p}^{\ensuremath{\star}}\ensuremath{\simeq}1.6$ GPa in LBCO-0.155, coexisting with a SC state with substantial superfluid density. In LBCO-0.17, a disordered magnetic state is present at all $p$. The present results indicate that static magnetic order and SC pairing correlations develop in a cooperative fashion in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_x{\mathrm{CuO}}₄$, and provide a new route of understanding the complex interplay between static magnetism and superconductivity in the stripe phase of cuprates.