Abstract
We have studied the magnetic flux pinning behavior and Meissner effect for the high-$T_{\rm c}$ single crystal La$_{2-x}$Sr$_{x}$CuO$_{4}$ ($x$ = 0.09) superconductor using the polarized neutron imaging method with varying magnetic field and temperature. In the Meissner state expulsion of magnetic field (switched on during the measurements) is visualized, and the signatures of mixed state with increasing temperature are observed. While, for flux pinning behavior between 5 K $\leq$ $T$ $\leq$ 15 K and $H_{\rm ext}$ = 63.5 mT (switched off during the measurements), the evolution of fringe pattern for both 0$^{o}$ and 90$^{o}$ sample orientation indicates magnetic flux pinning inside the bulk of the sample. At 25 K $\leq$ $T$ $\leq$ 32 K, a continuous decrease of inhomogeneously distribution pinned magnetic flux is observed, with the sample reaching a normal conducting state at $T_{\rm c}$ ($\approx$ 32 K). The flux pinning behavior is also explored as a function of $H_{\rm ext}$, at $T$ = 5 K. As expected, with increasing $H_{\rm ext}$ an increase in fringe density is observed, indicating an increase in magnetic flux pinning in the bulk of the sample. Therefore, in the present work for the first time we report bulk visualization of Meissner effect and flux pinning behavior in high-$T_{\rm c}$ La$_{2-x}$Sr$_{x}$CuO$_{4}$ ($x$ = 0.09) superconductor. This study clearly demonstrates the potential of real space polarized neutron imaging technique for the visualization of the superconducting mixed state, particularly in the field of high-$T_{\rm c}$ superconductors.