Lattice rotation vortex observed between polar nanoregions in relaxor-ferroelectric (1-x)Pb(Zn$_{\mathrm{1/3}}$Nb$_{\mathrm{2/3}})$O$_{\mathrm{3}}$-xPbTiO$_{\mathrm{3}}$ single crystal*

Domain walls (DWs) play a critical role in determining the polarization switching behavior in relaxor-based ferroelectric crystals. The domains in relaxor-ferroelectric crystals consist of polar nanoregions (PNRs) and their interface is poorly understood. Here, we report an energy-filtered (EF-) scanning convergent beam electron diffraction (SCBED) study for the identification of PNRs and determination of their interface. With the aid of electro dynamical diffraction simulation, nanometer-sized PNRs having monoclinic \textit{Pm} (M$_{\mathrm{C}})$ symmetry in single crystal PZN- 8{\%}PT were identified. Lattice rotation vortices having an average radius of \textasciitilde 7 nm at the 50$^{\circ}$ DWs were revealed by maps of crystal orientations, domain configurations, symmetry breaking. Such measurements suggest the merging of 2D and 1D topological defects, with implications for domain-switching mechanisms in relaxor ferroelectric crystals. The interplay between polarization, charge, and strain degrees of freedom suggests a complex landscape of topological defects in ferroelectrics that may be explored for a new form of nanoscale ferroelectric devices.