Large-Tiny Spin-Stripe SDW Order in La$_3$Ni$_2$O$_7$ via $^{139}$La-NQR Spectroscopy: Reconsideration Based on the $Am2m$ Structure

The lower-symmetry $Am2m$ structure was recently proposed as the intrinsic ambient-pressure phase of La$_3$Ni$_2$O$_7$ based on synchrotron x-ray diffraction, whereas earlier studies investigated its properties assuming the commonly accepted $Amam$ structure. Here, we reexamine the crystal structure