Multi-Q mesoscale magnetism in CeAuSb${}_2$

We report the discovery of a field driven transition from a striped to woven Spin Density Wave (SDW) in the tetragonal heavy fermion compound CeAuSb${}_2$. Polarized along $\mathbf{c}$, the sinusoidal SDW amplitude is 1.8(2) ${\mu }_B$/Ce for $T\ll T_N$=6.25(10) K with wavevector ${\bf q}{1}=( \eta, \eta, \frac{1}{2} )$($\eta=0.136(2)$)\mathrm{.}For${\bf H}\parallel{\bf c}$,harmonicsappearingat$2{\bf q}{1}$evidenceastripedmagnetictexturebelow$\mu_\circ H_{c1}=2.78(1)$T\mathrm{.}Above$H_{c1}$,thesearereplacedbywovenharmonicsat${\bf q}{1}+{\bf q}2=(2\eta, 0, 0)+{\bf c}^*$until$\mu\circ H{c2}=5.42(5)$ T, where satellites vanish and magnetization non-linearly approaches saturation at 1.64(2) ${\mu }_B$/Ce for ${\mu }_{\circ }H\approx 7$ T.