Anisotropic transport in unidirectional lateral superlattice around half filling of the second Landau level

We have observed marked transport anisotropy in short period $(a=92 \mathrm{nm})$ unidirectional lateral superlattices around filling factors $\ensuremath{\nu}=5/2$ and 7/2: magnetoresistance shows a sharp peak for current along the modulation grating while a dip appears for current across the grating. By altering the ratio $a/l$ (with $l=\sqrt{\ensuremath{\Elzxh}{/eB}_{\ensuremath{\perp}}}$ the magnetic length) via changing the electron density ${n}_{e},$ it is shown that the $\ensuremath{\nu}=5/2$ anisotropic features appear in the range $6.6\ensuremath{\lesssim}a/l\ensuremath{\lesssim}7.2$ varying their intensities, becoming most conspicuous at $a/l\ensuremath{\simeq}6.7.$ The peak/dip broadens with temperature roughly preserving its height and depth up to 250 mK. Tilt experiments reveal that the structures are slightly enhanced by an in-plane magnetic field ${B}_{\ensuremath{\Vert}}$ perpendicular to the grating but are almost completely destroyed by ${B}_{\ensuremath{\Vert}}$ parallel to the grating. The observations suggest the stabilization of a unidirectional charge-density-wave or stripe phase by weak external periodic modulation at the second Landau level.