Observation of a spin-density wave node on antiferromagnetic Cr(110) islands

We have performed a detailed study of the evolution of the charge-density wave (CDW) and spin-density wave (SDW) on the surface of nanoscale Cr islands grown on W(110). Using low-temperature scanning tunneling microscopy (STM), we find a striking nonmonotonic thickness dependence of the CDW wavelength at 50 K. As the local island thickness $\ensuremath{\Theta}$ decreases from about 50 to 5.2 nm, the CDW wavelength gradually increases from the bulk value by approximately 30$%$. We find a gap without any CDW at coverages ${\ensuremath{\Theta}}_{\mathrm{gap}}$ between 5.2 and 3.7 nm. Spin-resolved STM data reveal that within this CDW gap the SDW modulation also disappears on the Cr island surface. At $\ensuremath{\Theta}l3.7$ nm the CDW reappears. This unusual behavior of CDW and SDW in Cr nanoislands can be understood by a reorientation of the SDW wave vector Q which is potentially driven by the pinning of the SDW node at the island surface at ${\ensuremath{\Theta}}_{\mathrm{gap}}$.