Compass-like manipulation of electronic nematicity in Sr$_3$Ru$_2$O$_7$

Electronic nematicity has been found in a wide range of strongly correlated electron materials, resulting in the electronic states having a symmetry that is lower than that of the crystal that hosts them. One of the most astonishing examples is Sr$_3$Ru$_2$O$_7$, in which a small in-plane component of a magnetic field induces significant resistivity anisotropy. The direction of this anisotropy follows the direction of the in-plane field. The microscopic origin of this field-induced nematicity has been a long-standing puzzle, with recent experiments suggesting a field-induced spin density wave driving the anisotropy. Here, we report spectroscopic imaging of a field-controlled anisotropy of the electronic structure at the surface of Sr$_3$Ru$_2$O$_7$. We track the electronic structure as a function of the direction of the field, revealing a continuous change with the angle. This continuous evolution suggests a mechanism based on spin-orbit coupling resulting in compass-like control of the electronic bands. The anisotropy of the electronic structure persists to temperatures about an order of magnitude higher compared to the bulk, demonstrating novel routes to stabilize such phases over a wider temperature range.Comment: published version, 7 pages + 12 pages supplementary, 4 figures in main text + 7 supplementary figure