Emergence of a new magnetic state in Sr₂IrO₄ tunable by in situ B_2g strain

Due to the unique combination of electron correlation and spin-orbit coupling, Iridates have attracted great attention in recent years. A prominent example is Sr₂IrO₄ which is a quasi-two-dimensional J_eff =1/2 canted antiferromagnetic (AF) Mott insulator with a layered structure similar to the parent phase of high-Tc cuprates. However, unlike the S=1/2 moments of Cu ions, an interesting feature of the J_eff = 1/2 moments is that they can form significant inter-site quadrupoles that are highly sensitive to lattice distortion. The resulting magnetoelastic coupling leads to spontaneous B1g anisotropy when the AF order breaks the tetragonality. In our experiment, we compared the magnetic responses to in-situ B1g and B2g strains, which represent two orthogonal symmetry configurations. While the B_1g strain efficiently detwins the spontaneous AF domains, we observed a new state that breaks the translational symmetry along the c-axis. Our model analysis shows that such an emergent state is driven by an unusual quartic interaction, which is competing with the B1g anisotropy and can be in situ tuned by the applied strain.