Magnetic‐Field Tunable Intertwined Checkerboard Charge Order and Nematicity in the Surface Layer of Sr₂RuO₄

Abstract

In strongly correlated electron materials, the electronic, spin, and charge degrees of freedom are closely intertwined. This often leads to the stabilization of emergent orders that are highly sensitive to external physical stimuli promising opportunities for technological applications. In perovskite ruthenates, this sensitivity manifests in dramatic changes of the physical properties with subtle structural details of the RuO6 octahedra, stabilizing enigmatic correlated ground states, from a hotly debated superconducting state via electronic nematicity and metamagnetic quantum criticality to ferromagnetism. Here, it is demonstrated that the rotation of the RuO6 octahedra in the surface layer of Sr2RuO4 generates new emergent orders not observed in the bulk material. Through atomic‐scale spectroscopic characterization of the low‐energy electronic states, four van Hove singularities are identified in the vicinity of the Fermi energy. The singularities can be directly linked to intertwined nematic and checkerboard charge order. Tuning of one of these van Hove singularities by magnetic field is demonstrated, suggesting that the surface layer undergoes a Lifshitz transition at a magnetic field of ≈32T. The results establish the surface layer of Sr2RuO4 as an exciting 2D correlated electron system and highlight the opportunities for engineering the low‐energy electronic states in these systems.

Atomic-scale imaging of emergent order at a magnetic-field-induced Lifshitz transition

“…Although the crystal structure at the surface of Sr 3 Ru 2 O 7 is very similar to that of the surface layer of Sr 2 RuO 4 , except for the second RuO 6 layer, our data shows intriguingly different behaviours. Unlike the case of Sr 2 RuO 4 , where the C 4 -symmetry breaking can be described by a small nematic term in a tight-binding model [19], here we find a large C 4 symmetry breaking which cannot be easily captured by a small perturbative term. Although Sr 3 Ru 2 O 7 is already an orthorhombic system, and therefore does not exhibit C 4 symmetry, the orthorhombic distortion is tiny, and not expected to lead to a significant anisotropy of this scale.…”

“…The checkerboard charge order is reminiscent of the one observed at the surface of Sr 2 RuO 4 . [19] While Sr 3 Ru 2 O 7 has an orthorhombic crystal structure, [20] the orthorhombicity is tiny and often neglected, yet it does lead to subtle differences in the electronic structure in the crystallographic [110] and [1 10] directions. [21] Following the notation used in previous work [1,10], throughout this work we provide crystallographic directions in the tetragonal notation (Fig.…”

Atomic-scale imaging of emergent order at a magnetic field–induced Lifshitz transition

“…Although the crystal structure at the surface of Sr 3 Ru 2 O 7 is very similar to that of the surface layer of Sr 2 RuO 4 , except for the second RuO 6 layer, our data show different behaviors. Unlike the case of Sr 2 RuO 4 , where the C 4 symmetry breaking can be described by a small nematic term in a tight-binding model ( 19 ), here, we find a large C 4 symmetry breaking that cannot be easily captured by a small perturbative term. Although Sr 3 Ru 2 O 7 is already an orthorhombic system and therefore does not exhibit C 4 symmetry, the orthorhombic distortion is tiny and not expected to lead to a significant anisotropy of this scale.…”

“…1D), a checkerboard charge order can be detected as well as a breaking of C 4 symmetry near defects. The checkerboard charge order is reminiscent of the one observed at the surface of Sr 2 RuO 4 (19). While Sr 3 Ru 2 O 7 has an orthorhombic crystal structure (20), the orthorhombicity is tiny and often neglected, yet it does lead to subtle differences in the electronic structure in the crystallographic [110] and [1 1 ̄ 0] directions (21).…”

Evolution of Interorbital Superconductor to Intraorbital Spin-Density Wave in Layered Ruthenates

“…Further work is required to fully differentiate the two cases. Other recent experiments have studied surface layers of 214 [47], and the trilayer, Sr 4 Ru 3 O 10 [48], both of which feature staggered rotations. No SC is found in the surface layers nor the trilayer, consistent with the current theory.…”