Unveiling unconventional magnetism at the surface of Sr${}_2$RuO${}_4$

Abstract

Materials with strongly correlated electrons exhibit physical properties that are often difficult to predict as they result from the interactions of large numbers of electrons combined with several quantum degrees of freedom. The layered oxide perovskite Sr${}_2$RuO${}_4$ is a strongly correlated electron material that has been intensively investigated since its discovery due to its unusual physical properties. Whilst recent experiments have reopened the debate on the exact symmetry of the superconducting state in Sr${}_2$RuO${}_4$, a deeper understanding of the Sr${}_2$RuO${}_4$ normal state appears crucial as this is the background in which electron pairing occurs. Here, by using low-energy muon spin spectroscopy we discover the existence of magnetism at the surface of Sr${}_2$RuO${}_4$ in its normal state. We detect static weak dipolar fields yet manifesting below a relatively high onset temperature larger than 50 K, which reveals the unconventional nature of the observed magnetism. We relate the origin of this phase breaking time reversal symmetry to electronic ordering in the form of orbital loop currents that originate at the reconstructed Sr${}_2$RuO${}_4$ surface. Our observations set a reference for the discovery of the same magnetic phase in other materials and unveil an electronic ordering mechanism that can influence unconventional electron pairing with broken time reversal symmetry in those materials where the observed magnetic phase coexists with superconductivity.

arXiv comment20 pages, 5 figures

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• Materials challenges for SrRuO3: from conventional to quantum electronics
• Spontaneous superconducting diode effect in non-magnetic Nb/Ru/Sr${}_2$RuO${}_4$ topological junctions
• Spontaneous time-reversal symmetry breaking by disorder in superconductors
• Gate control of superconducting current: Mechanisms, parameters and technological potential
• Signatures of a surface spin-orbital chiral metal
• Destruction of surface states of ($d_{zx}+i{d}_{yz}$)-wave superconductor by surface roughness: application to Sr${}_2$RuO${}_4$
• Atomic-scale imaging of emergent order at a magnetic-field-induced Lifshitz transition
• Conditions for orbital selective altermagnetism in Sr${}_2$RuO${}_4$: tight binding model, similarities with cuprates and implications on superconductivity
• Orbital Gravito-Magnetoelectric response and Orbital magnetic quadrupole moment correction
• Surface State of Inter-orbital Pairing State in Sr${}_2$RuO${}_4$ Superconductor
• Magnetic exchange interaction in spin-valve with chiral spin-triplet superconductor
• Muon Knight shift as a precise probe of the superconducting symmetry of Sr${}_2$RuO${}_4$
• SrRuO3 under tensile strain: Thickness-dependent electronic and magnetic properties
• Implantation studies of low-energy positive muons in niobium thin films
• Tri-component-pairing chiral superconductivity on the honeycomb lattice with mixed $s$- and $d$-wave symmetries
• Signature of chiral superconducting order parameter evidenced in mesoscopic superconductors