Abstract
Materials with strongly correlated electrons often exhibit interesting physical properties. An example of these materials is the layered oxide perovskite Sr2RuO4, which has been intensively investigated due to its unusual properties. Whilst the debate on the symmetry of the superconducting state in Sr2RuO4 is still ongoing, a deeper understanding of the Sr2RuO4 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 surface magnetism in Sr2RuO4 in its normal state. We detect static weak dipolar fields yet manifesting at an onset temperature higher than 50 K. We ascribe this unconventional magnetism to orbital loop currents forming at the reconstructed Sr2RuO4 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 electron pairing with broken time reversal symmetry.
Highlights
Materials with strongly correlated electrons often exhibit interesting physical properties
To summarize our experimental findings, we detect a magnetic phase with 50 K < Ton < 75 K (Figs. 2 and 3b) and localized within the first 10–20 nm from the SRO214 surface (Fig. 3d), which induces a positive ΔBloc shift near the surface only in higher Bext combined with a positive Δλ shift independent on Bext (Fig. 3c, d)
The small magnitude of the moment in combination with the relatively high Ton suggests that the magnetic phase detected at the SRO214 surface is incompatible with conventional ferromagnetism
Summary
Materials with strongly correlated electrons often exhibit interesting physical properties. Apart from intense studies[7,8,9] aiming at determining the nature of the superconducting symmetry in SRO214, which remains under debate, evidence for spin fluctuations[10] or a b magnetism under uniaxial pressure[11] has been reported for SRO214 single crystals in the normal state. These investigations, do not provide any information about the SRO214 surface selectively but rather focus on the SRO214 bulk properties. Angle-resolved photoemission spectroscopy (ARPES) measurements on SRO214 reveal the presence of surface states[14], but the correlation between these surface states and magnetism is not conclusive[15]
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