Search for orbital magnetism in the kagome superconductor ${\rm CsV_3Sb_5}$ using neutron diffraction

TL;DR

This study used polarized neutron diffraction to search for orbital magnetic moments in CsV3Sb5, finding no evidence at one Brillouin zone point and a possible weak signal at another, suggesting limited orbital magnetism.

Contribution

First experimental search for orbital magnetism in CsV3Sb5 using neutron diffraction, providing upper bounds and hints of weak orbital moments.

Findings

No orbital magnetic order detected at M1 point within experimental uncertainty.

Possible weak orbital magnetic moment detected at M2 point near detection limit.

Orbital magnetic moments, if present, are at most ~0.02 μB per vanadium triangle.

Abstract

As many Kagome metals, the topological superconductor AV$_3$Sb$_5$ with (A = K,Rb,Cs) hosts a charge density wave . A related chiral flux phase that breaks the time-reversal symmetry has been further theoretically predicted in these materials. The flux phase is associated with loop currents that produce ordered orbital magnetic moments, which would occur at the momentum points, $\bf M$, characterizing the charge-density wave state. Polarized neutron-diffraction experiments have been performed on an assembly of single crystals of ${\rm CsV_3Sb_5}$ to search for such orbital magnetic moments. No evidence for the existence of a three-dimensionally ordered moment is found at any temperature at the first ${\bf M_1}$=(1/2,0,0) point in the Brillouin zone within an excellent experimental uncertainty, ${\it i.e.}$ ${\bf m}=0 \pm 0.01\mu_B$ per vanadium atom. However, a hint to a magnetic orbital moment is found in the second Brillouin zone at {\bf M$_2$}=(1/2,1/2,0) at the detection limit of the experiment. Some loop currents patterns flowing ${\it only}$ on vanadium triangles are able to account for this finding suggesting an ordered orbital magnetic moment of, at most, $\sim 0.02 \pm 0.01\mu_B$ per vanadium triangle.