Correlated electron metal properties of the honeycomb ruthenate Na${}_2$RuO${}_3$

Abstract

We report the synthesis and characterisation of polycrystalline Na${}_2$RuO${}_3$, a layered material in which the Ru${}^{4+}$ ($4d^4$ configuration) form a honeycomb lattice. The optimal synthesis condition was found to produce a nearly ordered Na${}_2$RuO${}_3$ ($C2/c$ phase), as assessed from the refinement of the time-of-flight neutron powder diffraction. Magnetic susceptibility measurements reveal a large temperature-independent Pauli paramagnetism (${\chi }_0\sim 1.42(2)\times 10^{-3}$ emu/mol Oe) with no evidence of magnetic ordering down to 1.5 K, and with an absence of dynamic magnetic correlations, as evidenced by neutron scattering spectroscopy. The intrinsic susceptibility (${\chi }_0$) together with the Sommerfeld coeficient of $\gamma =11.7(2)$ mJ/Ru mol K${}^2$ estimated from heat capacity measurements, gives an enhanced Wilson ratio of $R_W\approx 8.9(1)$, suggesting that magnetic correlations may be present in this material. While transport measurements on pressed pellets show nonmetallic behaviour, photoemission spectrocopy indicate a small but finite density of states at the Fermi energy, suggesting that the bulk material is metallic. Except for resistivity measurements, which may have been compromised by near surface and interface effects, all other probes indicate that Na${}_2$RuO${}_3$ is a moderately correlated electron metal. Our results thus stand in contrast to earlier reports that Na${}_2$RuO${}_3$ is an antiferromagnetic insulator at low temperatures.

9 pages, 6 figures

References in corpus (5)

• Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models
• Lattice-Tuned Magnetism of Ru4+(4d4) Ions in Single-Crystals of the Layered Honeycomb Ruthenates: Li2RuO3 and Na2RuO3
• Effective magnetic interactions in spin-orbit coupled $d^4$ Mott insulators
• First-order melting of a weak spin-orbit Mott insulator into a correlated metal
• Highly frustrated magnetism in relativistic ${\mathbf{d}}^4$ Mott insulators: Bosonic analog of Kitaev honeycomb model

Cited by in corpus (5)

• Gapless dynamic magnetic ground state in the charge-gapped trimer iridate Ba${}_4$NbIr${}_3$O${}_{12}$
• Novel quantum spin liquid ground state in the trimer rhodate Ba${}_4$NbRh${}_3$O${}_{12}$
• Defect control in the Heisenberg-Kitaev candidate material NaRuO${}_2$
• Fluctuation-induced first order phase transitions in Kitaev-like $d^4$ honeycomb magnet
• Geometrical frustration and incommensurate magnetic order in Na${}_3$RuO${}_4$ with two triangular motifs