Self-doping induced orbital-selective Mott transition inHg2Ru2O7

Abstract

Pyrochlore oxides are fascinating systems where strong, multi-orbital correlations in concert with geometrical frustration give rise to unanticipated physical properties. The detailed mechanism of the insulator-metal transitions (IMT) underpinning these phenomena is, however, ill-understood in general. Motivated thereby, we study the IMT in the pyrochlore Hg2Ru2O7 using LDA+DMFT. In contrast to the well-known examples of Mott transitions in TMO, we show that, in the negative charge-transfer situation characteristic of Hg2Ru2O7, self-doping plays a crucial role in the emergence of an orbital-selective IMT. We argue that this mechanism has broader relevance to other correlated pyrochlore oxides.

Non‐Fermi Liquids as Highly Active Oxygen Evolution Reaction Catalysts

“…Hg 2 Ru 2 O 7 (Ru 5+ : 4d, t 2g 3 e g 0 ) undergoes a metal–insulator transition at 108 K . However, the localized d‐bands of the Mott–Hubbard insulator (Figure a) are retained across the transition and the system adopts a non‐Fermi liquid state above 108 K (Figure b). Non‐Fermi liquid systems are d‐ or f‐electron systems characterized by strong electron–electron interactions that prevent entry into the Fermi liquid ground state and some of them exhibit superconductivity .…”

“…This work proposes a non‐Fermi liquid that satisfies the criterion for coexistence of localized d‐bands and the metallic state (Figure b). Specifically, the OER activity of the room‐temperature non‐Fermi liquid Hg 2 Ru 2 O 7 was evaluated in detail. Hg 2 Ru 2 O 7 (Ru 5+ : 4d, t 2g 3 e g 0 ) undergoes a metal–insulator transition at 108 K .…”

Metal–Insulator Transition and Magnetic Order in the Pyrochlore Oxide Hg2Ru2O7

“…Another point reported by Craco et al is the nearly localized character of the a 1g state in contrast to the more itinerant e ′ g carrier split by the trigonal crystal field. 27 We note that the antiferromagnetic order of the a 1g electrons alone should result in an ordered moment of 1 µ B .…”

“…The result that 1/(T 1 T K 2 iso ) is strictly independent of temperature with a value very close to S rules out strong spatial spin correlation at any specific wave vector. On the other hand, the density of states at the Fermi level calculated by the local-density approximation, ρ = 3.7 states/eV-Ru, 27,28 gives the bare spin susceptibility ρµ 2 B = 1.2×10 −4 emu/mol-Ru. Since the measured χ ∼ 5.5 × 10 −4 emu/mol-Ru is dominantly due to a spin contribution, we conclude that χ spin is enhanced by a factor of five.…”

“…The stability of the insulating state in Hg 2 Ru 2 O 7 has been examined theoretically by combining the localdensity approximation and the dynamical mean-field theory by Craco et al 27 They found that a significant reduction in the 4d electron number as a result of the charge transfer between Ru-O(1) and Hg-O(2) sublattices is necessary to stabilize a paramagnetic insulating state. It should be interesting to examine if the insulating state is stabilized without such a charge transfer in the presence of an antiferromagnetic order.…”