Rapidly fluctuating orbital occupancy above the orbital ordering transition in spin-gap compounds

Abstract

Several spin systems with low dimensionality develop a spin-dimer phase within a molecular orbital below TS, competing with long-range antiferromagnetic order. Very often, preferential orbital occupancy and ordering are the actual driving force for dimerization, as in the so-called orbitally-driven spin-Peierls compounds (MgTi2O4, CuIr2S4, La4Ru2O10, NaTiSi2O6, etc.). Through a microscopic analysis of the thermal conductivity k (T) in La4Ru2O10, we show that the orbital occupancy fluctuates rapidly above TS, resulting in an orbital-liquid state. The strong orbital-lattice coupling introduces dynamic bond-length fluctuations that scatter the phonons to produce a k (T) proportional to T (i.e. glass-like) above TS. This phonon-glass to phonon-crystal transition is shown to occur in other spin-dimer systems, like NaTiSi2O6, pointing to a general phenomenon.

submitted to Phys. Rev. B

References in corpus (5)

• Orbitally-driven Peierls state in spinels
• Orbital liquid in three dimensional Mott insulator: $LaTi{O}_3$
• Orbitally driven spin-singlet dimerization in $S$=1 La${}_4$Ru${}_2$O${}_{10}$
• High temperature magnetic ordering in La2RuO5
• Orbital-Driven Electronic Structure Changes and the Resulting Optical Anisotropy of the Quasi-Two-Dimensional Spin Gap Compound La4Ru2O10

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• Flux growth and physical properties of Mo3Sb7 single crystals
• Electrical and Thermal Transport Properties of the beta-Pyrochlore Oxide CsW2O6
• Exploring the Electronic Nature of Spinel Oxides: A Review of Their Electron Interactions and Prospects
• Orbital disorder and ordering in NaTiSi2O6: 29Si and 23Na NMR Study