Non-Fermi-liquid behaviour in La4Ru6O19

Khalifah, Peter G.; Nelson, Karl; Jin, Rongying; Mao, Z. Q.; Liu, Y.; Huang, Q.; Gao, Xuan; Ramirez, A. P.; Cava, R. J.

doi:10.1038/35079534

Cited by 102 publications

(90 citation statements)

References 13 publications

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“…[12][13][14][15] However, these systems do not exhibit a phase transition. The T dependent susceptibility due to the similar electronic configuration has also been reported for various complexes with metal ion pairs.…”

Section: )mentioning

confidence: 99%

New-Type Phase Transition of Li₂RuO₃ with Honeycomb Structure

et al. 2007

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A new-type structural transition has been found in Li 2 RuO 3 with honeycomb lattice of edge-sharing RuO 6 -octahedra. With decreasing temperature T, the electrical resistivity exhibits an anomalous increase at T=T c~5 40 K, suggesting the (metal to insulator)-like transition and the magnetic susceptibility also shows a sharp decrease. Detailed structure analyses have revealed that the high temperature space group C2/m changes to P2 1 /m at T c . The most striking fact is that a significant reduction of the bond lengths is found between two of six Ru-Ru pairs of the hexagon in the low temperature phase, indicating a new type phase transition by the mechanism of the formation of molecular orbits of these Ru-Ru pairs.KEYWORDS: Li 2 RuO 3 , honeycomb structure, structural transition *Corresponding author: e43247a@nucc.cc.nagoya-u.ac.jpCompounds with the honeycomb lattice often present interesting behavior originating from their characteristic structures. For example, in the course of the studies on the physical properties of localized spin systems of A 3 T 2 SbO 6 (A=Na, Li; T=Cu, Ni, Co) and Na 2 T 2 TeO 6 on the (distorted) honeycomb lattice, spin gap behaviors have been found for T=Cu, [1][2][3] while the magnetic transitions to the spin-ordered state have been observed for T=Co and Ni. 4)As one of possible examples of conductive electrons on honeycomb lattice, we have investigated physical properties of Li 2 RuO 3 . It has the layers of the honeycomb lattice of edge-sharing RuO 6 octahedra with a LiO 6 octahedron at the center of each hexagon of RuO 6 (Fig. 1). The Ru valence is +4 and the four electrons exist in the 4d t 2g orbits. For this system, we have found a phase transition at temperature T=T c~5 40 K, where the crystal symmetry changes from a monoclinic (space group C2/m) to another monoclinic (space group P2 1 /m) one with decreasing T. As described in detail later, the transition is associated with the molecular orbit formation of Ru 4+ -Ru 4+ ions of the edge-sharing RuO 6 pair, presenting a new mechanism of structural transitions.Polycrystalline samples of Li 2 RuO 3 were prepared by sintering pellets of mixtures of RuO 2 and Li 2 CO 3 with proper molar ratio at 1000 ˚C for 24 h in air. 5,6) The powder neutron diffraction patterns of these samples indicate that a small amount of RuO 2 (molar fraction of ∼1.20 %) exists. There also exists an impurity peak of the unidentified phase, which has the integrated intensity of ~4.5 % of the maximum integrated intensity of the main phase as shown later. The magnetic susceptibilities χ were measured using a Quantum Design SQUID magnetometer under a magnetic field H=1 T in the temperature range of 2-700 K. The electrical resistivities ρ were measured by the standard four-terminal method using an ac-resistance bridge from 4.6 K to 695 K. The specific heats C were measured by a thermal relaxation method in the temperature range of 5-60 K using a Physical Property Measurement System (PPMS, Quantum Design). Powder X-ray diffraction measurements were carrie...

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confidence: 99%

New-Type Phase Transition of Li₂RuO₃ with Honeycomb Structure

et al. 2007

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“…3 shows other examples of the violation of the Ioffe-Regel condition, namely Rb 3 C 60 (Hebard et al, 1993), La 4 Ru 6 O 19 (Khalifah et al, 2001) and Sr 2 RuO 4 (Tyler et al, 1998). (Hebard et al, 1993) La4Ru6O19 (Khalifah et al, 2001), Sr2RuO4 (Tyler et al, 1998), Nb3Sb (Fisk and Webb, 1976) and the Ioffe-Regel resistivity for Rb3C60. There is no sign of saturation at the Ioffe-Regel resistivity, but La4Ru6O19 may saturate at a much larger resistivity.…”

Section: Introductionmentioning

confidence: 99%

Colloquium: Saturation of electrical resistivity

Calandra²,

2003

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Resistivity saturation is observed in many metallic systems with large resistivities, i.e., when the resistivity has reached a critical value, its further increase with temperature is substantially reduced. This typically happens when the apparent mean free path is comparable to the interatomic separations -the Ioffe-Regel condition. Recently, several exceptions to this rule have been found. Here, we review experimental results and early theories of resistivity saturation. We then describe more recent theoretical work, addressing cases both where the Ioffe-Regel condition is satisfied and where it is violated. In particular we show how the (semiclassical) Ioffe-Regel condition can be derived quantum-mechanically under certain assumptions about the system and why these assumptions are violated for high-Tc cuprates and alkali-doped fullerides.

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“…This is related to the strong reduction of the kinetic energy due to strong correlation effects. The fulfilment of the Ioffe-Regel condition for conventional transition metal compounds is found to be somewhat accidental.Some strongly correlated metals [1][2][3][4], in particular many high T c cuprates [5][6][7][8][9][10][11][12][13][14], show an exceptionally large resistivity, ρ, at high temperatures T . Thus ρ can reach values of several mΩcm.…”

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Violation of Ioffe-Regel condition but saturation of resistivity of the high- T _c cuprates

Calandra

Gunnarsson

2003

Europhys. Lett.

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We demonstrate that the resistivity data of a number of high Tc cuprates, in particular La2−xSrxCuO4, are consistent with resistivity saturation, although the Ioffe-Regel condition is strongly violated. By using the f-sum rule together with calculations of the kinetic energy in the t − J model, we show that the saturation resistivity is unusually large. This is related to the strong reduction of the kinetic energy due to strong correlation effects. The fulfilment of the Ioffe-Regel condition for conventional transition metal compounds is found to be somewhat accidental.Some strongly correlated metals [1][2][3][4], in particular many high T c cuprates [5][6][7][8][9][10][11][12][13][14], show an exceptionally large resistivity, ρ, at high temperatures T . Thus ρ can reach values of several mΩcm. This is in strong contrast to almost all other metals. Typically, a metal with a very large resistivity shows resistivity saturation [15]. Thus when ρ reaches values of the order 0.1 mΩcm, the slope of ρ(T ) is typically reduced substantially, although not necessarily to zero. This happens when the apparent mean free path l becomes comparable to the separation, d, of two atoms, the Ioffe-Regel condition [16]. This kind of behavior has been observed for many metals and it used to be considered a universal behavior [17].The metals mentioned above and the alkali-doped fullerenes [18] are apparent exceptions to this saturation behavior, with the cuprates forming a particular challenge [19,20]. The deviation from the "universal" behavior can be illustrated by considering Ioffe-Regel condition for La 2−x Sr x CuO 4 . We assume a "large" Fermi surface of cylindrical shape, containing 1 − x electrons (or 1 + x holes) [21]. Assuming that l = a, where a is the lattice parameter in the CuO 2 plane, we obtain the saturation resistivityIf we instead assume a "small" Fermi surface, √ 1 ± x in the denominator is replaced by √ x. In either case, the experimental resistivity for small x is much larger than the saturation resistivity above, supporting the conclusion that there is no saturation in these systems.Here we demonstrate that the experimental data for the strongly correlated high T c cuprates are, nevertheless, consistent with saturation. The saturation resistivity can, however, be much larger than the Ioffe-Regel value. This is not entirely surprising, since the Ioffe-Regel condition is based on a semiclassical picture, which is not valid when l ∼ d. The good agreement between the IoffeRegel condition and the saturation for weakly correlated transition metal compounds is therefore somewhat accidental. The large saturation resistivity is shown to be due to a large reduction of the kinetic energy, due to strong correlation effects. Since the alkali-doped fullerenes appear to lack saturation [22], this puts these compounds in a special class, different from the cuprates.To discuss resistivity saturation, we use the f-sum rule in a form appropriate for the models discussed here (only nearest neighbor hopping and no on-site matrix ele...

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Non-Fermi-liquid behaviour in La4Ru6O19

Cited by 102 publications

References 13 publications

New-Type Phase Transition of Li₂RuO₃ with Honeycomb Structure

New-Type Phase Transition of Li₂RuO₃ with Honeycomb Structure

Colloquium: Saturation of electrical resistivity

Violation of Ioffe-Regel condition but saturation of resistivity of the high- T _c cuprates

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Non-Fermi-liquid behaviour in La4Ru6O19

Cited by 102 publications

References 13 publications

New-Type Phase Transition of Li2RuO3 with Honeycomb Structure

New-Type Phase Transition of Li2RuO3 with Honeycomb Structure

Colloquium: Saturation of electrical resistivity

Violation of Ioffe-Regel condition but saturation of resistivity of the high- T c cuprates

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Product

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New-Type Phase Transition of Li₂RuO₃ with Honeycomb Structure

New-Type Phase Transition of Li₂RuO₃ with Honeycomb Structure

Violation of Ioffe-Regel condition but saturation of resistivity of the high- T _c cuprates