Article

# Unconventional superconductivity in Na$_{0.35}$CoO$_{2}\cdot$1.3D$_{2}$O and proximity to a magnetically ordered phase

04/2004;

Source: arXiv

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Graeme Luke, Apr 05, 2013 Available from: Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

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**ABSTRACT:**We investigated orbital ordering states in the vicinity of the Mott transition in RTiO{sub 3} and LaTiO{sub 3.02} (R=Gd,Sm,Nd,La) using resonant x-ray scattering (RXS) at the 1s{yields}3d transition energy of the K absorption edge of Ti. We measured the energy and azimuthal angle dependences of the resonant signal at the reflections of Q=(1 0 0) (0 1 1), and (0 0 1). The RXS intensity gradually decreased with decreasing the GdFeO{sub 3}-type distortion. Although there is a magnetic phase boundary between GdTiO{sub 3} (ferromagnet) and SmTiO{sub 3} (antiferromagnet), the ratio among the magnitudes at those reflections was almost the same. The azimuthal angle dependence also showed an identical periodicity at each scattering vector. With further decreasing the GdFeO{sub 3}-type distortion, the magnitude of the RXS in LaTiO{sub 3} became small and almost isotropic. This means that the orbital state of LaTiO{sub 3} is different from those of RTiO{sub 3} (R=Y,Gd,Sm). Furthermore, when we approached the Mott transition by hole doping, the signal of the RXS disappeared in LaTiO{sub 3.02}, which is just located on the metal-insulator boundary. This indicates a disappearance of the orbital ordering at the Mott transition.Physical Review B 12/2004; 70(24). DOI:10.1103/PhysRevB.70.245125 · 3.66 Impact Factor -
##### Article: Pairing correlation functions in the triangular tJ model: d-wave and f-wave superconductivity

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**ABSTRACT:**Equal-time pairing correlation functions of the two-dimensional t-J model on the triangular lattice are studied using high-temperature expansions method. We calculate the pairing correlation lengths and the effective pairing interactions down to T∼0.2t, and find the growth of pairing correlations. When t>0 with hole doping, a rapid growth of effective d-wave pairing interaction is found that indicates the resonating-valence-bond superconductivity. In contrast, when t<0, where the ferromagnetic correlation and antiferromagnetic correlation compete, correlation lengths of triplet pairings as well as d-wave pairing grow at low temperatures, although they do not diverge for T→0 in the competing region, i.e., near half-filling. On the other hand, around n=0.4, f-wave pairing correlation tends to diverge, although its effective interaction is small. Relation of the present study to the recently discovered superconductor, NaxCoO2∙yH2O, is discussed.Physical Review B 10/2005; 72(13). DOI:10.1103/PhysRevB.72.134513 · 3.66 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Resonating Valence Bond states are quantum spin liquids, having low energy spin-half (spinon) or spin-1 excitations. Although spins are `disordered', they posses subtle topological orders and some times chiral orders. RVB states are easily appreciated and seem natural in the quantum fluctuation dominated 1D world. In 2 and 3D, competing orders such as antiferromagnetism, charge order or even superconductivity often hide an underlying robust quantum spin liquid state. Introduction of additional spin interactions or doping of delocalized charges, or finite temperatures, could frustrate the long range magnetic order and reveal a robust RVB state. To this extent they are natural in 2D and above. We present a brief history of insulating RVB states. Then we summarise our own recent theory of RVB states for 2 and 3D systems, including some newly synthesised ones: i) boron doped diamond, ii) \nxcob, iii) quasi 2D organic conductors and iv) a 2D graphene sheet.