Superconductivity in two-dimensional CoO2 layers

Takada, Kazunori; Sakuraï, H.; Takayama‐Muromachi, E.; Izumi, Fujio; Dilanian, Ruben A.; Sasaki, Takayoshi

doi:10.1038/nature01450

Cited by 1,804 publications

(1,531 citation statements)

References 5 publications

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“…7.2.2. Na x CoO 2 ·yH 2 O The water-intercalated cobalt oxide superconductor Na x CoO 2 · yH 2 O consists of thick insulating layers of Na ions and H 2 O molecules separating superconducting CoO 2 layers and has a T c of about 5 K [178]. This material has many similarities to the high-temperature cuprate superconductors, but also disparities; the Co ions form a triangular lattice, there are multiple bands around the Fermi level, and the system has a filling level far from half-filling.…”

Section: Srptasmentioning

confidence: 99%

Chirald-wave superconductivity in doped graphene

Black‐Schaffer

Honerkamp

2014

J. Phys.: Condens. Matter

171

176

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Abstract. A highly unconventional superconducting state with a spin-singlet d x 2 −y 2 ± id xy -wave, or chiral d-wave, symmetry has recently been proposed to emerge from electron-electron interactions in doped graphene. Especially graphene doped to the van Hove singularity at 1/4 doping, where the density of states diverges, has been argued to likely be a chiral d-wave superconductor. In this review we summarize the currently mounting theoretical evidence for the existence of a chiral d-wave superconducting state in graphene, obtained with methods ranging from mean-field studies of effective Hamiltonians to angle-resolved renormalization group calculations. We further discuss multiple distinctive properties of the chiral d-wave superconducting state in graphene, as well as its stability in the presence of disorder. We also review means of enhancing the chiral d-wave state using proximity-induced superconductivity. The appearance of chiral d-wave superconductivity is intimately linked to the hexagonal crystal lattice and we also offer a brief overview of other materials which have also been proposed to be chiral d-wave superconductors.

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Section: Srptasmentioning

confidence: 99%

Chirald-wave superconductivity in doped graphene

Black‐Schaffer

Honerkamp

2014

J. Phys.: Condens. Matter

171

176

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“…The de-intercalation and hydration of the layered sodium cobalt oxide Na x CoO 2 through an oxidation and subsequent hydration reaction results in the bilayer hydrate Na 0.3 CoO 2 ·1.4H 2 O, which is superconducting below 4~5 K [1]. An alternative synthesis route to make the superconductive Na 0.3 CoO 2 ·1.4H 2 O using aqueous Na 2 S 2 O 8 instead of Br 2 in acetonitrile and subsequently re-hydrating was introduced in a previous report [2].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and characterization of Na0.3RhO2·0.6H2O—a semiconductor with a weak ferromagnetic component

Park

Kang

et al. 2005

Solid State Communications

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We have prepared the oxyhydrate Na 0.3 RhO 2 ⋅0.6H 2 O by extracting Na + cations from NaRhO 2 and intercalating water molecules using an aqueous solution of Na 2 S 2 O 8 . Rietveld refinement, thermogravimetric analysis (TGA), and energy-dispersive x-ray analysis (EDX) reveal that a non-stoichiometric Na 0.3 (H 2 O) 0.6 network separates layers of edge-sharing RhO 6 octahedra containing Rh 3+ (4d 6 , S=0) and Rh 4+ (4d 5 , S=1/2). The resistivities of NaRhO 2 and Na 0.3 RhO 2 ·0.6H 2 O (T < 300) reveal insulating and semi-conducting behavior with activation gaps of 134 meV and 7.8 meV, respectively. Both Na 0.3 RhO 2 ⋅0.6H 2 O and NaRhO 2 show paramagnetism at room temperature, however, the sodium-deficient sample exhibits simultaneously a weak but experimentally reproducible ferromagnetic component. Both samples exhibit a temperature-independent Pauli paramagnetism, for NaRhO 2 at T > 50 K and for Na 0.

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“…Pellets were pressed at only moderate pressures (less than 10,000 pounds per square inch) to prevent dehydration of the superconducting phase. Powder X-ray diffraction studies indicated that the samples consisted solely of the superconducting Na x CoO 2 ·1.3H 2 O structure type (1,8).…”

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confidence: 99%

“…The crystal structure of Na 0.3 CoO 2 ⋅1.3H 2 O consists of electronically active triangular CoO 2 layers separated by spacer layers of sodium and water (1). The triangular CoO 2 lattice and the speculation that it might be a Mott-Hubbard insulator has made this superconductor of particular interest to theorists (2)(3)(4)(5)(6)(7).…”

mentioning

confidence: 99%

Specific heat study of the Na0.3CoO2· 1.3H2O superconductor: influence of the complex chemistry

Ueland

Schiffer

Schaak

et al. 2004

Physica C: Superconductivity

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We report results of specific heat measurements on polycrystalline samples of the layered superconductor, Na 0.3 CoO 2 ⋅1.3H 2 O. The electronic contribution to the specific heat, γ, is found to be 12.2 mJ/mol-K 2 . The feature at the superconducting transition is rather sharp, becoming broad and strongly suppressed in an applied magnetic field. The data indicate a residual normal state electronic specific heat at low temperatures, implying that there is a sizable population of normal state electrons in the samples even below T c . Inhomogeneity in the Na content, to which the superconducting state is exquisitely sensitive, appears to be the most likely explanation for these results. These results further indicate that special sample handling is required for an accurate characterization of the superconducting state in this material.

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Superconductivity in two-dimensional CoO2 layers

Cited by 1,804 publications

References 5 publications

Chirald-wave superconductivity in doped graphene

Chirald-wave superconductivity in doped graphene

Synthesis and characterization of Na0.3RhO2·0.6H2O—a semiconductor with a weak ferromagnetic component

Specific heat study of the Na0.3CoO2· 1.3H2O superconductor: influence of the complex chemistry

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