Search for Magnetic Excitation Spectra of NaxCoO2·yD2O –Neutron Scattering–

Moyoshi, Taketo; Yasui, Yukihiko; Soda, Minoru; Kobayashi, Yoshihiko; Sato, Masatoshi; Kakurai, Kazuhisa

doi:10.1143/jpsj.75.074705

Cited by 12 publications

(9 citation statements)

References 32 publications

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“…1.3D 2 O no signals of magnetic fluctuations were detected. 14) The results obtained by the present authors' group contradict the idea of the exotic superconductivity, but seem to be consistent with the phonon-mediated superconductivity proposed by Yada and Kontani. 15) In the present work, we have carried out further studies of the magnetic properties of Na 0:3 CoO 2 .…”

Section: Introductionsupporting

confidence: 89%

Magnetic Properties of Superconducting Cobalt Oxides Na_xCoO₂·yH₂O

et al. 2006

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Studies of the NMR Knight shift K of Na 0:3 CoO 2 . yH 2 O have been carried out in detail. The suppression of K by the occurrence of the superconductivity reported previously by the present authors in both magnetic field directions perpendicular and parallel to the c-axis has been confirmed, indicating that the Cooper pairs are in the singlet state. The anisotropy of the suppression amplitudes is consistent with the anisotropy of the hyperfine coupling constant A spin estimated from the K-plot. It has also been found that even samples that do not exhibit a significant the Curie-Weiss-like increase of the uniform magnetic susceptibility with decreasing temperature T, exhibit superconducting transition, which indicates that the superconducting Na 0:3 CoO 2 . 1.3H 2 O is not necessarily in the region of proximity of the ferromagnetic phase. It has also been confirmed that the superconducting transition temperature T c of the samples prepared by mixing Na 0:7 CoO 2 , H 2 O (or D 2 O) and bromine for 4 h, and separating the resultant powder from the solution by filtration, depends on the elapsed time t after filtration. For these samples, the Curie-Weiss component of estimated at low temperatures increases with t, supporting the idea that the number of lattice imperfections possibly due to oxygen-vacancy formation increases with t. Even for such samples, the superconductivity appears, which seems to exclude the possibility of an anisotropic superconducting order parameter. These results are favorable for full-gapped superconductivity.

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Section: Introductionsupporting

confidence: 89%

Magnetic Properties of Superconducting Cobalt Oxides Na_xCoO₂·yH₂O

et al. 2006

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“…(The peaks around h ¼ 0.5 is the contribution of the motions of the intercalated D 2 O.) [7]. These results are consistent with the fact that the Cooper pairs are in the singlet state.…”

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confidence: 78%

“…Inelastic neutron scattering studies have also been carried out [7] on aligned crystals of Na x CoO 2 Á yD 2 O, which contains the superconducting bilayer (y$1.3) phase and the non-superconducting monolayer (y$0.6) and nondeuterated (y ¼ 0; x$0.44 from the c value) phases, where the volume fractions of these phases are 0.64, 0.10, and 0.24, respectively. In the studies, weak spin fluctuations (not shown) have been detected at Q points in the reciprocal space of the non-deuterated part, which correspond to both intra-plane and inter-plane antiferromagnetic correlation.…”

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confidence: 99%

NMR and neutron scattering studies on NaxCoO2·yH2O

Sato

Kobayashi

Moyoshi

et al. 2007

Journal of Magnetism and Magnetic Materials

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“…59 Co-NMR and NQR measurements have been carried out using conventional coherent pulsed-NMR methods. The Na 0.7 CoO 2 single crystals were prepared by the floating zone method 10) and then Na de-intercalation and H 2 O intercalation were carried out as described before. 3) The obtained single crystals were confirmed to have the ν Q3 -values of ~12.7 MHz by NQR measurements, indicating that it is in the large-ν Q3 superconducting regions of the T-ν Q3 phase diagram shown in Fig.…”

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Co-NMR Knight Shift of Na_xCoO₂·yH₂O Studied in Both Superconducting Regions of the T_c–ν_Q3 Phase Diagram Divided by the Nonsuperconducting Phase

et al. 2008

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In the temperature (T)-ν Q3 phase diagram of Na x CoO 2 ⋅yH 2 O, there exist two superconducting regions of ν Q3 separated by the nonsuperconducting region, where ν Q3 is usually estimated from the peak position of the 59 Co-NQR spectra of the ±5/2↔ ±7/2 transition and well-approximated here as ν Q3~3 ν Q , ν Q being the interaction energy between the nuclear quadrupole moment and the electric field gradient. We have carried out measurements of the 59 Co-NMR Knight shift (K) for a single crystal in the higher-ν Q3 superconducting phase and found that K begins to decrease with decreasing T at T c for both magnetic field directions parallel and perpendicular to CoO 2 -planes. The result indicates together with the previous ones that the superconducting pairs are in the spin-singlet state in both phases, excluding the possibility of the spin-triplet superconductivity in this phase diagram. The superconductivity of this system spreads over the wide ν Q3 regions, but is suppressed in the narrow region located at the middle point of the region possibly due to charge instability. KEYWORDS: Na x CoO 2 ⋅yH 2 O, superconductivity, NMR, Knight shift, phase diagram Na 0.3 CoO 2 ⋅1.3H 2 O with the superconducting transition temperature T c of ∼4.5 K has the two-dimensional triangular lattice of Co atoms. 1) Due to this structural characteristic, not only this system and but also the mother system Na x CoO 2 have attracted much attention in relation to a possible geometrical frustration of the electron spins. 2) To identify the mechanism of the superconducting pairing, we have clarified various kinds of their physical properties: The T c value has been found to depend on the 59 Co nuclear quadrupole frequency ν Q , as summarized in the T−ν Q3 phase diagram shown in Fig. 1, ν Q3 (~3ν Q ) being the frequency corresponding to ±7/2 ↔ ±5/2 transition of the nuclear spin. The superconducting phase is divided into two regions by the nonsuperconducting phase, which can be understood by the appearance of a charge disproportionate state. 3) Because the increase of the crystal field q at Co sites, or the ν Q3 -increase induces the upper shift of the e g '-orbital band relatively to the a 1g one, one might expect that six hole pockets of the e g '-orbital band might be expected to appear with increasing ν Q3 in the Fermi surface near the K points in the reciprocal space. 4) If the hole pockets really appear, the ferromagnetic fluctuations with the wave vector of small q is expected to become strong and a triplet pairing state may become possible. 5) However, at least in the smaller-ν Q3 superconducting phase of the phase diagram, we have shown in previous papers that the Cooper pairs are in the singlet state, observing the suppression of the 59 Co-NMR Knight shifts by the superconductivity for both magnetic field directions parallel and perpendicular to the CoO 2 -plane. 6-8) It is consistent with results of photoemission experiments, which have observed only hole-like Fermi surface around Γ point from the a 1g -orbital band, and never ob...

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Search for Magnetic Excitation Spectra of Na_xCoO₂·yD₂O –Neutron Scattering–

Cited by 12 publications

References 32 publications

Magnetic Properties of Superconducting Cobalt Oxides Na_xCoO₂·yH₂O

Magnetic Properties of Superconducting Cobalt Oxides Na_xCoO₂·yH₂O

NMR and neutron scattering studies on NaxCoO2·yH2O

Co-NMR Knight Shift of Na_xCoO₂·yH₂O Studied in Both Superconducting Regions of the T_c–ν_Q3 Phase Diagram Divided by the Nonsuperconducting Phase

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Search for Magnetic Excitation Spectra of NaxCoO2·yD2O –Neutron Scattering–

Cited by 12 publications

References 32 publications

Magnetic Properties of Superconducting Cobalt Oxides NaxCoO2·yH2O

Magnetic Properties of Superconducting Cobalt Oxides NaxCoO2·yH2O

NMR and neutron scattering studies on NaxCoO2·yH2O

Co-NMR Knight Shift of NaxCoO2·yH2O Studied in Both Superconducting Regions of the Tc–νQ3 Phase Diagram Divided by the Nonsuperconducting Phase

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Product

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About

Search for Magnetic Excitation Spectra of Na_xCoO₂·yD₂O –Neutron Scattering–

Magnetic Properties of Superconducting Cobalt Oxides Na_xCoO₂·yH₂O

Magnetic Properties of Superconducting Cobalt Oxides Na_xCoO₂·yH₂O

Co-NMR Knight Shift of Na_xCoO₂·yH₂O Studied in Both Superconducting Regions of the T_c–ν_Q3 Phase Diagram Divided by the Nonsuperconducting Phase