Low-temperature specific heat of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si0009.gif" overflow="scroll"><mml:mi mathvariant="normal">β</mml:mi><mml:mtext>-pyrochlore</mml:mtext></mml:math> oxide superconductors under high pressure

Isono, T.; Iguchi, Daisuke; Machida, Yo; Izawa, K.; Salce, B.; Flouquet, J.; Ogusu, Hiroki; Yamaura, Jun‐ichi; Hiroi, Zenji

doi:10.1016/j.physe.2010.07.039

Cited by 1 publication

(5 citation statements)

References 16 publications

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“…In contrast, the pressure dependence of T c reported by Isono et al in their heat capacity measurements in a single crystal of RbOs 2 O 6 is substantially the same as ours, except for the values of P s ; their T c increases gradually with pressure, remains almost constant at 9.3 K above 3 GPa, and suddenly drops to 7 K at 5.8 GPa. 28,29) This confirms that our resistivity results essentially reflect the bulk nature, related to neither a surface event nor a filamentary path, as heat capacity probes bulk property. We do not know, however, the reason for the difference in P s , 4.9 and 5.8 GPa.…”

Section: Superconducting Transitionsupporting

confidence: 74%

“…23 and suddenly drops to 7 K at 5.8 GPa. 28,29) This confirms that our resistivity results essentially reflect the bulk nature, related to neither a surface event nor a filamentary path, as heat capacity probes bulk property. We do not know, however, the reason for the difference in P s , 4.9 and 5.8 GPa.…”

supporting

confidence: 71%

“…27) More recently, Isono and coworkers have carried out HP heat capacity measurements in a DAC filled with Ar on single crystals of KOs 2 O 6 , RbOs 2 O 6 , and CsOs 2 O 6 and observed abrupt drops in T c at 5.2, 5.8, and 10.5 GPa, respectively. [28][29][30][31] Interestingly, they show that these drops in T c take place at the same lattice volume of approximately 0.988 nm 3 under HP for all the compounds, in which similar structural transitions to those observed in KOs 2 O 6 may occur. 27) In this study, we carried out resistivity measurements on a high-quality single crystal of RbOs 2 O 6 under HPs of up to 6 GPa to investigate the effects of pressure on the superconductivity in more detail and the rattling in the β-pyrochlore oxides.…”

Section: Introductionmentioning

confidence: 86%

“…The phase diagram of RbOs 2 O 6 shares a common feature with that of KOs 2 O 6 . 27,29) In KOs 2 O 6 , T c increases slightly from 9.60 K at ambient pressure to 9.75 K at 1.0 GPa and then gradually decreases with pressure. 27) Above 1.3 GPa, two anomalies, T o1 and T o2 , appear and move to higher temperatures with increasing pressure.…”

Section: P-t Phase Diagrammentioning

confidence: 97%

“…Figure 3 shows a comparison of the pressure dependences of T c in the present study for crystals A and B with those obtained previously. 23,24,28,29) Muramatsu et al reported a domelike pressure dependence of T c in their resistivity measurements in a polycrystalline sample. However, it is clearly due to broad transitions in resistivity; 23) T c was defined at the midpoint of the broad transitions.…”

Section: Superconducting Transitionmentioning

confidence: 98%

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Superconductivity and Rattling under High Pressure in the β-Pyrochlore Oxide RbOs₂O₆

et al. 2011

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Rattling-induced superconductivity in the β-pyrochlore oxide RbOs 2 O 6 is investigated under high pressures up to 6 GPa. Resistivity measurements in a high-quality single crystal show that the superconducting transition temperature T c increases gradually from 6.3 K at ambient pressure to 8.8 K at 3.5 GPa, surprisingly remains almost constant at 8.8 ± 0.1 K in a wide pressure range between 3.5 (P o ) and 4.8 GPa, and suddenly drops to 6.3 K at P s = 4.9 GPa, followed by a gradual decrease with further pressure increase. Two anomalies in the temperature dependence of the normal-state resistivity are observed at P o < P < P s and P > P s , revealing the presence of two high-pressure phases corresponding to the changes in T c . The rattling of the Rb ion inside a cage made of Os and O atoms may be slightly and seriously modified in these high-pressure phases that probably have cages of reduced symmetry, respectively, so that electron-rattler interactions that govern the superconducting and transport properties of β-RbOs 2 O 6 are significantly affected. KEYWORDS: pyrochlore oxide, RbOs 2 O 6 , resistivity, high pressure, superconductivity, rattling to form a three-dimensional skeleton. 10) A virtual size mismatch between the guest A ion and the cage made of the octahedra allows the guest ion to move almost freely with an unusually large atomic excursion in an anharmonic potential inside the cage. 11) Since the mismatch becomes large from Cs to K with decreasing ionic radius of the A ions, the intensity of rattling is enhanced accordingly towards KOs 2 O 6 . Evidence of rattling in β-pyrochlore oxides has been obtained from structural analyses showing large atomic displacement parameters 10,12) or from heat capacity and spectroscopic measurements that showed Einstein-like modes with low energies of 2-7 meV. 5,6,[13][14][15][16][17] The rattling apparently affects the electronic properties of β-pyrochlores. A high resistivity and its anomalous temperature dependence, shown by a concave-downward curvature in a wide temperature range, have been observed and ascribed to a strong scattering of electrons by rattling. 18) Moreover, the increase observed in the spin-lattice relaxation rate of A-nucleus NMR arises from a strong electron-lattice coupling of the same origin. 18,19) Because of this large electron-rattler interaction, β-pyrochore oxides undergo superconducting transitions at relatively high temperatures of T c = 9.6, 6.3, and 3.3 K for A = K, Rb, and Cs, respectively. Nagao et al. suggested that superconductivity is induced by the rattling itself, because the estimated average frequency of phonons mediating Cooper pairing coincides with the energy of rattling for each of the three compounds. 7) Hattori and Tsunetsugu have investigated the role of rattling in the mechanism of superconductivity in the framework of a strong coupling theory of superconductivity and successfully reproduced the observed T c s. 20)Unique chemical trends for various parameters are observed in the series of β-pyrochlore oxides: the rattl...

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Section: Superconducting Transitionsupporting

confidence: 74%

supporting

confidence: 71%

Section: Introductionmentioning

confidence: 86%

Section: P-t Phase Diagrammentioning

confidence: 97%

Section: Superconducting Transitionmentioning

confidence: 98%

See 3 more Smart Citations

Superconductivity and Rattling under High Pressure in the β-Pyrochlore Oxide RbOs₂O₆

et al. 2011

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Low-temperature specific heat of the β-pyrochlore oxide superconductors under high pressure

Cited by 1 publication

References 16 publications

Superconductivity and Rattling under High Pressure in the β-Pyrochlore Oxide RbOs₂O₆

Superconductivity and Rattling under High Pressure in the β-Pyrochlore Oxide RbOs₂O₆

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Low-temperature specific heat of the β-pyrochlore oxide superconductors under high pressure

Cited by 1 publication

References 16 publications

Superconductivity and Rattling under High Pressure in the β-Pyrochlore Oxide RbOs2O6

Superconductivity and Rattling under High Pressure in the β-Pyrochlore Oxide RbOs2O6

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Superconductivity and Rattling under High Pressure in the β-Pyrochlore Oxide RbOs₂O₆

Superconductivity and Rattling under High Pressure in the β-Pyrochlore Oxide RbOs₂O₆