Superconducting and Structural Transitions in the β-Pyrochlore Oxide KOs2O6 under High Pressure

Ogusu, Hiroki; Takeshita, Nao; Izawa, K.; Yamaura, Jun‐ichi; Ohishi, Yasuo; Tsutsui, Satoshi; Hiroi, Zenji

doi:10.1143/jpsj.79.114710

Cited by 4 publications

(9 citation statements)

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“…The overall resistivity curves shift upward with increasing pressure, as observed in KOs 2 O 6 . 27) In addition to sharp drops below 10 K owing to superconducting transitions, two more anomalies are observed above 3.6 GPa, which were not detected in previous experiments using a polycrystalline sample. The three anomalies, which are a superconducting transition at T c , a subtle anomaly at T o , and a pronounced anomaly with a large thermal hysteresis at T s , will be described in sequence below.…”

Section: Resultsmentioning

confidence: 66%

“…26,27) The sudden drop has been ascribed to a structural transition, by which an enhancement in T c due to a strong electron-rattler interaction present in the low-pressure cubic phase is abrogated as the rattling of the K ion is completely suppressed or weakened in the high-pressure phase of reduced symmetry. 27) Moreover, two anomalies were observed in the temperature dependence of resistivity in the low-pressure phase of KOs 2 O 6 , which may be due to subtle changes in the crystal structure and thus in the rattling vibration. 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.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, Ogusu et al have carried out resistivity measurements under HPs of up to 5 GPa in a high-quality single crystal of KOs 2 O 6 and found a sudden drop in T c from 6.5 to 3.3 K at a pressure of 3.6 GPa. 26,27) The sudden drop has been ascribed to a structural transition, by which an enhancement in T c due to a strong electron-rattler interaction present in the low-pressure cubic phase is abrogated as the rattling of the K ion is completely suppressed or weakened in the high-pressure phase of reduced symmetry. 27) Moreover, two anomalies were observed in the temperature dependence of resistivity in the low-pressure phase of KOs 2 O 6 , which may be due to subtle changes in the crystal structure and thus in the rattling vibration.…”

Section: Introductionmentioning

confidence: 99%

“…27) Moreover, two anomalies were observed in the temperature dependence of resistivity in the low-pressure phase of KOs 2 O 6 , which may be due to subtle changes in the crystal structure and thus in the rattling vibration. 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.…”

Section: Introductionmentioning

confidence: 99%

“…[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. A reliable pressure dependence of T c , which is substantially different from those previously reported for polycrystalline samples, is obtained.…”

Section: Introductionmentioning

confidence: 99%

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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 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: Resultsmentioning

confidence: 66%