Superconductivity in a pyrochlore-related oxide KOs<sub>2</sub>O<sub>6</sub>

Yonezawa, Shigeki; Muraoka, Yuji; Matsushita, Yoshitaka; Hiroi, Zenji

doi:10.1088/0953-8984/16/3/l01

Cited by 206 publications

(191 citation statements)

References 11 publications

(18 reference statements)

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“…RbOs2O6 is one of only four pyrochlore superconductors known to date. These are the α-pyrochlore Cd2Re2O7 and the β-pyrochlores AOs2O6, where A = Cs, Rb, or K. [1,2,3] RbOs2O6 is a conventional s-wave superconductor with a critical temperature Tc = 6.4 K. [4,5,6,7] In this short paper, we provide evidence for an additional electronic mass enhancement beyond the contribution from the coupling to phonons. Specific heat measurements on RbOs2O6 show that the residual Sommerfeld coefficient in the superconducting state γr and the normal-state coefficient γ vary among the various samples measured.…”

Section: Introductionmentioning

confidence: 85%

Large mass enhancement in

Brühwiler

Казаков

Karpiński

et al. 2006

Physica B: Condensed Matter

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Heat capacity measurements on the recently discovered geometrically frustrated β-pyrochlore superconductor RbOs2O6 (Tc = 6.4 K) yield a Sommerfeld coefficient of 44 mJ/mol f.u. /K 2 . This is about 4 times larger than the one found in band structure calculations. In order to specify the enhancement due to electron-electron interactions, we have measured the electron-phonon enhancement. By a suitable analysis, an electron-phonon coupling constant λep = 1 ± 0.1 is derived from the specific heat jump at Tc. This leaves a significant additional λ add = 2.1 ± 0.3 for enhancement due to other mechanisms, possibly related to the triangular lattice. To arrive at these results, an appropriate analysis method for bulk thermodynamic data based on the condensation energy was applied.Key words: RbOs2O6, superconductivity, correlation, DOS enhancement, thermodynamic properties PACS: 74.25. Bt; 71.27.+a; Long standing interest in the pyrochlores stems from their inherent geometrical frustration due to the metal ions forming a network of corner-sharing tetrahedra. Thus, metallic pyrochlores constitute ideal systems to study to what degree itinerant electrons are affected by a lattice which is known to cause geometrical frustration for interactions among localized magnetic moments. For similar reasons, the superconductivity recently found in RbOs2O6 has been of considerable interest. RbOs2O6 is one of only four pyrochlore superconductors known to date. These are the α-pyrochlore Cd2Re2O7 and the β-pyrochlores AOs2O6, where A = Cs, Rb, or K. [1,2,3] RbOs2O6 is a conventional s-wave superconductor with a critical temperature Tc = 6.4 K. [4,5,6,7] In this short paper, we provide evidence for an additional electronic mass enhancement beyond the contribution from the coupling to phonons. Specific heat measurements on RbOs2O6 show that the residual Sommerfeld coefficient in the superconducting state γr and the normal-state coefficient γ vary among the various samples measured. The variation is consistent with the presence of a second metallic component, and subsequent x-ray diffraction analysis has confirmed the presence of OsO2 in the samples. We have therefore developed a suitable quantitative method to analyze thermodynamic data when dealing with a superconducting sample containing a metallic second phase. Since the analysis is based on the condensation energy of the superconductor of interest, we call it condensation energy analysis (CEA). It involves integrating the heat capacity to obtain the condensation energy which is a reliable measure of the superconducting fraction. From the systematic variation of the thermodynamic parameters on the superconducting fraction it is possible to extract the properties of the pure sample. [7] According to the CEA, the superconducting electronic specific heat Ces is extracted from the measurement by Ces(T ) = η −1 m ∆Cp + γ1T . Here, ηm is the superconducting mass fraction, ∆Cp = C0 T − C12 T is the difference in heat capacity between the superconducting and normal state, and γ1 is the ...

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Section: Introductionmentioning

confidence: 85%

Large mass enhancement in

Brühwiler

Казаков

Karpiński

et al. 2006

Physica B: Condensed Matter

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“…The pyrochlore superconductors AOs 2 O 6 (A = Cs, Rb, and K) attracted intense attention because of a possible unusual mechanism of superconductivity: rattling of the A atom is believed to play an important role in establishing the superconductivity [1][2][3]. To date, many studies seem to focus on the possibility; however correlations between the anomalous lattice properties and the superconductivity are still under debate [4][5][6][7][8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Magnetic and charge transport properties of the Na-based Os oxide pyrochlore

Shi¹,

Belik²,

Tachibana³

et al. 2009

Journal of Solid State Chemistry

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“…4 Furthermore, in metallic pyrochlore oxides, a frustration originating from the pyrochlore lattice might also lead to novel types of electronic properties. In fact, 4d and 5d transition-metal pyrochlore oxides have been reported to show various transport properties such as superconductivity in Cd 2 Re 2 O 7 5 and AOs 2 O 6 (where A = K, Rb, and Cs), 6 15 The strongly frustrated state can be relieved by the application of a magnetic field and pressure. Applying a magnetic field is the easiest method to lower the symmetry of the system.…”

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confidence: 99%

Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2O
Sakata
¹
,
Kagayama
²
,
Shimizu
³

et al. 2011
Phys. Rev. B

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We report the pressure dependence of electrical resistance R(T) of a frustrated pyrochlore oxide Nd 2 Ir 2 O 7 , which shows a second-order metal-insulator transition (MIT) at 36 K. This MIT is monotonically suppressed by the application of pressure. The insulating phase disappears at around 10 GPa. Then, in the pressure-induced metallic state above 10 GPa, a new pressure-induced phase transition emerges at around 3 K, which is characterized by a resistance drop. The new phase transition is due to a ferromagnetic (FM) ordering, which is suggested to be an ordered spin ice (two-in two-out) state of the Nd moment via the RKKY interaction. We succeeded in observing the phase competition between the MIT and the FM ordering by the application of high pressure. Geometrical frustration in a magnetic material can lead to novel phenomena such as a macroscopic degeneracy in the ground state with no long-range ordering (LRO). Pyrochlore oxides A 2 B 2 O 7 have attracted great interest because their structure, 1 which includes corner-shared tetrahedra whose vertices are occupied by spins, may show a strong geometrical frustration such as spin ice 2,3 and spin liquid states. 4 Furthermore, in metallic pyrochlore oxides, a frustration originating from the pyrochlore lattice might also lead to novel types of electronic properties. In fact, 4d and 5d transition-metal pyrochlore oxides have been reported to show various transport properties such as superconductivity in Cd 2 Re 2 O 7 5 and AOs 2 O 6 (where A = K, Rb, and Cs), 6 15 The strongly frustrated state can be relieved by the application of a magnetic field and pressure. Applying a magnetic field is the easiest method to lower the symmetry of the system. Actually, the application of a magnetic field in the [111] direction to the spin ice state induces a Kagomé ice state, where the macroscopic degeneracy is partially reduced. 16 On the other hand, applying pressure is an effective method to drive more dramatic change in various physical parameters such as magnetic interactions, bandwidth, and electron correlations. In fact, the application of high pressure to the spin liquid Tb 2 Ti 2 O 7 induces LRO. 17 Furthermore, the application of pressure on the MIT in pyrochlore oxides stabilizes it to a metallic state; the negative pressure dependence of the transition temperature (T MI ) has been observed in Cd 2 Os 2 O 7 (T MI = 226 K) 12 and Hg 2 Ru 2 O 7 (T MI = 107 K). 18 In particular, for Hg 2 Ru 2 O 7 , a Fermi liquid with an enhanced mass is realized above 6.5 GPa. 18 Thus, the application of pressure to the strongly frustrated state can lead to a novel phase.A recent study on pyrochlore iridates Ln 2 Ir 2 O 7 has revealed the occurrence of MITs for Ln = Nd, Sm, and Eu at T MI of 36, 117, and 120 K, respectively. 19 These MITs are second-order transitions and involve a magnetic anomaly caused by 5d electrons from Ir 4+ . It should be noted that T MI increases with decreasing the ionic radius of Ln 3+ . Furthermore, the electrical conductivity of the iridates also depends ...

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Superconductivity in a pyrochlore-related oxide KOs₂O₆

Cited by 206 publications

References 11 publications

Large mass enhancement in

Large mass enhancement in

Magnetic and charge transport properties of the Na-based Os oxide pyrochlore

Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2O
Sakata
¹
,
Kagayama
²
,
Shimizu
³

et al. 2011
Phys. Rev. B

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Superconductivity in a pyrochlore-related oxide KOs2O6

Cited by 206 publications

References 11 publications

Large mass enhancement in

Large mass enhancement in

Magnetic and charge transport properties of the Na-based Os oxide pyrochlore

Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2OSakata1, Kagayama2, Shimizu3 et al. 2011Phys. Rev. B

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Superconductivity in a pyrochlore-related oxide KOs₂O₆

Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2O
Sakata
¹
,
Kagayama
²
,
Shimizu
³

et al. 2011
Phys. Rev. B