Browsing by Author "Sun, CP"

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Comparative analysis of specific heat of YNi2B2C using nodal and two-gap models
(2006-01-01)
Huang, CL
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Lin, JY
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Sun, CP
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Lee, TK
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Kim, JD
The magnetic field dependence of low temperature specific heat in YNi2B2C was measured and analyzed using various pairing order parameters. At a zero magnetic field, the two-gap model, which has been successfully applied to MgB2 and the point-node model, appear to describe the superconducting gap function of YNi2B2C better than other models based on the isotropic s-wave, the d-wave line nodes, or the s+g wave. The two energy gaps, Delta(L)=2.67 meV and Delta(S)=1.19 meV, are obtained. The observed nonlinear field dependence of the electronic specific heat coefficient, gamma(H)similar to H-0.47, is quantitatively close to the gamma(H)similar to H-0.5 expected for nodal superconductivity or that can be qualitatively explained using a two-gap scenario. Furthermore, the positive curvature in H-c2(T) near T-c is qualitatively similar to that in the other two-gap superconductor MgB2.
Electronic and magnetic instability in Pr0.65Ca0.25Sr0.1MnO3
(2003-09-01)
Mollah, S
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Huang, HL
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Liu, SJ
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Ho, PL
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Huang, WL
Electronic and magnetic instability in polycrystalline Pr0.65Ca0.25Sr0.1MnO3 manganite has been established from a systematic study of resistivity (p), magnetization (M) and specific heat (C). The sample shows a charge ordering transition at T-CO similar to 200 K, an antiferromagnetic (AFM) ordering transition at T-N similar to 175 K, a metal-insulator (MI) transition at T-MI similar to 80 K and an unusual magnetic ordering transition at T-M(*) similar to 45 K in the absence of magnetic fields. Though the C data do not show any anomaly at T-MI for MI transition, these illustrate a much smaller anomaly than expected one at T-M* and is suppressed by magnetic fields. This indicates that the unusual magnetic ordering in this sample is of canted, fluctuated or phase separation of AFM and ferromagnetic in nature which is established from the T-H phase diagram, as well as the thermal and magnetic hysteresis in p, M and C. (C) 2003 Elsevier Science B.V. All rights reserved.
Evidence of nodal superconductivity in Na0.35CoO2 center dot 1.3 H2O: A specific-heat study
(2005-01-01)
Yang, HD
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Lin, JY
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Sun, CP
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Kang, YC
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Huang, CL
Comprehensive low-temperature specific-heat data C(T,H) of Na0.35CoO2.1.3 H2O with temperature T down to 0.6 K and the magnetic field H up to 8 T are presented. In the normal state, the values of gamma(n)=13.94 mJ/mol K-2 and Debye temperature Theta(D)=362 K are reported. At zero field, a very sharp superconducting anomaly was observed at T-c=4.5 K with DeltaC/gamma(ns)T(c)=1.45 if the specific-heat jump is normalized to the superconducting volume fraction, which is estimated to be 47.4% based on the consideration of entropy balance at T-c for the second-order superconducting phase transition. In the superconducting state, the electronic contribution C-es at H=0 can be well described by the model of the line nodal order parameter. In low H, deltagamma(H)proportional toH(1/2), which is also a manifestation of the line nodes. The behaviors of both T-c(H) and gamma(H) suggest the anisotropy of H-c2, or possible crossovers or transitions occurring in the mixed state.
Magnetic field dependence of low-temperature specific heat of the spinel oxide superconductor LiTi2O4
(2004-08-01)
Sun, CP
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Lin, JY
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Mollah, S
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Ho, PL
;
Yang, HD
Magnetic field dependence of low temperature specific heat of spinel oxide superconductor LiTi2O4 has been elaborately investigated. In the normal state, the obtained electronic coefficient of specific heat gamma(n)=19.15 mJ/mol K-2, the Debye temperature Theta(D)=657 K and some other parameters are compared with those reported earlier. The superconducting transition at T(c)similar to11.4 K is very sharp (DeltaT(c)similar to0.3 K) and the estimated deltaC/gamma(n)T(c) is similar to1.78. In the superconducting state, the best fit of data leads to the electronic specific heat C-es/gamma(n)T(c)=9.87 exp(-1.58 T-c/T) without field and gamma(H)proportional toH(0.95) with fields. In addition, H-c2(0)similar to11.7 T, H-c(0)similar to0.32 T, xi(GL)(0)similar to55 A, lambda(GL)(0)similar to1600 Angstrom, and H-c1(0)similar to26 mT are estimated from the Werthamer-Helfand-Hohenberg (WHH) theory or other relevant relations. All results from the present study indicate that LiTi2O4 can be well described by a typical type-II, BCS-like, moderate coupling, and fully gapped superconductor in the dirty limit. It is further suggested that LiTi2O4 is a moderately electron-electron correlated system.
The electronic structure change induced by stripe phase formation in cuprates
(2004-08-01)
Lin, JY
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Huang, CW
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Lin, PH
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Sun, CP
;
Lee, JM
It has been suggested that the stripe phase shows ID charge transport in the CuO2 planes instead of the 2D characteristics of the Zhang-Rice band. X-ray absorption near edge spectroscopy (XANES) has been used to study the electronic structure of the stripe phase compounds La2-xSrxCuO4, and La2-x-yNdySrxCuO4 for x around 1/8. The measurements were performed at both 300 and 28 K to examine the possible electronic structure change above and below the temperature of the stripe phase formation. (C) 2004 Elsevier B.V. All rights reserved.
Various analyses of specific heat for the order parameter of superconductor Na(0.35)coO(2) center dot 1.3H(2)O
(2006-05-01)
Sun, CP
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Lin, JY
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Kang, YC
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Huang, CL
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Takada, K
Low-temperature specific-heat data C(T) of two Na0.35CoO2. 1.3H(2)O samples (I and II) with temperature T down to 0.6 K without and with magnetic field of 8T are presented. The normal-state linear coefficient of specific heat gamma(n) Debye temperature Theta D, superconducting transition temperature T-c, specific heat jump at T-c, Delta C/T-gamma ns(c). and superconducting volume of fraction (SVF) are 14.89 mJ/mol K-2, 503, 4.7 K, 1.96, and 26.6% for sample I and 13.94 mJ/mol K-2, 362, 4.5 K, 1.45. and 47.4% for sample II, respectively. Because the superconducting properties may depend on the water content of sample, it is found that the better quality (higher SVF) of sample, the nodal order parameter is better than BCS isotropic s-wave model in describing the gap function of this interesting compound Na0.35CoO2. 1.3H(2)O. (c) 2006 Elsevier B.V. All rights reserved.