Browsing by Author "Sun, C. P."

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A low-temperature specific heat study of giant dielectric constant materials
(2008-07-16)
Sun, C. P.
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Liu, Jianjun
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Lin, J-Y
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Duan, Chun-Gang
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Mei, W. N.
A low-temperature specific heat study has been performed on the insulating giant dielectric constant material CaCu(3)Ti(4)O(12) and two related compounds, Bi(2/3)Cu(3)Ti(4)O(12) and La(0.5)Na(0.5)Cu(3)Ti(4)O(12), from 0.6 to 10 K. From analyzing the specific heat data in a very low-temperature range, 0.6-1.5 K, and moderately low-temperature range, 1.5-5 K, in addition to the expected Debye terms, we observed significant contributions originating from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurring at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behavior in both low and high frequency regions.
Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr(2)S(4)
(2010-03-22)
Sun, C. P.
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Huang, C. L.
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Lin, C. C.
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Her, J. L.
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Ho, C. J.
Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr(2)S(4) are reported. It is found that a metal-insulator transition in CdCr(2)S(4) is triggered by the electrical field. In magnetic fields, the resistivity rho of CdCr(2)S(4) responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr(2)S(4) the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.
Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4
(2010-03-22)
Sun, C. P.
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Huang, C. L.
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Lin, C. C.
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Her, J. L.
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Ho, C. J.
Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity rho of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.
Effect of Mn impurities on the superconductivity in NaxCoO2 center dot yH(2)O
(2007-09-01)
Chen, Y.-J.
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Liu, C.-J.
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Wang, J.-S.
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Lin, J.-Y.
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Sun, C. P.
To shed light on the symmetry of the superconducting order parameter in NaxCoO2 center dot yH(2)O, the Mn doping effects are studied. X-ray absorption spectroscopy verifies that the doped Mn impurities occupy the Co sites and are with a valance close to +4. Impurity scattering by Mn is in the unitary limit that, however, does not lead to strong T-c suppression. This absence of the strong impurity effects on T-c is inconsistent with the simple picture of a sign-changing order parameter. Coexistence of the s-wave superconducting order parameter and the nodal one is proposed to reconcile all the existing experiments and has been implied by the specific heat experiments.
Experimental evidence for a two-gap structure of superconducting NbSe(2): A specific-heat study in external magnetic fields
(2007-12-01)
Huang, C. L.
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Lin, J. -Y.
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Chang, Y. T.
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Sun, C. P.
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Shen, H. Y.
To resolve the discrepancies of the superconducting order parameter in quasi-two-dimensional NbSe(2), comprehensive specific-heat measurements have been carried out. By analyzing both the zero-field and mixed-state data with magnetic fields perpendicular (H perpendicular to c) to and parallel (H parallel to c) to the c axis of the crystal and using the two-gap model, we conclude that (1) more than one energy scale of the order parameter is required for superconducting NbSe(2) due to the thermodynamic consistency; (2) Delta(L)=1.26 meV and Delta(S)=0.73 meV are obtained; (3) N(S)(0)/N(0)=11%-20%; (4) the observation of the kink in gamma(H) curve suggests that the two-gap scenario is more favorable than the anisotropic s-wave model to describe the gap structure of NbSe(2); and (5) Delta(S) is more isotropic and has a three-dimensional-like feature and is located either on the Se or the bonding Nb Fermi sheets.
Experimental evidence for a two-gap structure of superconducting NbSe2: A specific-heat study in external magnetic fields
(2007-12-01)
Huang, C. L.
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Lin, J. -Y.
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Chang, Y. T.
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Sun, C. P.
;
Shen, H. Y.
To resolve the discrepancies of the superconducting order parameter in quasi-two-dimensional NbSe2, comprehensive specific-heat measurements have been carried out. By analyzing both the zero-field and mixed-state data with magnetic fields perpendicular (H perpendicular to c) to and parallel (H parallel to c) to the c axis of the crystal and using the two-gap model, we conclude that (1) more than one energy scale of the order parameter is required for superconducting NbSe2 due to the thermodynamic consistency; (2) Delta(L)=1.26 meV and Delta(S)=0.73 meV are obtained; (3) N-S(0)/N(0)=11%-20%; (4) the observation of the kink in gamma(H) curve suggests that the two-gap scenario is more favorable than the anisotropic s-wave model to describe the gap structure of NbSe2; and (5) Delta(S) is more isotropic and has a three-dimensional-like feature and is located either on the Se or the bonding Nb Fermi sheets.
Induced magnetic moment by Mn doping in NaxCo1-zMnzO2 center dot yH(2)O
(2007-03-01)
Lin, J.-Y.
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Chen, Y.-J.
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Liu, C.-J.
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Wang, J.-S.
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Sun, C. P.
Impurity effects on NaxCoO2 (.) yH(2)O are studied by Mn doping. Spectroscopic evidence reveals that the doped Mn ions occupy the Co sites and the valence is +4. The magnetic local moment induced by Mn doping was observed and mu(eff) 3: 20 mB. The induced local moment could lead to magnetic pair-breaking and is likely to be responsible for the Tc suppression by Mn impurities in Na(x)Co(1-z)MnzO(2) (.) yH(2)O. (c) 2006 Elsevier B. V. All rights reserved.
Magnetism-induced ferroelectric polarization in the c-axis-oriented orthorhombic HoMnO(3) thin films
(2009-11-15)
Lin, T. H.
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Hsieh, C. C.
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Luo, C. W.
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Lin, J. -Y.
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Sun, C. P.
The magnetism-induced ferroelectricity in the E-type orthorhombic HoMnO(3) (o-HMO) films grown on Nb-doped and undoped SrTiO(3)(001) substrates was studied. The temperature dependent magnetization in these films evidently exhibits an antiferromagnetic ordering around 44 K and an anomalous second magnetic ordering along the c-axis near 35 K. Interestingly, at this anomalous transition temperature, an associated ferroelectric polarization was probed by the P-E hysteresis measurements, indicating the intimated coupling between the ferroelectric response and the reordering of Mn spins, which has never been disclosed previously by dielectric constant measurements. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3260241]
Magnetism-induced ferroelectric polarization in the c-axis-oriented orthorhombic HoMnO3 thin films
(2009-11-15)
Lin, T. H.
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Hsieh, C. C.
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Luo, C. W.
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Lin, J. -Y.
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Sun, C. P.
The magnetism-induced ferroelectricity in the E-type orthorhombic HoMnO3 (o-HMO) films grown on Nb-doped and undoped SrTiO3(001) substrates was studied. The temperature dependent magnetization in these films evidently exhibits an antiferromagnetic ordering around 44 K and an anomalous second magnetic ordering along the c-axis near 35 K. Interestingly, at this anomalous transition temperature, an associated ferroelectric polarization was probed by the P-E hysteresis measurements, indicating the intimated coupling between the ferroelectric response and the reordering of Mn spins, which has never been disclosed previously by dielectric constant measurements. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3260241]
Specific heat of Mn-doped NaxCoO2 center dot yH(2)O
(2007-09-01)
Lin, J.-Y.
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Chen, Y.-J.
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Liu, C.-J.
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Wang, J.-S.
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Sun, C. P.
C(T) of NaxCo0.99Mn0.01O2 center dot yH(2)O is studied to reveal more details on the nature of the doped Mn ions and the T-c suppression. The extra specific heat contribution in NaxCo0.99Mn0.01O2 center dot yH(2)O manifests the induced local magnetic moment due to Mn doping. The absence of the superconducting transition peak in C(T) of NaxCo0.99Mn0.01O2 center dot yH(2)O suggests a reduced superconducting volume fraction. (C) 2007 Elsevier B.V. All rights reserved.
Specific heat of YNi2B2C analyzed using two-gap model
(2006)
Huang, C. L.
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Sun, C. P.
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Lin, J. -Y.
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Kim, H. J.
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Choi, E. M.
New specific-heat data of YNi2B2C Single crystal were measured and analyzed using two-gap model. The obtained T-c = 13.77K, gamma(n) = 19.74 mJ/mol K-2, theta(D) = 533K, Delta C/gamma(n) T-c = 1.57 are consistent with those of previously reported indicating a good quality of crystal. In the superconducting state, the C, can not be fitted to a simple isotropic-gap BCS relation. Instead, it can be well described by a two-gap model. The large gap Delta(L) = 2.67meV and small gap Delta s = 1.19meV can be obtained with 71% and 29% weighting for the density of states at Fermi surface, respectively. These results are compared with those taken by point-contact spectroscopy recently.