Browsing by Author "Yang, HD"

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Absence of the paramagnetic contribution in the low-temperature specific heat of La1.9Sr0.1Cu0.98Zn0.02O4
(2000-11-01)
Lin, JY
;
Chang, CF
;
Yang, HD
;
物理研究所
;
Institute of Physics
The absence of the paramagnetic contribution in the low-temperature specific heat (C) of Zn-doped cuprates has attracted much attention recently. The phenomenon was usually explained as possible screening in the superconducting state. We have measured C of La1.9Sr0.1Cu0.98Zn0.02O4 which is not superconducting. Intriguingly, The upper limit of the magnetic contribution is found to be two orders of magnitude smaller than the expected value with no screening effect. This result puts the above explanation in a serious jeopardy.
Anisotropic impurity scattering effects on T-c and H-c2 in YBa2Cu3Ox
(1999-03-01)
Lin, JY
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Chen, SJ
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Chen, SY
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Chang, CF
;
Yang, HD
We have studied the impurity effects on the superconducting transition temperature T-c and the upper critical field H-c2 in electron irradiated YBa2Cu3Oy with in-plane oxygen defects and YBa2(Cu1-xZnx)(3)O-y. It is found that the effects of the same type of defects or impurities on T-c are the same regardless of the oxygen contents of the samples. Furthermore, T-c decreases slower in irradiated YBa2Cu3Oy than in YBa2(Cu1-xZnx)(3)O-y. This may be well explained by the model that the scattering due to in-plane oxygen defects is more anisotropic than that due to Zn impurities. The different behavior of the reduced slopes (dH(c2)/dT)(Tc)/(dH(c2)/dT)(Tc0) these two types of samples can also be understood in this context. [S0163-1829(99)08309-5].
BCS-like superconductivity in MgCNi3
(2003-02-01)
Lin, JY
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Ho, PL
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Huang, HL
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Lin, PH
;
Zhang, YL
The low-temperature specific heat C(T,H) of the superconductor MgCNi3 has been measured in detail. DeltaC/gamma(n)T(c)=1.97 is estimated from the anomaly at T-c. At low temperatures, the electronic contribution in the superconducting state follows C-es/gamma(n)T(c)approximate to7.96 exp(-1.46T(c)/T). The magnetic-field dependence of gamma(H) is found to be linear with respect to H. T-c estimated from the McMillan formula agrees well with the observed value. All the specific-heat data appear to be consistent with each other within the moderate-coupling BCS context. It is amazing that such a superconductor unstable to ferromagnetism behaves so conventionally. The Debye temperature Theta(D)=287 K and the normal state gamma(n)=33.6 mJ/mol K-2 are determined for the present sample.
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
;
Lee, TK
;
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.
Contributions of CuO2 planes and CuO chains on the transport properties of YBa2Cu4O8
(1999-01-20)
Chatterjee, S
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Weng, SS
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Hong, IP
;
Chang, CF
;
Yang, HD
We have investigated the contributions of CuO2 planes and CuO chains on the transport properties of YBa2Cu4O8 by measuring the electrical resistivity and thermoelectric power (S) of Y1-xPrxBa2(Cu1-yZny)(4)O-8, Y1-xCaxBa2Cu4O8 and YBa2(Cu1-xGax)(4)O-8. Pr reduces the mobile carrier concentration in the CuO2 planes in YBa2Cu4O8, as a consequence, the superconducting transition temperature is progressively decreased with increasing Pr. The S(T) data suggest that the metallic behavior at lower temperature of the Pr and Zn doped compounds is contributed by the double CuO chains. On the other hand, the S(T) behavior of Ca doped samples is opposite to that of the Pr doped samples because the doping of Ca in Y-site introduces holes in the CuO2 planes. However, the substitution of Ga in Cu(1)-site suppresses the carrier concentration in CuO chains and increases the normal-state resistivity revealing the important contribution from CuO chains on the metallic behavior of YBa2Cu4O8 and PrBa2Cu4O8. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Depression of quasiparticle density of states at zero energy in La1.9Sr0.1Cu1-xZnxO4
(2000-06-12)
Chang, CF
;
Lin, JY
;
Yang, HD
;
物理研究所
;
Institute of Physics
We have measured low-temperature specific hear C(T, H) of La1.9Sr0.1Cu1-xZnxO4 (x = 0, 0.01, and 0.02) in both zero and applied magnetic fields. A pronounced dip of C/T below 2 K was observed in Zn-doped samples, which is absent in the nominally clean one. If the origin of the dip in CIT is electronic, the quasiparticle density of states N(E) in Zn-doped samples may be depressed below a small energy scale Eo. The present data can be well described by the model N(E) = N(0) + alpha E-1/2, with a nonzero N(0) and positive alpha. Magnetic fields depress N(0) and lead to an increase in E-0, while leaving the energy dependence of N(E) unchanged. This novel depression of N(E) below Eo in impurity-doped cuprates cannot be reconciled with the semiclassical self-consistent approximation model. Discussions in the framework based on the nonlinear sigma model field theory and other possible explanations are presented.
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
;
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.
H-c2 of MgCNi3 determined from the specific heat and resistivity measurements
(2002-10-01)
Lin, JY
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Lin, PH
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Ho, PL
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Huang, HL
;
Zhang, YL
H-c2 of MgCNi3 has been determined from the specific heat C and resistivity rho measurements in the same sample. The results from rho are nearly identical with those determined from the anomaly in C. Furthermore, utilizing the relation gamma(H) proportional to H and the value of dgamma/dH, the obtained value of H-c2 is the same as that by the WHH model, if the spin paramagnetic effect and the spin-orbit interaction are taken into account. The results of this comparison have strong implications on the order parameter of MgCNi3.
Hole distribution in YxPr1-xBa2Cu4O8 and YxPr1-xBa2Cu3O7 probed by X-ray absorption spectroscopy
(2004-08-01)
Chen, JM
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Liu, SJ
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Lee, JM
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Lin, JY
;
Gou, YS
Utilizing high-resolution O K-edge X-ray absorption spectra, we report a comparative study on the variation of hole states with Pr doping for Y-x Pr1-xBa2Cu3O7 and YxPr1-xBa2 Cu-4 O-8. The depletion rate of hole carriers in the CuO2 planes with Pr doping in YxPr1-xBa2Cu4 O-8 is considerably slower than that in YxPr1-xBa2Cu3O7. The oxygen content affects the depletion rate of hole carriers in cuprates with Pr doping. (C) 2004 Elsevier B.V. All rights reserved.
Impurity scattering effects on the low-temperature specific heat of d-wave superconductors
(2000-06-01)
Chang, CF
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Lin, JY
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Yang, HD
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物理研究所
;
Institute of Physics
Recently, impurity scattering effects on quasiparticles in d-wave superconductors have attracted much attention. In particular, the thermodynamic properties in magnetic fields are of interest. We have measured the low-temperature specific heat C(T,H) of La1.78Sr0.22Cu1-xNixO4. The impurity scattering effects on C(T,H) of cuprate superconductors were clearly observed and are compared with the theory of d-wave superconductivity. It is found that impurity scattering leads to the relation gamma(H) = gamma(o)[1 + D(H/H-c2)ln(H-c2/H)] in small magnetic fields. Surprisingly, the sealing of C(T,H) is broken down by impurity scattering.
Low temperature specific heat studies on the pairing states of high-T-c superconductors: a brief review
(2001-09-01)
Yang, HD
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Lin, JY
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物理研究所
;
Institute of Physics
Low temperature specific heat (LTSH) data on a variety of high-T-c superconductors, such as YBa2Cu3O7, La1-xSrxCuO4, Bi2Sr2CaCu2O8, and Ba0.6K0.4BiO3 are reviewed. The agreement between the experimental data and theoretical predictions, such as T-2-dependence of specific heat at zero magnetic field and H-1/2-dependence of electronic specific heat is widely discussed within the scenario of d-wave superconductivity. Impurity scattering effects and scaling model on d-wave superconductivity are verified using Zn- and Ni-doped La1-xSrxCuO4. The low energy quasiparticle density of states N(E) = N(0) + E-1/2 are deduced from dirty d-wave superconductors. Absence of paramagnetic contribution to LTSH is found both in superconducting and nonsuperconducting underdoped samples suggesting that a mechanism beyond Kondo screening model maybe required to explain its magnetic property. (C) 2001 Elsevier Science Ltd. All rights reserved.
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
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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.
Magnetic field dependence of the low-temperature specific heat of MgCNi3
(2003-05-01)
Lin, JY
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Yang, HD
;
Jin, CQ
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物理研究所
;
Institute of Physics
The specific heat of a superconductor carries crucial signatures of its order parameter. The newly discovered superconductor MgCNi3 is predicted to be unstable to ferromagnetism, and the symmetry of its order parameter symmetry is of current interest. To shed light on this issue, we have measured the low-temperature specific heat of MgCNi3 in H. Careful analysis of the data suggests that gamma(H) proportional to H. Together with other physical properties, the results imply that MgCNi3 is a moderate-coupling BCS superconductor. (C) 2003 Elsevier Science B.V. All rights reserved.
Magnetic-field dependence of the low-temperature specific heat of La2-xSrxCuO4
(1998-12-01)
Chen, SJ
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Chang, CF
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Tsay, HL
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Yang, HD
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Lin, JY
Recently, possible evidence from the low-temperature specific heat (LTSH) for the lines of nodes in the superconducting order parameter of cuprate superconductors has attracted much attention and is still debated. To clarify this issue and to cover the studies in different carrier doping regimes, we have measured LTSH of La2-xSrxCuO4 (s = 0.10, 0.16, and 0.22) both in zero and applied magnetic fields. In all doping regimes, it is found that the increase in the Linear-T coefficient gamma is proportional to H-1/2, consistent with d-wave supercon ductivity. The data shows clear evidence for an alpha T-2 term at zero magnetic field in LTSH of La1.78Sr0.22CuO4. Furthermore, our results are compared with the recently proposed scaling theory.
Magnetic-field dependence of the low-temperature specific heat of La2-xSrxCuO4
(1998-12-01)
Chen, SJ
;
Chang, CF
;
Tsay, HL
;
Yang, HD
;
Lin, JY
Recently, possible evidence from the low-temperature specific heat (LTSH) for the lines of nodes in the superconducting order parameter of cuprate superconductors has attracted much attention and is still debated. To clarify this issue and to cover the studies in different carrier doping regimes, we have measured LTSH of La2-xSrxCuO4 (s = 0.10, 0.16, and 0.22) both in zero and applied magnetic fields. In all doping regimes, it is found that the increase in the Linear-T coefficient gamma is proportional to H-1/2, consistent with d-wave supercon ductivity. The data shows clear evidence for an alpha T-2 term at zero magnetic field in LTSH of La1.78Sr0.22CuO4. Furthermore, our results are compared with the recently proposed scaling theory.
Order parameter of MgB2: A fully gapped superconductor
(2001-10-15)
Yang, HD
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Lin, JY
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Li, HH
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Hsu, FH
;
Liu, CJ
We have measured the low-temperature specific heat C(T) for polycrystalline MgB2 prepared by high pressure synthesis. C(T) below 10 K vanishes exponentially, which unambiguously indicates a fully opened superconducting energy gap. However, this gap is found to be too small to account for T, of MgB2. Together with the small specific heat jump DeltaC/gamma T-n(c) = 1.09, scenarios such as anisotropic s-wave or multicomponent order parameter are called for. The magnetic field dependence of gamma (H) is neither linear for a fully gapped s-wave superconductor nor H-1/2 for nodal order parameter. It seems that this intriguing behavior of gamma (H) is associated with the intrinsic electronic properties other than flux pinning.
Origin of size effect on superconductivity in (R-0.8 Pr-0.2)Ba2Cu3O7 studied by soft X-ray absorption spectroscopy
(2001-03-30)
Chen, JM
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Nachimuthu, P
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Lin, JY
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Hong, IP
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Chang, CF
O K-edge X-ray absorption near-edge structure (XANES) spectroscopy of (R-0.8 Pr-0.2)Ba2Cu3O7 (R = Y, Tm, Dy, Gd, Eu and Sm) has been performed to investigate the dependence of hole distribution on ionic size of the R3+ ions. Near the O Is absorption edge, pre-peaks at similar to 527.8 and similar to 528.5 eV are assigned to transitions into O 2p hole states located in the CuO3 ribbons and CuO2 planes, respectively. As deduced from O K-edge X-ray absorption spectra, the hole concentrations in the CuO2 planes decrease monotonically with increasing ionic size of the rare-earth elements. The present XANES results clearly demonstrate that the suppression of superconductivity in (R1-x Pr-x)Ba2Cu3O7 With ionic radius of the R3+ ions results predominantly from the hole-depletion effect. (C) 2001 Elsevier Science B.V. All rights reserved.
Possible evidence for the existence of the Fehrenbacher-Rice band: O K-edge XANES study on Pr1-xCaxBa2Cu3O7
(2002-04-01)
Hong, IP
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Lin, JY
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Chen, JM
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Chatterjee, S
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Liu, SJ
X-ray absorption near edge structure (XANES), resistivity, and thermoelectric power have been measured on Pr1-xCaxBa2Cu3O7. These data reveal an intriguing electronic structure in Pr-doped cuprates. The absorption peak in XANES associated with the Fehrenbacher-Rice (FR) band has been identified. The Ca-doped holes in Pr1-xCaxBa2Cu3O7 go to both the Zhang-Rice (ZR) and FR bands. Comparative studies on the related samples suggest that the FR band is partially filled and highly localized. Implications of these results on other recent experiments, such as the observation of superconductivity in PrBa2Cu3O7 single crystals, are discussed.
Pr-induced superconductivity suppression in YxPr1-xBa2Cu4O8 probed by soft-X-ray absorption spectroscopy: a comparative studies of YxPr1-xBa2Cu4O8 and YxPr1-xBa2Cu3O7
(2003-03-07)
Chen, JM
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Liu, SJ
;
Lee, JM
;
Hong, IP
;
Lin, JY
The variation of hole states with Pr doping for YxPr1-x Ba2Cu3O7 and YxPr1-xBa2Cu4O8 has been investigated by O K-edge X-ray absorption spectroscopy. Upon Pr substitution, T-c suppression rate in YxPr1-xBa2Cu4O8 is slower than that in YxPr1-xBa2Cu3O7. For both systems, hole carriers in the CuO2 planes and CuO chains decrease monotonically with increasing Pr doping level. The depletion rate of hole carriers in the CuO2 planes with Pr doping in YxPr1-xBa2Cu4O8 is considerably slower than that in YxPr1-xBa2Cu3O7. The oxygen content affects the depletion rate of hole carriers in cuprates with Pr doping. (C) 2003 Elsevier Science B.V. All rights reserved.