Browsing by Author "Yu, RC"

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BCS-like superconductivity in MgCNi3
(2003-02-01)
Lin, JY
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Ho, PL
;
Huang, HL
;
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.
H-c2 of MgCNi3 determined from the specific heat and resistivity measurements
(2002-10-01)
Lin, JY
;
Lin, PH
;
Ho, PL
;
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.
Order parameter of MgB2: A fully gapped superconductor
(2001-10-15)
Yang, HD
;
Lin, JY
;
Li, HH
;
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.
Pressure effects on the transition temperature of superconducting MgCxNi3
(2003-09-01)
Yang, HD
;
Mollah, S
;
Huang, WL
;
Ho, PL
;
Huang, HL
The effect of hydrostatic pressure (P) up to 17 kbar on the superconducting transition temperature (T-C) of the newly discovered intermetallic nonoxide perovskite superconductor MgCxNi3 has been reported. T-C is found to increase with increasing P at a rate of dT(C)/dPsimilar to0.0134 to 0.0155 K/kbar depending on the value of carbon content x. The absolute value of dT(C)/dP for MgCxNi3 is about the same as that of intermetallic RNi2B2C (R denotes rare earth) and metallic superconductors but about one order of magnitude smaller than that of the most recently and intensively studied superconductor MgB2. However, the d ln T-C/dPsimilar to0.001 81 to 0.002 24 kbar(-1) and the rate of change of T-C with unit cell volume (V), d ln T-C/d ln Vsimilar to-3.18 to -2.58 of MgCxNi3 are having the comparable magnitude to that of MgB2 with opposite sign. The increase of T-C with P in MgCxNi3 can be explained in the framework of density of states (DOS) effect.