H. D. Yang

Order Parameter of MgB2: A Fully Gapped Superconductor

We have measured the low-temperature specific heat C(T) for polycrystalline MgB(2) 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(c) of MgB(2). Together with the small specific heat jump Delta C/gamma(n)T(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.

BCS-like superconductivity in MgCNi3

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.

Coexistence of isotropic and extended s-wave order parameters in FeSe as revealed by low-temperature specific heat

The comprehensive low-temperature specific heat C(T) data identify both an isotropic s-wave and an extended s-wave order parameters coexisting in a superconducting single crystal FeSe with Tc=8.11 K. The isotropic gap {\Delta}0=1.33 meV on the hole Fermi sheets and the extended s-wave gap {\Delta}={\Delta}e(1+\alpha*cos2_theta) with {\Delta}e=1.13 meV and \alpha=0.78 on the electron Fermi sheets. The extended s-wave is rather anisotropic but the low energy quasiparticle excitations demonstrate no sign of the accidental nodes. The coefficient \gamma(H) manifesting the quasiparticle contribution to C is a non-linear function of the applied magnetic field H in the mixed state in accord with the anisotropic multi-order parameters.

Magnetocaloric effect in charge ordered Nd0.5Ca0.5MnO3 manganite

The magnetocaloric effect (MCE) has been observed in three well-defined temperature intervals (region I: 2–115 K, region II: around charge order transition TCO, and region III: around room temperature) in polycrystalline Nd0.5Ca0.5MnO3 (NCMO) manganite system showing a first order (CO) transition at a temperature, TCO∼250 K. The magnitude of ΔSM(H) increases monotonically with applied magnetic field but does not reach saturation even at fields as high as 60 kOe. In the three given temperature regions, negligible magnetic and thermal hysteresis are found, which satisfies the requirements of using NCMO as an effective magnetocaloric material for magnetic refrigeration.

Comparative analysis of specific heat of YNi2B2C using nodal and two-gap models

The magnetic field dependence of low temperature specific heat in

Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4

{\mathrm{YNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}

Effects of Ca substitution on the structural, electrical and magnetic properties of PrBa2Cu3O7−y

was measured and analyzed using various pairing order parameters. At a zero magnetic field, the two-gap model, which has been successfully applied to

Suppression of Superconductivity in Y1-xPrxBa2Cu4O8 Prepared by Nitrite Pyrolysis Method

{\mathrm{MgB}}_{2}

Experimental evidence for a two-gap structure of superconducting NbSe2 : A specific-heat study in external magnetic fields

and the point-node model, appear to describe the superconducting gap function of

Structure, superconductivity and magnetism of YBa2(Cu1−xMx)4O8 (MFe, Co, Ni, Zn and Ga)

{\mathrm{YNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}