Jin Duo

Anomalous Specific Heat Behavior of Nanocrystalline Fe at Low Temperatures

The specific heat of nanocrystalline iron with grain size of 40 nm has been measured in the low temperature range from 1.8 to 26 K. The anomalous specific heat behavior of nanocrystalline iron is compared to that of the standard bulk iron. It is found that the electronic specific heat coefficient γ obtained at low temperatures decreases by about 50%. A T2 term in the heat capacity associated with surface modes has been clearly observed. A large enhancement of the specific heat at temperatures above 16 K may be interpreted as the Einstein oscillator contributions.

Low-temperature specific heat of superconducting MgB2

The specific heat of the recently discovered superconductor MgB2 has been measured at temperatures ranging from 4.5 to 80 K. The superconducting anomaly ΔC at Tc is clearly observed. The total specific heat in the normal state can be well fitted by electronic and phonon contributions. The Debye temperature θD is found to be 737 K, much larger than other intermetallic superconductors. The normal-state electronic specific heat coefficient γ is found to be 2.48±0.5 mJ/molK2 and ΔC/γTc is between 1.41 and 2.15.

Superconductivity in Mg-Doped Layered Intermetallic Compound NbB2

We have performed low temperature resistivity ?(T) and specific heat C(T) measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperature is ~ 4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat ?n = 4.51 mJmol?1K2 and the Debye temperature ?D = 419K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows Ces/?nTc = 2.84exp(-1.21Tc/T). This indicates that the superconducting pairing in Nb0.75Mg0.25B2 has s-wave symmetry.

The structure-induced abnormal critical current characteristics of vortex line in Bi2212 whisker

The current-voltage characteristics in different magnetic fields are measured on a whisker (2 mm x 0.037 mm x 0.007 mm) of highly anisotropic material Bi2212 with field H parallel to c-axis and H parallel to b-axis, respectively. When H parallel to c-axis, the j(c) versus T relation remains normal for all fields. However, when the field H is along the b-axis, we obtained an abnormal j(c) versus T relation with a peak value appearing at T = 25 K in H = 4 T. The possible explanations are discussed

The effect of current along c direction on the ab plane superconducting properties of Bi2212 crystal

Abstract We found a normal-state reentrant behavior in zero field near the critical temperature of a Bi2212 crystal when we applied current along c-axis direction and measured the ab plane voltage. A similar phenomenon is observed in a Zn substituted Bi2212 crystal. The new phenomenon may be due to destroying of the Cooper pairs in the ab plane by the injected normal electrons.

New Resistance Anomaly in Superconducting Bi2Sr2CaCu2O8 Single Crystals

We have measured the resistance of some Bi2Sr2CaCu2O8 superconducting single crystals along ab plane and the c axis. For some of the single crystals, a resistivity anomaly near the superconducting transition temperature is observed in the ab plane. This giant resistance peak is independent of the small driving current (I less than or equal to 40 mA), and the peak is suppressed and vanished gradually with the increasing applied magnetic field (> 100 G). We proposed that the resistance peak is a quasi-reentrant behavior due to the superconducting phase inhomogeneous distribution.

Microstructure near 2 1 1 phase in high Jc MTG YBCO

The microstructures of MTG YBCO near 2 1 1 phase clusters inside the sample are studied by means of transmission electron microscopy. The results indicate that crystal defects around 2 1 1 phase are closely related to the distance between 2 1 1 particles (d2 1 1). With the decrease ofd2 1 1, the twin spacing increases. Simultaneously, the thickness of the twin boundary decreases. Whend2 1 1 is less than 0.51 Μm, there are almost no defects between 2 1 1 particles. According to the established crack model, the mechanism of the appearance of a defect-free-zone is explained. The relationship betweend2 1 1 and Jc is discussed in this paper.