Investigation On The Electromagnetic Properties Of Two-band Single-junction Superconducting Rings

In 2001 Japanese scientists discovered that the magnesium diboride MgB2 becomes superconducting at a high transition temperature about 39K.MgB2 can not be treated as a simple BCS superconductor but a two-gap superconductor,and the existance of two energy gaps has been demonstrated by the band structure and phonon spectrum calculation.Furthermore,this two-gap picture was clearly confirmed by specific heat measurements,nuclear magnetic resonance,scanning tunneling microscopy and angle-resolved photoemission spectrum experiments.Based on the two-band Ginzburg-Landau theory,we study the electromagnetic properties of non-centrosymmetric superconductor LaNiC2.The exact solutions of upper critical field and London penetration depth of LaNiC2 are obtained,and the calculations produce the experiment data in a broad temperature range.With two-band Ginzburg-Landau theory,we also study electromagnetic properties of the two-band single-junction(microbridge structure)superconducting rings with directly connected current source.For two-band superconducting ring,the phase difference of two superconducting order parameters satisfies the sine-Gordon equation,and from its soliton solution we obtain the linear relation between this phase difference at both ends of the junction and the total magnetic flux in the ring.Then with the Josephson relation in the microbridge,we establish the dependence between the magnetic flux in the superconducting ring and the applied external current.Our analysis shows that the soliton solution and the fractional flux quantization in the two-band superconducting ring can be verified by measuring the electromagnetic properties of the single-junction structure.