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

In 2001,Japanese scientists discovered binary superconducting compounds MgB2 with the critical temperature 39 K.MgB2 is a two-gap superconductor,and the Fermi surface of this compound consists of two nearly cylindrical sheets from the two-dimensional ? band and two three-dimensional sheets from the ? band.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 two-band Ginzburg-Landau theory,we study the thermoelectric effect of two-band single-junction superconducting rings.For two-band superconductor,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(microbridge structure)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 temperature difference.Our analysis shows that the soliton solution and the fractional flux quantization in the two-band superconducting ring can be verified by measuring the thermoelectric effect of this single-junction structure.We also analyse the electromagnetic properties of two-band single-junction superconducting rings with the external magnetic field,and obtain the similar theoretical results.