Magnetic field penetration depth and the lower critical field in YBa2Cu3O7 (YBCO) high temperature superconductors (HTSC)

In this work the penetration depth and the lower critical field were measured in YBCO superconducting crystals by an LC resonating method. In low temperature limit, penetration depth and critical field in ab plane have been obtained as λab(0) #approx ident to# 200 nm and Hc-l''a''b#aprox ident to# 850 Oe respectively. The variation curves between the penetration depths and the reduced temperatures were compared with the BCS-type behaviour. As a result this comparison a fitting parameter A has been obtained as 1.2. The real part of the surface conductivity and the penetration depth at about 45 K show non-monotonic behaviour with large peak and they have a slope value of 2.2 AA/K to 2,5 AA/K up to 20 K. An interpretation of this smaller slope in terms of the generally accepted d-wave order parameter symmetry