Experimental Observation on Superconducting Single Crystals
Single Crystals of Bi-system have been grown by self-flux method. Incommensurate structure in 2212, 2223 structure and anti-phase boundary have been observed. The optical, magnetic, thermal and transport properties have been measured. For example, the resistivity along c axis shows semiconducting behavior just above Tc with a minimum between 140 – 180 K and in the a-b plane is metallic. At 250 K, ρc/ρab≳1000 indicates the even stronger anisotropy in Bi2Sr2CaCu2Oy than in YBCO. The thermopower measurement shows in a-b plane the sign of carriers is hole-like, but cross at 250 K. The spin fluctuation has been observed in Bi-Sr-Ca-Cu-O system. The center frequencies of the excitations are about 1900 – 2300 cm−1, which correspond to the value of the exchange constant J ≃ 690–840 cm−1. The measurements of superconducting transition under high pressure show that the transition width and the Tc change. The Tc maximum is related to the minimum of resistivity under pressure. Some new results in details will be given in the talk.