Epitaxial growth and superconducting anisotropy ofPbSr2Y1−xCa

Abstract

Thin films of single-crystal Pb 1−y Bi y Sr 2 Y 1−x Ca x Cu 2 O 7+δ (PbBi1212) were grown on SrTiO 3 (100) substrates by a two-step growth technique in which an amorphous film is annealed at 970 • C in a closed ceramic container prepared using the same material as the film. We find that PbBi1212 exhibits superconductivity when the Ca concentration x exceeds 0.3. The effective number of holes per Cu atom n eff is well described as n eff = 0.34x. The highest onset temperature for the superconducting transition attained in the present study is 65 K. The resistivity measurement in a magnetic field reveals that the coherence lengths of Pb1212 (y = 0) are approximately 25 and 2.7Å along the ab plane and the c axis, respectively.

90 K superconductivity of clean Pb1212 epitaxial films

“…The interception of the extrapolation in figure 1(a) is approximately 0.1 mΩ cm, which is considerably smaller than that for samples with lower T c . Thus, we estimate that the scattering rate of the present film is 2-4 times lower than that of the previous films [16]. This also indicates great improvement of the lattice homogeneity in the present work claiming higher T c .…”

“…). Details of the sample with = x 0.34 are mentioned in [16]. Consequently, the anisotropy parameter,γ,is determined as x x = 0 0 4.7 ab c ( ) ( ) , which is smaller than that of the underdoped sample with = x 0.34 (g = 9.…”

“…In this paper, we report the first observation of superconductivity above 70 K in a single-phase Pb1212 epitaxial film and its superconducting anisotropy. The Pb1212 epitaxial film was grown using a two-step technique [16] in which an amorphous film deposited on a SrTiO 3 (STO) substrate via room-temperature sputtering is annealed in a closed ceramic container prepared using the same material as that of the film. Similar techniques are often used for precise control of the composition of Hg-and Tl-based cuprates [17,18] whose chemical composition is difficult to maintain during the growth due to the high vapor pressures of heavy metal elements.…”