Coherence length in deoxygenated (1 0 3)/(0 1 3) oriented YBCO superconductor films Carlo Camerlingo a, * , Grzegorz Jung b a Consiglio Nazionale delle Ricerche, Istituto di Cibernetica ‘‘E. Caianiello’’, Via Campi Flegrei 34, 80078 Pozzuoli (NA), Italy b Department of Physics, Ben Gurion University of Negev, 84105 Beer Sheva, Israel Available online 14 April 2007 Abstract The coherence length n c along c-axis direction in (1 0 3)/(0 1 3) oriented YBCO superconductor thin films has been evaluated from the temperature dependence of current–voltage (I–V) characteristics of micro-bridges in the framework of a model taking in account ther- mally activated magnetic flux creep in the intrinsic potential of the layered structure of the superconductor. The coherence length grad- ually increased from the initial value n c = 0.14 nm to n c = 0.33 nm in the sample subjected to subsequent annealing steps performed in air at increasing temperatures from a range T a = 190–275 °C. Structural modifications of deoxygenated samples were monitored by micro- Raman spectroscopy. The critical temperature T c slightly increases after the initial annealing steps while a significant T c decrease has been observed after T a = 275 °C stage accompanied by appearance of the tetragonal phase in the crystal structure. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Coherence length; YBCO films; Micro-Raman spectroscopy 1. Model We have evaluated the out-of-plane coherence length n c from current–voltage (I–V) characteristics recorded in the thermally activated vortex creep regime for vortices mov- ing across CuO 2 planes in (1 0 3)/(0 1 3) oriented YBCO films. The I–V characteristics of w = 20 lm wide micro- bridges patterned in (1 0 3)/(0 1 3) oriented YBCO films were analyzed in the framework of the model proposed for layered superconductors by Barone et al. [1]. In the presence of a bias current I, thermal fluctuations will result in a creep of vortices across intrinsic potential originated by CuO 2 planes. The voltage V due to vortex dissipation is related to I by logðV =I Þ¼ constant  a½1 ðI =wtj cr Þ 2  5=4 ; ð1Þ where t = 120 nm is the film thickness and a is a constant independent from I [2]. The critical current j cr is given by j cr ¼ j 0 ðT Þ 16p 4 ð3CÞ 1=2 n c s 1=2 d   7=2 exp 2pC n c s 1=2 d   ; ð2Þ where s = (1  T/T c ), C = 2.51 and d is the CuO 2 plane interlayer distance. The value of j cr was evaluated by fitting the experimental I–V characteristics to (1). Finally, the coherence length n c was evaluated by fitting the tempera- ture dependence of thus obtained j cr to Eq. (2), assuming d = 1.165 nm. 2. Experimental results and discussion The coherence length n c and the critical temperature T c were evaluated in several (1 0 3)/(0 1 3) YBCO micro- bridges. All measurements were performed with bias cur- rent flowing inside the CuO 2 plane. Results are reported in Fig. 1, where T c and n c values are plotted versus the hole doping level p, as calculated from T c values by using the relation [3]: T c T MAX c ¼ 1  82:6ðp  0:16Þ 2 : ð3Þ 0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.04.077 * Corresponding author. E-mail address: c.camerlingo@cib.na.cnr.it (C. Camerlingo). www.elsevier.com/locate/physc Physica C 460–462 (2007) 805–806