Original Paper Ann. Phys. (Berlin), 1600283 (2017) / DOI 10.1002/andp.201600283 Tunable pinning efects produced by non-uniform antidot arrays in YBCO thin flms J. George 1 , A. Jones 1 , M. Al-Qurainy 1 , S. A. Fedoseev 1,2 , A. Rosenfeld 2 , and A. V. Pan 1,3,∗ Received 29 September 2016, revised 3 January 2017, accepted 5 January 2017 Published online 3 February 2017 Uniform, graded and spaced arrays of 3 μm triangular an- tidots in pulsed laser deposited YBa 2 Cu 3 O 7 (YBCO) super- conducting thin flms are compared by examining the im- provements in the critical current density J c they produced. The comparison is made to establish the role of their litho- graphically defned (non-)uniformity and the efectiveness to control and/or enhance the critical current density. It is found that almost all types of non-uniform arrays, includ- ing graded ones enhance J c over the broad applied mag- netic feld and temperature range due to the modifed criti- cal state. Whereas uniform arrays of antidots either reduce or produce no efect on J c compared to the original (as- deposited) thin flms. 1 Introduction Extending the operating range in applied magnetic fields ( B a ) and controlling the critical current density ( J c ) in su- perconducting thin films have always been the research focus with the potential impact in electronics and appli- cations based on coated conductors. Indeed, if the ap- plied magnetic field B a is increased around a supercon- ducting thin film, vortices begin to enter from its edges organising themselves in the Bean-like critical state [1]. In the presence of driving currents every vortex experi- ences the Lorentz force. If this force exceeds the other forces, such as repulsive vortex-vortex interactions and pinning, then the vortices start to move inducing energy losses and resistance. Mechanisms for arresting the mo- tion of vortices by controlling collective vortex interac- tions with various pinning landscapes in the presence of driving currents and/or high magnetic fields and tem- peratures have been investigated in both low and high temperature superconductors [2–17]. In as-grown plain films, vortices naturally arrange themselves in lattice-like structures as the result of pin- ning, intervortex interactions, vortex line tensions and thermal energy [6]. To reinforce pinning, at high applied fields, certain pinning structures have been introduced by modification of deposition and film growth parame- ters [5, 18, 32]. At low fields with just few vortices at play, vortex motion is mostly affected by individual intrinsic pinning centres that hold vortices in place [8, 19, 34]. This knowledge has led to development of lithographi- cally defined pinning arrays, producing J c enhancement at certain, controllable low fields [9, 10, 20]. If such an array has a period that matches the vortex lattice period then significant enhancement of the critical current den- sity can be obtained at the so-called matching fields, cor- responding to the multiple integers of the vortex lattice periods [9, 10, 20]. These types of artificial arrays were also found to be susceptible to flux-jump instabilities and flux chan- nelling [12, 21, 29]. To prevent these effects a number of different arrays were examined and compared [12, 21, 23–25]. One such type was a linearly graded array that demonstrated the resistance to flux-jumps and also flux channelling, hence the effective enhancement of cur- rent carrying ability. However, the underlying origin be- hind the details of these findings remained too vague or unexplained, in particular with respect to the flux- slipping. There was a certain inconsistency in the ex- planation and results obtained, claiming that the graded array produced larger enhancement than the uniform ar- ray, while it was the opposite [21]. Indeed, J c was found to be higher at high fields, as well as the flux-jumps ∗ Corresponding author E-mail: pan@uow.edu.au 1 Institute for Superconducting and Electronic Materials, Univer- sity of Wollongong, Northfelds Avenue, Wollongong, NSW 2522, Australia 2 Centre for Medical Radiation Physics, University of Wollongong, Northfelds Avenue, Wollongong, NSW 2522, Australia 3 National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 31 Kashirskoye Shosse, 115409, Moscow, Russian Federation C  2017 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (1 of 7) 1600283