High transition temperature (Tc) copper oxide superconductors (HTSc) have been intensively investigated throughout the last two decades. Apart from their promising application potential, they remain a challenge in solid state physics, due to the still unknown microscopic mechanism of superconductivity in these materials. Within this project, we intend to develop a technology to fabricate high quality thin films and thin film superconductor-insulator-superconductor (SIS) heterostructures of an type class of HTSc materials, namely Sr_1-xLa_xCuO₂ (SLCO), for x=0.15-0.175, in order to study the order parameter symmetry in this system.

For this, phase-sensitive experiments with 0- and π-SQUIDs (Superconducting QUantum Interference Devices) based on grain boundary and SLCO/N/Nb (N=Au, Ag) ramp-type junctions will be performed and then compared. The success of this project may enable a variety of further studies on basic properties of the HTSc materials and the implementation of SIS tunnel junctions, SQUIDs, and superconducting transistors as key elements for superconductor electronic devices.

This project is financed by Romanian National Authority for Scientific Research, CNCS-UEFISCDI, project number PN-II-ID-PCE-2011-3-1065, with total funding of 1.265.000 lei (~ 281.000 euro) for the 2011-2016 period.

The distribution of the project budget (as of December 2015) is given in Table 1: 

Table 1. Distribution of the project budget, on chapters.

The main objectives of the project are:
- the fabrication by Pulsed Laser Deposition (PLD) of superconducting single-phase Sr_1-xLa_xCuO₂ thin films (for x=0.15-0.175) in order to have a better understanding on the interdependence between the synthesis method/growth parameters on the structural and electrical transport properties of these films; by this, we hope we will have a better understanding on why it is so difficult to synthesis this class of materials as thin films; 
- experimental studies on the order parameter symmetry by using, for the first time, 0- and p-SQUIDs based on epitaxially grown c-axis oriented thin films of these compounds. Knowledge of basic physical properties of these materials, such as the orbital pairing symmetry, is important for their integration in electronic devices.
To address the question of whether the pairing symmetry changes with doping or with temperature from (presumably) a d_x2_-y2 wave to an s-wave behavior (or vice versa), the experiments will be performed for optimally-doped (x=0.15) and over-doped (x=0.175) samples, as well as over a temperature range, from 2 K to TC. The optimum doping is taken at x=0.15 based on theoretical considerations, and on latest experimental work on PLD grown thin films. A d_x2_-y2 wave symmetry may induce an additional phase shift in a superconducting loop and, therefore, SQUIDs are suitable for phase sensitive experiments.