Interplay between Superconductivity and Strain
The influence of strain on electronic properties of functional materials like superconductors or ferroelectrics has drawn much attention in the scientific community during the last years. The major approaches to study this influence are the application of static pressure experiments or the use of epitaxial strain in thin films having a defined lattice mismatch with the underlying substrate.
The application of piezoelectric substrates is a promising alternative to these approaches for the investigation of strain-dependent properties of functional materials. The applied strain can be changed continuously and reversibly by using an electric field on such substrates due to the inverse piezoelectric effect (Fig. 1). Therefore, superconducting YBa2Cu3O7-x (YBCO), La1.85Sr0.15CuO4 (LSCO) and BaFe1.8Co0.2As2 (Ba122) layers were grown on buffered single crystalline (001) oriented Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (PMN-PT) substrates using pulsed laser deposition. X-ray measurements revealed an undisturbed epitaxial growth of these materials on the piezocrystals and verified the strain transfer from the substrate to the superconductor under an applied electric field. The applicable strain values at low temperatures were determined by a Pt strain gauge deposited on the buffered PMN-PT substrates to enable a correlation between the change of the superconducting properties and the applied electrical field. A reversible shift of the superconducting transition temperature Tc of 0.4 K for LSCO and 0.2 K for Ba122 was observed on applying biaxial strains of 0.022% and 0.017%, respectively (Fig. 2). The change of the transition temperature is almost one order of magnitude smaller for optimally doped YBCO. The observed Tc shift in LSCO is in good agreement to literature data, which confirms the suitability of the piezocrystalline approach for the study of strain-dependent properties in superconductors.
Research Funding: DFG - Deutsche Forschungsgemeinschaft (German Research Foundation)
P. Pahlke, S. Trommler, B. Holzapfel, L. Schultz, R. Hühne
Dynamic variation of biaxal strain in optimally doped and underdoped YBa2Cu3O7-δ thin films
J. Appl. Phys. 113 (2013) 123907
S. Trommler, R. Hühne, K. Iida, S. Haindl, P. Pahlke, L. Schultz, B. Holzapfel
Reversible shift in the superconducting transition for La1.85Sr0.15CuO4 and BaFe1.8Co0.2As2 using piezoelectric substrates
New J. Phys. 12 (2010) 103030
S. Trommler, P. Pahlke, R. Hühne, L. Schultz, B. Holzapfel
Preparation of epitaxial La2-xSrxCuO4 thin films for dynamic investigations of epitaxial strain
J. Phys.: Conf. Ser. 234 (2010) 012045
Hühne, R., Okai, D., Dörr, K., Trommler, S., Herklotz, A., Holzapfel, B., Schultz, L.
Dynamic investigations on the influence of epitaxial strain on the superconducting transition in YBa2Cu3O7-x
Supercond. Sci. Technol. 21 (2008) 075020