thin film at low temperature*

In the SrRuO₃ (SRO) system, the structural symmetry plays an important role in its physical properties. Structural investigation of SRO at high temperatures reveals the cubic symmetry above approximately 920 K. With reducing temperature, SRO undergoes a series of phase transitions, first from the cubic to tetragonal and then from the tetragonal to orthorhombic phases. At ambient temperature, SrRuO₃ exhibits the orthorhombic phase with the Pbnm space group, where mirror symmetry is present. The SRO thin film grown on SrTiO₃ (001) substrate shows a ferromagnetic phase transition with a Curie temperature (T_c) of about 150 K, below which a Weyl metal phase was recently discovered.  However, the possible structural evolution in the ferromagnetic SRO film is not experimentally studied in detail. In this study, we utilized high-precision synchrotron X-ray to investigate the structural properties of the SRO thin film down to around 10 K. The SRO thin film maintains the distorted orthorhombic phase with the Pbnm space group above T_c. Below T_c, the SRO (012) reflection appears and remains nearly unchanged with reducing temperature down to about 10 K, which can be associated with the P2₁/c symmetry with the absence of mirror planes. A systematic study on the temperature dependent structural evolution in SrRuO₃ /SrTiO₃ film will be presented and discussed.