NSRRC Activity Report 2022

012 NSRRC ACTIVITY REPORT 2022 Fig. 2 : Twisted oxide lateral homostructures with orientation and orbital conjunction tunability. (a) PFM images of a designed 90° twisted (110)-BFO. (b) XLAS mapping of the patterned 90° twisted (110)-BFO. (c) Fe L 2 -edge XLAS spectra of the BFO AG and BFO FS areas. (d) Schematic of the designed twisted YBCO homostructures. (e) Corresponding orbital arrangement of the designed twisted YBCO homostructure. (f) XRD line scan along the surface normal direction and phi-scan of the freestanding (orange) and pristine (blue) areas. [Reproduced from Ref. 1] (a) (c) (f) (b) (d) (e) The detailed fabrication process that they recently established is illustrated in Fig. 1 . Firstly, an SrTiO 3 (STO) thin film is deposited on a (La,Sr)MnO 3 (LSMO) sacrificial layer grown on a (110)-oriented STO substrate. The heterostructure is then immersed in a light acid solution, which is used to selectively etch the LSMO sacrificial layer, thus separating the (110)- STO thin film and the single crystal substrate. The freestanding (110)-oriented STO thin film (FS-STO) is then lifted off and transferred onto another (110)-oriented STO substrate, forming a natural but adjustable twisted angle (denoted as phi). In this manner, a new template composed of (110)-oriented STO but with an artificial twist angle can be delivered. In the article, multiferroic BiFeO 3 (BFO) is chosen to demonstrate the growth of the twisted lateral homostructures. As shown in the topography images of BFO on the pristine STO region, BFO on the FS-STO region and the twisted boundary in Fig. 1(b) , the stripe patterns that strictly follow the [001] direction of the BFO serve as direct evidence distinguishing the twist angles of the two identical epitaxial segments. This suggests that the twisted oxide lateral homostructures could be successfully fabricated using weave epitaxy. The structural details of the twisted lateral homostructures have been analyzed and verified via high- resolution X-ray diffraction (XRD) at TLS 13A1 , TLS 17A1 , TLS 17B1 , and TPS 09A of the NSRRC. Yang’s group has further demonstrated the controllability and generic capability of fabricating different twisted lateral homostructures. In terms of controllability, they created designer patterns to artificially control the arrangements of the ferroelectric polarizations and antiferromagnetic directions in BFO. The BFO thin film grown on the patterned twisted template exhibits an in-plane twisted angle of 90° with respect to their individual [001] directions. As shown in Fig. 2(a) , piezo-force microscopy (PFM) analysis with respect to different cantilever orientations was carried out to identify the arrangement of the ferroelectric domains. Additionally, to investigate the direction of the antiferromagnetic axes in the patterned BFO(110) thin film, X-ray linear absorption spectroscopy (XLAS) measurement on the Fe L 2,3 -edge was carried out at the TPS 45A , as shown in the results in Figs. 2(b) and 2(c) . The controllable arrangements of both the ferroelectric and antiferromagnetic axes validate the feasibility of designing lateral crystalline orientation/domain patterns and related homostructures with conjunction twisted-angle tunability. To examine the generic capability of weave epitaxy, they extended the same concept to the classic high-temperature superconductor, YBa 2 Cu 3 O 7− x (YBCO). The artificially designed twisted YBCO lateral homostructures with controlled crystal arrangements and representative d z ² orbital configurations are schematically illustrated in Figs. 2(d) and 2(e) . To reveal the structural nature in greater detail, further XRD data was collected at TLS 13A1 , TLS 17A1 , TLS 17B1 , and TPS 09A. The XRD surface normal scans and phi-scans along off-normal planes of YBCO grown on (110) FS - and (001) SUB -oriented STO areas ( Fig. 3(f) ) both affirm the well-defined crystal structure and lattice symmetry of the crystals grown on the designed twisted templates underneath. These results indicate the crystal geometry of other complex oxides could also follow corresponding twisted frames and thus validates the universal capability of manufacturing twisted lateral systems using weave epitaxy.