Thin films of the pyrochlore iridates along the [111] direction have drawn significant attention to investigate exotic correlated topological phenomena. Here, we report the fabrication of Eu2Ir2O7 thin films via reactive solid phase epitaxy using the pulsed laser deposition technique. We mainly focus on the transport properties of the films below the magnetic phase transition at 105 K. Analyses on the temperature and the field dependences of resistivity unveil the presence of weak antilocalization, a characteristic signature of the Weyl semimetallic state that has been “buried” by magnetism. Moreover, it is noteworthy that the contribution from many-body interactions in Eu2Ir2O7 thin films is enhanced at lower temperatures and competes with the weak antilocalization effect, and eventually drives the crossover to weak localization at 2 K.

The discovery of ferromagnetism in van der Waals (vdW) materials has enriched the understanding of two-dimensional (2D) magnetic orders and opened new avenues for fundamental physics research and next generation spintronics. However, achieving ferromagnetic order at room temperature, along with strong perpendicular magnetic anisotropy, remains a significant challenge. In this work, we report wafer-scale growth of vdW ferromagnet Fe3GaTe2 using molecular beam epitaxy. The epitaxial Fe3GaTe2 films exhibit robust ferromagnetism, exemplified by high Curie temperature (TC = 420 K) and large perpendicular magnetic anisotropy (PMA) constant KU = 6.7 x 105 J/m3 at 300 K for nine-unit-cell film. Notably, the ferromagnetic order is preserved even in the one-unit-cell film with TC reaching 345 K, benefiting from the strong PMA (KU = 1.8x105 J/m3 at 300 K). In comparison to exfoliated Fe3GaTe2 flakes, our epitaxial films with the same thickness show the significant enhancement of TC, which could be ascribed to the tensile strain effect from the substrate. The successful realization of wafer-scale ferromagnetic Fe3GaTe2 films with TC far above room temperature represents a substantial advancement (in some aspects or some fields, e.g. material science), paving the way for the development of 2D magnet-based spintronic devices.

Two-dimensional (2D) magnetic transition metal compounds with atomic thickness exhibit intriguing physics in fundamental research and great potential for device applications. Understanding the correlations between their macrosopic magnetic properties and the dimensionality of microscopic magnetic exchange interactions are valuable for the designing and applications of 2D magnetic crystals. Here, using spin-polarized scanning tunneling microscopy, magnetization and magneto-transport measurements, we identify the zigzag-antiferromagnetism in monolayer CrTe2, incipient ferromagnetism in bilayer CrTe2, and robust ferromagnetism in bilayer Cr3Te4 films. Our density functional theory calculations unravel that the magnetic ordering in ultrathin CrTe2 is sensitive to the lattice parameters, while robust ferromagnetism with large perpendicular magnetic anisotropy in Cr3Te4 is stabilized through its anisotropic 3D magnetic exchange interactions.

Delicate competition between comparable energy scales of spin-orbit coupling, electron correlation, and electronic bandwidth in iridates drives the emergence of exotic quantum states. Here, we report the epitaxial growth of monoclinic SrIrO3 (001) films on SrTiO3 (111) substrates and the observation of a transition from a semimetallic to a correlated insulating state upon reducing thickness. The insulating state is associated with robust and long-range ordered magnetism with a saturated moment of similar to 0.6 mu (B)/Ir. We reveal that the semimetal to insulator transition and emergent magnetism is triggered by the enhanced electron correlation as a consequence of spatial confinement. Our work indicates monoclinic SrIrO3 can be a platform for tailoring nontrivial electronic and magnetic ground state.

The interplay among symmetry of lattices, electronic correlations, and Berry phase of the Bloch states in solids has led to fascinating quantum phases of matter. A prototypical system is the magnetic Weyl candidate SrRuO3, where designing and creating electronic and topological properties on artificial lattice geometry is highly demanded yet remains elusive. Here, we establish an emergent trigonal structure of SrRuO3 by means of heteroepitaxial strain engineering along the [111] crystallographic axis. Distinctive from bulk, the trigonal SrRuO3 exhibits a peculiar XY-type ferromagnetic ground state, with the coexistence of high-mobility holes likely from linear Weyl bands and low-mobility electrons from normal quadratic bands as carriers. The presence of Weyl nodes are further corroborated by capturing intrinsic anomalous Hall effect, acting as momentum-space sources of Berry curvatures. The experimental observations are consistent with our first-principles calculations, shedding light on the detailed band topology of trigonal SrRuO3 with multiple pairs of Weyl nodes near the Fermi level. Our findings signify the essence of magnetism and Berry phase manipulation via lattice design and pave the way towards unveiling nontrivial correlated topological phenomena.

Spin texture in k-space is a consequence of spin splitting due to strong spin-orbit coupling and inversion symmetry breaking. It underlies fertile spin transport phenomena and is of crucial importance for spintronics. Here, we observe the spin texture in k-space of nominally centrosymmetric SrIrO3 grown on NdGaO3 (110) substrates, using non-linear magnetotransport measurements. We demonstrate that the spin texture is not only induced by the interface, which inherently breaks the inversion symmetry in strong spin-orbit coupled SrIrO3 films, but also originates from the film bulk. Structural analysis reveals that thicker SrIrO3 films exhibit a strain gradient, which could be considered as a continuous change in the lattice constant across different layers and breaks the inversion symmetry throughout the entire SrIrO3 films, giving rise to the spin texture in k-space. First-principles calculations reveal that the strain gradient creates large spin-splitting bands, inducing the spin texture with anisotropy, which is consistent with our experimental observations. Our results offer an efficient method for inducing the spin textures in k-space.

Electron-phonon coupling (EPC) and phonon-phonon scattering (PPS) are at the core of the microscopic physics mechanisms of vast quantum materials. However, to date, there are rarely reports that these two processes can be spatially separated, although they are usually temporally detached with different characteristic lifetimes. Here, by employing ultrafast spectroscopy to investigate the photo-carrier ultrafast dynamics in a LaCoO3 thin film on a (100) SrTiO3 substrate, intriguing evidence is found that the two interactions are indeed spatially separated. The EPC mainly occurs in the thin film, whereas PPS is largely in the substrate, especially at the several atomic layers near the interface. Across-interface penetration and decay of optical phonons into acoustic phonons thus naturally occur. An EPC strength λEg  = 0.30 is also obtained and an acoustic phonon mode at 45.3 GHz is observed. The finding lays out a cornerstone for future quantum nano device designs.

Due to a combination of the interplay between electron- electron correlation (EEC) and spin-orbit coupling, 3d-Sd transition-metal oxide interfaces have been an intriguing platform for the exploration of emergent quantum phenomena. In this work, we investigate the 3d-Sd electron coupling by designing SrIrO3/CaMnO3 superlattices and studying their electrical transport behaviors. The [(SrIrO3)(n)/(CaMnO3)(n)](m) super-lattices show a metal-nonmetal crossover (MNC) with the critical temperature increasing monotonically with decreasing n, until n = 1, a nonmetallic behavior is observed up to room temperature. Detailed analyses reveal that the MNC is the consequence of the weak localization modified by the enhanced EEC in SrIrO3 competing with the effective field of spin- orbital relaxation, with the interfaces with CaMnO3 being introduced to the superlattices. This study provides a framework for understanding the microscopic picture of 3d-Sd electron coupling.