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Controlling defect densities in SrRuO3films is the cornerstone for probing the intricate relationship among its structural, electrical, and magnetic properties. We combine film growth, electrical transport, and magnetometry to demonstrate the adsorption-controlled growth of phase-pure, epitaxial, and stoichiometric SrRuO3films on SrTiO3(001) substrates using solid source metal–organic molecular beam epitaxy. Across the growth window, we show that the anomalous Hall curves arise from two distinct magnetic domains. Domains with similar anomalous Hall polarities generate the stepped feature observed within the growth window, and those with opposite polarities produce the hump-like feature present exclusively in the highly Ru-poor film. We achieve a residual resistivity ratio (RRR = ρ300K/ρ2K) of 87 in a 50 nm-thick, coherently strained, and stoichiometric SrRuO3film, the highest reported value to date on SrTiO3(001) substrates. We hypothesize further improvements in the RRR through strain engineering to control the tetragonal-to-orthorhombic phase transformation and the domain structure of SrRuO3films.

Electronic flat-band materials host quantum states characterized by a quenched kinetic energy. These flat bands are often conducive to enhanced electron correlation effects and emergent quantum phases of matter1. Long studied in theoretical models2–4, these systems have received renewed interest after their experimental realization in van der Waals heterostructures5,6and quasi-two-dimensional (2D) crystalline materials7,8. An outstanding experimental question is if such flat bands can be realized in three-dimensional (3D) networks, potentially enabling new materials platforms9,10and phenomena11–13. Here we investigate the C15 Laves phase metal CaNi2, which contains a nickel pyrochlore lattice predicted at a model network level to host a doubly-degenerate, topological flat band arising from 3D destructive interference of electronic hopping14,15. Using angle-resolved photoemission spectroscopy, we observe a band with vanishing dispersion across the full 3D Brillouin zone that we identify with the pyrochlore flat band as well as two additional flat bands that we show arise from multi-orbital interference of Ni d-electrons. Furthermore, we demonstrate chemical tuning of the flat-band manifold to the Fermi level that coincides with enhanced electronic correlations and the appearance of superconductivity. Extending the notion of intrinsic band flatness from 2D to 3D, this provides a potential pathway to correlated behaviour predicted for higher-dimensional flat-band systems ranging from tunable topological15to fractionalized phases16.

Monoclinic β-Ga2O3, an ultra-wide bandgap semiconductor, has seen enormous activity in recent years. However, the fundamental study of the plasmon–phonon coupling that dictates electron transport properties has not been possible due to the difficulty in achieving higher carrier density (without introducing chemical disorder). Here, we report a highly reversible, electrostatic doping of β-Ga2O3films with tunable carrier densities using ion-gel-gated electric double-layer transistor configuration. Combining temperature-dependent Hall effect measurements, transport modeling, and comprehensive mobility calculations using ab initiobased electron–phonon scattering rates, we demonstrate an increase in the room-temperature mobility to 201 cm2V–1s–1followed by a surprising decrease with an increasing carrier density due to the plasmon–phonon coupling. The modeling and experimental data further reveal an important “antiscreening” (of electron–phonon interaction) effect arising from dynamic screening from the hybrid plasmon–phonon modes. Our calculations show that a significantly higher room-temperature mobility of 300 cm2V–1s–1is possible if high electron densities (>1020cm–3) with plasmon energies surpassing the highest energy LO mode can be realized. As Ga2O3and other polar semiconductors play an important role in several device applications, the fundamental understanding of the plasmon–phonon coupling can lead to the enhancement of mobility by harnessing the dynamic screening of the electron–phonon interactions.

Hysteretic magnetoresistance (MR) is often used as a signature of ferromagnetism in conducting oxide films and heterostructures. Here, magnetotransport is investigated in a nonmagnetic La-doped SrSnO3film. A 12 nm La:SrSnO3/2 nm SrSnO3/GdScO3(110) film with insulating behavior exhibited a robust hysteresis loop in the MR at T< 5 K accompanied by an anomaly at ∼±3 T at T< 2.5 K. Furthermore, MR with the field in-plane yielded a value exceeding 100% at 1.8 K. Using detailed temperature-, angle- and magnetic field-dependent resistance measurements, we illustrate the origin of hysteresis is not due to magnetism in the film but rather is associated with the magnetocaloric effect of the substrate. Given GdScO3and similar substrates are commonly used, this work highlights the importance of thermal coupling to processes in the substrates which must be carefully accounted for in the data interpretation for heterostructures utilizing these substrates.

We report a more than 10-fold enhancement of the piezoelectric coefficient d33of polycrystalline CH3NH3PbI3(MAPbI3) films when interfacing them with ferroelectric PbZr0.2Ti0.8O3(PZT). Piezoresponse force microscopy (PFM) studies reveal d33MAPbI3values of 0.3–0.4 pm/V for MAPbI3deposited on Au, indium tin oxide, and SrTiO3surfaces, with small phase angle fluctuating at length scales smaller than the grain size. In sharp contrast, on samples prepared on epitaxial PZT films, we observe large-scale polar domains exhibiting clear, close to 180° PFM phase contrasts, pointing to polar axes along the film normal. By separating the piezoresponse contributions from the MAPbI3and PZT layers, we extract a significantly higher d33MAPbI3of ∼4 pm/V, which is attributed to the enhanced alignment of the MA molecular dipoles promoted by the unbalanced surface potential of PZT. We also discuss the effect of the interfacial screening layer on the preferred polar direction.

Here, we present a family of titanium-based kagome metals of the form LnTi3Bi4(Ln: La···Gd3+, Eu2+, Yb2+). Four previously unreported compounds are presented: YbTi3Bi4, GdTi3Bi4, NdTi3Bi4, and PrTi3Bi4. Single-crystal growth methods are provided alongside detailed magnetic and thermodynamic measurements across the entire series. The LnTi3Bi4family of compounds are orthorhombic (Fmmm), layered compounds that exhibit slightly distorted titanium-based kagome nets interwoven with zigzag lanthanide-based (Ln) chains. Crystals are easily exfoliated parallel to the kagome sheets, and angular resolved photoemission (ARPES) measurements highlight the intricacy of the electronic structure in these compounds. Density functional theory (DFT) and ARPES studies find Dirac points near the Fermi level, consistent with the kagome-derived band structure. The magnetic properties and the associated anisotropy emerge from the quasi-1D zigzag chains of Ln and impart a wide array of magnetic ground states ranging from anisotropic ferromagnetism to complex antiferromagnetism with a cascade of metamagnetic transitions. The combination of the kagome-based electronic structure and highly anisotropic Ln-based magnetism on an exfoliatable platform cements the LnTi3Bi4family as an interesting addition to the ever-expanding suite of kagome metals.