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Abstract Superlattice formation dictates the physical properties of many materials, including the nature of the ground state in magnetic materials. Chemical composition is commonly considered to be the primary determinant of superlattice identity, especially in intercalation compounds. Nevertheless, in this work, we find that kinetic control of superlattice growth leads to the coexistence of disparate crystallographic domains within a compositionally perfect single crystal. We demonstrate that Cr_1/4TaS₂is a noncollinear antiferromagnet in which scattering between majority and minority superlattice domains engenders complex magnetotransport below the Néel temperature, including an anomalous Hall effect. We characterize the magnetic phases in different domains, image their nanoscale morphology, and propose a mechanism for nucleation and growth using a suite of experimental probes coupled with first-principles calculations and symmetry analysis. These results provide a blueprint for the deliberate engineering of macroscopic transport responses via microscopic tuning of magnetic exchange interactions in superlattice domains. 

Abstract Under-oil open microfluidic system, utilizing liquid-liquid boundaries for confinements, offers inherent advantages including clogging-free flow channels, flexible access to samples, and adjustable gas permeation, making it well-suited for studying multi-phase chemical reactions that are challenging for closed microfluidics. However, reports on the novel system have primarily focused on device fabrication and functionality demonstrations within biology, leaving their application in broader chemical analysis underexplored. Here, we present a visualization-enhanced under-oil open microfluidic system for in situ characterization of multi-phase chemical reactions with Raman spectroscopy. The enhanced system utilizes a semi-transparent silicon (Si) nanolayer over the substrate to enhance visualization in both inverted and upright microscope setups while reducing Raman noise from the substrate. We validated the system’s chemical stability and capability to monitor gas evolution and gas-liquid reactions in situ. The enhanced under-oil open microfluidic system, integrating Raman spectroscopy, offers a robust open-microfluidic platform for label-free molecular sensing and real-time chemical/biochemical process monitoring in multi-phase systems. 

Abstract Magnetic frustration is a route for novel ground states, including spin liquids and spin ices. Such frustration can be introduced through either lattice geometry or incompatible exchange interactions. Here, we find that epitaxial strain is an effective tool for tuning antiferromagnetic exchange interactions in a square-lattice system. By studying the magnon excitations in La₂NiO₄films using resonant inelastic x-ray scattering, we show that the magnon displays substantial dispersion along the antiferromagnetic zone boundary, at energies that depend on the lattice of the film’s substrate. Using first principles simulations and an effective spin model, we demonstrate that the antiferromagnetic next-nearest neighbour coupling is a consequence of the two-orbital nature of La₂NiO₄. Altogether, we illustrate that compressive epitaxial strain enhances this coupling and, as a result, increases the level of incompatibility between exchange interactions within a model square-lattice system. 

Abstract Charge ordering (CO), characterized by a periodic modulation of electron density and lattice distortion, has been a fundamental topic in condensed matter physics, serving as a potential platform for inducing novel functional properties. The charge-ordered phase is known to occur in a doped system with highd-electron occupancy, rather than low occupancy. Here, we report the realization of the charge-ordered phase in electron-doped (100) SrTiO₃epitaxial thin films that have the lowestd-electron occupancy i.e.,d¹-d⁰. Theoretical calculation predicts the presence of a metastable CO state in the bulk state of electron-doped SrTiO₃. Atomic scale analysis reveals that (100) surface distortion favors electron-lattice coupling for the charge-ordered state, and triggering the stabilization of the CO phase from a correlated metal state. This stabilization extends up to six unit cells from the top surface to the interior. Our approach offers an insight into the means of stabilizing a new phase of matter, extending CO phase to the lowest electron occupancy and encompassing a wide range of 3dtransition metal oxides. 

Abstract Terahertz (THz) technology is critical for quantum material physics, biomedical imaging, ultrafast electronics, and next‐generation wireless communications. However, standing in the way of widespread applications is the scarcity of efficient ultrafast THz sources with on‐demand fast modulation and easy on‐chip integration capability. Here the discovery of colossal THz emission is reported from a van der Waals (vdW) ferroelectric semiconductor NbOI₂. Using THz emission spectroscopy, a THz generation efficiency an order of magnitude higher than that of ZnTe, a standard nonlinear crystal for ultrafast THz generation is observed. The underlying generation mechanisms associated are further uncovered with its large ferroelectric polarization by studying the THz emission dependence on excitation wavelength, incident polarization, and fluence. Moreover, the ultrafast coherent amplification and annihilation of the THz emission and associated coherent phonon oscillations by employing a double‐pump scheme are demonstrated. These findings combined with first‐principles calculations, inform a new understanding of the THz light–matter interaction in emergent vdW ferroelectrics and pave the way to develop high‐performance THz devices on them for quantum materials sensing and ultrafast electronics. 

Abstract Unconventional spin‐orbit torques arising from electric‐field‐generated spin currents in anisotropic materials have promising potential for spintronic applications, including for perpendicular magnetic switching in high‐density memory applications. Here, all the independent elements of the spin torque conductivity tensor allowed by bulk crystal symmetries for the tetragonal conductor IrO₂are determined via measurements of conventional (in‐plane) anti‐damping torques for IrO₂thin films in the high‐symmetry (001) and (100) orientations. It is then tested whether rotational transformations of this same tensor can predict both the conventional and unconventional anti‐damping torques for IrO₂thin films in the lower‐symmetry (101), (110), and (111) orientations, finding good agreement. The results confirm that spin‐orbit torques from all these orientations are consistent with the bulk symmetries of IrO₂, and show how simple measurements of conventional torques from high‐symmetry orientations of anisotropic thin films can provide an accurate prediction of the unconventional torques from lower‐symmetry orientations. 

Abstract In recent years,T_dtransition metal dichalcogenides have been heavily explored for their type‐II Weyl topology, gate‐tunable superconductivity, and nontrivial edge states in the monolayer limit. Here, the Fermi surface characteristics and fundamental transport properties of similarly structured 2M‐WSe₂bulk single crystals are investigated. The measurements of the angular dependent Shubnikov–de Haas oscillations, with support from first‐principles calculations, reveal multiple three‐ and two‐dimensional Fermi pockets, one of which exhibits a nontrivial Berry's phase. In addition, it is shown that the electronic properties of 2M‐WSe₂are similar to those of orthorhombic MoTe₂and WTe₂, having a single dominant carrier type at high temperatures that evolves into coexisting electron and hole pockets with near compensation at temperatures below 100 K, suggesting the existence of a Lifshitz transition. Altogether, the observations provide evidence towards the topologically nontrivial electronic properties of 2M‐WSe₂and motivate further investigation on the topological properties of 2Mtransition metal dichalcogenides in the atomically thin limit. 

Glasses prepared by physical vapor deposition (PVD) can have advantageous material properties, such as highly enhanced thermal stability and denser molecular packing, and thin glassy films prepared by PVD are utilized as active layers in organic light emitting diodes (OLEDs). However, the stability and density of PVD glasses with compositions typical of OLED devices are not well studied. Here, we prepared Ir(ppy)3 doped vapor-deposited glasses in three different organic semiconductor hosts; Ir(ppy)3 in a dilute concentration is often used as a light emitter in phosphorescent OLEDs. We studied these glasses during temperature ramping using spectroscopic ellipsometry and found that the Ir(ppy)3 doped PVD glasses have high kinetic stability and high density. Surprisingly, the observed kinetic stability exceeds that of single-component PVD glasses. This work allows further understanding of the material properties influencing OLED performance, thus facilitating the design of durable and stable devices. 

The 5drare Earth iridate is an intriguing material with exhibiting exotic electronic and magnetic phases due to spin‐orbit coupled states. Ternary iridium oxidesLn₃IrO₇contain an unusual Ir⁵⁺(5d⁴) system, which remain a subject of active research. Fabricating epitaxialLn₃IrO₇films is challenging due to substrate compatibility, but it offers a valuable platform to explore electronic and magnetic behaviors under reduced dimensionality and substrate interactions, revealing novel phenomena based on Ir⁵⁺(5d⁴). In this regard, this demonstrates that Pr₃IrO₇with its highly anisotropic orthorhombic structure can be epitaxially grown on a cubic (111)‐oriented yttrium‐stabilized ZrO₂(YSZ) substrate. Pr₃IrO₇film exhibits six epitaxial domains, where the (220) and (202) planes aligning epitaxially to YSZ (111) with the threefold symmetry. This diverse domain configuration in Pr₃IrO₇film leads to unique magnetic properties, exhibiting spin‐glass‐like behavior. Pr₃IrO₇thin film offers a platform for exploring unconventional magnetic states, and their successful heteroepitaxy on YSZ substrates opens new avenues for discovering novel physical phenomena.