Ordered corundum oxides introduce new prospects in the field of functional oxides thin films, complementing the more widely studied class of ABO3 perovskites. In this work, we take advantage of the layer-by-layer growth regime to fabricate epitaxial CrVO3 superlattice thin films with atomic-scale accuracy on the periodic arrangement of chromium and vanadium layers. By means of X-ray diffraction, scanning transmission electron microscopy and Raman spectroscopy, we confirm the thickness control in the sub-unit cell scale, alternating 3, 2 or 1 single atomic layers of Cr2O3 and V2O3. We stabilize the ilmenite phase of CrVO3 (space group $${{\rm{R}}}\bar{3}$$) and compare the functional properties of the thin film with those calculated by density functional theory. This approach to the growth of ordered corundum oxides opens the path towards the stabilization of complex oxides with tailored properties by varying the composition and the superlattice period, ultimately broadening the family of functional rhombohedral oxides. Ordered corundum oxides offer promising alternatives to traditional perovskites in functional oxide thin films. Here, the authors utilize layer-by-layer growth to fabricate CrVO3 superlattice thin films, achieving atomic-scale precision and stabilizing the ilmenite phase, potentially expanding the range of customizable rhombohedral oxides with unique properties.

We present a characterization platform for extensive multi-functional testing of electrical properties of different oxide layers in a heterogeneously integrated stack simultaneously, at different fabrication levels. We investigated the integration of a ferroelectric oxide (hafnium zirconium oxide) with a strongly correlated oxide (vanadium oxide) that exhibits a metal-insulator transition (MIT). The platform offers crucial insights into how functional properties, such as ferroelectric switching and correlated transport, evolve with processing. It revealed an increase in the hafnia leakage and the loss of MIT during the crystallization step, with and without alumina oxygen-blocking layers. Having been implemented using open-source design and layout tools, this concurrent in-process electrical characterization platform can serve as a diagnostic and optimization tool for the integration of reactive oxides.

We present the results of a search for gravitational-wave transients associated with core-collapse supernova SN 2023ixf, which was observed in the galaxy Messier 101 via optical emission on 2023 May 19, during the LIGO–Virgo–KAGRA 15th Engineering Run. We define a five-day on-source window during which an accompanying gravitational-wave signal may have occurred. No gravitational waves have been identified in data when at least two gravitational-wave observatories were operating, which covered ∼14% of this five-day window. We report the search detection efficiency for various possible gravitational-wave emission models. Considering the distance to M101 (6.7 Mpc), we derive constraints on the gravitational-wave emission mechanism of core-collapse supernovae across a broad frequency spectrum, ranging from 50 Hz to 2 kHz, where we assume the gravitational-wave emission occurred when coincident data are available in the on-source window. Considering an ellipsoid model for a rotating proto-neutron star, our search is sensitive to gravitational-wave energy 1 × 10 −4 M ⊙ c 2 and luminosity 2.6 × 10 −4 M ⊙ c 2 s −1 for a source emitting at 82 Hz. These constraints are around an order of magnitude more stringent than those obtained so far with gravitational-wave data. The constraint on the ellipticity of the proto-neutron star that is formed is as low as 1.08, at frequencies above 1200 Hz, surpassing past results.

We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO-Virgo-KAGRA network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received with low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wave Transient Catalogs (GWTC-3). Targeted searches were carried out on the entire GW sample using the maximum-likelihood Non-imaging Transient Reconstruction and Temporal Search pipeline on the BAT data made available via the GUANO infrastructure. We do not detect any significant electromagnetic emission that is temporally and spatially coincident with any of the GW candidates. We report flux upper limits in the 15-350 keV band as a function of sky position for all the catalog candidates. For GW candidates where the Swift-BAT false alarm rate is less than 10(-3) Hz, we compute the GW-BAT joint false alarm rate. Finally, the derived Swift-BAT upper limits are used to infer constraints on the putative electromagnetic emission associated with binary black hole mergers.

Continuous gravitational waves (CWs) emission from neutron stars carries information about their internal structure and equation of state, and it can provide tests of General Relativity. We present a search for CWs from a set of 45 known pulsars in the first part of the fourth LIGO--Virgo--KAGRA observing run, known as O4a. We conducted a targeted search for each pulsar using three independent analysis methods considering the single-harmonic and the dual-harmonic emission models. We find no evidence of a CW signal in O4a data for both models and set upper limits on the signal amplitude and on the ellipticity, which quantifies the asymmetry in the neutron star mass distribution. For the single-harmonic emission model, 29 targets have the upper limit on the amplitude below the theoretical spin-down limit. The lowest upper limit on the amplitude is $6.4\!\times\!10^{-27}$ for the young energetic pulsar J0537-6910, while the lowest constraint on the ellipticity is $8.8\!\times\!10^{-9}$ for the bright nearby millisecond pulsar J0437-4715. Additionally, for a subset of 16 targets we performed a narrowband search that is more robust regarding the emission model, with no evidence of a signal. We also found no evidence of non-standard polarizations as predicted by the Brans-Dicke theory.

With the continuous need for faster, smaller, and more energy-efficient electronics and with traditional scaling of silicon-based semiconductor technology reaching its limits, there is a surge for materials with superior properties. Among those are functional oxides, which can have applications as a semiconductor, conductor, ferroelectric, ferromagnet, or superconductor. Within the functional oxides, quasi-2D delafossite minerals such as CuCrO2 are of special interest since they have the potential of high hole mobility, which opens the way toward high-performance p-type thin-film transistors. In this paper, we report on the layer-by-layer growth of CuCrO2 delafossite thin films on Al2O3 surfaces via atomic-oxygen-assisted molecular beam epitaxy (MBE) at growth temperatures near 700 degrees C. The structural quality of the epitaxial films is demonstrated by X-ray diffraction and high-resolution scanning transmission electron microscopy. Moreover, tailoring of the growth parameters in the layer-by-layer approach enables us to achieve the CuCrO2 hexagonal phase, coexisting with the commonly reported rhombohedral CuCrO2 phase. The flexibility and high level of control over growth conditions provided by layer-by-layer MBE offer great potential for stabilizing specific phases of the layered delafossite materials.

Al2O3 thin films are fabricated on Si wafer substrates using direct liquid injection-low pressure chemical vapor deposition (DLI-LPCVD). In DLI-LPCVD, a vaporization chamber supplies vaporized precursors separated from solvents to the deposition chamber, preventing undesired decomposition or premature reactions. DLI-LPCVD is an eco-friendly process that does not require ozone or toxic oxidizing gases; additionally, it is a simple process that eliminates the necessity for precursor injection and purging cycles. Al2O3 thin films are prepared by controlling key process variables, such as substrate temperature and Al(acac)3 solution concentration, which is used as a safe, non-toxic precursor. Their physical and chemical properties are characterized by X-ray reflectivity and grazing incidence X-ray diffraction (GIXRD). Uniform and flat thin films with a surface roughness of 1.9-2.1 nm are fabricated. GIXRD analysis shows that the film fabricated at 550 degrees C is amorphous. In contrast, a log-scale GIXRD pattern reveals that most of the 800 degrees C sample is predominantly amorphous, with some cubic gamma-Al2O3 present, as confirmed through TEM analysis. Based on XPS results, the ratio of O to Al in thin films fabricated via DLI-LPCVD is 1.43-1.67, close to the stoichiometric ratio of Al2O3. Furthermore, the growth rate controllability of Al2O3 thin film deposition using DLI-LPCVD is 1.9-28 & Aring;/min, depending on the substrate temperature and precursor solution concentration. This study demonstrates the potential of introducing DLI-LPCVD with a vaporization chamber as a new metal oxide thin film deposition process, confirming its ability to control the growth rate precisely.

Dimensional confinement has shown to be an effective strategy to tune competing degrees of freedom in complex oxides. Here, we achieved atomic layered growth of trigonal vanadium sesquioxide (V2O3) by means of oxygen-assisted molecular beam epitaxy. This led to a series of high-quality epitaxial ultrathin V2O3 films down to unit cell thickness, enabling the study of the intrinsic electron correlations upon confinement. By electrical and optical measurements, we demonstrate a dimensional confinement-induced metal-insulator transition in these ultrathin films. We shed light on the Mott-Hubbard nature of this transition, revealing an abrupt vanishing of the quasiparticle weight as demonstrated by photoemission spectroscopy. Furthermore, we prove that dimensional confinement acts as an effective out-of-plane stress. This highlights the structural component of correlated oxides in a confined architecture, while opening an avenue to control both in-plane and out-of-plane lattice components by epitaxial strain and confinement, respectively.

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass $M>70$ $M_\odot$) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities $0 < e \leq 0.3$ at $0.33$ Gpc$^{-3}$ yr$^{-1}$ at 90\% confidence level.

The magnetar SGR 1935+2154 is the only known Galactic source of fast radio bursts (FRBs). FRBs from SGR 1935+2154 were first detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB and the Survey for Transient Astronomical Radio Emission 2 in 2020 April, after the conclusion of the LIGO, Virgo, and KAGRA Collaborations' O3 observing run. Here, we analyze four periods of gravitational wave (GW) data from the GEO600 detector coincident with four periods of FRB activity detected by CHIME/FRB, as well as X-ray glitches and X-ray bursts detected by NICER and NuSTAR close to the time of one of the FRBs. We do not detect any significant GW emission from any of the events. Instead, using a short-duration GW search (for bursts <= 1 s) we derive 50% (90%) upper limits of 10(48) (10(49)) erg for GWs at 300 Hz and 10(49) (10(50)) erg at 2 kHz, and constrain the GW-to-radio energy ratio to <= 10(14)-10(16). We also derive upper limits from a long-duration search for bursts with durations between 1 and 10 s. These represent the strictest upper limits on concurrent GW emission from FRBs.

Resistive switching is the fundamental process that triggers the sudden change of the electrical properties in solid-state devices under the action of intense electric fields. Despite its relevance for information processing, ultrafast electronics, neuromorphic devices, resistive memories and brain-inspired computation, the nature of the local stochastic fluctuations that drive the formation of metallic nuclei out of the insulating state has remained hidden. Here, using operando X-ray nano-imaging, we have captured the early-stages of resistive switching in a V2O3-based device under working conditions. V2O3 is a paradigmatic Mott material, which undergoes a first-order metal-to-insulator transition coupled to a lattice transformation that breaks the threefold rotational symmetry of the rhombohedral metal phase. We reveal a new class of volatile electronic switching triggered by nanoscale topological defects of the lattice order parameter of the insulating phase. Our results pave the way to the use of strain engineering approaches to manipulate topological defects and achieve the full control of the electronic Mott switching. The concept of topology-driven reversible electronic transition is of interest for a broad class of quantum materials, comprising transition metal oxides, chalcogenides and kagome metals, that exhibit first-order electronic transitions coupled to a symmetry-breaking order.

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for $U(1)_{B-L}$ gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the $U(1)_{B-L}$ gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM.

The structural, electronic and magnetic properties of 2D transition metal halides (HfX, X=F, Cl, Br) and transition metal oxides (V 2 O 3 ) are investigated using first-principles simulations, based on density functional theory. The 2D hafnium halides are predicted to be topological insulators, with bulk energy band gaps in the range of 0.12-0.3S eV. On the other hand, 2D V 2 O 3 is predicted to be a Dirac half-metal, hosting the anomalous quantum Hall state, due to the coexistence of topological and ferromagnetic phases. These 2D materials are potentially interesting for novel electronic and spintronic devices, due to the (dissipationless) transport of carriers along spin-polarized edge states.

Managing light-matter interactions on timescales faster than the loss of electronic coherence is key for achieving full quantum control of the final products in solid-solid transformations. In this work, we demonstrate coherent electronic control of the photoinduced insulator-to-metal transition in the prototypical Mott insulator V$_2$O$_3$. Selective excitation of a specific interband transition with two phase-locked light pulses manipulates the orbital occupation of the correlated bands in a way that depends on the coherent evolution of the photoinduced superposition of states. A comparison between experimental results and numerical solutions of the optical Bloch equations provides an electronic coherence time on the order of 5 fs. Temperature-dependent experiments suggest that the electronic coherence time is enhanced in the vicinity of the insulator-to-metal transition critical temperature, thus highlighting the role of fluctuations in determining the electronic coherence. These results open new routes to selectively switch the functionalities of quantum materials and coherently control solid-solid electronic transformations.

Transition metal oxides are known to have a strong interplay of many degrees of freedom giving rise to their rich phase diagrams with competing ground states. The Mott material V2O3 hosting a room- and low-temperature metal-insulator transition is a great example where electronic, structural and magnetic ordering are the directors at play. By combining first-principle calculations and Raman spectroscopy, we study the phonon dynamics of V2O3 to gain further understanding in the interplay of these ordering mechanisms driving the transitions. Firstprinciple calculations show that the Raman active vibrations correspond to the structural distortions occurring in the phase diagram. Additionally, Raman spectroscopy is performed on a unique series of epitaxial strained 1.5% Cr-doped V2O3 thin films, where both paramagnetic insulating, metallic, as well as intermediate electronic states are stabilized. This has led to identifying the importance of the local V-V dimer elongation that drives both the room- and low-temperature MIT in V2O3 compounds.

Understanding ferroelectricity is of both fundamental and technological importance to further stimulate the development of new materials designs and manipulations. Here, we perform an in-depth first-principle study on the well-known ferroelectric barium titanate BaTiO$_{3}$ under a hydrostatic negative pressure, showing an isosymmetric phase transition to a supertetragonal phase with high $c/a$ ratio of $\sim1.3$. The microscopic origin and driving mechanisms of this phase transition are identified as a drastic change of the covalently $\pi$-bonded electrons. These findings provide guidance in the search for new supertetragonal phases, with great opportunities for novel multiferroic materials; and can be generalized in the understanding of other isosymmetric phase transitions.

Managing light-matter interaction on timescales faster than the loss of electronic coherence is key for achieving the full quantum control of final products in solid-solid transformations. In this work, we demonstrate coherent electronic control of the photoinduced insulator-to-metal transition in the prototypical Mott insulator V$_2$O$_3$. Selective excitation of a specific interband transition with two phase-locked light pulses manipulates the orbital occupation of the correlated bands in a way that depends on the coherent evolution of the photoinduced superposition of states. Comparison between experimental results and numerical solutions of the optical Bloch equations provides an electronic coherence time on the order of 5 fs. Temperature dependent experiments suggest that the electronic coherence time is enhanced in the vicinity of the insulator-to-metal transition critical temperature, thus highlighting the role of fluctuations in determining the electronic coherence. These results open new routes to selectively switch functionalities of quantum materials and coherently control solid-solid electronic transformations.

Recent experimental success in the realization of two-dimensional (2D) magnetism has stimulated the search for new magnetic 2D materials with strong magnetic anisotropy and high Curie temperature. One promising subgroup of 2D magnetic systems are Dirac half-metals (DHM) which have gained a lot of interest recently, as they host a high-temperature quantum anomalous Hall effect (QAHE). This article discusses predictions for intrinsic DHMs and identifies them as realizations of the Kane-Mele Hubbard model at quarter filling. This proposed unification contributes to a firmer understanding of these materials and suggests pathways for the discovery of new DHM systems.

The possibility of dissipationless chiral edge states without the need of an external magnetic field in the quantum anomalous Hall effect (QAHE) offers a great potential in electronic/spintronic applications. The biggest hurdle for the realization of a room-temperature magnetic Chern insulator is to find a structurally stable material with a sufficiently large energy gap and Curie temperature that can be easily implemented in electronic devices. This work based on first-principle methods shows that a single atomic layer of V2O3 with honeycomb-kagome (HK) lattice is structurally stable with a spin-polarized Dirac cone which gives rise to a room-temperature QAHE by the existence of an atomic on-site spin-orbit coupling (SOC). Moreover, by a strain and substrate study, it was found that the quantum anomalous Hall system is robust against small deformations and can be supported by a graphene substrate.

Complementary to the development of highly three-dimensional (3D) integrated circuits in the continuation of Moore's law, there has been a growing interest in new 3D deformation strategies to improve the device performance. To continue this search for new 3D deformation techniques, it is essential to explore beforehand, using computational predictive methods, which strain tensor leads to the desired properties. In this work, we study germanium (Ge) under an isotropic 3D strain on the basis of first-principles methods. The transport and optical properties are studied by a fully ab initio Boltzmann transport equation and many-body Bethe-Salpeter equation (BSE) approach, respectively. Our findings show that a direct band gap in Ge could be realized with only 0.70% triaxial tensile strain (negative pressure) and without the challenges associated with Sn doping. At the same time, a significant increase in the refractive index and carrier mobility, particularly for electrons, is observed. These results demonstrate that there is a huge potential in exploring the 3D deformation space for semiconductors, and potentially many other materials, to optimize their properties.