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Nonlinear optical materials of atomic thickness--such as non-centrosymmetric 2H transition metal dichalcogenide monolayers--have a second order nonlinear susceptibility ($\chi^{(2)}$) whose intensity can be tuned by strain. However, whether $\chi^{(2)}$ is enhanced or reduced by tensile strain is a subject of conflicting reports. Here, we grow high-quality MoSe$_2$ monolayers under controlled biaxial strain created by two different substrates, and study their linear and non-linear optical responses with a combination of experimental and theoretical approaches. A 15-fold overall enhancement in second harmonic generation (SHG) intensity is observed on MoSe$_2$ monolayers grown on SiO$_2$ when compared to its value when on a Si$_3$N$_4$ substrate. A seven-fold enhancement was ascertained to substrate interference, and a factor of two to the enhancement of $\chi^{(2)}$ arising from biaxial strain: substrate interference and strain are independent handles to engineer the SHG strength of non-centrosymmetric 2D materials.

The recent discovery of ferroelectric behavior in few-layer materials, accompanied by the observation of antipolar domains in hexagonal boron nitride and transition metal dichalcogenide moir\'e bilayers, is paving the way for revolutionary advancements in the generation and manipulation of intrinsic electric dipoles through stacking. In addition, these cutting-edge quantum materials are reshaping our comprehension of phase transitions. Within the present study, we unveil a hitherto unreported size-dependent sliding behavior that marks a significant departure from conventional ferroelectrics. We also shed light on thermally induced spontaneous hyperlubric sliding within moir\'e bilayers, which can be used as a signal to distinguish topological phase transitions from an antipolar onto a ferroelectric bilayer. Our findings also suggest that the (topological) pinning of AA nodes in antipolar moir\'e homobilayers prevents the occurrence of an antipolar-to-paraelectric transformation., Comment: Accepted at Physical Review Materials on March 18, 2024

In this position paper, we reflect on fictional stories dealing with the infinite and how they connect with the current, fast-evolving field of image generation models. We draw attention to how some of these literary constructs can serve as powerful metaphors for guiding human-centered design and technical thinking in the space of these emerging technologies and the experiences we build around them. We hope our provocations seed conversations about current and yet-to-be developed interactions with these emerging models in ways that may amplify human agency.

The vertical shear instability (VSI) is a promising mechanism to drive turbulence in protoplanetary disks. Numerical simulations in the literature demonstrate that the VSI non-linear saturation is predominated by the linear corrugation modes. These modes possess vertical wavelengths crucially longer than radial wavelengths. This paper aims to investigate the natural radial wavelength of corrugation modes upon VSI saturation, by a series of numerical simulations conducted in Athena++ at different grid resolutions, disk aspect ratios, and viscosity parameterized by $\nu$. We find a sign of convergence emerges at 64 cells per gas scale height for fiducial simulations, below which a continuous reduction of wavelengths with grid resolution is observed. Synthetic ALMA molecular line observations of $^{12}\rm CO(2-1)$ are performed to inspect the observability of the corrugation modes feature, which is significantly diminished with more than 32 cells per scale height. Flared and viscous disks, exhibiting longer saturation wavelengths, may mitigate the observational difficulty., Comment: 9 pages, 5 figures, accepted for publication in MNRAS

Context. Planets are thought to form inside weakly ionized regions of protoplanetary disks, where turbulence creates ideal conditions for solid growth. However, the nature of this turbulence is still uncertain. In this zone, vertical shear instability (VSI) can operate, inducing a low level of gas turbulence and large-scale motions. Resolving kinematic signatures of VSI may reveal the origin of turbulence in planet-forming disks. However, an exploration of kinematic signatures of the interplay between VSI and forming planets is needed for a correct interpretation of radio interferometric observations. Robust detection of VSI would lead to a deeper understanding of the impact of gas turbulence on planet formation. Aims. The goal of this study is to explore the effect of VSI on the disk substructures triggered by an embedded massive planet. We focus on the impact of this interplay on CO kinematic observations with ALMA. Methods. We conduct global 3D hydrodynamical simulations of VSI-unstable disks with and without embedded massive planets, exploring Saturn- and Jupiter-mass cases. We study the effect of planets on the VSI gas dynamics, comparing with viscous disks. Post-processing the simulations with a radiative transfer code, we examine the kinematic signatures expected in CO molecular line emission, varying disk inclination. Further, we simulate ALMA high-resolution observations to test the observability of VSI and planetary signatures. Results. The embedded planet dampens the VSI along a radial region, most effective at the disk midplane. For the Saturn case, the VSI modes are distorted by the planet's spirals producing mixed kinematic signatures. For the Jupiter case, the planet's influence dominates the disk gas kinematics. Conclusions. The presence of massive embedded planets can weaken the VSI large-scale gas flows, limiting its observability in CO kinematic observations., Comment: Accepted for publication in Astronomy & Astrophysics. 27 pages, 17 figures and 2 tables

We present a hybrid classical-quantum computing paradigm where the quantum part strictly runs within the coherence time of a quantum annealer, a method we call variational coherent quantum annealing (VCQA). It involves optimizing the schedule functions governing the quantum dynamics by employing a piecewise family of tailored functions. We also introduce auxiliary Hamiltonians that vanish at the beginning and end of the evolution to increase the energy gap during the process, subsequently reducing the algorithm times. We develop numerical tests using z-local terms as the auxiliary Hamiltonian while considering linear, cyclic, and star connectivity. Moreover, we test our algorithm for a non-stoquastic Hamiltonian such as a Heisenberg chain, showing the potential of the VCQA proposal in different scenarios. In this manner, we achieve a substantial reduction in the ground-state error with just six variational parameters and a duration within the device coherence times. Therefore, the proposed VCQA paradigm offers exciting prospects for current quantum annealers., Comment: 7+1 pages and 6 figures

In the burgeoning field of artificial intelligence (AI), the unprecedented progress of large language models (LLMs) in natural language processing (NLP) offers an opportunity to revisit the entire approach of traditional metrics of machine intelligence, both in form and content. As the realm of machine cognitive evaluation has already reached Imitation, the next step is an efficient Language Acquisition and Understanding. Our paper proposes a paradigm shift from the established Turing Test towards an all-embracing framework that hinges on language acquisition, taking inspiration from the recent advancements in LLMs. The present contribution is deeply tributary of the excellent work from various disciplines, point out the need to keep interdisciplinary bridges open, and delineates a more robust and sustainable approach., Comment: 14 pages, 1 table, 2 figures

Accuracy measures such as Recall, Precision, and Hit Rate have been a standard way of evaluating Recommendation Systems. The assumption is to use a fixed Top-N to represent them. We propose that median impressions viewed from historical sessions per diner be used as a personalized value for N. We present preliminary exploratory results and list future steps to improve upon and evaluate the efficacy of these personalized metrics., Comment: Accepted to evalRS 2023@KDD

Star-planet interactions play, among other things, a crucial role in planetary orbital configurations by circularizing orbits, aligning the star and planet spin and synchronizing stellar rotation with orbital motions. This is especially true for innermost giant planets, which can be schematized as binary systems with a very large mass ratio. Despite a few examples where spin-orbit synchronization has been obtained, there is no demographic study on synchronous regimes in those systems yet. Here we use a sample of 1,055 stars with innermost planet companions to show the existence of three observational loci of star-planet synchronization regimes. Two of them have dominant fractions of subsynchronous and supersynchronous star-planet systems, and a third less populated regime of potentially synchronized systems. No synchronous star-planet system with a period higher than 40 days has been detected yet. This landscape is different from eclipsing binary systems, most of which are synchronized. We suggest that planets in a stable asynchronous spin state belonging to star-planet systems in a supersynchronized regime offer the most favourable conditions for habitability., Comment: 15 pages, 1 figure in main paper, 6 supplementary figures. Published in Nature Astronomy, May 2023

Two-dimensional (2D) materials are being explored as a novel multiferroic platform. One of the most studied magnetoelectric multiferroic 2D materials are antiferromagnetically-coupled (AFM) CrI$_3$ bilayers. Neglecting magnetism, those bilayers possess a crystalline point of inversion, which is only removed by the antiparallel spin configuration among its two constituent monolayers. The resultant intrinsic electric dipole on those bilayers has a magnitude no larger than 0.04 pC/m, it points out-of-plane, and it reverts direction when the--Ising-like--cromium spins are flipped (toward opposite layers {\em versus} away from opposite layers). The combined presence of antiferromagnetism and a weak intrinsic electric dipole makes this material a two-dimensional magnetoelectric multiferroic. Here, we remove the crystalline center of inversion of the bilayer by a relative $60^{\circ}$ rotation of its constituent monolayers. This process {\em enhances} the out-of-plane intrinsic electric dipole tenfold with respect to its magnitude in the non-rotated AFM bilayer and also creates an even stronger and switchable in-plane intrinsic electric dipole. The ability to create a three-dimensional electric dipole is important, because it enhances the magnetoelectric coupling on this experimentally accessible 2D material, which is explicitly calculated here as well., Comment: Accepted at PRB on May 1, 2023

We study a 4-orbital tight-binding (TB) model for ZrSiS from the square sublattice generated by the Si atoms. After studying three other alternatives, we endow such model with a new effective spin-orbit coupling (SOC) consistent with {\em ab initio} dispersions around the Fermi energy ($E_F$) in four systematic steps: (1) We calculate the electronic dispersion of bulk ZrSiS using an implementation of density-functional theory (DFT) based on numeric atomic orbitals [{\em J. Phys.: Condens. Matter} {\bf 14}, 2745 (2002)] in which on-site and off-site SOC can be told apart. As a result, we determine that local SOC-induced band gaps around $E_F$ are predominantly created by the on-site contribution. (2) Gradually reducing the atomic basis set size, we then create an electronic band structure with 16 orbitals per unit cell (u.c.) which retains the qualitative features of the dispersion around $E_F$, including SOC-induced band gaps. (3) Zr is the heaviest element on this compound and it has a non-negligible contribution to the electronic dispersion around $E_F$; we show that it provides the strongest contribution to the SOC-induced band gap. (4) Using L\"{o}wdin partitioning approach, we project the effect of SOC onto the 4-orbital Hamiltonian. This way, we facilitate an effective SOC interaction that was explicitly informed by {\em ab initio} input., Comment: 15 pages, 12 figures

Low-buckled silicene, germanene, and stanene are group$-IV$ graphene allotropes. They form a honeycomb lattice out of two interpenetrating ($A$ and $B$) triangular sublattices that are vertically separated by a small distance $\Delta_z$. The atomic numbers $Z$ of silicon, germanium, and tin are larger to carbon's ($Z_C=6$), making them the first experimentally viable two-dimensional topological insulators. Those materials have a twice-energy-degenerate atomistic structure characterized by the buckling direction of the $B$ sublattice with respect to the $A$ sublattice [whereby the $B-$atom either protrudes {\em above} ($\Delta_z>0$) or {\em below} ($\Delta_z<0$) the $A-$atoms], and the consequences of that energy degeneracy on their elastic and electronic properties have not been reported thus far. Here, we uncover {\em ferroelastic, bistable} behavior on silicene, which turns into an {\em average} planar structure at about 600 K. Further, the creation of electron and hole puddles obfuscates the zero-temperature SOC induced band gaps at temperatures as low as 200 K, which may discard silicene as a viable two-dimensional topological insulator for room temperature applications. Germanene, on the other hand, never undergoes a low-buckled to planar 2D transformation, becoming amorphous at around 675 K instead, and preserving its SOC-induced bandgap despite of band broadening. Stanene undergoes a transition onto a crystalline 3D structure at about 300 K, preserving its SOC-induced electronic band gap up to that temperature. Unlike what is observed in silicene and germanene, stanene readily develops a higher-coordinated structure with a high degree of structural order. The structural phenomena is shown to have deep-reaching consequences for the electronic and vibrational properties of those two dimensional topological insulators., Comment: 16 pages, 21 figures. Originally submitted on December 5, 2022

This report is a summary of the mini-conference Workforce Development Through Research-Based, Plasma-Focused Science Education and Public Engagement held during the 2022 American Physical Society Division of Plasma Physics (APS DPP) annual meeting. The motivation for organizing this mini-conference originates from recent studies and community-based reports highlighting important issues with the current state of the plasma workforce. Here we summarize the main findings presented in the two speaker sessions of the mini-conference, the challenges and recommendations identified in the discussion sessions, and the results from a post-conference survey. We further provide information on initiatives and studies presented at the mini-conference, along with references to further resources., Comment: 15 pages, 4 figures