Publications by authors named "SG Louie"

Topological design of π electrons in zigzag-edged graphene nanoribbons (ZGNRs) leads to a wealth of magnetic quantum phenomena and exotic quantum phases. Symmetric ZGNRs typically show antiferromagnetically coupled spin-ordered edge states. Eliminating cross-edge magnetic coupling in ZGNRs not only enables the realization of a class of ferromagnetic quantum spin chains, enabling the exploration of quantum spin physics and entanglement of multiple qubits in the one-dimensional limit, but also establishes a long-sought-after carbon-based ferromagnetic transport channel, pivotal for ultimate scaling of GNR-based quantum electronics.

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Atomically thin semiconductors, encompassing both 2D materials and quantum wells, exhibit a pronounced enhancement of excitonic effects due to geometric confinement. Consequently, these materials have become foundational platforms for the exploration and utilization of excitons. Recent ab initio studies have demonstrated that phonons can substantially screen electron-hole interactions in bulk semiconductors and strongly modify the properties of excitons.

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Nicotinamide adenine dinucleotide (NAD) is required for a myriad of metabolic, signaling, and post-translational events in cells. Its levels in tissues and organs are closely associated with health conditions. The homeostasis of NAD is regulated by biosynthetic pathways and consuming enzymes.

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Excitons are vital in the photophysics of materials, especially in low-dimensional systems. The conceptual and quantitative understanding of excitonic effects in nonlinear optical (NLO) processes is more challenging compared to linear ones. Here, we present an ab initio approach to second-order NLO responses, incorporating excitonic effects, that employs an exciton-state coupling formalism and allows for a detailed analysis of the role of individual excitonic states.

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Article Synopsis
  • The study predicts how phonons (vibrations of atoms) can lead to two-gap superconductivity in infinite-layer nickelates, specifically Nd_{1-x}Sr_{x}NiO_{2}.
  • Advanced calculations show that self-energy effects significantly change the electronic properties and strengthen the interaction between electrons and phonons compared to traditional methods.
  • The research finds two main superconducting gaps that vary in size based on the type of electronic orbitals and also notes that as more holes are added to the material, the superconducting critical temperature (T_{c}) drops quickly, aligning with experimental findings.
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  • A new method has been developed to accurately convert plane-wave (PW) results from density functional theory (DFT) into a format compatible with atomic-orbital (AO) basis, addressing a significant limitation in previous deep neural networks used for electronic structure calculations.
  • This reconstruction method is significantly faster than traditional approaches and maintains the accuracy of the PW electronic structure, effectively linking AO-based deep learning models with PW DFT.
  • By integrating the high accuracy and flexibility of PW methods into deep learning techniques, this advancement enables the creation of large-scale datasets that enhance the development of robust electronic structure models.
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Early evidence-based medical interventions to improve patient outcomes after traumatic brain injury (TBI) are lacking. In patients admitted to the ICU after TBI, optimization of nutrition is an emerging field of interest. Specialized enteral nutrition (EN) formulas that include immunonutrition containing omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been developed and are used for their proposed anti-inflammatory and proimmune properties; however, their use has not been rigorously studied in human TBI populations.

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The properties of excitons, or correlated electron-hole pairs, are of paramount importance to optoelectronic applications of materials. A central component of exciton physics is the electron-hole interaction, which is commonly treated as screened solely by electrons within a material. However, nuclear motion can screen this Coulomb interaction as well, with several recent studies developing model approaches for approximating the phonon screening of excitonic properties.

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One-dimensional (1D) interacting electrons are often described as a Luttinger liquid having properties that are intrinsically different from those of Fermi liquids in higher dimensions. In materials systems, 1D electrons exhibit exotic quantum phenomena that can be tuned by both intra- and inter-1D-chain electronic interactions, but their experimental characterization can be challenging. Here we demonstrate that layer-stacking domain walls (DWs) in van der Waals heterostructures form a broadly tunable Luttinger liquid system, including both isolated and coupled arrays.

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Article Synopsis
  • Phonon engineering at gigahertz frequencies supports applications like microwave acoustic filters and quantum transducers, while terahertz phonon engineering promises faster and higher bandwidth technologies.
  • Researchers demonstrated effective generation, detection, and manipulation of terahertz phonons using atomically thin materials, specifically few-layer graphene and monolayer WSe, within van der Waals heterostructures.
  • The study showcases high-quality terahertz phononic cavities and the ability of WSe embedded in hexagonal boron nitride to block terahertz phonon transmission, paving the way for advanced acoustic filters and thermal engineering techniques.
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Despite the weak, van der Waals interlayer coupling, photoinduced charge transfer vertically across atomically thin interfaces can occur within surprisingly fast, sub-50 fs time scales. An early theoretical understanding of charge transfer is based on a noninteracting picture, neglecting excitonic effects that dominate optical properties of such materials. We employ an many-body perturbation theory approach, which explicitly accounts for the excitons and phonons in the heterostructure.

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Article Synopsis
  • The study presents a method for integrating low-energy zero-modes into graphene nanoribbons (GNRs) to create materials with custom electronic properties for nanoelectronics.
  • The researchers successfully synthesized [3]triangulene-GNRs, which are chains of linked [3]triangulenes, demonstrating a narrow band gap of about 0.7 eV and the existence of topological end states verified by scanning tunneling spectroscopy.
  • Through theoretical calculations, the work reveals the mechanisms behind the selective synthesis and the role of gold-carbon bonds in the polymerization process on surfaces.
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The covalent interaction of N-heterocyclic carbenes (NHCs) with transition metal atoms gives rise to distinctive frontier molecular orbitals (FMOs). These emergent electronic states have spurred the widespread adoption of NHC ligands in chemical catalysis and functional materials. Although formation of carbene-metal complexes in self-assembled monolayers on surfaces has been explored, design and electronic structure characterization of extended low-dimensional NHC-metal lattices remains elusive.

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Topological phases in laterally confined low-dimensional nanographenes have emerged as versatile design tools that can imbue otherwise unremarkable materials with exotic band structures ranging from topological semiconductors and quantum dots to intrinsically metallic bands. The periodic boundary conditions that define the topology of a given lattice have thus far prevented the translation of this technology to the quasi-zero-dimensional (0D) domain of small molecular structures. Here, we describe the synthesis of a polycyclic aromatic hydrocarbon (PAH) featuring two localized zero modes (ZMs) formed by the topological junction interface between a trivial and nontrivial phase within a single molecule.

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Retinal degenerative diseases, including age-related macular degeneration and retinitis pigmentosa, significantly contribute to adult blindness. The Royal College of Surgeons (RCS) rat is a well-established disease model for studying these dystrophies; however, molecular investigations remain limited. We conducted a comprehensive analysis of retinal degeneration in RCS rats, including an immunodeficient RCS (iRCS) sub-strain, using ocular coherence tomography, electroretinography, histology, and molecular dissection using transcriptomics and immunofluorescence.

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Targeted delivery of small-molecule drugs via covalent attachments to monoclonal antibodies has proved successful in clinic. For this purpose, full-length antibodies are mainly used as drug-carrying vehicles. Despite their flexible conjugation sites and versatile biological activities, intact immunoglobulins with conjugated drugs, which feature relatively large molecular weights, tend to have restricted tissue distribution and penetration and low fractions of payloads.

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The emergence and mutation of pathogenic viruses have been occurring at an unprecedented rate in recent decades. The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has developed into a global public health crisis due to extensive viral transmission. In situ RNA mapping has revealed angiotensin-converting enzyme 2 (ACE2) expression to be highest in the nose and lower in the lung, pointing to nasal susceptibility as a predominant route for infection and the cause of subsequent pulmonary effects.

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Acute liver failure caused by alcoholic hepatitis (AH) is only effectively treated with liver transplantation. Livers of patients with AH show a unique molecular signature characterized by defective hepatocellular redox metabolism, concurrent to hepatic infiltration of neutrophils that express myeloperoxidase (MPO) and form neutrophil extracellular traps (NETs). Exacerbated NET formation and MPO activity contribute to liver damage in mice with AH and predicts poor prognosis in AH patients.

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Article Synopsis
  • - Moiré superlattices are a promising platform for studying new quantum states and phenomena, including correlated insulators and moiré excitons.
  • - Scanning tunnelling microscopy has been critical in examining the atomic-scale behaviors of these moiré correlated ground states, but visualizing quantum excited states remains difficult.
  • - The authors introduce a new technique called photocurrent tunnelling microscopy, which uses laser excitation to visualize the distribution of electrons and holes in a moiré exciton, revealing important insights about charge transfer and electron-hole interactions in twisted bilayer WS.
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Article Synopsis
  • The study explores optical dynamics in van der Waals heterobilayers, focusing on a new many-electron channel that converts excitations from one layer to another.
  • Using a time-dependent adiabatic GW approach, researchers found that strong electron-hole interactions significantly enhance optical responses in these materials.
  • The findings indicate a rise time of about 300 femtoseconds in MoSe₂/WSe₂ heterobilayers, aligning well with experimental observations.
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Transition metal dichalcogenide (TMD) moiré superlattices provide an emerging platform to explore various light-induced phenomena. Recently, the discoveries of novel moiré excitons have attracted great interest. The nonlinear optical responses of these systems are however still underexplored.

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Docosahexaenoic acid [22:6(-3), DHA], a polyunsaturated fatty acid, has an important role in regulating neuronal functions and in normal brain development. Dysregulated brain DHA uptake and metabolism are found in individuals carrying the APOE4 allele, which increases the genetic risk for Alzheimer's disease (AD), and are implicated in the progression of several neurodegenerative disorders. However, there are limited tools to assess brain DHA kinetics that can be translated to humans.

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Background: Early evidence-based medical interventions to improve patient outcomes after traumatic brain injury (TBI) are lacking. In patients admitted to the ICU after TBI, optimization of nutrition is an emerging field of interest. Specialized enteral nutrition (EN) formulas that include immunonutrition containing omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been developed and are used for their proposed anti-inflammatory and pro-immune properties; however, their use has not been rigorously studied in human TBI populations.

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Article Synopsis
  • The study investigates the semimetal-to-semiconductor transition in the material TaNi(Se,S), focusing on how excitons form when electrons and holes attract each other near the zero-band-gap point.
  • Using techniques like angle-resolved photoemission spectroscopy (ARPES) and synchrotron x-ray diffraction (XRD), researchers observed a broken symmetry phase that decreases as the system transitions from semimetal to semiconductor, challenging previous theories about excitonic instability.
  • The findings highlight the significant role of strong interband electron-phonon coupling in promoting symmetry breaking on the semimetal side and contribute to the understanding of intertwined orders and electronic instabilities in strongly coupled materials.
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An NAD featuring an adenosyl 4'-azido functions as a general substrate for poly-ADP-ribose polymerases. Its derived mono- and poly-ADP-ribosylated proteins can be adequately recognized by distinct ADP-ribosylation-specific readers. This molecule represents the first ribose-functionalized NAD with versatile activities across different ADP-ribosyltransferases and provides insight into developing new probes for ADP-ribosylation.

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