Strong Coupling Research Articles

Degrees of Freedom in Modified Teleparallel Gravity

I discuss the issue of degrees of freedom in modified teleparallel gravity. These theories do have an extra structure on top of the usual (pseudo)Riemannian manifold, that of a flat parallel transport. This structure is absolutely abstract and unpredictable (pure gauge) in GRequivalent models, however, it becomes physical upon modifications. The problem is that, in the most popular models, this local symmetry is broken but not stably So, hence the infamous strong coupling issues. The Hamiltonian analyses become complicated and with contradictory results. A funny point is that what we see in available linear perturbation treatments of f (T) gravity is much closer to the analysis with less dynamical degrees of freedom which has got a well-known mistake in it, while the more accurate work predicts much more of dynamics than what has ever been seen till now. I discuss possible reasons behind this puzzle, and also argue in favor of studying the most general New GR models which are commonly ignored due to suspicion of ghosts.

Cavity-Mediated Enhancement of the Energy Transfer in the Reduced Fenna-Matthews-Olson Complex.

Strong light-matter interaction leads to the formation of hybrid polariton states and can alter the light-harvesting properties of natural photosynthetic systems without modifying their chemical structure. In the present study, we computationally investigate the effect of the resonant cavity on the efficiency and the rate of the population transfer in a quantum system coupled to the cavity and the dissipative environment. The parameters of the model system were chosen to represent the Fenna-Matthews-Olson natural light-harvesting complex reduced to the three essential sites. The dynamics of the total system was propagated using the hierarchical equations of motion. Our results show that the strong light-matter interaction can accelerate the population transfer process compared to the cavity-free case but at the cost of lowering the transfer efficiency. The transition to the strong coupling regime was found to coincide with the degeneracy of polariton eigenvalues. Our findings indicate the potential and the limit of tuning the energy transfer in already efficient natural light-harvesting systems.

Strongly Coupled NiMo@Alloy‐LDH Interfaces with Low‐Barrier Schottky Junctions for Oxygen Evolution Reaction

AbstractThe main challenge in developing Schottky‐contact OER catalytic devices based on layered double hydroxides (LDHs) is to achieve metal–semiconductor junctions with low contact resistance and high charge transfer capacity. However, due to the presence of high potential barriers and Fermi pinning, conventional Schottky contacts are usually unsatisfactory, resulting in poor‐working electrode performance and high energy consumption. In this study, a new concept of “hindrance factor” is introduced to quantify the difficulty of electron transfer, and a low‐hindrance factor Schottky contact formed by strong coupling of semiconductor LDH and NiMo alloy clusters is designed. This interface guides charge redistribution, optimizes the bonding and orbital states of adsorption sites, and enhances the targeted adsorption of OH intermediates. The results show that the configured NiMo@NiFeCe‐LDH working electrode only needs 1.445 V (vs RHE) to drive the reaction and shows excellent durability in 400 h of testing. At the same time, based on this study, a strategy for screening high‐performance Schottky junctions is developed. This strategy provides a bridge for studying interface properties, orbital hybridization, and charge transfer, reveals the potential mechanism for reducing contact resistance, and has important guiding significance for screening high‐performance metal–semiconductor electrocatalysts and stability.

Decomposing Imaginary-Time Feynman Diagrams Using Separable Basis Functions: Anderson Impurity Model Strong-Coupling Expansion

We present a deterministic algorithm for the efficient evaluation of imaginary-time diagrams based on the recently introduced discrete Lehmann representation (DLR) of imaginary-time Green’s functions. In addition to the efficient discretization of diagrammatic integrals afforded by its approximation properties, the DLR basis is separable in imaginary-time, allowing us to decompose diagrams into linear combinations of nested sequences of one-dimensional products and convolutions. Focusing on the strong-coupling bold-line expansion of generalized Anderson impurity models, we show that our strategy reduces the computational complexity of evaluating an Mth-order diagram at inverse temperature β and spectral width ωmax from O((βωmax)2M−1) for a direct quadrature to O(M(log(βωmax))M+1), with controllable high-order accuracy. We benchmark our algorithm using third-order expansions for multiband impurity problems with off-diagonal hybridization and spin-orbit coupling, presenting comparisons with exact diagonalization and quantum Monte Carlo approaches. In particular, we perform a self-consistent dynamical mean-field theory calculation for a three-band Hubbard model with strong spin-orbit coupling representing a minimal model of Ca2RuO4, demonstrating the promise of the method for modeling realistic strongly correlated multiband materials. For both strong and weak coupling expansions of low and intermediate order, in which diagrams can be enumerated, our method provides an efficient, straightforward, and robust blackbox evaluation procedure. In this sense, it fills a gap between diagrammatic approximations of the lowest order, which are simple and inexpensive but inaccurate, and those based on Monte Carlo sampling of high-order diagrams. Published by the American Physical Society 2024

K -inflation: The legitimacy of the classical treatment

In this paper we consider a general theory of k-inflation and find out that it may be in a strong coupling regime. We derive accurate conditions of classical description validity using unitarity bounds for this model. Next, we choose a simple toy model of k-inflation and obtain the explicit condition, which guarantees that the generation of perturbations is performed in a controllable way, i.e., the exit from the effective horizon occurs in the weak coupling regime. However, for the same toy model the corresponding experimental bounds on a nonlinear parameter fNLequil associated with non-Gaussianities of the curvature perturbation provide much stronger constraint than strong coupling absence condition. Nevertheless, for other known models of inflation this may not be the case. Generally, one should always check if classical description is legitimate for chosen models of inflation. Published by the American Physical Society 2024

Quantum States Induced by Strong Interface Coupling in a 2D VSe2/Bi2Se3 Heterostructure.

We have successfully fabricated single-layer (SL) 1T-VSe2/Bi2Se3 heterostructures using molecular beam epitaxy (MBE), which exhibits uniform moiré patterns on the heterostructure surface. Scanning tunneling microscopy/spectroscopy (STM/STS) reveals a notable quantum state near the Fermi energy, robust across the entire moiré lattice. This quantum state peak shifts slightly across different domain ranges, suggesting an elastic strain dependence in SL VSe2, confirmed by geometric phase analysis (GPA) simulations. Density functional theory (DFT) calculations indicate that the enhanced quantum state results from charge redistribution between the substrate and the epifilm with the orbitals of Se atoms in the deformed VSe2 playing a dominant role.

Transition metal oxides: a new frontier in spintronics driven by novel quantum states and efficient charge-spin interconversion

Transition metal oxides (TMOs) have emerged as promising candidates for spintronic applications due to their unique electronic properties and novel quantum states. The intricate interplay between strong spin-orbit coupling and electronic correlations in TMOs gives rise to distinct spin and orbital textures, leading to enhanced spin-momentum locking and efficient charge-spin interconversion. Remarkably, recent researches have unveiled the significant and highly tunable nature of charge-spin interconversion efficiency in TMOs, which can be manipulated through strategies such as electric field gating, epitaxial strain, and heterostructure engineering. This review provides a comprehensive overview of the recent advances in understanding the electronic band structures of TMOs and their correlation with charge-spin interconversion mechanisms. We summarize the tunability of these properties through various experimental approaches and discuss the potential implications for spintronic device applications. The insights gained from this review can guide future research efforts towards the development of high-performance, energy-efficient spintronic devices based on TMOs.

Long- and short-term coupling of sea surface temperature and atmospheric CO2 during the late Paleocene and early Eocene

The late Paleocene and early Eocene (LPEE) are characterized by long-term (million years, Myr) global warming and by transient, abrupt (kiloyears, kyr) warming events, termed hyperthermals. Although both have been attributed to greenhouse (CO2) forcing, the longer-term trend in climate was likely influenced by additional forcing factors (i.e., tectonics) and the extent to which warming was driven by atmospheric CO2 remains unclear. Here, we use a suite of new and existing observations from planktic foraminifera collected at Pacific Ocean Drilling Program Sites 1209 and 1210 and inversion of a multiproxy Bayesian hierarchical model to quantify sea surface temperature (SST) and atmospheric CO2 over a 6-Myr interval. Our reconstructions span the initiation of long-term LPEE warming (~58 Ma), and the two largest Paleogene hyperthermals, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) and Eocene Thermal Maximum 2 (ETM-2, ~54 Ma). Our results show strong coupling between CO2 and temperature over the long- (LPEE) and short-term (PETM and ETM-2) but differing Pacific climate sensitivities over the two timescales. Combined CO2 and carbon isotope trends imply the carbon source driving CO2 increase was likely methanogenic, organic, or mixed for the PETM and organic for ETM-2, whereas a source with higher δ13C values (e.g., volcanic degassing) is associated with the long-term LPEE. Reconstructed emissions for the PETM (5,800 Gt C) and ETM-2 (3,800 Gt C) are comparable in mass to future emission scenarios, reinforcing the value of these events as analogs of anthropogenic change.

Optimization of liquid cooling plate considering coupling effects of heat generation and aging characteristics in power batteries

The heat generation and aging characteristics of power batteries exhibit a strong coupling relationship, and thus designing liquid cooling plates (LCPs) requires considering both aspects to achieve optimal thermal management. In this study, an electric-thermal-aging model (ETAM) correlating internal resistance, capacity, and temperature was developed. Based on this model, the effects of a serpentine LCP on the heat generation and aging characteristics of battery pack under different operating conditions were investigated using a combined simulation of zero-dimensional numerical model and three-dimensional CFD methods. Furthermore, the LCP channel widths in the length and width directions and the number of channels were optimized using orthogonal tests, artificial neural networks, and genetic algorithms, aiming to minimize battery capacity degradation. Results showed that increasing the mass flow rate of the coolant reduced the maximum temperature, temperature difference, capacity loss, and aging inconsistency of the battery pack. Conversely, reducing the coolant inlet temperature could decrease the maximum temperature and capacity loss but increased the temperature difference and aging inconsistency of the battery pack. The orthogonal test results indicated that the number of channels had the greatest impact on the heat generation and aging characteristics of the battery pack, followed by the channel width in the length direction, and the channel width in the width direction had the least impact. After optimization, the maximum temperature of the battery pack decreased by 0.57 %, the maximum temperature difference increased by 1.41 %, and the average capacity degradation decreased by 0.20 %. Moreover, with the increasing mass flow rate, the pressure drop reduction improved from 27.90 % to 33.90 %. This study may provide guidance for the design of LCPs that take battery aging into account.

Strong electron coupling between amorphous WP and MoSe2/ZnCdS S-scheme heterojunction for enhanced wide spectrum photocatalytic hydrogen production

The photogenerated carrier separation efficiency is a key factor for limiting the photocatalytic activity. In this work, an amorphous WP modified S-scheme MoSe2/ZnCdS (WP/MoSe2/ZCS) heterojunction was synthesized for wide spectrum photocatalytic hydrogen production. After initially forming an S-scheme heterojunction by compositing ZnCdS with nano flower-shaped MoSe2, the light absorption ability of the bimetallic sulfide was significantly enhanced, along with an improved photogenerated carrier separation efficiency. Additionally, the introduction of WP as a co-catalyst not only provides more active sites for photocatalytic reactions, but also enhances the photogenerated electrons transfer through the synergistic effect of strong electronic coupling and S-scheme MoSe2/ZCS heterojunction.The significant enhancement of photocatalytic hydrogen evolution activity of 7％WP/MoSe2/ZCS reached 47.7 mmol g−1 h−1, which is 4.72 times higher than that of ZnCdS (10.1 mmol g−1 h−1). The strong electron coupling effects and S-scheme electron ransfer mechanism was proved by in-situ XPS and Density functional theory (DFT) calculations. This work provides a new strategy for the construction of high-efficiency photocatalyst with strong electronic coupling.

Zinc indium sulfide coupling with graphitic carbon nitride containing non-intrinsic oxygen vacancies to form Z-scheme heterojunction for boosting photodegradation of tetracycline

A novel graphitic carbon nitride containing non-intrinsic oxygen vacancies (Vo-CN) is interfacial coupling with zinc indium sulfide (ZIS) to form Z-scheme heterojunction (VCZ) for efficient tetracycline (TC) degradation. The TC removal rate by VCZ-1 (mass ratio of Vo-CN: ZIS is 1:20, 0.2 g/L) achieves 99.86 %. VCZ-1 reveals outstanding reusability and stability with an unchanged TC degradation rate after undergoing five cycles. VCZ-1 achieves high-efficiency TC degradation in various water matrices. The experimental and DFT calculations indicate that the built-in electric field drives charges on Vo-CN transfer to ZIS, forming a Z-scheme VCZ-1 heterojunction. The strong electronic coupling effect between Vo-CN and ZIS facilitates charge exchange at the heterojunction interface. Non-intrinsic oxygen vacancies in VCZ, as binding sites for electrons and holes, effectively lower the energy barrier for singlet excitons converting to triplet excitons. The triplet excitons are induced to transfer energies to dissolved oxygen and expedite 1O2 production. 1O2 synergizes with •O2– and •OH to attack O-containing groups and hexatomic rings in TC, inducing demethylation, hydroxylation, dihydroxylation, and ring-opening reactions. Three possible degradation pathways are inferred by UPLC/MS/MS and Fukui index of TC. The ecotoxicity evaluation of intermediate products highlights the benefits of VCZ-1 photocatalytic oxidation in ensuring environmental safety. This work proposes a novel idea for constructing efficient Z-scheme photocatalysts for environmental remediation.

Construction of Surface Ruoct─O─Cooct Units With Optimized Cooct Spin States for Enhanced Oxygen Reduction and Evolution.

The introduction of noble metal into spinel structure is an effective strategy to develop efficient oxygen evolution/reduction reaction (OER/ORR) catalysts. Herein, surface Cooct is substituted by Ruoct in Rux-Mn0.5Co2.5-xO4/NCNTs by ion-exchange, where presence of Ruoct─O─Cooct unit facilitates electron transfer. This strong electron coupling effect leads downward shift in d-band center and a narrowing of d-p bandgap. The increased charge density of Cooct bridged with Ruoct dioxygen optimizes adsorption of oxygen intermediates (*OH) and occupation of electrons in eg-orbital octahedral. The measured ORR/OER voltage difference is only 0.71V. The peak power density of assembled zinc-air battery reaches 148.8mW h cm-2, and energy density at 100mA cm-2 reaches 813.6mA h gZn -1, approaching a theoretical value of 820mA h gZn -1. The catalyst demonstrates stable operation for over 500h at 10mA cm-2 and over 200h at 50mA cm-2. This work provides new insights to guide fabrication of advanced oxygen electrocatalysts.

Strong coupling between excitons and chiral quasibound states in the continuum of the bulk WS2 metasurface

In the fields of optics and photonics, the topic of light-matter interactions, particularly strong coupling effects, is a developing area of research. Exciton polariton, a hybridized state brought about by strong coupling, is a hot topic, especially from the standpoint of chiral optics. Under the incidence of right circularly polarized light and left circularly polarized (RCP and LCP) light, we investigate the strong coupling between excitons and quasibound states in the continuum (Q-BICs) resonance in a bulk WS2 metasurface. It is discovered that the Q-BICs are affected obviously on center frequencies and linewidth by structure parameters; while the exciton peaks are impacted insignificantly. Furtherly Q-BIC shows chiral enhancing features. When we take into account both Q-BIC and excitons of the metasurface simultaneously, there is a strong coupling as evidenced by the Rabi splitting up to 182 meV and the clear anti-crossing behavior in the transmittance and reflectance spectra of left and right circularly polarized light, respectively. Notably, a quasi-induced transparency window forms in the circular dichroism (CD) spectrum around the exciton band due to the non-chirality of exciton peaks. This enables the removal of excitons that are not involved in the strong coupling. The bulk WS2 chiral metasurface as a strong coupling system not only provides a way to understand the strong Light-matter interaction, but also generate a potential possibility for realizing the application of chiral optics. Additionally, it can realize the strong chiral coupling with a single self-hybridized element in the structure. Our results have potential implications in the chiral optical field and provide a chiral perspective on the study of strong photon-exciton coupling.

Effective charge separation in CdS@PANI heterostructure for ultrafast visible light-driven photocatalytic reduction of uranium(VI)

The efficient treatment of uranium-containing wastewater provides guarantee for sustainable development of nuclear energy. In this work, a heterogeneous interface structure for photocatalytic reduction of U(VI) was proposed by in-situ decoration of cadmium sulfide (CdS) nanoparticles on polyaniline (PANI) nanorods. The strong coupling between CdS and PANI precisely modulated the interface electronic structure, which promoted the photogenerated charge separation. Multiple spectroscopic characterizations revealed that the interfacial charge polarization with the electrons gathering at the CdS surface and the holes gathering at the PANI, facilitating the performance of photocatalytic reduction of U(VI) under visible light irradiation. The optimal CdS@PANI-10 shows ultrafast U(VI) reduction with efficiency of over 96 % in 5 min. Moreover, the photocatalytic reduction of U(VI) over CdS@PANI-10 can also be activated by direct natural sunlight irradiation. The improvement of catalytic activity of CdS@PANI nanocomposite is due to faster charge separation and migration at the interface between CdS and PANI, as well as the formation of Type-II heterojunction, which was also beneficial for suppressing the CdS photocorrosion. This work introduces a potential strategy to design advanced photocatalysts with efficient electrons and holes separation toward practical application in uranyl ion conversion.

Fall into the pseudo-decoupling trap: Type identification, trend characterization and solution path of carbon decoupling trap in urban agglomerations of China

This study investigates the stability and sustainability of carbon decoupling in urban agglomerations across China, where the strong coupling between economic growth and carbon emissions poses significant challenges. Despite efforts in energy conservation and emission reduction, urban agglomerations have seen unsatisfactory results. By analyzing the real-pseudo decoupling states in 19 urban agglomerations from 2007 to 2020, the objective of this study is to identify the type and trend characteristics of carbon decoupling traps and to propose solution paths for maintaining decoupling stability. Major Findings: (1) The decoupling state exhibits volatility and instability in urban agglomerations, making them susceptible to decoupling traps. (2) Most urban agglomerations remain un-decoupled, with a few cities achieving real decoupling and gradually shifted from northeast to southeast, while pseudo-decoupling and un-decoupled cities consistently cluster in the southwest and northwest regions. (3) Real-pseudo decoupling is driven by a combination of endogenous and exogenous factors, with energy structure, population density, and environmental regulation intensity emerging as pivotal influencers. (4) Geographical factors exhibit both commonalities and variations in their impact on real-pseudo decoupling. By identifying real-pseudo decoupling states and their driving factors, this study proposes strategic solution paths to overcome carbon constraints and achieve stable decoupling in urban agglomerations, contributing to the broader goals of sustainable economic and environmental development.

Hybrid spin-orbit exciton-magnon excitations in FePS3

FePS3 is a layered van der Waals (vdW) Ising antiferromagnet that has recently been studied in the context of true 2D magnetism and emerged as an ideal material platform for investigating strong spin-phonon coupling, and non-linear magneto-optical phenomena. In this work, we demonstrate an important unresolved role of spin-orbit coupling (SOC) in the ground state and excitations of this compound. Combining first-principles calculations with linear flavor wave theory (LFWT), we find strong mixing and spectral overlap of different spin-orbital single-ion states. Low-lying excitations form hybrid spin-orbit exciton/magnon modes. Complete parameterization of the low-energy model requires nearly half a million coupling constants. Despite this complexity, such a model can be inexpensively derived using local many-body-based approaches, which yield quantitative agreement with recent experiments. The results highlight the importance of SOC even in first-row transition metals and provide essential insight into the properties of 2D magnets with unquenched orbital moments.

Measuring Kinetics under Vibrational Strong Coupling: Testing for a Change in the Nucleophilicity of Water and Alcohols.

Vibrational Strong Coupling (VSC) has been reported to change the rate of organic reactions. However, a lack of convenient and reliable methods to measure reaction kinetics under VSC makes it challenging to obtain mechanistic insight into its influence, hindering progress in the field. Here, we use recently developed fixed-width optical cavities to obtain large kinetic datasets under VSC with small errors (± 1-5%) in an operationally simple manner using UV-vis spectroscopy. The setup is used to test whether VSC changes a fundamental kinetic property of polar reactions, nucleophilicity, for water and alcohols, species commonly used in VSC-modified chemistry. We determined the rate constants for nucleophilic capture with a library of benzhydrilium ions as reference electrophiles with and without strong coupling of the nucleophile's key vibrations. For all investigated combinations of electrophiles and nucleophiles, only minor changes in the observed rate constants of the reactions were observed, independently of the coupled bands. These results indicate that VSC does not substantially alter the nucleophilicity of water and alcohols, suggesting that polar reactions are modified through other, presently unknown mechanisms. Fixed-width cavities allow for convenient and reproducible UV-vis kinetics, facilitating mechanistic studies of VSC-modified chemistry.

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Exact solution for the collective non-Markovian decay of two fully excited quantum emitters

Waveguide quantum electrodynamics constitutes a modern paradigm for the interaction of light and matter, in which strong coupling, bath structure, and propagation delays can break the radiative conditions that quantum emitters typically encounter in free space. These characteristics intertwine the excitations of quantum emitters and guided radiation modes to form complex multiphoton dynamics. So far, combining the collective decay of the emitters with the non-Markovian effects induced by the modes has escaped a full solution and the detailed physics behind these systems remains unknown. Here we analyze such a collective non-Markovian decay in a minimal system of two excited emitters coupled to a one-dimensional single-band waveguide. We develop an exact solution for this system in terms of elementary functions that unveils hidden symmetries and predicts new forms of spontaneous decay. The collective non-Markovian dynamics, which are strongly dependent on the vacuum coupling and the detuning from the center of the band, show exotic features that can be characterized with a simple and readily available criterion. Our analytic methods shed light on the complexity of collective light-matter interactions and open up a pathway for understanding multiparticle open quantum systems. Published by the American Physical Society 2024

Measuring Kinetics under Vibrational Strong Coupling: Testing for a Change in the Nucleophilicity of Water and Alcohols

Vibrational Strong Coupling (VSC) has been reported to change the rate of organic reactions. However, a lack of convenient and reliable methods to measure reaction kinetics under VSC makes it challenging to obtain mechanistic insight into its influence, hindering progress in the field. Here, we use recently developed fixed‐width optical cavities to obtain large kinetic datasets under VSC with small errors (± 1‐5%) in an operationally simple manner using UV‐vis spectroscopy. The setup is used to test whether VSC changes a fundamental kinetic property of polar reactions, nucleophilicity, for water and alcohols, species commonly used in VSC‐modified chemistry. We determined the rate constants for nucleophilic capture with a library of benzhydrilium ions as reference electrophiles with and without strong coupling of the nucleophile’s key vibrations. For all investigated combinations of electrophiles and nucleophiles, only minor changes in the observed rate constants of the reactions were observed, independently of the coupled bands. These results indicate that VSC does not substantially alter the nucleophilicity of water and alcohols, suggesting that polar reactions are modified through other, presently unknown mechanisms. Fixed‐width cavities allow for convenient and reproducible UV‐vis kinetics, facilitating mechanistic studies of VSC‐modified chemistry.