Local Density Of States Research Articles

Asymmetricity in fluorescence peaks of a three level Λ-type quantum emitter placed near a spherical metal nanoparticle

Abstract A generalized master equation is derived here for a hybrid three level Λ-type quantum emitter-metal nanoparticle (MNP) system in the presence of strong external fields. With this new master equation, we show the spectral reshaping of the fluorescence peaks leading to asymmetric peak heights. This asymmetricity is attributed to dressed state-reservoir coupling and strong coherent fields. The coupling of reservoir with dressed states results in different sampling of local density of states (LDOS) of the vacuum field by dressed state transitions, giving different transition probabilities to each peak. We have further explored the directional features of the resonance fluorescence spectrum in the hybrid system. These observations of spectral reshaping in a three-level-MNP system opens new directions for studying tunable electromagnetically induced transparency utilizing ‘tailored vacuum’ in quantum plasmonics.

Tuning the local structure of (Sm, Co) Co-doped Al2O3 system for optical band gap and low dielectric loss

This study is about the qualitative description of the high dielectric constant (>103) and low dielectric loss in a two co-existing phases. According to earlier beliefs, a material with high dielectric constant will exhibit high dielectric loss. However, this study gives the opposite, where a material with high dielectric constant can exhibit low loss. Herein, we report on the effect of tetrahedral – octahedral interaction in a γ- Al2O3 and CoAl2O4 biphasic system. Phase identification was carried out using Synchrotron x-ray carrying a wavelength of 0.7 Å. The disorder caused by varying cobalt (Co) concentration results in a two co-existing phase system with varying local polarizability due to mixing of cations in a host matrix. In addition, a decreasing trend in the band gap energy has been observed for both the phases as a function of increasing Co concentration, which is attributed to the intra-gap localized density of states determined from the UV–Vis diffuse reflectance spectroscopy (DRS).

A tiny Drude scatterer can accurately model a coherent emitter in nanophotonics

Abstract We add a missing element to the set of directly computable scenarios of light-matter-interaction within classical numerical Maxwell solvers, i.e., light scattering from hybrid systems of resonators and individual Fourier-limited emitters. In particular, individual emitters are incorporated as tiny polarizable and resonant spherical scatterers. This emitter model is based on well-known extremal properties of Mie modes. The spherical emitter is made from an artificial Drude metal with ϵ ( ω ) = ϵ b − ω p 2 / ( ω 2 + i Γ ω ) ${\epsilon}(\omega )={{\epsilon}}_{b}-{\omega }_{p}^{2}/({\omega }^{2}+i{\Gamma }\omega )$ . By tuning ϵ b and ω p we adjust the resonance frequency and the Fourier-limited linewidth and by adjusting Γ we may add non-radiative damping or dephasing. This approach automatically reproduces the ideal text book coherent scattering cross-section of Fourier-limited two level quantum systems of σ 0 = 3λ 2/(2πϵ out) which is not possible with typically used Lorentz permittivities which only mimic optical resonances. Further, the emitter’s linewidth adopts to the surrounding optical local density of states (LDOS). To demonstrate this we successfully benchmark our approach with prominent examples from the literature.

Investigation of Mn–Co oxides loaded ceramic structured catalyst for microwave enhanced catalytic degradation of benzene

Compared with traditional heating, microwave heating has unique advantage and can enhance the chemical reaction. It is a promising technology for catalytic degradation of VOCs gas. Here we prepared a structured catalyst (Mn–Co/SiC) suitable for VOCs degradation under microwave. The catalyst shown excellent stability under microwave heating and microwave empowered the catalyst with good water resistance. Microwave heating exhibits high energy efficiency. Density functional theory is employed to investigate the microwave-enhanced catalytic degradation of VOCs. The theoretical calculation results indicate that the adsorption energy is more negative under microwave electric field, suggesting that microwave electric field is conducive to the activation of benzene. The electrons on the adsorption surface of the catalyst are redistributed to different degrees under the action of different microwave electric fields, thus affecting the activation of adsorbed molecules and chemical reaction process. The local density of states further reveals that electric fields may facilitate the electron transport.

Impact of Mo+2 addition and thermal annealing on the surface morphology, electrical transport properties and Mott's parameters of WO3 films for potential photonic devices

This work investigates the compositional dependence and thermal annealing of the morphological properties, electrical conductivity mechanisms and Mott's parameters of sprayed MoxW1-xO3 (x = 0, 0.05, 0.10 and 0,20) thin films. The prepared thin films were examined using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX) and Fourier transform infrared spectroscopy (FTIR) techniques. In addition, the two-point probe method was used to calculate the electrical properties of MoxW1-xO3 thin films. The FTIR results revealed that; the tungsten hydroxyl bond (W-OH) and the surface hydroxyl group vibrated within the ranges of 1558.62–1645.56 cm−1 and, 3296.76 and 3424.34 cm−1, respectively. Furthermore, a prominent band in the spectrum spanning from 850 to 650 cm−1 represents the W-O-W bridge mode. The FE-SEM investigations found that the molybdenum (Mo) dopant caused significant changes in the surface morphology of the films. The EDX results showed that the percentages of the isotropic elements MoxW1-xO3 agreed well with those obtained by atomic weight. Studies of the conduction mechanism indicate that the transition temperature was approximately 393K. Corresponding to Mott's model, the conduction mechanism below this temperature was across the variable hopping conduction band near the Fermi level. The mechanism exhibited a cycle of localised states through activated thermionic emission above 393K. Mott parameters were also estimated in addition to barrier potential energies, trapping state energies, local state densities, and other variables. The results revealed that both temperature areas had a rise in ρo and ρ1 values during and after annealing. The ΔEo and ΔE1 values in each temperature area decreased as the Mo-ion concentration increased. Furthermore, the conversion temperature gradually reduced as Mo was added. Based on these properties, the study's overall findings indicate that MoxW1-xO3 is suitable for future photonic devices and optoelectronic applications.

Impact of Fe-impurity centers on phonon subsystem of wurtzite-type ZnO

The paper addresses the question of the structural and vibrational properties of Fe-doped ZnO in the wurtzite structure with a lattice without an inversion center. The ZnO crystals containing Fe impurities in different charged states are studied by means of density functional theory (DFT) and potential-based methods. A first-principles simulation is performed to determine the local atomic configurations near the considered defects. The DFT results are compared with those obtained using the shell model. Both approaches give a similar pattern of lattice distortion around the Fe-impurity centers occupying cation sites in the isoelectronic charge state Fe2＋ and single-positive-charge state Fe3＋. The phonon local symmetrized densities of states projected onto the displacement of ions surrounding the defects are calculated by a well-established recursion method. The frequencies of defect vibrations of various symmetry types induced by Fe impurities are determined. The calculations made it possible to interpret the structure of the phonon sideband accompanying the zero-phonon line in polarized emission spectra attributed to the Fe3＋ intracenter transitions, as well as to estimate the role of Fe ions in the formation of observed peaks.

Ni thin-films on Pd surfaces and effects of oxygen adsorption: Ab-initio study of structures, electronic properties, magnetic anisotropy

We report first-principles electronic structure calculations of the structural, electronic, and magnetic properties of model epitaxial layers consisting of nickel (Ni) atomic layers deposited on palladium (Pd) substrate, i.e., Ni(001)m∣Pd(001)n where m=1,2,6 and n=3,10, are layer thicknesses. We also investigate the effect of oxygen adsorption on the calculated properties. We found variation in magnetization of between ≈0.6μB to 1.00 μB across the nickel layers. Also, finite magnetic moments albeit of small values of between 0.2 μB and 0.3 μB is found on the Pd at the interface. This magnetic moment on an otherwise non-magnetic Pd atoms has been adduced to interfacial strain due to lattice mismatch between the Ni and Pd layers at the Ni|Pd interface. The effect of adsorbed oxygen on the Nim∣Pdn is that it increases the magnetic moment on the nickel layers. Also, regarding the magnitude of magnetic anisotropy energy (MAE), we found a high perpendicular values of 1.63 meV and 1.37 meV per unit cell respectively for Nim∣Pd10 (m=2,6) which are relatively higher than those reported for other transition metal epitaxial layers. However, the presence of oxygen atom on the Ni∣Pd changes the direction and magnitude of MAE. Indeed, O adsorption favours or enhances in-plane magnetization direction depending on the thickness of the Ni layers for a fixed Pd thickness. Plots of local density of states (LDOS) which include the effect of spin–orbit coupling (SOC), show that in the case of Ni∣Pd having perpendicular MAE, there appears a new SOC-induced electronic states below and above the Fermi level. These states appears to stabilize this type of magnetic anisotropy. On the other hand, in-plane MAE is characterized by SOC-induced localized states below the Fermi level (EF) as well as the lowering of the DOS at the EF. Our work explores the physical, magnetic and electronic properties that may be useful in designing Ni∣Pd-based superlattices for magnetic or spintronic applications.

Optical memcapacitor based on MoS2 quantum capacitance

It is imperative to study neuromorphic devices where the behavior of artificial synapses is regulated by external conditions. The quantum capacitance of 2D materials is determined by the local density of states near the Fermi level and usually exhibits a sensitive response to external stimuli. This study explores the use of MoS2 quantum capacitance in a memcapacitor (MoS2 quantum memcapacitor, MQM), emulating biological synapse behavior and showcasing higher sensitivity. Notably, without altering the physical structure, MQM realizes the potentiation and depression of capacitance through light and gas coupling manipulation, establishing a memory effect for the device. This enables MQM to reproduce the learning-forgetting cycle multiple times with good repeatability. Moreover, MQM can simulate various biological synaptic behaviors, encompassing short-term memory to long-term memory conversions, short-term depression to long-term depression conversions, and higher pair-pulse-facilitation behavior. These characteristics offer a fresh direction and possibilities for artificial synaptic device research.

Computational and Experimental Investigations of the Au and NiOOH Interface in the Oxygen Evolution Reaction

The transition to renewable energy sources is crucial for combating climate change, and hydrogen (H2) is a promising clean fuel. Electrolysis of water, specifically the oxygen evolution reaction (OER), is a key process for producing H2. Prior experimental results have shown that gold (Au) could improve the apparent activities of the OER electrocatalysts such as nickel hydroxide (Ni(OH)2) in alkaline electrolytes.1-3 However, the detailed interfacial atomic structure and mechanisms of the increased catalytic activity remain poorly understood.To understand the interfacial effect between Au and Ni(OH)2 in the OER process, our research uses the model system of Au nanoparticles (NPs) and nickel oxyhydroxide (NiOOH), which is the active phase of Ni(OH)2 layers in the OER, to investigate their interfacial interactions with both experimental and computational approaches. We hypothesize that the Au NPs on NiOOH enhances the OER activity by promoting electron transfer at the interface. Our studies involve computational analysis using Density Functional Theory (DFT) calculations to obtain the local density of states (LDOS), which can help us better visualize and compare the local electronic structure of NiOOH in the presence and in the absence of AuNPs. Two architectures of the Au and NiOOH interface will be investigated: Au NPs on a NiOOH film and NiOOH NPs on a Au film.Additionally, Bader analysis is employed to determine the Bader charge, offering a more detailed understanding of how electrons are distributed across the AuNPs/NiOOH interface. Furthermore, the catalytic efficacy of AuNPs on NiOOH is assessed through electrodepositions followed by cyclic voltammetry(CV) measurements. The experimental and computational results will be directly compared, and this research is expected to contribute to the insights of substrate and catalyst interactions for design of more efficient electrocatalysts.

(Invited) Manipulating Interfacial Electrochemistry with Moiré Superlattices

At electrode–electrolyte interfaces, crystallographic defects are frequently implicated as active sites that mediate interfacial electron transfer (ET) by introducing high densities of localized electronic states (DOS). However, conventional defects are challenging to deterministically synthesize and control at an atomic level, hindering the direct study of how electronic localization impacts interfacial reactivity. Azimuthal misalignment of atomically thin layers produces moiré superlattices and alters the electronic band structure, in a manner that is systematically dependent on the interlayer twist angle. Using van der Waals nanofabrication of two-dimensional heterostructures, scanning electrochemical cell microscopy measurements, and four-dimensional scanning transmission electron microscopy, we report a strong twist angle dependence of heterogeneous charge transfer kinetics at twisted bilayer and trilayer graphene electrodes with the greatest enhancement observed near the ‘magic angles’. These effects are driven by the angle-dependent engineering of moiré flat bands that dictate the electron transfer processes with the solution-phase redox couple, and the structure of the relaxed moiré superlattice. Moiré superlattices therefore serve as an unparalleled platform for systematically interrogating and exploiting the dependence of interfacial ET on local electronic structure.

(Keynote) Engineering Lead Halide Perovskite Nanocrystals for Fast Single-Particle and Collective Light Emission

Colloidal lead halide perovskite (LHP) nanocrystals (NCs), with bright and spectrally narrow photoluminescence (PL) tunable over the entire visible spectral range, are of immense interest as classical and quantum light sources. Fast (bright) and pure single-photon emission is key for many quantum technologies, from optical quantum computing to quantum key distribution and quantum imaging.The brightness of an emitter is ultimately described by Fermi’s golden rule, with a radiative rate proportional to its oscillator strength (intrinsic emitter property) times the local density of photonic states (photonic engineering, i.e. cavity). With perovskite NCs, we present a record-low sub-100 ps radiative decay time for CsPb(Br/Cl)3, almost as short as the reported exciton coherence time, by the NC size increase to 30 nm. The characteristic dependence of radiative rates on QD size, composition, and temperature suggests the formation of giant transition dipoles, as confirmed by effective-mass calculations for the case of the giant oscillator strength. Importantly, the fast radiative rate is achieved along with the single-photon emission despite the NC size being ten times larger than the exciton Bohr radius. NC self-assembly is a versatile platform for materials engineering, particularly for attaining collective phenomena with perovskite NCs, such as superfluorescence in perovskite NC superlattices. Thus far, LHP NCs have been co-assembled with building blocks that acted solely as spacers to promote the tuning of the mutual arrangement of LHP nanocubes [2]. However, the functionality of the second SL component can give rise to the enhancement of the LHP NCs properties or the emergence of new collective effects. We present the formation of multicomponent SLs made from the CsPbBr3 NCs of two different sizes. The diversity of obtained SLs encompassed the binary ABO6-, ABO3-, and NaCl-type structures, all of which contained orientationally and positionally confined NCs. For the selected model system, the ABO6-type SL, we observed efficient NC coupling and Förster-like energy transfer from strongly confined 5.3 nm CsPbBr3 NCs to weakly confined 17.6 nm CsPbBr3 NCs. Exciton spatiotemporal dynamics measurements reveal that binary SLs exhibit enhanced exciton diffusivity compared to one-component SLs across the entire temperature range (from 5 K to 298 K). Observed incoherent NC coupling and controllable excitonic transport within the solid NC SLs hold promise for potential applications in optoelectronic devices.[1]C. Zhu, S. C. Boehme, L. G. Feld, A. Moskalenko, D. N. Dirin, R. F. Mahrt, T. Stöferle, M. I. Bodnarchuk, A. L. Efros, P. C. Sercel, M. V. Kovalenko, G. Rainò. In review.[2] Ihor Cherniukh et al. Nature, 2021, 593, 535–542. [3] T. Sekh et al. Submitted

(Invited) Simple and Optimized Silicon Nano-Antennas for Quantum Emitter Control

Improving the brightness and efficiency of single photon sources by the mean of optically resonant nanostructures is a major stake for the development of efficient nanodevices for quantum communications.For a couple of decades, these resonant nanostructures have mainly been made of noble metal that sustain strong localized resonances (LSPR) that can be used to manipulate, concentrate or redirect visible light. Such properties have led to numerous actual or potential applications in integrated optics, sensors, nonlinear optics, field-enhanced spectroscopies, or photovoltaics. Recently, an alternative emerged with high refractive index dielectric nanostructures, which offer the same range of applications as plasmonics by manipulating Mie optical resonances instead of LSPR [1].These resonances can be efficiently tuned by modifying the size, shape, and material of those nanostructures (e.g. silicon, n ~ 4) [2]. Furthermore, high index dielectric nanostructures offer several key advantages when compared to their metallic counterparts: absorption losses are far weaker for wavelengths longer than the direct band gap, access to semiconductor (CMOS) technology for nanostructure fabrication, and presence of intrinsic strong magnetic and electric resonances, providing an unique opportunity to spatially separate and redistribute the energy of the magnetic and electric parts of the electromagnetic field in the near field, otherwise inextricably connected in the far field [3].We discuss here the effect of simple high-index dielectric nanoantennas on the spontaneous emission of model quantum emitters. First, we accurately positioned arrays of nanodiamonds hosting NV colored centers in the gap of silicon dimer nanoantennas, using atomic force microscopy (AFM – [4]) nanoxerography [5]. The NV center is an ideal model system exhibiting single photon emission properties at room temperature, which is well adapted for proof of concept experiments in quantum nano-optics. Since the local density of photonic states (LDOS) is modified by the nanostructure, we show by the mean of time-resolved photoluminescence acquisitions that the photodynamics of these quantum emitters can be enhanced by the coupling to the nanoantenna, down to the single photon emission regime [5]. Our experimental results are in good agreement with multipolar analysis and numerical simulations based on the Green Dyadic Method - GDM.Second, in order to go a step further, we explore the control of the directive emission from quantum dipolar sources by the mean of complex silicon antennas. The latter, made of a given number of building (nano)blocks, are optimized by an Evolutionary Algorithm (EA) coupled to full-field electrodynamical GDM simulations. The geometries obtained allow to tailor the emission direction of a single dipolar source, maximizing the intensity of the emitted light within a given solid angle. Our numerical and preliminary experimental results demonstrate the efficiency of such compact EA-optimized antennas for the control of quantum nanosources. Acknowledgements : This work was supported by Programme Investissements d’Avenir through the grants ANR-10-LABX-0037-NEXT (MILO) and NanoX n° ANR-17-EURE- 0009 (Q-META), by the HiLight ANR project ANR-19-CE24-0026, by LAAS-CNRS micro and nanotechnologies platform member of the French Renatech network, by the CNRS and INSA (PhD grant), by the Région Midi-Pyrénées via the Institute for Quantum technologies in Occitanie (IQO), and by the computing facility center CALMIP of the University of Toulouse under grants P12167 and P1107. References : Kallel et al, Tunable enhancement of light absorption and scattering in Si1xGex nanowires, Phys. Rev. B 12: 085318, 2012.P.R. Wiecha et al., Strongly directional scattering from dielectric nanowires, ACS Photonics 4: pp 2036–2046, 2017.Montagnac et al., Control of light emission of quantum emitters coupled to silicon nanoantenna using cylindrical vector beams, Light : Science and Applications 12 (1), 239, 2023.Humbert et al., Versatile, rapid and robust nanopositioning of single-photon emitters by AFM-nanoxerography, Nanotechnology 33, 215301, 2022.Humbert et al., Large-scale controlled coupling of single-photon emitters to high index dielectric nanoantennas using AFM nanoxerography, Nanoscale 15, 599-608, 2023. Figure 1

(Invited) Mie Resonant Silicon Nanosphere Nanoantenna for Fluorescence Enhancement

A nanoantenna is a device that manipulates light propagation and enhances light-matter interaction at the nanoscale. Integration of an emitter into a nanoantenna capable of increasing local density of photonic states at the emission wavelength results in the enhancement of the spontaneous emission rate (Purcell effect) and modifies the emission spectrum. A nanoantenna can also control the directionality and radiation pattern of an emitter. Traditionally, plasmonic nanoantennas made from gold or silver nanostructures supporting localized surface plasmon resonances had been the main stream of the nanoantenna research. Recently, high refractive index nanoparticles having low-order Mie resonances have been attracting attention as a new type of dielectric nanoantennas. Advantages of a dielectric nanoantenna compared to a plasmonic one are the smaller loss and the possession of magnetic type Mie resonances arising from light-induced displacement current. By properly controlling the overlap of the magnetic and electric multipole resonances, radiation patters of an emitter placed nearby can be tailored with high degree of freedom. Furthermore, magnetic-type Mie resonances can couple with higher-order optical transitions of an emitter such as a magnetic-dipole transition, and thus can enhance and control radiation from otherwise weak forbidden transitions.Recently, we have succeeded in producing perfectly spherical nanoparticles of crystalline silicon (Si) in 100-300 nm in diameters. These Si nanospheres exhibit the electric and magnetic multipole resonances at the optical frequency [1]. In this presentation, we first show scattering and absorption properties of the Mie resonant Si nanospheres. Especially, we show that solutions of size-purified Si nanospheres exhibit vivid structural color and the solutions can be used as structural color inks. We then show that the solutions can preserve helicity of incoming circularly-polarized light and can enhance local chiral fields around nanospheres [2, 3]. This property can be used to improve the sensitivity of enantiomer-selective chiral molecular sensing. We then show some examples of enhanced light-matter interaction by Si nanoparticles. These include enhancement of magnetic dipole transitions of an emitter by magnetic-type Mie resonances of Si nanospheres (magnetic Purcell effect) [4, 5], enhancement of excitation and emission processes of in-plane dipoles of monolayer transition metal dichalcogenides (TMDC) [6], and enhancement of a spin forbidden singlet-to-triplet absorption transition of a molecule by Si nanodisks [7, 8].

Scanning Near-Field Optical Microscopy: Recent Advances in Disordered and Correlated Disordered Photonics

Disordered and correlated disordered photonic materials have emerged in the past few decades and have been rapidly proposed as a complementary alternative to ordered photonics. These materials have thrived in the field of photonics, revealing the considerable impact of disorder with and without structural correlations on the scattering, transport, and localization of light in matter. Scanning near-field optical microscopy (SNOM) has proven to be a fundamental tool for the study of the interaction between light and matter at the nanoscale in such systems, allowing for the investigation of optical properties and local electromagnetic fields with extremely high spatial resolution, surpassing the diffraction limit of conventional optical microscopy. In this review, the most important and recent advances obtained for disordered and correlated disordered luminescent structures by means of the aperture SNOM technique are addressed, showing how it allows the tailoring of local density of states (LDOS), as well as providing access to statistical analysis for multi-resonance disordered and hyperuniform disordered structures at telecom wavelengths.

Local density of states induced near impurities in Mott insulators

Local density of states induced near impurities in Mott insulators

Edge‐Effect Modulated Noble Metal Electrocatalysts for Efficient and pH‐Universal Hydrogen Evolution Reaction

AbstractThe catalytic activity of metal nanoparticles is closely pertinent to the substrate, while the influence of the support on the catalytic activity is acquainted scarcely. Herein, the edge selective decoration of noble metal nanoparticles into an edge‐rich carbon foam (CF) matrix for efficient pH‐universal hydrogen evolution (HER) reaction is reported. The highly localized density of states of the graphene edges enables increased reactivity to noble metal nanoparticles and tunes their electronic states. As expected, the Pt nanoparticles decorated on CF (Pt NPs@CF) exhibit low overpotentials (η10) of only 35, 49, and 53 mV under acidic, alkaline, and neutral conditions, respectively. Moreover, it can deliver the ampere‐level current density of 1000 mA cm−2 with an overpotential of 97 mV in acidic solutions. Above all, the other noble metal NPs decorated on CF also possess efficient pH‐universal HER performance. This work presents a new avenue for developing high‐activity electrocatalysts via support engineering.

Variable-order fractional diffusion: Physical interpretation and simulation within the multiple trapping model

The physical interpretation of a variable-order fractional diffusion equation within the framework of the multiple trapping model is presented. This interpretation enables the development of a numerical Monte Carlo algorithm to solve the associated subdiffusion equation. An important feature of the model is variation in energy density of localized states, when the detailed balance condition between localized and mobile particles is satisfied. The variable order anomalous diffusion equations under consideration can be applied to the description of transient subdiffusion in inhomogeneous materials, the order of which depends on the considered spatial and/or time scale. Examples of numerical solutions for different situations are demonstrated. Considering variable-order fractional drift, we calculate and analyze the transient current curves of the time-of-flight method for samples with varying density of localized states.

Band Structure Calculations, Magnetic Properties and Magnetocaloric Effect of GdCo1.8M0.2 Compounds with M = Fe, Mn, Cu, Al

The magnetic properties, band structure results, and magnetocaloric effect of GdCo1.8M0.2 with M = Fe, Mn, Cu, and Al are reported. The band structure calculations demonstrate that all the samples have a ferrimagnetically ordered ground state, in perfect agreement with the magnetic measurements. Calculated magnetic moments and variation with the alloy composition are strongly influenced by hybridisation mechanisms as sustained by an analysis of the orbital projected local density of states. The XPS measurements reveal no significant shift in the binding energy of the investigated Co core levels with a change in the dopant element. The Co 3s core-level spectra gave us direct evidence of the local magnetic moments on Co sites and an average magnetic moment of 1.3 µB /atom was found, being in good agreement with the theoretical estimation and magnetic measurements. From the Mn 3s core-level spectra, a value of 2.1 µB/Mn was obtained. The symmetric shapes of magnetic entropy changes, the Arrott plots, and the temperature dependence of Landau coefficients clearly indicate a second-order phase transition. The relative cooling power, RCP(S), normalized relative cooling power, RCP(∆S)/∆B, and temperature-averaged entropy change values indicate that these compounds could be promising candidates for applications in magnetic refrigeration devices.

Tunable single emitter-cavity coupling strength through waveguide-assisted energy quantum transfer

The emitter-cavity strong coupling manifests crucial significance for exploiting quantum technology, especially in the scale of individual emitters. However, due to the small light-matter interaction cross-section, the single emitter-cavity strong coupling has been limited by its harsh requirement on the quality factor of the cavity and the local density of optical states. Herein, we present a strategy termed waveguide-assisted energy quantum transfer (WEQT) to improve the single emitter-cavity coupling strength by extending the interaction cross-section. Multiple ancillary emitters are optically linked by a waveguide, providing an indirect coupling channel to transfer the energy quantum between target emitter and cavity. An enhancement factor of coupling strength g̃/g>10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\widetilde{g}/g > 10$$\\end{document} can be easily achieved, which dramatically release the rigorous design of cavity. As an extension of concept, we further show that the ancillae can be used as controlling bits for a photon gate, opening up new degrees of freedom in quantum manipulation.

Computational investigation of quantum capacitance enhancement in Mg-substituted MgB[formula omitted]-based supercapacitor electrodes

The investigation into surface functionalization’s effect on magnesium diboride (MgB2) presents a captivating research direction, shedding light on the modifications in its electronic structure resulting from functionalization systematically analysed through density functional theory (DFT) calculations. This study systematically investigates the effects of varying functionalization concentrations on MgB2, unveiling a profound influence on its quantum capacitance(CQ). Maximum enhancement is found within an optimal doping range; however, impurity ad-atom interactions may cause quantum capacitance to decrease above this barrier. Notably, these ad-atoms act as magnetic impurities, generating a localized density of states near the Fermi energy, thereby increasing charge carrier density and resulting in a remarkable increase in quantum capacitance. We also emphasize the importance of functionalized MgB2 as an example of a two-dimensional supercapacitor electrode material in the advancement of energy storage technology. These materials promise improved charge storage capacities and tailored electronic properties, which will accelerate the development of effective energy storage technologies. This paper highlights the potential direction of two-dimensional electrode materials in developing supercapacitor technology towards superior energy storage systems by elucidating fundamental mechanisms using quantum capacitance enhancement.