Florence Nightingale (1820-1910): The Founder of Modern Nursing.

Florence Nightingale, a pioneering figure in the field of nursing during the 19th century, revolutionized medical practices through her innovative approaches to healthcare and dedication to improving patient outcomes. Her advocacy for sanitation significantly reduced mortality rates among patients. Nightingale's pioneering use of data analysis in healthcare and her establishment of nursing education standards laid the foundation for the nursing profession as we know it today.

Efficient High-Order Harmonic Generation from the van der Waals Layered Crystal Copper Indium Thiophosphate.

Layered metal thio- and selenophosphates (MTPs) are a family of van der Waals gapped materials that exhibit a multitude of functionalities in terms of magnetic, ferroelectric, and optical properties. Despite the recent progress in terms of understanding the material properties of these compounds, the potential of MTPs as a material class yet needs further scrutiny, especially in terms of nonlinear optical properties. Recent reports of efficient low-order harmonic generation and extremely high third-order nonlinear optical properties in MTPs suggest the potential application of these materials in integrated nanophotonics.

Anomalous isotope effect on the optical bandgap in a monolayer transition metal dichalcogenide semiconductor.

Isotope effects have received increasing attention in materials science and engineering because altering isotopes directly affects phonons, which can affect both thermal properties and optoelectronic properties of conventional semiconductors. However, how isotopic mass affects the optoelectronic properties in 2D semiconductors remains unclear because of measurement uncertainties resulting from sample heterogeneities. Here, we report an anomalous optical bandgap energy red shift of 13 (±7) milli-electron volts as mass of Mo isotopes is increased in laterally structured MoS-MoS monolayers grown by a two-step chemical vapor deposition that mitigates the effects of heterogeneities.

Superradiant emission in a high-mobility two-dimensional electron gas.

We use terahertz time-domain spectroscopy to study gallium arsenide two-dimensional electron gas samples in external magnetic field. We measure cyclotron decay as a function of temperature from 0.4 to10Kand a quantum confinement dependence of the cyclotron decay time belowT0=1.

Electron-phonon interaction and ultrafast photoemission from doped monolayer MoS.

We have examined the effect of electron-phonon coupling on photoluminescence and ultrafast response of electron doped monolayer MoS, using a combination of density functional theory, time dependent density functional theory, and many-body theory. For small doping (∼1-3%) of interest here, the electron-phonon coupling parameter is modest (∼0.1-0.

Bright and Dark Exciton Coherent Coupling and Hybridization Enabled by External Magnetic Fields.

Magnetic field- and polarization-dependent measurements on bright and dark excitons in monolayer WSe combined with time-dependent density functional theory calculations reveal intriguing phenomena. Magnetic fields up to 25 T parallel to the WSe plane lead to a partial brightening of the energetically lower lying exciton, leading to an increase of the dephasing time. Using a broadband femtosecond pulse excitation, the bright and partially allowed excitonic state can be excited simultaneously, resulting in coherent quantum beating between these states.

Excited states in hydrogenated single-layer MoS.

Our calculations of the excitation spectrum of single-layer MoS at several hydrogen coverages, using a density-matrix based time-dependent density-functional theory (TDDFT) show that the fully hydrogenated system is metallic, while at lower coverages the spectrum consists of spin-polarized partially filled localized mid-gap states. The calculated absorption spectrum of the system reveals standard excitonic peaks corresponding to the bound valence-band hole and conduction-band electron, as well as excitonic peaks that involve the mid-gap states. Binding energies of the excitons of the hydrogenated system are found to be relatively large (few tens of meV), making their experimental detection facile and suggesting hydrogenation as a knob for tuning the optical properties of single-layer MoS.

Electron-electron correlations and structural, spectral and polarization properties of tetragonal BaTiO.

To analyze the role of electron-electron correlation effects in structural (local-geometry), spectral and polarization properties of tetragonal BaTiOwe apply DFT +approach. We demonstrate that the system properties drastically change when the value of the local Coulomb repulsioncrosses the critical value≈ 7 eV. In particular, the correlation effects cause a change of the ratio of the in-plane and inter-plane Ti-O bond lengths, which results in a flip of the order of the Ti-bands and change of the polarizability of the system.

Ultrafast Electron Correlations and Memory Effects at Work: Femtosecond Demagnetization in Ni.

Experimental observations of the ultrafast (less than 50 fs) demagnetization of Ni have so far defied theoretical explanations particularly since its spin-flipping time is much less than that resulting from spin-orbit and electron-lattice interactions. Through the application of an approach that benefits from spin-flip time-dependent density-functional theory and dynamical mean-field theory, we show that proper inclusion of electron correlations and memory (time dependence of electron-electron interaction) effects leads to demagnetization at the femtosecond scale, in good agreement with experimental observations. Furthermore, our calculations reveal that this ultrafast demagnetization results mainly from spin-flip transitions from occupied to unoccupied orbitals implying a dynamical reduction of exchange splitting.

Electron correlations and memory effects in ultrafast electron and hole dynamics in VO.

By applying an approach based on time-dependent density functional theory and dynamical mean-field theory (TDDFT+DMFT) we examine the role of electron correlations in the ultrafast breakdown of the insulating M phase in bulk VO. We consider the case of a spatially homogeneous ultrafast (femtosecond) laser pulse perturbation and present the dynamics of the melting of the insulating state, in particular the time-dependence of the excited charge density. The time-dependence of the chemical potential of the excited electron and hole subsystems shows that even for such short times the dynamics of the system is significantly affected by memory effects-the time-resolved electron-electron interactions.

Plasmon Excitations in Mixed Metallic Nanoarrays.

Features of the surface plasmon from macroscopic materials emerge in molecular systems, but differentiating collective excitations from single-particle excitations in molecular systems remains elusive. The rich interactions between single-particle electron-hole and collective electron excitations produce phenomena related to the chemical physics aspects within the atomic array. We study the plasmonic properties of atomic arrays of noble (Au, Ag, and Cu) and transition-metal (Pd, Pt) homonuclear chains using time-dependent density functional theory and their Kohn-Sham transition contributions.

Biexcitons in monolayer transition metal dichalcogenides tuned by magnetic fields.

We present time-integrated four-wave mixing measurements on monolayer MoSe in magnetic fields up to 25 T. The experimental data together with time-dependent density function theory calculations provide interesting insights into the biexciton formation and dynamics. In the presence of magnetic fields the coherence at negative and positive time delays is dominated by intervalley biexcitons.

Pentacene Excitons in Strong Electric Fields.

Electroluminescence spectroscopy of organic semiconductors in the junction of a scanning tunneling microscope (STM) provides access to the polarizability of neutral excited states in a well-characterized molecular geometry. We study the Stark shift of the self-trapped lowest singlet exciton at 1.6 eV in a pentacene nanocrystal.

Nonadiabatic exchange-correlation kernel for strongly correlated materials.

We formulate a rigorous method for calculating a nonadiabatic (frequency-dependent) exchange-correlation (XC) kernel appropriate for accurate description of both equilibrium and nonequilibrium properties of strongly correlated systems within the time-dependent density functional theory (TDDFT) via the charge susceptibility, which is in turn obtained from dynamical mean field theory (DMFT) based on the effective multi-orbital Hubbard model. Application to the simple case of the one-orbital Hubbard model already shows the importance of the nonadiabatic kernel as it leads to significant modification of the excitation spectrum-shifting the (adiabatic) peak and disclosing another that is reminiscent of the solution from DMFT. The impact of dynamical effects, naturally included through the nonadiabaticity of the XC kernel, becomes even more transparent in our consideration of the nonequilibrium charge-density response of a multi-orbital perovskite, YTiO, to a perturbation by a femtosecond (fs) laser pulse.

Strong Quantum Coherence between Fermi Liquid Mahan Excitons.

In modulation doped quantum wells, the excitons are formed as a result of the interactions of the charged holes with the electrons at the Fermi edge in the conduction band, leading to the so-called "Mahan excitons." The binding energy of Mahan excitons is expected to be greatly reduced and any quantum coherence destroyed as a result of the screening and electron-electron interactions. Surprisingly, we observe strong quantum coherence between the heavy hole and light hole excitons.

Nanoscale plasmonic phenomena in CVD-grown MoS monolayer revealed by ultra-broadband synchrotron radiation based nano-FTIR spectroscopy and near-field microscopy: publisher's note.

This publisher's note amends the Acknowledgments of a recent publication [Opt. Express24, 1154 (2016)10.1364/OE.

Nanoscale plasmonic phenomena in CVD-grown MoS(2) monolayer revealed by ultra-broadband synchrotron radiation based nano-FTIR spectroscopy and near-field microscopy.

Nanoscale plasmonic phenomena observed in single and bi-layers of molybdenum disulfide (MoS(2)) on silicon dioxide (SiO(2)) are reported. A scattering type scanning near-field optical microscope (s-SNOM) with a broadband synchrotron radiation (SR) infrared source was used. We also present complementary optical mapping using tunable CO(2)-laser radiation.

A DFT+nonhomogeneous DMFT approach for finite systems.

For reliable and efficient inclusion of electron-electron correlation effects in nanosystems we formulate a combined density functional theory/nonhomogeneous dynamical mean-field theory (DFT+DMFT) approach which employs an approximate iterated perturbation theory impurity solver. We further apply the method to examine the size-dependent magnetic properties of iron nanoparticles containing 11-100 atoms. We show that for the majority of clusters the DFT+DMFT solution is in very good agreement with experimental data, much better compared to the DFT and DFT+U results.

Complementary roles of benzylpiperazine and iodine 'vapor' in the strong enhancement of orange photoluminescence from CuI(1 1 1) thin film.

We have employed density functional theory, corrected by the on-site electron-electron repulsion energy U, to clarify the mechanism behind the enhanced orange photoluminescence (PL) of a CuI(1 1 1) thin film conjugated with a benzylpiperazine (BZP) molecule in the presence of an iodine 'vapor' atom. Our results demonstrated that the adsorbed molecule and the 'vapor' atom play complementary roles in producing the PL. The latter, in attaching to the film surface, creates a hole-trapping surface state located ~0.

Nonadiabatic time-dependent spin-density functional theory for strongly correlated systems.

We propose a nonadiabatic time-dependent spin-density functional theory (TDSDFT) approach for studying single-electron excited states and the ultrafast response of systems with strong electron correlations. The correlation part of the nonadiabatic exchange-correlation (XC) kernel is constructed by using exact results for the Hubbard model of strongly correlated electrons. We demonstrate that the corresponding nonadiabatic XC kernel reproduces the main features of the spectrum of the Hubbard dimer and the 2D, 3D and infinite-dimensional Hubbard models, some of which are impossible to obtain within the adiabatic approach.

Optical generation of collective plasmon modes in small gold chains induced by doping transition-metal impurities.

Our examination of the optical properties of small gold chains containing up to 24 atoms doped with a transition metal (TM) atom (Ni, Rh, Fe), using the time-dependent density functional theory, show the splitting of the collective plasmon peak. We associate the additional peak with a local plasmonic mode which corresponds to charge oscillations around the potential created by the d orbitals of the impurity atoms. The effect is almost independent of the position of the TM atom in the chain, as long as it is not at the chain edge.

Linker-induced anomalous emission of organic-molecule conjugated metal-oxide nanoparticles.

Semiconductor nanoparticles conjugated with organic- and dye-molecules to yield high efficiency visible photoluminescence (PL) hold great potential for many future technological applications. We show that folic acid (FA)-conjugated to nanosize TiO(2) and CeO(2) particles demonstrates a dramatic increase of photoemission intensity at wavelengths between 500 and 700 nm when derivatized using aminopropyl trimethoxysilane (APTMS) as spacer-linker molecules between the metal oxide and FA. Using density-functional theory (DFT) and time-dependent DFT calculations we demonstrate that the strong increase of the PL can be explained by electronic transitions between the titania surface oxygen vacancy (OV) states and the low-energy excited states of the FA/APTMS molecule anchored onto the surface oxygen bridge sites in close proximity to the OVs.

Dynamical mean-field theory for molecules and nanostructures.

Dynamical mean-field theory (DMFT) has established itself as a reliable and well-controlled approximation to study correlation effects in bulk solids and also two-dimensional systems. In combination with standard density-functional theory (DFT), it has been successfully applied to study materials in which localized electronic states play an important role. It was recently shown that this approach can also be successfully applied to study correlation effects in nanostructures.

The quantum magnetism of individual manganese-12-acetate molecular magnets anchored at surfaces.

The high intrinsic spin and long spin relaxation time of manganese-12-acetate (Mn(12)) makes it an archetypical single molecular magnet. While these characteristics have been measured on bulk samples, questions remain whether the magnetic properties replicate themselves in surface supported isolated molecules, a prerequisite for any application. Here we demonstrate that electrospray ion beam deposition facilitates grafting of intact Mn(12) molecules on metal as well as ultrathin insulating surfaces enabling submolecular resolution imaging by scanning tunneling microscopy.

A DFT + DMFT approach for nanosystems.

We propose a combined density-functional-theory-dynamical-mean-field-theory (DFT + DMFT) approach for reliable inclusion of electron-electron correlation effects in nanosystems. Compared with the widely used DFT + U approach, this method has several advantages, the most important of which is that it takes into account dynamical correlation effects. The formalism is illustrated through different calculations of the magnetic properties of a set of small iron clusters (number of atoms 2 ≤ N ≤ 5).