Asymmetric dynamic behaviors of magnetic domain wall in trapezoid-cross-section nanostrip

Field-driven magnetic domain wall propagation in ferromagnetic nanostrips with trapezoidal cross section has been systematically investigated by means of micromagnetic simulation. Asymmetric dynamic behaviors of domain wall, depending on the propagation direction, were observed under an external magnetic field. When the domain walls propagate in the opposite direction along the long axis of the nanostrip, the Walker breakdown fields as well as the average velocities are different. The asymmetric landscape of demagnetization energies, which arises from the trapezoidal geometry, is the main origin of the asymmetric propagation behavior. Furthermore, a trapezoid-cross-section nanostrip will become a nanotube if it is rolled artificially along its long axis, and thus a two-dimensional transverse domain wall will become a three-dimensional one. Interestingly, it is found that the asymmetric behaviors observed in two-dimensional nanostrips with trapezoidal cross section are similar with some dynamic properties occurring in three-dimensional nanotubes.

Probing the upper band gap of atomic rhenium disulfide layers

Here,we investigate the ultrafast carrier dynamics and electronic states of exfoliated ReS2 films using time-resolved second harmonic generation(TSHG)microscopy and density functional theory(DFT)calculations.The second harmonic generation(SHG)of layers with various thicknesses is probed using a 1.19-eV beam.Up to~13 nm,a gradual increment is observed,followed by a decrease caused by bulk interferometric light absorption.The addition of a pump pulse tuned to the exciton band gap(1.57 eV)creates a decay-to-rise TSHG profile as a function of the probe delay.The power and thickness dependencies indicate that the electron–hole recombination is mediated by defects and surfaces.The two photon absorptions of 2.38 eV in the excited state that are induced by pumping from 1.57 to 1.72 eV are restricted because these transitions highly correlate with the forbidden d–d intrasubshell orbital transitions.However,the combined usage of a frequency-doubled pump(2.38 eV)with wavelength-variant SHG probes(2.60–2.82 eV)allows us to vividly monitor the variations in TSHG profiles from decay-to-rise to rise-to-decay,which imply the existence of an additional electron absorption state(s-orbital)at an approximate distance of 5.05 eV from the highest occupied molecular orbital states.This observation was critically examined by considering the allowance of each electronic transition and a small upper band gap(~0.5 eV)using modified DFT calculations.

Single-crystalline-level properties of ultrathin SrRuO_(3) flexible membranes with wide and clean surface

Transferring single-crystalline(SC)membranes to flexible substrates has been increasingly studied,enabling emerging functionality and enhanced performance of various devices.A commonly used support-assisted transfer process inevitably leaves dirty residue on material surfaces,limiting the further development of surface-related applications.Here,we scale down the thickness of flexible SC SrRuO_(3)(SRO)membranes to 15 nm with a clean surface area of 2.5×2.5 mm^(2).This is accomplished by making the polyethylene terephthalate(PET)substrate surface hydrophilic via oxygen plasma treatment,thereby reducing the surface tension.The ultrathin,clean,wide,and flexible SC SRO membranes guarantee a high transmittance of up to 60%,a low resistivity of 10^(−4)−10^(−3)Ωcm at room temperature,and band ferromagnetism below 150 K with a high magnetic moment of~0.5μB/Ru at 10 K.The SC-level properties of our SRO membranes imply their potential use in state-of-the-art platforms for next-generation electronics and energy devices.

Hybridization of different types of exceptional points

A large number of different types of second-order non-Hermitian degeneracies called exceptional points(EPs)were found in various physical systems depending on the mechanism of coupling between eigenstates.We show that these EPs can be hybridized to form higher-order EPs,which preserve the original properties of the initial EPs before hybridization.For a demonstration,we hybridize chiral and supermode second-order EPs,where the former and the latter are the results of intra-disk and inter-disk mode coupling in an optical system comprised of two Mie-scale microdisks and one Rayleigh-scale scatterer.The high sensitivity of the resulting third-order EP against external perturbations in our feasible system is emphasized.

Time-resolved photoemission of infinitely periodic atomic arrangements:correlation-dressed excited states of solids

A theory of the time-resolved photoemission spectroscopy(TRPES)is developed,which enables to explore the real-time electron dynamics of infinitely periodic crystalline solids.In the strongly correlated electron systems NiO and CuO,the early-stage dynamics of the valence band edge are found to be sharply contrasted between those in the spectra of TRPES.This provides a new dynamical insight to the Zaanen–Sawatzky–Allen(ZSA)classification scheme of correlated insulators and makes us assert that NiO dynamically behaves like the Mott–Hubbard insulator(MHI)and CuO like the charge transfer insulator(CTI).In the two-dimensional carbon layer graphene,the real-time electron dynamics of quantum-phase-dressed excited states,i.e.,due to the Berry phase and the pseudospin correlation,are investigated in an unprecedented way through the time-resolved angle-resolved photoemission spectroscopy(TR-ARPES).In particular,the dephasing dynamics of optically doped electrons and holes in the massless Dirac band,accompanying a field-induced gliding of the Dirac cone,are discovered.

Impact of non-Hermitian mode interaction on inter-cavity light transfer

Understanding inter-site mutual mode interaction in coupled physical systems is essential to comprehend large compound systems,as this local interaction determines the successive multiple inter-site energy transfer efficiencies.In the present study,we demonstrate that only the non-Hermitian coupling can correctly account for the light transfer between two coupled optical cavities.We also reveal that the non-Hermitian coupling effect becomes crucial as the system dimension decreases.Our results provide important insight for handling general-coupled devices in the subwavelength regime.

Vertically aligned nanocomposite films by self-assembled epitaxial nucleation for super-broadband transparent conductors

Designing super-broadband transparent conductors is challenging because of the exclusive nature of conductivity and infrared transmittance.Here,using a one-step process,we created vertically aligned nanocomposite conducting films with high transparency across a super-broad wavelength range.Vertically aligned transparent Ba_(3)V_(2)O_(8)nanocolumns with lateral-100-nm widths enable high transmittance(>50%,even at a 4-μm wavelength)for all incident light and outperform that of Sn-doped In_(2)O_(3),while the conducting SrVO_(3)matrix retains low resistivity(<0.56 mΩcm at room temperature).A combined study of scanning transmission electron microscopy,scattering scanning nearfield infrared microscopy,and X-ray diffraction revealed that spontaneous phase separation of Ba_(3)V_(2)O_(8)nanocolumns in a SrVO_(3)matrix film occurs via self-assembled epitaxial nucleation.Our vertically aligned nanocomposite films provide a fertile platform for next-generation optoelectronics.

Stretchable and colorless freestanding microwire arrays for transparent solar cells with flexibility

Transparent solar cells(TSCs)are emerging devices that combine the advantages of visible transparency and light-toelectricity conversion.Currently,existing TSCs are based predominantly on organics,dyes,and perovskites;however,the rigidity and color-tinted transparent nature of those devices strongly limit the utility of the resulting TSCs for realworld applications.Here,we demonstrate a flexible,color-neutral,and high-efficiency TSC based on a freestanding form of n-silicon microwires(SiMWs).Flat-tip SiMWs with controllable spacing are fabricated via deep-reactive ion etching and embedded in a freestanding transparent polymer matrix.The light transmittance can be tuned from ~10 to 55% by adjusting the spacing between the microwires.For TSCs,a heterojunction is formed with a p-type polymer in the top portion of the n-type flat-tip SiMWs.Ohmic contact with an indium-doped ZnO film occurs at the bottom,and the side surface has an Al2O3 passivation layer.Furthermore,slanted-tip SiMWs are developed by a novel solventassisted wet etching method to manipulate light absorption.Finite-difference time-domain simulation revealed that the reflected light from slanted-tip SiMWs helps light-matter interactions in adjacent microwires.The TSC based on the slanted-tip SiMWs demonstrates 8%efficiency at a visible transparency of 10% with flexibility.This efficiency is the highest among Si-based TSCs and comparable with that of state-of-the-art neutral-color TSCs based on organic–inorganic hybrid perovskite and organics.Moreover,unlike others,the stretchable and transparent platform in this study is promising for future TSCs.