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Interlayer coupling plays a critical role in tuning the electronic structures and magnetic ground states of two-dimensional materials, influenced by the number of layers, interlayer distances, and stacking order. However, its effect on the orientation of the magnetic easy axis remains underexplored. In this study, we demonstrate that interlayer coupling can significantly alter the magnetic easy-axis orientation, as shown by the magnetic easy-axis of monolayer 1T-MnSe2 tilting 67{\deg} from the z-axis, while aligning with the z-axis in the bilayer. This change results from variations in orbital occupations near the Fermi level, particularly involving nonmetallic Se atoms. Contrary to the traditional focus on magnetic metal atoms, our findings reveal that Se orbitals play a key role in influencing the easy-axis orientation and topological Chern numbers. Furthermore, we validated our conclusions by changing stacking orders, introducing charge doping, applying in-plane biaxial strains, and substituting non-metallic atoms. Our results highlight the pivotal role of interlayer coupling in tuning the magnetic properties of layered materials, with important implications for spintronic applications.

Mismatched lattice-constants at a van-der-Waals epitaxy interface often introduce in-plane strains to the lattice of the epitaxial layer, termed epitaxy-strain, where the strains do not follow the intra-layer Poisson's relation. Here, we presented the magnetic phase diagrams of the CrSe2 and CrTe2 mono- and bi-layers under epitaxy-strain up to 8 %, as predicted using density-functional-theory calculations. They show that the in-plane epitaxy-strain manipulates either the intra- or inter-layer magnetism of them. The in-plane strain varies the interlayer distance, defined using an inter-layer Poisson's ratio, which governs the inter-layer magnetism in two opposite ways depending on the in-plane magnetism. The tunability of the intra-layer magnetism is a result of competing intra-layer Cr-Cr super-exchange interactions. A graphene substrate was introduced to examine the validity of our diagrams in practice. Our work also gives a tentative explanation on the controversially reported magnetizations in CrSe2 and CrTe2 epitaxial mono- or bi-layers under epitaxy-strains.

Twisted two-dimensional bi-layers offer exquisite control on the electronic bandstructure through the interlayer rotation and coupling, enabling magic-angle flat-band superconductivity and moir\'e excitons. Here, we demonstrate how analogous principles, combined with large anisotropy, enable extreme control and manipulation of the photonic dispersion of phonon polaritons (PhPs) in van der Waals (vdW) bi-layers. We experimentally observe tunable topological transitions from open (hyperbolic) to closed (elliptic) dispersion contours in twisted bi-layered {\alpha}-MoO3 at photonic magic angles, induced by polariton hybridization and robustly controlled by a topological quantity. At these transitions the bilayer dispersion flattens, exhibiting low-loss tunable polariton canalization and diffractionless propagation with resolution below {\lambda}0/40. Our findings extend twistronics and moir\'e physics to nanophotonics and polaritonics, with great potential for nano-imaging, nanoscale light propagation, energy transfer and quantum applications., Comment: Nature, in press

We observe the signature of zero-field ground-state skyrmions in BiSb topological insulator / MnGa bi-layers by using the topological Hall effect (THE). We observe a large critical interfacial Dzyaloshinskii-Moriya-Interaction energy (5.0 pJ/m) at the BiSb/MnGa interface that can be tailored by controlling the annealing temperature of the MnGa template. The THE was observed at room temperature even under absence of an external magnetic field, which gives the strong evidence for the existence of thermodynamically stable skyrmions in MnGa/BiSb bi-layers. Our results will give insight into the role of interfacial DMI tailored by suitable material choice and growth technique for generation of stable skyrmions at room temperature.

Our previous work show that in the molecular cluster regime, the band blue shift associated with cluster growth can be understood by a model that assume electrons are confined to a spherical potential well and the clusters are made of some basic units. A formula is given for the lowest excited electronic state energy. This expression contains an electron-hole-pair (EHP) delocalization constant as an adjustable parameter which, however, can be anchored to a definite value through the known transition energy at the spectra turn-around point. We also proposed symmetry and probability principles in molecular cluster growth range to explain the molecular cluster electron absorption spectra turn-around phenomena and unusual isotopic properties of small silver bromide clusters. In this paper, based on systematical review of Quasi-Elastic Light Scattering (QELS), Fourier-transform infrared spectroscopy (FTIR) and Direct Laser Desorption Mass Spectra (DLD-MS) experiments of silver bromide clusters prepared via the electroporation of vesicles, we show how the symmetry and probability principles in molecular cluster growth range can be used to explain the lager silver bromide molecular cluster formation in a bilayer formation mechanism. The turn round curve of energy gap vs confine sphere size had been proved to be a right curve to describe the molecular cluster quantum confinement behavior. We also defined Electron Delocalized Status (EDS), Electron Localized Status (ELS), and EDS/ELS switch or quantum confinement switch (QCS) in the quantum confine system. These studies pave the theoretical and technical ways for advanced device technology continue shrink and new concept device generation in the atomic and molecular cluster size range., Comment: 32 pages, 11 figures, 2 tables

We investigate different mechanical effects which accompany the nerve pulse propagation by using mathematical modeling. The propagation process is composed by three connected phenomena: (i) the action potential (electrical signal) which is usually considered when nerve pulses are discussed, (ii) the mechanical wave propagating in the biomembrane and (iii) the pressure wave in the axoplasm inside the axon. The main goal of the present study is to investigate numerically how the mechanical wave is generated by the action potential and how the characteristics of the system are reflected in the emerging wave ensemble. %the existence and characteristics of the mechanical wave influence the parameters of an action potential part of the wave ensemble. The key characteristics for the coupled model system are: (i) the velocity of the peak of the mechanical pulse is associated with the velocity of the action potential regardless of the sound velocity value in the lipid bi-layer, (ii) the velocity of the front and the shape of the mechanical wave depends on sound velocity in the lipid bi-layer, (iii) the shape of the mechanical wave can have an effect on the velocity and shape of the action potential., Comment: The Tenth IMACS International Conference on Nonlinear Evolution Equations and Wave Phenomena: Computation and Theory, March 29 - April 01, 2017. Georgia, USA

We study the scattering of a long longitudinal radiating bulk strain solitary wave in the delaminated area of a two-layered elastic structure with soft (`imperfect') bonding between the layers within the scope of the coupled Boussinesq equations. The direct numerical modelling of this and similar problems is challenging and has natural limitations. We develop a semi-analytical approach, based on the use of several matched asymptotic multiple-scale expansions and averaging with respect to the fast space variable, leading to the coupled Ostrovsky equations in bonded regions and uncoupled Korteweg-de Vries equations in the delaminated region. We show that the semi-analytical approach agrees well with direct numerical simulations and use it to study the nonlinear dynamics and scattering of the radiating solitary wave in a wide range of bi-layers with delamination. The results indicate that radiating solitary waves could help us to control the integrity of layered structures with imperfect interfaces., Comment: 17 pages, 10 figures. Accepted for publication in Chaos (2017)

Here, we investigated the influence of grain formation on the magnetization reversal of SmCo5/Co at low temperature. A set of SmCo5/Co bi-layer samples were fabricated under identical conditions on MgO(100) and glass substrates with a Cr underlayer. Analysis of each magnetic layer by an Atomic Force Microscope (AFM) reveals that MgO(100) results small and uniform grain formation of 23 nm in contrast to 57 nm on glass, and x-ray diffraction studies show that the sample on MgO(100) has high crystallinity with SmCo5(11 0) phase. At room temperature, both samples exhibit good hard magnetic properties with coercivity (HC) of 13.2 kOe and 12.5 kOe, and energy products (BH)max of 14.5 MGOe and 5.3 MGOe for samples on MgO(100) and glass, respectively. Low temperature hysteresis measurements show an exchange decoupling at low temperatures for the sample on glass, and this is due to the formation of large grains on glass that reduces the effective inter-grain exchange coupling between phases., Comment: 13 pages, 5 figures

We show that obliquely-incident, transversely-magnetic-polarized plane waves can be totally transmitted (with zero reflection) through epsilon-near-zero (ENZ) bi-layers characterized by balanced loss and gain with parity-time (PT) symmetry. This tunneling phenomenon is mediated by the excitation of a surface-wave localized at the interface separating the loss and gain regions. We determine the parameter configurations for which the phenomenon may occur and, in particular, the relationship between the incidence direction and the electrical thickness. We show that, below a critical threshold of gain and loss, there always exists a tunneling angle which, for moderately thick (wavelength-sized) structures, approaches a critical value dictated by the surface-wave phase-matching condition. We also investigate the unidirectional character of the tunneling phenomenon, as well as the possible onset of spontaneous symmetry breaking, typical of PT-symmetric systems. Our results constitute an interesting example of a PT-symmetry-induced tunneling phenomenon, and may open up intriguing venues in the applications of ENZ materials featuring loss and gain., Comment: 11 pages, 12 figures (minor revisions in the text and figures)

We study the D3/probe D5 system with two domain wall hypermultiplets. The conformal symmetry can be broken by a magnetic field, B, (or running coupling) which promotes condensation of the fermions on each individual domain wall. Separation of the domain walls promotes condensation of the fermions between one wall and the other. We study the competition between these two effects showing a first order phase transition when the separation is ~ 0.56 lambda^1/4 B^-1/2. We identify extremal brane configurations which exhibit both condensations simultaneously but they are not the preferred ground state., Comment: 5 pages, 4 pdf figures, added references

The effect of etching time on the statistical properties of the hydrophilic surface of SiO_2/TiO_2/Glass nano bi-layer has been studied using Atomic Force Microscopy (AFM) and stochastic approach based on the level crossing analysis. We have created a rough surface of the hydrophilic SiO_2/TiO_2 nano bi-layer system by using 26% Potassium Hydroxide (KOH) solution. Measuring the average apparent contact angle assessed the degree of hydrophilicity and the optimum condition was determined at 10 min etching time. Level crossing analysis based on AF images provided deeper insight into the microscopic details of the surface topography. For different etching time, it has been shown that the average frequency of visiting a height with positive slope behaves Gaussian for heights near the mean value and obeys power law for the heights far away from the mean value. Finally, by applying the generalized total number of crossings with positive slope, it was found that the both high heights and deep valleys of the surface are extremely effective in hydrophilic degree of the SiO_2/TiO_2/Glass nano bi-layer investigated system.

Recently, attention has been given to a system of He$^3$ bi-layers where a quantum criticality similar to the one in heavy fermion compounds has been observed [Science 317, 1356 92007)] In our previous analysis [Phys. Rev. B 79, 045112 (2007)], based on the Kondo breakdown scenario, we addressed successfully most of the features observed in that experiment. Here, we consider the activation energy $\Delta$ observed experimentally in the specific heat measurements at low temperatures in the heavy Fermi liquid phase. Within our previous study of this system, this is identified with the gap opening when the upper hybridized band is emptied due to a strong hybridization between the nearly localized first layer and the fluid second one. We discuss the successes and limitations of our approach. An additional prediction is proposed., Comment: 6 pages, 6 figures - replaced with the published version

Transformation-media designed by standard transformation-optics (TO) approaches, based on real-valued coordinate-mapping, cannot exhibit single-negative (SNG) character unless such character is already possessed by the domain that is being transformed. In this paper, we show that, for a given field polarisation, pseudo-SNG transformation media can be obtained by transforming a domain featuring double positive (or double-negative) character, via complex analytic continuation of the coordinate transformation rules. Moreover, we apply this concept to the TO-based interpretation of phenomena analogous to the tunnelling effects observable in bi-layers made of complementary epsilon-negative (ENG) and mu-negative (MNG) media, and explore their possible TO-inspired extensions and generalizations., Comment: 13 pages, 1 table, 6 figures; minor changes in the title and text

We consider the recent experiments on He3 bi-layers, showing evidence for a quantum critical point (QCP) at which the first layer localizes. Using the Anderson lattice in two dimensions with the addition of a small dispersion of the f-fermion, we modelize the system of adsorbed He3 layers. The first layer represents the f-fermions at the brink of localization while the second layer behaves as a free Fermi sea. We study the quantum critical regime of this system, evaluate the effective mass in the Fermi liquid phase and the coherence temperature and give a fit of the experiments and interpret its main features. Our model can serve as well as a predictive tool used for better determination of the experimental parameters., Comment: 15 pages, 15 figures. Submitted to PRB

We present results from an X-ray photoemission spectroscopy (XPS) study of CoFeB/MgO bi-layers where we observe process-dependent formation of B, Fe, and Co oxides at the CoFeB/MgO interface due to oxidation of CoFeB during MgO deposition. Vacuum annealing reduces the Co and Fe oxides but further incorporates B into the MgO forming a composite MgBxOy layer. Inserting an Mg layer between CoFeB and MgO introduces an oxygen sink, providing increased control over B content in the barrier., Comment: 13 pages, 3 figures

We study superconductor-ferromagnet bi-layers, not only for s-wave but also for d-wave superconductors. We observe oscillations of the critical temperature when varying the thickness of the ferromagnetic layer for both s-wave and d-wave superconductors. However, for a rotated d-wave order parameter the critical temperature differs considerably from that for the unrotated case. In addition we calculate the density of states for different thicknesses of the ferromagnetic layer; the results reflect the oscillatory behaviour of the superconducting correlations., Comment: 11 pages, 5 figures, accepted for publication in J. Phys.: Condens. Matter