We present a theoretical study on the interaction between high-intensity electric fields and quantum well width modulation in an asymmetric GaAsSb/GaAs Morse quantum well. The gradual change in antimony concentration creates a position-dependent effective mass and highly asymmetric potential. Solving the effective mass Schro & uml;dinger equation with the finite-element method shows that narrower wells produce blue shifts and stronger confinement of heavy-hole wavefunctions. Under strong electric fields, bound states evolve into quasi-bound resonances, the enabling calculation of tunneling rates and carrier lifetimes. The Stark effect reveals asymmetry: positive fields shift energy levels downward, while negative fields enhance localization and strengthen both linear and third-order nonlinear optical responses. Combined control of well width and electric field allows precise tuning of energy spectra, tunneling dynamics, and optical nonlinearities. These findings provide insights for designing field-tunable optoelectronic devices and highlight the promise of asymmetric Morse quantum wells for enhanced performance under reverse-bias conditions.
We investigate the emergence and manipulation of topological phases in monolayer jacutingaite Pt2HgSe3 by modeling its low-energy electronic structure with an effective Kane-Mele Hamiltonian subjected to electrostatic gating and time-periodic irradiation. This material provides an ideal platform for such a study, as its large intrinsic spin-orbit coupling (SOC) stabilizes a robust quantum spin Hall phase with an experimentally accessible bulk gap. Rather than relying on momentum-resolved probes or explicit edge-state calculations, we demonstrate that the topological nature of the system can be inferred entirely from the structure of the electronic density of states (DOS), focusing on the number, separation, and magnitude of spectral discontinuities. These discontinuities arise from band extrema and gap openings induced by SOC and light-driven band renormalization. In particular, a quantum spin Hall phase is characterized by fewer than two closely spaced steps in the DOS, while the absence of any pronounced features near the chemical potential signals a semimetallic regime. The appearance of two well-separated discontinuities marks a fully gapped phase, which may correspond either to a trivial band insulator or to a quantum Hall insulator; these two cases are unambiguously distinguished by the relative heights of the DOS steps, reflecting their underlying band degeneracies. By establishing a direct correspondence between topological phases and simple, experimentally measurable DOS features, our work provides a transparent and broadly applicable framework for identifying topological order in driven two-dimensional materials without requiring edge-sensitive measurements.
Based on the recent synthesis of two-dimensional (2D) 1T-phase GeO2, the piezoelectric and thermoelectric properties of a Janus GeSO monolayer were systematically investigated using first-principles calculations. Compared to its 1T-GeO2 counterpart, the GeSO monolayer exhibits a direct band gap of 1.476 eV, distinct Raman spectrum, strong visible-light optical absorption, pronounced in-plane and out-of-plane piezoelectric response, and a small exciton binding energy. Owing to its small effective mass and deformation potential, the electron mobility is significantly higher than the hole mobility. Furthermore, the presence of heavy sulfur atoms in the asymmetric Janus structure suppresses phonon group velocity while enhancing anharmonic scattering, leading to a low thermal conductivity of 2.92 W/mK. At 550 K and under an achievable electron concentration of 2.46 & times;1013 cm-2, a notable n-type thermoelectric figure of merit (ZT) of 0.52 is obtained. These results demonstrate the promising potential of the Janus GeSO monolayer for applications in piezoelectric and low-temperature thermoelectric devices.
SF6 decomposition gas sensors are key devices for detecting the insulation status of electrical equipment. This manuscript proposes using Cun, Pdn, and Rhn(n = 1-3) clusters modified HfSe2 monolayers to detect three SF6 decomposition gases (SO2, SOF2, and SO2F2). To study the application of metal cluster-doped two-dimensional nanomaterials in gas sensors, density functional theory (DFT) calculations are used to investigate their adsorption properties, sensitivity, and electronic behavior. The adsorption mechanisms and electronic properties of target gases on the modified substrates are systematically studied through DFT analysis of adsorption energy, density of states, and deformation charge density. The results show that TMnclusters enhance the reactivity of HfSe2 surfaces, leading to varying improvements in conductivity and adsorption capacity. The research results confirm the applicability of Cun-, Pdn-, and Rhn-doped HfSe2 monolayers for detecting SF6 decomposition gases. This analysis is of great significance for exploring the application of HfSe2-based gas sensors as SF6 decomposition gas detectors in the insulation monitoring of electrical equipment.
Water adsorption at metal interfaces influences elementary steps in corrosion, electrocatalysis, and heterogeneous catalysis under aqueous or humid conditions. In this work, H2O adsorption on the (100) and (110) surfaces of Co, Ni, Pd, and Pt is studied using spin-polarized density functional theory within the PAW-PBE framework. Adsorption energies, optimized geometries, metal-oxygen distances, and spin-resolved d-band centers are analyzed to assess the influence of metal type, surface orientation, and spin polarization. The results show that spin polarization significantly stabilizes adsorption on magnetic 3d metals, revealing the limitations of the classical d-band center model for spin-polarized surfaces. An extended description using two spin-resolved d-band centers, epsilon up arrow d and epsilon down arrow d, is required to capture the observed trends. Co(100) and Co(110) exhibit the strongest water binding, while Pt surfaces show the weakest adsorption. A clear correlation is found between the position of the d-band center and adsorption strength, and the on-top site is identified as the most favorable adsorption configuration.
The study of Majorana fermions offers application potential for quantum information processing and quantum computing, particularly in enhancing qubit stability and resistance to noise. Here, we theoretically investigate the magnetic field control of the transport properties of helical Majorana edge mode (HMEM) in a hybrid structure. The structure is composed of an antiferromagnetic quantum spin Hall insulator (AFQSHI) and a topological superconductor (TSC), along with a cavity and a Josephson junction. Within a lattice Bogoliubovde Gennes (BdG) Hamiltonian, we employ the nonequilibrium Green's function method to compute the band structure and the scattering coefficients. The variations in the scattering coefficients can serve as a basis for determining changes in the transport paths. The study shows that as the chemical potential varies, the transmission coefficient transitions from total reflection to total tunneling. As the magnetic field changes, the Josephson junction undergoes a topological phase transition, which induces a zero-energy Majorana bound state in the cavity. Furthermore, by tuning the geometry of the TSC region, we can controllably modify the resonant tunneling between this zero-energy state and the edge of the HMEM, in the nontrivial phase of the Josephson junction. The results demonstrate that tuning the magnetic flux, chemical potential and TSC geometry enables controlled manipulation of the propagation paths of HMEM. This provides a feasible theoretical route for the functional design of topological quantum devices based on Majorana fermions.
Scanning gate microscopy technique as well as standard magnetotransport measurements were used to investigate peculiarities of random telegraph noise in field effect transistors made of doped InAs nanowires at helium (T = 4.2 K) temperatures. Using scanning gate microscopy technique we demonstrate the possibility of allocation of Coulomb charge traps causing random telegraph noise in InAs nanowires. Experimental investigations of magnetotransport show the importance of the Coulomb interaction of an electron capture by trap and nearby positioned resonance scatterer inside the nanowire on the amplitude of the conductance oscillations of random telegraph noise. The influence of presence of the random telegraph noise signal in magnetoconductance data on correct extraction of fractal dimension of Brownian motion of magnetoconductance curve is investigated as well.
Low-energy fermionic excitations in two-dimensional materials deviate from the conventional Schr & ouml;dinger description and are instead governed by Dirac equations. Such Dirac fermions give rise to a variety of unconventional quantum phenomena that have no direct analogues in traditional condensed matter systems. Among these materials, graphene and transition metal dichalcogenides (TMDs) represent two prototypical platforms, hosting massless and massive Dirac particles, respectively, and exhibiting rich electronic, optical, and valley dependent properties. Here we review the effect of the quantum confinement in these two-dimensional hexagonal materials that provides a powerful route to enhance Coulomb interactions and stabilizing correlated quantum states. In graphene-and TMD-based quantum dots and other nanostructures, externally imposed confinement leads to discrete levels or quantized subbands, where interaction effects are strongly amplified. In twisted van der Waals heterostructures, the moir & eacute; superlattices generate emergent confinement and induce nontrivial band topology, giving rise to a wealth of novel phenomena. More generally, reduced dimensionality and spatial localization in two-dimensional materials promote a diverse range of correlated states. Recent experimental and theoretical advances highlight the central role of confinement in shaping quantum behavior and reveal new opportunities for applications based on these states. In this review, we provide an overview of recent progress in confinement-induced correlated phenomena in two-dimensional materials from both theoretical and experimental perspectives.
Altermagnets represent an emerging class of collinear magnetic materials characterized by zero net magnetization yet exhibiting spin splitting even in the absence of spin-orbit coupling, making them highly attractive for next-generation spintronic and magnetoelectric devices. In this work, we report a comprehensive investigation of the structural, magnetic, electronic, and transport properties of the Ca(CoO)2 monolayer. The system adopts a square lattice and is confirmed to be dynamically, mechanically, and thermodynamically stable. It stabilizes in an antiferromagnetic ground state, lying 280 meV below the ferromagnetic state, and exhibits semiconducting behavior with a band gap of 0.96 eV and a notable spin splitting of 0.36 eV. Mechanically, the monolayer shows flexible characteristics, while magnetically, it possesses out-of-plane magnetic anisotropy. Notably, we find a high piezoelectric coefficient d31 = 3.51, along with a significant anomalous Hall conductivity of -36 S/cm, underscoring its promise for spintronic applications. Furthermore, the system demonstrates strong thermoelectric potential, with a large Seebeck coefficient of 1.5 mV/K at 300 K and a high power factor of 0.7 & times; 1011 Wm- 1K- 2s- 1 at 500 K. Together, these results establish the Ca(CoO)2 monolayer as a versatile multifunctional altermagnetic material.
The helical edge states of two-dimensional topological insulators, which carry electrons with opposite spins, have been confirmed by various experiments. Although the influences of spin-preserving and spin-flipping tunneling processes on the transport properties of helical edge states have been studied both experimentally and theoretically, quantitatively determining the spin-preserving and spin-flipping tunneling strengths between the two helical edge channels remains unresolved. In this work, the average current, differential conductance, and finite-frequency shot noise of electron transport through a topological insulator quantum well involving spin-preserving and spin-flipping tunneling processes are studied. It is demonstrated that the positions of the average current step and the differential conductance peak cannot be used to determine the inter-edge spin-preserving and spin-flipping tunneling strengths, as these are strongly influenced by temperature and depend significantly on the applied bias voltage. In contrast, the positions of the finite-frequency shot noise peaks, which are only slightly affected by temperature and are not sensitive to the magnitude of the applied bias voltage, can be used to quantitatively determine these strengths. Therefore, the positions of the finite-frequency shot noise peaks provide an alternative method to quantitatively determine the inter-edge spin-preserving and spin-flipping tunneling strengths.
With the advancement of society, increasing attention has been directed toward hydrogen energy due to environmental pollution and the depletion of fossil fuels. In this work, a total of 84 heterostructures combining III-VI and III-V compounds are systematically investigated using first-principles calculations, among which five are found to be stable van der Waals (vdW) heterostructures.The stability of these heterostructures is comprehensively evaluated, revealing a periodic trend in formation and binding energies with respect to the atomic number of the III-V component. In particular, GaAs/InSe-TL1 is identified as a promising photocatalyst with a band gap of 1.61 eV and a Delta G value of 0.21 eV. Compared with the corresponding individual monolayers, the heterostructure exhibits significantly enhanced photocatalytic performance.Overall, this study systematically explores the stability, electronic band structures, and photocatalytic potential of vdW heterostructures formed by III-VI and III-V compounds.
We present a comprehensive theoretical study of strain-engineered quantum transport in monolayer tungsten diselenide (WSe2) in the presence of an electrostatic scalar potential. By incorporating strain effects within a low-energy Dirac framework, we analyze their impact on spin-and valley-resolved transmission, conductance, and polarization. The applied potential barrier partitions the system into three distinct regions, allowing for an analytical derivation of the wave functions in each domain. Enforcing continuity conditions at the interfaces yields exact expressions for the transmission and reflection amplitudes. The transmission probability is evaluated from the corresponding current densities, while the conductance is obtained using the Landauer-B & uuml;ttiker formalism, enabling a quantitative determination of spin and valley polarizations. Our numerical analysis reveals that strain acts as a powerful tuning parameter that reshapes the electronic dispersion and strongly modifies transport characteristics. In particular, the transmission and conductance exhibit pronounced oscillatory behavior driven by quantum interference and resonant tunneling mechanisms. More importantly, both spin and valley polarizations display substantial and highly controllable variations as functions of strain, barrier height, and incident energy. These results demonstrate that strain and electrostatic engineering provide an efficient and versatile platform for manipulating spin-valley degrees of freedom in WSe2. The ability to tailor polarization and interference effects suggests promising opportunities for the design of next-generation spintronic, valleytronic, and optoelectronic devices based on two-dimensional transition-metal dichalcogenides.
Two-dimensional GaN has significant promise for optoelectronic device applications owing to its high breakdown electric field and excellent electron mobility. It is crucial to enhance its electronic and optical properties for the demands in future optoelectronic devices. This work employed first-principle calculations to study the electronic structures and optical properties in pristine two-dimensional monolayer GaN and its N-vacancy, Ga-vacancy and Ga-N vacancy systems. The stability of the pristine two-dimensional monolayer GaN and its vacancy defect systems is analyzed through formation energy calculations. The results indicate that the Ga-N vacancy system has the lowest formation energy, making it the most readily synthesized. Ga-vacancy introduce defect levels between the conduction band and the valence band of two-dimensional GaN that result in p-type semiconductor characteristics, while N-vacancy lead to n-type characteristics. The calculated band gaps of the N-vacancy, Ga-vacancy, and Ga-N vacancy systems are smaller than that in pristine monolayer GaN. The emergence of defect levels facilitates improvements in electron mobility and photo-response capabilities. The absorption spectra of all vacancy systems demonstrate red shift, and their absorption coefficients in the low energy region exceed those of pristine two-dimensional GaN. This results suggests that the formation of N, Ga, and Ga-N vacancies can effectively enhance the visible light absorption capacity of two-dimensional GaN.
We investigate the interplay between spatial localization and coherent quantum state transfer (QST) in finite one-dimensional Aubry-Andr & eacute; chains within a source-channel-receiver architecture. While the metal-insulator transition at the critical potential strength lambda(c) = 2 formally separates extended from localized eigenstates, our numerical analysis reveals a significant degradation of transport efficiency well before this threshold. In the regime 1 less than or similar to lambda < 2, we identify a dynamic transport crossover where the state transfer fidelity collapses despite the persistence of spatially extended eigenstates. By comparing the participation ratio with the Thouless energy, we demonstrate that this transport breakdown is not driven by wave-packet confinement, but is instead a consequence of spectral fragmentation and a strongly suppressed effective transport velocity. Furthermore, we evaluate the spectral correlation between boundary sites as a static diagnostic for transport robustness. Our results indicate that while the phase-averaged band-center mode (E-0 = 0) retains substantial spectral connectivity up to the vicinity of the critical point, slightly detuned states (E-0 not equal 0) undergo a rapid suppression of boundary correlations for lambda greater than or similar to 1. These findings highlight that spatial delocalization is a necessary but insufficient condition for high-fidelity communication in aperiodic channels. Consequently, we conclude that optimal QST in finite quasiperiodic systems is achieved deep within the extended regime (lambda less than or similar to 1), requiring weak system-lead coupling and near-resonant injection at the band center.
Perfluoroisobutyronitrile (C4F7N) is a promising eco-friendly SF6 alternative, requiring reliable decomposition monitoring. Using first-principles calculations, we systematically investigated transition metal (Au, Ag, Pt, Pd)-doped GeS monolayers for sensing characteristic by-products (CF4, COF2, C2N2, CF3CN). Results reveal that metal doping facilitates a transition from physisorption to chemisorption via robust d-orbital hybridization. Notably, Pt-doped GeS exhibits superior adsorption energy (-2.184 eV). Differentiated work function modulations provide a theoretical basis for multi-channel sensor arrays. Modified GeS emerges as a high-performance candidate for real-time monitoring of C4F7N-insulated equipment.
A crucial first stage in the hydrogen economy is the creation of a non-precious HER catalyst that is highly conductive, durable, and effective. To improve HER activity, we have computationally screened a number of transition metal (TM) atoms contained in two-dimensional Nb2S2C, including Rh, Ir, Cd, Cu, and Pt. Our findings demonstrate that substitutional doping of monolayer Nb2S2C with a single atom Ir resulted in potential HER catalysts with a reduced Gibbs free energy of 0.34 eV. The process of HER was also examined using nudged elastic band simulations. Each phase's response rate is regulated by the Tafel step, whose maximal activation barrier of 1.60 eV affects the assessment of HER activity. Ir-Nb2S2C's thermal and structural stability have been confirmed via ab initio Molecular Dynamics (MD) simulations. By synthesizing TM's anchored Nb2S2C under carefully monitored experimental conditions, it is possible to create extremely efficient H2 generation catalysts.
We study field-controlled spin-valley transport in monolayer MoS2 through a single electrostatic barrier and a uniform off-resonant elliptically polarized irradiation. Starting from the massive Dirac Hamiltonian with intrinsic spin-orbit coupling, we use a high-frequency Floquet expansion to obtain an effective static model with a laser-renormalized mass (gap) term. We solve the scattering problem by spinor matching and derive the exact analytic expression for the transmission. The numerical results show that the drive tunes both the spin-valley-dependent propagation threshold inside the barrier and the Fabry-P & eacute;rot phase, creating controllable pass/stop bands. By varying both the laser intensity (amplitude) and the polarization shape, we show that the same junction can be switched between broadband valley filtering and resonance-selective operation, and the valley contrast remains visible in the Landauer conductance. Our findings establish an efficient route for realizing optically reconfigurable valleytronic and spintronic functionalities in MoS2.
In this work, we theoretically investigate the time-dependent quantum uncertainties and Fisher information for charge carriers in monolayers of two-dimensional anisotropic semiconductors described by the effective mass approximation in the presence of a perpendicularly applied time-dependent magnetic field B(t). Using the Lewis-Riesenfeld dynamical invariant method, we obtain the exact wave functions of the system, which allows us to derive analytical expressions for the position and momentum uncertainties (Delta(x, y,) Delta p(x,y)) and for the Fisher information (F-x,F-y, F-px,F-py) in terms of an auxiliary function rho(t) that obeys a Milne-Pinney-like nonlinear differential equation. We analyze three distinct regimes of the temporal dependencies of magnetic-field variations, corresponding to exponential, oscillatory, and linear decay of the cyclotron frequency. Our results for phosphorene and arsenene reveal a rich phenomenology, including squeezing in position and momentum observables, the manifestation of which is strongly influenced by the effective mass anisotropy and the temporal profile of the field. We demonstrate that the precision in determining the electron's position and momentum is inherently directional, reflecting the material's anisotropy. Additionally, we establish a new upper bound for the product of the total Fisher information in position and momentum spaces, <= F-r(t)F-p(t) <= 4[(m(x)/m(y))(1/2) + (m(y)/mx)(1/2)](2), where m(x,y) indicates the charge carrier effective masses along the {x, y} crystallographic direction, which generalizes the known result for isotropic systems (m(x) = m(y)) and proves to be universal for the investigated fields, depending only on the material's effective mass ratio.
We present a theoretical investigation of surface magnon-polaritons in a hybrid heterostructure composed of two semi-infinite magnonic crystals (antiferromagnetic superlattices) separated by a spacer layer, with graphene sheets located at the interfaces. Two configurations are considered, corresponding to magnetic and nonmagnetic spacer layers. The analysis is performed within the framework of Maxwell's electromagnetic theory using an effective-medium approach, while graphene is described by its frequency-dependent surface conductivity including a constant phenomenological scattering rate. The dispersion relations of transverse-electric (TE) polarized surface modes are derived and numerically evaluated for different values of the graphene Fermi energy controlled via electronic doping.The spectra are symmetric with respect to the wave vectork, indicating reciprocal behavior and preservation of time-reversal symmetry.We show that graphene strongly modifies the dispersion characteristics of surface magnon-polaritons through electromagnetic coupling between magnons and charge carriers. In the vicinity of the resonance frequencies, multiple weakly dispersive branches with low group velocity are observed, indicating strong field localization. Increasing the Fermi energy leads to further reduction of the group velocity and compression of the mode spectrum at large wave vectors. A key result of this work is the behavior at small wave vectors, where an inter-branch frequency gap exists between low-and high-frequency modes at low doping levels. As the Fermi energy increases, this gap progressively decreases and eventually closes at E(1) F = E(2) F = 1.0eV signaling strong hybridization between magnonic and plasmonic excitations. This transition gives rise to fast-propagating hybrid modes with significantly enhanced group velocity. For a nonmagnetic contact slab, both acoustic-like and optical-like localized modes are identified, and the dependence of their wavevector gaps on graphene doping is discussed. These findings demonstrate that graphene provides an efficient and tunable platform for controlling the dispersion, localization, and propagation of surface magnon-polaritons, with potential applications in terahertz magnonic and plasmonic devices.
In this study, we derive analytical results for two-dimensional single-layer orthorhombic monochalcogenides in the presence of substrate-induced electron surface optical (SO) phonon interactions. The Lee-Low-Pines variational approximation within conventional polaron theory is employed to examine substrate effects within a low-energy effective model. Based on this framework, we construct a phonon-dressed Hamiltonian to elucidate the influence of SO phonons on the electronic band structure. We further investigate the bulk photovoltaic effect, focusing on the shift-current mechanism by which illumination generates a coherent zero-bias direct current. Our results demonstrate that substrate-induced SO phonons not only renormalize the band structure of inversion symmetry-breaking systems but also give rise to a stable photocurrent under light exposure, corresponding to a phonon-assisted second-order nonlinear optical response. These findings reveal that the shift current is highly sensitive to structural modifications, offering a viable route for tuning photovoltaic performance in two-dimensional materials.
