arXiv subjects

Fanhao Jia

Publications and source records attributed to Fanhao Jia.

13 recordsLinked to original sources

arXiv2026

Magnetically induced Circular Photogalvanic Effect in Symmetric Two-dimensional Materials

Photocurrents that depend on the helicity of the incident light can be generated in both bulk and low-dimensional materials lacking inversion symmetry, known as the circular photogalvanic effect (CPGE). We propose that by employing a magnetic effect, the limitation on the inversion symmetry broken materials can be overcome, such that helicity-dependent photocurrent can be generated in a symmetric material, i.e., a magneto-circular photogalvanic effect (MCPGE). As a proof of principle, we elucidate the mechanism of such an MCPGE through an effective Hamiltonian of a monolayer SbH on a magnetic substrate with an adjustable magnetization. Moreover, the associated response in optical absorption is analyzed, both single-particle and excitonic, through a Bethe-Salpeter equation to describe the Coulomb interaction in excitons. Our result broadens the mechanism of CPGE and opens new opportunities for optoelectronic devices.

cond-mat.mes-hall↗

arXiv2026

Profound impacts of interlayer interactions in bilayer altermagnetic V2S2O

Two-dimensional altermagnets exhibit exceptional potential for low-power spintronics via nonrelativistic spin splitting and zero net magnetization. Here, we systematically investigate the influence of interlayer interactions on the electronic, magnetic and quantum transport properties of bilayer vanadium oxysulfide (V2S2O), a prototypical layered altermagnet, using DFT and NEGF calculations. Our results reveal that interlayer interactions predominantly modulate the p-orbital derived top valence bands, inducing a profound competitive valence band maximum position between Gamma-point pz and X/Y-point pxy orbitals, with an energy difference as small as 9 meV. Furthermore, interlayer interactions suppress the piezomagnetic effect and impose additional requirements on the type of strain for the bilayer system, compared to its monolayer counterpart. Out-of-plane external electric fields effectively weaken interlayer coupling by enlarging the energy difference of Gamma/X-Y top valence bands to 170 meV. Quantum transport simulations on a bilayer Au/V2S2O/Au two-probe device demonstrate the presence of pronounced spin current. Interlayer interactions reduce the transmission spin polarization from nearly 100% (monolayer) to 60% (bilayer) for energies above the Fermi level. Notably, gate-voltage modulation exhibits significant asymmetry in controlling charge-to-spin current conversion efficiency, originating from the out-of-plane symmetry breaking induced by the electrode geometry. Specifically, a positive gate voltage markedly enhances the contribution of the bottom layer to the overall spin polarization, while a negative gate voltage induces a marginal reduction of transmission spin polarization, attributed to the inherently weak polarization contribution of the bottom layer. These findings provide essential insights for the design and optimization of multilayer altermagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Chemical control of polymorphism and ferroelectricity in PbTiO3 and SrTiO3 monolayers and bilayers

Layers of perovskites, found in 3D materials, 2D heterostructures, and nanotubes, often distort from high symmetry to facilitate dipole polarisation that is exploitable in many applications. Using density-functional theory calculations, ferroelectricity in bilayers of the 2D materials PbTiO3 and SrTiO3 is shown to be controlled by bond breakage and formation processes that act as binary switches. These stacking-dependent processes turn on and off as a function of relaxation from high-symmetry structures and the application of biaxial strain, and their concerted rearrangements lead to low energy barriers for ferroelectric polarisation switching. Structures with symmetry intermediate between high-symmetry octahedral forms and low-symmetry ferroelectric forms are identified, allowing the intrinsic processes associated with traditional "ferrodistortive" and "antiferrodistortive" distortions of TiO6 octahedra to be identified. Ferrodistortive-mode activity is shown to be generated by the simultaneous application of two different types of curvilinear antiferrodistortive motions. In this way, four angular variabes control polarisation switching through the concerted making and breaking of chemical bonds. These subltities make the polarisation sensitive to chemical-environment and temperature effects that manipulate strain and structure, features exploitable in futuristic devices.

cond-mat.mtrl-sci↗

arXiv2025

Out-of-plane displacement of quantum color centers in monolayer h-BN

Color centers exhibiting deep-level states within the wide bandgap h-BN monolayer possess substantial potential for quantum applications. Uncovering precise geometric characteristics at the atomic scale is crucial for understanding defect performance. In this study, first-principles calculations were performed on the most extensively investigated CBVN and NBVN color centers in h-BN, focusing on the out-of-plane displacement and their specific impacts on electronic, vibrational, and emission properties. We demonstrate the competition between the {\sigma}*-like antibonding state and the {\pi}-like bonding state, which determines the out-of-plane displacement. The overall effect of vibronic coupling on geometry is elucidated using a pseudo Jahn-Teller model. Local vibrational analysis reveals a series of distinct quasi-local phonon modes that could serve as fingerprints for experimental identification of specific point defects. The critical effects of out-of-plane displacement during the quantum emission process are carefully elucidated to answer the distinct observations in experiments, and these revelations are universal in quantum point defects in other layered materials.

cond-mat.mes-hall↗

arXiv2024

Manipulating the Optical Response of TaIrTe4 Heterostructures through Band Alignment Strategy

Weyl semimetals, such as $TaIrTe_{4}$, characterized by their unique band structures and exotic transport phenomena, have become a central focus in modern electronics. Despite extensive research, a systematic understanding of the impact of heterogeneous integration on the electronic and optical properties of TaIrTe4 device remains elusive. We have carried out density functional theory combined with nonequilibrium Green's function formalism calculations for $TaIrTe_{4}/WTe_{2}$, $TaIrTe_{4}/MoTe_{2}$ and $TaIrTe_{4}/h-BN$ heterostructures, aiming to understand the manipulation of photoresponse through various band alignment strategies. The underlying impacts of interlayer interactions, charge transfer and build-in electric field on the electronic properties are carefully investigated. We design a dual-probe photodetector device to understand the overall photoresponse enhancement of the heterogeneous integration by decomposing into the specific strain, interlayer transition, band overlap and symmetry lowering mechanics. These van der Waals integrations provide an ideal platform for studying band alignment physics in self-powered optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Quasiparticle and Excitonic Structures of Few-layer and Bulk GaSe: Interlayer Coupling, Self-energy, and Electron-hole Interaction

Metal monochalcogenide GaSe is a classic layered semiconductor that has received increasing research interest due to its highly tunable electronic and optical properties for ultrathin electronics applications. Despite intense research efforts, a systematic understanding of the layer-dependent electronic and optical properties of GaSe remains to be established, and there appear significant discrepancies between different experiments. We have performed GW plus Bethe-Salpeter equation (BSE) calculations for few-layer and bulk GaSe, aiming at understanding the effects of interlayer coupling and dielectric screening on excited state properties of GaSe, and how the electronic and optical properties evolve from strongly two-dimensional (2D) like to intermediate thick layers, and to three-dimensional (3D) bulk character. Using a new definition of the exciton binding energy, we are able to calculate the binding energies of all excitonic states. Our results reveal an interesting correlation between the binding energy of an exciton and the spread of its wave function in the real and momentum spaces. We find that the existence of (nearly) parallel valence and conduction bands facilitates the formation of excitonic states that spread out in the momentum space. Thus, these excitons tend to be more localized in real space and have large exciton binding energies. The interlayer coupling substantially suppresses the Mexican-hat-like dispersion of the top valence band seen in monolayer system, explaining the greatly enhanced photoluminescence (PL) as layer thickness increases. Our results also help resolve apparent discrepancies between different experiments. After including the quasiparticle and excitonic effects as well the optical activities of excitons, our results compare well with available experimental results.

cond-mat.mtrl-sci↗

arXiv2023

Intrinsic Piezoelectric Anisotropy of Tetragonal ABO3 Perovskites: A High-Throughput Study

A comprehensive understand of the intrinsic piezoelectric anisotropy stemming from diverse chemical and physical factors is a key step for the rational design of highly anisotropic materials. We performed high-throughput calculations on tetragonal ABO3 perovskites to investigate the piezoelectricity and the interplay between lattice, displacement, polarization and elasticity. Among the 123 types of perovskites, the structural tetragonality is naturally divided into two categories: normal tetragonal (c/a ratio < 1.1) and super-tetragonal (c/a ratio > 1.17), exhibiting distinct ferroelectric, elastic, and piezoelectric properties. Charge analysis revealed the mechanisms underlying polarization saturation and piezoelectricity suppression in the super-tetragonal region, which also produces an inherent contradiction between high d33 and large piezoelectric anisotropy ratio |d33/d31|. The polarization axis and elastic softness direction jointly determine the maximum longitudinal piezoelectric response d33 direction. The validity and deficiencies of the widely utilized |d33/d31| ratio for representing piezoelectric anisotropy were reevaluated.

cond-mat.mtrl-sci↗

arXiv2022

Stacking up electron-rich and electron-deficient monolayers to achieve extraordinary mid- to far-infrared excitonic absorption: Interlayer excitons in the C3B/C3N bilayer

Our ability to efficiently detect and generate far-infrared (i.e., terahertz) radiation is vital in areas spanning from biomedical imaging to interstellar spectroscopy. Despite decades of intense research, bridging the terahertz gap between electronics and optics remains a major challenge due to the lack of robust materials that can efficiently operate in this frequency range, and two-dimensional (2D) type-II heterostructures may be ideal candidates to fill this gap. Herein, using highly accurate many-body perturbation theory within the GW plus Bethe-Salpeter equation approach, we predict that a type-II heterostructure consisting of an electron rich C3N and an electron deficient C3B monolayers can give rise to extraordinary optical activities in the mid- to far-infrared range. C3N and C3B are two graphene-derived 2D materials that have attracted increasing research attention. Although both C3N and C3B monolayers are moderate gap 2D materials, and they only couple through the rather weak van der Waals interactions, the bilayer heterostructure surprisingly supports extremely bright, low-energy interlayer excitons with large binding energies of 0.2 ~ 0.4 eV, offering an ideal material with interlayer excitonic states for mid-to far-infrared applications at room temperature. We also investigate in detail the properties and formation mechanism of the inter- and intra-layer excitons.

cond-mat.mtrl-sci↗

arXiv2022

Prediction of protected band edge states and dielectric tunable quasiparticle and excitonic properties of monolayer MoSi$_2$N$_4$

The electronic structure of two-dimensional (2D) materials are inherently prone to environmental perturbations, which may pose significant challenges to their applications in electronic or optoelectronic devices. A 2D material couples with its environment through two mechanisms: local chemical coupling and nonlocal dielectric screening effects. The local chemical coupling is often difficult to predict or control experimentally. Nonlocal dielectric screening, on the other hand, can be tuned by choosing the substrates or layer thickness in a controllable manner. Therefore, a compelling 2D electronic material should offer band edge states that are robust against local chemical coupling effects. Here it is demonstrated that the recently synthesized MoSi$_2$N$_4$ is an ideal 2D semiconductor with robust band edge states protected from capricious environmental chemical coupling effects. Detailed many-body perturbation theory calculations are carried out to illustrate how the band edge states of MoSi$_2$N$_4$ are shielded from the direct chemical coupling effects, but its quasiparticle and excitonic properties can be modulated through the nonlocal dielectric screening effects. This unique property, together with the moderate band gap and the thermodynamic and mechanical stability of this material, paves the way for a range of applications of MoSi$_2$N$_4$ in areas including energy, 2D electronics, and optoelectronics.

cond-mat.mtrl-sci↗

arXiv2021

Two-dimensional Ferroelectric Ferromagnetic Half Semiconductor in VOF monolayer

Two-dimensional (2D) multiferroics have been casted great attention owing to their promising prospects for miniaturized electronic and memory devices.Here, we proposed a highly stable 2D multiferroic, VOF monolayer, which is an intrinsic ferromagnetic half semiconductor with large spin polarization ~2 $μ_{B}/V$ atom and a significant uniaxial magnetic anisotropy along a-axis (410 $μeV/V$ atom). Meanwhile, it shows excellent ferroelectricity with a large spontaneous polarization 32.7 $μC/cm^{2}$ and a moderate energy barrier (~43 meV/atom) between two ferroelectric states, which can be ascribed to the Jahn-Teller distortion.Moreover, VOF monolayer harbors an ultra-large negative Poisson's ratio in the in-plane direction (~-0.34). The Curie temperature evaluated from the Monte Carlo simulations based on the Ising model is about 215 K, which can be enhanced room temperature under -4% compressive biaxial strain.The combination of ferromagnetism and ferroelectricity in the VOF monolayer could provide a promising platform for future study of multiferroic effects and next-generation multifunctional nanoelectronic device applications.

cond-mat.mtrl-sci↗

arXiv2021

Predicting Intrinsic Antiferromagnetic and Ferroelastic MnF4 monolayer with Controllable Magnetization

Two-dimensional (2D) multiferroic materials with controllable magnetism have promising prospects in miniaturized quantum device applications, such as high-density data storage and spintronic devices. Here, using first-principles calculations, we propose a coexistence of antiferromagnetism and ferroelasticity in multiferroic $MnF_{4}$ monolayer. The $MnF_{4}$ monolayer is found to be an intrinsic wide-gap semiconductor with large spin polarization ~3 $μ_{B}$/Mn, in which the antiferromagnetic order originates from the cooperation and competition of the direct exchange and super exchange. $MnF_{4}$ monolayer is also characterized by strongly uniaxial magnetic anisotropic behavior, that can be manipulated by the reversible ferroelastic strain and carrier doping. Remarkably, the carrier doping not only leads to an antiferromagnetic to ferromagnetic phase transformation, bult also could switch the easy magnetization axis between the in-plane and out-of-plane directions. In addition, the Néel temperature was evaluated to be about 140 K from the Monte Carlo simulations based on the Heisenberg model. The combination of antiferromagnetic and ferroelastic properties in $MnF_{4}$ monolayer provides a promising platform for studying the magnetoelastic effects, and brings about new concepts for next-generation nonvolatile memory and multi-stage storage.

cond-mat.mtrl-sci↗

arXiv2020

Predicting the Structural, Electronic and Magnetic Properties of Few Atomic-layer Polar Perovskite

Density functional theory (DFT) calculations are performed to predict the structural, electronic and magnetic properties of electrically neutral or charged few-atomic-layer (AL) oxides whose parent systems are based on polar perovskite $KTaO_{3}$. Their properties vary greatly with the number of ALs ($n_{AL}$) and the stoichiometric ratio. In the few-AL limit ($n_{AL}\leqslant 14$), the even AL (EL) systems with chemical formula $(KTaO_{3})_{n}$ are semiconductors, while the odd AL (OL) systems with formula ($K_{n+1}Ta_{n}O_{3n+1}$ or $K_{n}Ta_{n+1}O_{3n+2}$) are half-metal except for the unique $KTa_{2}O_{5}$ case which is a semiconductor due to the large Peierls distortions. After reaching certain critical thickness ($n_{AL}>14$), the EL systems show ferromagnetic surface states, while ferromagnetism disappears in the OL systems. These predictions from fundamental complexity of polar perovskite when approaching the two-dimensional (2D) limit may be helpful for interpreting experimental observations later.

cond-mat.mtrl-sci↗

arXiv2020

Tunable Magnetism and Insulator-Metal Transition in Bilayer Perovskites

Two-dimensional (2D) transition-metal oxide perovskites greatly expand the field of available 2D multifunctional material systems. Here, based on density functional theory calculations, we predicted the presence of ferromagnetism orders accompanying with an insulator-metal phase transition in bilayer $KNbO_{3}$ and $KTaO_{3}$ by applying strain engineering and/or external electric field. Our results will contribute to the applications of few-layer transition metal oxide perovskites in the emerging spintronics and straintronics.

cond-mat.mtrl-sci↗