arXiv subjects

Gaoyang Gou

Publications and source records attributed to Gaoyang Gou.

9 recordsLinked to original sources

arXiv2026

Two-dimensional vertically polarized Hg3AsSe4I monolayer for efficient photocatalytic water-splitting: promoting carrier separation by intrinsic electric field and Rashba effect

Efficient separation of photo-excited electron-hole pairs is essential for developing the high performance photocatalysts towards light-driven water-splitting applications. To this end, pho tocatalytic performances of two-dimensional (2D) semiconducting ferroelectric (FE) materials with out-of-plane polarizations have been extensively explored. However, out-of-plane polarizations in 2D FE materials are susceptible to the critical thickness limitation and can be easily compensated by surface adsorbates. On the other hand, 2D vertically polarized materials with stable and ir reversible out-of-plane polarizations may overcome the critical thickness limitation, enabling the practical advantage for spatial separation of photo-excited electron-hole pairs during the photo catalytic reactions. In the current work, 2D vertically polarized Hg3AsSe4I, an experimentally synthesized van der Waals (vdW) layered material, has been systematically investigated as a high performance 2D photocatalyst. Owing to its semiconducting band gap suitable for visible-light absorption, high carrier mobility, and desirable band edge alignment ideally matching water reduc tion and oxidation potentials, Hg3AsSe4I monolayer fulfills both optical and electronic prerequisites for photocatalytic water-splitting reactions. Besides the stable vertical polarization able to persist in Hg3AsSe4I monolayer, the dual mechanism for efficient separation of photo-excited carriers has also been demonstrated. Rashba spin-orbit coupling (SOC) of large strength emerges within 2D Hg3AsSe4I, splitting the band edges into spin-resolved band branches with unique spin-momentum locking characters.........

cond-mat.mtrl-sci↗

arXiv2026

2D Ferroelectric Ruddlesden-Popper Perovskites: an Emerging Fully Electronically Controllable Shift Current and Persistent Spin Helix

Two-dimensional (2D) hybrid organic--inorganic perovskites (HOIPs) are promising candidates for next-generation optoelectronic and spintronic applications. This work systematically investigates the relationship between structural distortions and functional responses in three $C_{2v}$-symmetric Ruddlesden--Popper (RP) ferroelectric perovskites, $(4,4\text{-DFPD})_{2}\mathrm{PbI}_{4}$, $(\mathrm{DFCHA})_{2}\mathrm{PbI}_{4}$, and PEPI, using first-principles calculations combined with irreducible representation decomposition and wave-vector point-group symmetry (WPGS) analysis. The results reveal that the lead--iodide framework yields shift-current (SC) magnitudes comparable to, and in specific cases even an order of magnitude larger than, those of traditional ferroelectric oxides, with PEPI reaching a maximum of $69.16\ μ\mathrm{A}/\mathrm{V}^{2}$. The SC magnitude correlates positively with the octahedral distortion index ($D_i$), while a competition mechanism is identified between covalent bond strength and structural asymmetry, where increased average bond lengths can offset the enhancement induced by $D_i$. Regarding spintronics, $C_{2v}$ symmetry-protected persistent spin textures (PST) are identified. A transition to $C_2$-protected quasi-PST occurs in monoclinic $(4,4\text{-DFHHA})_{2}\mathrm{PbI}_{4}$, leading to a persistent spin helix (PSH) with long-distance spin transport. The synergy among ferroelectricity, SC, and PST enables nonvolatile electrical control of both photocurrent direction and spin configurations. This work provides evaluation criteria and practical guidance for designing high-performance integrated spintronic--photovoltaic devices.

cond-mat.mtrl-sci↗

arXiv2025

Distinguish the Orientation of Sliding Ferroelectricity by Second-Harmonic Generation

As the emerging ferroelectric (FE) materials, the ultrathin two-dimensional (2D) sliding ferroelectrics without phase-matching bottleneck, usually exhibit the pronounced second harmonic generation (SHG) responses. Despite the structural polarity of sliding ferroelectrics can be precisely detected via SHG characterizations, distinguishing the orientations of sliding ferroelectricity based on SHG responses has rarely been realized, as SHG intensities for upward and downward polarization states are supposed to be same. In current work, combining computational simulations and experimental characterizations, the orientation of sliding ferroelectricity is demonstrated to be readily distinguishable via SHG responses in 2D SnP2S6 (SnP2Se6), a new sliding FE material. Specifically, owing to the unique symmetry operation within FE-SnP2S6 (SnP2Se6), the intersection between \c{hi}xxx and \c{hi}yyy SHG susceptibility coefficients with opposite signs leads to the effective rotation of SHG polar directions upon switching of sliding ferroelectricity. Moreover, the remarkable dependence of SHG polar directions on the orientation of sliding ferroelectricity is further validated by experimental characterizations performed on SnP2S6 crystal in a single FE domain structural form. This work opens up the avenue for in-situ detecting the ferroelectricity orientation of 2D sliding ferroelectrics based on SHG nonlinear optical responses, and also demonstrates the controllable optical nonlinearly for new "slidetronics" applications.

cond-mat.mtrl-sci↗

arXiv2025

Unraveling Shear Strain Induced Ferroelectric-to-Antiferroelectric Phase Transition and Accessing Intrinsic Antiferroelectricity in Two-dimensional NbOCl2

Compared to the well studied two-dimensional (2D) ferroelectricity, much rare is the appearance of 2D antiferroelectricity, where local dipoles from the nonequivalent sublattices within 2D monolayers are oppositely orientated. Using NbOCl2 monolayer with competing ferroelectric (FE) and antiferroelectric (AFE) phases as a 2D material platform, we demonstrate the emerging of intrinsic antiferroelectricity in NbOCl2 monolayer under the experimentally accessible shear strain, and new functionality associated with electric field induced AFE-to-FE phase transition. Specifically, the complex configuration space accommodating FE and AFE phases, polarization switching kinetics and finite temperature thermodynamic properties of 2D NbOCl2, are all accurately predicted by large-scale molecular dynamic (MD) simulations based on deep learning interatomic potential (DP) model. Moreover, room temperature stable antiferroelectricity with low polarization switching barrier and one-dimensional (1D) collinear polarization arrangement is predicted in shear deformed NbOCl2 monolayer. Transition from AFE to FE phase in 2D NbOCl2 can be triggered by the low critical electric field, leading to the double polarization-electric (P-E) loop with small hysteresis. A new type optoelectronic device composed of AFE-NbOCl2, enabling electric "writing" and nonlinear optical "reading" logical operation with fast operation speed and low power consumption is also proposed.

cond-mat.mtrl-sci↗

arXiv2025

Unconventional Magnetism, Sliding Ferroelectricity, and Magneto-Optical Kerr Effects in a Multiferroic Bilayer

Antiferromagnetic (AFM) materials offer a promising platform for exploring novel couplings between altermagnetic (AM) spin-splitting and magneto-optical Kerr effect (MOKE), with potential applications in next-generation quantum technologies. In this work, first-principles calculations, symmetry analysis, and kp modeling are employed to demonstrate how interlayer sliding in AFM multiferroic bilayers enables engineering of the electronic, magnetic, and magneto-optical properties. This study reveals an unprecedented dimension-driven AM crossover, where the 2D paraelectric (PE) bilayer exhibits spin-degenerate bands protected by the [C2||Mc] spin-space symmetry, while the 3D counterpart manifests AM spin-splitting along kz not equal to 0 paths. Furthermore, interlayer sliding breaks the Mc symmetry and stabilizes a ferroelectric (FE) state characterized by compensated ferrimagnetism and a Zeeman effect, which produces non-relativistic spin-split bands. In the FE phase, the inclusion of spin-orbit coupling (SOC) lifts accidental degeneracies, creating `alternating' spin-polarized bands due to the interplay of Zeeman and Rashba effects. Crucially, the spin polarization, ferro-valley polarization, and Kerr angle are simultaneously reversible by switching either interlayer sliding or the Neel vector. These findings highlight the rich coupling between electronic, magnetic, and optical orders in sliding multiferroics, thereby paving the way for ultra-low-power spintronics and optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2013

A Nanoscale Shape Memory Oxide

Stimulus-responsive shape memory materials have attracted tremendous research interests recently, with much effort focused on improving their mechanical actuation. Driven by the needs of nanoelectromechnical devices, materials with large mechanical strain particularly at nanoscale are therefore desired. Here we report on the discovery of a large shape memory effect in BiFeO3 at the nanoscale. A maximum strain of up to ~14% and a large volumetric work density can be achieved in association with a martensitic-like phase transformation. With a single step, control of the phase transformation by thermal activation or electric field has been reversibly achieved without the assistance of external recovery stress. Although aspects such as hysteresis, micro-cracking etc. have to be taken into consideration for real devices, the large shape memory effect in this oxide surpasses most alloys and therefore demonstrates itself as an extraordinary material for potential use in state-of-art nano-systems.

cond-mat.mtrl-sci↗

arXiv2013

Strain-induced isosymmetric ferri-to-ferroelectric transition with large piezoelectricity

We identify a first-order, isosymmetric transition between a ferrielectric (FiE) and ferroelectric (FE) state in $A$-site ordered LaScO$_{3}$/BiScO$_{3}$ and LaInO$_{3}$/BiInO$_{3}$ superlattices. Such a previously unreported ferroic transition is driven by the easy switching of cation displacements without changing the overall polarization direction or crystallographic symmetry. Epitaxial strains less than 2% are predicted to be sufficient to transverse the phase boundary, across which we capture a ~5X increase in electric polarization. In a fashion similar to classic Pb-based perovskite ceramics with a morphotropic phase boundary (MPB), we predict a large electromechanical response up to 131 pC/N in the vicinity of FiE-FE phase boundary. We propose this transition as alternative ferroic transition to obtain large piezoelectricity, with the additional advantage of operating under extreme conditions in benign chemistries and without chemical disorder.

cond-mat.mtrl-sci↗

arXiv2011

Lattice normal modes and electronic properties of the correlated metal LaNiO$_3$

We use density functional theory (DFT) calculations to study the lattice vibrations and electronic properties of the correlated metal LaNiO$_3$. To characterize the rhombohedral to cubic structural phase transition of perovskite LaNiO$_3$, we examine the evolution of the Raman-active phonon modes with temperature. We find that the $A_{1g}$ Raman mode, whose frequency is sensitive to the electronic band structure, is a useful signature to characterize the octahedral rotations in rhombohedral LaNiO$_3$. We also study the importance of electron--electron correlation effects on the atomic structure with two approaches which go beyond the conventional band theory (local spin density approximation): the local spin density+Hubbard $U$ method (LSDA$+U$) and hybrid exchange-correlation density functionals which include portions of exact Fock-exchange. We find the conventional LSDA accurately reproduces the delocalized nature of the valence states in LaNiO$_3$ and gives the best structural and vibrational agreement to the available experimental data. Based on our calculations, we show that the electronic screening effect from the delocalized Ni 3$d$ and O-2$p$ states mitigate the electronic correlations of the $d^7$ Ni cations, making LaNiO$_3$ a weakly correlated metal.

cond-mat.mtrl-sci↗

arXiv2011

Post density functional theoretical studies of highly polar semiconductive Pb(Ti$_{1-x}$Ni$_{x}$)O$_{3-x}$ solid solutions: The effects of cation arrangement on band gap

We use a combination of conventional density functional theory (DFT) and post-DFT methods, including the local density approximation plus Hubbard $U$ (LDA+$U$), PBE0, and self-consistent $GW$ to study the electronic properties of Ni-substituted PbTiO$_{3}$ (Ni-PTO) solid solutions. We find that LDA calculations yield unreasonable band structures, especially for Ni-PTO solid solutions that contain an uninterrupted NiO$_{2}$ layer. Accurate treatment of localized states in transition-metal oxides like Ni-PTO requires post-DFT methods. $B$-site Ni/Ti cation ordering is also investigated. The $B$-site cation arrangement alters the bonding between Ni and O, and therefore strongly affects the band gap ($E_{\rm g}$) of Ni-PTO. We predict that Ni-PTO solid solutions should have a direct band gap in the visible light energy range, with polarization similar to the parent PbTiO$_{3}$. This combination of properties make Ni-PTO solid solutions promising candidate materials for solar energy conversion devices.

cond-mat.mtrl-sci↗