arXiv subjects

Jun-Hui Yuan

Publications and source records attributed to Jun-Hui Yuan.

17 recordsLinked to original sources

arXiv2026

Design A Family of 2D Nb-Based Multilayer Kagome Semimetals with High Fermi Velocity and Low Thermal Conductivity

Although two-dimensional (2D) multilayer kagome materials have opened up new windows of opportunity for exploring novel physical properties, their development has been constrained by the scarcity of available material systems. In light of this, in this study, relying on our previously proposed innovative "1+3" design strategy for multilayer kagome materials, we have successfully designed nine stable 2D niobium-based multilayer kagome monolayers with tunable compositions: Nb 6 Cl 2 S 3 Br 6 , Nb 6 Cl 2 S 4 Br 6 , Nb 6 Cl 2 Se 3 Br 6 , Nb 6 Cl 2 Se 4 Br 6 , Nb 6 Cl 2 S 1 Se 3 Br 6 , Nb 6 Cl 2 S 3 Se 1 Br 6 , Nb 6 S 4 Cl 8 , Nb 6 Se 4 Br 8 , and Nb 6 Br 2 S 3 Se 1 Cl 6 . These nine new materials all belong to the category of Dirac semimetals, with their Dirac cone structures primarily arising from the dz 2 orbitals based on Nb-based kagome lattice. Hybrid functional calculations reveal that these materials boast Fermi velocities as high as 2.36-3.04*10 5 m/s. Moreover, these materials generally exhibit characteristics of relatively low phonon group velocities and shorted phonon lifetimes. Under room temperature conditions, they possess comparatively low lattice thermal conductivities, with values ranging from 1.704-8.149 Wm -1 K -1 . Our research not only robustly confirms the feasibility of the "1+3" multilayer kagome lattices design strategy in the realm of kagome material development but also sets an exemplary benchmark for the study of Nb-based multilayer kagome materials.

cond-mat.mtrl-sci↗

arXiv2026

Designing a family of 2D kagome monolayer $B_{18}S_{8}$, $B_{18}S_{8}H_{2}$, $B_{18}S_{6}X_{2}$ (X=Cl,Br,I) with tunable Dirac cones and high Fermi velocity

Two-dimensional (2D) kagome materials have become a hot research topic in the current scientific community due to their unique electronic structural properties, and the design of novel 2D kagome materials represents a significant exploration direction in this field. In this study, by employing the "1+3" design strategy, surface passivation and charge balance strategies, we successfully designed a novel family of 2D kagome material $B_{18}S_{8}$, $B_{18}S_{8}H_{2}$, $B_{18}S_{6}X_{2}$ (X=Cl,Br,I). Electronic structure analysis revealed that although $B_{18}S_{8}$ exhibits excellent kagome band characteristics, its Dirac cone is located approximately 1 eV above the Fermi level, making it difficult to utilize. However, by surface hydrogen passivation, the Dirac cone can be effectively adjusted to the Fermi level. Further research found that introducing halogen atoms to replace surface sulfur atoms can similarly adjust the position of the Dirac cone to the Fermi level. The Fermi velocities near the Dirac cone for these five materials reach as high as 2.69 to 3.07*$10^5$ m/s. Additionally, spin-orbit coupling can open a bandgap of approximately 20 to 55 meV at the Dirac cone. Our research not only provides an outstanding example for the design of 2D boron-based kagome materials but also fully demonstrates the immense potential of such materials in the electronics field.

cond-mat.mtrl-sci↗

arXiv2026

Design of 2D V 6 S n Se 6-n Cl 6 (n=0, 2, 3, 5) with multilayer kagome lattice and ultrahigh electron mobility

Two-dimensional (2D) kagome materials have attracted considerable attention due to their unique electronic properties. Based on first-principles calculations and employing the "1+3" design strategy, we designed a class of composition-tunable 2D multilayer kagome materials, V 6 S n Se 6-n Cl 6 , and identified four stable structures: V 6 Se 6 Cl 6 , V 6 S 2 Se 4 Cl 6 , V 6 S 3 Se 3 Cl 6 , and V 6 S 5 Se 1 Cl 6 . 2D V 6 S n Se 6-n Cl 6 possesses three kagome layers, two of which are vanadium-based kagome layers, and the other is a sulfur or selenium atomic layer. Electronic structure analysis reveals that 2D V 6 S n Se 6-n Cl 6 is a narrow direct-bandgap semiconductor with a bandgap ranging from 0.568 to 0.742 eV, and exhibits ultrahigh electron mobility up to 4*10 4 cm 2 V -1 s -1 . Orbital analysis further demonstrates that the bands contributed by the V-based kagome layers form flat bands and Dirac cones below the Fermi level, and show a relatively high Fermi velocity. In summary, 2D V 6 S n Se 6-n Cl 6 provides an excellent platform for kagome physics research and the fabrication of nanoelectronic devices, adaptable to various device scenarios.

cond-mat.mtrl-sci↗

arXiv2025

Two-Dimensional Na2LiAlP2 Crystal for High-Performance Field-Effect Transistors

High-performance, low-power transistors are core components of advanced integrated circuits, and the ultimate limitation of Moore's law has made the search for new alternative pathways an urgent priority. Two-dimensional (2D) materials have become the most promising exploration target due to their exceptional electronic properties and scalability. In this work, we conducted device transport research on the previously proposed 2D quaternary semiconductor Na2LiAlP2 using the non-equilibrium Green's function method. The results demonstrate that even with a channel length of 5 nm, Na2LiAlP2 still exhibits excellent n-type transistor characteristics, fully meeting and surpassing the technical specifications outlined in the International Roadmap for Devices and Systems (IRDS). Encouragingly, the device can easily achieve the required on-state current of 900 μA/μm under low operating voltages of 0.1 V and 0.2 V. Moreover, at 0.1 V operating voltage, the device's subthreshold swing breaks through the theoretical limit of 60 mV/dec, reaching an astonishing value 30.33 mV/dec. Additionally, its p-type transistor performance also stands out with a subthreshold swing of ~50 mV/dec when the channel length is 7 nm. Our research not only showcases the exceptional transistor properties of Na2LiAlP2 but also further expands the research scope of 2D high-performance transistors.

cond-mat.mtrl-sci↗

arXiv2025

High-Throughput Screening of Transition Metal-Based 2D Multilayer Kagome Materials via the "1 + 3" Design Strategy

Two-dimensional (2D) kagome materials have drawn extensive research interest due to their unique electronic properties, like flat bands, magnetic frustration, and topological quantum states, which enable precise quantum state control and novel device innovation. Yet, simultaneously achieving high stability, tunability, and multifunctionality in 2D kagome systems remains a key material design challenge. In this study, we innovatively propose a new paradigm for constructing two-dimensional multi-kagome-layer materials based on the "1+3" design concept. By seamlessly integrating high-throughput screening techniques, we have successfully identified 6,379 novel 2D multilayer kagome candidates from a vast pool of candidates. These materials exhibit a rich diversity of types, encompassing 173 metals, 27 semimetals, 166 ferromagnetic semiconductors, and as many as 6,013 semiconductors. Furthermore, based on the 2D flat-band scoring criteria, we conducted a detailed analysis of the flat-band characteristics of the energy bands near the Fermi level in the predicted systems. Our findings reveal that approximately two-thirds of the systems meet the 2D flat-band scoring criteria, and notably, several systems exhibit nearly perfect flat-band characteristics. Our work provides an excellent paradigm for the design and research of 2D multilayer kagome materials

cond-mat.mtrl-sci↗

arXiv2025

The occupation dependent DFT-1/2 method

There has been a high demand in rectifying the band gap under-estimation problem in density functional theory (DFT), while keeping the computational load at the same level as local density approximation. DFT-1/2 and shell DFT-1/2 are useful attempts, as they correct the spurious electron self-interaction through the application of self-energy potentials, which pull down the valence band. Nevertheless, the self-energy potential inevitably disturbs the conduction band, and these two methods fail for semiconductors whose hole and electron are entangled in the same shell-like regions. In this work, we introduce the occupation-dependent DFT-1/2 method, where conduction band states are not subject to the additional self-energy potential disturbance. This methodology works for difficult cases such as $\text{Li}_2\text{O}_2$, $\text{Cu}_2\text{O}$ and two-dimensional semiconductors. Using a shell-like region for the self-energy potential, and allowing for downscaling of the atomic self-energy potential (with an $A$ < 1 factor), the occupation-dependent shell DFT+$A$-1/2 method yields more accurate conduction band and valence band edge levels for monolayer $\text{MoS}_2$, compared with the computationally demanding hybrid functional approach.

cond-mat.mtrl-sci↗

arXiv2022

Designing wake-up free ferroelectric capacitors based on the $\mathrm{HfO_2/ZrO_2}$ superlattice structure

The wake-up phenomenon widely exists in hafnia-based ferroelectric capacitors, which causes device parameter variation over time. Crystallization at higher temperatures have been reported to be effective in eliminating wake-up, but high temperature may yield the monoclinic phase or generate high concentration oxygen vacancies. In this work, a unidirectional annealing method is proposed for the crystallization of $\mathrm{Hf_{0.5}Zr_{0.5}O_2}$ (HZO) superlattice ferroelectrics, which involves heating from the $\mathrm{Pt/ZrO_2}$ interface side. Nanoscale $\mathrm{ZrO_2}$ is selected to resist the formation of monoclinic phase, and the chemically inert Pt electrode can avoid the continuous generation of oxygen vacancies during annealing. It is demonstrated that $\mathrm{600^oC}$ annealing only leads to a moderate content of monoclinic phase in HZO, and the TiN/HZO/Pt capacitor exhibits wake-up free nature and a $2P_\mathrm{r}$ value of 27.4 $μ\mathrm{C/cm^2}$. On the other hand, heating from the $\mathrm{TiN/HfO_2}$ side, or using $\mathrm{500^oC}$ annealing temperature, both yield ferroelectric devices that require a wake-up process. The special configuration of $\mathrm{Pt/ZrO_2}$ is verified by comparative studies with several other superlattice structures and HZO solid-state solutions. It is discovered that heating from the $\mathrm{Pt/HfO_2}$ side at $\mathrm{600^oC}$ leads to high leakage current and a memristor behavior. The mechanisms of ferroelectric phase stabilization and memristor formation have been discussed. The unidirectional heating method can also be useful for other hafnia-based ferroelectric devices.

cond-mat.mtrl-sci↗

arXiv2022

Shell DFT-1/2 method towards engineering accuracy for semiconductors: GGA versus LDA

The Kohn-Sham gaps of density functional theory (DFT) obtained in terms of local density approximation (LDA) or generalized gradient approximation (GGA) cannot be directly linked to the fundamental gaps of semiconductors, but in engineering there is a strong demand to match them through certain rectification methods. Shell DFT-1/2 (shDFT-1/2), as a variant of DFT-1/2, is a potential candidate to yield much improved band gaps for covalent semiconductors, but its accuracy depends on the LDA/GGA ground state, including optimized lattice parameters, basic Kohn-Sham gap before self-energy correction and the amount of self-energy correction that is specific to the exchange-correlation (XC) functional. In this work, we test the LDA/GGA as well as shDFT-1/2 results of six technically important covalent semiconductors Si, Ge, GaN, GaP, GaAs and GaSb, with an additional ionic insulator LiF for comparison. The impact of XC flavor (LDA, PBEsol, PBE and RPBE), either directly on the gap value, or indirectly through the optimized lattice constant, is examined comprehensively. Moreover, we test the impact of XC flavor on LDA/GGA and shDFT-1/2 gaps under the condition of fixed experimental lattice constants. In-depth analysis reveals the rule of reaching the best accuracy in calculating the electronic band structures of typical covalent semiconductors. Relevant parameters like lattice constant, self-consistency in shDFT-1/2 runs, as well as the exchange enhancement factor of GGA, are discussed in details.

cond-mat.mtrl-sci↗

arXiv2022

Hafnia for analog memristor: Influence of stoichiometry and crystalline structure

The highly non-linear switching behavior of hafnia memristor actually hinders its wide application in neuromorphic computing. Theoretical understanding into its switching mechanism has been focused on the processes of conductive filament generation and rupture, but possible phase transition and crystallization around the region of conductive filaments (CFs) due to the variation of O content have been paid less attention to. In this paper, HfO$\mathrm{_x}$ structural models covering the full stoichiometries from Hf to HfO$\mathrm{_2}$ were established, and the crystal structure evolution during the reduction process of hafnia was obtained through first-principles calculation. The electronic structures and O vacancy migration characteristics of these structures were analyzed. A criterion was prescribed to predict the mode of abrupt binary switching or gradual conductance modulation according to the structure evolution of the CFs. In particular, factors that influence the merging of tiny conductive channels into strong filaments are intensively discussed, including the anisotropy of O vacancy migration and the size effect. The feasibility of Mg doping to achieve robust gradual switching is discussed.

cond-mat.mtrl-sci↗

arXiv2022

Ferroelectricity in $\mathrm{HfO_2}$ from a chemical perspective

Ferroelectricity observed in thin film $\mathrm{HfO_2}$, either doped with Si, Al, etc. or in the $\mathrm{Hf_{0.5}Zr_{0.5}O_2}$ form, has gained great technical significance. However, the soft mode theory faces a difficulty in explaining the origin of such ferroelectricity. In this work, we propose that the 7 cation coordination number of $\mathrm{HfO_2/ZrO_2}$ lies at the heart of this ferroelectricity, which stems from the proper ionic radii of Hf/Zr compared with O. Among the numerous compounds with non-centrosymmetric nature, e.g., $mm2$ point group, $\mathrm{HfO_2}$ and $\mathrm{ZrO_2}$ are special in that they are close to the border of 7 and 8 cation coordination, such that the 8-coordination tetragonal intermediate phase could greatly reduce the switching barrier. Other 7-coordination candidates, including $\mathrm{SrI_2}$, TaON, YSBr and YOF are also studied in comparison to $\mathrm{HfO_2}$/$\mathrm{ZrO_2}$, and six switching paths are analyzed in detail for the $Pca2_1$ phase. A rule of preferred switching path in terms of ionic radii ratio and coordination number has been established. We also show the possible route from ferroelectric $Pca2_1$ phase to monoclinic $P2_1/c$ phase in $\mathrm{HfO_2}$, which is relevant to the fatigue phenomenon.

cond-mat.mtrl-sci↗

arXiv2019

$\mathrm{BaAs_3}$: A narrow gap 2D semiconductor with vacancy-induced semiconductor-metal transition

Searching for novel two-dimensional (2D) materials is highly desired in the field of nanoelectronics. We here propose a new 2D crystal barium tri-arsenide ($\mathrm{BaAs_3}$) with a series of encouraging functionalities. Being kinetically and thermally stable, the monolayer and bilayer forms of $\mathrm{BaAs_3}$ possess narrow indirect band gaps of 0.87 eV and 0.40 eV, respectively, with high hole mobilities on the order of ~$\mathrm{10^3\ cm^{2}\,V^{-1}\,s^{-1}}$. The electronic properties of 2D $\mathrm{BaAs_3}$ can be manipulated by controlling the layer thickness. The favorable cleavage energy reveals that layered $\mathrm{BaAs_3}$ can be produced as a freestanding 2D material. Furthermore, by introducing vacancy defects monolayer $\mathrm{BaAs_3}$ can be transformed from a semiconductor to a metal. 2D $\mathrm{BaAs_3}$ may find promising applications in nanoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2018

Ab initio simulation of $\mathrm{Ta_2O_5}$: A high symmetry ground state phase with application to interface calculation

We suggest a tetragonal $I4_1/amd$ phase ($η$-phase) as the ground state of $\mathrm{Ta_2O_5}$ at zero temperature, which is a high symmetry version of the triclinic $γ$-phase $\mathrm{Ta_2O_5}$ predicted by Yang and Kawazoe. Our calculation shows that $γ$-phase $\mathrm{Ta_2O_5}$ will automatically be transformed into the $η$-phase during structural relaxation. Phonon dispersion confirms that the $η$-phase is dynamically stable, while the high temperature $α$-phase $\mathrm{Ta_2O_5}$, which also has the $I4_1/amd$ symmetry, is unstable at zero temperature. A thorough energy comparison of the $β_{AL}$, $δ$, $λ$, $\mathrm{B}$, $\mathrm{L_{SR}}$, $β_R$, $Pm$, $Cmmm$, $γ$, $η$ and $α$ phases of $\mathrm{Ta_2O_5}$ is carried out. The GGA-1/2 method is applied in calculating the electronic structure of various phases, where the $η$-phase demonstrates a 4.24 eV indirect band gap, close to experimental value. The high symmetry tetragonal phase together with computationally efficient GGA-1/2 method greatly facilitate the $ab\ initio$ simulation of $\mathrm{Ta_2O_5}$-based devices. As an example, we have explicitly shown the Ohmic contact nature between metal Ta and $\mathrm{Ta_2O_5}$ by calculating an interface model of $b.c.c.$ Ta and $η$-$\mathrm{Ta_2O_5}$, using GGA-1/2.

cond-mat.mtrl-sci↗

arXiv2018

Planar penta-transition metal phosphide and arsenide as narrow-bandgap semiconductors from first principle calculations

Searching for materials with single atom-thin as well as planar structure, like graphene and borophene, is one of the most attractive themes in two dimensional materials. Herein, using density functional theory calculations, we have proposed a series of single layer planar penta-transition metal phosphide and arsenide, i.e. TM$\mathrm{_2}$X$\mathrm{_4}$ (TM= Ni, Pd and Pt; X=P, As). According to the calculated phonon dispersion relation and elastic constants, as well as ab initio molecular dynamics simulation results, monolayers of planar penta-TM$\mathrm{_2}$X$\mathrm{_4}$ are dynamically, mechanically, and thermally stable. In addition, the band structures calculated with the screened HSE06 hybrid functional including spin-orbit coupling show that these monolayers are direct-gap semiconductors with sizeable band gaps ranging from 0.14 eV to 0.69 eV. Besides, the optical properties in these monolayers are further investigated, where strong in-plane optical absorption with wide spectral range has been revealed. Our results indicate that planar penta-TM$\mathrm{_2}$X$\mathrm{_4}$ monolayers are interesting narrow gap semiconductors with excellent optical properties, and may find potential applications in photoelectronics.

cond-mat.mtrl-sci↗

arXiv2018

Two dimensional silicon chalcogenides with high carrier mobility for photocatalytic water splitting

Highly-efficient water splitting based on solar energy is one of the most attractive research focuses in the energy field. Searching for more candidate photocatalysts that can work under visible-light irradiation are highly demanded. Herein, using first principle calculations based on density functional theory, we predict that the two dimensional silicon chalcogenides, i.e. SiX (X=S, Se, Te) monolayers, as semiconductors with 2.43 eV~3.00 eV band gaps, exhibit favorable band edge positions for photocatalytic water splitting. The optical adsorption spectra demonstrate that the SiX monolayers have pronounced optical absorption in the visible light region. Moreover, the band gaps and band edge positions of silicon chalcogenides monolayers can be tuned by applying biaxial strain or increasing the number of layers, in order to better fit the redox potentials of water. The combined novel electronic, high carrier mobility, and optical properties render the two dimensional SiX a promising photocatalyst for water splitting.

cond-mat.mtrl-sci↗

arXiv2018

$\mathrm{TlP_5}$: An unexplored direct band gap 2D semiconductor with ultra-high carrier mobility

Two-dimensional materials with a proper band gap and high carrier mobility are urgently desired in the field of nanoelectronics. We propose a novel two-dimensional crystal monolayer $\mathrm{TlP_5}$, which is dynamically and thermodynamically stable and possesses a direct band gap of 2.02 eV with high carrier mobilities (13960 $\mathrm{cm^2\ V^{-1}s^{-1}}$ for electrons and 7560 $\mathrm{cm^2\ V^{-1}s^{-1}}$ for holes), comparable to that of phosphorene. The band gap value and band characteristics of monolayer $\mathrm{TlP_5}$ can be adjusted by biaxial and uniaxial strains, and excellent optical absorption over the visible-light range is predicted. These properties, especially for the balanced high mobilities for not only the electrons but also the holes, render monolayer $\mathrm{TlP_5}$ an exciting functional material for future nanoelectronics and optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2018

KTlO: A metal shrouded 2D semiconductor with high carrier mobility and tunable magnetism

Two-dimensional (2D) materials with high carrier mobility and tunable magnetism are in high demand for nanoelectronics and spintronic applications. Herein, we predict a novel two-dimensional monolayer KTlO that possesses an indirect band gap of 2.25 eV (based on HSE06) and high carrier mobility (1860 $\mathrm{cm^2\ V^{-1}s^{-1}}$ for electron and 2540 $\mathrm{cm^2\ V^{-1}s^{-1}}$ for hole) by means of ab initio calculations. KTlO monolayer has a calculated cleavage energy of 0.56 $\mathrm{J\ m^{-2}}$, which suggests exfoliation of bulk material as viable means for the preparation of mono- and few-layer materials. Remarkably, the KTlO monolayer suggests tunable magnetism and half-metallicity with hole doping, which are attributed to the novel Mexican-hat-like bands and van Hove singularities in its electron structure. Furthermore, monolayer KTlO exhibits moderate optical absorption over visible light and ultraviolet region. The band gap value and band characteristics of monolayer KTlO can be strongly manipulated by biaxial and uniaxial strains to meet the requirements of various applications. All these novel properties render monolayer KTlO a promising functional material for future nanoelectronics and spintronic applications.

cond-mat.mes-hall↗

arXiv2017

Improved self-energy correction method for accurate and efficient band structure calculation

The LDA-1/2 method for self-energy correction is a powerful tool for calculating accurate band structures of semiconductors, while keeping the computational load as low as standard LDA. Nevertheless, controversies remain regarding the arbitrariness of choice between (1/2)e and (1/4)e charge stripping from the atoms in group IV semiconductors, the incorrect direct band gap predicted for Ge, and inaccurate band structures for III-V semiconductors. Here we propose an improved method named shell-LDA-1/2 (shLDA-1/2 for short), which is based on a shell-like trimming function for the self-energy potential. With the new approach, we obtained accurate band structures for group IV, and for III-V and II-VI compound semiconductors. In particular, we reproduced the complete band structure of Ge in good agreement with experimental data. Moreover, we have defined clear rules for choosing when (1/2)e or (1/4)e charge ought to be stripped in covalent semiconductors, and for identifying materials for which shLDA-1/2 is expected to fail.

physics.comp-ph↗