arXiv subjects

Yanfeng Ge

Publications and source records attributed to Yanfeng Ge.

At least 37 records · Page 2Linked to original sources

arXiv2024

First-principles study of two-dimensional transition metal carbide M n+1 C n O 2(M=Nb,Ta)

In the present work, the three stable MXenes M n+1 C n O 2 (M=Nb,Ta) are explored based onfirst-principles calculations. These materials are important derivatives of 2D materials and exhib-it distinctive properties, holding vast potential in nanodevices. All these M n+1 C n O 2 (M=Nb,Ta)materials exhibit outstanding superconducting performance, with corresponding superconductingtransition temperatures of 23.00K, 25.00K, and 29.00K. Analysis reveals that the high supercon-ducting transition temperatures of MXenes M n+1 C n O 2 (M=Nb,Ta) are closely associated with thehigh value of the logarithmic average of phonon frequencies, ω log , and the strong electron-phononcoupling (EPC), attributed to the crucial contribution of low-frequency phonons. Additionally, weapplied strain treatments of 2% and 4% to M n+1 C n O 2 (M=Nb,Ta), resulting in varying changes insuperconducting transition temperatures under different strains.

cond-mat.supr-con↗

arXiv2023

Superconductivity in graphite intercalation compounds with sodium

The discovery of superconductivity in CaC6 with a critical temperature (Tc) of 11.5 K reignites much interest in exploring high-temperature superconductivity in graphite intercalation compounds (GICs). Here we identify a GIC NaC4, discovered by ab initio evolutionary structure search, as a superconductor with a computed Tc of 41.2 K at 5 GPa. This value is eight times higher than that of the synthesized GIC NaC2 and possesses the highest Tc among available GICs. The remarkable superconductivity of GIC NaC4 mainly arises from the coupling of π electrons in graphene with the low-frequency vibrations involving both Na and C atoms. These findings suggest that Na-GICs may hold great promise as high-Tc superconductors.

cond-mat.supr-con↗

arXiv2023

First-principles calculations on the mechanical, electronic, magnetic and optical properties of two-dimensional Janus Cr$_2$TeX (X= P, As, Sb) monolayers

Janus materials possess extraordinary physical, chemical, and mechanical properties caused by symmetry breaking. Here, the mechanic properties, electronic structure, magnetic properties, and optical properties of Janus Cr$_2$TeX (X= P, As, Sb) monolayers are systematically investigated by the density functional theory. Janus Cr$_2$TeP, Cr$_2$TeAs, and Cr$_2$TeSb are intrinsic ferromagnetic (FM) half-metals with wide spin gaps and half-metallic gaps. Monte Carlo simulations based on the Heisenberg model estimate the Curie temperature (\emph{T}$_c$) of these monolayers are about 583, 608, and 597 K, respectively. Additionally, it is found that Cr$_2$TeX (X= P, As, Sb) monolayers still exhibit FM half-metallic properties under biaxial strain from -6% to 6%. At last, the Cr$_2$TeP monolayer has a higher absorption coefficient than the Cr$_2$TeAs and Cr$_2$TeSb monolayers in the visible region. The results predict that Janus Cr$_2$TeX (X= P, As, Sb) monolayers with novel properties have good potential for applications in future nanodevices.

cond-mat.mtrl-sci↗

arXiv2023

The unexpected magnetism in 2D group-IV-doped GaN for spintronic applications

In this study, the structural and magnetic properties of group-IV-doped monolayer GaN were systematically investigated by first-principles calculations. Among all the group-IV dopants, only Ge and Sn atoms prefer to substitute the Ga atom of monolayer GaN and form a buckling structure with a magnetic moment of 1 $μ_B$ per dopant. The N-rich growth conditions are more desirable for such a substitution process than the Ga-rich grow conditions. With a large diffusion barrier vertical to the monolayer GaN, both Ge and Sn atoms tend to stay on the same side of monolayer GaN with an antiferromagnetic coupling between them. When intrinsic vacancies exist in monolayer GaN, the magnetic moments of group-IV dopants vanish due to the charge transferring from the dopants to Ga or N vacancies. The precondition creation of Ga vacancies, a plentiful supply of Ge or Sn dopants, and the N-rich conditions can be adopted to maintain the magnetic properties of group-IV-doped monolayer GaN. These theoretical results help to promote the applications of 2D GaN-based materials in spintronics.

cond-mat.mtrl-sci↗

arXiv2023

2D-XY ferromagnetism with high transition temperature in Janus monolayer V$_{2}$XN (X = P, As)

Two-dimensional (2D) XY magnets with easy magnetization planes support the nontrivial topological spin textures whose dissipationless transport is highly desirable for 2D spintronic devices. Here, we predicted that Janus monolayer V$_{2}$XN (X = P, As) with a square lattice are 2D-XY ferromagnets by first-principles calculations. Both the magnetocrystalline anisotropy and magnetic shape anisotropy favor an in-plane magnetization, leading to an easy magnetization $xy$-plane in Janus monolayer V$_{2}$XN. Resting on the Monte Carlo simulations, we observed the Berezinskii-Kosterlitz-Thouless (BKT) phase transition in monolayer V$_{2}$XN with transition temperature $T_{\rm BKT}$ being above the room temperature. Especially, monolayer V$_{2}$AsN has a magnetic anisotropy energy (MAE) of 292.0 $μ$eV per V atom and a $T_{\rm BKT}$ of 434 K, which is larger than that of monolayer V$_{2}$PN. Moreover, a tensile strain of 5\% can further improve the $T_{\rm BKT}$ of monolayer V$_{2}$XN to be above 500 K. Our results indicated that Janus monolayer V$_{2}$XN (X = P, As) were candidate materials to realize high-temperature 2D-XY ferromagnetism for spintronics applications.

cond-mat.mtrl-sci↗

arXiv2022

Topological semimetal phases in a family of monolayer X3YZ6 (X=Nb,Ta, Y=Si,Ge,Sn, Z=S,Se,Te) with abundant nodal lines and nodes

The electronic and topological properties of single-layer X3YZ6 (X=Nb,Ta, Y=Si,Ge,Sn, Z=S,Se,Te) materials have been studied with the aid of first principles calculations. This kind of materials belong to topological semimetals (TMs) with abundant nodal lines and nodes. Considering their similar properties, we focus on the analysis of Ta3SnTe6 and Ta3SiSe6. The present of spin-orbit coupling (SOC) leads to the transition from type-I nodal lines to Dirac points as well as the disappear of type-II Dirac points. The three-dimensional (3D) band diagrams reproduce vividly the characteristics of nodes and nodal lines. The appearance of the flat bands in (110) edge states further confirm their nontrivial topological properties. We also explore the relationship among different nodal lines (nodes), crystal symmetry and SOC. The type-I nodal lines are protected by Mz and My symmetry in the absent of SOC. Symmetry breaking leads to band splitting even in the presence of SOC. The single-layer X3YZ6 can be used as candidates for two-dimensional (2D) TMs and provide a platform for further study of interesting physical phenomena.

cond-mat.mtrl-sci↗

arXiv2022

Novel boron nitride polymorphs with graphite-diamond hybrid structure

Both boron nitride (BN) and carbon (C) have sp, sp2 and sp3 hybridization modes, and thus resulting in a variety of BN and C polymorphs with similar structures, such as hexagonal BN (hBN) and graphite, cubic BN (cBN) and diamond. Here, five types of BN polymorph structures were proposed theoretically, inspired by the graphite-diamond hybrid structures discovered in recent experiment. These BN polymorphs with graphite-diamond hybrid structures possessed excellent mechanical properties with combined high hardness and high ductility, and also exhibited various electronic properties such as semi-conductivity, semi-metallicity, and even one- and two-dimensional conductivity, differing from known insulators hBN and cBN. The simulated diffraction patterns of these BN hybrid structures could account for the unsolved diffraction patterns of intermediate products composed of "compressed hBN" and diamond-like BN, caused by phase transitions in previous experiments. Thus, this work provides a theoretical basis for the presence of these types of hybrid materials during phase transitions between graphite-like and diamond-like BN polymorphs.

cond-mat.mtrl-sci↗

arXiv2022

First-principles study the structural, magnetic, optical properties and doping effect in chromium arsenide

We systematically study the pristine and doped chromium arsenide (CrAs) in six different crystal structures to investigate the structural, magnetic, and optical properties for real applications by first-principles calculations. First, we found that the ground-state structure is an orthorhombic MnP-type structure with antiferromagnetic spin order. The rocksalt structure is an low-energy metastable phase and a ferromagnetic metal with high spin polarization at the Fermi level. Secondly, the NiAs structure and MnP structure have a higher absorption coefficient than other structures in the infrared region and ultraviolet region, respectively. In the visible light region, the wurtzite and zincblende structures are more transparent than other structures. At last, we found that Ti substitution of Cr and Te substitution of As can lead to a phase transition in ground-state structure and ground-state magnetic order, respectively. These results can promote the application of the CrAs system into spintronics.

cond-mat.mtrl-sci↗

arXiv2021

Two-dimensional antiferromagnetic semiconductor T'-MoTeI from first principles

Two-dimensional intrinsic antiferromagnetic semiconductors are expected to stand out in the spintronic field. The present work finds the monolayer T'-MoTeI is intrinsically an antiferromagnetic semiconductor by using first-principles calculation. Firstly, the dimerized distortion of the Mo atoms causes T'-MoTeI to have dynamic stability, which is different from the small imaginary frequency in the phonon spectrum of T-MoTeI. Secondly, T'-MoTeI is an indirect-bandgap semiconductor with 1.35 eV. Finally, in the systematic study of strain effects, there are significant changes in the electronic structure as well as the bandgap, but the antiferromagnetic ground state is not affected. Monte Carlo simulations predict that the Neel temperature of T'-MoTeI is 95 K. The results suggest that the monolayer T'-MoTeI can be a potential candidate for spintronics applications.

cond-mat.mtrl-sci↗

arXiv2021

Superconductivity in graphite-diamond hybrid

Search for new high-temperature superconductors and insight into their superconducting mechanism are of fundamental importance in condensed matter physics. The discovery of near-room temperature superconductivity at more than a million atmospheres ushers in a new era for superconductors. However, the critical task of identifying materials with comparable superconductivity at near or ambient pressure remains. Carbon materials can always lead to intriguing surprises due to their structural diversity and electronic adjustability. Insulating diamond upon doping or external stimuli has achieved superconducting state. Thus, it still has a great opportunity to find superconducting ones with higher transition temperature (Tc). Here, we report an intrinsic superconducting graphite-diamond hybrid through first-principles calculations, whose atomic-resolution structural characteristics have been experimentally determined recently. The predicted Tc is approximated at 39 K at ambient pressure, and strain energizing can further boost Tc to 42 K. The strong electron-phonon coupling associated with the out-of-plane vibration of carbon atoms at the junction plays a dominant role in the superconducting transition. Our work demonstrates the great potential of such carbon materials as high-Tc superconductors, which will definitely attract extensive research.

cond-mat.mtrl-sci↗

arXiv2021

Quantum spin Hall effect in two-dimensional transition-metal chalcogenides

Based on first-principles calculations, we have found a family of 2D transition-metal (TM) chalcogenides MX5 (M = Zr, Hf and X = S, Se and Te) can host quantum spin Hall (QSH) effect. The molecular dynamics simulation indicate that they are all thermal-dynamically stable at room temperature, the largest band gap is 0.19 eV. We have investigated MX5's electronic properties and found their properties are very similar. The single-layer ZrX5 are all gapless semimetals without consideration of spin-orbit coupling (SOC). The consideration of SOC will result in insulating phases with band gaps of 0.05 eV (direct), 0.18 eV (direct) and 0.13 eV (indirect) for ZrS5, ZrSe5 to ZrTe5, respectively. The evolution of Wannier charge centers and edge states confirm they are all QSH insulators. The mechanisms for QSH effect in ZrX5 originate from the special nonsymmorphic space group features. In addition, the QSH state of ZrS5 survives at a large range of strain as long as the interchain coupling is not strong enough to reverse the band ordering. The single-layer ZrS5 will occur a topological insulator (TI)-to-semimetal (metal) or metal-to-semimetal transition under certain strain. Monolayer MX5 expand the TI materials based on TM chalcogenides and may open up a new way to fabricate novel low power spintronic devices at room temperature.

cond-mat.mtrl-sci↗

arXiv2021

Strain Tunable Intrinsic Ferromagnetic in 2D Square CrBr$_2$

Two-dimensional (2D) intrinsic magnetic materials with high Curie temperature (Tc) coexisting with 100% spin-polarization are highly desirable for realizing promising spintronic devices. In the present work, the intrinsic magnetism of monolayer square CrBr2 is predicted by using first-principles calculations. The monolayer CrBr2 is an intrinsic ferromagnetic (FM) half-metal with the half-metallic gap of 1.58 eV. Monte Carlo simulations based on the Heisenberg model estimates Tc as 212 K. Furthermore, the large compressive strain makes CrBr2 undergo ferromagnetic-antiferromagnetic phase transition, when the biaxial tensile strain larger than 9.3% leads to the emergence of semiconducting electronic structures. Our results show that the intrinsic half-metal with a high Tc and controllable magnetic properties endow monolayer square CrBr2 a potential material for spintronic applications.

cond-mat.mtrl-sci↗

arXiv2021

Robust large-gap topological insulator phase in transition-metal chalcogenide ZrTe$_4$Se

Based on density functional theory (DFT), we investigate the electronic properties of bulk and single-layer ZrTe$_4$Se. The band structure of bulk ZrTe$_4$Se can produce a semimetal-to-topological insulator (TI) phase transition under uniaxial strain. The maximum global band gap is 0.189 eV at the 7\% tensile strain. Meanwhile, the Z$_2$ invariants (0; 110) demonstrate conclusively it is a weak topological insulator (WTI). The two Dirac cones for the (001) surface further confirm the nontrivial topological nature. The single-layer ZrTe$_4$Se is a quantum spin Hall (QSH) insulator with a band gap 86.4 meV and Z$_2$=1, the nontrivial metallic edge states further confirm the nontrivial topological nature. The maximum global band gap is 0.211 eV at the tensile strain 8\%. When the compressive strain is more than 1\%, the band structure of single-layer ZrTe$_4$Se produces a TI-to-semimetal transition. These theoretical analysis may provide a method for searching large band gap TIs and platform for topological nanoelectronic device applications.

cond-mat.mtrl-sci↗

arXiv2020

Room-Temperature Superconductivity in Boron-Nitrogen Doped Lanthanum Superhydride

Recent theoretical and experimental studies of hydrogen-rich materials at megabar pressures (i.e., >100 GPa) have led to the discovery of very high-temperature superconductivity in these materials. Lanthanum superhydride LaH$_{10}$ has been of particular focus as the first material to exhibit a superconducting critical temperature (T$_c$) near room temperature. Experiments indicate that the use of ammonia borane as the hydrogen source can increase the conductivity onset temperatures of lanthanum superhydride to as high as 290 K. Here we examine the doping effects of B and N atoms on the superconductivity of LaH$_{10}$ in its fcc (Fm-3m) clathrate structure at megabar pressures. Doping at H atomic positions strengthens the H$_{32}$ cages of the structure to give higher phonon frequencies that enhance the Debye frequency and thus the calculated T$_c$. The predicted T$_c$ can reach 288 K in LaH$_{9.985}$N$_{0.015}$ within the average high-symmetry structure at 240 GPa.

cond-mat.supr-con↗

arXiv2020

Hole-Doped Room-Temperature Superconductivity in H$_{3}$S$_{1-x}$Z$_x$ (Z=C, Si)

We examine the effects of the low-level substitution of S atoms by C and Si atoms on the superconductivity of H$_3$S with the $Im\bar{3}m$ structure at megabar pressure. The hole doping can fine-tune the Fermi energy to reach the electronic density-of-states peak maximizing the electron-phonon coupling. This can boost the critical temperature from the original 203 K to 289 K and 283 K, respectively, for H$_3$S$_{0.962}$C$_{0.038}$ at 260 GPa and H$_3$S$_{0.960}$Si$_{0.040}$ at 230 GPa. The former may provide an explanation for the recent experimental observation of room-temperature superconductivity in a highly compressed C-S-H system [Nature 586, 373-377 (2020)]. Our work opens a new avenue for substantially raising the critical temperatures of hydrogen-rich materials.

cond-mat.supr-con↗

arXiv2020

Diverse magnetism in stable and metastable structures of CrTe

In this paper, we systematically investigated the structural and magnetic properties of CrTe by combining particle swarm optimization algorithm and first-principles calculations. With the electronic correlation effect considered, we predicted the ground-state structure of CrTe to be NiAs-type (space group P63/mmc) structure at ambient pressure, consistent with the experimental observation. Moreover, we found two extra meta-stable Cmca and R3m structure which have negative formation enthalpy and stable phonon dispersion at ambient pressure. The Cmca structure is a layered antiferromagnetic metal. The cleaved energy of a single layer is 0.464 J/m2, indicating the possible synthesis of CrTe monolayer. R3m structure is a ferromagnetic half-metal. When the pressure was applied, the ground-state structure of CrTe transitioned from P63/mmc to R3m, then to Fm3m structure at a pressure about 34 and 42 GPa, respectively. We thought these results help to motivate experimental studies the CrTe compounds in the application of spintronics.

cond-mat.mtrl-sci↗

arXiv2020

High Curie Temperature Ferromagnetic Semiconductor: Bimetal Transition Iodide V$_2$Cr$_2$I$_9$

Bimetal transition iodides in two-dimensional scale provide an interesting idea to combine a set of single-transition-metal ferromagnetic semiconductors together. Motivated by structural engineering on bilayer CrI$_3$ to tune its magnetism and works that realize ideal properties by stacking van der Waals transitional metal dichalcogenides in a certain order. Here we stack monolayer VI$_3$ onto monolayer CrI$_3$ with a middle-layer I atoms discarded to construct monolayer V$_2$Cr$_2$I$_9$. Based on this crystal model, the stable and metastable phases are determined among 7 possible phases by first-principles calculations. It is illustrated that both the two phases have Curie temperature $\sim$ 6 (4) times higher than monolayer CrI$_3$ and VI$_3$. The reason can be partly attributed to their large magnetic anisotropy energy (the maximum value reaches 412.9 $μ$eV/atom). More importantly, the Curie temperature shows an electric field and strain dependent character and can even surpass room temperature under a moderate strain range. At last, we believe that the bimetal transition iodide V$_2$Cr$_2$I$_9$ monolayer would support potential opportunities for spintronic devices.

cond-mat.mtrl-sci↗

arXiv2020

Large magnetic anisotropy energy and robust half-metallic ferromagnetism in 2D MnXSe$_4$ (X = As, Sb)

In recent years, intrinsic two-dimensional (2D) magnetism aroused great interest because of its potential application in spintronic devices. However, low Curie temperature (\emph{T}$_c$) and magnetic anisotropy energy (MAE) limit its application prospects. Here, using first-principles calculations based on density-functional theory (DFT), we predicted a series of stable MnXSe$_4$ (X=As, Sb) single-layer. The MAE of single-layer MnAsSe$_4$ and MnSbSe$_4$ was 648.76 and 808.95 $μ$eV per Mn atom, respectively. Monte Carlo (MC) simulations suggested the \emph{T}$_c$ of single-layer MnAsSe$_4$ and MnSbSe$_4$ was 174 and 250 K, respectively. The energy band calculation with hybrid Heyd-Scuseria-Ernzerhof (HSE06) function indicated the MnXSe$_4$ (X = As, Sb) were ferromagnetic (FM) half-metallic. Also it had 100\% spin-polarization ratio at the Fermi level. For MnAsSe$_4$ and MnSbSe$_4$, the spin-gap were 1.59 and 1.48 eV, respectively. These excellent magnetic properties render MnXSe$_4$ (X = As, Sb) promising candidate materials for 2D spintronic applications.

cond-mat.mtrl-sci↗