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Modeling Interlayer Interactions and Phonon Thermal Transport in Silicene Bilayer. (arXiv:2305.15423v1 [cond-mat.mtrl-sci])

2023-05-28T08:31:00+00:00May 28th, 2023|Categories: Publications|Tags: , , |

We develop an accurate interlayer pairwise potential derived from the $textit{ab-initio}$ calculations and investigate the thermal transport of silicene bilayers within the framework of equilibrium molecular dynamics simulations. We find that the electronic properties are sensitive to the temperature with the opening of band gap in the $Gammarightarrow M$ direction at the room temperature. The calculated phonon thermal conductivity of bilayer silicene is surprisingly higher than that of the monolayer silicene, contrary to the trends reported for other class of 2D materials like graphene and hBN bilayers. We attribute this counterintuitive result to the higher velocity of LA$_1$/LA$_2$ phonon modes arising from the interlayer interaction effects and buckling, inherent to silicene bilayer. Interestingly, the thermal conductivity of both the mono- and bilayer silicene decreases with temperature as $kappasim T^{-0.9}$ because of the strong correlations between heat current decay characteristic timescales and temperature ($tausim T^{-0.75}$). The mechanisms underlying phonon thermal transport in silicene bilayer are further established by analyzing the temperature induced changes in acoustic group velocity.

Published in: "arXiv Material Science".

Thermally-driven phase transitions in freestanding low-buckled silicene, germanene, and stanene. (arXiv:2303.08237v1 [cond-mat.mtrl-sci])

2023-03-16T02:29:39+00:00March 16th, 2023|Categories: Publications|Tags: , , , |

Low-buckled silicene, germanene, and stanene are group$-IV$ graphene allotropes. They form a honeycomb lattice out of two interpenetrating ($A$ and $B$) triangular sublattices that are vertically separated by a small distance $Delta_z$. The atomic numbers $Z$ of silicon, germanium, and tin are larger to carbon’s ($Z_C=6$), making them the first experimentally viable two-dimensional topological insulators. Those materials have a twice-energy-degenerate atomistic structure characterized by the buckling direction of the $B$ sublattice with respect to the $A$ sublattice [whereby the $B-$atom either protrudes {em above} ($Delta_z>0$) or {em below} ($Delta_z

Published in: "arXiv Material Science".

Transferability of force fields for 2D silicon (silicene). (arXiv:2303.01001v1 [cond-mat.mtrl-sci])

2023-03-03T02:29:21+00:00March 3rd, 2023|Categories: Publications|Tags: |

An ability of various interatomic potentials to reproduce the properties of silicene (2D silicon) polymorphs were examined. Structural and mechanical properties of the flat (FS), low-buckled (LBS), trigonal dumbbell (TDS), honeycomb dumbbell (HDS) and large honeycomb dumbbell (LHDS) single-layer silicon (silicene) phases, were obtained using density functional theory (DFT) and molecular statics (MS) calculations with Tersoff, MEAM, Stillinger-Weber, EDIP, ReaxFF, COMB and machine-learning-based (ML-IAP) interatomic potentials. A quantitative systematic comparison and discussion of the results obtained are reported.

Published in: "arXiv Material Science".

Deformation Effect on Graphene Quantum Dot/Graphane and Silicene Quantum Dot/Silicane array. (arXiv:2212.14793v1 [cond-mat.mes-hall])

2023-01-02T04:30:22+00:00January 2nd, 2023|Categories: Publications|Tags: , , , |

This article presents a design for the two-dimensional heterostructure (2DH) systems of graphane quantum dot array in graphane (GQD/Graphane), and silicene quantum dot array in silicane (SiQD/Silicane). A first-principles method was used to evaluate the deformation effect for magnetism as well as the electronic properties for the 2DH systems. The energy levels of quantum dot (QD) array and the band structure of its hydrogenated counterpart are coupling for both 2DH systems of C and Si. The hydrogenated part shares part of strain on QD array, however, the strain sharing effect is stronger in SiQD/silicane than in GQD/graphane. The strain sharing enhances the band coupling of the QD and its hydrogen counterpart in the low energy region. The band coupling alters the electronic properties of the 2DH systems and change the magnetic properties of triangular and parallelogram of SiQD/Silicane array under compressive strain larger than 5%. Strain modulates the band gap of the 2DH system. For SiQD/Silicane systems, the homogeneous strain not only induces the phase transition of from semiconductor to metal, but also remove the magnetism of triangular and parallelogram SiQD array. The 2DH system can be used in the design of nanoelectronic devices and binary logic based on nanoscale magnetism.

Published : "arXiv Mesoscale and Nanoscale Physics".

A new efficient ab-initio approach for calculating the bending stiffness of 2D materials. (arXiv:2212.11913v1 [cond-mat.mtrl-sci])

2022-12-23T02:29:27+00:00December 23rd, 2022|Categories: Publications|Tags: , , , |

This work proposes a new efficient approach for calculating the bending stiffness of two-dimensional materials using simple atomistic tests on small periodic unit cells. The tests are designed such that bending deformations are dominating and membrane deformations are minimized. Atomistic ab-initio simulations then allow for the efficient computation of bending energies. Density functional theory is used for this. Atomistic bending energies are then compared to classical models from structural mechanics. Two different models are considered for this — one based on beam theory and one based on rigid linkage theory — and their results are compared with each other. Four different materials with 2D hexagonal (honeycomb) structure are chosen as a case study: graphene, hexagonal boron nitride, silicene, and blue phosphorene. The calculated bending stiffnesses converge with increasing unit cell size, such that small unit cells already provide accurate results that are in good agreement with the literature. Using the same atomistic tests, it is shown that the bending stiffness of graphene can still be considered constant at moderately large deformations. Apart from being efficient and accurate, the proposed approach allows for various extensions.

Published in: "arXiv Material Science".

Engineering quantum tunneling effect of carriers in silicene field-effect transistors. (arXiv:2212.06072v1 [cond-mat.mes-hall])

2022-12-13T04:30:29+00:00December 13th, 2022|Categories: Publications|Tags: , |

This paper theoretically investigates the impact of rectangular barrier potential on the quantum transport properties of silicene field-effect transistors. In particular, approximate analytical solutions of the Dirac equation are given to obtain the transmission and reflection probabilities. The Landauer-B”{u}ttiker formalism has been implemented in a developed computer program to compute the conductance in terms of different scattering parameters. The transport properties of silicene field-effect transistors can be manipulated by a rectangular barrier. In particular, it is found that the transmission probability is very sensitive to the barrier height and incident energy. The results show the occurrence of Klein tunneling and resonant tunneling, which strongly depend on the barrier width. A rectangular potential barrier significantly enhances the Klein tunneling effect of Dirac electrons. In fact, the perfect transmission can occur at a variety of oblique incidence angles and is not just restricted to normal incidence. Besides, the transmission profile shows a much more fragmented structure with increasing barrier width, as occurred in Fabry-P'{e}rot resonances. On the other hand, the conductance exhibits a non-monotonic Fermi energy dependence and oscillates rapidly with increasing barrier height. However, at a fixed value of barrier height, there is almost no difference among the conductance profiles for a high Fermi energy value. When the Fermi energy and the barrier height are equal, the conductance drops to a local minimum. For a thin barrier, the conductance is significantly reduced, unlike its oscillating behavior for a thicker one. Our findings demonstrate the development of silicene field-effect transistors and offer

Published : "arXiv Mesoscale and Nanoscale Physics".

Dynamical optical conductivity for gapped $alpha-mathcal{T}_3$ materials with a curved “flat” band. (arXiv:2212.05303v1 [cond-mat.mtrl-sci])

2022-12-13T02:29:38+00:00December 13th, 2022|Categories: Publications|Tags: , , |

We have calculated the dynamical optical conductivity for $alpha-mathcal{T}_3$ materials in the presence of a finite bandgap in their energy bandstructure. This is a special type of energy dispersions because for all $alpha-mathcal{T}_3$ materials with a bandgap, except graphene and a dice lattice limits, the flat band receives a non-zero dispersion and assumes a curved shape. The infinite ${bf k}$-degeneracy of the flat energy band is also lifted. Such a low-energy bandstructure could be obtained if an $alpha-mathcal{T}_3$ material is irradiated off-resonant with circularly polarized light. We have calculated the optical conductivity for the zero and finite temperatures, as well as for the cases of a finite and nearly-zero doping. We have demonstrated that analytical expressions could be in principle obtained for all types of gapped $alpha-mathcal{T}_3$ materials and provided the closed-form analytical expressions for a gapped dice lattice. Our numerical results reveal some well-known signatures of the optical conductivity in $alpha-mathcal{T}_3$ and silicene with two non-equivalent bandgaps, as well as demonstrate some very specific features which have not been previously found in any existing Dirac materials.

Published in: "arXiv Material Science".

First-principle calculations of plasmon excitations in graphene,silicene and germanene. (arXiv:2210.11736v1 [physics.comp-ph])

2022-10-24T02:29:38+00:00October 24th, 2022|Categories: Publications|Tags: , |

Plasmon excitations in graphene, silicene and germanene are studied using linear-response time dependent density functional theory within the random phase approximation (RPA). Here, we examine both the plasmon dispersion behavior and lifetime of extrinsic and intrinsic plasmons for these three materials. For extrinsic plasmons, we found that their properties are closely related to Landau damping. In the region without single-particle excitation (SPE), the plasmon dispersion shows a sqrt{q} behavior and the lifetime is infinite at the RPA level, while in the single-particle excitation region, the plasmon dispersion shows a quasilinear behavior and the lifetime is finite. Moreover, for intrinsic plasmons, unlike graphene, the plasmon dispersion behavior of silicene and germanene exhibits a two-peak structure, which can be attributed to the complex and hybridized band structure of these two materials.

Published in: "arXiv Material Science".

Tunneling magnetoresistance and spin-valley polarization of aperiodic magnetic silicene superlattices. (arXiv:2209.13783v1 [cond-mat.mes-hall])

2022-09-29T04:30:14+00:00September 29th, 2022|Categories: Publications|Tags: |

Magnetic silicene superlattices (MSSLs) are versatile structures with spin-valley polarization and tunneling magnetoresistance (TMR) capabilities. However, the oscillating transport properties related to the superlattice periodicity impede stable spin-valley polarization states reachable by reversing the magnetization direction. Here, we show that aperiodicity can be used to improve the spin-valley polarization and TMR by reducing the characteristic conductance oscillations of periodic MSSLs (P-MSSLs). Using the Landauer-B”uttiker formalism and the transfer matrix method, we investigate the spin-valley polarization and the TMR of Fibonacci (F-) and Thue-Morse (TM-) MSSLs as typical aperiodic superlattices. Our findings indicate that aperiodic superlattices with higher disorder provide better spin-valley polarization and TMR values. In particular, TM-MSSLs reduce considerably the conductance oscillations giving rise to two well-defined spin-valley polarization states and a better TMR than F- and P-MSSLs. F-MSSLs also improve the spin-valley polarization and TMR, however they depend strongly on the parity of the superlattice generation.

Published : "arXiv Mesoscale and Nanoscale Physics".

Unconventional Gapless Semiconductor in Extended Martini Network in Honeycomb Covalent Materials. (arXiv:2209.00775v1 [cond-mat.mtrl-sci])

2022-09-05T04:30:17+00:00September 5th, 2022|Categories: Publications|Tags: , |

We study characteristic electronic structures in the extended martini lattice model and propose its materialization in $pi$-electron networks constructed by designated chemisorption on graphene and silicene. By investigating the minimal tight-binding model, we reveal rich electronic structures tuned by the ratio of hopping parameters, ranging from the band insulator to the unconventional gapless semiconductor. Remarkably, the unconventional gapless semiconductor is characterized by the flat band at the Fermi level. Further, the density functional theory calculations for candidate materials reveal that the characteristic electronic structures can be realized by the designated chemisorption or the chemical substitution on graphene and silicene, and that the electronic structure near the Fermi level is tunable by the choice of the atomic species of adsorbed atoms. Our results open the way to search exotic electronic structures and their functionalities induced by the extended martini lattice.

Published : "arXiv Mesoscale and Nanoscale Physics".

Unconventional Gapless Semiconductor in Extended Martini Network in Honeycomb Covalent Materials. (arXiv:2209.00775v1 [cond-mat.mtrl-sci])

2022-09-05T02:29:15+00:00September 5th, 2022|Categories: Publications|Tags: , |

We study characteristic electronic structures in the extended martini lattice model and propose its materialization in $pi$-electron networks constructed by designated chemisorption on graphene and silicene. By investigating the minimal tight-binding model, we reveal rich electronic structures tuned by the ratio of hopping parameters, ranging from the band insulator to the unconventional gapless semiconductor. Remarkably, the unconventional gapless semiconductor is characterized by the flat band at the Fermi level. Further, the density functional theory calculations for candidate materials reveal that the characteristic electronic structures can be realized by the designated chemisorption or the chemical substitution on graphene and silicene, and that the electronic structure near the Fermi level is tunable by the choice of the atomic species of adsorbed atoms. Our results open the way to search exotic electronic structures and their functionalities induced by the extended martini lattice.

Published in: "arXiv Material Science".

Switching modulation of spin transport in ferromagnetic tetragonal silicene. (arXiv:2207.12676v1 [cond-mat.mes-hall])

2022-07-27T04:30:26+00:00July 27th, 2022|Categories: Publications|Tags: , |

We study the band structure and transport properties of ferromagnetic tetragonal silicene nanoribbons by using the non-equilibrium Green’s function method. The band structure and spin-dependent conductance are discussed under the combined effect of the external electric field, potential energy, exchange field and the spin-orbit coupling. One can easily realize a phase transition from a semimetallic to a semiconducting state by changing the transverse width of the nanoribbon. Separation of spin-dependent conductances arises from the effect of exchange field and the spin-orbit coupling, while zero-conductance behaviors exhibit spin-dependent band gaps induced by the electric field. We propose a device configuration of four-terminal tetragonal silicene nanoribbon with two central channels. It is found that spin current can be controlled by utilizing two switches. The switch with a high potential barrier can block electrons flowing from the central scattering region into other terminals. Interestingly, applying only one switch can realize spin-dependent zero conductance and large spin polarization. Two switches can provide multiple operations for controlling spin-dependent transport properties. The two-channel ferromagnetic tetragonal silicene nanoribbon can realize an effective separation of spin current, which may be a potential candidate for spintronic devices.

Published : "arXiv Mesoscale and Nanoscale Physics".

Atomically-thin metallic Si and Ge allotropes with high Fermi velocities. (arXiv:2207.06669v1 [cond-mat.mtrl-sci])

2022-07-15T02:29:34+00:00July 15th, 2022|Categories: Publications|Tags: , |

Silicon and germanium are the well-known materials used to manufacture electronic devices for the integrated circuits but they themselves are not considered as promising options for interconnecting the devices due to their semiconducting nature. We have discovered that both Si and Ge atoms can form unexpected metallic monolayer structures which are more stable than the extensively studied semimetallic silicene and germanene, respectively. More importantly, the newly discovered two-dimensional allotropes of Si and Ge have Fermi velocities superior to the Dirac fermions in graphene, indicating that the metal wires needed in the silicon-based integrated circuits can be made of Si atom itself without incompatibility, allowing for all-silicon-based integrated circuits.

Published in: "arXiv Material Science".

Comment on “Anisotropic peridynamics for homogenized microstructured materials” by Vito Diana, Andrea Bacigalupo, Marco Lepidi and Luigi Gambarotta [Comput. Methods Appl. Mech. Engrg. 392 (2022) 114704]. (arXiv:2206.01632v2 [cond-mat.mtrl-sci] UPDATED)

2022-06-28T02:29:52+00:00June 28th, 2022|Categories: Publications|Tags: |

Recently, Vito Diana, Andrea Bacigalupo, Marco Lepidi and Luigi Gambarotta proposed an anisotropic continuum-molecular model based on pair potentials for describing the linear behavior of periodic heterogeneous Cauchy materials in the framework of peridynamic theory. Unfortunately, the proposed model for an isotropic material may have zero or even negative shear stiffness and this will be the case for Silicene or Germanene, for example. In addition, 2D symmetries were confused with 3D symmetries, and hence the limits for the Poisson’s ratio.

Published in: "arXiv Material Science".

Aluminum functionalized silicene: a potential anode material for alkali metal ion batteries. (arXiv:2206.09079v1 [cond-mat.mtrl-sci])

2022-06-22T02:29:44+00:00June 22nd, 2022|Categories: Publications|Tags: |

We have investigated the possibility of using aluminum functionalized silicene trilayers (ABC-Si$_4$Al$_2$) as an anode material for alkali metal ion batteries (AMIBs). First, we studied the thermodynamic stability of ABC-Si$_4$Al$_2$ using ab-initio molecular dynamics simulations, showing that this material remains stable up to 600 K. Then, we explored the properties of alkali metal atoms (Li, Na, K) adsorption in ABC-Si$_4$Al$_2$, finding several available sites with high adsorption energies. Moreover, we computed the diffusion properties of those atoms along high-symmetry paths using the nudged elastic band method. The results indicated diffusion barriers as low as those in graphite, especially for Na (0.32 eV) and K (0.22 eV), which allows those ions to migrate easily on the material’s surface. Our studies also revealed that the full loaded Li$_4$Si$_4$Al$_2$, Na$_2$Si$_4$Al$_2$, and K$_2$Si$_4$Al$_2$ systems provide low open-circuit voltage, ranging from 0.14 to 0.49 V, and large theoretical capacity of 645 mAh/g for Li- and 322 mAh/g for Na- and K-ion batteries, values that are close to the ones in other anode materials, such as graphite, TiO$_2$, and silicene-based systems. Those results indicate that aluminum functionalized few-layer silicene is a promising material for AMIBs anodes, particularly for Na- and K-ion batteries.

Published in: "arXiv Material Science".

Electrically switchable giant Berry curvature dipole in silicene, germanene and stanene. (arXiv:2205.06966v1 [cond-mat.mes-hall])

2022-05-17T04:30:23+00:00May 17th, 2022|Categories: Publications|Tags: , |

The anomalous Hall effect in time-reversal symmetry broken systems is underpinned by the concept of Berry curvature in band theory. However, recent experiments reveal that the nonlinear Hall effect can be observed in non-magnetic systems without applying an external magnetic field. The emergence of nonlinear Hall effect under time-reversal symmetric conditions can be explained in terms of non-vanishing Berry curvature dipole arising from inversion symmetry breaking. In this work, we availed realistic tight-binding models, first-principles calculations, and symmetry analyses to explore the combined effect of transverse electric field and strain, which leads to a giant Berry curvature dipole in the elemental buckled honeycomb lattices — silicene, germanene, and stanene. The external electric field breaks the inversion symmetry of these systems, while strain helps to attain an asymmetrical distribution of Berry curvature of a single valley. Furthermore, the topology of the electronic wavefunction switches from the band inverted quantum spin Hall state to normal insulating one at the gapless point. This band gap closing at the critical electric field strength is accompanied by an enhanced Berry curvature and concomitantly a giant Berry curvature dipole at the Fermi level. Our results predict the occurrence of an electrically switchable nonlinear electrical and thermal Hall effect in a new class of elemental systems that can be experimentally verified.

Published : "arXiv Mesoscale and Nanoscale Physics".

Electrically switchable giant Berry curvature dipole in silicene, germanene and stanene. (arXiv:2205.06966v1 [cond-mat.mes-hall])

2022-05-17T02:29:37+00:00May 17th, 2022|Categories: Publications|Tags: , |

The anomalous Hall effect in time-reversal symmetry broken systems is underpinned by the concept of Berry curvature in band theory. However, recent experiments reveal that the nonlinear Hall effect can be observed in non-magnetic systems without applying an external magnetic field. The emergence of nonlinear Hall effect under time-reversal symmetric conditions can be explained in terms of non-vanishing Berry curvature dipole arising from inversion symmetry breaking. In this work, we availed realistic tight-binding models, first-principles calculations, and symmetry analyses to explore the combined effect of transverse electric field and strain, which leads to a giant Berry curvature dipole in the elemental buckled honeycomb lattices — silicene, germanene, and stanene. The external electric field breaks the inversion symmetry of these systems, while strain helps to attain an asymmetrical distribution of Berry curvature of a single valley. Furthermore, the topology of the electronic wavefunction switches from the band inverted quantum spin Hall state to normal insulating one at the gapless point. This band gap closing at the critical electric field strength is accompanied by an enhanced Berry curvature and concomitantly a giant Berry curvature dipole at the Fermi level. Our results predict the occurrence of an electrically switchable nonlinear electrical and thermal Hall effect in a new class of elemental systems that can be experimentally verified.

Published in: "arXiv Material Science".

Plasmon damping rates in Coulomb-coupled two-dimensional layers in a heterostructure. (arXiv:2205.00053v1 [cond-mat.mes-hall])

2022-05-03T04:30:23+00:00May 3rd, 2022|Categories: Publications|Tags: , , |

The Coulomb excitations of charge density oscillation are calculated for a double-layer heterostructure. Specifically, we consider two-dimensional (2D) layers of silicene and graphene on a substrate. From the obtained surface response function, we calculated the plasmon dispersion relations which demonstrate the way in which the Coulomb coupling renormalizes the plasmon frequencies. Additionally, we present a novel result for the damping rates of the plasmons in this Coulomb coupled heterostructure and compare these results as the separation between layers is varied.

Published : "arXiv Mesoscale and Nanoscale Physics".

Plasmon damping rates in Coulomb-coupled two-dimensional layers in a heterostructure. (arXiv:2205.00053v1 [cond-mat.mes-hall])

2022-05-03T02:29:36+00:00May 3rd, 2022|Categories: Publications|Tags: , , |

The Coulomb excitations of charge density oscillation are calculated for a double-layer heterostructure. Specifically, we consider two-dimensional (2D) layers of silicene and graphene on a substrate. From the obtained surface response function, we calculated the plasmon dispersion relations which demonstrate the way in which the Coulomb coupling renormalizes the plasmon frequencies. Additionally, we present a novel result for the damping rates of the plasmons in this Coulomb coupled heterostructure and compare these results as the separation between layers is varied.

Published in: "arXiv Material Science".

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