اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNegative Poissons ratios in few-layer orthorhombic arsenic from first-principles calculations
114
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
A material exhibiting a negative Poissons ratio is always one of the leading topics in materials science, which is due to the potential applications in those special areas such as defence and medicine. In this letter, we demonstrate a new material, few-layer orthorhombic arsenic, also possesses the negative Poissons ratio. For monolayer arsenic, the negative Poissons ratio is predicted to be around -0.09, originated from the hinge-like structure within the single layer of arsenic. When the layer increases, the negative Poissons ratio becomes more negative and finally approaches the limit at four-layer, which is very close to the bulks value of -0.12. The underlying mechanism is proposed for this layer-dependent negative Poissons ratio, where the internal bond lengths as well as the normal Poissons ratio within layer play a key role. The study like ours sheds new light on the physics of negative Poissons ratio in those hinge-like nano-materials.
قيم البحث
اقرأ أيضاً
We employ a tight-binding parametrization based on the Slater Koster model in order to fit the band structures of single-layer, bilayer and bulk black phosphorus obtained from first-principles calculations. We find that our model, which includes 9 or
17 parameters depending on whether overlap is included or not, reproduces quite well the ab-initio band structures over a wide energy range, especially the occupied bands. We also find that the inclusion of overlap parameters improves the quality of the fit for the conduction bands. On the other hand, hopping and on-site energies are consistent throughout the different systems, which is an indication that our model is suitable for calculations on multilayer black phosphorus and more complex situations in which first-principles calculations become prohibitive, such as disordered systems and heterostructures with a large lattice mismatch. We also discuss the limitations of the model and how the fit procedure can be improved for a more accurate description of bands in the vicinity of the Fermi energy.
We have given a summary on our theoretical predictions of three kinds of topological semimetals (TSMs), namely, Dirac semimetal (DSM), Weyl semimetal (WSM) and Node-Line Semimetal (NLSM). TSMs are new states of quantum matters, which are different wi
th topological insulators. They are characterized by the topological stability of Fermi surface, whether it encloses band crossing point, i.e., Dirac cone like energy node, or not. They are distinguished from each other by the degeneracy and momentum space distribution of the nodal points. To realize these intriguing topological quantum states is quite challenging and crucial to both fundamental science and future application. In 2012 and 2013, Na$_3$Bi and Cd$_3$As$_2$ were theoretically predicted to be DSM, respectively. Their experimental verifications in 2014 have ignited the hot and intensive studies on TSMs. The following theoretical prediction of nonmagnetic WSM in TaAs family stimulated a second wave and many experimental works have come out in this year. In 2014, a kind of three dimensional crystal of carbon has been proposed to be NLSM due to negligible spin-orbit coupling and coexistence of time-reversal and inversion symmetry. Though the final experimental confirmation of NLSM is still missing, there have been several theoretical proposals, including Cu$_3$PdN from us. In the final part, we have summarized the whole family of TSMs and their relationship.
The bulk photovoltaic effect (BPVE) refers to current generation due to illumination by light in a homogeneous bulk material lacking inversion symmetry. In addition to the intensively studied shift current, the ballistic current, which originates fro
m asymmetric carrier generation due to scattering processes, also constitutes an important contribution to the overall kinetic model of the BPVE. In this letter, we use a perturbative approach to derive a formula for the ballistic current resulting from the intrinsic electron-phonon scattering in a form amenable to first-principles calculation. We then implement the theory and calculate the ballistic current of the prototypical BPVE material ch{BaTiO3} using quantum-mechanical density functional theory. The magnitude of the ballistic current is comparable to that of shift current, and the total spectrum (shift plus ballistic) agrees well with the experimentally measured photocurrents. Furthermore, we show that the ballistic current is sensitive to structural change, which could benefit future photovoltaic materials design.
We report first-principles density-functional theory studies of native point defects and defect complexes in olivine-type LiFePO4, a promising candidate for rechargeable Li-ion battery electrodes. The defects are characterized by their formation ener
gies which are calculated within the GGA+U framework. We find that native point defects are charged, and each defect is stable in one charge state only. Removing electrons from the stable defects always generates defect complexes containing small hole polarons. Defect formation energies, hence concentrations, and defect energy landscapes are all sensitive to the choice of atomic chemical potentials which represent experimental conditions. One can, therefore, suppress or enhance certain native defects in LiFePO4 via tuning the synthesis conditions. Based on our results, we provide insights on how to obtain samples in experiments with tailored defect concentrations for targeted applications. We also discuss the mechanisms for ionic and electronic conduction in LiFePO4 and suggest strategies for enhancing the electrical conductivity.
We present calculations for electronic and magnetic properties of surface states confined by a circular quantum corral built of magnetic adatoms (Fe) on a Cu(111) surface. We show the oscillations of charge and magnetization densities within the corr
al and the possibility of the appearance of spin--polarized states. In order to classify the peaks in the calculated density of states with orbital quantum numbers we analyzed the problem in terms of a simple quantum mechanical circular well model. This model is also used to estimate the behaviour of the magnetization and energy with respect to the radius of the circular corral. The calculations are performed fully relativistically using the embedding technique within the Korringa-Kohn-Rostoker method.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
