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17 results on '"Grassano D"'

1. Work function, deformation potential, and collapse of Landau levels in strained graphene and silicene

Author

Grassano, D., D'Alessandro, M., Pulci, O., Sharapov, S. G., Gusynin, V. P., and Varlamov, A. A.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We perform a systematic {\it ab initio} study of the work function and its uniform strain dependence for graphene and silicene for both tensile and compressive strains. The Poisson ratios associated with armchair and zigzag strains are also computed. Based on these results, we obtain the deformation potential, crucial for straintronics, as a function of the applied strain. Further, we propose a particular experimental setup with a special strain configuration that generates only the electric field, while the pseudomagnetic field is absent. Then, applying a real magnetic field, one should be able to realize experimentally the spectacular phenomenon of the collapse of Landau levels in graphene or related two-dimensional materials., Comment: 9 pages, 7 figures; final version published in PRB

Published
2020
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2. Entropy Signatures of Topological Phase Transitions

Author

Galperin, Y. M., Grassano, D., Gusynin, V. P., Kavokin, A. V., Pulci, O., Sharapov, S. G., Shubnyi, V. O., and Varlamov, A. A.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We review the behavior of the entropy per particle in various two-dimensional electronic systems. The entropy per particle is an important characteristic of any many body system that tells how the entropy of the ensemble of electrons changes if one adds one more electron. Recently, it has been demonstrated how the entropy per particle of a two-dimensional electron gas can be extracted from the recharging current dynamics in a planar capacitor geometry. These experiments pave the way to the systematic studies of entropy in various crystal systems including novel two-dimensional crystals such as gapped graphene, germanene and silicene. Theoretically, the entropy per particle is linked to the temperature derivative of the chemical potential of the electron gas by the Maxwell relation. Using this relation, we calculate the entropy per particle in the vicinity of topological transitions in various two-dimensional electronic systems. We show that the entropy experiences quantized steps at the points of Lifshitz transitions in a two-dimensional electronic gas with a parabolic energy spectrum. In contrast, in doubled-gapped Dirac materials, the entropy per particles demonstrates characteristic spikes once the chemical potential passes through the band edges. The transition from a topological to trivial insulator phase in germanene is manifested by the disappearance of a strong zero-energy resonance in the entropy per particle dependence on the chemical potential. We conclude that studies of the entropy per particle shed light on multiple otherwise hidden peculiarities of the electronic band structure of novel two-dimensional crystals., Comment: 33 pages,15 figures. Accepted for publication in JETP. arXiv admin note: text overlap with arXiv:1803.02083, arXiv:1712.09118, arXiv:1703.08962, arXiv:1512.08450

Published
2018
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3. Detection of topological phase transitions through entropy measurements: the case of germanene

Author

Grassano, D., Pulci, O., Shubnyi, V. O., Sharapov, S. G., Gusynin, V. P., Kavokin, A. V., and Varlamov, A. A.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We propose a characterization tool for studies of the band structure of new materials promising for the observation of topological phase transitions. We show that a specific resonant feature in the entropy per electron dependence on the chemical potential may be considered as a fingerprint of the transition between topological and trivial insulator phases. The entropy per electron in a honeycomb two-dimensional crystal of germanene subjected to the external electric field is obtained from the first principle calculation of the density of electronic states and the Maxwell relation. We demonstrate that, in agreement to the recent prediction of the analytical model, strong spikes in the entropy per particle dependence on the chemical potential appear at low temperatures. They are observed at the values of the applied bias both below and above the critical value that corresponds to the transition between the topological insulator and trivial insulator phases, while the giant resonant feature in the vicinity of zero chemical potential is strongly suppressed at the topological transition point, in the low temperature limit. In a wide energy range, the van Hove singularities in the electronic density of states manifest themselves as zeros in the entropy per particle dependence on the chemical potential., Comment: 8 pages, 5 figures; final version published in PRB

Published
2018
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4. High-throughput screening of Weyl semimetals

Author

Grassano, D, Marzari, N, Campi, D, Grassano D., Marzari N., Campi D., Grassano, D, Marzari, N, Campi, D, Grassano D., Marzari N., and Campi D.

Abstract

Topological Weyl semimetals represent a novel class of nontrivial materials, where band crossings with linear dispersions take place at generic momenta across reciprocal space. These crossings give rise to low -energy properties akin to those of Weyl fermions, and are responsible for several exotic phenomena. Up to this day, only a handful of Weyl semimetals have been discovered, and the search for new ones remains a very active area. The main challenge on the computational side arises from the fact that many of the tools used to identify the topological class of a material do not provide a complete picture in the case of Weyl semimetals. In this work, we propose an alternative and inexpensive, procedure to screen for possible Weyl fermions, starting from the analysis of the band structure along high -symmetry directions in the absence of spin -orbit coupling. We test the method by running a high -throughput screening on a set of 5455 inorganic bulk materials and identify 49 possible candidates for topological properties. A further analysis, carried out by identifying and characterizing the crossings in the Brillouin zone, shows us that three of these candidates are Weyl semimetals. Interestingly, while these three materials underwent other high -throughput screenings, none had revealed their topological behavior before.

Published
2024

5. Complementary screening for quantum spin Hall insulators in two-dimensional exfoliable materials

Author

Grassano, D, Campi, D, Marrazzo, A, Marzari, N, Grassano D., Campi D., Marrazzo A., Marzari N., Grassano, D, Campi, D, Marrazzo, A, Marzari, N, Grassano D., Campi D., Marrazzo A., and Marzari N.

Abstract

Quantum spin Hall insulators are a class of topological materials that has been extensively studied during the past decade. One of their distinctive features is the presence of a finite band gap in the bulk and gapless, topologically protected edge states that are spin-momentum locked. These materials are characterized by a Z(2) topological order where, in the two-dimensional case, a single topological invariant can be even or odd for a trivial or a topological material, respectively. Thanks to their interesting properties, such as the realization of dissipationless spin currents, spin pumping, and spin filtering, they are of great interest in the field of electronics, spintronics, and quantum computing. In this work we perform a high-throughput screening of quantum spin Hall insulators starting from a set of 783 two-dimensional exfoliable materials, recently identified from a systematic screening of the Inorganic Crystal Structure Database, Crystallography Open Database, and Materials Platform for Data Science databases. We find four Z(2) topological insulators and seven direct gap metals that have the potential of becoming quantum spin Hall insulators under a reasonably weak external perturbation.

Published
2023

8. Strain-induced effects on the electronic properties of 2D materials

Author

Postorino, S, Grassano, D, D'Alessandro, M, Pianetti, A, Pulci, O, Palummo, M, Postorino S., Grassano D., D'Alessandro M., Pianetti A., Pulci O., Palummo M., Postorino, S, Grassano, D, D'Alessandro, M, Pianetti, A, Pulci, O, Palummo, M, Postorino S., Grassano D., D'Alessandro M., Pianetti A., Pulci O., and Palummo M.

Abstract

Thanks to the ultrahigh flexibility of 2D materials and to their extreme sensitivity to applied strain, there is currently a strong interest in studying and understanding how their electronic properties can be modulated by applying a uniform or nonuniform strain. In this work, using density functional theory (DFT) calculations, we discuss how uniform biaxial strain affects the electronic properties, such as ionization potential, electron affinity, electronic gap, and work function, of different classes of 2D materials from X-enes to nitrides and transition metal dichalcogenides. The analysis of the states in terms of atomic orbitals allows to explain the observed trends and to highlight similarities and differences among the various materials. Moreover, the role of many-body effects on the predicted electronic properties is discussed in one of the studied systems. We show that the trends with strain, calculated at the GW level of approximation, are qualitatively similar to the DFT ones solely when there is no change in the character of the valence and conduction states near the gap.

Published
2020

13. Strain-induced effects on the electronic properties of 2D materials

Author

Maurizia Palummo, Olivia Pulci, Sara Postorino, Davide Grassano, Andrea Pianetti, Marco D'Alessandro, Postorino, S, Grassano, D, D'Alessandro, M, Pianetti, A, Pulci, O, and Palummo, M

Subjects
Flexibility (engineering), Materials science, Settore FIS/03, Strain (chemistry), 02 engineering and technology, 021001 nanoscience & nanotechnology, Class file, 01 natural sciences, Electronic, Optical and Magnetic Materials, 0103 physical sciences, Ceramics and Composites, Sensitivity (control systems), Electrical and Electronic Engineering, Composite material, 010306 general physics, 0210 nano-technology, LaTeX2e, Biotechnology, Electronic properties
Abstract

Thanks to the ultrahigh flexibility of 2D materials and to their extreme sensitivity to applied strain, there is currently a strong interest in studying and understanding how their electronic properties can be modulated by applying a uniform or nonuniform strain. In this work, using density functional theory (DFT) calculations, we discuss how uniform biaxial strain affects the electronic properties, such as ionization potential, electron affinity, electronic gap, and work function, of different classes of 2D materials from X-enes to nitrides and transition metal dichalcogenides. The analysis of the states in terms of atomic orbitals allows to explain the observed trends and to highlight similarities and differences among the various materials. Moreover, the role of many-body effects on the predicted electronic properties is discussed in one of the studied systems. We show that the trends with strain, calculated at the GW level of approximation, are qualitatively similar to the DFT ones solely when there is no change in the character of the valence and conduction states near the gap.

Published
2020

14. Excitonic Fine Structure in Emission of Linear Carbon Chains.

Author

Kutrovskaya S, Osipov A, Baryshev S, Zasedatelev A, Samyshkin V, Demirchyan S, Pulci O, Grassano D, Gontrani L, Hartmann RR, Portnoi ME, Kucherik A, Lagoudakis PG, and Kavokin A

Abstract

We studied monatomic linear carbon chains stabilized by gold nanoparticles attached to their ends and deposited on a solid substrate. We observe spectral features of straight chains containing from 8 to 24 atoms. Low-temperature PL spectra reveal characteristic triplet fine structures that repeat themselves for carbon chains of different lengths. The triplet is invariably composed of a sharp intense peak accompanied by two broader satellites situated 15 and 40 meV below the main peak. We interpret these resonances as an edge-state neutral exciton and positively and negatively charged trions, respectively. The time-resolved PL shows that the radiative lifetime of the observed quasiparticles is about 1 ns, and it increases with the increase of the length of the chain. At high temperatures a nonradiative exciton decay channel appears due to the thermal hopping of carriers between parallel carbon chains. Excitons in carbon chains possess large oscillator strengths and extremely low inhomogeneous broadenings.

Published
2020
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15. Giant excitonic absorption and emission in two-dimensional group-III nitrides.

Author

Prete MS, Grassano D, Pulci O, Kupchak I, Olevano V, and Bechstedt F

Abstract

Absorption and emission of pristine-like semiconducting monolayers of BN, AlN, GaN, and InN are systematically studied by ab-initio methods. We calculate the absorption spectra for in-plane and out-of-plane light polarization including quasiparticle and excitonic effects. Chemical trends with the cation of the absorption edge and the exciton binding are discussed in terms of the band structures. Exciton binding energies and localization radii are explained within the Rytova-Keldysh model for excitons in two dimensions. The strong excitonic effects are due to the interplay of low dimensionality, confinement effects, and reduced screening. We find exciton radiative lifetimes ranging from tenths of picoseconds (BN) to tenths of nanoseconds (InN) at room temperature, thus making 2D nitrides, especially InN, promising materials for light-emitting diodes and high-performance solar cells.

Published
2020
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16. 2N+4-rule and an atlas of bulk optical resonances of zigzag graphene nanoribbons.

Author

Payod RB, Grassano D, Santos GNC, Levshov DI, Pulci O, and Saroka VA

Abstract

Development of on-chip integrated carbon-based optoelectronic nanocircuits requires fast and non-invasive structural characterization of their building blocks. Recent advances in synthesis of single wall carbon nanotubes and graphene nanoribbons allow for their use as atomically precise building blocks. However, while cataloged experimental data are available for the structural characterization of carbon nanotubes, such an atlas is absent for graphene nanoribbons. Here we theoretically investigate the optical absorption resonances of armchair carbon nanotubes and zigzag graphene nanoribbons continuously spanning the tube (ribbon) transverse sizes from 0.5(0.4) nm to 8.1(12.8) nm. We show that the linear mapping is guaranteed between the tube and ribbon bulk resonance when the number of atoms in the tube unit cell is [Formula: see text], where [Formula: see text] is the number of atoms in the ribbon unit cell. Thus, an atlas of carbon nanotubes optical transitions can be mapped to an atlas of zigzag graphene nanoribbons.

Published
2020
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17. Validity of Weyl fermion picture for transition metals monopnictides TaAs, TaP, NbAs, and NbP from ab initio studies.

Author

Grassano D, Pulci O, Mosca Conte A, and Bechstedt F

Abstract

We investigate electronic and optical properties of the topological Weyl semimetals TaAs, TaP, NbAs and NbP crystallizing in bct geometry by means of the ab initio density functional theory with spin-orbit interaction within the independent-particle approximation. The small energetical overlap of Ta5d or Nb4d derived conduction and valence bands leads to electron and/or hole pockets near the Fermi energy at the 24 Weyl nodes. The nodes give rise to two-(three-)dimensional Dirac cones for the W 1 (W 2 ) Weyl type. The band dispersion and occupation near the Weyl nodes determine the infrared optical properties. They are dominated by interband transitions, which lead to a deviation from the expected constant values of the imaginary part of the dielectric function. The resulting polarization anisotropy is also visible in the real part of the optical conductivity, whose lineshape deviates from the expected linearity. The details of the Weyl nodes are discussed in relation to recent ARPES results for TaAs and NbP, and compared with measured optical spectra for TaAs. The spectral features of the anisotropic and tilted Weyl fermions are restricted to low excitation energies above absorption onsets due to the band occupation.

Published
2018
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