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Exploring Low Internal Reorganization Energies for Silicene Nanoclusters. (arXiv:1708.05369v1 [cond-mat.mtrl-sci])

2017-08-18T19:59:59+00:00 August 18th, 2017|Categories: Publications|Tags: |

By Ricardo Pablo-Pedro, Hector Lopez-Rios, Jose-L Mendoza-Cortes, Jing Kong, Serguei Fomine, Troy Van Voorhis, Mildred S. Dresselhaus

High-performance materials rely on small reorganization energies to facilitate both charge separation and charge transport. Here, we performed DFT calculations to predict small reorganization energies of rectangular silicene nanoclusters with hydrogen-passivated edges denoted by H-SiNC. We observe that across all geometries, H-SiNCs feature large electron affinities and highly stabilized anionic states, indicating their potential as n-type materials. Our findings suggest that fine-tuning the size of H-SiNCs along the zigzag and armchair directions may permit the design of novel n-type electronic materials and spinctronics devices that incorporate both high electron affinities and very low internal reorganization energies.

Published in: "arXiv Material Science".

Assessing existent possibility of 2D materials through a simple mechanical model. (arXiv:1708.05284v1 [cond-mat.mtrl-sci])

2017-08-18T19:59:59+00:00 August 18th, 2017|Categories: Publications|

By H-Lin Ding, Zhen Zhen, Haroon Imtiaz, Hongwei Zhu, B. Liu

Physical and chemical properties of 2D material are highly sensitive to its structures whose regularity are seldom investigated, here we proposed a simple mechanical model whose covalent bonds are connected by angle springs, with which we gave insight into stability, bending stiffness and some other properties of 2D structures. It is found that Flat, Chair and Washboard possess larger existent possibilities, which are consistent with existing 2D materials’ structures. This model is a tool to evaluate existent possibilities of periodic 2D structures from mechanical viewpoint.

Published in: "arXiv Material Science".

Emerging trends in Topological Insulator and Topological Superconductor. (arXiv:1611.04252v2 [cond-mat.mes-hall] UPDATED)

2017-08-18T19:58:47+00:00 August 18th, 2017|Categories: Publications|Tags: |

By Arijit Saha, Arun M. Jayannavar

Topological insulators are new class of materials which are characterized by a bulk band gap like ordinary band insulator but have protected conducting states on their edge or surface. These states emerge out due to the combination of spin-orbit coupling and time reversal symmetry. Also these states are insensitive to scattering by non-magnetic impurities. A two-dimensional (2D) topological insulator has one dimensional (1D) edge states in which the spin-momentum locking of the electrons gives rise to quantum spin Hall effect. A three-dimensional (3D) topological insulator supports novel spin-polarized 2D Dirac fermions on its surface. These topological insulator materials have been theoretically predicted and experimentally observed in a variety of 2D and 3D systems, including $rm HgTe$ quantum wells, $rm BiSb$ alloys, and $rm Bi_{2}Te_{3}$, $rm Bi_{2}Se_{3}$ crystals. Moreover, proximity induced superconductivity in these systems can lead to a state that supports zero energy Majorana fermion and the phase is known as topological superconductors. In this article, the basic idea of topological insulators and topological superconductors are presented along with their experimental development.

Published : "arXiv Mesoscale and Nanoscale Physics".

Coherent Manipulation of Thermal Transport by Tunable Electron-Photon and Electron-Phonon Interaction. (arXiv:1609.07584v2 [cond-mat.mes-hall] UPDATED)

2017-08-18T19:58:47+00:00 August 18th, 2017|Categories: Publications|Tags: , |

By Federico Paolucci, Giuliano Timossi, Paolo Solinas, Francesco Giazotto

We propose a system where coherent thermal transport between two reservoirs in non-galvanic contact is modulated by independently tuning the electron-photon and the electron-phonon coupling. The scheme is based on two gate-controlled electrodes capacitively coupled through a dc-SQUID as intermediate phase-tunable resonator. Thereby the electron-photon interaction is modulated by controlling the flux threading the dc-SQUID and the impedance of the two reservoirs, while the electron-phonon coupling is tuned by controlling the charge carrier concentration in the electrodes. To quantitatively evaluate the behavior of the system we propose to exploit graphene reservoirs. In this case, the scheme can work at temperatures reaching 1 K, with unprecedented temperature modulations as large as 245 mK, transmittance up to 99% and energy conversion efficiency up to 50%. Finally, the accuracy of heat transport control allows to use this system as an experimental tool to determine the electron-phonon coupling in two dimensional electronic systems (2DES).

Published : "arXiv Mesoscale and Nanoscale Physics".

Acousto-electric transport in MgO/ZnO-covered graphene on SiC. (arXiv:1708.05236v1 [cond-mat.mes-hall])

2017-08-18T19:58:46+00:00 August 18th, 2017|Categories: Publications|Tags: |

By Yi-Ting Liou, Alberto Hernández-Mínguez, Jens Herfort, João Marcelo J. Lopes, Abbes Tahraoui, Paulo V. Santos

We investigate the acousto-electric transport induced by surface acoustic waves (SAWs) in epitaxial graphene (EG) coated by a MgO/ZnO film. The deposition of a thin MgO layer protects the EG during the sputtering of a piezoelectric ZnO film for the efficient generation of SAWs. We demonstrate by Raman and electric measurements that the coating does not harm the EG structural and electronic properties. We report the generation of two SAW modes with frequencies around 2 GHz. For both modes, we measure acousto-electric currents in EG devices placed in the SAW propagation path. The currents increase linearly with the SAW power, reaching values up to two orders of magnitude higher than in previous reports for acousto-electric transport in EG on SiC. Our results agree with the predictions from the classical relaxation model of the interaction between SAWs and a two dimensional electron gas.

Published : "arXiv Mesoscale and Nanoscale Physics".

Strong plasmon-phonon splitting and hybridization in 2D materials revealed through a self-energy approach. (arXiv:1708.05167v1 [cond-mat.mes-hall])

2017-08-18T19:58:46+00:00 August 18th, 2017|Categories: Publications|Tags: , |

By Mikkel Settnes, J. R. M. Saavedra, Kristian S. Thygesen, Antti-Pekka Jauho, F. Javier García de Abajo, N. Asger Mortensen

We reveal new aspects of the interaction between plasmons and phonons in 2D materials that go beyond a mere shift and increase in plasmon width due to coupling to either intrinsic vibrational modes of the material or phonons in a supporting substrate. More precisely, we predict strong plasmon splitting due to this coupling, resulting in a characteristic avoided crossing scheme. We base our results on a computationally efficient approach consisting in including many-body interactions through the electron self-energy. We specify this formalism for a description of plasmons based upon a tight-binding electron Hamiltonian combined with the random-phase approximation. This approach is accurate provided vertex corrections can be neglected, as is is the case in conventional plasmon-supporting metals and Dirac-fermion systems. We illustrate our method by evaluating plasmonic spectra of doped graphene nanotriangles with varied size, where we predict remarkable peak splittings and other radical modifications in the spectra due to plasmons interactions with intrinsic optical phonons. Our method is equally applicable to other 2D materials and provides a simple approach for investigating coupling of plasmons to phonons, excitons, and other excitations in hybrid thin nanostructures.

Published : "arXiv Mesoscale and Nanoscale Physics".

van der Waals Bonded Co/h-BN Contacts to Ultrathin Black Phosphorus Devices. (arXiv:1708.05162v1 [cond-mat.mes-hall])

2017-08-18T19:58:45+00:00 August 18th, 2017|Categories: Publications|Tags: , |

By Ahmet Avsar, Jun Y. Tan, Luo Xin, Khoong Hong Khoo, Yuting Yeo, Kenji Watanabe, Takashi Taniguchi, Su Ying Quek, Barbaros Ozyilmaz

Due to the chemical inertness of 2D hexagonal-Boron Nitride (h-BN), few atomic-layer h-BN is often used to encapsulate air-sensitive 2D crystals such as Black Phosphorus (BP). However, the effects of h-BN on Schottky barrier height, doping and contact resistance are not well known. Here, we investigate these effects by fabricating h-BN encapsulated BP transistors with cobalt (Co) contacts. In sharp contrast to directly Co contacted p-type BP devices, we observe strong n-type conduction upon insertion of the h-BN at the Co/BP interface. First principles calculations show that this difference arises from the much larger interface dipole at the Co/h-BN interface compared to the Co/BP interface, which reduces the work function of the Co/h-BN contact. The Co/h-BN contacts exhibit low contact resistances (~ 4.5 k-ohm), and are Schottky barrier free. This allows us to probe high electron mobilities (4,200 cm2/Vs) and observe insulator-metal transitions even under two-terminal measurement geometry.

Published : "arXiv Mesoscale and Nanoscale Physics".

Mach-Zehnder interferometry using spin- and valley-polarized quantum Hall edge states in graphene

2017-08-18T18:31:37+00:00 August 18th, 2017|Categories: Publications|Tags: |

By Wei, D. S., van der Sar, T., Sanchez-Yamagishi, J. D., Watanabe, K., Taniguchi, T., Jarillo-Herrero, P., Halperin, B. I., Yacoby, A.

Confined to a two-dimensional plane, electrons in a strong magnetic field travel along the edge in one-dimensional quantum Hall channels that are protected against backscattering. These channels can be used as solid-state analogs of monochromatic beams of light, providing a unique platform for studying electron interference. Electron interferometry is regarded

Published in: "Science Advances".

Large scale green production of ultra-high capacity anode consisting of graphene encapsulated silicon nanoparticles

2017-08-18T15:17:57+00:00 August 18th, 2017|Categories: Publications|Tags: |

J. Mater. Chem. A, 2017, Accepted ManuscriptDOI: 10.1039/C7TA04335J, PaperAli Reza Kamali, Hyun-Kyung Kim, Kwang Bum Kim, Ramachandran Vasant Kumar, Derek FrayGraphite, which is commercially used as anode material in Li-ion batteries, has a low theoretical capacity of 372 mA h g-1, and therefore

Published in: "Journal of Materials Chemistry A".

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