Graphene for Magnetoresistive Junctions

2011 ◽  
Vol 1284 ◽  
Author(s):  
J. Inoue ◽  
T. Hiraiwa ◽  
R. Sato ◽  
A. Yamamura ◽  
S. Honda ◽  
...  
Keyword(s):  
Dirac Point ◽  
Electron Tunneling ◽  
Tight Binding ◽  
Metal Electrodes ◽  
Binding Model ◽  
Transition Metal Alloys ◽  
Dependent Change ◽  
Band Mixing ◽  
Junction Structure ◽  
Very High

ABSTRACTInfluence of the linear energy-momentum relationship in graphene on conductance and magnetoresistance (MR) in ferromagnetic metal (FM)/graphene/FM lateral junctions is studied in a numerical simulation formulated using the Kubo formula and recursive Green’s function method in a tight-binding model. It is shown that the contribution of electron tunneling through graphene should be considered in the electronic transport in metal/graphene/metal junctions, and that the Dirac point (DP) is effectively shifted by the band mixing between graphene and metal electrodes. It is shown that MR appears due to spin-dependent shift of DP or spin-dependent change in the electronic states at DPs. It is shown that the MR ratio caused by the latter mechanism can be very high when certain transition metal alloys are used for electrodes. These results do not essentially depend on the shape of the junction structure. However, to obtain high MR ratios, the effects of roughness should be small.

Electron Transport of Right-Angle Graphene Nanoribbons

2011 ◽  
Vol 295-297 ◽  
pp. 1451-1455
Author(s):  
Hai Dong Li ◽  
Jin Zhong Niu
Keyword(s):  
Electron Transport ◽  
Impurity Concentration ◽  
Dirac Point ◽  
Electron Tunneling ◽  
Graphene Nanoribbons ◽  
Resonance Effect ◽  
Tight Binding ◽  
Gate Bias ◽  
Width Difference ◽  
Tight Binding Method

By the tight-binding method, we study the transport properties of right-angle L-shaped graphene nanoribbons. We found a universal conclusion is that the resonance of electron tunneling will present at the Dirac point when the system is metallic and the ribbons widths satisfy (NBAB=2NBZB-1). Further research suggests that the conductance resonance effect will be destroyed by impurity scatterer, especially the impurity concentration and strength are nontrivially large. We also found that antiresonance effect will result in a strong conductance suppression when the width difference () of the two ribbons is very big. In addition, when the system is semiconducting, the center of the well-defined insulating band can be easily tuned by a gate bias exerted on the armchair-edged graphene nanoribbon.

Thermoelectric properties of T-shaped graphene nanodevice

2015 ◽  
Vol 29 (20) ◽  
pp. 1550133
Author(s):  
A. Jafari ◽  
M. Ghoranneviss ◽  
A. Boochani ◽  
M. R. Hantehzadeh
Keyword(s):  
Transmission Coefficient ◽  
Thermoelectric Properties ◽  
Linear Dependence ◽  
Dirac Point ◽  
Tight Binding ◽  
Tight Binding Model ◽  
Thermoelectric Devices ◽  
Binding Model ◽  
Thermoelectric Measurements ◽  
Thermal Current

The thermoelectric properties of a T-shaped graphene nanodevice (TGN) are investigated by means of the Landauer approach using the π-electron tight-binding model. The dependence of thermopower on the temperature is studied and the results are qualitatively in agreement with many features recently observed in thermoelectric measurements on graphene nanodevice which suggests the existence of a minimum when the EF is several kBT away from the Dirac point. Thermoconductance κ is proportional to transmission coefficient and thermal current has a linear dependence on the temperature. Further, both the electrical and thermal current of electrons in TGN are calculated. The results could be useful in designing efficient graphene-based thermoelectric devices.

Electron-Phonon Scattering in Very High Electric Fields

1997 ◽  
Vol 468 ◽  
Author(s):  
B. K. Ridley
Keyword(s):  
Electric Fields ◽  
Phonon Scattering ◽  
Tight Binding ◽  
Three Dimensional ◽  
Binding Model ◽  
Usual Model ◽  
Scattering Rate ◽  
High Electric Fields ◽  
Very High ◽  
Electron Phonon Scattering

ABSTRACTLarge-bandgap materials can support very high electric fields (>lMV/cm) without breaking down. The possibility then exists for an electron in a conduction band to become quasi-localized in Wannier-Stark states, a possibility that depends on the scattering rate being less than the Bloch oscillation frequency. If this condition is met the scattering rate itself is affected and the description of transport must be changed from the usual model in which the electron is assumed to be virtually free. Here, we examine the feasibility of obtaining this condition in GaN using a simple three-dimensional tight-binding model for the bandstructure and taking the dominant scattering mechanism to be the polar and non-polar interaction with optical phonons and short-wavelength acoustic phonons.

scholarly journals Cobalt-based magnetic Weyl semimetals with high-thermodynamic stabilities

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Wei Luo ◽  
Yuma Nakamura ◽  
Jinseon Park ◽  
Mina Yoon
Keyword(s):  
Tight Binding ◽  
Three Dimensional ◽  
Interlayer Coupling ◽  
First Principles Calculation ◽  
Optimization Approach ◽  
Binding Model ◽  
Nodal Lines ◽  
Weyl Semimetal ◽  
Topological Quantum ◽  
First Time

AbstractRecent experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM). Using first-principles calculation with a global optimization approach, we explore the structural stabilities and topological electronic properties of cobalt (Co)-based shandite and alloys, Co3MM’X2 (M/M’ = Ge, Sn, Pb, X = S, Se, Te), and identify stable structures with different Weyl phases. Using a tight-binding model, for the first time, we reveal that the physical origin of the nodal lines of a Co-based shandite structure is the interlayer coupling between Co atoms in different Kagome layers, while the number of Weyl points and their types are mainly governed by the interaction between Co and the metal atoms, Sn, Ge, and Pb. The Co3SnPbS2 alloy exhibits two distinguished topological phases, depending on the relative positions of the Sn and Pb atoms: a three-dimensional quantum anomalous Hall metal, and a MWSM phase with anomalous Hall conductivity (~1290 Ω−1 cm−1) that is larger than that of Co2Sn2S2. Our work reveals the physical mechanism of the origination of Weyl fermions in Co-based shandite structures and proposes topological quantum states with high thermal stability.

scholarly journals Single-crystalline epitaxial TiO film: A metal and superconductor, similar to Ti metal

2021 ◽  
Vol 7 (2) ◽  
pp. eabd4248
Author(s):  
Fengmiao Li ◽  
Yuting Zou ◽  
Myung-Geun Han ◽  
Kateryna Foyevtsova ◽  
Hyungki Shin ◽  
...  
Keyword(s):  
Transition Metal ◽  
Density Functional ◽  
Tight Binding ◽  
Crystal Form ◽  
Titanium Monoxide ◽  
Binding Model ◽  
Functional Theory ◽  
Single Crystalline ◽  
First Time ◽  
Lattice Matched

Titanium monoxide (TiO), an important member of the rock salt 3d transition-metal monoxides, has not been studied in the stoichiometric single-crystal form. It has been challenging to prepare stoichiometric TiO due to the highly reactive Ti2+. We adapt a closely lattice-matched MgO(001) substrate and report the successful growth of single-crystalline TiO(001) film using molecular beam epitaxy. This enables a first-time study of stoichiometric TiO thin films, showing that TiO is metal but in proximity to Mott insulating state. We observe a transition to the superconducting phase below 0.5 K close to that of Ti metal. Density functional theory (DFT) and a DFT-based tight-binding model demonstrate the extreme importance of direct Ti–Ti bonding in TiO, suggesting that similar superconductivity exists in TiO and Ti metal. Our work introduces the new concept that TiO behaves more similar to its metal counterpart, distinguishing it from other 3d transition-metal monoxides.

scholarly journals Enabling Large-Scale Simulations of Quantum Transport with Manycore Computing

Electronics ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 253
Author(s):  
Yosang Jeong ◽  
Hoon Ryu
Keyword(s):  
Quantum Transport ◽  
Large Scale ◽  
Performance Enhancement ◽  
Silicon Nanowire ◽  
Matrix Multiplication ◽  
Tight Binding ◽  
Optimization Techniques ◽  
Wide Energy Range ◽  
Processing Unit ◽  
Binding Model

The non-equilibrium Green’s function (NEGF) is being utilized in the field of nanoscience to predict transport behaviors of electronic devices. This work explores how much performance improvement can be driven for quantum transport simulations with the aid of manycore computing, where the core numerical operation involves a recursive process of matrix multiplication. Major techniques adopted for performance enhancement are data restructuring, matrix tiling, thread scheduling, and offload computing, and we present technical details on how they are applied to optimize the performance of simulations in computing hardware, including Intel Xeon Phi Knights Landing (KNL) systems and NVIDIA general purpose graphic processing unit (GPU) devices. With a target structure of a silicon nanowire that consists of 100,000 atoms and is described with an atomistic tight-binding model, the effects of optimization techniques on the performance of simulations are rigorously tested in a KNL node equipped with two Quadro GV100 GPU devices, and we observe that computation is accelerated by a factor of up to ∼20 against the unoptimized case. The feasibility of handling large-scale workloads in a huge computing environment is also examined with nanowire simulations in a wide energy range, where good scalability is procured up to 2048 KNL nodes.

scholarly journals Optoelectronic properties of one-dimensional molecular chains simulated by a tight-binding model

AIP Advances ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 015127
Author(s):  
Qiuyuan Chen ◽  
Jiawei Chang ◽  
Lin Ma ◽  
Chenghan Li ◽  
Liangfei Duan ◽  
...  
Keyword(s):  
Tight Binding ◽  
Optoelectronic Properties ◽  
Tight Binding Model ◽  
Binding Model ◽  
One Dimensional
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