The Hartman effect in graphene systems

2017 ◽  
Vol 31 (01) ◽  
pp. 1650250 ◽  
Author(s):  
Mohammad Esmailpour ◽  
Hakimeh Mohammadpour ◽  
Hamideh Hadavifar
Keyword(s):  
Incident Energy ◽  
Energy Levels ◽  
Single Layer ◽  
Normal Incidence ◽  
Bilayer Graphene ◽  
Single Layer Graphene ◽  
Monolayer Graphene ◽  
Tunneling Time ◽  
Layer Graphene ◽  
Hartman Effect

The present paper investigates that the tunneling time for bilayer graphene potential barrier with monolayer graphene leads to all range of energy. Numerical results reveal that parameters such as the incident energy and angle plays a significant role in inducing of the Hartman effect. In contrast to single-layer graphene, in the bilayer graphene, due to the chirality of quasi-particles induction of Klein and Hartman effects occur in the normal incidence case. Moreover, it is demonstrated that even for energy levels above barrier, the Hartman effect is present.

Large and tunable thermoelectric effect in single layer graphene on bilayer graphene

2015 ◽  
Vol 29 (03) ◽  
pp. 1550003 ◽  
Author(s):  
Z. Z. Alisultanov
Keyword(s):  
Simple Model ◽  
Band Gap ◽  
Single Layer ◽  
Bilayer Graphene ◽  
Single Layer Graphene ◽  
Monolayer Graphene ◽  
Thermoelectric Effect ◽  
Layer Graphene ◽  
Trilayer Graphene

The conductivity and thermopower of a trilayer graphene based system have been studied within the framework of a simple model. It has been shown that kinks of the conductivity and peaks of the thermopower of the monolayer graphene formed on a tunable bilayer graphene appear near the edges of the band gap of the tunable bilayer graphene.

scholarly journals Single-layer and bilayer graphene superlattices: collimation, additional Dirac points and Dirac lines

2010 ◽  
Vol 368 (1932) ◽  
pp. 5499-5524 ◽  
Author(s):  
Michaël Barbier ◽  
Panagiotis Vasilopoulos ◽  
François M. Peeters
Keyword(s):  
Ballistic Transport ◽  
Single Layer ◽  
Bilayer Graphene ◽  
Single Layer Graphene ◽  
Fermi Velocity ◽  
Type I ◽  
Layer Graphene ◽  
Beam Incident ◽  
Analytical Expressions ◽  
Electron Beam Incident

We review the energy spectrum and transport properties of several types of one-dimensional superlattices (SLs) on single-layer and bilayer graphene. In single-layer graphene, for certain SL parameters an electron beam incident on an SL is highly collimated. On the other hand, there are extra Dirac points generated for other SL parameters. Using rectangular barriers allows us to find analytical expressions for the location of new Dirac points in the spectrum and for the renormalization of the electron velocities. The influence of these extra Dirac points on the conductivity is investigated. In the limit of δ -function barriers, the transmission T through and conductance G of a finite number of barriers as well as the energy spectra of SLs are periodic functions of the dimensionless strength P of the barriers, , with v F the Fermi velocity. For a Kronig–Penney SL with alternating sign of the height of the barriers, the Dirac point becomes a Dirac line for P = π /2+ nπ with n an integer. In bilayer graphene, with an appropriate bias applied to the barriers and wells, we show that several new types of SLs are produced and two of them are similar to type I and type II semiconductor SLs. Similar to single-layer graphene SLs, extra ‘Dirac’ points are found in bilayer graphene SLs. Non-ballistic transport is also considered.

scholarly journals Magneto-tunnelling transport of chiral charge carriers

2021 ◽  
Author(s):  
◽  
Luke Pratley
Keyword(s):  
Magnetic Field ◽  
Single Layer ◽  
Bilayer Graphene ◽  
Single Layer Graphene ◽  
Two Dimensional ◽  
Dimensional Electron ◽  
Electron Gases ◽  
Tunnel Coupling ◽  
Layer Graphene ◽  
Spectroscopic Tool

<p>We study magneto-tunnelling between two parallel two-dimensional electron gases theoretically, where the electrons have a pseudo-spin-½ degree of freedom that is coupled to their momentum. The two-dimensional electron gases focused on in this work are single layer graphene, bilayer graphene, and single layer molybdenum disulphide. The results are derived using a linear response theory formalism in the weak tunnelling regime, and it is assumed that the electron gases are at zero temperature, with no interactions or disorder. The linear magneto-tunnelling conductance characteristics for an applied in-plane and tilted magnetic field are found to strongly depend on the pseudo-spin structure of the tunnelling matrix and the pseudo-spin's dependence on momentum. For instance, resonances in the linear magneto-tunnelling conductance are sensitive to the pseudo-spin tunnel-coupling across the barrier and how the pseudo-spin eigenstates are coupled to momentum. We discuss how measurements of the magneto-tunnelling conductance can be applied as a spectroscopic tool. We explain how to measure the pseudo-spin tunnel-coupling through least squares parameter fitting of the magneto-tunnelling conductance. We show that the parameters are interdependent, one can use the interdependency to test the consistency between theory and experiment. It is expected that measurements of pseudo-spin tunnel-coupling will be a function of the lattice structure of the double layer system, which suggests these measurements can be used as a spectroscopic tool. Additionally, we investigate in-plane electric fields in single layer graphene to see if their effects can be observed in magneto-tunnelling transport. Then, we perturbatively include the effects of electron-electron interactions in single layer graphene, and find it should dampen the linear tunnelling conductance. We investigate tunnel-coupled , parallel , single layer and bilayer graphene systems. We find that using an in-plane magnetic field, one can generate a valley polarized tunnelling current. This method is unique because it does not require manipulation of the single and bilayer graphene samples through nano-structuring, coupling to electromagnetic fields, application of mechanical strain, or the presence of defects. In particular, the valley polarization is dependent on the pseudo-spin tunnel-coupling between the single and bilayer graphene systems, and the strength of an applied in-plane magnetic field. We explicitly show through analytic derivations how an understanding of linear magneto-tunnelling transport (zero bias limit) can be used to understand non-linear magneto-tunnelling transport (finite bias).</p>

scholarly journals Magneto-tunnelling transport of chiral charge carriers

2021 ◽  
Author(s):  
◽  
Luke Pratley
Keyword(s):  
Magnetic Field ◽  
Single Layer ◽  
Bilayer Graphene ◽  
Single Layer Graphene ◽  
Two Dimensional ◽  
Dimensional Electron ◽  
Electron Gases ◽  
Tunnel Coupling ◽  
Layer Graphene ◽  
Spectroscopic Tool

<p>We study magneto-tunnelling between two parallel two-dimensional electron gases theoretically, where the electrons have a pseudo-spin-½ degree of freedom that is coupled to their momentum. The two-dimensional electron gases focused on in this work are single layer graphene, bilayer graphene, and single layer molybdenum disulphide. The results are derived using a linear response theory formalism in the weak tunnelling regime, and it is assumed that the electron gases are at zero temperature, with no interactions or disorder. The linear magneto-tunnelling conductance characteristics for an applied in-plane and tilted magnetic field are found to strongly depend on the pseudo-spin structure of the tunnelling matrix and the pseudo-spin's dependence on momentum. For instance, resonances in the linear magneto-tunnelling conductance are sensitive to the pseudo-spin tunnel-coupling across the barrier and how the pseudo-spin eigenstates are coupled to momentum. We discuss how measurements of the magneto-tunnelling conductance can be applied as a spectroscopic tool. We explain how to measure the pseudo-spin tunnel-coupling through least squares parameter fitting of the magneto-tunnelling conductance. We show that the parameters are interdependent, one can use the interdependency to test the consistency between theory and experiment. It is expected that measurements of pseudo-spin tunnel-coupling will be a function of the lattice structure of the double layer system, which suggests these measurements can be used as a spectroscopic tool. Additionally, we investigate in-plane electric fields in single layer graphene to see if their effects can be observed in magneto-tunnelling transport. Then, we perturbatively include the effects of electron-electron interactions in single layer graphene, and find it should dampen the linear tunnelling conductance. We investigate tunnel-coupled , parallel , single layer and bilayer graphene systems. We find that using an in-plane magnetic field, one can generate a valley polarized tunnelling current. This method is unique because it does not require manipulation of the single and bilayer graphene samples through nano-structuring, coupling to electromagnetic fields, application of mechanical strain, or the presence of defects. In particular, the valley polarization is dependent on the pseudo-spin tunnel-coupling between the single and bilayer graphene systems, and the strength of an applied in-plane magnetic field. We explicitly show through analytic derivations how an understanding of linear magneto-tunnelling transport (zero bias limit) can be used to understand non-linear magneto-tunnelling transport (finite bias).</p>

scholarly journals Low Voltage Graphene-Based Amplitude Modulator for High Efficiency Terahertz Modulation

Nanomaterials ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 585 ◽  
Author(s):  
Qianying Zheng ◽  
Liangping Xia ◽  
Linlong Tang ◽  
Chunlei Du ◽  
Hongliang Cui
Keyword(s):  
High Efficiency ◽  
Low Voltage ◽  
Modulation Depth ◽  
High Capacity ◽  
Single Layer ◽  
Single Layer Graphene ◽  
Monolayer Graphene ◽  
Layer Graphene ◽  
Amplitude Modulator ◽  
Polarization Insensitive

In this paper, a high-efficiency terahertz amplitude modulation device based on a field-effect transistor has been proposed. The polarization insensitive modulator is designed to achieve a maximum experimental modulation depth of about 53% within 5 V of gate voltages using monolayer graphene. Moreover, the manufacturing processes are inexpensive. Two methods are adopted to improve modulation performance. For one thing, the metal metamaterial designed can effectively enhance the electromagnetic field near single-layer graphene and therefore greatly promote the graphene’s modulation ability in terahertz. For another, polyethylene oxide-based electrolytes (PEO:LiClO4) acts as a high-capacity donor, which makes it possible to dope single-layer graphene at a relatively low voltage.

Comparative study of electron transfer on various graphene-metallic contacts

2019 ◽  
Vol 33 (31) ◽  
pp. 1950384
Author(s):  
Di Lu ◽  
Yu-E Yang ◽  
Weichun Zhang ◽  
Caixia Wang ◽  
Jining Fang ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Single Layer ◽  
Annealing Treatment ◽  
Single Layer Graphene ◽  
Strain Effect ◽  
Graphene Surface ◽  
Layer Graphene ◽  
Metallic Contacts ◽  
Nonuniform Strain ◽  
Main Factor

We have investigated Raman spectra of the G and 2D lines of a single-layer graphene (SLG) with metallic contacts. The shift of the G and 2D lines is correlated to two different factors. Before performing annealing treatment or annealing under low temperature, the electron transfer on graphene surface is dominated by nonuniform strain effect. As the annealing treatment is enhanced, however, a suitable annealing treatment can eliminate the nonuniform strain effect where the relative work function (WF) between graphene and metal becomes a main factor to determine electronic transfer. Moreover, it is confirmed that the optimized annealing treatment can also decrease effectively the structural defect and induced disorder in graphene due to metallic contacts.

scholarly journals Millisecond lattice gasification for high-density CO2- and O2-sieving nanopores in single-layer graphene

2021 ◽  
Vol 7 (9) ◽  
pp. eabf0116
Author(s):  
Shiqi Huang ◽  
Shaoxian Li ◽  
Luis Francisco Villalobos ◽  
Mostapha Dakhchoune ◽  
Marina Micari ◽  
...  
Keyword(s):  
Single Layer ◽  
High Density ◽  
Single Layer Graphene ◽  
Pore Density ◽  
Vacancy Defects ◽  
Carbon Gasification ◽  
Layer Graphene ◽  
Gas Molecules ◽  
Good Agreement

Etching single-layer graphene to incorporate a high pore density with sub-angstrom precision in molecular differentiation is critical to realize the promising high-flux separation of similar-sized gas molecules, e.g., CO2 from N2. However, rapid etching kinetics needed to achieve the high pore density is challenging to control for such precision. Here, we report a millisecond carbon gasification chemistry incorporating high density (>1012 cm−2) of functional oxygen clusters that then evolve in CO2-sieving vacancy defects under controlled and predictable gasification conditions. A statistical distribution of nanopore lattice isomers is observed, in good agreement with the theoretical solution to the isomer cataloging problem. The gasification technique is scalable, and a centimeter-scale membrane is demonstrated. Last, molecular cutoff could be adjusted by 0.1 Å by in situ expansion of the vacancy defects in an O2 atmosphere. Large CO2 and O2 permeances (>10,000 and 1000 GPU, respectively) are demonstrated accompanying attractive CO2/N2 and O2/N2 selectivities.

Sign in / Sign up

Export Citation Format

Share Document