다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.

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The electronic properties of graphene

Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

We report the measurement of the thermal conductivity of a suspended single-layer graphene. The room temperature values of the thermal conductivity in the range ∼(4.84 ± 0.44) × 103 to (5.30 ± 0.48) × 103 W/mK were extracted for a single-layer graphene from the dependence of the Raman G peak frequency on the excitation laser power and independently measured G peak temperature coefficient. The extremely high value of the thermal conductivity suggests that graphene can outperform carbon nanotubes in heat conduction. The superb thermal conduction property of graphene is beneficial for the proposed electronic applications and establishes graphene as an excellent material for thermal management.

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Superior Thermal Conductivity of Single-Layer Graphene

Graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes because it is produced mostly by exfoliating graphite. We grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane. The films are predominantly single-layer graphene, with a small percentage (less than 5%) of the area having few layers, and are continuous across copper surface steps and grain boundaries. The low solubility of carbon in copper appears to help make this growth process self-limiting. We also developed graphene film transfer processes to arbitrary substrates, and dual-gated field-effect transistors fabricated on silicon/silicon dioxide substrates showed electron mobilities as high as 4050 square centimeters per volt per second at room temperature.

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Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils

In this paper we derive general relations for the band-struc ture of an array of quantum dots and compute its transport properties when connected to two perfect leads The exact lattice Green’s functions for the perfect array and with an attached adatom are derived The expressions for the linear conductance for the perfect array as well as for the array with a defect are presented The calculations are illustrated for a dot made of three atoms The results derived here are also the starting point to inclu de the effect of electron-electron and electron-phonon interactions on the transport properties of quantum dot arr ays Different derivations of the exact lattice Green’s functions are discussed

Lattice Green's function approach to the solution of the spectrum of an array of quantum dots and its linear conductance

Based on two dissipative models, universal asymptotic behavior of flow equations for Hamiltonians is found and discussed. Universal asymptotic behavior only depends on fundamental bath properties but not on initial system parameters, and the integro-differential equations possess a universal attractor. The asymptotic flow of the Hamiltonian can be characterized by a nonlocal differential equation which only depends on one parameter---independent of the dissipative system or truncation scheme. Since the fixed-point Hamiltonian is trivial, the physical information is completely transferred to the transformation of the observables. This yields a more stable flow which is crucial for the numerical evaluation of correlation functions. Furthermore, the low-energy behavior of correlation functions is determined analytically. The presented procedure can also be applied if relevant perturbations are present as is demonstrated by evaluating dynamical correlation functions for sub-Ohmic environments. It can further be generalized to other dissipative systems.

Universal asymptotic behavior in flow equations of dissipative systems

The dynamical and nonlocal dielectric function of a two-dimensional electron gas with finite-energy bandwidth is computed within a random-phase approximation. For large bandwidth, the plasmon dispersion has two separate branches at small and large momenta. The large-momenta branch exhibits negative quasiflat dispersion. The two branches merge with decreasing bandwidth. We discuss how the maximum-energy plasmon mode, which resides at energies larger than all particle-hole continuum, can potentially open a route to low-loss plasmons. Moreover, we discuss the bandwidth effects on the static screening of the charged and magnetic impurities.

Plasmons and screening in finite-bandwidth two-dimensional electron gas

We study the electronic relaxation in a quantum dot within the polaron approach by focusing on the reversible anharmonic decay of longitudinal optical (LO) phonons forming the polaron into longitudinal-acoustic (LA) phonons. The coherent coupling between the LO and LA phonons is treated within a mean-field approach. We derive a temperature-dependent interlevel coupling parameter, related to the Gr\"uneisen parameter and the thermal-expansion coefficient, which characterizes an effective decay channel for the electronic (or excitonic) states. Within this theory, we obtain a characteristic anharmonic decay time of 1 ns, 2--3 orders of magnitude longer than previous predictions based on the Fermi's Golden Rule. We suggest that coherent relaxation due to carrier-carrier interaction is an efficient alternative to the (too slow) polaron decay.

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Polaron relaxation in a quantum dot due to anharmonic coupling within a mean-field approach

We investigate the field and spin-momentum coupling of edge plasmons hosted by general two-dimensional materials and identify sweet spots depending on the polarisation plane, ellipticity and the position of an electric dipole relative to the plane and edge. Exciting the dipole at these sweet spots by propagating light leads to uni-directional propagating edge plasmons or edge modes are totally suppressed. We also extent previous approximate treatments [A. Fetter Phys. Rev. B 32, 7676 (1985)] to include anisotropy and hyperbolic systems, elucidating its predictions for the existence of edge modes. A thorough assessment of the approximate description is carried out, comparing its spin-momentum coupling features in the near field with exact results from Wiener-Hopf techniques. Simulations are also performed confirming the overall picture. Our results shed new light on the quest of chiral plasmonics in 2D materials and should be relevant for future experiments.

Tobias Stauber

Papers

Lattice Green's function approach to the solution of the spectrum of an array of quantum dots and its linear conductance

Universal asymptotic behavior in flow equations of dissipative systems

Plasmons and screening in finite-bandwidth two-dimensional electron gas

Polaron relaxation in a quantum dot due to anharmonic coupling within a mean-field approach

Unidirectional plasmonic edge modes on general two-dimensional materials