BROWSE VOLUME

Year Range:  

October 2008

Volume 34, Issue 10,  pp. 777-874

Graphene and graphene-based nanostructures (Preface)

Low Temp. Phys. 34, 777 (2008) (1 page)

Online Publication Date: 5 November 2008

Full Text: PDF (29 kB)

+
 Abstract Unavailable
Show PACS
61.46.-w, 72.20.Jv, 73.43.-f, 72.80.Sk, 62.20.dq, 81.40.Jj
back to top

GRAPHENE AND GRAPHITE MULTILAYERS

Edge states in quantum Hall effect in graphene (Review Article)

V. P. Gusynin, V. A. Miransky, S. G. Sharapov, and I. A. Shovkovy

Low Temp. Phys. 34, 778 (2008) (12 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (1031 kB)

Show Abstract
We review recent results concerning the spectrum of edge states in the quantum Hall effect in graphene. In particular, special attention is paid to the derivation of the conditions under which gapless edge states exist in the spectrum of graphene with “zigzag” and “armchair” edges. It is found that in the case of a half-plane or a ribbon with zigzag edges, there are gapless edge states only when a spin gap dominates over a Dirac mass gap. In the case of a half-plane with an armchair edge, the existence of the gapless edge states depends on the specific type of Dirac mass gaps. The implications of these results for the dynamics in the quantum Hall effect in graphene are discussed.
Show PACS
73.43.-f, 75.30.Ds

Toward a theory of the quantum Hall effect in graphene

E. V. Gorbar, V. P. Gusynin, and V. A. Miransky

Low Temp. Phys. 34, 790 (2008) (4 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (85 kB)

Show Abstract
We analyze a gap equation for the propagator of Dirac quasiparticles and conclude that in graphene in a magnetic field, the order parameters connected with the quantum Hall ferromagnetism dynamics and those connected with the magnetic catalysis dynamics necessarily coexist (the latter have the form of Dirac masses and correspond to excitonic condensates). This feature of graphene could lead to important consequences, in particular, for the existence of gapless edge states. Solutions of the gap equation corresponding to recently experimentally discovered novel plateaus in graphene in strong magnetic fields are described.
Show PACS
73.43.Cd, 73.63.-b, 73.43.Lp, 73.22.Lp, 75.50.Dd, 75.75.+a

The Berry phase in graphene and graphite multilayers

G. P. Mikitik and Yu. V. Sharlai

Low Temp. Phys. 34, 794 (2008) (7 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (441 kB)

Show Abstract
We discuss the electron energy spectra and the Berry phases for graphene, a graphite bilayer, and bulk graphite, allowing for a small spin-orbit interaction. If an electron orbit in the Brillouin zone surrounds several Dirac points (band-contact lines in graphite), one can find the relative signs of the Berry phases generated by these points (lines) by taking this interaction into account.
Show PACS
71.70.Ej, 73.22.-f, 79.20.Uv

Disorder effect on the density of states in Landau quantized graphene

B. Dóra

Low Temp. Phys. 34, 801 (2008) (4 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (240 kB)

Show Abstract
We study the effect of Gaussian potential (on-site) and unidirectional bond disorder on the density of states (DOS) of Landau quantized graphene. The broadening of the Landau levels depends weakly on energy and the symmetry of the disorder except at the Dirac point. There, the peak in the DOS is enhanced significantly by bond disorder. For stronger disorder, Landau quantization becomes irrelevant, the discrete structures from Landau levels disappear, and we recover the zero field DOS.
Show PACS
71.20.Tx, 61.46.Hk, 71.70.Di

Tight-binding study of nonmagnetic-defect-induced magnetism in graphene

H. Kumazaki and D. S. Hirashima

Low Temp. Phys. 34, 805 (2008) (7 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (477 kB)

Show Abstract
This review describes a study of nonmagnetic-defect-induced magnetism of graphene on the basis of a tight-binding model. A vacancy induces around itself a quasilocalized impurity state at the chemical potential and leads to formation of local magnetic moments. The connection between a quasilocalized state around a vacancy and the edge localized states near a zigzag edge is studied in detail. Magnetism associated with many vacancies and edge structures is also reviewed. Some new results of magnetism associated with many vacancies are presented.
Show PACS
71.20.Tx, 71.15.Ap, 61.48.-c, 75.30.Cr, 61.72.jd, 65.80.+n

Effect of next-nearest-neighbor hopping on the electronic properties of graphene

Y. F. Suprunenko, E. V. Gorbar, V. M. Loktev, and S. G. Sharapov

Low Temp. Phys. 34, 812 (2008) (6 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (210 kB)

Show Abstract
In the tight-binding approximation, we take into account the next-nearest-neighbor hopping in graphene that leads to nonrelativistic-like corrections in its low energy spectrum. The electronic density of states in a magnetic field is found and the fan diagram is plotted, which interpolates between those for the relativistic and nonrelativistic limiting cases. It is shown that the Berry phase for the system under consideration coincides exactly with its value for the relativistic system.
Show PACS
71.15.Ap, 72.20.Ee, 73.63.-b, 73.22.-f

Spectral function of graphene with short-range impurity centers

Yu. V. Skrypnyk and V. M. Loktev

Low Temp. Phys. 34, 818 (2008) (8 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (881 kB)

Show Abstract
The spectral function of graphene with point substitutional defects is calculated for different impurity concentrations. It is demonstrated that features in the spectral function of graphene observed in ARPES experiments can be caused by the presence of a well-defined resonance state and are clearly pronounced at the impurity concentrations, which are of the order of the critical concentration for the impurity-induced spectrum rearrangement.
Show PACS
61.72.sd, 61.72.J-, 79.60.Bm

Vacuum polarization in graphene with a topological defect

Yu. A. Sitenko and N. D. Vlasii

Low Temp. Phys. 34, 826 (2008) (8 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (134 kB)

Show Abstract
The influence of a topological defect in graphene on the ground state of electronic quasiparticle excitations is studied in the framework of the long-wavelength continuum model originating in the tight-binding approximation for the nearest-neighbor interaction in the graphitic lattice. A topological defect that rolls up a graphitic sheet into a nanocone is represented by a pointlike pseudomagnetic vortex with a flux which is related to the deficit angle of the cone. The method of self-adjoint extensions is employed to define the set of physically acceptable boundary conditions at the apex of the nanocone. The electronic system on a graphitic nanocone is found to acquire a ground-state condensate and current of special type, and we determine the dependence of these quantities on the deficit angle of the nanocone, the continuous parameter of the boundary condition at the apex, and the distance from the apex.
Show PACS
73.22.-f, 61.72.Hh, 71.15.Ap
back to top

CARBON NANOTUBES, QUANTUM WIRES AND LUTTINGER LIQUID

Local heating method for growth of aligned carbon nanotubes at low ambient temperature

S. Dittmer, S. Mudgal, O. A. Nerushev, and E. E. B. Campbell

Low Temp. Phys. 34, 834 (2008) (4 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (478 kB)

Show Abstract
We use a highly localized resistive heating technique to grow vertically aligned multiwalled nanotube films and aligned single-walled nanotubes on substrates with an average temperature of less than 100  °C. The temperature at the catalyst can easily be as high as 1000  °C but an extremely high temperature gradient ensures that the surrounding chip is held at much lower temperatures, even as close as 1  µm away from the local heater. We demonstrate the influence of temperature on the height of multiwalled nanotube films, illustrate the feasibility of sequential growth of single-walled nanotubes by switching between local heaters and also show that nanotubes can be grown over temperature-sensitive materials such as resist polymer.
Show PACS
68.65.-k, 81.16.Hc, 81.40.Gh, 61.48.De

Semiclassical approach to the description of the basic properties of nanoobjects

Y. Kornyushin

Low Temp. Phys. 34, 838 (2008) (8 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (177 kB)

Show Abstract
A review of results obtained in the framework of the semiclassical approach in nanophysics is presented. A semiclassical description based on electrostatics and the Thomas-Fermi model is used to calculate the dimensions of the electronic shell of a fullerene molecule and a carbon nanotube. This simplified approach yields surprisingly accurate results in some cases. The semiclassical approach provides a rather good description of the dimensions of the electronic shell of a fullerene molecule. Two types of dipole oscillations in a fullerene molecule are considered and their frequencies calculated. Similar calculations are performed for a carbon nanotube also. These results look rather reasonable. Three types of dipole oscillations in a carbon nanotube are considered and their frequencies calculated. The frequencies of the longitudinal collective oscillations of delocalized electrons in a carbon peapod are calculated as well. A metallic cluster is modeled as a spherical ball. It is shown that the metallic cluster is stable; its bulk modulus and the frequency of the dipole oscillation of the electronic shell relative to the ions are calculated.
Show PACS
71.20.Tx, 73.22.Lp, 61.46.Bc, 71.45.-d, 71.15.-m

Index of refraction of a photonic crystal of carbon nanotubes and homogenization of optically anisotropic periodic composites

L. N. Gumen and A. A. Krokhin

Low Temp. Phys. 34, 846 (2008) (7 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (333 kB)

Show Abstract
We consider the long-wavelength limit for a periodic arrangement of carbon nanotubes. Using the Fourier expansion method, we develop an effective-medium theory for a photonic crystal of aligned optically anisotropic cylinders. Exact analytical formulas for the effective dielectric constants for the E (TM) and H (TE) eigenmodes are obtained for arbitrary 2D Bravais lattice and arbitrary cross-section of anisotropic cylinders. It is shown that, depending on the symmetry of the unit cell, a photonic crystal of anisotropic cylinders behaves in the low-frequency limit like a uniaxial or biaxial optical crystal. The developed theory of homogenization is in a good agreement with existing experimental results for the dielectric tensor of photonic crystals of carbon nanotubes.
Show PACS
78.67.Ch, 61.48.De, 78.20.Ci, 42.70.Qs, 77.22.Ch

Microwave-induced forward scattering and Luttinger liquid interferences in magnetically confined quantum wires

A. Nogaret, J.-C. Portal, H. E. Beere, D. A. Ritchie, and C. Phillips

Low Temp. Phys. 34, 853 (2008) (5 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (376 kB)

Show Abstract
We report on the photoresistance of a magnetic quantum wire obtained by applying a gradient of magnetic field to a two-dimensional electron gas. Electron transmission through the magnetic wire increases by an order of magnitude under microwave irradiation and exhibits frequency-dependent magneto-oscillations as a function of the in-plane magnetic field. Both results are fully consistent with microwave-coupled Luttinger liquid edge channels which interfere at two pinning sites in the fashion of a Mach-Zehnder interferometer.
Show PACS
73.63.Nm, 71.10.Pm, 72.40.+w, 73.21.Hb

Luttinger liquid and polaronic effects in electron transport through a molecular transistor

G. A. Skorobagat'ko and I. V. Krive

Low Temp. Phys. 34, 858 (2008) (7 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (401 kB)

Show Abstract
Electron transport through a single-level quantum dot weakly coupled to Luttinger liquid leads is considered in the master equation approach. It is shown that for a weak or moderately strong interaction the differential conductance demonstrates resonant-like behavior as a function of bias and gate voltages. The inelastic channels associated with vibron-assisted electron tunneling can even dominate electron transport for a certain region of interaction strength. In the limit of strong interaction resonant behavior disappears and the differential conductance scales as a power law in temperature (linear regime) or in bias voltage (nonlinear regime).
Show PACS
85.65.+h, 73.40.Gk, 71.38.-k, 73.63.Kv

Electrostatic screening and Friedel oscillations in semiconducting nanotubes

A. V. Chaplik, L. I. Magarill, and R. Z. Vitlina

Low Temp. Phys. 34, 865 (2008) (3 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (71 kB)

Show Abstract
In 3D and 2D electronic systems the singular contribution to the static permittivity epsilon (Kohn singularity) is a small correction to the regular part of epsilon but it results in the leading term in asymptotic behavior of the screened potential (Friedel oscillations). In the present letter we show that for nanotubes quite different results are valid: epsilon becomes infinitely large at the singular point and the Friedel oscillations do not play the dominant role in the screening at the large distances. Moreover, the zero and highest cylindrical harmonics of the effective potential are screened by quite different mechanisms.
Show PACS
73.63.Fg

Giant magnetization of a superconductor-two-dimensional electron gas-superconductor structure

I. A. Romanovsky, E. N. Bogachek, Uzi Landman, and I. V. Krive

Low Temp. Phys. 34, 868 (2008) (7 pages)

Online Publication Date: 5 November 2008

Full Text: PDF (491 kB)

Show Abstract
Superconductivity-induced phase-controlled mesoscopic magnetic effects in a two-dimensional electron gas that bridges two superconducting reservoirs are investigated. Giant paramagnetic response of the junction, occurring at certain values of the phase difference of the order parameter, is predicted. A geometrically similar system, consisting of a graphene ribbon stretched between two superconducting leads, is also considered. The magnetic effects in this system are found to be small, and the difference between the magnetic properties of the two systems is discussed.
Show PACS
74.45.+c, 74.25.Ha, 75.60.Ej, 75.75.+a, 74.78.Na, 75.20.-g