Absence of Diffusion in Certain Random Lattices

P. W. Anderson
Bell Telephone Laboratories, Murray Hill, New Jersey

Received 10 October 1957

This paper presents asimple model for such processes as spin diffusion or conduction in the"impurity band." These processes involve transport in a lattice whichis in some sense random, and in them diffusion is expected to takeplace via quantum jumps between localized sites. In this simple modelthe essential randomness is introduced by requiring the energy to varyrandomly from site to site. It is shown that at low enough densities nodiffusion at all can take place, and the criteria for transport tooccur are given.


©1958 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRev.109.1492
DOI: 10.1103/PhysRev.109.1492


b0057725_Absence_of_Diffusion_in_Certain_Random_Lattices.pdf

by youngsphya | 2009/03/20 13:01 | 트랙백 | 덧글(0)

Fermi surface nesting in several transition metal dichalcogenides

D S Inosov1, V B Zabolotnyy1, D V Evtushinsky1, A A Kordyuk1,2, B Büchner1, R Follath3, H Berger4 and S V Borisenko1,5
1 Institute for Solid State Research, IFW Dresden, P O Box 270116, D-01171 Dresden, Germany
2 Institute of Metal Physics of National Academy of Sciences of Ukraine, 03142 Kyiv, Ukraine
3 BESSY GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany
4 Institut de Physique de la Matière Complexe, EPFL, 1015 Lausanne, Switzerland
5 Author to whom any correspondence should be addressed.
E-mail: s.borisenko@ifw-dresden.de
Part of Focus on Advances in Surface and Interface Science 2008

Abstract.By means of high-resolution angle-resolved photoelectron spectroscopy(ARPES), we have studied the fermiology of 2H transition metaldichalcogenide polytypes TaSe2, NbSe2 and Cu0.2NbS2.The tight-binding model of the electronic structure, extracted fromARPES spectra for all three compounds, was used to calculate theLindhard function (bare spin susceptibility), which reflects thepropensity to charge density wave (CDW) instabilities observed in TaSe2 and NbSe2.We show that though the Fermi surfaces of all three compounds possessan incommensurate nesting vector in the close vicinity of the CDW wavevector, the nesting and ordering wave vectors do not exactly coincide,and there is no direct relationship between the magnitude of thesusceptibility at the nesting vector and the CDW transitiontemperature. The nesting vector persists across the incommensurate CDWtransition in TaSe2 as a function of temperature despite the observable variations of the Fermi surface geometry in this temperature range. In Cu0.2NbS2,the nesting vector is present despite different doping levels, whichleads us to expect a possible enhancement of the CDW instability withCu intercalation in the CuxNbS2 family of materials.



Fermi_surface_nesting_in_several_transition_metal_dichalcogenides.pdf

by youngsphya | 2009/01/25 00:14 | 트랙백 | 덧글(0)

Model for a Quantum Hall Effect without Landau Levels: Condensed-Matter Realization of the "Parity A

F. D. M. Haldane
Department of Physics, University of California, San Diego, La Jolla, California 92093

Received 16 September 1987

A two-dimensional condensed-matter lattice model is presented which exhibits a nonzero quantization of the Hall conductance σxy in the absence of an external magnetic field. Massless fermions without spectral doublingoccur at critical values of the model parameters, and exhibit theso-called "parity anomaly" of (2+1)-dimensional field theories.


©1988 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevLett.61.2015
DOI: 10.1103/PhysRevLett.61.2015
PACS: 05.30.Fk, 11.30.Rd


p2015_1.pdf

by youngsphya | 2009/01/22 23:05 | 트랙백 | 덧글(0)

Electronic conductance of a two-dimensional electron gas in the presence of periodic potentials

Y. Takagaki and D. K. Ferry
Center for Solid State Electronics Research, Arizona State University, Tempe, Arizona 85287-6202

Received 13 November 1991

We utilize mode-matching and transfer-matrix methods to study the transport properties of an electron through two-dimensionally modulated periodic potentials. The model structures treated here are finite-size one- and two-dimensional arrays of quantum boxes (lateral surface superlattice)and antidots. The structure is divided into a chain of uniform waveguide sections in the direction of current flow, and mode matching is imposed across the boundaries. The transfer-matrix technique is utilized to obtain the transmission probability for the composite superlattice structures. Energy dependences of the two-terminal conductance are presented in terms of the transition from one-dimensional to two-dimensional transport. Increasing the number of quantum boxes in the lateral surface superlattice shows that Lorentzian-shaped transmission resonances in a single quantum box are brought together to form a Bloch band structure. Complete reflections over broad energy ranges, due to the formation of minigaps, and a strong resonant behaviour due to discrete states in minibands are observed in the energy dependence of the conductance. For the antidot lattice, the formation of the Bloch band structure is found to arise as a drop in the conductance. If attractive scattering centers are embedded in a two-dimensional electron gas, transmission resonances due to quasibound states are observed.


©1992 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevB.45.8506
DOI: 10.1103/PhysRevB.45.8506
PACS: 73.50.Bk, 71.50.+t, 73.20.Dx

Electronic_conductance_of_a_two_dimensional_electron_gas_in_the_presence_of_periodic_potentials.pdf

by youngsphya | 2008/12/31 17:39 | 트랙백 | 덧글(0)

Ab initio static dielectric matrices from the density-functional approach. I. Formulation and applic

Mark S. Hybertsen and Steven G. Louie
Department of Physics, University of California, Berkeley, California 94720

Received 22 September 1986

As a ground-stateexpectation value, the static dielectric response function can beobtained exactly within the density-functional approach. This approachis developed in the present paper within the local-densityapproximation. The ab initiopseudopotential method is used, extending the techniques that giveexcellent structural properties to the calculation of dielectricresponse functions. In particular, the full dielectric matrix iscalculated, and so complete information about local fields is obtained.In contrast to recently proposed direct methods for obtaining thedielectric response matrices, the present approach is based on theusual perturbation formulation for the independent-particlepolarizability. The results agree well with results obtained with useof direct methods. The advantage of the perturbative approach is thatit allows calculation of the response matrices on a systematic grid ofpoints in the Brillouin zone without significant extra computation orloss of accuracy for points of low symmetry. The response matrices forsuch a grid are required to describe the response to arbitraryperturbations, e.g., a local change in the potential due to an impurityor defect. The role of exchange and correlation is carefully developedand the relation of the response functions calculated within thedensity-functional approach to the usual random-phase approximation isillustrated. Results from first principles for the full staticdielectric matrices are given for a series of semiconductors andinsulators: diamond, Si, Ge, and LiCl. Comparison is made to previousresults based on empirical potentials. The importance of local fieldsis illustrated for the macroscopic dielectric function and by using theconcept of the dielectric band structure. Sufficient details of themethod and results are included to serve as a reference for developmentof the dielectric matrix as a tool to be used in other applications. Inparticular, the additional terms in the long-wavelength dielectricmatrix due to nonlocal terms in the ionic pseudopotential are presented.


©1987 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevB.35.5585
DOI: 10.1103/PhysRevB.35.5585
PACS: 71.45.Gm, 77.90.+k

Ab_initio_static_dielectric_matrices_from_the_density-functional_approach_I_Formulation_and_application_to_semiconductors_and_insulators.pdf

by youngsphya | 2008/12/31 16:34 | 트랙백 | 덧글(0)

Spin-Density Functionals from Current-Density Functional Theory and Vice Versa: A Road towards New A

K. Capelle and E. K. U. Gross
Institut für Theoretische Physik, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany

Received 9 August 1996

It is shown that the exchange-correlation functional of spin-density functional theory is identical, on a certain set of densities, with the exchange-correlation functional of current-density functional theory. This rigorous connection is used to construct new approximations of the exchange-correlation functionals. These include a conceptually new generalized-gradient spin-density functional and a nonlocal current-density functional.


©1997 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevLett.78.1872
DOI: 10.1103/PhysRevLett.78.1872
PACS: 31.15.Ew, 31.10.+z, 31.25.Eb
Spin-Density_Functionals_from_Current-Density_Functional_Theory_and_Vice_Versa.pdf

by youngsphya | 2008/12/31 16:16 | 트랙백 | 덧글(0)

Effects of Configuration Interaction on Intensities and Phase Shifts

U. Fano
National Bureau of Standards, Washington, D.C.

Received 14 July 1961

The interference of adiscrete autoionized state with a continuum gives rise tocharacteristically asymmetric peaks in excitation spectra. The earlierqualitative interpretation of this phenomenon is extended and revised.A theoretical formula is fitted to the shape of the 2s2p 1P resonance of He observed in the inelastic scattering of electrons. The fitting determines the parameters of the 2s2p 1P resonance as follows: E=60.1 ev, Γ∼0.04 ev, f∼2 to 4×10-3.The theory is extended to the interaction of one discrete level withtwo or more continua and of a set of discrete levels with onecontinuum. The theory can also give the position and intensity shiftsproduced in a Rydberg series of discrete levels by interaction with alevel of another configuration. The connection with the nuclear theoryof resonance scattering is indicated.


©1961 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRev.124.1866
DOI: 10.1103/PhysRev.124.1866


Effects_of_Configuration_Interaction_on_Intensities_and_Phase_Shifts.pdf

by youngsphya | 2008/12/26 20:14 | 트랙백 | 덧글(0)

Electric transport theory of Dirac fermions in graphene

Xin-Zhong Yan,1,2 Yousef Romiah,1 and C. S. Ting1
1Texas Center for Superconductivity, University of Houston, Houston, Texas 77204, USA
2Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080, China

Received 19 December 2007; revised 15 January 2008; published 13 March 2008

Using the self-consistent Born approximation to the Dirac fermions under finite-range impurity scatterings, we show that the current-current correlation function is determined by four-coupled integral equations. This is very different from the case of impurities with short-range potentials. As a test of the present approach, we calculate the electric conductivity in graphene for charged impurities with screened Coulomb potentials. The obtained conductivity at zero temperature varies linearly with the carrier concentration, and the minimum conductivity at zero doping is larger than the existing theoretical predictions, but still smaller than that of the experimental measurement. The overall behavior of the conductivity obtained by the present calculation at room temperature is similar to that at zero temperature except that the minimum conductivity is slightly larger.

©2008 The American Physical Society

URL:http://link.aps.org/doi/10.1103/PhysRevB.77.125409
DOI:10.1103/PhysRevB.77.125409

Electric_transport_theory_of_Dirac_fermions_in_graphene.pdf

by youngsphya | 2008/12/20 19:27 | 트랙백 | 덧글(0)

Theory of charged impurity scattering in two dimensional graphene

S. Adam, E. H. Hwang, E. Rossi, S. Das Sarma
Abstract: We review the physics of charged impurities in the vicinity of graphene. Thelong-range nature of Coulomb impurities affects both the nature of the groundstate density profile as well as graphene's transport properties. We discussthe screening of a single Coulomb impurity and the ensemble averaged densityprofile of graphene in the presence of many randomly distributed impurities.Finally, we discuss graphene's transport properties due to scattering offcharged impurities both at low and high carrier density.
Comments:Invited review for the graphene special issue of Solid State Communications. Related papers available at this http URL
Subjects:Mesoscopic Systems and Quantum Hall Effect (cond-mat.mes-hall)
Cite as:arXiv:0812.1795v1 [cond-mat.mes-hall]

by youngsphya | 2008/12/12 21:41 | 트랙백 | 덧글(0)

Carbon Nanotube Electron Windmills: A Novel Design for Nanomotors

S. W. D. Bailey, I. Amanatidis, and C. J. Lambert
Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom
Received 20 March 2008; published 24 June 2008

We propose a new drive mechanism for carbon nanotube (CNT) motors, based upon the torque generated by a flux of electrons passing through a chiral nanotube. The structure of interest comprises a double-walled CNT formed from, for example, an achiral outer tube encompassing a chiral inner tube. Through a detailed analysis of electrons passing through such a “windmill,” we find that the current, due to a potential difference applied to the outer CNT, generates sufficient torque to overcome the static and dynamic frictional forces that exist between the inner and outer walls, thereby causing the inner tube to rotate.

©2008 The American Physical Society

URL:http://link.aps.org/doi/10.1103/PhysRevLett.100.256802
DOI:10.1103/PhysRevLett.100.256802
PACS:85.65.+h; 61.46.Fg; 68.35.Af; 73.63.Fg
windmills.pdf

by youngsphya | 2008/12/11 15:07 | 트랙백 | 덧글(0)

Periodic Graphene Nanobuds

Xiaojun Wu and Xiao Cheng Zeng*
Departmentof Chemistry and Nebraska Center for Materials and Nanoscience,University of NebraskaLincoln, Lincoln, Nebraska 68588
Nano Lett., Article ASAP
Publication Date (Web): December 10, 2008
Copyright © 2008 American Chemical Society

Abstract

Abstract Image

Periodic graphene nanobuds (PGNBs) can be engineered by attaching C60 buckyballs onto a graphene monolayer, where C60molecules form a periodic lattice structure. Structural and electronicproperties of two prototype PGNBs are investigated for the first timeby using the first-principles methods. In type I PGNB, C60buckyballs are covalently bonded to a graphene monolayer, while in typeII the fragmented buckyballs are fused onto the graphene monolayer. Itis found that type I PGNBs can be either semiconducting orsemimetallic, depending on the pattern of chemical bonding between C60and graphene. Type II PGNBs are generally semimetallic. In particular,one hallmark electronic structure of the graphene monolayer, i.e.,conic Dirac points, is still preserved in type II PGNBs except for the“ripped” graphene monolayer. The diversity in electronic structuresrenders PGNB a promising carbon material for applications innanoelectronics and cold electron field emission. Furthermore,multilayer PGNBs form a porous network structure with surface areasgreater than 2000 m2/g, which can be exploited for gas storage.


Periodic_Graphene_Nanobuds.pdf

by youngsphya | 2008/12/11 14:47 | 트랙백 | 덧글(0)

Quantum blockade and loop currents in graphene with topological defects

Yanyang Zhang,1,2 Jiang-Ping Hu,3 B. A. Bernevig,4 X. R. Wang,2 X. C. Xie,5,1 and W. M. Liu1

1BeijingNational Laboratory for Condensed Matter Physics, Institute of Physics,Chinese Academy of Sciences, Beijing 100080, People's Republic of China
2Physics Department, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China
3Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA
4Princeton Center for Theoretical Physics and Department of Physics, Jadwin Hall,Princeton University, Princeton, New Jersey 08544, USA
5Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078, USA

(Received 2 July 2008; revised 16 July 2008; published 9 October 2008)

We investigate the effect of topological defects on the transport properties of a narrow ballistic ribbon of graphene with zigzag edges. Our results show that the longitudinal conductance vanishes at several discrete Fermi energies where the system develops loop orbital electric currents with certain chirality. The chirality depends on the direction of the applied bias voltage and the sign of the local curvature created by the topological defects. This quantum localization phenomenon provides a way to generate a magnetic moment by an external electric field, which can prove useful in nanotronics.

URL: http://link.aps.org/abstract/PRB/v78/e155413

doi:10.1103/PhysRevB.78.155413

PACS: 73.20.Fz, 72.10.Fk, 72.15.Rn, 73.20.At


Quantum_blockade_and_loop_currents_in_graphene_with_topological_defects.pdf

by youngsphya | 2008/12/09 18:29 | 트랙백 | 덧글(0)

Two theorems on the Hubbard model

Elliott H. Lieb

Departments of Physics and Mathematics, Princeton University, P.O. Box 708, Princeton, New Jersey 08544

 See Also: Erratum

Received 12 December 1988

In the attractive Hubbard Model (and some extended versions of it), the ground state is proved to have spin angular momentum S=0 for every (even) electron filling. In the repulsive case, and with a bipartite lattice and a half-filled band, the ground state has S=(1/2)(‖B‖-‖A‖), where ‖B‖ (‖A‖) is the number of sites in the B(A) sublattice. In both cases the ground state is unique. The second theorem confirms an old, unproved conjecture in the ‖B‖=‖A‖ case and yields, with ‖B‖‖A‖, the first  provable example of itinerant-electron ferromagnetism. The theorems hold in all dimensions without even the necessity of aperiodic lattice structure.


©1989 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevLett.62.1201
DOI: 10.1103/PhysRevLett.62.1201
PACS: 75.10.Lp, 71.20.Ad, 74.65.+n

See Also

Erratum: Elliott H. Lieb, Two Theorems on the Hubbard Model, Phys. Rev. Lett. 62, 1927 (1989)

Two_theorems_on_the_Hubbard_model.pdf
Two_theorems_on_the_Hubbard_model_erratum.pdf


by youngsphya | 2008/12/09 18:10 | 트랙백 | 덧글(0)

Quantum size effect on the magnetism of finite systems

Feng Liu, S. N. Khanna, and P. Jena
Physics Department, Virginia Commonwealth University, Richmond, Virginia 23284-2000

Received 8 February 1990

The magnetic momentsof the ferromagnetic transition metals, Fe, Co, and Ni confined toone-dimensional chains are found to fluctuate with increasing chainlength before converging to the infinite limit. This quantum sizeeffect is derived from a simple first-principles theory that we havedeveloped to study the evolution of the electronic structure of systemas a function of size and dimensionality. The quantitative accuracy ofthe predictions of this simple formulation is confirmed by carrying outab initio self-consistentcalculations using the molecular-orbital approach. The convergence ofmoments to the respective infinite limit is found to depend on thedimensionality of the system.


©1990 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevB.42.976
DOI: 10.1103/PhysRevB.42.976
PACS: 73.20.Dx, 31.20.Gm, 36.40.+d, 75.70.Ak

Quantum_size_effect_on_the_magnetism_of_finite_systems.pdf

by youngsphya | 2008/12/09 18:03 | 트랙백 | 덧글(0)

The Ferromagnetism of Nickel

J. C. Slater
Massachusetts Institute of Technology

Received 11 February 1936

By using metallicenergy levels extrapolated from copper to nickel, the energy differencebetween a nonmagnetic and a ferromagnetic state with permanent magneticmoment is calculated for nickel, and it is shown that the ferromagneticstate is the stable one. Both saturation magnetic moment and Curiepoint are calculated, in agreement with experiment within the limits oferror of the calculation. Extrapolation further into the iron group,though less justified than to nickel, indicates that ferromagnetismshould persist in that group down approximately to iron. The criterionfor ferromagnetism previously suggested by the author, the existence ofinner unfilled electron shells (the 3d),small in proportion to their distance apart, is justified. Thecalculation is not made according to Heisenberg's method, which isconsidered to be unsuitable for application to ferromagnetism, exceptin its general principle of explaining the energy of orientation ofelementary magnets in terms of exchange energy.


©1936 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRev.49.537
DOI: 10.1103/PhysRev.49.537

The_Ferromagnetism_of_Nickel.pdf

by youngsphya | 2008/12/09 17:58 | 트랙백 | 덧글(0)

Peculiar Localized State at Zigzag Graphite Edge

Mitsutaka Fujita, Katsunori Wakabayashi, Kyoko Nakada and Koichi Kusakabe1

Institute of Materials Science, University of Tsukuba, Tsukuba 305
1Institute for Solid State Physics, University of Tokyo, Roppongi, Tokyo 106

(Received April 30, 1996)

We study the electronic states of graphite ribbons with edges oftwo typical shapes, armchair and zigzag, by performing tight binding band calculations, and find that the graphite ribbons show striking contrastin the electronic states depending on the edge shape. In particular, a zigzag ribbon shows a remarkably sharp peak of density of states at the Fermi level, which does not originate from infinite graphite. We find that the singular electronic states arise from the partly flat bands at the Fermi level, whose wave functions are mainlylocalized on the zigzag edge. We reveal the puzzle for the emergence of the peculiar edge state by deriving the analytic form in the case of semi-infinite graphite with a zigzag edge. Applying the Hubbard model within the mean-field approximation, we discuss the possible magnetic structure in nanometer-scale micrographite.©1996 The Physical Society of Japan

KEYWORDS: edge state, micrographite, nanometer scale, flat band, localizedstate, graphite edge
URL: http://jpsj.ipap.jp/link?JPSJ/65/1920/
DOI: 10.1143/JPSJ.65.1920


Peculiar_Localized_State_at_Zigzag_Graphite_Edge.pdf

by youngsphya | 2008/12/09 17:34 | 트랙백 | 덧글(0)

Edge state in graphene ribbons: Nanometer size effect and edge shape dependence

Kyoko Nakada and Mitsutaka Fujita
Institute of Materials Science, University of Tsukuba, Tsukuba 305, Japan


Gene Dresselhaus
and Mildred S. Dresselhaus
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307

Received 26 June 1996

Finite graphitesystems having a zigzag edge exhibit a special edge state. Thecorresponding energy bands are almost flat at the Fermi level andthereby give a sharp peak in the density of states. The charge densityin the edge state is strongly localized on the zigzag edge sites. Nosuch localized state appears in graphite systems having an armchairedge. By utilizing the graphene ribbon model, we discuss the effect ofthe system size and edge shape on the special edge state. By varyingthe width of the graphene ribbons, we find that the nanometer sizeeffect is crucial for determining the relative importance of the edgestate. We also have extended the graphene ribbon to have edges of ageneral shape, which is defined as a mixture of zigzag and armchairsites. Examining the relative importance of the edge state for grapheneribbons with general edges, we find that a non-negligible edge statesurvives even in graphene ribbons with less developed zigzag edges. Wedemonstrate that such an edge shape with three or four zigzag sites persequence is sufficient to show an edge state, when the system size ison a nanometer scale. The special characteristics of the edge stateplay a large role in determining the density of states near the Fermilevel for graphite networks on a nanometer scale.


©1996 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevB.54.17954
DOI: 10.1103/PhysRevB.54.17954

Edge_state_in_graphene_ribbons_Nanometer_size_effect_and_edge_shape_dependence.pdf

by youngsphya | 2008/12/09 17:27 | 트랙백 | 덧글(0)

Berry's Phase and Absence of Back Scattering in Carbon Nanotubes

Tsuneya Ando, Takeshi Nakanishi and Riichiro Saito

The absence of back scattering in carbon nanotubes is shown to be ascribed to Berry's phase which corresponds to a sign change of the wave function under a spin rotation of a neutrino-like particle in a two-dimensional graphite.Effects of trigonal warping of the bands appearing in a higher order k· p approximation are shown to give rise to a small probability of back scattering.©1998 The Physical Society of Japan

Journal of the Physical Society of Japan, 67, 2857
JPSJ-67-2857.pdf

by youngsphya | 2008/12/08 22:53 | 트랙백 | 덧글(0)

Manifestations of Berry’s phase in molecules and condensed matter

Raffaele Resta
INFM—Dipartimento di Fisica Teorica, Universit`a di Trieste, Strada Costiera 11, I-34014 Trieste,
Italy
Received 28 July 1999
Abstract. Since the appearance of Berry’s seminal paper in 1984, geometric phases have been discovered in virtually all fields of physics. Here we address molecules and solids, and we limit our scope to the Berry’s phases of the many-electron wavefunction. Many advances have occurred in very recent years relating to the theory of such phases and their observable consequences. After discussing the basic features of Berry’s phases in a generic quantum system, we specialize to selected examples taken from molecular physics and condensed matter physics; in each of these cases, a Berry’s phase of the electronic wavefunction leads to measurable effects.

Contents
1. Introduction
2. Fundamentals
2.1. The discrete (Pancharatnam’s) geometric phase
2.2. Berry’s geometric phase
2.3. Connection and curvature
2.4. The paradigm: the Aharonov–Bohm effect

3. Features of the geometric phase
3.1. Parallel transport
3.2. Computing a Berry’s phase
3.3. The open-path geometric phase
3.4. The single-point Berry’s phase

4. The electronic Berry’s phase
4.1. Wavefunctions and density matrices
4.2. Independent electrons
4.3. Bloch orbitals
4.4. Zak’s phase

5. Manifestations of Berry’s phase
5.1. The molecular Aharonov–Bohm effect
5.2. Adiabatic approximation in a magnetic field
5.3. Semiclassical electron dynamics in crystals
5.4. Bloch oscillations and the Wannier–Stark ladder
5.5. Spin-wave dynamics in crystals

6. Macroscopic polarization
6.1. The problem
6.2. Polarization as a Berry’s phase
6.3. A lone electron in a periodic box
6.4. The position operator in extended systems
6.5. A crystalline system of independent electrons
6.6. King-Smith and Vanderbilt’s formula
6.7. Non-crystalline systems
6.8. Correlated electrons and topological phase transitions

7. Conclusions

J. Phys.: Condens. Matter 12 (2000) R107–R143. Printed in the UK
0953-8984_12_9_201.pdf


by youngsphya | 2008/12/08 22:23 | 트랙백 | 덧글(0)

Quantum interference and Klein tunneling in graphene heterojunctions

Andrea F. Young and Philip Kim
Department of Physics, Columbia University, New York, New York 10027, USA
(Dated: December 1, 2008)

The observation of quantum conductance oscillations in mesoscopic systems has traditionally required the confinement of the carriers to a phase space of reduced dimensionality1,2,3,4. While electron optics such as lensing5 and focusing6 have been demonstrated experimentally, building a collimated electron interferometer in two unconfined dimensions has remained a challenge due to the difficulty of creating electrostatic barriers that are sharp on the order of the electron wavelength
7. Here, we report the observation of conductance oscillations in extremely narrow graphene heterostructures where a resonant cavity is formed between two electrostatically created bipolar junctions. Analysis of the oscillations confirms that p-n junctions have a collimating effect on ballistically transmitted carriers.8,9 The phase shift observed in the conductance fringes at low magnetic fields is a signature of the perfect transmission of carriers normally incident on the junctions10 and
thus constitutes a direct experimental observation of “Klein Tunneling.”11

http://arxiv.org/pdf/0808.0855v3

by youngsphya | 2008/12/08 22:10 | 트랙백 | 덧글(0)

Fe-based superconductors: unity or diversity?

Steven A. Kivelson and Hong Yao
Department of Physics, Stanford University, Stanford, California 94305

Does the high temperature superconductivity observed in the newly discovered iron-pnictide materials represent another example of the same essential physics responsible for superconductivity in the cuprates, or does it embody a new mechanism?

http://arxiv.org/pdf/0811.3973v1

by youngsphya | 2008/12/08 13:01 | 트랙백 | 덧글(0)

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