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2007 APS March Meeting Monday–Friday, March 5–9, 2007; Denver, Colorado

Bulletin of the American Physical Society

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file:///E|/Acheng/my%20papers/PUBLICATIONS/Confere...tin%20of%20the%20American%20Physical%20Society.htm2007/3/16 上午 12:04:36

C1.00236 One-beam coherent control effect at Si(111) surfaces: linear optical formalism andlayer-by-layer analysis , A.I. SHKREBTII, University of Ontario Institute of Technology, Oshawa, ON, Canada, J.E.N. ARZATE, J.L. CABELLOS,B. MENDOZA, Centro de Investigaciones en Optica, Leon, Mexico, F. NASTOS, J.E. SIPE, Department of Physics, University of Toronto, Canada — Wedemonstrated how the so-called one-beam coherent control effect might be used as a complementary probe in surface physics to extract information aboutsurface structure, electronic states, bonding, etc. In [1] this effect has been developed in terms of a nonlinear optical formalism. In contrast to [1], we presenteda complementary ballistic photocurrent formalism that is linear. We demonstrated that the non-diagonal elements of the linear optical tensor contribute to thiscoherent control effect, which is due to the quantum interference between the two orthogonally polarized beams. Such ballistic photocurrent injection dependson the relative phase between these beams (φb - φc) as dJ a/dt = η abc|Eb| |Ec| sin(φb - φc). As the second step, we developed a microscopic formalism toseparate the optical response produced by each atomic layer of a semi-infinite crystal. Finally, we applied this formalism to the clean Si(111) (2×1), Si(111):H(1×1) and Si(111):As(1×1) surfaces. The research was supported by NSERC Discovery Grant. [1] J.E. Sipe and A.I. Shkrebtii, Phys. Rev. B, 61, 5337 (2000)

C1.00237 Low-energy Landau levels and magneto-optical properties of the zigzag grapheneribbons1 , Y.C. HUANG, C.P. CHANG, M.F. LIN, Center for General Education, Kao Yuan University — The Peierl’s coupling tight-binding model isemployed to investigate low-energy Landau levels and magneto-absorption spectra of the zigzag graphene ribbons. The Landau-level features vary with theribbon width: the greater the ribbon width, the more the Landau levels. What should be noticed is that the positions of Landau levels change little in spite of

the increasing of the ribbon width. The Landau level energy satisfy the relation En ∝√|n|B , where n is subband index and B is field strength. The associated

absorption spectra exhibits richer discrete Landau peaks. The transition channels related to Landau peaks are identified. The peak positions are independentof the ribbon width. Above all, a formula is presented to simulate the magneto-absorption spectra of a graphene in a very simple form.

1The authors gratefully acknowledge the support of the Taiwan National Science Council under the contract Nos. NSC 95-2112-M-165-001; NSC95-2112-M-006-0002.

C1.00238 Magnetoelectronic properties of a single-layer graphite , Y.H. LAI, J.H. HO, M.F. LIN, Departmentof Physics, NCKU, Taiwan — The magnetoelectronic structure of a single-layer graphite is mainly determined by the strength, the period, and the direction ofthe modulated magnetic field. Such field could induce the destruction of state degeneracy, the drastic change of energy dispersion, the increment of band-edgestates, and the alternation of band width. Most of energy bands become nondegenerate, and the flat bands are replaced by the parabolic bands. Density ofstates exhibits the linear energy dependence, the square-root divergences, the logarithmic divergences, the discontinuous structures, and the delta-function-likedivergences. These special structures directly reflect rich energy spectra.

C1.00239 Theoretical study of adsortion of Sb on GaAs(110) surface1 , NORBERTO ARZATE, RAULVAZQUEZ, BERNARDO MENDOZA, Centro de Investigaciones en Optica, A. C. — We present a model for studying the adsorption of Sb atoms on a cleanGaAs(110) surface and analyse the consequences of the adsorption on the reflectance anisotropy spectroscopy (RAS). A 1× 3 unit cell is taken as a basis of theSb-covered GaAs(110) structure. The relaxed coordinates of each configuration have been obtained thanks the use of the ABINIT code [1,2], that is based onpseudopotentials and planewaves. We allow the Sb-covered surface to be disordered by letting every surface atom move freely around its equilibrium position. Inorder to obtain a representative RAS spectrum of the surface we generate an ensemble with N different structural realizations of the surface and the ensembleRAS average is performed.[1] X. Gonze, et al., Computational Materials Science 25, 478 (2002).[2] X. Gonze, et al., Zeit. Kristallogr. 220, 558 (2005).[3] Bernardo S. Mendoza, N. Arzate and R.A. Vazquez-Nava, phys. stat. soli. (c) 2, 4031 (2005).

1SEP-2004-C01-48142 and SEP-2003-C02-42576.

C1.00240 Examination of the Properties of the Ab-Initio Calculations for the Electronic Struc-ture of GaAs and InAs , G.L. ZHAO, H. JIN, D. BAGAYOKO, Southern University and A&M College — At present, most of the ab-initio densityfunctional calculations for the studies of the electronic structure of solid state materials utilized non-orthogonal basis sets. The mathematical and physicalproperties of these methods have not been carefully studied and can be different from those utilizing orthogonal basis sets in quantum mechanics theory. Wepresent some of the mathematical properties of the methods, based on the variational theory of Ritz-process. The utilizations of non-orthogonal basis sets in theab-initio calculations could lead to a non-uniformity in approaching their solutions. We also studied the properties of the ab-initio calculations for the electronicstructure of GaAs and InAs. Acknowledgments: this work was funded in part by NSF (Award No. 0508245) and ONR (Grant No: N00014-05-1-0009).

C1.00241 Reflectance anisotropy spectroscopy of CdTe(001) surfaces1 , RAUL VAZQUEZ, NORBERTOARZATE, BERNARDO MENDOZA, Centro de Investigaciones en Optica, A. C. — The spectroscopical reflectance anisotropy (RA) response of (001) surfacesof CdTe, which exhibits a (2 × 1) and (2 × 1) surface reconstructions, is studied using two theoretical aproaches: an ab initio pseudopotential calculation inthe framework of the density functional theory and within the local density approximation (DFT-LDA) is used to obtain the relaxed atomic positions, and amicroscopic formulation based on a semi-empirical tight binding (SETB) approach which includes spin-orbit (SO) interactions[1] is used to obtain the RA spectra.We show RA spectrum of each surface reconstruction and compare our theoretical results with experimental results[2]. We find a good agreement betweenexperimental and theoretical spectra. We show how the RA changes when SO is taken into account and compare our theoretical results with experimentalmeasurements of Ref. 2. [1] R.A. Vazquez-Nava, B.S. Mendoza and C. Castillo, Phys. Rev. B 70, 165306 (2004). [2] R. E. Balderas-Navarro, K. Hingerl, W.Hilber, D. Stifter, A. Bonanni and H. Sitter, J. Vac. Sci. Technol. B 18, 2224 (2000).

1CONACYT Mexico SEP-2004-C01-48142 and SEP-2003-C02-42576

C1.00242 Effects of spin filter on singlet and triplet exciton fractions in organic light-emittingdevices , LIANBIN NIU, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, XIAOHONG ZHANG, Nano-organic Photo-electronic Laboratory,IPC,CAS,Beijing 100101, FUJIA ZHANG, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, SCHOOLOF PHYSICAL SCIENCE AND TECHNOLOGY, LANZHOU UNIVERSITY TEAM, NANO-ORGANIC PHOTOELECTRONIC LABORATORY, IPC, CAS COL-LABORATION — In recent years spin and magnetic field effects are investigated in organic light-emitting devices (OLEDs). We studied the electroluminescencecurrent efficiency at room temperature under parallel and antiparallel magnetic field in OLEDs with spin filter. The magnetic field applied parallel to theelectrode allows the magnetization of the electrode to be switched independently. The current efficiency for the antiparallel magnetic field is found to beenhanced as compared to the parallel one. We show that this increase is an evidence of spin injection and a consequence of the magnetic-field dependenceof the singlet-to-triplet exciton ratio in OLEDs, suggesting that the spin-polarized electrons were injected into the organic molecules from the spin filter underelectrical excitation. Therefore, the use of spin filter demonstrates a pathway to tune the optoelectronic properties that are related to singlet and triplet statesin OLEDs.

Event - Low-energy Landau levels and magneto-optical properties of the zigzag graphene ribbons

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2007 APS March Meeting Monday–Friday, March 5–9, 2007; Denver, Colorado

Session C1: Poster Session I2:00 PM–2:00 PM, Monday, March 5, 2007 Colorado Convention Center - Exhibit Hall F, 2:00pm - 5:00pm

Abstract: C1.00238 : Low-energy Landau levels and magneto-optical properties of the zigzag graphene ribbons

Preview Abstract

Authors: Y.C. Huang ( Center for General Education, Kao Yuan University)

C.P. Chang ( Center for General Education, Kao Yuan University)

M.F. Lin ( Center for General Education, Kao Yuan University)

The Peierl's coupling tight-binding model is employed to investigate low-energy Landau levels and magneto-absorption spectra of the zigzag graphene ribbons. The Landau-level features vary with the ribbon width: the greater the ribbon width, the more the Landau levels. What should be noticed is that the positions of Landau levels change little in spite of the increasing of the ribbon width. The Landau level energy satisfy the relation $E_n\propto\sqrt{|n|B}$ , where n is subband index and B is field strength. The associated absorption spectra exhibits richer discrete Landau peaks. The transition channels related to Landau peaks are identified. The peak positions are independent of the ribbon width. Above all, a formula is presented to simulate the magneto-absorption spectra of a graphene in a very simple form.

file:///E|/Acheng/my%20papers/PUBLICATIONS/Conferen...erties%20of%20the%20zigzag%20graphene%20ribbons.htm2007/3/16 上午 12:25:40