ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 24 Jan 2021 10:34:42 GMT2021-01-24T10:34:42Z50291- A Heisenberg model of a two-component magnetic superlatticehttps://scholarbank.nus.edu.sg/handle/10635/95630Title: A Heisenberg model of a two-component magnetic superlattice
Authors: Chen, F.; Sy, H.K.
Abstract: We study an (m, n) superlattice consisting of two alternating magnetic materials (components) of m and n atomic layers, respectively. The superlattice is modelled by a simple cubic lattice of spins coupled via nearest-neighbour exchange (Heisenberg model). Using recurrence relations, the dispersion equations of surface and bulk spin waves are derived for both finite and semi-infinite systems. The numerical results of the (1, 1), (3, 1) and (3, 2) cases are shown graphically. For a range of the surface exchange Js, the maximum number of surface modes, equal to m+n, is obtained.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956301995-01-01T00:00:00Z
- Phase diagrams of the transverse Ising model with a four-spin interactionhttps://scholarbank.nus.edu.sg/handle/10635/97518Title: Phase diagrams of the transverse Ising model with a four-spin interaction
Authors: Teng, B.H.; Sy, H.K.
Abstract: This paper investigates the phase diagrams of a ferroelectric thin film described by the transverse Ising model with a four-spin interaction. Within the framework of the higher decoupling approximation, the phase diagrams for the first-order and second-order transitions in a ferroelectric thin film are obtained, respectively, while increasing and decreasing temperature. The effects of various parameters and film thickness on the phase diagrams are shown, and the comparison between the higher decoupling approximation and the usual mean-field approximation is illustrated. © EDP Sciences.
Wed, 15 Feb 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975182006-02-15T00:00:00Z
- Curie temperature for a finite alternating magnetic superlatticehttps://scholarbank.nus.edu.sg/handle/10635/96138Title: Curie temperature for a finite alternating magnetic superlattice
Authors: Sy, H.K.; Ow, M.H.
Abstract: The authors study a spin-one-half Ising model of an alternating magnetic superlattice. They use the mean-field approximation and express their results for the Curie temperature in terms of two types of determinants. The dependence of the Curie temperature on the film thickness is obtained. The effects of surface modification on finite superlattices are studied numerically for two types of modification to the surface exchange constants.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/961381992-01-01T00:00:00Z
- Magnetostatic modes in a two-component magnetic superlattice using recurrence relationshttps://scholarbank.nus.edu.sg/handle/10635/97140Title: Magnetostatic modes in a two-component magnetic superlattice using recurrence relations
Authors: Sy, H.K.; Chen, F.
Abstract: We have studied finite and infinite superlattices with alternating layers of two types of ferromagnetic materials. The magnetostatic limit is used, and the magnetic potential in every region is obtained by solving recurrence relations. The equations giving the frequency of all the spin waves for a finite as well as a semi-infinite system are derived for two superlattice models. In addition to surface modes characteristic of ferromagnetic/ferromagnetic interfaces, new types of surface modes appear. The numerical results for seven layers and for infinite systems are shown.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/971401996-01-01T00:00:00Z
- Surface modification in ferroelectric transitionshttps://scholarbank.nus.edu.sg/handle/10635/98133Title: Surface modification in ferroelectric transitions
Authors: Sy, H.K.
Abstract: The author studies the phase transitions of finite and infinite ferroelectric systems using the Ising model in a transverse field. The mean-field layer approximation is used and the results for the Curie temperature are expressed in terms of general determinants. The effects of surface modification are introduced through a surface exchange constant J0 and a surface transverse field Omega 0. It is shown that above a critical curve in J0- Omega 0 space, surface polarization is possible, even when there is no phase transition in the bulk. The dependence of the Curie temperature on the film thickness is obtained for two types of surface modification.
Fri, 01 Jan 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/981331993-01-01T00:00:00Z
- Surface effects in an alternating magnetic superlatticehttps://scholarbank.nus.edu.sg/handle/10635/98131Title: Surface effects in an alternating magnetic superlattice
Authors: Sy, H.K.
Abstract: We study surface magnetism in a semi-infinite alternating magnetic superlattice. The spin-1/2 Ising model with alternating exchange constants JA and JB is used in the mean-field approximation. The effects of surface modification on the magnetic properties are expressed in terms of two types of determinants. The numerical results for the critical exchange constants and the surface transition temperatures are obtained for two types of surface modification. © 1992 The American Physical Society.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/981311992-01-01T00:00:00Z
- Internal Tamm states in finite and infinite superlatticeshttps://scholarbank.nus.edu.sg/handle/10635/96969Title: Internal Tamm states in finite and infinite superlattices
Authors: Sy, H.K.; Chua, T.C.
Abstract: We study a model of a finite semiconductor superlattice with the last quantum well embedded in contact with an internal potential barrier of arbitrary height. By solving recurrence relations in the envelope-function approximation, we have obtained an explicit equation giving the energy levels of the electronic states. In the infinite limit, it is shown that ''Tamm'' surface states are possible below (or above) critical curves. The Tamm-state energies are computed as a function of the last well width W. Finally, for a finite typical superlattice, the energies of all the electronic modes are shown as a function of the width W. © 1993 The American Physical Society.
Fri, 01 Jan 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/969691993-01-01T00:00:00Z
- Localized magnetism in a superlatticehttps://scholarbank.nus.edu.sg/handle/10635/97088Title: Localized magnetism in a superlattice
Authors: Sy, H.K.
Abstract: We study a magnetic superlattice in which one of the inner atomic layers has been modified. We use the Ising model in the mean-field approximation. We find that if the modified exchange constant J0 is greater than that in the bulk, localized magnetism occurs, with the magnetization decaying in both directions for the infinite superlattice. The transition temperatures for finite and infinite systems are calculated for both uniform and alternating superlattices. © 1992 The American Physical Society.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970881992-01-01T00:00:00Z
- Transition regions in the parameter space based on the transverse Ising model with a four-spin interactionhttps://scholarbank.nus.edu.sg/handle/10635/98437Title: Transition regions in the parameter space based on the transverse Ising model with a four-spin interaction
Authors: Teng, B.H.; Sy, H.K.
Abstract: By taking into account the four-spin interaction in the transverse Ising model (TIM), the transition feature of the ferroelectric thin film is investigated within the framework of the Green's function technique. Various transition regions in the parameter space with respect to the ratios of the tunneling frequency and the four-spin interaction to the two-spin interaction are calculated by a higher-order decoupling approximation beyond the usual mean-field approximation. The results show that the transition regions are greatly different from the ones obtained within the framework of the mean-field approximation. It is suggested that the usual mean-field approximation exaggerates not only the second-order but also the first-order ferroelectric transition regions for a ferroelectric thin film. © EDP Sciences.
Thu, 01 Dec 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984372005-12-01T00:00:00Z
- Spin correlations in the Ising chainshttps://scholarbank.nus.edu.sg/handle/10635/97989Title: Spin correlations in the Ising chains
Authors: Teng, B.; Sy, H.K.
Abstract: Combining the Green's function method with the transfer matrix technique, the three-site spin correlations in the one-chain and two-chain Ising lattices are studied exactly. The results show that although the magnetizations of the Ising chains vanish when the external magnetic field is zero, the spins are strongly correlated in these chains. The dependence of the spin correlations of the two-chain on the inter-chain interaction indicates that the inter-chain interaction has significant effect on the spin correlations but there does not exist a dimensional crossover from the one-dimensional model to the two-dimensional one. © 2004 Elsevier Ltd. All rights reserved.
Thu, 01 Apr 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979892004-04-01T00:00:00Z
- Surface and bulk magnetostatic modes in a ferromagnetic/nonmagnetic superlatticehttps://scholarbank.nus.edu.sg/handle/10635/98120Title: Surface and bulk magnetostatic modes in a ferromagnetic/nonmagnetic superlattice
Authors: Sy, H.K.; Chen, F.
Abstract: We have studied finite and infinite ferromagnetic/nonmagnetic superlattices in which the surface layer has a different magnetization. The magnetostatic limit is used, and the magnetic potentials in any region are obtained by solving recurrence relations. The equation giving the frequency for all the spin waves for a finite system is derived. It is shown that in the infinite limit, in addition to the usual Damon and Eshbach mode, two additional surface modes appear when the surface magnetization is larger than the host one. The finite results for eight layers are also shown. © 1994 The American Physical Society.
Sat, 01 Jan 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/981201994-01-01T00:00:00Z
- Plasmons in finite type-II semiconductor multilayershttps://scholarbank.nus.edu.sg/handle/10635/97558Title: Plasmons in finite type-II semiconductor multilayers
Authors: Sy, H.K.; Song, L.M.
Abstract: We study finite type-II semiconductor multilayers consisting of alternate layers of two-dimensional electron and hole carriers. The collective excitation is investigated with use of the coupled Boltzmann equations. We obtain the equation determining the plasma modes for N (even) layers. For N=6, we have shown the numerical results for two cases of different electron and hole masses. The total number of plasmons, and the existence of Giuliani-Quinn surface plasmons which are not Landau damped, depend on the parameters used. © 1988 The American Physical Society.
Fri, 01 Jan 1988 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975581988-01-01T00:00:00Z
- Green's function investigation of transition properties of the transverse Ising modelhttps://scholarbank.nus.edu.sg/handle/10635/96748Title: Green's function investigation of transition properties of the transverse Ising model
Authors: Teng, B.; Sy, H.K.
Abstract: With the help of the equations of motion method for the Green's function, the transition properties of ferroelectric thin films are investigated on the basis of the transverse Ising model. By decoupling the Fermi-type Green's functions to a higher order, the results beyond those of the usual mean-field approximation are obtained. The dependences of the polarizations on exchange interaction, transverse field, film thickness, and temperature are more complicated, and the polarizations become coupled with the transverse components of pseudospins via the eigenvalue equations of the Green's functions. The numerical results for phase diagrams and polarizations show that the higher decoupling approximation is better than the usual mean-field approximation. It suggests also that the usual mean-field approximation underestimates to some extent the tunneling role of the transverse Ising model and exaggerates the ferroelectric feature of thin films.
Wed, 01 Sep 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967482004-09-01T00:00:00Z
- Mean-field renormalization group study of the long-range Ising modelhttps://scholarbank.nus.edu.sg/handle/10635/97157Title: Mean-field renormalization group study of the long-range Ising model
Authors: Khoo, K.H.; Sy, H.K.
Abstract: In this paper, we study the one-dimensional long-range Ising model with a spin-spin interaction that decays as 1/r1+σ using the mean-field renormalization group. The critical coupling Kc and critical exponents Yt and Yh are computed using cluster sizes of up to sixteen spins. We then apply the alternating-alpha VBS (Vanden Broeck-Schwartz) transformation to accelerate the convergence of results for different cluster sizes.
Mon, 08 Jan 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/971572001-01-08T00:00:00Z
- Exact analytical solution to the electronic transport in an N-coupled quantum dot arrayhttps://scholarbank.nus.edu.sg/handle/10635/96537Title: Exact analytical solution to the electronic transport in an N-coupled quantum dot array
Authors: Teng, B.H.; Sy, H.K.; Wang, Z.C.; Sun, Y.Q.; Yang, H.C.
Abstract: Based on the exact Green's function calculation for an N -coupled quantum dot array, the rigorous expressions for the dc current, differential conductance, and density of states, which show analytically algebraic structures, are obtained. Our new findings indicate that for the quantum transport properties there exists an optimal tunneled coupling for which the density of states of the electrons in the quantum dot is smoothened to the fullest extent and consequently the dc current and differential conductance reach their extrema. © 2007 The American Physical Society.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/965372007-01-01T00:00:00Z
- Erratum: Transition regions in the parameter space based on the transverse Ising model with a four-spin interaction (Europhysics Letters (2005) 72:5 (823-829 ))https://scholarbank.nus.edu.sg/handle/10635/98975Title: Erratum: Transition regions in the parameter space based on the transverse Ising model with a four-spin interaction (Europhysics Letters (2005) 72:5 (823-829 ))
Authors: Teng, B.H.; Sy, H.K.
Thu, 01 Dec 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989752005-12-01T00:00:00Z
- Parameter modifications in the phase diagrams of the transverse field Ising modelhttps://scholarbank.nus.edu.sg/handle/10635/97486Title: Parameter modifications in the phase diagrams of the transverse field Ising model
Authors: Teng, B.; Sy, H.K.
Abstract: By taking into account three different exchange interaction parameters (the surface, the inter-layer, and the intra-layer couplings) and two different transverse field parameters (on the surface and inside the film), the phase diagrams of the n-layer ferroelectric thin film described by the transverse field Ising model have been studied in the framework of the mean field approach. The results show that the features of the phase diagrams can be greatly modified by changing the exchange interactions or transverse field parameters. The crossover features of the parameters from the ferroelectric dominant phase diagram to the paraelectric dominant phase diagram are determined for the first time. © 2004 Elsevier B.V. All rights reserved.
Sat, 01 May 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974862004-05-01T00:00:00Z
- Surface plasmons studied by the method of recurrence relationshttps://scholarbank.nus.edu.sg/handle/10635/98139Title: Surface plasmons studied by the method of recurrence relations
Authors: Sy, H.K.
Abstract: The author studies the plasma oscillations in a finite number of layers of a 2DEG. It is shown that by matching electromagnetic boundary conditions and solving the recurrence relations for the coefficients of the electric potential in different regions, a general equation can be obtained for the frequencies of all the plasmons under different types of surface discontinuity. Numerical results are shown for six layers with nonidentical surface charge layers.
Fri, 01 Jan 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/981391993-01-01T00:00:00Z
- Mean field theory for compositionally modulated magnetic superlatticeshttps://scholarbank.nus.edu.sg/handle/10635/97156Title: Mean field theory for compositionally modulated magnetic superlattices
Authors: Sy, H.K.
Abstract: We study a two-constituent ferromagnetic superlattice modulated compositionally. It is found that, within the molecular field approximation and in the continuum limit, the Curie temperature varies linearly with wavevector for a sinusoidal modulation. © 1987.
Mon, 16 Feb 1987 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/971561987-02-16T00:00:00Z
- Defect plasmons using recurrence relationshttps://scholarbank.nus.edu.sg/handle/10635/96156Title: Defect plasmons using recurrence relations
Authors: Sy, H.K.
Abstract: We study the plasmons in a finite semiconductor superlattice in which there is an inner defect layer of different charge density. The solutions of the recurrence relations, obtained by matching boundary conditions, are used to obtain a general equation for the frequencies of all the modes. Numerical results are given when only the localised mode is the defect mode, and when the defect mode interacts with the two dielectric surface modes. © 1995.
Mon, 27 Mar 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/961561995-03-27T00:00:00Z
- Field theoretical treatment of plasma modes in coupled two-dimensional systemshttps://scholarbank.nus.edu.sg/handle/10635/96629Title: Field theoretical treatment of plasma modes in coupled two-dimensional systems
Authors: Sy, H.K.
Abstract: We investigate an assembly of two-dimensional electron systems, separated spatially but coupled by Coulomb interaction. The acoustic and the optical plasma modes are studied using a field theoretical method. It is found that a certain approximation in treating one class of diagrams gives an effective exchange potential equal to that calculated using the method of Kohn and Sham [1]. For small wave-vector, expressions equivalent to Boltzmann equations are obtained. Numerical results are finally obtained for the dependence of the frequency on wave vector and densities of the electron systems. © 1987.
Thu, 01 Jan 1987 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/966291987-01-01T00:00:00Z
- Superlattice surface plasmonshttps://scholarbank.nus.edu.sg/handle/10635/98114Title: Superlattice surface plasmons
Authors: Sy, H.K.
Abstract: We study a semi-infinite superlattice consisting of a doped surface layer in addition to a periodic array of underlying two-dimensional charge layers. The difference in dielectric constant inside and outside is considered. The possible existence, and the dispersion relation of the surface plasmons are discussed. Numerical results are shown for different surface densities and positions of the surface layer. © 1992.
Sat, 01 Aug 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/981141992-08-01T00:00:00Z
- Surface plasmons in type II superlatticeshttps://scholarbank.nus.edu.sg/handle/10635/98138Title: Surface plasmons in type II superlattices
Authors: Sy, H.K.; Song, L.M.
Abstract: A semi-infinite type II semiconductor superlattice is studied using coupled Boltzmann equations. The exact equation is obtained for the surface plasma modes when the dielectric media inside and outside the surface are different. The number of solutions which are free from Landau damping depends on the parameters used.
Sat, 01 Oct 1988 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/981381988-10-01T00:00:00Z
- Tamn states in internal superlattice surfaceshttps://scholarbank.nus.edu.sg/handle/10635/98213Title: Tamn states in internal superlattice surfaces
Authors: Sy, H.K.; Chua, T.C.
Abstract: We consider a model of finite semiconductor superlattice with embedded well(s) of arbitrary width adjacent to internal potential barrier(s) of arbitrary height. Using envelope-function-approximation and solving recurrence relations, the explicit equation giving the electronic state energies is obtained. Numerical results are shown for finite GaAs ALxGa1-xAs superlattices with identical double embedded wells. © 1994.
Wed, 02 Feb 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/982131994-02-02T00:00:00Z
- Traffic noise survey and analysis in Singaporehttps://scholarbank.nus.edu.sg/handle/10635/98429Title: Traffic noise survey and analysis in Singapore
Authors: Sy, H.K.; Ong, P.P.; Tang, S.H.; Tan, K.L.
Abstract: A comprehensive survey and statistical analysis of daytime traffic noise in Singapore was carried out. The results are presented in terms of average L10, L50 and L90 for four different classes of sites. By clearly distinguishing between temporal and spatial noise fluctuations, it is possible, on the basis of the Gaussian noise distributions obtained, to verify that the overall noise fluctuation can also be derivable from the respective temporal and spatial noise fluctuations. The traffic noise index (TNI) and the noise pollution index (LNP) are determined and a correlation is established between the traffic noise levels and the corresponding volume of traffic. © 1985.
Tue, 01 Jan 1985 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984291985-01-01T00:00:00Z
- Bound states in a semiconductor superlatticehttps://scholarbank.nus.edu.sg/handle/10635/95885Title: Bound states in a semiconductor superlattice
Authors: Sy, H.K.
Abstract: We study an infinite type I semiconductor superlattice. The screening of a point charge due to the charge carriers of the superlattice is discussed. The binding energies of bound states in such a screened potential is studied as a function of superlattice spacing. © 1990.
Sat, 01 Sep 1990 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958851990-09-01T00:00:00Z
- Curie temperatures for a two-component ising ferromagnetic superlatticehttps://scholarbank.nus.edu.sg/handle/10635/96139Title: Curie temperatures for a two-component ising ferromagnetic superlattice
Authors: Sy, H.K.; Chen, F.
Abstract: We consider magnetic superlattices in which the elementary unit cell is made up of m atomic layers of type A and n layers of type B. Recurrence relations are solved to give compact equations for the Curie temperature of phase transitions for both finite and infinite structures. The effect of the surface constants on the phase transition is investigated. Numerical results are obtained for the dependence of the Curie temperature on the bulk as well as the surface exchanges for typical superlattices. The critical curves for the onset of surface transition are also obtained. © 1997 Elsevier Science Ltd.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/961391998-01-01T00:00:00Z
- Plasmons in a superlattice with an electric fieldhttps://scholarbank.nus.edu.sg/handle/10635/97557Title: Plasmons in a superlattice with an electric field
Authors: Sy, H.K.
Abstract: We study superlattices in which charge movement in the superlattice direction cannot be neglected. By solving Boltzmann equations, we have obtained the general dispersion relation for the plasmons when there is an additional d.c. electric field in the superlattice direction. An expansion is also made for the case when the wavevector in the superlattice direction is small. © 1989.
Fri, 01 Sep 1989 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975571989-09-01T00:00:00Z
- Plasmons in multilayers with doped surfaceshttps://scholarbank.nus.edu.sg/handle/10635/97559Title: Plasmons in multilayers with doped surfaces
Authors: Sy, H.K.; Chua, T.C.
Abstract: We study finite semiconductor superlattices with the top and bottom surface layers having charge density different from the underlying layers. The plasmon frequency can be obtained from a determinant equation. Numerical results are given for different surface densities. © 1992.
Mon, 14 Sep 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975591992-09-14T00:00:00Z