Showing papers by "Solid State Physics Laboratory published in 1999"
TL;DR: A Hanbury Brown and Twiss experiment for a beam of electrons has been realized in a two-dimensional electron gas in the quantum Hall regime, demonstrating that fermions exclude each other.
Abstract: A Hanbury Brown and Twiss experiment for a beam of electrons has been realized in a two-dimensional electron gas in the quantum Hall regime. A metallic split gate serves as a tunable beam splitter to partition the incident beam into transmitted and reflected partial beams. In the nonequilibrium case the fluctuations in the partial beams are shown to be fully anticorrelated, demonstrating that fermions exclude each other. In equilibrium, the cross-correlation of current fluctuations at two different contacts is also found to be negative and nonzero, provided that a direct transmission exists between the contacts.
337 citations
TL;DR: In this article, the interplay between orbital ordering, Jahn-Teller and GdFeO-type lattice distortions in perovskite-type transition-metal oxides using model Hartree-Fock calculations was studied.
Abstract: We have studied the interplay between orbital ordering, Jahn-Teller and ${\mathrm{GdFeO}}_{3}$-type lattice distortions in perovskite-type transition-metal oxides using model Hartree-Fock calculations. It has been found that the covalency between A-site cations and oxygens causes interaction between the Jahn-Teller and ${\mathrm{GdFeO}}_{3}$-type distortions. The present calculations explain why the d-type Jahn-Teller distortion and orbital ordering compatible with it are realized in ${\mathrm{LaMnO}}_{3},$ ${\mathrm{YVO}}_{3},$ and ${\mathrm{YTiO}}_{3}.$
131 citations
TL;DR: In this article, the Coulomb and charge transfer energies in oxide layers deposited on a highly polarizable medium like a metal, are reduced from their bulk values, by as much as 1.8 eV and 2.5 eV, respectively.
Abstract: Using the MgO/Ag(100) interface as a model system, we demonstrate that Coulomb and charge-transfer energies in oxide layers deposited on a highly polarizable medium like a metal, are reduced from their bulk values, by as much as 1.8 eV and 2.5 eV, respectively. The use of efficient image potential screening may provide a new method to alter various transition temperatures and properties of correlated oxides.
69 citations
TL;DR: In contrast to theoretical expectations based on an asymmetry induced zero-field spin splitting, no beating effect is observed in this paper, and no indication of spin splitting at zero magnetic field was observed in spite of highly resolved Shubnikov-de Haas oscillations up to filling factors of 200.
Abstract: We present magnetotransport experiments on high-quality InAs-AlSb quantum wells that show a perfectly clean single-period Shubnikov-de Haas oscillation down to very low magnetic fields. In contrast to theoretical expectations based on an asymmetry induced zero-field spin splitting, no beating effect is observed. The carrier density has been changed by the persistent photo conductivity effect as well as via the application of hydrostatic pressure in order to influence the electric field at the interface of the electron gas. Still no indication of spin splitting at zero magnetic field was observed in spite of highly resolved Shubnikov- de Haas oscillations up to filling factors of 200. This surprising and unexpected result is discussed in view of other recently published data.
69 citations
TL;DR: In this paper, the lattice constant, dc resistivity, dielectric constant, saturation magnetization and Curie temperature were studied on a series of Cr-substituted Li-Sb ferrite systems.
Abstract: The lattice constant, dc resistivity, dielectric constant, saturation magnetization and Curie temperature were studied on a series of Cr-substituted Li-Sb ferrite systems. The dc resistivity increases with increase of the chromium level. A change in slope was observed in the variation of resistivity with temperature and hence two regions of different activation energy. The study of dielectric permittivity with frequency showed dispersion for the whole system. The saturation magnetization and the Curie temperature were found to decrease with increase of the substitution level.
50 citations
TL;DR: In this paper, infrared reflectance spectroscopy measurements were made on four members of the $M{\mathrm{Fe}}_{4}{P}}_{12} family of filled skutterudites, with $M = ε,$ Th, Ce, and U, and it was shown that filling atoms have only a small effect on lattice dynamics.
Abstract: Infrared reflectance spectroscopy measurements were made on four members of the $M{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$ family of filled skutterudites, with $M=\mathrm{La},$ Th, Ce, and U. In progressing from $M=\mathrm{La}$ to U the system undergoes a metal-insulator transition. It is shown that, although the filling atom induces such dramatic changes in the transport properties of the system, it has only a small effect on lattice dynamics. We discuss this property of the compounds in the context of their possible thermoelectric applications.
49 citations
TL;DR: A metal-insulator transition in two-dimensional electron gases at $B\phantom{\rule{0ex}{0ex}}= \phantom{ 0ex}{ 0ex}}0$ is found in Ga[Al]As heterostructures, where a high density of self-assembled InAs quantum dots is incorporated just 3 nm below the heterointerface as discussed by the authors.
Abstract: A metal-insulator transition in two-dimensional electron gases at $B\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ is found in Ga[Al]As heterostructures, where a high density of self-assembled InAs quantum dots is incorporated just 3 nm below the heterointerface. The transition occurs at resistances around ${h/e}^{2}$ and critical carrier densities of $1.2\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{cm}}^{\ensuremath{-}2}$. Effects of electron-electron interactions are expected to be rather weak in our samples, while disorder plays a crucial role.
49 citations
TL;DR: In this article, the problem of qualitatively different Raman spectra of boron-rich solids obtained by conventional and FT (Fourier-transform) spectroscopy has been solved.
41 citations
TL;DR: In this article, spectroscopic and scintillation properties of BaY2F8 :Ce3+, BaLu 2F8 and BaLu2F 8 :ce3+ are presented.
36 citations
TL;DR: In this paper, the direct room temperature synthesis of magnetic composites of a copolymer with nanosized particles of Mn-Zn ferrites in different sizes was studied.
33 citations
TL;DR: The magnetic circular X-ray dichroism (MCXD) of CoO nanoparticles was measured at low temperatures and in high magnetic fields as discussed by the authors, and the particles showed a superparamagnetic behaviour at room temperature, and a large orbital contribution to the magnetic moment was observed.
Abstract: The magnetic circular X-ray dichroism (MCXD) of CoO nanoparticles was measured at low temperatures and in high magnetic fields. The particles show a superparamagnetic behaviour at room temperature, and a large orbital contribution to the magnetic moment at low temperatures was observed. This enhancement of orbital magnetism is largely determined by the contribution of the surface atoms. The larger spin–orbit coupling of the electrons of the surface atoms of the particle can cause a change in magnetic ordering in the core of the particles.
TL;DR: In this article, a tunable quantum point contact with modes occupied in both transverse directions is studied by magnetotransport experiments, where the mode spectrum is determined as a function of the magnetic field of different orientations with respect to the quantum wire.
Abstract: A tunable quantum point contact with modes occupied in both transverse directions is studied by magnetotransport experiments. We find conductance quantization that can be suppressed by degeneracies of one-dimensional modes. The mode spectrum is determined as a function of the magnetic field of different orientations with respect to the quantum wire. A magnetic field applied parallel to the direction of the current flow couples the modes. This can be described by an extension of the Darwin-Fock model. Anticrossings are observed as a function of the parallel magnetic field, but not for zero field or perpendicular field directions, indicating coupling of the subbands due to nonparabolicity in the electrical confinement.
TL;DR: In this paper, various growth rates and growth temperatures were tried to get device quality epitaxial layers suitable for solar cell applications, and it was observed that the growth temperatures and the growth rates affect the surface morphology, optical and interface properties and crystalline quality of the epitaxal layers.
TL;DR: In this article, an analytical model of an integrated QWIP and light-emitting diode (LED) operating as a pixelless image up-converter is developed and used to estimate the device performance.
Abstract: An analytical model of an integrated quantum-well infrared photodetector (QWIP) and light-emitting diode (LED) operating as a pixelless image up-converter is developed and used to estimate the device performance. It is shown that the reabsorption of the near-infrared photons trapped in the LED due to total internal reflection and their reemission can significantly influence the quality of the output image.
TL;DR: In this article, the scattering times of electrons in two subbands of a parabolic quantum well have been studied at constant electron sheet density and different positions of the electron distribution along the growth direction.
Abstract: The Drude scattering times of electrons in two subbands of a parabolic quantum well have been studied at constant electron sheet density and different positions of the electron distribution along the growth direction. The scattering times obtained by magnetotransport measurements decrease as the electrons are displaced towards the well edges, although the lowest-subband density increases. By comparing the measurements with calculations of the scattering times of a two-subband system, new information on the location of the relevant scatterers and the anisotropy of intersubband scattering is obtained. It is found that the scattering time of electrons in the lower subband depends sensitively on the position of the scatterers, which also explains the measured dependence of the scattering on the carrier density. The measurements indicate segregation of scatterers from the substrate side towards the quantum well during growth.
TL;DR: In this paper, two series of Zn-substituted LiMg and LMgTi ferrites were prepared by the solid state reaction method with a view to investigate their elastic behaviour.
TL;DR: In this paper, the variations in the responsivity, minority carrier lifetime and shunt resistance have been measured as a function of the gate potential in a HgCdTe gated photoconductor test structure.
TL;DR: In this paper, the authors performed transport experiments on two-dimensional electron gases in a GaAsAl 0.3 Ga 0.7 As heterostructure containing InAs self-assembled quantum dots in close proximity to the heterointerface.
TL;DR: In this article, a theoretical approach was developed on the basis of solution of the Boltzmann kinetic equation and corresponding formulae were derived employing clearly understood physical parameters of intra-and inter-subband scattering frequencies.
Abstract: Classical magnetotransport coefficients were studied in a parabolic quantum well (PQW) structure with two subbands occupied which occupancies were determined using the Shubnikov - de Haas effect. Unexpectedly, a very low magnetoresistivity effect was observed in comparison with what was predicted from the classical point of view for a system with two kinds of carriers possessing high mobilities around 10-20 m2 V-1 s-1. It was shown that methods, including the mobility spectrum technique, based on multilayer approach were inconsistent to describe the magnetotransport in a PQW system because of a strong intersubband scattering. For analysis of the data, a theoretical approach was developed on the basis of solution of the Boltzmann kinetic equation and corresponding formulae were derived employing clearly understood physical parameters of intra- and intersubband scattering frequencies. Based on this theoretical approach the scattering frequencies were deduced from the experimental data. In the PQW the intersubband scattering was much stronger than the intrasubband scattering and it determined the main features of the magnetotransport coefficients.
TL;DR: In this article, Nitrogen plasma exposure (NPE) effects on indium doped bulk n-CdTe Schottky diodes are reported, with an increase in barrier height, and large reverse breakdown voltages.
Abstract: Nitrogen plasma exposure (NPE) effects on indium doped bulk n-CdTe are reported here. Excellent rectifying characteristics of Au/n-CdTe Schottky diodes, with an increase in the barrier height, and large reverse breakdown voltages are observed after the plasma exposure. Surface damage is found to be absent in the plasma exposed samples. The breakdown mechanism of the heavily doped Schottky diodes is found to shift from the Zener to avalanche after the nitrogen plasma exposure, pointing to a change in the doping close to the surface which was also verified by C-V measurements. The thermal stability of the plasma exposure process is seen up to a temperature of 350 °C, thereby enabling the high temperature processing of the samples for device fabrication. The characteristics of the NPE diodes are stable over a year implying excellent diode quality. A plausible model based on Fermi level pinning by acceptor-like states created by plasma exposure is proposed to explain the observations.
01 Jan 1999
TL;DR: In this article, the authors demonstrate that tunable nanostructures in Ga[Al] can be patterned with an atomic force microscope (AFM) by applying suitable voltages to the conductive tip of the AFM, the sample can be oxidized in close vicinity of the tip Both the semiconductor surface itself as well as gate electrodes on top of it can be modified this way.
Abstract: We demonstrate that tunable nanostructures in Ga[Al]As heterostructures can be patterned with an atomic force microscope (AFM) By application of suitable voltages to the conductive tip of the AFM, the sample can be oxidized in close vicinity of the tip Both the semiconductor surface itself as well as gate electrodes on top of it can be modified this way While sufficiently thin metallic electrode films can be cut into electronically isolated parts by oxidizing them, an oxidation of the GaAs cap layer of a shallow heterostructure leads to depletion of the electron gas underneath the oxide Here, we discuss AFM lithography as a tool to fabricate tunable semiconductor nanostructures
TL;DR: In this paper, the consequences of van Hove singularities close to the Fermi level in the HTCS cuprates were discussed and the Coulomb interaction between carriers in these disordered compounds was attributed to the Coulombo interaction.
Abstract: We review the consequences of the presence of van Hove singularities close to the Fermi level in the HTCS cuprates We show that it may explain the properties of these materials such as the high T
c, anomalous isotope effect, marginal Fermi liquid properties, gap anisotropy, etc We show that the pseudogap observed in the normal state can be attributed to the Coulomb interaction between carriers in these disordered compounds
TL;DR: In this article, it was shown that the degree of spin polarization is strongly dependent on the transition metal 3d orbital orientation relative to the Poynting vector of the light.
Abstract: We have recently demonstrated that it is possible to obtain spin-resolved valence band spectra with a very high degree of spin polarization from macroscopically non-magnetic transition metal materials if the excitation light is circularly polarized and has an energy close to the cation 2p3/2 (L3) white line. Using the layered compound Sr2CuO2Cl2 as a test system, we report in this paper that the degree of spin polarization is strongly dependent on the transition metal 3d orbital orientation relative to the Poynting vector of the light.
TL;DR: In this article, the authors obtained structural information on thallium-rich caesium-thallium alloys by means of neutron diffraction and interpreted the results with the help of a'swimming cluster' model.
Abstract: The purpose of the work presented here is to obtain structural information on thallium-rich caesium-thallium alloys by means of neutron diffraction. The alloys exhibit a long-range (>1 nm) superstructure. This range increases with the thallium content. The results are interpreted with the help of a 'swimming cluster' model in which units CsmTln are dissolved in liquid thallium. (C) 1999 Elsevier Science B.V. All rights reserved.
01 Jun 1999-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the authors considered an additional set of reactions between experimentally observed extended defects (metal colloids, gas bubbles and voids) and point defects, and they gave a strong evidence for the formation of vacancy voids, which cannot be explained by the Jain-Lidiard model used up to date for description of metal colloids and dislocation loops formed in ionic crystals during earlier stages of irradiation.
Abstract: Results of experimental and theoretical investigations are presented on heavily irradiated natural and synthetic NaCl crystals in the temperature range where anion defects are mobile. They give a strong evidence for the formation of vacancy voids, which cannot be explained by the Jain–Lidiard model used up to date for description of metal colloids and dislocation loops formed in ionic crystals during earlier stages of irradiation. We consider an additional set of reactions between experimentally observed extended defects (metal colloids, gas bubbles and voids) and point defects. The latter include F and H centers that are the primary defects produced by irradiation, and cation vacancies (with a trapped hole) that are secondary defects, produced in the process of dislocation climb due to absorption of extra H centers. We show that highly overpressurized bubbles of fluid halogen are strongly biased for absorption of H centers, which makes them grow via punching out interstitial dislocation loops. The loops grow and produce cation vacancies that are subsequently trapped at the incoherent colloids together with extra F centers giving rise to the colloid–void transition. Elastic interaction between extended defects and point defects is shown to play a major role, since it determines the bias factors of extended defects, which is a major driving force of the microstructural evolution under irradiation. A quantitative comparison of the new model for radiation damage in NaCl with experimental data is presented. Mean sizes and volume fractions of all types of observed defects are calculated. It is shown that voids formed due to agglomeration of F centers and cation vacancies can grow to the dimensions exceeding the mean distance between colloids and bubbles, eventually absorbing them, hence, bringing the halogen gas and metal to a back reaction. Impurities play a major role in the void development with increasing irradiation dose, which strongly affects the radiation stability of NaCl.
TL;DR: In this paper, the performance of a pixelless imaging device based on an integrated quantum well photodetector and light-emitting diode is studied theoretically, and it is shown that the photon reabsorption and reemission processes substantially influence the electron spatial distribution and limit the quality of output image.
Abstract: The performance of pixelless imaging device based on an integrated quantum well photodetector and light-emitting diode is studied theoretically. It is shown that the photon reabsorption and reemission processes substantially influence the electron spatial distribution and limit the quality of output image.
TL;DR: In this paper, the existence of van Hove singularities close to the Fermi level in all high Tc cuprates has been experimentally established and a theory using these singularities which enables us to compute the main physical properties: Tc gap and gap anisotropy, specific heat and magnetic susceptibility.
Abstract: The existence of van Hove singularities close to the Fermi level in all high Tc cuprates has been experimentally established. We develop a theory using these singularities which enables us to compute the main physical properties: Tc gap and gap anisotropy, specific heat and magnetic susceptibility. All these results agree well with the experimental data in the optimal and overdoped regime. In the underdoped regime, we use the theory of electron-electron interaction in disordered conductors to explain the pseudo-gap behaviour.
TL;DR: In this paper, a quantum point contact with one-dimensional subbands described by two quantum numbers has been realized by laterally confining a quasi two-dimensional electron gas of a AlGaAs parabolic quantum well by split-gate electrodes.
TL;DR: In this paper, the authors examined some trade-offs and difficulties of the proposed structure and proposed a two-dimensional long-wavelength infrared region focal plane arrays (LWIR FPAs).