Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session R25: Focus Session: Computational Studies of Heterostructures |
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Sponsoring Units: DCOMP Chair: Shiwei Zhang, College of William and Mary Room: 327 |
Wednesday, March 20, 2013 2:30PM - 3:06PM |
R25.00001: Competition of magnetism and Kondo physics in heterostructures Invited Speaker: Simone Chiesa Heterostructures made of atomically thin strongly correlated materials have been the focus of intense experimental and theoretical study. We report on results obtained using an unbiased numerical technique on a simple model of a metal-magnetic insulator interface: a multilayer system governed by a tight-binding Hamiltonian in which the interaction is nonzero on one set of adjacent planes and zero on another. As the interface hybridization is tuned, magnetic and metallic properties undergo an evolution that reflects the competition between antiferromagnetism and (Kondo) singlet formation, in a scenario similar to that occurring in heavy-fermion materials. Remarkably, for a few-layer system at intermediate hybridization, a Kondo insulating phase results, where magnetic order and conductivity are suppressed in all layers. As more insulating layers are added, magnetic order is restored in all correlated layers except the one at the interface and no evidence of long-range magnetic order induced in the metallic layers is found. [Preview Abstract] |
Wednesday, March 20, 2013 3:06PM - 3:42PM |
R25.00002: Mechanisms of Electronic Reconstruction at Oxide Interfaces with 001 and 111 Orientation Invited Speaker: Rossitza Pentcheva Remarkably rich electronic behavior has been recently discovered at oxide interfaces ranging from two-dimensional conductivity, superconductivity and magnetism to confinement induced metal-to-insulator transitions. Most of the interest so far has been directed at 001 oriented interfaces as e.g. the ones between the two band insulators LaAlO$_{\mathrm{3}}$ and SrTiO$_{\mathrm{3}}$ or in superlattices containing the correlated metal LaNiO$_{\mathrm{3\thinspace }}$and the band insulator LaAlO$_{\mathrm{3}}$. However, 111 oriented superlattices promise to host even more exotic, possibly topological phases. Despite the difference in stacking with AO and BO$_{\mathrm{2}}$ planes of the perovskite ABO$_{\mathrm{3}}$ structure in 001 oriented superlattices versus AO$_{\mathrm{3}}$ and B layers in the 111 crystallographic direction, analogous effects such as polar discontinuity arise in both cases when the A and B cations are varied across the interface. Based on density functional theory calculations we will compare mechanisms of electronic reconstruction in 001 and 111 oriented superlattices. We will thereby focus on the effect of confinement, band filling, magnetic coupling, structural distortions and substrate strain. Work in collaboration with David Doennig and Warren E. Pickett. Funding by the German Science Foundation, SFB/TR80, is gratefully acknowledged. [Preview Abstract] |
Wednesday, March 20, 2013 3:42PM - 3:54PM |
R25.00003: Electronic properties of graphene-MoS2 contacts Brandon Cook, Kalman Varga Single layer MoS$_2$ is a two-dimensional semiconductor which has attracted interest due to its electronic and optical properties. However, experimental studies of the material are limited by poor contacts. Graphene, a two-dimensional semimetal, is often touted as an ideal contact material. We investigate graphene-MoS$_2$ contacts with first-principles calculations. The density functional calculations predict the possibility of good charge injection from graphene to the MoS$_2$. [Preview Abstract] |
Wednesday, March 20, 2013 3:54PM - 4:06PM |
R25.00004: Density of States and Magnetic Correlations at a Metal-Mott Insulator Interface Mi Jiang, George Batrouni, Richard Scalettar The possibility of novel behavior at interfaces between strongly and weakly correlated materials has come under increased study recently. In this paper, we use determinant Quantum Monte Carlo to determine the inter-penetration of metallic and Mott insulator physics across an interface in the two dimensional Hubbard Hamiltonian. We quantify the behavior of the density of states at the Fermi level and the short and long range antiferromagnetism as functions of the distance from the interface and with different interaction strength, temperature and hopping across the interface. Induced metallic behavior into the insulator is evident over several lattice spacings, whereas antiferromagnetic correlations remain small on the metallic side. At large interface hopping, singlets form between the two boundary layers, shielding the two systems from each other. [Preview Abstract] |
Wednesday, March 20, 2013 4:06PM - 4:18PM |
R25.00005: Numerical simulation study of inhomogeneous metal-semiconductor contact with discrete distribution of varying barrier heights patches Priyanka Kaushal, Subhash Chand The Poisson's equation and the drift diffusion equations were solved by numerical simulation to calculate the potential and electron and hole concentrations inside the bulk semiconductor near the metal-semiconductor contact. The current density was then estimated from the calculated potential and electron-hole concentrations using the continuity equations. The current as a function of bias was calculated by imposing external bias through the boundary condition during the numerical simulation using silicon parameters to obtain the current-voltage characteristics of metal-semiconductor contact. From the simulated current-voltage characteristics the diode parameters were extracted by fitting the current-voltage data into the thermionic emission diffusion current equation. The simulations were performed for the inhomogeneous metal-semiconductor contact having randomly distributed patches of varying barrier heights. The patch size was varied to see its effect of the current-voltage characteristics and the derived apparent barrier parameters. The derived barrier parameters were analyzed to study the effect of inhomogeneities on the current-voltage characteristics on metal-semiconductor contact. The simulations were carried out for discrete distribution of barrier height patches at the metal-semiconductor contact. It is observed that the apparent barrier height of the inhomogeneous contact decreases and ideality factor increases with increasing the deviation of barrier heights in the distribution. [Preview Abstract] |
Wednesday, March 20, 2013 4:18PM - 4:30PM |
R25.00006: ABSTRACT WITHDRAWN |
Wednesday, March 20, 2013 4:30PM - 4:42PM |
R25.00007: Plasma instability and wave propagation in gate-controlled semiconductor conduction channels Sergey Rudin, Greg Rupper The plasma wave in the conduction channel of a semiconductor heterostructure high electron mobility transistor is an electron density excitation, possible at frequencies significantly higher than the cut-off frequency in a short channel device. When the electron-electron collision limited mean free path is much smaller than the wavelength of the density variations, the electron gas in the channel can be treated as a two-dimensional fluid. The flow is described by the Navier-Stokes equation and the heat conduction equation. The quality of the plasma resonance is limited by the electron mobility and the viscosity of the electron fluid. We use the hydrodynamic model derived as the balance equations from the quasi-classical Boltzmann equation, starting with a drifted Fermi-Dirac distribution as a zero order term in the expansion of the distribution function in orders of the Knudsen number. The charge flow can become unstable because of plasma wave amplification at the boundaries. The device then can be used as a tunable source of terahertz range radiation. We show that in such configuration the charge flow also develops shock waves due to hydrodynamic nonlinearities. [Preview Abstract] |
Wednesday, March 20, 2013 4:42PM - 4:54PM |
R25.00008: Investigation of the effect of core/shell interface on exciton binding energy and electron-hole recombination probability in CdSe/ZnS quantum dots Jennifer Elward, Arindam Chakraborty The explicitly correlated configuration interaction (XCCI) method is a variational technique in which an explicitly correlated reference wavefunction is used for performing the CI calculations. This work presents a multi-faceted study of the effect of heterojunction in nanoparticles and detailed analysis of various influential factors. The XCCI method was used for the study and the calculations were performed in three stages. In stage 1, the CdSe core was kept at a fixed size and the ZnS shell thickness was increased. In stage 2, the dot size was kept fixed and volume ratio between the core and the shell was varied. In stage 3, the sharpness of the core/shell interface was investigated by performing calculations on a core/alloy/shell system. Exciton binding energy (EB) and electron-hole recombination probability (eh-RP) were computed and the results were compared with CdSe quantum dots with similar radii. The presence of the heterojunction was found to effect the scaling of EB and eh-RP as a function of dot size. It was also found that EB and eh-RP scale very differently with respect to dot sizes. Expectation value of $r_{\mathrm{eh}}$ and radial 2-particle eh-reduced density matrix were used for analysis of spatial distribution of the quasiparticles in the multilayered qdots. [Preview Abstract] |
Wednesday, March 20, 2013 4:54PM - 5:06PM |
R25.00009: Effects of Nonlocal Exact Exchange on Electrons in Core/Shell Nanowires Bryan Wong, Andrew Long The unique properties of semiconducting heterostructure nanowires hold great promise for their incorporation in next-generation transistors, circuits, and nanoscale devices. The reduction in dimensionality produced by confining electrons in these heterostructure nanowires results in a dramatic change in their electronic structure, leading to novel properties such as ballistic transport and conductance quantization. In order to understand the formation of electron gases in core-shell nanowires, we developed a new pseudospectral approach for incorporating many-body, nonlocal exact exchange interactions within a self-consistent Schrodinger-Poisson formalism. Our approach is efficiently implemented in the open-source software package PAMELA (Pseudospectral Analysis Method with Exchange {\&} Local Approximations) that can calculate electronic energies, densities, wavefunctions, and band-bending diagrams. Furthermore, in order to present a general-purpose set of tools that both experimentalists and theorists can easily use to predict electron gas formation in core-shell nanowires, we document and provide our efficient and user-friendly PAMELA source code that is freely available at http://alum.mit.edu/www/usagi. [Preview Abstract] |
Wednesday, March 20, 2013 5:06PM - 5:18PM |
R25.00010: Kondo screening and Magnetism at Interfaces Axel Euverte, George Batrouni, Simone Chiesa, Richard Scalettar As clean heterostructures synthesis and analysis become experimentally accessible, the question of the nature of magnetic and transport properties at correlated interfaces arise. We study a simple Hubbard model of an interface between a metal and an antiferromagnetic insulator using a finite temperature quantum Monte Carlo method. Focusing on the effect of the hybridization at the interface, we show the singlet formation leads in thin systems to an intermediate non-magnetic insulating phase that involves metallic and correlated layers that are not in direct contact with each other. In thicker heterostructures, magnetic proximity effect of correlated layers farther from the interface defeats the formation of that intermediate phase. The large hybridization case is also discussed, showing decoupling of outer layers from the singlet interface. [Preview Abstract] |
Wednesday, March 20, 2013 5:18PM - 5:30PM |
R25.00011: Engineering three dimensional topological insulator in layered heterostructures T. Das, A.V. Balatsky We show that three dimensional topological insulator can be designed artificially via staking layers of two-dimensional Fermi gases (2DEGs) with finite inter-layer tunneling. The approach is based on stacking bilayers of Rashba-type spin-orbit coupled 2DEG with opposite spin-orbit coupling on opposite planes of bilayers. Spin Orbit interaction locks electronic states with respective spin projections, i.e.$+$/-a(k*s) with `a' is the Rashba-spin-orbit coupling strength, `k' is the momentum, and `s' is Pauli matrices for spin. We find that in the stack of bilayers grown along (001)-direction, a topological phase transition occurs above a critical number of Rashba-bilayers, with formation of a single spin-polarized Dirac cone at the $\backslash $Gamma-momentum . This approach offers a path to design artificial topological insulators in a set up that takes full advantage of atomic layer deposition approach, is free from crystal geometry, and is tunable. Work is supported by US DOE and Nordita. [Preview Abstract] |
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