Physics

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We consider the conductance distributions in chaotic mesoscopic cavities for all three invariant classes of random matrices for the arbitrary number of channels N1, N2 in the connecting leads. We show that the Laplace transforms of the distributions can be expressed in terms of determinants in the unitary case and Pfaffians in the orthogonal and symplectic cases. The inverse Laplace transforms then give the exact distributions. This formalism is particularly useful for small values of N = min (N1, N2), and thus is of direct experimental relevance. We also obtain the conductance distributions for orthogonal-unitary and symplectic-unitary crossover ensembles. © 2010 IOP Publishing Ltd.

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Journal of Physics A: Mathematical and Theoretical

Conductance distributions in chaotic mesoscopic cavities

We study the transition in conductance properties of chaotic mesoscopic cavities as time-reversal symmetry is broken. We consider the Brownian motion model for transmission eigenvalues for both types of transitions, namely, orthogonal-unitary and symplectic-unitary crossovers depending on the presence or absence of spin-rotation symmetry of the electron. In both cases the crossover is governed by a Brownian motion parameter τ, which measures the extent of time-reversal symmetry breaking. It is shown that the results obtained correspond to the Jacobi crossover ensembles of random matrices. We derive the level density and the correlation functions of higher orders for the transmission eigenvalues. We also obtain the exact expressions for the average conductance, average shot-noise power and variance of conductance, as functions of τ, for the arbitrary number of modes (channels) in the two leads connected to the cavity. Moreover, we give the asymptotic result for the variance of shot-noise power for both the crossovers, the exact results being too long. In the τ → 0 and τ → ∞ limits, the known results for the orthogonal (or symplectic) and unitary ensembles are reproduced. In the weak time-reversal symmetry breaking regime, our results are shown to be in agreement with the semiclassical predictions. © 2010 IOP Publishing Ltd.

Jacobi crossover ensembles of random matrices and statistics of transmission eigenvalues

In this paper detailed studies on modification of structural and magnetic properties of Ni-doped hafnium oxide (HfO2) thin films are reported. We used 200 keV Ni beam for doping of Ni. For homogeneous dispersion and activation of doped Ni ions, 120 MeV Ni swift heavy ions (SHI) irradiation was used. This unique combination of Ni doping by ion beam and dispersing and activating by Ni SHI irradiation of HfO2 films is reported for the first time. The origin of ferromagnetism in the Ni-doped HfO2 thin films is investigated. We demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization versus temperature data. Rutherford backscattering data are used to establish that Ni ions are implanted in the HfO2 matrix at the predicted location. Dispersion of implanted Ni and lattice defects such as oxygen vacancies are attributed to be the main source of ferromagnetism. The observed magnetic moment is too large to be attributed to any secondary phase/magnetic clusters. © 2010 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Room temperature ferromagnetism in Ni-doped HfO2 thin films

APS March Meeting Abstracts

Dipole-forbidden 5d-5f Electronic Structure in Actinide Systems

We report nonresonant inelastic x-ray scattering from the semicore 5d levels of several actinide compounds. Dipole-forbidden, high-multipole features form a rich bound-state spectrum dependent on valence electron configuration and spin-orbit and Coulomb interactions. Cross-material comparisons, together with the anomalously high Coulomb screening required for agreement between atomic-multiplet theory and experiment, demonstrate sensitivity to the neighboring electronic environment, such as is needed to address longstanding questions of electronic localization and bonding in 5f compounds. {\textcopyright} 2010 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Probing electronic correlations in actinide materials using multipolar transitions

A copolymer comprising 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) and thieno[3,2-b]thiophene moieties, PDBT-co-TT, shows high hole mobility of up to 0.94 cm2 V-1 s-1 in organic thin-film transistors. The strong intermolecular interactions originated from π-π stacking and donor-acceptor interaction lead to the formation of interconnected polymer networks having an ordered lamellar structure, which have established highly efficient pathways for charge carrier transport. © 2010 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Advanced Materials

A high mobility P-type DPP-thieno[3,2-b]thiophene copolymer for organic thin-film transistors

Random matrix model for the Nakagami-q (Hoyt) fading in multiple-input multiple-output (MIMO) communication channels with arbitrary number of transmitting and receiving antennas is considered. The joint probability density for the eigenvalues of H† H† (or {H H†), where H† is the channel matrix, is shown to correspond to the Laguerre crossover ensemble of random matrices and is given in terms of a Pfaffian. Exact expression for the marginal density of eigenvalues is obtained as a series consisting of associated Laguerre polynomials. This is used to study the effect of fading on the Shannon channel capacity. Exact expressions for higher order density correlation functions are also given which can be used to study the distribution of channel capacity. © 2010 IEEE.}, author_keywords={Channel capacity; Fading distributions; Hoyt distribution; Laguerre crossover ensemble; Multiple-input multiple-output (MIMO) channels; Nakagami-q distribution; Random matrices}, keywords={Hoyt distribution; Laguerre; Multiple-input multiple-output channels; Nakagami; Nakagami-q distribution; Random matrices, Distribution functions; Eigenvalues and eigenfunctions; Fading channels; Probability density function; Receiving antennas, Channel capacity}, funding_details={Council of Scientific and Industrial Research, IndiaCouncil of Scientific and Industrial Research, India, CSIR}, funding_text_1={Manuscript received August 03, 2009; revised December 08, 2009. Current version published April 21, 2010. S. Kumar was supported by CSIR India through a fellowship. The authors are with the School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India (e-mail: skumar.physics@gmail.com; ap0700@mail.jnu.ac.in). Communicated by A. L. Moustakas, Associate Editor for Communications. Digital Object Identifier 10.1109/TIT.2010.2044060}, references={Simon, M.K., Alouini, M.-S., (2000) Digital Communication Over Fading Channels: A Unified Approach to Performance Analysis, , Hoboken, NJ: Wiley; Simon, M.K., Alouini, M.-S., A unified approach to the performance analysis of digital communication over generalized fading channels (1998) Proc. IEEE, 86 (9), pp. 1860-1877. , Sep; Foschini, G.J., Gans, M.J., On limits of wireless communications in a fading environment when using multiple antennas (1998) Wireless Pers. Commun., 6 (2), pp. 311-335. , Mar; Telatar, I.E., Capacity of multi-antenna Gaussian channels (1999) Eur. Trans. 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IEEE Transactions on Information Theory

Random matrix model for nakagamihoyt fading

Flash lamp annealing induced rapid melting of a near surface Ge enriched Si wafer and the subsequent formation of SiGe layers were demonstrated. The formation of an undesirable facetted liquid/solid interface, well known for pulse melting in the millisecond time regime, was found to decrease significantly due to the increasing melting temperature of Si with reducing Ge concentration at the SiGe/Si interface. A dislocation network and the existence of strain, which were evidenced by transmission electron microscopy and μ-Raman measurements, respectively, are expected to play an important role to form thin SiGe layers. © 2010 Elsevier B.V. All rights reserved.

Current Applied Physics

Subsecond melt processing for achieving SiGe layers

We report on effects of Fe implantation dopinginduced changes in structural, optical, morphological, and vibrational properties of cadmium sulfide thin films. Films were implanted with 90 keV Fe+ ions at room temperature for a wide range of fluences from 0.1 × 1016 to 3.6 × 1016 ions cm-2 (corresponding to 0.38-12.03 at.% of Fe). Glancing angle X-ray diffraction analysis revealed that the implanted Fe atoms tend to supersaturate by occupying the substitutional cationic sites rather than forming metallic clusters or secondary phase precipitates. In addition, Fe doping does not lead to any structural phase transformation although it induces structural disorder and lattice contraction. Optical absorption studies show a reduction in the optical band gap from 2.39 to 2.17 eV with increasing Fe concentration. This is attributed to disorder-induced band tailing in semiconductors and ion-beam-induced grain growth. The strain associated with a lattice contraction is deduced from micro-Raman scattering measurements and is found that size and shape fluctuations of grains, at higher fluences, give rise to inhomogeneity in strain. © Springer-Verlag 2010.

Applied Physics A: Materials Science and Processing

Effect of Fe-ion implantation doping on structural and optical properties of CdS thin films

The furnace and flash-lamp annealing (FLA) temperature dependent variation in the room temperature 1.53 μm Er photoluminescence (PL) from Er-doped Ge-rich SiO2 layers is investigated. The appearance of the 1.53 μm Er PL is discussed in the framework of the phonon-assisted fluorescent resonant energy transfer from Ge-related luminescence-centers (LCs) to the Er 3+. Detailed analyses suggest that in case of FLA the decrease in the 1.53 μm Er PL intensity is governed by the temperature dependent recrystallization of Ge nanoclusters, while for furnace-annealing it is associated with the reduction in the LC- Er3+ coupling due to Ge out-diffusion and the formation of Er-rich clusters with increasing temperature. © 2010 American Institute of Physics.