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653 results on '"McCulloch I"'

110. Conformal data from finite entanglement scaling

Author

Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Stojevic, Vid, Haegeman, Jutho, McCulloch, I. P., Tagliacozzo, Luca, Verstraete, Frank, Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Stojevic, Vid, Haegeman, Jutho, McCulloch, I. P., Tagliacozzo, Luca, and Verstraete, Frank

Abstract

In this paper, we apply the formalism of translation invariant (continuous) matrix product states in the thermodynamic limit to (1 + 1)-dimensional critical models. Finite bond dimension bounds the entanglement entropy and introduces an effective finite correlation length, so that the state is perturbed away from criticality. The assumption that the scaling hypothesis holds for this kind of perturbation is known in the literature as finite entanglement scaling. We provide further evidence for the validity of finite entanglement scaling and based on this formulate a scaling algorithm to estimate the central charge and critical exponents of the conformally invariant field theories describing the critical models under investigation. The algorithm is applied to three exemplary models; the cMPS version to the nonrelativistic Lieb-Liniger model and the relativistic massless boson, and MPS version to the one-dimensional quantum Ising model at the critical point. Another new aspect to our approach is that we directly use the (c)MPS induced correlation length rather than the bond dimension as scaling parameter. This choice is motivated by several theoretical arguments as well as by the remarkable accuracy of our results., Peer Reviewed, Postprint (author’s final draft)

Published
2015

112. The Influence of Polymer Purification on Photovoltaic Device Performance of a Series of Indacenodithiophene Donor Polymers

Author

Ashraf, RS, Schroeder, BC, Bronstein, HA, Huang, Z, Thomas, S, Kline, RJ, Brabec, CJ, Rannou, P, Anthopoulos, TD, Durrant, JR, and McCulloch, I

Subjects
Silicon, Materials science, Organic solar cell, Polymers, Band gap, Dispersity, chemistry.chemical_element, Thiophenes, 02 engineering and technology, 010402 general chemistry, 7. Clean energy, 01 natural sciences, law.invention, law, Solar cell, Polymer chemistry, Solar Energy, General Materials Science, chemistry.chemical_classification, business.industry, Mechanical Engineering, Photovoltaic system, Polymer, 021001 nanoscience & nanotechnology, Solar energy, 6. Clean water, 0104 chemical sciences, chemistry, Chemical engineering, Mechanics of Materials, Electronics, 0210 nano-technology, business
Abstract

A series of low bandgap indacenodithiophene polymers is purified by recycling SEC in order to isolate narrow polydispersity fractions. This additional purification step is found to have a significant beneficial influence on the solar cell performance and the reasons for this performance increase are investigated.

Published
2013
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114. Charge photogeneration in donor/acceptor organic solar cells

Author

Shoaee S., Clarke T.M., Eng M.P., Huang C., Barlow S., Espíldora E., Delgado J.L., Campo B., Marder S.R., Heeney M., McCulloch I., Martín N., Vanderzande D., Durrant J.R. and The authors are grateful to Solvay SA and the EPSRC from the UK Office of Science and Technology. Work was also supported financially by the Science and Technology Center Program of the National Science Foundation (DMR-0120967) and by the Office of Naval Research (N00014-04-1-0120). Dr. Keivanidis and Professor Nelson provided helpful discussions, and John Seddon allowed the use of his light microscope. MPE acknowledges the Knut and Alice Wallenberg foundation for funding. This work has been supported by the European Science Foundation (05-SONS-FP-021 SOHYD), the Spanish Ministry of Education and Science (CT2008-00795/BQU), Consolider-Ingenio (2010C-07-25200, Nanociencia Molecular), and Comunidad de Madrid (P-PPQ-000225-0505). JLD thanks the Ministry of Science and Innovation for a Ramón y Cajal Fellowship, cofinanced by the EU Social Funds. The research of BC is funded by a PhD grant of the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen). Supporting information is available online from Wiley InterScience or from the author.

Published
2012

115. Probing the relaxation towards equilibrium in an isolated strongly correlated one-dimensional Bose gas

Author

Trotzky, S., Chen, Y-A., Flesch, A., McCulloch, I. P., Schollwöck, U., Eisert, J., and Bloch, I.

Subjects
Institut für Physik und Astronomie
Abstract

The problem of how complex quantum systems eventually come to rest lies at the heart of statistical mechanics. The maximum-entropy principle describes which quantum states can be expected in equilibrium, but not how closed quantum many-body systems dynamically equilibrate. Here, we report the experimental observation of the non-equilibrium dynamics of a density wave of ultracold bosonic atoms in an optical lattice in the regime of strong correlations. Using an optical superlattice, we follow its dynamics in terms of quasi-local densities, currents and coherences-all showing a fast relaxation towards equilibrium values. Numerical calculations based on matrix-product states are in an excellent quantitative agreement with the experimental data. The system fulfills the promise of being a dynamical quantum simulator, in that the controlled dynamics runs for longer times than present classical algorithms can keep track of.

Published
2012

116. Thin-film morphology of inkjet-printed single-droplet organic transistors using polarized Raman spectroscopy: effect of blending TIPS-pentacene with insulating polymer

Author

James, D.T., Kjellander, B.K.C., Smaal, W.T.T., Gelinck, G.H., Combe, C., McCulloch, I., Wilson, R., Burroughes, J.H., Bradley, D.D.C., and Kim, J.S.

Subjects
inkjet printing, TS - Technical Sciences, Industrial Innovation, morphology, Raman spectroscopy, HOL - Holst, pentacene, Mechatronics, Mechanics & Materials, Materials, organic transistors
Abstract

We report thin-film morphology studies of inkjet-printed single-droplet organic thin-film transistors (OTFTs) using angle-dependent polarized Raman spectroscopy. We show this to be an effective technique to determine the degree of molecular order as well as to spatially resolve the orientation of the conjugated backbones of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) molecules. The addition of an insulating polymer, polystyrene (PS), does not disrupt the p-p stacking of the TIPS-Pentacene molecules. Blending in fact improves the uniformity of the molecular morphology and the active layer coverage within the device and reduces the variation in molecular orientation between polycrystalline domains. For OTFT performance, blending enhances the saturation mobility from 0.22 ± 0.05 cm2/ (V·s) (TIPS-Pentacene) to 0.72 ± 0.17 cm2/(V·s) (TIPS-Pentacene:PS) in addition to improving the quality of the interface between TIPS-Pentacene and the gate dielectric in the channel, resulting in threshold voltages of ~0 V and steep subthreshold slopes. © 2011 American Chemical Society.

Published
2011

118. Bias stress effect and recovery in organic field effect transistors: proton migration mechanism

Author

Sharma, A., Mathijssen, S.G.J., Kemerink, M., Leeuw, de, D.M., Bobbert, P.A., Bao, Z., McCulloch, I., Soft Matter and Biological Physics, and Molecular Materials and Nanosystems

Subjects
Organic electronics, Materials science, Condensed matter physics, business.industry, Transistor, Gate dielectric, Biasing, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, law.invention, Threshold voltage, Computer Science::Hardware Architecture, Computer Science::Emerging Technologies, Semiconductor, law, Gate oxide, Field-effect transistor, business
Abstract

Organic field-effect transistors exhibit operational instabilities when a gate bias is applied. For a constant gate bias the threshold voltage shifts towards the applied gate bias voltage, an effect known as the bias-stress effect. We have performed a detailed experimental and theoretical study of operational instabilities in p-type transistors with silicon-dioxide gate dielectric. We propose a mechanism in which holes in the semiconductor are converted into protons in the presence of water and a reversible migration of these protons into the gate dielectric to explain the instabilities in organic transistors. We show how redistribution of charge between holes in the semiconductor and protons in the gate dielectric can consistently explain the experimental observations. Furthermore, we explain in detail the recovery of a pres-stressed transistor on applying zero gate bias. We show that recovery dynamics depends strongly on the extent of stressing. Our mechanism is consistent with the known aspects of bias-stress effect like acceleration due to humidity, constant activation energy and reversibility.

Published
2010

133. Charge photogeneration in donor/acceptor organic solar cells

Author

Shoaee S., Clarke T.M., Eng M.P., Huang C., Barlow S., Espíldora E., Delgado J.L., Campo B., Marder S.R., Heeney M., McCulloch I., Martín, Nazario, Vanderzande D., Durrant J.R., Shoaee S., Clarke T.M., Eng M.P., Huang C., Barlow S., Espíldora E., Delgado J.L., Campo B., Marder S.R., Heeney M., McCulloch I., Martín, Nazario, Vanderzande D., and Durrant J.R.

Published
2012

134. Local charge trapping in conjugated polymers resolved by scanning Kelvin probe microscopy

Author

Hallam, T., Lee, M., Zhao, N., Nandhakumar, I., Kemerink, M., Heeney, M., McCulloch, I., Sirringhaus, H., Hallam, T., Lee, M., Zhao, N., Nandhakumar, I., Kemerink, M., Heeney, M., McCulloch, I., and Sirringhaus, H.

Abstract

The microstructure of conjugated polymers is heterogeneous on the length scale of individual polymer chains, but little is known about how this affects their electronic properties. Here we use scanning Kelvin probe microscopy with resolution-enhancing carbon nanotube tips to study charge transport on a 100 nm scale in a chain-extended, semicrystalline conjugated polymer. We show that the disordered grain boundaries between crystalline domains constitute preferential charge trapping sites and lead to variations on a 100 nm scale of the carrier concentration under accumulation conditions.

Published
2009

135. High-performance organic integrated circuits based on solution processable polymer-small molecule blends

Author

Smith, J., Hamilton, R., Heeney, M., Leeuw, de, D.M., Cantatore, E., Anthony, J.E., McCulloch, I., Bradley, D.D.C., Athopoulos, T.D., Smith, J., Hamilton, R., Heeney, M., Leeuw, de, D.M., Cantatore, E., Anthony, J.E., McCulloch, I., Bradley, D.D.C., and Athopoulos, T.D.

Abstract

The prospect of realizing high-performance organic circuits via large-area fabrication is attractive for many applications of organic microelectronics. Here we report solution processed organic field-effect transistors and circuits based on polymer-small molecule blends comprising of polytriarylamine and 5,11-bis(triethylsilylethynyl) anthradithiophene. By optimizing blend composition and deposition conditions we are able to demonstrate short channel, bottom-gate, bottom-contact transistors with high mobility and excellent reproducibility. Using these transistors we have built unipolar voltage inverters and ring oscillators with a single stage delay of 712 ns. These are among the fastest organic circuits reported to date and could satisfy the performance requirements of low-end electronic applications.

Published
2008

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