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Author Magnus, W.; Brosens, F.
Title Occupation numbers in a quantum canonical ensemble : a projection operator approach Type A1 Journal article
Year (down) 2019 Publication Physica: A : theoretical and statistical physics Abbreviated Journal Physica A
Volume 518 Issue 518 Pages 253-264
Keywords A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Abstract Recently, we have used a projection operator to fix the number of particles in a second quantization approach in order to deal with the canonical ensemble. Having been applied earlier to handle various problems in nuclear physics that involve fixed particle numbers, the projector formalism was extended to grant access as well to quantum-statistical averages in condensed matter physics, such as particle densities and correlation functions. In this light, the occupation numbers of the subsequent single-particle energy eigenstates are key quantities to be examined. The goal of this paper is (1) to provide a sound extension of the projector formalism directly addressing the occupation numbers as well as the chemical potential, and (2) to demonstrate how the emerging problems related to numerical instability for fermions can be resolved to obtain the canonical statistical quantities for both fermions and bosons. (C) 2018 Elsevier B.V. All rights reserved.
Address
Corporate Author Thesis
Publisher Place of Publication Editor
Language Wos 000456359200021 Publication Date 2018-11-28
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0378-4371 ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 2.243 Times cited 1 Open Access
Notes ; ; Approved Most recent IF: 2.243
Call Number UA @ admin @ c:irua:157468 Serial 5223
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Author Magnus, W.; Lemmens, L.; Brosens, F.
Title Quantum canonical ensemble : a projection operator approach Type A1 Journal article
Year (down) 2017 Publication Physica: A : theoretical and statistical physics Abbreviated Journal Physica A
Volume 482 Issue Pages 1-13
Keywords A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Abstract Knowing the exact number of particles N, and taking this knowledge into account, the quantum canonical ensemble imposes a constraint on the occupation number operators. The constraint particularly hampers the systematic calculation of the partition function and any relevant thermodynamic expectation value for arbitrary but fixed N. On the other hand, fixing only the average number of particles, one may remove the above constraint and simply factorize the traces in Fock space into traces over single-particle states. As is well known, that would be the strategy of the grand-canonical ensemble which, however, comes with an additional Lagrange multiplier to impose the average number of particles. The appearance of this multiplier can be avoided by invoking a projection operator that enables a constraint-free computation of the partition function and its derived quantities in the canonical ensemble, at the price of an angular or contour integration. Introduced in the recent past to handle various issues related to particle-number projected statistics, the projection operator approach proves beneficial to a wide variety of problems in condensed matter physics for which the canonical ensemble offers a natural and appropriate environment. In this light, we present a systematic treatment of the canonical ensemble that embeds the projection operator into the formalism of second quantization while explicitly fixing N, the very number of particles rather than the average. Being applicable to both bosonic and fermionic systems in arbitrary dimensions, transparent integral representations are provided for the partition function Z(N) and the Helmholtz free energy F-N as well as for two- and four-point correlation functions. The chemical potential is not a Lagrange multiplier regulating the average particle number but can be extracted from FN+1 – F-N, as illustrated for a two-dimensional fermion gas. (C) 2017 Elsevier B.V. All rights reserved.
Address
Corporate Author Thesis
Publisher Place of Publication Amsterdam Editor
Language Wos 000405885500001 Publication Date 2017-04-20
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0378-4371 ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 2.243 Times cited 1 Open Access
Notes ; ; Approved Most recent IF: 2.243
Call Number UA @ lucian @ c:irua:145145 Serial 4722
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Author Sels, D.; Brosens, F.; Magnus, W.
Title Wigner distribution functions for complex dynamical systems : a path integral approach Type A1 Journal article
Year (down) 2013 Publication Physica: A : theoretical and statistical physics Abbreviated Journal Physica A
Volume 392 Issue 2 Pages 326-335
Keywords A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Abstract Starting from Feynmans Lagrangian description of quantum mechanics, we propose a method to construct explicitly the propagator for the Wigner distribution function of a single system. For general quadratic Lagrangians, only the classical phase space trajectory is found to contribute to the propagator. Inspired by Feynmans and Vernons influence functional theory we extend the method to calculate the propagator for the reduced Wigner function of a system of interest coupled to an external system. Explicit expressions are obtained when the external system consists of a set of independent harmonic oscillators. As an example we calculate the propagator for the reduced Wigner function associated with the CaldeiraLegett model.
Address
Corporate Author Thesis
Publisher Place of Publication Amsterdam Editor
Language Wos 000311135200004 Publication Date 2012-09-14
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0378-4371; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 2.243 Times cited 9 Open Access
Notes ; ; Approved Most recent IF: 2.243; 2013 IF: 1.722
Call Number UA @ lucian @ c:irua:101414 Serial 3921
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Author Sels, D.; Brosens, F.; Magnus, W.
Title On the path integral representation of the Wigner function and the BarkerMurray ansatz Type A1 Journal article
Year (down) 2012 Publication Physics letters : A Abbreviated Journal Phys Lett A
Volume 376 Issue 6/7 Pages 809-812
Keywords A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Abstract The propagator of the Wigner function is constructed from the WignerLiouville equation as a phase space path integral over a new effective Lagrangian. In contrast to a paper by Barker and Murray (1983) [1], we show that the path integral can in general not be written as a linear superposition of classical phase space trajectories over a family of non-local forces. Instead, we adopt a saddle point expansion to show that the semiclassical Wigner function is a linear superposition of classical solutions for a different set of non-local time dependent forces. As shown by a simple example the specific form of the path integral makes the formulation ideal for Monte Carlo simulation.
Address
Corporate Author Thesis
Publisher Place of Publication Amsterdam Editor
Language Wos 000301167300005 Publication Date 2012-01-17
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0375-9601; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 1.772 Times cited 7 Open Access
Notes ; ; Approved Most recent IF: 1.772; 2012 IF: 1.766
Call Number UA @ lucian @ c:irua:94006 Serial 2445
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Author Sels, D.; Brosens, F.; Magnus, W.
Title Classical trajectories : a powerful tool for solving tunneling problems Type A1 Journal article
Year (down) 2012 Publication Physica: A : theoretical and statistical physics Abbreviated Journal Physica A
Volume 391 Issue 1/2 Pages 78-81
Keywords A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Abstract In the realm of Ehrenfests theorem, classical trajectories obeying Newtons laws have been proven useful to construct explicit solutions to the time-dependent WignerLiouville equation. Whereas previous works have particularly focused on the initial distribution function as a vehicle found to carry the signatures of quantum statistics into the time-dependent solution, the present paper shows that the LagrangeCharpit method based on classical trajectories can be successfully invoked as well to tackle quantum mechanical features with no classical counterpart, such as tunneling.
Address
Corporate Author Thesis
Publisher Place of Publication Amsterdam Editor
Language Wos 000297230700010 Publication Date 2011-08-25
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0378-4371; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 2.243 Times cited 7 Open Access
Notes ; ; Approved Most recent IF: 2.243; 2012 IF: 1.676
Call Number UA @ lucian @ c:irua:92359 Serial 370
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Author Bertoni, G.; Verbeeck, J.; Brosens, F.
Title Fitting the momentum dependent loss function in EELS Type A1 Journal article
Year (down) 2011 Publication Microscopy research and technique Abbreviated Journal Microsc Res Techniq
Volume 74 Issue 3 Pages 212-218
Keywords A1 Journal article; Electron microscopy for materials research (EMAT); Theory of quantum systems and complex systems
Abstract Momentum dependent inelastic plasmon scattering can be measured by electron energy loss in a transmission electron microscope. From energy filtered diffraction, the characteristic angle of scattering and the cutoff angle are measured, using a thin film of aluminum as a model test. Rather than deconvolving the data (as done in previous works), a fitting technique is used to extract the loss function from angular resolved spectra, starting from a simple model simulation.
Address
Corporate Author Thesis
Publisher Place of Publication New York, N.Y. Editor
Language Wos 000288095200002 Publication Date 2010-07-06
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1059-910X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 1.147 Times cited 6 Open Access
Notes Fwo; Esteem; Iap; Goa Approved Most recent IF: 1.147; 2011 IF: 1.792
Call Number UA @ lucian @ c:irua:88782UA @ admin @ c:irua:88782 Serial 1222
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Author Brosens, F.; Magnus, W.
Title Newtonian trajectories : a powerful tool for solving quantum dynamics Type A1 Journal article
Year (down) 2010 Publication Solid state communications Abbreviated Journal Solid State Commun
Volume 150 Issue 43/44 Pages 2102-2105
Keywords A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Abstract Since Ehrenfests theorem, the role and importance of classical paths in quantum dynamics have been examined by several means. Along this line, we show that the classical equations of motion provide a solution to quantum dynamics, if appropriately incorporated into the Wigner distribution function, exactly reformulated in a type of Boltzmann equation. Also the quantum-mechanical features of the canonical ensemble can be studied in this framework of Newtonian dynamics, if the initial distribution function is appropriately constructed from the statistical operator.
Address
Corporate Author Thesis
Publisher Place of Publication New York, N.Y. Editor
Language Wos 000284251700006 Publication Date 2010-09-20
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0038-1098; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 1.554 Times cited 7 Open Access
Notes ; The authors thank J.T. Devreese and J. Tempere for interesting and helpful discussions, and, in particular, L.F. Lemmens for several valuable suggestions. One of the authors (F.B.) acknowledges the FWO projects G.0115.06 and G.0365.08 as well as the WOG project WO.033.09N, for financial support. ; Approved Most recent IF: 1.554; 2010 IF: 1.981
Call Number UA @ lucian @ c:irua:85795 Serial 2338
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Author Zhang, L.; Turner, S.; Brosens, F.; Verbeeck, J.
Title Model-based determination of dielectric function by STEM low-loss EELS Type A1 Journal article
Year (down) 2010 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B
Volume 81 Issue 3 Pages 035102
Keywords A1 Journal article; Electron microscopy for materials research (EMAT); Theory of quantum systems and complex systems
Abstract Dielectric properties of materials are crucial in describing the electromagnetic response of materials. As devices are becoming considerably smaller than the optical wavelength, the conventional measuring methods based on optical response are limited by their spatial resolution. Electron energy loss spectroscopy performed in a scanning transmission electron microscope is a good alternative to obtain the dielectric properties with excellent spatial resolution. Due to the overlap of diffraction discs in scanning transmission electron microscopy, it is difficult to apply conventional experimental settings to suppress retardation losses. In this contribution, a relativistic dielectric model for the loss function is presented which is used in a model based optimization scheme to estimate the complex dielectric function of a material. The method is applied to experiments on bulk diamond and SrTiO3 and shows a good agreement with optical reference data when retardation effects are included. Application of this technique to nanoparticles is possible but several theoretical assumptions made in the model of the loss function are violated and interpretation becomes problematic.
Address
Corporate Author Thesis
Publisher Place of Publication Lancaster, Pa Editor
Language Wos 000274002300027 Publication Date 2010-01-08
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1098-0121;1550-235X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 3.836 Times cited 9 Open Access
Notes Esteem – 026019; Fwo Approved Most recent IF: 3.836; 2010 IF: 3.774
Call Number UA @ lucian @ c:irua:81258UA @ admin @ c:irua:81258 Serial 2098
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Author Magnus, W.; Brosens, F.; Sorée, B.
Title Time dependent transport in 1D micro- and nanostructures: solving the Boltzmann and Wigner-Boltzmann equations Type A1 Journal article
Year (down) 2009 Publication Journal of physics : conference series Abbreviated Journal
Volume 193 Issue 1 Pages 012004,1-012004,4
Keywords A1 Journal article; Condensed Matter Theory (CMT); Theory of quantum systems and complex systems
Abstract For many decades the Boltzmann distribution function has been used to calculate the non-equilibrium properties of mobile particles undergoing the combined action of various scattering mechanisms and externally applied force fields. When the latter give rise to the occurrence of inhomogeneous potential profiles across the region through which the particles are moving, the numerical solution of the Boltzmann equation becomes a highly complicated task. In this work we highlight a particular algorithm that can be used to solve the time dependent Boltzmann equation as well as its quantum mechanical extension, the WignerBoltzmann equation. As an illustration, we show the calculated distribution function describing electrons propagating under the action of both a uniform and a pronouncedly non-uniform electric field.
Address
Corporate Author Thesis
Publisher Place of Publication Bristol Editor
Language Wos 000277100400004 Publication Date 2009-11-17
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1742-6596; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor Times cited 2 Open Access
Notes Approved Most recent IF: NA
Call Number UA @ lucian @ c:irua:82861 Serial 3667
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Author Magnus, W.; Brosens, F.; Sorée, B.
Title Modeling drive currents and leakage currents : a dynamic approach Type A1 Journal article
Year (down) 2009 Publication Journal of computational electronics Abbreviated Journal J Comput Electron
Volume 8 Issue 3/4 Pages 307-323
Keywords A1 Journal article; Condensed Matter Theory (CMT); Theory of quantum systems and complex systems
Abstract The dynamics of electrons and holes propagating through the nano-scaled channels of modern semiconductor devices can be seen as a widespread manifestation of non-equilibrium statistical physics and its ruling principles. In this respect both the devices that are pushing conventional CMOS technology towards the final frontiers of Moores law and the upcoming set of alternative, novel nanostructures grounded on entirely new concepts and working principles, provide an almost unlimited playground for assessing physical models and numerical techniques emerging from classical and quantum mechanical non-equilibrium theory. In this paper we revisit the Boltzmann as well as the WignerBoltzmann equation which offers a valuable platform to study transport of charge carriers taking part in drive currents. We focus on a numerical procedure that regained attention recently as an alternative tool to solve the time-dependent Boltzmann equation for inhomogeneous systems, such as the channel regions of field-effect transistors, and we discuss its extension to the WignerBoltzmann equation. Furthermore, we pay attention to the calculation of tunneling leakage currents. The latter typically occurs in nano-scaled transistors when part of the carrier distribution sustaining the drive current is found to tunnel into the gate due the presence of an ultra-thin insulating barrier separating the gate from the channel region. In particular, we discuss the paradox related to the very existence of leakage currents established by electrons occupying quasi-bound states, while the (real) wave functions of the latter cannot carry net currents. Finally, we describe a simple model to resolve the paradox as well as to estimate gate currents provided the local carrier generation rates largely exceed the tunneling rates.
Address
Corporate Author Thesis
Publisher Place of Publication S.l. Editor
Language Wos 000208236100009 Publication Date 2009-09-28
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1569-8025;1572-8137; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 1.526 Times cited 4 Open Access
Notes Approved Most recent IF: 1.526; 2009 IF: NA
Call Number UA @ lucian @ c:irua:89503 Serial 2110
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Author Brosens, F.; Magnus, W.
Title Carrier transport in nanodevices: revisiting the Boltzmann and Wigner distribution functions Type A1 Journal article
Year (down) 2009 Publication Physica status solidi: B: basic research Abbreviated Journal Phys Status Solidi B
Volume 246 Issue 7 Pages 1656-1661
Keywords A1 Journal article; Condensed Matter Theory (CMT); Theory of quantum systems and complex systems
Abstract In principle, transport of charged carriers in nanometer sized solid-state devices can be fully characterized once the non-equilibrium distribution function describing the carrier ensemble is known. In this light, we have revisited the Boltzmann and the Wigner distribution functions and the framework in which they emerge from the classical respectively quantum mechanical Liouville equation. We have assessed the method of the characteristic curves as a potential workhorse to solve the time dependent Boltzmann equation for carriers propagating through spatially non-uniform systems, such as nanodevices. In order to validate the proposed solution strategy, we numerically solve the Boltzmann equation for a one-dimensional conductor mimicking the basic features of a biased low-dimensional transistor operating in the on-state. Finally, we propose a computational scheme capable of extending the benefits of the above mentioned solution strategy when it comes to solve the Wigner-Liouville equation.
Address
Corporate Author Thesis
Publisher Place of Publication Berlin Editor
Language Wos 000268659100033 Publication Date 2009-04-22
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0370-1972;1521-3951; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 1.674 Times cited 8 Open Access
Notes Approved Most recent IF: 1.674; 2009 IF: 1.150
Call Number UA @ lucian @ c:irua:77953 Serial 284
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Author Shanenko, A.A.; Tempère, J.; Brosens, F.; Devreese, J.T.
Title Mesoscopic samples: the superconducting condensate via the Gross.Pitaevskii scenario Type A1 Journal article
Year (down) 2004 Publication Solid state communications Abbreviated Journal Solid State Commun
Volume 131 Issue Pages 409-414
Keywords A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Abstract
Address
Corporate Author Thesis
Publisher Place of Publication New York, N.Y. Editor
Language Wos 000223011700012 Publication Date 2004-03-20
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0038-1098; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 1.554 Times cited 1 Open Access
Notes Approved Most recent IF: 1.554; 2004 IF: 1.523
Call Number UA @ lucian @ c:irua:48282 Serial 2000
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Author Brosens, F.; Fomin, V.M.; Lemmens, L.; Peeters, F.M.
Title Liber amicorum in honour of Jozef T. Devreese Type ME3 Book as editor
Year (down) 2003 Publication Abbreviated Journal
Volume Issue Pages
Keywords ME3 Book as editor; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Abstract
Address
Corporate Author Thesis
Publisher Wiley Place of Publication Weinheim Editor
Language Wos Publication Date 0000-00-00
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN ISBN Additional Links UA library record; WoS full record;
Impact Factor Times cited Open Access
Notes Approved Most recent IF: NA
Call Number UA @ lucian @ c:irua:43416 Serial 1817
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Author Backes, W.H.; Peeters, F.M.; Brosens, F.; Devreese, J.T.
Title Dispersion of longitudinal plasmons for a quasi-two-dimensional electron gas Type A1 Journal article
Year (down) 1992 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B
Volume 45 Issue 15 Pages 8437-8442
Keywords A1 Journal article; Condensed Matter Theory (CMT); Theory of quantum systems and complex systems
Abstract Confinement of electrons in ultrathin metallic films leads to subbands. By increasing the thickness of the electron layer, the subbands will dissolve into a quasicontinuum, with the number of electrons per unit volume kept constant. Within the random-phase approximation, the two-dimensional plasmon, which originally follows Stern's dispersion relation, becomes a longitudinal surface plasmon. The plasmon excitations of a model metallic film are investigated by including all subbands. Single-particle excitations, which exhibit the depolarization shift, converge into the plasma excitation spectrum. With further increases in the film thickness, the bulk plasmon arises and the surface plasmon remains. Our analysis shows how quantum size effects evolve into hydrodynamical classical size effects with increasing thickness of the film.
Address
Corporate Author Thesis
Publisher Place of Publication Lancaster, Pa Editor
Language Wos A1992HR33600028 Publication Date 2002-07-27
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0163-1829;1095-3795; ISBN Additional Links UA library record; WoS full record; WoS citing articles
Impact Factor 3.736 Times cited 37 Open Access
Notes Approved no
Call Number UA @ lucian @ c:irua:2738 Serial 737
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