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“Tunable exciton Aharonov-Bohm effect in a quantum ring”. Li B, Magnus W, Peeters FM, Journal of physics : conference series
T2 –, Proceedings of the 11th International Conference on Optics of Excitons in Confined Systems, September 7-11, 2009, Spain / Vina, L. [edit.], et al. [edit.] 210, 012030 (2010). http://doi.org/10.1088/1742-6596/210/1/012030
Abstract: We studied the optical Aharonov-Bohm effect for an exciton in a semiconductor quantum ring. A perpendicular electric field applied to a quantum ring with large height, is able to tune the exciton ground state energy such that it exhibits a weak observable Aharonov-Bohm oscillations. This Aharonov-Bohm effect is tunable in strength and period.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 3
DOI: 10.1088/1742-6596/210/1/012030
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“The breakdown of Kohn's theorem in few-electron parabolic quantum dots doped with a single magnetic impurity Mn2+”. Nguyen NTT, Peeters FM, Journal of physics : conference series
T2 –, Conference on Quantum Dots 2010 (QD2010), APR 26-30, 2010, Nottingham, ENGLAND , 012031 (2010). http://doi.org/10.1088/1742-6596/245/1/012031
Abstract: The cyclotron resonance (CR) absorption spectrum is calculated for a II-VI parabolic quantum dot (QD) containing few electrons and a single magnetic dopant (Mn(2+)). We find that Kohn's theorem no longer holds for this system and that the CR spectrum depends on the number of electrons inside the QD. The electron-Mn-ion interaction strength can be tuned for example by the magnetic field and by moving the Mn-ion to different positions inside the QD. We demonstrate that due to the presence of the Mn-ion the relative motion of the electrons couple with their center-of-mass motion through the electron-Mn-ion spin-spin exchange term resulting in an electron-electron interaction dependence of the magneto-optical absorption spectrum. At the ferromagnetic-antiferromagnetic transition we observe significant discontinuities in the CR lines.
Keywords: P1 Proceeding; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Times cited: 1
DOI: 10.1088/1742-6596/245/1/012031
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“Phase-diagram for the magnetic states of the Mn-ion subsystem in a magnetic quantum dot”. Nguyen NTT, Peeters FM, Journal of physics : conference series
T2 –, Conference on Quantum Dots 2010 (QD2010), APR 26-30, 2010, Nottingham, ENGLAND , 012032 (2010). http://doi.org/10.1088/1742-6596/245/1/012032
Abstract: The interplay between two types of spin-spin exchange interaction (namely of the electron with the Mn-ions and the Mn-ions with each other) that are governed by the positions of the Mn-ions and the magnetic field is studied in the case of a Mn-ion doped CdTe quantum dot. We investigate the formation of different magnetic phases and the existence of frustrated magnetic states due to the dominant contribution of the Mn-Mn energy.
Keywords: P1 Proceeding; Engineering sciences. Technology; Condensed Matter Theory (CMT)
DOI: 10.1088/1742-6596/245/1/012032
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“Plasma chemistry modeling for an inductively coupled plasma used for the growth of carbon nanotubes”. Mao M, Bogaerts A, Journal of physics : conference series 275, 012021 (2011). http://doi.org/10.1088/1742-6596/275/1/012021
Abstract: A hybrid model, called the hybrid plasma equipment model (HPEM), is used to describe the plasma chemistry in an inductively coupled plasma, operating in a gas mixture of C2H2 with either H2 or NH3, as typically used for carbon nanotube (CNT) growth. Two-dimensional profiles of power density, electron temperature and density, gas temperature, and densities of some plasma species are plotted and analyzed. Besides, the fluxes of the various plasma species towards the substrate (where the CNTs can be grown), as well as the decomposition rates of the feedstock gases (C2H2, NH3 and H2), are calculated as a function of the C2H2 fraction in both gas mixtures.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
DOI: 10.1088/1742-6596/275/1/012021
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“Terahertz radiation from crystals of nanomagnets”. Benedict MG, Földi P, Peeters FM, Journal of physics : conference series 36, 12 (2006). http://doi.org/10.1088/1742-6596/36/1/003
Abstract: Certain crystals, consisting of molecules with unusually large spin, exhibit macroscopically observable signatures of quantum tunneling, when a slowly varying external magnetic field is applied parallel to the easy axis of the crystal. Recently it has been observed that jumps in the magnetization are sometimes accompanied by the emission of infrared radiation. We discuss the connection of the tunneling with the electromagnetic transition, and we address the questions: to what extent can the radiation be considered as a collective, superradiant emission, and what is the role played by the cavity in the experiments? Our conclusion is that among the reported experimental coditions the radiation is not superradidance, but rather a maserlike effect.
Keywords: P1 Proceeding; Condensed Matter Theory (CMT)
Times cited: 1
DOI: 10.1088/1742-6596/36/1/003
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“Modeling of plasma and plasma-surface interactions for medical, environmental and nano applications”. Bogaerts A, Aerts R, Snoeckx R, Somers W, Van Gaens W, Yusupov M, Neyts E, Journal of physics : conference series 399, 012011 (2012). http://doi.org/10.1088/1742-6596/399/1/012011
Abstract: In this paper, an overview is given of modeling investigations carried out in our research group for a better understanding of plasmas used for medical, environmental and nano applications. The focus is both on modeling the plasma chemistry and the plasma-surface interactions. The plasma chemistry provides the densities and fluxes of the important plasma species. This information can be used as input when modeling the plasma-surface interactions. The combination of plasma simulations and plasma – surface interaction simulations provides a more comprehensive understanding of the underlying processes for these applications.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Times cited: 7
DOI: 10.1088/1742-6596/399/1/012011
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“Two kinds of vortex states in thin mesoscopic superconductors”. Baelus BJ, Kanda A, Peeters FM, Ootuka Y, Kadowaki K, Journal of physics : conference series
T2 –, Journal of physics: conference series 43, 647 (2006). http://doi.org/10.1088/1742-6596/43/1/158
Abstract: Experimentally, multivortex states and giant vortex states in mesoscopic superconductors can be distinguished directly by using the multiple-small-tunnel-junctions, and indirectly by studying the temperature dependence of the expulsion fields. These experimental results are compared with the theoretical prediction from the nonlinear Ginzburg- Landau theory.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
DOI: 10.1088/1742-6596/43/1/158
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“The effect of Y2O3 and YFeO3 additions on the critical current density of YBCO coated conductors”. Lao M, Eisterer M, Stadel O, Meledin A, Van Tendeloo G, 1-4 (2014). http://doi.org/10.1088/1742-6596/507/2/022012
Abstract: The pinning mechanism of MOCVD-grown YBCO coated conductors with Y2O3 precipitates was investigated by angle-resolved transport measurement of Je in a wide range of temperature and magnetic fields. Aside from the Y2O3 nanoprecipitates, a-axis grains and threading dislocation along the c-axis were found in the YBCO layer. The Y2O3 precipitates are less effective pinning centers at lower temperature. The tapes with precipitates show a higher anisotropy with larger J(c) at H parallel to ab than H parallel to c. This behavior was attributed to the preferred alignment of the nanoprecipitates along the ab-plane.
Keywords: P1 Proceeding; Electron microscopy for materials research (EMAT)
Times cited: 1
DOI: 10.1088/1742-6596/507/2/022012
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“Quantitative annular dark field scanning transmission electron microscopy for nanoparticle atom-counting : what are the limits?”.de Backer A, De wael A, Gonnissen J, Martinez GT, Béché, A, MacArthur KE, Jones L, Nellist PD, Van Aert S, Journal of physics : conference series 644, 012034 (2015). http://doi.org/10.1088/1742-6596/644/012034
Abstract: Quantitative atomic resolution annular dark field scanning transmission electron microscopy (ADF STEM) has become a powerful technique for nanoparticle atom-counting. However, a lot of nanoparticles provide a severe characterisation challenge because of their limited size and beam sensitivity. Therefore, quantitative ADF STEM may greatly benefit from statistical detection theory in order to optimise the instrumental microscope settings such that the incoming electron dose can be kept as low as possible whilst still retaining single-atom precision. The principles of detection theory are used to quantify the probability of error for atom-counting. This enables us to decide between different image performance measures and to optimise the experimental detector settings for atom-counting in ADF STEM in an objective manner. To demonstrate this, ADF STEM imaging of an industrial catalyst has been conducted using the near-optimal detector settings. For this experiment, we discussed the limits for atomcounting diagnosed by combining a thorough statistical method and detailed image simulations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
DOI: 10.1088/1742-6596/644/012034
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“Quantitative annular dark field scanning transmission electron microscopy for nanoparticle atom-counting: What are the limits?”.De Backer A, De Wael A, Gonnissen J, Martinez GT, Béché, A, MacArthur KE, Jones L, Nellist PD, Van Aert S, Journal of physics : conference series 644Electron Microscopy and Analysis Group Conference (EMAG), JUN 02-JUL 02, 2015, Manchester, ENGLAND, 012034 (2015). http://doi.org/10.1088/1742-6596/644/1/012034
Abstract: Quantitative atomic resolution annular dark field scanning transmission electron microscopy (ADF STEM) has become a powerful technique for nanoparticle atom-counting. However, a lot of nanoparticles provide a severe characterisation challenge because of their limited size and beam sensitivity. Therefore, quantitative ADF STEM may greatly benefit from statistical detection theory in order to optimise the instrumental microscope settings such that the incoming electron dose can be kept as low as possible whilst still retaining single-atom precision. The principles of detection theory are used to quantify the probability of error for atom-counting. This enables us to decide between different image performance measures and to optimise the experimental detector settings for atom-counting in ADF STEM in an objective manner. To demonstrate this, ADF STEM imaging of an industrial catalyst has been conducted using the near-optimal detector settings. For this experiment, we discussed the limits for atom-counting diagnosed by combining a thorough statistical method and detailed image simulations.
Keywords: P1 Proceeding; Electron microscopy for materials research (EMAT)
DOI: 10.1088/1742-6596/644/1/012034
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“Many-body electron correlations in graphene”. Neilson D, Perali A, Zarenia M, (mbt18) 702, 012008 (2016). http://doi.org/10.1088/1742-6596/702/1/012008
Abstract: The conduction electrons in graphene promise new opportunities to access the region of strong many-body electron-electron correlations. Extremely high quality, atomically flat two-dimensional electron sheets and quasi-one-dimensional electron nanoribbons with tuneable band gaps that can be switched on by gates, should exhibit new many-body phenomena that have long been predicted for the regions of phase space where the average Coulomb repulsions between electrons dominate over their Fermi energies. In electron nanoribbons a few nanometres wide etched in monolayers of graphene, the quantum size effects and the van Hove singularities in their density of states further act to enhance electron correlations. For graphene multilayers or nanoribbons in a double unit electron-hole geometry, it is possible for the many-body electron-hole correlations to be made strong enough to stabilise high-temperature electron- hole superfluidity.
Keywords: P1 Proceeding; Condensed Matter Theory (CMT)
Times cited: 3
DOI: 10.1088/1742-6596/702/1/012008
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“New insights into the nanostructure of innovative thin film solar cells gained by positron annihilation spectroscopy”. Eijt SWH, Shi W, Mannheim A, Butterling M, Schut H, Egger W, Dickmann M, Hugenschmidt C, Shakeri B, Meulenberg RW, Callewaert V, Saniz R, Partoens B, Barbiellini B, Bansil A, Melskens J, Zeman M, Smets AHM, Kulbak M, Hodes G, Cahen D, Brück E, Journal of physics : conference series 791, 012021 (2017). http://doi.org/10.1088/1742-6596/791/1/012021
Abstract: Recent studies showed that positron annihilation methods can provide key insights into the nanostructure and electronic structure of thin film solar cells. In this study, positron annihilation lifetime spectroscopy (PALS) is applied to investigate CdSe quantum dot (QD) light absorbing layers, providing evidence of positron trapping at the surfaces of the QDs. This enables one to monitor their surface composition and electronic structure. Further, 2D-Angular Correlation of Annihilation Radiation (2D-ACAR) is used to investigate the nanostructure of divacancies in photovoltaic-high-quality a-Si:H films. The collected momentum distributions were converted by Fourier transformation to the direct space representation of the electron-positron autocorrelation function. The evolution of the size of the divacancies as a function of hydrogen dilution during deposition of a-Si:H thin films was examined. Finally, we present a first positron Doppler Broadening of Annihilation Radiation (DBAR) study of the emerging class of highly efficient thin film solar cells based on perovskites.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 1
DOI: 10.1088/1742-6596/791/1/012021
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“Surface states and positron annihilation spectroscopy: results and prospects from a first-principles approach”. Callewaert V, Saniz R, Barbiellini B, Partoens B, Journal of physics : conference series 791, 012036 (2017). http://doi.org/10.1088/1742-6596/791/1/012036
Abstract: The trapping of positrons at the surface of a material can be exploited to study quite selectively the surface properties of the latter by means of positron annihilation spectroscopy techniques. To support these, it is desirable to be able to theoretically predict the existence of such positronic surface states and to describe their annihilation characteristics with core or valence surface electrons in a reliable way. Here, we build on the well-developed first-principles techniques for the study of positrons in bulk solids as well as on previous models for surfaces, and investigate two schemes that can improve the theoretical description of the interaction of positrons with surfaces. One is based on supplementing the local-density correlation potential with the corrugated image potential at the surface, and the other is based on the weighted-density approximation to correlation. We discuss our results for topological insulators, graphene layers, and quantum dots, with emphasis on the information that can be directly related to experiment. We also discuss some open theoretical problems that should be addressed by future research.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 1
DOI: 10.1088/1742-6596/791/1/012036
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“Reaction mechanisms and thin a-C:H film growth from low energy hydrocarbon radicals”. Neyts E, Bogaerts A, van de Sanden MCM, Journal of physics : conference series 86, 12020 (2007). http://doi.org/10.1088/1742-6596/86/1/012020
Abstract: Molecular dynamics simulations using the Brenner potential have been performed to investigate reaction mechanisms of various hydrocarbon radicals with low kinetic energies on amorphous hydrogenated carbon (a-C:H) surfaces and to simulate thin a-C:H film growth. Experimental data from an expanding thermal plasma setup were used as input for the simulations. The hydrocarbon reaction mechanisms were studied both during growth of the films and on a set of surface sites specific for a-C:H surfaces. Thin film growth was studied using experimentally detected growth species. It is found that the reaction mechanisms and sticking coefficients are dependent on the specific surface sites, and the structural properties of the growth radicals. Furthermore, it is found that thin a-C:H films can be densified using an additional H-flux towards the substrate.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Times cited: 22
DOI: 10.1088/1742-6596/86/1/012020
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“StatSTEM: An efficient program for accurate and precise model-based quantification of atomic resolution electron microscopy images”. De Backer A, van den Bos KHW, Van den Broek W, Sijbers J, Van Aert S, Journal of physics : conference series
T2 –, Electron Microscopy and Analysis Group Conference 2017 (EMAG2017), 3-6 July 2017, Manchester, UK 902, 012013 (2017). http://doi.org/10.1088/1742-6596/902/1/012013
Abstract: An efficient model-based estimation algorithm is introduced in order to quantify the atomic column positions and intensities from atomic resolution (scanning) transmission electron microscopy ((S)TEM) images. This algorithm uses the least squares estimator on image segments containing individual columns fully accounting for the overlap between neighbouring columns, enabling the analysis of a large field of view. For this algorithm, the accuracy and precision with which measurements for the atomic column positions and scattering cross-sections from annular dark field (ADF) STEM images can be estimated, is investigated. The highest attainable precision is reached even for low dose images. Furthermore, advantages of the model- based approach taking into account overlap between neighbouring columns are highlighted. To provide end-users this well-established quantification method, a user friendly program, StatSTEM, is developed which is freely available under a GNU public license.
Keywords: P1 Proceeding; Electron microscopy for materials research (EMAT); Vision lab
Times cited: 1
DOI: 10.1088/1742-6596/902/1/012013
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“Application of Gielis transformation to the design of metamaterial structures”. de Jong van Coevorden CM, Gielis J, Caratelli D, Journal of physics : conference series 963, Unsp 012008 (2018). http://doi.org/10.1088/1742-6596/963/1/012008
Abstract: In this communication, the use of Gielis transformation to design more compact metamaterial unit cells is explored. For this purpose, transformed complementary split ring resonators and spiral resonators are coupled to micro-strip lines and theirbehaviour is investigated. The obtained results confirm that the useof the considered class of supershaped geometries enables the synthesis of very compact scalable microwave components.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1088/1742-6596/963/1/012008
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“Domain coexistence of magnetism and superconductivity : appearance of confined vortex loops”. Doria MM, de Romaguera ARC, Milošević, MV, Peeters FM, Journal of physics : conference series 97, 012070 (2008). http://doi.org/10.1088/1742-6596/97/1/012070
Abstract: A magnetic moment inside an extreme type II superconductor can have three, but not one or two, confined vortex loops near to the core. For a sub-micron superconducting particle the confined vortex loops eventually break up and reach the surface turning into external vortex pairs.
Keywords: P1 Proceeding; Condensed Matter Theory (CMT)
DOI: 10.1088/1742-6596/97/1/012070
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“Formation of vortex clusters and giant vortices in mesoscopic superconducting disks with strong disorder”. Escoffier W, Grigorieva IV, Misko VR, Baelus BJ, Peeters FM, Vinnikov LY, Dubnos S, Journal of physics : conference series 97, 012172 (2008). http://doi.org/10.1088/1742-6596/97/1/012172
Abstract: Merged, or giant, multi-quanta vortices (GVs) appear in very small superconductors near the superconducting transition due to strong confinement of magnetic flux. Here we present evidence for a new, pinning-related, mechanism for vortex merger. Using Bitter decoration to visualise vortices in small Nb disks, we show that confinement in combination with strong disorder causes individual vortices to merge into clusters/GVs well below Tc and Hc2, in contrast to well-defined shells of individual vortices found in the absence of pinning.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
DOI: 10.1088/1742-6596/97/1/012172
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“New generation monitoring devices for heritage guardians to detect multiple events and hazards”. Schalm O, Anaf W, Callier J, Leyva Pernia D, IOP conference series : materials science and engineering 364, Unsp 012056 (2018). http://doi.org/10.1088/1757-899X/364/1/012056
Abstract: Environmental parameters such as temperature, relative humidity, visible light, UV radiation and pollution influence the deterioration rate of heritage items. To judge on the environmental appropriateness for heritage conservation, it is therefore important to monitor the environment. Often, an incomplete set of environmental parameters is measured, or sporadic or time-averaged measurements are performed. As a result, a wide range of undesirable situations and hazards remain unnoticed. This might lead to an underestimation of environmental dangers (i.e., inaccurate judgement) or to inappropriate mitigation measures (i.e., inaccurate decision making). We present an innovative and user-friendly monitoring device that simultaneously and continuously measures (1) environmental parameters and (2) material behavior. An extended combination of off-the-shelf sensors for temperature, relative humidity, air speed, CO2, NO2, O-3 and particulate matter are connected to a multipurpose datalogger. In-house developed sensors for the shrinkage and expansion behavior of wood, as well as sensors for metal corrosion rates are connected to the same datalogger. Such extended monitoring shows the identification of a wider range of undesirable situations, and it facilitates the search for correlations between such situations and the sources that cause them, i.e., the hazards.
Keywords: P1 Proceeding; Engineering sciences. Technology; Art; History; Antwerp Systems and software Modelling (AnSyMo); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Antwerp Cultural Heritage Sciences (ARCHES)
DOI: 10.1088/1757-899X/364/1/012056
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“Atmospheric composition and micro-climate in the Alhambra monument, Granada (Spain), in the context of preventive conservation”. Horemans B, Schalm O, De Wael K, Cardell C, Van Grieken R, IOP conference series : materials science and engineering 37, 012002 (2012). http://doi.org/10.1088/1757-899X/37/1/012002
Abstract: The world famous Alhambra monument in Granada, Southern Spain, listed as UNESCO world cultural heritage since 1984, represents probably the most beautiful example of Islamic art and architecture from the Middle Ages in Europe. It is visited by ca. 2 million people annually. Granada is situated in a natural basin, surrounded by mountains with altitudes up to 3500 m. Due to this topography and the prevailing low wind speeds, pollution-derived and especially traffic-derived particulate matter often accumulates in the urban air. In order to evaluate the potential conservation risks from the surrounding air, the atmospheric composition in the Alhambra monument was evaluated. Indoor temperature and relative humidity fluctuations were evaluated for their potential degenerative effects. Furthermore, the atmospheric composition in the Alhambra was analyzed in terms of inorganic gases (NO2, SO2, O3, and NH3) and black carbon. It was found that the open architecture protected the indoor environments from developing a potentially harmful microclimate, such as the build-up of humidity resulting from the huge number of daily tourists. On the downside, the strong ventilation made the indoor air hardly different from outdoor air, as characterized by strong diurnal temperature and relative humidity gradients and high traffic-derived pollutant levels.
Keywords: P1 Proceeding; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Times cited: 1
DOI: 10.1088/1757-899X/37/1/012002
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“Prospects for out-of-plane magnetic field measurements through interference of electron vortex modes in the TEM”. Guzzinati G, Béché, A, McGrouther D, Verbeeck J, Journal of optics 21, 124002 (2019). http://doi.org/10.1088/2040-8986/AB51FC
Abstract: Magnetic field mapping in transmission electron microscopy is commonplace, but all conventional methods provide only a projection of the components of the magnetic induction perpendicular to the electron trajectory. Recent experimental advances with electron vortices have shown that it is possible to map the out of plane magnetic induction in a TEM setup via interferometry with a specifically prepared electron vortex state carrying high orbital angular momentum (OAM). The method relies on the Aharonov?Bohm phase shift that the electron undergoes when going through a longitudinal field. Here we show how the same effect naturally occurs for any electron wave function, which can always be described as a superposition of OAM modes. This leads to a clear connection between the occurrence of high-OAM partial waves and the amount of azimuthal rotation in the far field angular distribution of the beam. We show that out of plane magnetic field measurement can thus be obtained with a much simpler setup consisting of a ring-like aperture with azimuthal spokes. We demonstrate the experimental setup and explore the achievable sensitivity of the magnetic field measurement.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.741
Times cited: 3
DOI: 10.1088/2040-8986/AB51FC
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“Current-induced birefringent absorption and non-reciprocal plasmons in graphene”. Van Duppen B, Tomadin A, Grigorenko AN, Polini M, 2D materials 3, 015011 (2016). http://doi.org/10.1088/2053-1583/3/1/015011
Abstract: We present extensive calculations of the optical and plasmonic properties of a graphene sheet carrying a dc current. By calculating analytically the density-density response function of current-carrying states at finite temperature, we demonstrate that an applied dc current modifies the Pauli blocking mechanism and that absorption acquires a birefringent character with respect to the angle between the in-plane light polarization and current flow. Employing the random phase approximation at finite temperature, we show that graphene plasmons display a degree of non-reciprocity and collimation that can be tuned with the applied current. We discuss the possibility to measure these effects.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 5
DOI: 10.1088/2053-1583/3/1/015011
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“Magnetic field dependence of the atomic collapse state in graphene”. Moldovan D, Masir MR, Peeters FM, 2D materials 5, 015017 (2018). http://doi.org/10.1088/2053-1583/AA9647
Abstract: <script type='text/javascript'>document.write(unpmarked('Quantum electrodynamics predicts that heavy atoms (Z \u003E Z(c) approximate to 170) will undergo the process of atomic collapse where electrons sink into the positron continuum and a new family of so-called collapsing states emerges. The relativistic electrons in graphene exhibit the same physics but at a much lower critical charge (Z(c) approximate to 1) which has made it possible to confirm this phenomenon experimentally. However, there exist conflicting predictions on the effect of a magnetic field on atomic collapse. These theoretical predictions are based on the continuum Dirac-Weyl equation, which does not have an exact analytical solution for the interplay of a supercritical Coulomb potential and the magnetic field. Approximative solutions have been proposed, but because the two effects compete on similar energy scales, the theoretical treatment varies depending on the regime which is being considered. These limitations are overcome here by starting from a tight-binding approach and computing exact numerical results. By avoiding special limit cases, we found a smooth evolution between the different regimes. We predict that the atomic collapse effect persists even after the magnetic field is activated and that the critical charge remains unchanged. We show that the atomic collapse regime is characterized: (1) by a series of Landau level anticrossings and (2) by the absence of root B scaling of the Landau levels with regard to magnetic field strength.'));
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 13
DOI: 10.1088/2053-1583/AA9647
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“Electric-field modulation of linear dichroism and Faraday rotation in few-layer phosphorene”. Li LL, Partoens B, Xu W, Peeters FM, 2D materials 6, 015032 (2019). http://doi.org/10.1088/2053-1583/AAF47F
Abstract: Electro-optical modulators, which use an electric voltage (or an electric field) to modulate a beam of light, are essential elements in present-day telecommunication devices. Using a self-consistent tight-binding approach combined with the standard Kubo formula, we show that the optical conductivity and the linear dichroism of few-layer phosphorene can be modulated by a perpendicular electric field. We find that the field-induced charge screening plays a significant role in modulating the optical conductivity and the linear dichroism. Distinct absorption peaks are induced in the conductivity spectrum due to the strong quantum confinement along the out-of-plane direction and to the field-induced forbidden-to-allowed transitions. The field modulation of the linear dichroism becomes more pronounced with increasing number of phosphorene layers. We also show that the Faraday rotation is present in few-layer phosphorene even in the absence of an external magnetic field. This optical Hall effect is induced by the reduced lattice symmetry of few-layer phosphorene. The Faraday rotation is greatly influenced by the field-induced charge screening and is strongly dependent on the strength of perpendicular electric field and on the number of phosphorene layers.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 23
DOI: 10.1088/2053-1583/AAF47F
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“Carrier transport in two-dimensional topological insulator nanoribbons in the presence of vacancy defects”. Tiwari S, Van de Put ML, Sorée B, Vandenberghe WG, 2D materials 6, 025011 (2019). http://doi.org/10.1088/2053-1583/AB0058
Abstract: Using the non-equilibrium Green's function formalism, we study carrier transport through imperfect two-dimensional (2D) topological insulator (TI) ribbons. In particular, we investigate the effect of vacancy defects on the carrier transport in 2D TI ribbons with hexagonal lattice structure. To account for the random distribution of the vacancy defects, we present a statistical study of varying defect densities by stochastically sampling different defect configurations. We demonstrate that the topological edge states of TI ribbons are fairly robust against a high concentration (up to 2%) of defects. At very high defect densities, we observe an increased inter-edge interaction, mediated by the localisation of the edge states within the bulk region. This effect causes significant back-scattering of the, otherwise protected, edge-states at very high defect concentrations (>2%), resulting in a loss of conduction through the TI ribbon. We discuss how this coherent vacancy scattering can be used to our advantage for the development of TI-based transistors. We find that there is an optimal concentration of vacancies yielding an ON-OFF current ratio of up to two orders of magnitude. Finally, we investigate the importance of spin-orbit coupling on the robustness of the edge states in the TI ribbon and show that increased spin-orbit coupling could further increase the ON-OFF ratio.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 3
DOI: 10.1088/2053-1583/AB0058
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“Probing the structure and composition of van der Waals heterostructures using the nonlocality of Dirac plasmons in the terahertz regime”. Lavor IR, Cavalcante LSR, Chaves A, Peeters FM, Van Duppen B, 2d Materials 8, 015014 (2021). http://doi.org/10.1088/2053-1583/ABBECC
Abstract: Dirac plasmons in graphene are very sensitive to the dielectric properties of the environment. We show that this can be used to probe the structure and composition of van der Waals heterostructures (vdWh) put underneath a single graphene layer. In order to do so, we assess vdWh composed of hexagonal boron nitride and different types of transition metal dichalcogenides (TMDs). By performing realistic simulations that account for the contribution of each layer of the vdWh separately and including the importance of the substrate phonons, we show that one can achieve single-layer resolution by investigating the nonlocal nature of the Dirac plasmon-polaritons. The composition of the vdWh stack can be inferred from the plasmon-phonon coupling once it is composed by more than two TMD layers. Furthermore, we show that the bulk character of TMD stacks for plasmonic screening properties in the terahertz regime is reached only beyond 100 layers.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 4
DOI: 10.1088/2053-1583/ABBECC
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“Magnetic properties and critical behavior of magnetically intercalated WSe₂, : a theoretical study”. Reyntjens PD, Tiwari S, van de Put ML, Sorée B, Vandenberghe WG, 2d Materials 8, 025009 (2021). http://doi.org/10.1088/2053-1583/ABD1CC
Abstract: Transition metal dichalcogenides, intercalated with transition metals, are studied for their potential applications as dilute magnetic semiconductors. We investigate the magnetic properties of WSe2 doped with third-row transition metals (Co, Cr, Fe, Mn, Ti and V). Using density functional theory in combination with Monte Carlo simulations, we obtain an estimate of the Curie or Neel temperature. We find that the magnetic ordering is highly dependent on the dopant type. While Ti and Cr-doped WSe2 have a ferromagnetic ground state, V, Mn, Fe and Co-doped WSe2 are antiferromagnetic in their ground state. For Fe doped WSe2, we find a high Curie-temperature of 327 K. In the case of V-doped WSe2, we find that there are two distinct magnetic phase transitions, originating from a frustrated in-plane antiferromagnetic exchange interaction and a ferromagnetic out-of-plane interaction. We calculate the formation energy and reveal that, in contrast to earlier reports, the formation energy is positive for the intercalated systems studied here. We also show that in the presence of W-vacancies, it becomes favorable for Ti, Fe, and Co to intercalate in WSe2.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 1
DOI: 10.1088/2053-1583/ABD1CC
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“Direct observation of layer-stacking and oriented wrinkles in multilayer hexagonal boron nitride”. Chen L, Elibol K, Cai H, Jiang C, Shi W, Chen C, Wang HS, Wang X, Mu X, Li C, Watanabe K, Taniguchi T, Guo Y, Meyer JC, Wang H, 2d Materials 8, 024001 (2021). http://doi.org/10.1088/2053-1583/ABD41E
Abstract: Hexagonal boron nitride (h-BN) has long been recognized as an ideal substrate for electronic devices due to its dangling-bond-free surface, insulating nature and thermal/chemical stability. These properties of the h-BN multilayer are mainly determined by its lattice structure. Therefore, to analyse the lattice structure and orientation of h-BN crystals becomes important. Here, the stacking order and wrinkles of h-BN are investigated by transmission electron microscopy. It is experimentally confirmed that the layers in the h-BN flakes are arranged in the AA ' stacking. The wrinkles in a form of threefold network throughout the h-BN crystal are oriented along the armchair direction, and their formation mechanism was further explored by molecular dynamics simulations. Our findings provide a deep insight about the microstructure of h-BN and shed light on the structural design/electronic modulations of two-dimensional crystals.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.937
DOI: 10.1088/2053-1583/ABD41E
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“Superconductivity in gallenene”. Petrov M, Bekaert J, Milošević, MV, 2d Materials 8, 035056 (2021). http://doi.org/10.1088/2053-1583/AC0713
Abstract: Among the large variety of two-dimensional (2D) materials discovered to date, elemental monolayers that host superconductivity are very rare. Using ab initio calculations we show that recently synthesized gallium monolayers, coined gallenene, are intrinsically superconducting through electron-phonon coupling. We reveal that Ga-100 gallenene, a planar monolayer isostructural with graphene, is the structurally simplest 2D superconductor to date, furthermore hosting topological edge states due to its honeycomb structure. Our anisotropic Eliashberg calculations show distinctly three-gap superconductivity in Ga-100, in contrast to the alternative buckled Ga-010 gallenene which presents a single anisotropic superconducting gap. Strikingly, the critical temperature (T ( c )) of gallenene is in the range of 7-10 K, exceeding the T ( c ) of bulk gallium from which it is exfoliated. Finally we explore chemical functionalization of gallenene with hydrogen, and report induced multigap superconductivity with an enhanced T ( c ) in the resulting gallenane compound.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 8
DOI: 10.1088/2053-1583/AC0713
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“Tunable coupling of terahertz Dirac plasmons and phonons in transition metal dichalcogenide-based van der Waals heterostructures”. Lavor IR, Chaves A, Peeters FM, Van Duppen B, 2d Materials , 015018 (2021). http://doi.org/10.1088/2053-1583/AC37A8
Abstract: Dirac plasmons in graphene hybridize with phonons of transition metal dichalcogenides (TMDs) when the materials are combined in so-called van der Waals heterostructures (vdWh), thus forming surface plasmon-phonon polaritons (SPPPs). The extend to which these modes are coupled depends on the TMD composition and structure, but also on the plasmons' properties. By performing realistic simulations that account for the contribution of each layer of the vdWh separately, we calculate how the strength of plasmon-phonon coupling depends on the number and composition of TMD layers, on the graphene Fermi energy and the specific phonon mode. From this, we present a semiclassical theory that is capable of capturing all relevant characteristics of the SPPPs. We find that it is possible to realize both strong and ultra-strong coupling regimes by tuning graphene's Fermi energy and changing TMD layer number.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 1
DOI: 10.1088/2053-1583/AC37A8
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