Results for "N. Claessens"

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Origin of the photoemission final-state effects in Bi2Sr2CaCu2O8 by very-low-energy electron diffractionOct 09 2002Apr 19 2003Very-low-energy electron diffraction with a support of full-potential band calculations is used to achieve the energy positions, K// dispersions, lifetimes and Fourier compositions of the photoemission final states in Bi2Sr2CaCu2O8 at low excitation energies. ... More
Convolutional Neural Networks For Automatic State-Time Feature Extraction in Reinforcement Learning Applied to Residential Load ControlApr 28 2016Direct load control of a heterogeneous cluster of residential demand flexibility sources is a high-dimensional control problem with partial observability. This work proposes a novel approach that uses a convolutional neural network to extract hidden state-time ... More
Unoccupied Band Structure of NbSe2 by Very-Low-Energy Electron Diffraction: Experiment and TheoryJul 25 2002A combined experimental and theoretical study of very-low-energy electron diffraction at the (0001) surface of 2H-NbSe2 is presented. Electron transmission spectra have been measured for energies up to 50 eV above the Fermi level with k|| varying along ... More
Band Mapping in One-Step Photoemission Theory: Multi-Bloch-Wave Structure of Final States and Interference EffectsJan 29 2006A novel Bloch-waves based one-step theory of photoemission is developed within the augmented plane wave formalism. Implications of multi-Bloch-wave structure of photoelectron final states for band mapping are established. Interference between Bloch components ... More
Three-dimensional band structure of layered TiTe2: Photoemission final-state effectsApr 11 2006Three-dimensional band structure of unoccupied and occupied states of the prototype layered material TiTe2 is determined focusing on the GammaA line of the Brillouin zone. Dispersions and lifetimes of the unoccupied states, acting as the final states ... More
Band- and k-dependent Self-Energy Effects in the Unoccupied and Occupied Quasiparticle Band Structure of CuJul 25 2002Oct 18 2002Excited-state self-energy effects in the electronic structure of Cu, a prototype weakly correlated system containing states with different degrees of localization, are investigated with emphasis on the unoccupied states up to 40 eV above the Fermi level. ... More
Heat conductivity of the spin-Peierls compounds TiOCl and TiOBrFeb 10 2010We report experimental results on the heat conductivity \kappa of the S=1/2 spin chain compounds TiOBr and TiOCl for temperatures 5K<T<300K and magnetic fields up to 14. Surprisingly, we find no evidence of a significant magnetic contribution to \kappa, ... More
Gas sensing properties of multiwall carbon nanotubes decorated with Rh nanoparticlesMay 02 2016In the present work, multiwalled carbon nanotubes were decorated with rhodium nanoparticles using a colloidal solution in the post-discharge of an RF atmospheric plasma of argon (Ar) or argon/oxygen (Ar:O$_2$). The properties of these hybrid materials ... More
Automatic brain tissue segmentation in fetal MRI using convolutional neural networksJun 11 2019MR images of fetuses allow clinicians to detect brain abnormalities in an early stage of development. The cornerstone of volumetric and morphologic analysis in fetal MRI is segmentation of the fetal brain into different tissue classes. Manual segmentation ... More
Locust: C++ software for simulation of RF detectionJul 25 2019The Locust simulation package is a new C++ software tool developed to simulate the measurement of time-varying electromagnetic fields using RF detection techniques. Modularity and flexibility allow for arbitrary input signals, while concurrently supporting ... More
Electronic structure of GaAs1-xNx alloy by soft-X-ray absorption and emission: Origin of the reduced optical efficiencyJul 31 2002The local electronic structure of N atoms in a diluted GaAs1-xNx (x=3%) alloy, in view of applications in optoelectronics, is determined for the first time using soft-X-ray absorption (SXA) and emission (SXE). Deviations from crystalline GaN, in particular ... More
Two-Spinon and Orbital Excitations of the Spin-Peierls System TiOClJul 28 2011Sep 20 2011We combine high-resolution resonant inelastic x-ray scattering with cluster calculations utilizing a recently derived effective magnetic scattering operator to analyze the polarization, excitation energy, and momentum dependent excitation spectrum of ... More
Carbon nanotubes decorated with gold, platinum and rhodium clusters by injection of colloidal solutions into the post-discharge of a RF atmospheric plasmaMay 02 2016In this paper, we present a new, simple, robust and efficient technique to decorate multi-wall carbon nanotubes (MWCNT) with metal nanoparticles. As case studies, Au, Pt and Rh nanoparticles are grafted onto MWCNTs by spraying a colloidal solution into ... More
Direct k-space mapping of the electronic structure in an oxide-oxide interfaceJan 13 2013Jun 18 2013The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found and attributed to local moments. ... More
Double Band Inversion in $ α$-Sn: Appearance of Topological Surface States and the Role of Orbital CompositionJan 12 2017Feb 16 2017The electronic structure of \graySn(001) thin films strained compressively in-plane was studied both experimentally and theoretically. A new topological surface state (TSS) located entirely within the gapless projected bulk bands is revealed by \textit{ab ... More
Nitrogen local electronic structure in Ga(In)AsN alloys by soft-X-ray absorption and emission: Implications for optical propertiesMar 10 2003Sep 02 2003Soft-X-ray emission and absorption spectroscopies with their elemental specificity are used to determine the local electronic structure of N atoms in Ga(In)AsN diluted semiconductor alloys (N concentrations about 3%) in view of applications of such materials ... More
Automatic segmentation of the intracranialvolume in fetal MR imagesJul 31 2017MR images of the fetus allow non-invasive analysis of the fetal brain. Quantitative analysis of fetal brain development requires automatic brain tissue segmentation that is typically preceded by segmentation of the intracranial volume (ICV). This is challenging ... More
Grid-Constrained Distributed Optimization for Frequency Control with Low-Voltage FlexibilityMar 11 2019Providing frequency control services with flexible assets connected to the low-voltage distribution grid, amongst which residential battery storage or electrical hot water boilers, can lead to congestion problems and voltage issues in the distribution ... More
Optimal Combination of Frequency Control and Peak Shaving with Battery Storage SystemsJun 17 2019Combining revenue streams by providing multiple services with battery storage systems increases profitability and enhances the investment case. In this work, we present a novel optimisation and control framework that enables a storage system to optimally ... More
Combined Stochastic Optimization of Frequency Control and Self-Consumption with a BatteryOct 23 2017Optimally combining frequency control with self-consumption can increase revenues from battery storage systems installed behind-the-meter. This work presents an optimized control strategy that allows a battery to be used simultaneously for self-consumption ... More
Techno-Economic Analysis and Optimal Control of Battery Storage for Frequency Control Services, Applied to the German MarketMar 11 2019Optimal investment in battery energy storage systems, taking into account degradation, sizing and control, is crucial for the deployment of battery storage, of which providing frequency control is one of the major applications. In this paper, we present ... More
Convolutional Neural Networks For Automatic State-Time Feature Extraction in Reinforcement Learning Applied to Residential Load ControlApr 28 2016Oct 11 2016Direct load control of a heterogeneous cluster of residential demand flexibility sources is a high-dimensional control problem with partial observability. This work proposes a novel approach that uses a convolutional neural network to extract hidden state-time ... More
Tailoring Materials for Mottronics: Excess Oxygen Doping of a Prototypical Mott InsulatorJul 16 2018The Mott transistor is a paradigm for a new class of electronic devices---often referred to by the term Mottronics---, which are based on charge correlations between the electrons. Since correlation-induced insulating phases of most oxide compounds are ... More
Atomic correlations in itinerant ferromagnets: quasi-particle bands of nickelApr 05 2002We measure the band structure of nickel along various high-symmetry lines of the bulk Brillouin zone with angle-resolved photoelectron spectroscopy. The Gutzwiller theory for a nine-band Hubbard model whose tight-binding parameters are obtained from non-magnetic ... More
Dimensionality-tuned electronic structure of nickelate superlattices explored by soft-x-ray angle resolved photoelectron spectroscopyNov 26 2014The electronic and magnetic properties of epitaxial LaNiO3/LaAlO3 superlattices can be tuned by layer thickness and substrate-induced strain. Here, we report on direct measurements of the k-space-resolved electronic structure of buried nickelate layers ... More
Model-Free Control of Thermostatically Controlled Loads Connected to a District Heating NetworkJan 27 2017Feb 24 2017Optimal control of thermostatically controlled loads connected to a district heating network is considered a sequential decision- making problem under uncertainty. The practicality of a direct model-based approach is compromised by two challenges, namely ... More
Circular dichroism and bilayer splitting in the normal state of underdoped (Pb,Bi)$_2$Sr$_2$(Ca$_x$Y$_{1-x}$)Cu$_2$O$_{8+δ}$ and overdoped (Pb,Bi)$_2$Sr$_2$CaCu$_2$O$_{8+δ}$Dec 01 2003We report an ARPES investigation of the circular dichroism in the first Brillouin zone (BZ) of under- and overdoped Pb-Bi2212 samples. We show that the dichroism has opposite signs for bonding and antibonding components of the bilayer-split CuO-band and ... More
Learning Agent for a Heat-Pump Thermostat With a Set-Back Strategy Using Model-Free Reinforcement LearningJun 02 2015Jun 25 2015The conventional control paradigm for a heat pump with a less efficient auxiliary heating element is to keep its temperature set point constant during the day. This constant temperature set point ensures that the heat pump operates in its more efficient ... More
New Model System for a One-Dimensional Electron Liquid: Self-Organized Atomic Gold Chains on Ge(001)Aug 28 2008Oct 24 2008Unique electronic properties of self-organized Au atom chains on Ge(001) in novel c(8x2) long-range order are revealed by scanning tunneling microscopy. Along the nanowires an exceptionally narrow conduction path exists which is virtually decoupled from ... More
Spin Chains and Electron Transfer at Stepped Silicon SurfacesJan 27 2016Mar 31 2016High-index surfaces of silicon with adsorbed gold can reconstruct to form highly ordered linear step arrays. These steps take the form of a narrow strip of graphitic silicon. In some cases - specifically, for Si(553)-Au and Si(557)-Au - a large fraction ... More
Cytoskeletal bundle bending, buckling, and stretching behaviorJul 24 2006Mar 15 2007F-actin bundles constitute principal components of a multitude of cytoskeletal processes including stereocilia, filopodia, microvilli, neurosensory bristles, cytoskeletal stress fibers, and the sperm acrosome. The bending, buckling, and stretching behaviors ... More
Phenomenological Modeling of Photoemission Spectra in Strongly Correlated Electron SystemsMay 08 2002A phenomenological approach is presented that allows one to model, and thereby interpret, photoemission spectra of strongly correlated electron systems. A simple analytical formula for the self-energy is proposed. This self-energy describes both coherent ... More
Conduction States with Vanishing Dimerization in Pt Nanowires on Ge(001) Observed with Scanning Tunneling MicroscopyMar 20 2006The low-energy electronic properties of one-dimensional nanowires formed by Pt atoms on Ge(001) are studied with scanning tunneling microscopy down to the millivolt-regime. The chain structure exhibits various dimerized elements at high tunneling bias, ... More
Hipster: Integrating Theory Exploration in a Proof AssistantMay 14 2014This paper describes Hipster, a system integrating theory exploration with the proof assistant Isabelle/HOL. Theory exploration is a technique for automatically discovering new interesting lemmas in a given theory development. Hipster can be used in two ... More
Trajectory tracking with an aggregation of domestic hot water heaters: Combining model-based and model-free control in a commercial deploymentMay 11 2018Scalable demand response of residential electric loads has been a timely research topic in recent years. The commercial coming of age or residential demand response requires a scalable control architecture that is both efficient and practical to use. ... More
The use of distributed thermal storage in district heating grids for demand side managementFeb 06 2017The work presented in this paper relates to a small scale district heating network heated by a gas fired CHP. In most common situations, such a CHP is heat driven operated, meaning that the CHP will switch on whenever heat is needed, while not taking ... More
A Supervisory Control Algorithm Based on Property-Directed ReachabilityNov 17 2017We present an algorithm for synthesising a controller (supervisor) for a discrete event system (DES) based on the property-directed reachability (PDR) model checking algorithm. The discrete event systems framework is useful in both software, automation ... More
Non-trivial topological valence bands of common diamond and zinc-blende semiconductorsApr 10 2019The diamond and zinc-blende semiconductors are well-known and have been widely studied for decades. Yet, their electronic structure still surprises with unexpected topological properties of the valence bands. In this joint theoretical and experimental ... More
Spin-Polarized Standing Waves in the Fermi Surface of a Ferromagnetic Thin FilmApr 26 2005The spin-selective electron reflection at a ferromagnetic-paramagnetic interface is investigated using Fe films on a W(110) substrate. Angle-resolved photoemission of the majority and minority Fermi surfaces of the Fe film is used to probe standing wave ... More
Fermi Surface and Electron Correlation Effects of Ferromagnetic IronJan 25 2005The electronic band structure of bulk ferromagnetic iron is explored by angle-resolved photoemission for electron correlation effects. Fermi surface cross-sections as well as band maps are contrasted with density functional calculations. The Fermi vectors ... More
Quantized anti de Sitter spaces and non-formal deformation quantizations of symplectic symmetric spacesMay 29 2007We realize quantized anti de Sitter space black holes, building Connes spectral triples, similar to those used for quantized spheres but based on Universal Deformation Quantization Formulas (UDF) obtained from an oscillatory integral kernel on an appropriate ... More
Microscopic origin of the mobility enhancement at a spinel/perovskite oxide heterointerface revealed by photoemission spectroscopyOct 16 2017The spinel/perovskite heterointerface $\gamma$-Al$_2$O$_3$/SrTiO$_3$ hosts a two-dimensional electron system (2DES) with electron mobilities exceeding those in its all-perovskite counterpart LaAlO$_3$/SrTiO$_3$ by more than an order of magnitude despite ... More
Elemental Topological Insulator with a Tunable Fermi Level: Strained α-Sn on InSb(001)Aug 04 2013Sep 09 2013We report on the epitaxial fabrication and electronic properties of a topological phase in strained \alpha-Sn on InSb. The topological surface state forms in the presence of an unusual band order not based on direct spin-orbit coupling, as shown in density ... More
Surface characterization and surface electronic structure of organic quasi-one-dimensional charge transfer saltsAug 22 2002Jan 08 2003We have thoroughly characterized the surfaces of the organic charge-transfer salts TTF-TCNQ and (TMTSF)2PF6 which are generally acknowledged as prototypical examples of one-dimensional conductors. In particular x-ray induced photoemission spectroscopy ... More
Symmetry-Breaking Phase Transition without Peierls Mechanism in Conducting Monoatomic ChainsSep 27 2011The one-dimensional (1D) model system Au/Ge(001), consisting of linear chains of single atoms on a surface, is scrutinized for lattice instabilities predicted in the Peierls paradigm. By scanning tunneling microscopy and electron diffraction we reveal ... More
Residential Demand Response Applications Using Batch Reinforcement LearningApr 08 2015Driven by recent advances in batch Reinforcement Learning (RL), this paper contributes to the application of batch RL to demand response. In contrast to conventional model-based approaches, batch RL techniques do not require a system identification step, ... More
Direct Load Control of Thermostatically Controlled Loads Based on Sparse Observations Using Deep Reinforcement LearningJul 26 2017This paper considers a demand response agent that must find a near-optimal sequence of decisions based on sparse observations of its environment. Extracting a relevant set of features from these observations is a challenging task and may require substantial ... More
Correlation-driven charge order in a frustrated two-dimensional atom latticeFeb 01 2018Mar 18 2019We thoroughly examine the ground state of the triangular lattice of Pb on Si(111) using scanning tunneling microscopy. We detect charge-order, accompanied by a subtle structural reconstruction. Applying the extended variational cluster approach we map ... More
Mechanics of bundled semiflexible polymer networksNov 29 2006Aug 30 2007While actin bundles are used by living cells for structural fortification, the microscopic origin of the elasticity of bundled networks is not understood. Here, we show that above a critical concentration of the actin binding protein fascin, a solution ... More
Two-dimensional crossover and strong coupling of plasmon excitations in arrays of one-dimensional atomic wiresJan 20 2016The collective electronic excitations of arrays of Au chains on regularly stepped Si(553) and Si(775) surfaces were studied using electron loss spectroscopy with simultaneous high energy and momentum resolution (ELS-LEED) in combination with low energy ... More
Momentum-resolved single-particle spectral function for TiOCl from a combination of density functional and variational cluster calculationsOct 14 2008Aug 28 2009We present results for the momentum-resolved single-particle spectral function of the low-dimensional system TiOCl in the insulating state, obtained by a combination of ab initio Density Functional Theory (DFT) and Variational Cluster (VCA) calculations. ... More
Spectroscopic signatures of spin-charge separation in the quasi-one-dimensional organic conductor TTF-TCNQJan 30 2002The electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ is studied by angle-resolved photoelectron spectroscopy (ARPES). The experimental spectra reveal significant discrepancies to band theory. We demonstrate that the measured ... More
Spin-Peierls transition in TiOClMar 09 2005Temperature-dependent x-ray diffraction of the low-dimensional spin 1/2 quantum magnet TiOCl shows that the phase transition at T_{c2} = 90 K corresponds to a lowering of the lattice symmetry. Below T_{c1} = 66 K a twofold superstructure develops, that ... More
Experimental analysis of data-driven control for a building heating systemJul 13 2015Feb 16 2016Driven by the opportunity to harvest the flexibility related to building climate control for demand response applications, this work presents a data-driven control approach building upon recent advancements in reinforcement learning. More specifically, ... More
Tomonaga-Luttinger liquid in the edge channels of a quantum spin Hall insulatorJan 18 2019Topological quantum matter is characterized by non-trivial global invariants of the bulk which induce gapless electronic states at its boundaries. A case in point are two-dimensional topological insulators (2D-TI) which host one-dimensional (1D) conducting ... More
Evidence for Long-Range Spin Order Instead of a Peierls Transition in Si(553)-Au ChainsSep 04 2013Stabilization of the Si(553) surface by Au adsorption results in two different atomically defined chain types, one of Au atoms and one of Si. At low temperature these chains develop two- and threefold periodicity, respectively, previously attributed to ... More
Results from the Project 8 phase-1 cyclotron radiation emission spectroscopy detectorMar 16 2017The Project 8 collaboration seeks to measure the absolute neutrino mass scale by means of precision spectroscopy of the beta decay of tritium. Our technique, cyclotron radiation emission spectroscopy, measures the frequency of the radiation emitted by ... More
Project 8 Phase III Design ConceptMar 16 2017We present a working concept for Phase III of the Project 8 experiment, aiming to achieve a neutrino mass sensitivity of $2~\mathrm{eV}$ ($90~\%$ C.L.) using a large volume of molecular tritium and a phased antenna array. The detection system is discussed ... More
Pressure dependence of the Verwey transition in magnetite: an infrared spectroscopic point of viewSep 13 2012We investigated the electronic and vibrational properties of magnetite at temperatures from 300 K down to 10 K and for pressures up to 10 GPa by far-infrared reflectivity measurements. The Verwey transition is manifested by a drastic decrease of the overall ... More
Project 8 detector upgrades for a tritium beta decay spectrum using cyclotron radiationMar 16 2017Following the successful observation of single conversion electrons from $^{83m}$Kr using Cyclotron Radiation Emission Spectroscopy (CRES), Project 8 is now advancing its focus toward a tritium beta decay spectrum. A tritium spectrum will be an important ... More
Anharmonic mixing in a magnetic trapJan 07 2005We have experimentally observed re-equilibration of a magnetically trapped cloud of metastable neon atoms after it was put in a non-equilibrium state. Using numerical simulations we show that anharmonic mixing, equilibration due to the collisionless dynamics ... More
Absence of metallicity in K-doped picene: Importance of electronic correlationsOct 15 2012Apr 29 2013Potassium-doped picene (K$_x$picene) has recently been reported to be a superconductor at $x=3$ with critical temperatures up to 18 K. Here we study the electronic structure of K-doped picene films by photoelectron spectroscopy and {\it ab initio} density ... More
Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopyFeb 20 2012Jun 01 2012The optical properties of magnetite at room temperature were studied by infrared reflectivity measurements as a function of pressure up to 8 GPa. The optical conductivity spectrum consists of a Drude term, two sharp phonon modes, a far-infrared band at ... More
Cluster Dynamical Mean-field calculations for TiOClDec 06 2006Oct 30 2007Based on a combination of cluster dynamical mean field theory (DMFT) and density functional calculations, we calculated the angle-integrated spectral density in the layered $s=1/2$ quantum magnet TiOCl. The agreement with recent photoemission and oxygen ... More
Heat capacity of the quantum magnet TiOClJan 21 2005Measurements of the heat capacity C(T,H) of the one-dimensional quantum magnet TiOCl are presented for temperatures 2K < T < 300K and magnetic fields up to 5T. Distinct anomalies at 91K and 67K signal two subsequent phase transitions. The lower of these ... More
Correlation-driven charge order in a frustrated two-dimensional atom latticeFeb 01 2018The triangular lattice of localised electrons is the canonical example for a geometrically frustrated spin arrangement. In conjunction with strong local Coulomb interactions, it leads to a competition of antiferromagnetic order and spin liquid behaviour. ... More
The Hubbard model description of the photoemission TCNQ singular featuresJul 24 2003Mar 16 2006In this paper we use the pseudofermion dynamical theory (PDT) in the study of the one-electron removal singular spectral features the one-dimensional Hubbard model. The PDT reveals that in the whole $(k, \omega)$-plane such features are of power-law type ... More
Reinforcement Learning Applied to an Electric Water Heater: From Theory to PracticeNov 29 2015Electric water heaters have the ability to store energy in their water buffer without impacting the comfort of the end user. This feature makes them a prime candidate for residential demand response. However, the stochastic and nonlinear dynamics of electric ... More
Transient Binding and Dissipation in Semi-flexible Polymer NetworksFeb 27 2008While polymer solutions lack the mechanical stability only transiently cross-linked networks can fulfill the competing requirements of structural stability and maximal energy dissipation. Here, we show that transient cross-links entail local stress relaxation ... More
Probing the interface of Fe3O4/GaAs thin films by hard x-ray photoelectron spectroscopyMar 13 2009Magnetite (Fe3O4) thin films on GaAs have been studied with HArd X-ray PhotoElectron Spectroscopy (HAXPES) and low-energy electron diffraction. Films prepared under different growth conditions are compared with respect to stoichiometry, oxidation, and ... More
Correlation-driven charge order in a frustrated two-dimensional atom latticeFeb 01 2018Aug 28 2019We thoroughly examine the ground state of the triangular lattice of Pb on Si(111) using scanning tunneling microscopy. We detect charge-order, accompanied by a subtle structural reconstruction. Applying the extended variational cluster approach we map ... More
Effects of finite-range interactions on the one-electron spectral properties of TTF-TCNQJul 29 2019The electronic dispersions of the quasi-one-dimensional organic conductor TTF-TCNQ are studied by angle-resolved photoelectron spectroscopy (ARPES) with higher angular resolution and accordingly smaller step width than in previous studies. Our experimental ... More
Electron Radiated Power in Cyclotron Radiation Emission Spectroscopy ExperimentsJan 09 2019The recently developed technique of Cyclotron Radiation Emission Spectroscopy (CRES) uses frequency information from the cyclotron motion of an electron in a magnetic bottle to infer its kinetic energy. Here we derive the expected radio frequency signal ... More
Bismuthene on a SiC Substrate: A Candidate for a New High-Temperature Quantum Spin Hall ParadigmAug 02 2016Quantum spin Hall (QSH) materials promise revolutionary device applications based on dissipationless propagation of spin currents. They are two-dimensional (2D) representatives of the family of topological insulators, which exhibit conduction channels ... More
Are the renormalized band widths in TTF-TCNQ of structural or electronic origin? - An angular dependent NEXAFS studyAug 10 2007We have performed angle-dependent near-edge x-ray absorption fine structure measurements in the Auger electron yield mode on the correlated quasi-one-dimensional organic conductor TTF-TCNQ in order to determine the orientation of the molecules in the ... More
One-dimensional versus two-dimensional correlation effects in the oxyhalides TiOCl and TiOBrOct 04 2006We have performed a comparative study of the electronic structures of the spin-Peierls systems TiOCl and TiOBr by means of photoemission spectroscopy and density functional calculations. While the overall electronic structure of these isostructural compounds ... More
Pressure-induced insulator-to-metal transition in low-dimensional TiOClMar 14 2006We studied the transmittance and reflectance of the low-dimensional Mott-Hubbard insulator TiOCl in the infrared and visible frequency range as a function of pressure. The strong suppression of the transmittance and the abrupt increase of the near-infrared ... More
Terahertz Conductivity at the Verwey Transition in MagnetiteMar 24 2005The complex conductivity at the (Verwey) metal-insulator transition in Fe_3O_4 has been investigated at THz and infrared frequencies. In the insulating state, both the dynamic conductivity and the dielectric constant reveal a power-law frequency dependence, ... More
Unoccupied electronic structure of TiOCl studied by x-ray absorption near-edge spectroscopyOct 25 2011We study the unoccupied electronic structure of the spin-1/2 quantum magnet TiOCl by x-ray absorption near-edge spectroscopy (XANES) at the Ti L and O K edges. Data is acquired both in total electron and fluorescence yield mode (TEY and FY, respectively). ... More
Photoemission of a doped Mott insulator: spectral weight transfer and qualitative Mott-Hubbard descriptionMay 09 2009Feb 06 2011The spectral weight evolution of the low-dimensional Mott insulator TiOCl upon alkali-metal dosing has been studied by photoelectron spectroscopy. We observe a spectral weight transfer between the lower Hubbard band and an additional peak upon electron-doping, ... More
Magnetic-Order Induced Spectral-Weight Redistribution in a Triangular Surface SystemDec 21 2011The Sn-induced $\sqrt3 \times \sqrt3$ surface reconstruction on Si(111) has been investigated by material-specific many-body calculations and by angle-resolved photoelectron spectroscopy (ARPES). This triangular surface system in the low adatom coverage ... More
Strictly One-Dimensional Electron System in Au Chains on Ge(001) Revealed By Photoelectron K-Space MappingApr 25 2010Dec 16 2010Atomic nanowires formed by Au on Ge(001) are scrutinized for the band topology of the conduction electron system by k-resolved photoemission. Two metallic electron pockets are observed. Their Fermi surface sheets form straight lines without undulations ... More
Testing Topological Protection of Edge States in Hexagonal Quantum Spin Hall Candidate MaterialsMar 07 2018Oct 23 2018We analyze the detailed structure of topological edge mode protection occuring in hexagonal quantum spin Hall (QSH) materials. We focus on bismuthene, antimonene, and arsenene on a SiC substrate, which, due to their large bulk gap, may offer new opportunities ... More
Entropy of water and the temperature-induced stiffening of amyloid networksDec 20 2017In water, networks of semi-flexible fibrils of the protein $\alpha$-synuclein stiffen significantly with increasing temperature. We make plausible that this reversible stiffening is a result of hydrophobic contacts between the fibrils that become more ... More
Triangular Spin-Orbit-Coupled Lattice with Strong Coulomb Correlations: Sn Atoms on a SiC(0001) SubstrateJan 19 2015Two-dimensional (2D) atom lattices provide model setups for Coulomb correlations inducing competing ground states, partly with topological character. Hexagonal SiC(0001) is an intriguing wide-gap substrate, spectroscopically separated from the overlayer ... More
A new paradigm for the quantum spin Hall effect at high temperaturesJul 25 2018The quantum spin Hall effect (QSHE) has formed the seed for contemporary research on topological quantum states of matter. Since its discovery in HgTe/CdTe quantum wells and AlGaAs/GaAs heterostructures, all such systems have so far been suffering from ... More
Towards Topological Quasi-Freestanding Stanene via Substrate EngineeringJul 24 2018Nov 06 2018In search for a new generation of spintronics hardware, material candidates for room temperature quantum spin Hall effect (QSHE) have become a contemporary focus of investigation. Inspired by the original proposal for QSHE in graphene, several heterostructures ... More
Bosonic stimulation of cold 1s excitons into a harmonic potential minimum in Cu$_2$OFeb 07 2003Density distribution of cold exciton clouds generated into a strain-induced potential well by two-photon excitation in Cu$_2$O is studied at 2 K. We find that an anomalous spike, which can be interpreted as accumulation of the excitons into the ground ... More
The Universal Equation of State near the Critical Point of QCDJan 12 2004Jun 18 2004We study the universal properties of the phase diagram of QCD near the critical point using the exact renormalization group. For two-flavour QCD and zero quark masses we derive the universal equation of state in the vicinity of the tricritical point. ... More
Analytical Estimate of the Effect of Spherical Inhomogeneities on Luminosity Distance and RedshiftFeb 06 2008Jun 25 2008We provide an analytical estimate of the effect of a spherical inhomogeneity on light beams that travel through it. We model the interior of the inhomogeneity in terms of the Lemaitre-Tolman-Bondi metric. We assume that the beam source is located outside ... More
Heavy quark skyrmionsMay 18 2009The description of the heavy baryons as heavy-meson--soliton bound systems is reviewed. We outline how such bound systems arise from effective lagrangians that respect both chiral symmetry and heavy quark symmetry. Effects due to finite heavy quark masses ... More
Wind of presupernova IIn SN~1997egJan 15 2019Spectra and phototometry of type IIn supernova SN 1997eg are used to determine properties of the circumstellar gas lost by the presupernova during the latest 200 years before the explosion. The analysis of narrow H$\alpha$ and [Fe X] 6374 \AA\ results ... More
Connection between Diffraction and Small-$x$Nov 30 2001A brief review of the modern QCD theory of diffractive DIS is given.
Diffractive DIS: Where Are We?Nov 12 2001Nov 20 2001A brief review of the modern QCD theory of diffractive DIS is given. The recent progress has been remarkably rapid, all the principal predictions from the color dipole approach to diffraction - the $(Q^2+m_V^2)$ scaling, the pattern of SCHNC, shrinkage ... More
Diffractive Vector Mesons in DIS: Meson Structure and QCDSep 15 2000I review the modern status of QCD theory of diffractive vector meson production with the focus on shrinkage of photons with Q2 and (Q2+mV2)$scaling, j-plane properties of the QCD pomeron and Regge shrinkage of diffraction cone, $s$-channel helicity non-conservation ... More
Spin dependence of diffractive DISMay 31 1999I review the recent progress in the theory of s-channel helicity nonconservation (SCHNC) effects in diffractive DIS including the unitarity driven demise of the Burkhardt-Cottingham sum rule and strong scaling departure from the Wandzura-Wilczek relation. ... More
New upper bound for a class of vertex Folkman numbersJan 11 2006We improve the previuosly known bound for some vertex Folkman numbers.
Radiative decays of phi-meson about nature of light scalar resonancesSep 11 2003We show on gauge invariance grounds that the fine threshold phenomenon is discovered in the radiative decays phi->gamma a0->gamma pi0 eta and phi->gamma f0->gamma pi0pi0. This enables to conclude that production of the lightest scalar mesons a0(980) and ... More
Nature of the scalar $a_0(980)$ and $f_0(980)$-mesonsMar 10 1998Oct 28 1998It is presented a critical consideration of all unusual properties of the scalar $a_0(980)$ and $f_0(980)$-mesons in the four-quark, two-quark and molecular models. The arguments are adduced that the four-quark model is more preferable. It is discussed ... More
Production of pseudovector heavy quarkonia by virtual Z boson in electron-positron collisionsApr 03 1996Apr 09 1996It is shown that $BR(\chi_{b1}(1P)\rightarrow Z\rightarrow e^+e^-)\simeq 3.3\cdot 10^{-7}$, $BR(\chi_{b1}(2P)\rightarrow Z\rightarrow e^+e^-)\simeq 4.1\cdot 10^{-7}$ and $BR(\chi_{c1}(1P)\rightarrow Z\rightarrow e^+e^-)\simeq 10^{-8}$ that give a good ... More