Theoretical prediction of multiferroicity in double perovskite Y$_2$NiMnO$_6$ (2009)
Kumar, Sanjeev, Giovannetti, Gianluca, Brink, Jeroen Van Den, Picozzi, Silvia
We put forward double perovskites of the R$_2$NiMnO$_6$ family (with $R$ a rare-earth atom) as a new class of multiferroics on the basis of {\it ab initio} density functional calculations. We show...
Evidence for multiferroicity in TTF-CA organic molecular crystals (2009)
Giovannetti, Gianluca, Kumar, Sanjeev, Stroppa, Alessandro, Brink, Jeroen Van Den, Picozzi, Silvia
We show by means of ab-initio calculations that the organic molecular crystal TTF-CA is multiferroic: it has an instability to develop spontaneously both ferroelectric and magnetic ordering....
Multiferroicity in rare-earth nickelates RNiO3 (2009)
Giovannetti, Gianluca, Kumar, Sanjeev, Khomskii, Daniel, Picozzi, Silvia, Brink, Jeroen Van Den
We show that charge ordered rare-earth nickelates of the type RNiO3 (R= Ho, Lu, Pr and Nd) are multiferroic with very large magnetically induced ferroelectric (FE) polarizations. This we determine...
Spin-spiral states in undoped manganites (2009)
Kumar, Sanjeev, Brink, Jeroen Van Den, Kampf, Arno P.
The experimental observation of multiferroic behavior in perovskite manganites with a spiral spin structure demands to clarify the origin of these magnetic states and their relation to...
Magnetically induced electronic ferroelectricity in half-doped manganites (2008)
Giovannetti, Gianluca, Kumar, Sanjeev, Brink, Jeroen Van Den, Picozzi, Silvia
Using a joint approach of density functional theory and model calculations, we demonstrate that a prototypical charge ordered half-doped manganite, La$_{1/2}$Ca$_{1/2}$MnO$_3$ is multiferroic. The...
Charge ordering and magnetism in quarter-filled Hubbard-Holstein model (2008)
Kumar, Sanjeev, Brink, Jeroen Van Den
We study a two-dimensional Hubbard-Holstein model with phonons treated in the adiabatic limit. A Hartree-Fock decomposition is employed for the Hubbard term. A range of electronic densities are...
Giovannetti, Gianluca, Kumar, Sanjeev, Brink, Jeroen Van Den
We investigate the magnetic phase diagram of the newly discovered iron-based high temperature oxypnictide superconductors of the type RO$_{1-x}$F$_x $FeAs, with rare earths R=La, Sm, Nd, Pr and Ce by...
Schrodinger-Newton equation as a possible generator of quantum state reduction (2008)
Van Wezel, Jasper, Brink, Jeroen Van Den
It has been suggested by Diosi and Penrose that the occurrence of quantum state reduction in macroscopic objects is related to a manifestation of gravitational effects in quantum mechanics. Although...
Multiferroicity due to charge ordering (2008)
Brink, Jeroen Van Den, Khomskii, Daniel I.
In this contribution to the special issue on multiferroics we focus on multiferroicity driven by different forms of charge ordering. We will present the generic mechanisms by which charge ordering...
Electronic correlations decimate the ferroelectric polarization of multiferroic HoMn2O5 (2008)
Giovannetti, Gianluca, Brink, Jeroen Van Den
We show that electronic correlations decimate the intrinsic ferroelectric polarization of the recently discovered class of multiferroic manganites RMn$_2$O$_5$, where R is a rare earth element. Such...
KCrF_3: Electronic Structure, Magnetic and Orbital Ordering from First Principles (2007)
Giovannetti, Gianluca, Margadonna, Serena, Brink, Jeroen Van Den
The electronic, magnetic and orbital structures of KCrF_3 are determined in all its recently identified crystallographic phases (cubic, tetragonal, and monoclinic) with a set of {\it ab initio} LSDA...
Spontaneous Symmetry Breaking and Decoherence in Superconductors (2007)
Van Wezel, Jasper, Brink, Jeroen Van Den
We show that superconductors have a thin spectrum associated with spontaneous symmetry breaking similar to that of antiferromagnets, while still being in full agreement with Elitzur's theorem, which...
Magnetic Excitations in La2CuO4 probed by Indirect Resonant Inelastic X-ray Scattering (2007)
Forte, Filomena, Ament, Luuk J. P., Brink, Jeroen Van Den
Recent experiments on La$_2$CuO$_4$ suggest that indirect resonant inelastic X-ray scattering (RIXS) might provide a probe for transversal spin dynamics. We present in detail a systematic expansion...
Thin Spectrum States in Superconductors (2007)
Van Wezel, Jasper, Brink, Jeroen Van Den
We show that finite size superconductors have a spectrum of states at extremely low energy, i.e. inside the superconducting gap. The presence of this {\it thin spectrum} is a generic feature and...
Substrate-induced bandgap in graphene on hexagonal boron nitride (2007)
Giovannetti, Gianluca, Khomyakov, Petr A., Brocks, Geert, Kelly, Paul J., Brink, Jeroen Van Den
We determine the electronic structure of a graphene sheet on top of a lattice-matched hexagonal boron nitride (h-BN) substrate using ab initio density functional calculations. The most stable...
Multiferroicity induced by dislocated spin-density waves (2006)
Betouras, Joseph J., Giovannetti, Gianluca, Brink, Jeroen Van Den
We uncover a new pathway towards multiferroicity, showing how magnetism can drive ferroelectricity without relying on inversion symmetry breaking of the magnetic ordering. Our free-energy analysis...
Ultrashort Lifetime Expansion for Indirect Resonant Inelastic X-ray Scattering (2006)
Ament, Luuk J. P., Forte, Filomena, Brink, Jeroen Van Den
In indirect resonant inelastic X-ray scattering (RIXS) an intermediate state is created with a core-hole that has a ultrashort lifetime. The core-hole potential therefore acts as a femtosecond pulse...
Spontaneous Symmetry Breaking in Quantum Mechanics (2006)
Van Wezel, Jasper, Brink, Jeroen Van Den
We present a clear and mathematically simple procedure explaining spontaneous symmetry breaking in quantum mechanical systems. The procedure is applicable to a wide range of models and can be easily...
Giovannetti, Gianluca, Brocks, Geert, Brink, Jeroen Van Den
We investigate the changes in the electronic structure of copper phthalocyanine (CuPc) crystals that is caused by intercalation with potassium. This is done by means of {\it ab initio} LSDA and...
Limit to manipulation of qubits due to spontaneous symmetry breaking (2006)
Van Wezel, Jasper, Brink, Jeroen Van Den
We consider a two-spin qubit that is subject to the orderparameter field of a symmetry broken manipulation device. It is shown that the thin spectrum of the manipulation device limits the coherence...
On the relation between decoherence and spontaneous symmetry breaking (2006)
Van Wezel, Jasper, Zaanen, Jan, Brink, Jeroen Van Den
We have recently shown that there is a limit to quantum coherence in many-particle spin qubits due to spontaneous symmetry breaking. These results were derived for the Lieb-Mattis spin model. Here we...
Orbital-Peierls State in NaTiSi2O6 (2005)
Van Wezel, Jasper, Brink, Jeroen Van Den
Does the quasi one-dimensional titanium pyroxene NaTiSi2O6 exhibit the novel {\it orbital-Peierls} state? We calculate its groundstate properties by three methods: Monte Carlo simulations, a...
New light on magnetic excitations: indirect resonant inelastic X-ray scattering on magnons (2005)
Recent experiments show that indirect resonant inelastic X-ray scattering (RIXS) is a new probe of spin dynamics. Here I derive the cross-section for magnetic RIXS and determine the momentum...
An intrinsic limit to quantum coherence due to spontaneous symmetry breaking (2004)
Van Wezel, Jasper, Brink, Jeroen Van Den, Zaanen, Jan
We investigate the influence of spontaneous symmetry breaking on the decoherence of a many-particle quantum system. This decoherence process is analyzed in an exactly solvable model system that is...
Theory of indirect resonant inelastic X-ray scattering (2003)
Brink, Jeroen Van Den, Van Veenendaal, Michel
We express the cross section for indirect resonant inelastic X-ray scattering in terms of an intrinsic dynamic correlation function of the system that is studied with this technique. The cross...
Orbital order in classical models of transition-metal compounds (2003)
Nussinov, Zohar, Biskup, Marek, Chayes, Lincoln, Brink, Jeroen Van Den
We study the classical 120-degree and related orbital models. These are the classical limits of quantum models which describe the interactions among orbitals of transition-metal compounds. We...
Charge order versus Zener polarons: ferroelectricity in manganites (2003)
Efremov, Dmitry V., Brink, Jeroen Van Den, Khomskii, Daniel I.
We show that in manganites close to half-doping novel non-bipartite magnetic phases appear due to the interplay between double exchange, superexchange and orbital ordering. In considerable part of...
Electronic Correlations in Oligo-acene and -thiophene Organic Molecular Crystals (2003)
Brocks, Geert, Brink, Jeroen Van Den, Morpurgo, Alberto F.
From first principles calculations we determine the Coulomb interaction between two holes on oligo-acene and -thiophene molecules in a crystal, as a function of the oligomer length. The relaxation of...
Orbital effects in manganites (2002)
Brink, Jeroen Van Den, Khaliullin, Giniyat, Khomskii, Daniel
We review some aspects related to orbital degrees of freedom in manganites. The Mn$^{3+}$ ions in these compounds have double orbital degeneracy and are strong Jahn-Teller ions, causing structural...
Orbital excitations in LaMnO$_3$ (2001)
We study the recently observed orbital excitations, orbitons, and treat electron-electron correlations and lattice dynamics on equal footing. It is shown that the orbiton energy and dispersion are...
Coulomb interaction and stability of CE-type structure in half-doped manganites, reply (2001)
Brink, Jeroen Van Den, Khaliullin, Giniyat, Khomskii, Daniel
In his Comment (cond-mat/0104353), Shen points out that the on-site Coulomb interaction, that can cause charge order in half-doped manganites, also destabilizes the magnetic CE-phase observed in...
Photoemission spectra of LaMnO3 controlled by orbital excitations (2001)
Brink, Jeroen Van Den, Horsch, Peter, Oles, Andrzej M.
We investigate the spectral function of a hole moving in the orbital-ordered ferromagnetic planes of LaMnO$_3$, and show that it depends critically on the type of orbital ordering. While the hole...
Ab initio calculation of resonant X-ray scattering in Manganites (2000)
Benedetti, Patrizia, Brink, Jeroen Van Den, Pavarini, Eva, Vigliante, Assunta, Wochner, Peter
We study the origin of the resonant x-ray signal in manganites and generalize the resonant cross-section to the band structure framework. With {\it ab initio} LSDA and LSDA+U calculations we...
Charge and orbital order in half-doped manganites (1999)
Brink, Jeroen Van Den, Khaliullin, Giniyat, Khomskii, Daniel
An explanation is given for the charge order, orbital order and insulating state observed in half-doped manganese oxides, such as Nd$_{1/2}$Sr$_{1/2}$MnO$_{3}$. The competition between the kinetic...
Orbital dynamics in ferromagnetic transition metal oxides (1998)
Brink, Jeroen Van Den, Horsch, Peter, Mack, Frank, Oles, Andrzej M.
We consider a model of strongly correlated $e_g$ electrons interacting by superexchange orbital interactions in the ferromagnetic phase of LaMnO$_3$. It is found that the classical orbital order with...
Double-exchange via degenerate orbitals (1998)
Brink, Jeroen Van Den, Khomskii, Daniel
We consider the double-exchange for systems in which doped electrons occupy degenerate orbitals, treating the realistic situation with double degenerate $e_g$ orbitals. We show that the orbital...