Publications (27)
Dependence of band gaps in d-electron perovskite oxides on magnetism
Julien Varignon, Oleksandr I. Malyi, Alex Zunger
Understanding the controlling principles of band gaps trends in d electron perovskites is needed both for gauging metal-insulator transitions, as well as their application in catal…
Structural instabilities of infinite-layer nickelates from first-principles simulations
Ãlvaro Adrián Carrasco Ãlvarez, Sébastien Petit, Lucia Iglesias +3
Rare-earth nickelates RNiO adopting an infinite-layer phase show superconductivity once La, Pr or Nd are substituted by a divalent cation. Either in the pristine or doped form,…
Mott gapping in 3d ABO3 perovskites without Mott-Hubbard interelectronic U
Julien Varignon, Manuel Bibes, Alex Zunger
The existence of band gaps in Mott insulators such as perovskite oxides with partially filled 3d shells has been traditionally explained in terms of strong, dynamic inter-electroni…
First-principles study of electron and hole doping in perovskite nickelates
Lucia Iglesias, Manuel Bibes, Julien Varignon
Rare-earth nickelates RNiO (R=Lu-Pr, Y) show a striking metal-insulator transition in their bulk phase whose temperature can be tuned by the rare-earth radius. Th…
Electric field control of Jahn-Teller distortions in bulk perovskites
Julien Varignon, Nicholas C. Bristowe, Philippe Ghosez
The Jahn-Teller distortion, by its very nature, is often at the heart of the various electronic properties displayed by perovskites and related materials. Despite the Jahn-Teller m…
Can we prevent the "dead layer" formation at manganite interfaces?
AyÅegül Begüm Koçak, Julien Varignon, Sébastien Lemal +2
The present work theoretically studies the possibility to hinder the formation of a "dead" layer at the interfaces in manganite superlattices. We showed that this goal can be reach…
Electron-phonon mediated superconductivity in LaNiO nickel oxides
Alvaro Adrian Carrasco Alvarez, Sebastien Petit, Lucia Iglesias +3
Nickel oxide superconductors offer an alternative playground for understanding the formation of Cooper pairs in correlated materials such as the famous cuprates. By studying the La…
Charge ordering as the driving mechanism for superconductivity in rare-earth nickel oxides
Ãlvaro Adrián Carrasco Ãlvarez, Lucia Iglesias, Sébastien Petit +3
Superconductivity is one of the most intriguing properties of matter described by an attractive interaction that bounds electrons into Cooper pairs. To date, the highest critical t…
ARPES and transport studies of the elemental topological insulator -Sn
Quentin Barbedienne, Julien Varignon, Nicolas Reyren +11
Gray tin, also known as -Sn, can be turned into a three-dimensional topological insulator (3D-TI) by strain and finite size effects. Such room temperature 3D-TI is peculiarly i…
Switchable and tunable Rashba-type spin splitting in covalent perovskite oxides
Julien Varignon, Jacobo Santamaria, Manuel Bibes
In transition metal perovskites (ABO3) most physical properties are tunable by structural parameters such as the rotation of the BO6 octahedra. Examples include the Néel temperatu…
Analysis of the multiferroicity in the hexagonal manganite YMnO3
Kiran Singh, Marie-Bernadette Lepetit, Charles Simon +4
We performed magnetic and ferroelectric measurements, associated with Landau theory and symmetry analysis, in order to clarify the situation of the YMnO3 system, a classical exampl…
A multiferroic two-dimensional electron gas
Julien Bréhin, Yu Chen, Maria D'Antuono +6
Multiferroics are compounds in which at least two ferroic orders coexist - typically (anti)ferromagnetism and ferroelectricity. While magnetic order can arise in both insulating an…
Origins Vs. fingerprints of the Jahn-Teller effect in d-electron ABX perovskites
Julien Varignon, Manuel Bibes, Alex Zunger
The Jahn-Teller (JT) distortion that can remove electronic degeneracies in partially occupied states and results in systematic atomic displacements is a common underlying feature t…
Improper ferroelectricity and multiferroism in 2HBaMnO
Julien Varignon, Philippe Ghosez
Using first-principles calculations, we study theoretically the stable 2H hexagonal structure of BaMnO3. We show that from the stable high temperature P63/mmc structure, the compou…
First principles calculation of the phonons modes in the hexagonal ferroelectric and paraelectric phases
Julien Varignon, Sébastien Petit, Marie-Bernadette Lepetit
The lattice dynamics of the magneto-electric compound has been investigated using density functional calculations, both in the ferroelectric and the paraelectric phase…
Bulk NdNiO2 is thermodynamically unstable with respect to decomposition while hydrogenation reduces the instability and transforms it from metal to insulator
Oleksandr I. Malyi, Julien Varignon, Alex Zunger
Through CaH2 chemical reduction of a parent R3+Ni3+O3 perovskite form, superconductivity was recently achieved in Sr-doped NdNiO2 on SrTiO3 substrate. Using density functional theo…
Origin of the orbital and spin orderings in rare-earth titanates
Julien Varignon, Mathieu N. Grisolia, Daniele Preziosi +2
Rare-earth titanates RTiO are Mott insulators displaying a rich physical behavior, featuring most notably orbital and spin orders in their ground state. The origin of their fer…
Origin of band gaps in 3d perovskite oxides
Julien Varignon, Manuel Bibes, Alex Zunger
With their broad range of magnetic, electronic and structural properties, transition metal perovskite oxides ABO3 have long served as a platform for testing condensed matter theori…
Role of the ferromagnetic component in the ferroelectricity of YMnO3
Kiran Singh, Natalia Bellido, Charles Simon +4
We performed magnetic and ferroelectric measurements, first principle calculations and Landau theory analysis on hexagonal YMnO3. The polarization and the AFM order parameter were…
Reconciling the ionic and covalent pictures in rare-earth nickelates
Julien Varignon, Mathieu N. Grisolia, Jorge Ãñiguez +2
The properties of AMO3 perovskite oxides, where M is a 3d transition metal, depend strongly on the level of covalency between the metal d and oxygen p orbitals. With their complex…
Novel magneto-electric multiferroics from first-principles
Julien Varignon, Nicholas C. Bristowe, Eric Bousquet +1
Interest in first-principles calculations within the multiferroic community has been rapidly on the rise over the last decade. Initially considered as a powerful support to explain…
Origin of superconductivity in hole doped SrBiO3 bismuth oxide perovskite from parameter-free first-principles simulations
Julien Varignon
The recent discovery nickel oxides superconductors have highlighted the importance of first-principles simulations for understanding the formation of the bound electrons at the cor…
Bond disproportionation, charge self-regulation and ligand holes in s-p and in d electron ABX3 perovskites by density functional theory
Gustavo Martini Dalpian, Qihang Liu, Julien Varignon +2
Some ABX3 perovskites exhibit different local environments (DLE) for the same B atoms in the lattice, an effect referred to as disproportionation, distinguishing such compounds fro…
Coupling and Electrical Control of Structural, Orbital and Magnetic Orders in Perovskites
Julien Varignon, Nicholas C. Bristowe, Eric Bousquet +1
Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed in these materials. The…
Accurate evaluation of magnetic coupling between atoms with numerous open-shells : an ab-initio method
Alain Gellé, Julien Varignon, Marie-Bernadette Lepetit
We propose a new ab initio method designed for the accurate calculation of effective exchange integrals between atoms with numerous open-shells. This method applies to ferromagneti…
Unexpected antagonism between ferroelectricity and Rashba effects in epitaxially strained SrTiO
Julien Varignon
The Rashba parameter is usually assumed to scale linearly with the amplitude of polar displacements by construction of the spin-orbit interaction. On the basis of first-pr…
Magnetism tailored by mechanical strain engineering in PrVO thin films
Deepak Kumar, Adrian David, Arnaud Fouchet +8
Transition-metal oxides with an ABO perovskite structure exhibit strongly entangled structural and electronic degrees of freedom and thus, one expects to unveil exotic phases a…