0000000000023013
AUTHOR
Martin Jansen
showing 13 related works from this author
Gold(i) sulfide: Unusual bonding and an unexpected computational challenge in a simple solid
2019
We report the experimental high-pressure crystal structure and equation of state of gold(I) sulfide (Au2S) determined using diamond-anvil cell synchrotron X-ray diffraction. Our data shows that Au2S has a simple cubic structure with six atoms in the unit cell (four Au in linear, and two S in tetrahedral, coordination), no internal degrees of freedom, and relatively low bulk modulus. Despite its structural simplicity, Au2S displays very unusual chemical bonding. The very similar and relatively high electronegativities of Au and S rule out any significant metallic or ionic character. Using a simple valence bond (Lewis) model, we argue that the Au2S crystal possesses two different types of cov…
Structural and vibrational behavior of cubic Cu1.80(3)Se cuprous selenide, berzelianite, under compression
2020
[EN] We have performed an experimental study of the crystal structure and lattice dynamics of cubic Cu1.80(3)Se at ambient temperature and high pressures. Two reversible phase transitions were found at 2.9 and 8.7 GPa. The indexation of the angle-dispersive synchrotron x-ray diffraction patterns suggests a large orthorhombic cell and a monoclinic cell for the high-pressure phases. Raman measurements provide additional information on the local structure. The compressibility of the three ambient temperature phases has been determined and compared to that of other sulphides and selenides.
Pressure induced insulator/half-metal/metal transition in a strongly correlatedp-electron system
2012
Mixed-valent Rb${}_{4}$O${}_{6}$ provides an exceptional prototype material for studying the interplay between local correlations (Hubbard $U$) and electron kinetic energy ($W$) in the open $sp$-electron shell. Based on a first-principles calculation we show that depending on $U/W$ ratio, when tuned by external pressure, Rb${}_{4}$O${}_{6}$ exhibits a surprising sequence of phase transitions between strongly correlated antiferromagnetic insulator, ferromagnetic insulator ($U/W\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gg}\phantom{\rule{-0.16em}{0ex}}1$), moderately correlated ferromagnetic half-metal ($U/W\phantom{\rule{-0.16em}{0ex}}\ensuremath{\sim}\phantom{\rule{-0.16em}{0ex}}1$), and fin…
Challenge of magnetism in strongly correlated open-shell 2p systems.
2009
We report on theoretical investigations of the exotic magnetism in rubidium sesquioxide ${\mathrm{Rb}}_{4}{\mathrm{O}}_{6}$, a model correlated system with an open $2p$ shell. Experimental investigations indicated that ${\mathrm{Rb}}_{4}{\mathrm{O}}_{6}$ is a magnetically frustrated insulator. The frustration is explained here by electronic structure calculations that incorporate the correlation between the oxygen $2p$ electrons and deal with the mixed-valent oxygen. This leads to a physical picture where the symmetry is reduced because one third of the oxygen in ${\mathrm{Rb}}_{4}{\mathrm{O}}_{6}$ is nonmagnetic while the remaining two thirds assemble in antiferromagnetic arrangements. A d…
Lattice Instability and Competing Spin Structures in the Double Perovskite InsulatorSr2FeOsO6
2013
The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron-osmium layers along the tetragonal c axis. Neutron powder diffraction experiments, 57Fe Mossbauer spectra, and density functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom.
Lattice-Site-Specific Spin Dynamics in Double PerovskiteSr2CoOsO6
2014
Magnetic properties and spin dynamics have been studied for the structurally ordered double perovskite Sr2CoOsO6. Neutron diffraction, muon-spin relaxation, and ac-susceptibility measurements reveal two antiferromagnetic (AFM) phases on cooling from room temperature down to 2 K. In the first AFM phase, with transition temperature TN1=108 K, cobalt (3d7, S=3/2) and osmium (5d2, S=1) moments fluctuate dynamically, while their average effective moments undergo long-range order. In the second AFM phase below TN2=67 K, cobalt moments first become frozen and induce a noncollinear spin-canted AFM state, while dynamically fluctuating osmium moments are later frozen into a randomly canted state at…
Challenging the Prediction of Anionogenic Ferromagnetism for Rb4O6
2007
It has been suggested that Rb4O6 should be a half-metallic ferromagnet with the magnetic moment carried by the hyperoxide anions and a Curie temperature above room temperature. In the present work,...
Exotic magnetism in the alkali sesquioxidesRb4O6andCs4O6
2009
Among the various alkali oxides the sesquioxides ${\text{Rb}}_{4}{\text{O}}_{6}$ and ${\text{Cs}}_{4}{\text{O}}_{6}$ are of special interest. Electronic-structure calculations using the local spin-density approximation predicted that ${\text{Rb}}_{4}{\text{O}}_{6}$ should be a half-metallic ferromagnet, which was later contradicted when an experimental investigation of the temperature-dependent magnetization of ${\text{Rb}}_{4}{\text{O}}_{6}$ showed a low-temperature magnetic transition and differences between zero-field-cooled and field-cooled measurements. Such behavior is known from spin glasses and frustrated systems. ${\text{Rb}}_{4}{\text{O}}_{6}$ and ${\text{Cs}}_{4}{\text{O}}_{6}$ c…
Structural phase transitions on AgCuS stromeyerite mineral under compression.
2012
The structural behavior of mineral Stromeyerite, AgCuS, has been studied by means of angle-dispersive X-ray diffraction measurements up to 13 GPa and ab initio total-energy calculations. Two high-pressure phase transitions are found at 1.4 and 5.7 GPa, from the initial distorted Ni(2)In-type phase (AuRbS-type, RP, space group Cmc2(1)) through an anti-PbClF-type phase (HP1, space group P4/nmm) to a monoclinic distortion of this latter phase (HP2, space group P2(1)/m). The collapse of the metal-metal interatomic distances at the RP-HP1 transition suggests a stronger metallic behavior of the high-pressure phase. The compressibility of the lattice parameters and the equation of state of the fir…
Pressure-induced phase transformations in mineral chalcocite, Cu2S, under hydrostatic conditions
2014
Abstract High-pressure room-temperature angle-dispersive powder X-ray diffraction measurements on Cu2S chalcocite were performed up to 30 GPa using a diamond-anvil cell, He as pressure transmitting medium and synchrotron radiation. Two first-order phase transitions were found at 3.2 and 7.4 GPa. The indexation of the powder diffraction patterns suggests three different monoclinic cells for the low-pressure chalcocite and the two high-pressure phases. Subtle changes in the X-ray diffraction patterns suggest a third pressure-induced transition above 26 GPa. Structural parameters and compressibility are discussed and compared to those reported in a previous study on Cu2S nanowires.
Effect of pressure on superconductivity in NaAlSi
2012
The ternary superconductor NaAlSi, isostructural with LiFeAs, the ``111'' iron pnictide superconductor, is investigated under pressure. The structure remains stable up to 15 GPa. Resistivity and susceptibility measurements show an increase of ${T}_{c}$ up to 2 GPa, followed by a decrease until superconductivity disappears at 4.8 GPa. Band structure calculations show that pressure should have a negligible effect on the electronic structure and the Fermi surface and thus the disappearance of superconductivity under pressure must have a different origin. We compare the electronic structure of NaAlSi under pressure with that of nonsuperconducting isostructural NaAlGe.
A large-energy-gap oxide topological insulator based on the superconductor BaBiO3
2013
Mixed-valent perovskite oxides based on BaBiO3 (BBO) are, like cuperates, well-known high-Tc superconductors. Recent ab inito calculations have assigned the high-Tc superconductivity to a correlation-enhanced electron--phonon coupling mechanism, stimulating the prediction and synthesis of new superconductor candidates among mixed-valent thallium perovskites. Existing superconductivity has meant that research has mainly focused on hole-doped compounds, leaving electron-doped compounds relatively unexplored. Here we demonstrate through ab inito calculations that BBO emerges as a topological insulator (TI) in the electron-doped region, where the spin-orbit coupling (SOC) effect is significant.…
CSD 1784742: Experimental Crystal Structure Determination
2012
Related Article: Leslie Schoop, Lukas Müchler, Jennifer Schmitt, Vadim Ksenofontov, Sergey Medvedev, Jürgen Nuss, Frederick Casper, Martin Jansen, R. J. Cava, Claudia Felser|2012|Phys.Rev.B|86|174522|doi:10.1103/PhysRevB.86.174522