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ABSTRACT: The crystal structure and magnetic ordering pattern of PdAs2O6 were
investigated by neutron powder diffraction. While the magnetic structure of
PdAs2O6 is identical to the one of its isostructural 3d-homologue NiAs2O6, its
N\'{e}el temperature (140 K) is much higher than the one of NiAs2O6 (30 K).
This is surprising in view of the long distance and indirect exchange path
between the magnetic Pd$^{2+}$ ions. Density functional calculations yield
insight into the electronic structure and the geometry of the exchange-bond
network of both PdAs2O6 and NiAs2O6, and provide a semi-quantitative
explanation of the large amplitude difference between their primary exchange
interaction parameters.
03/2012;
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M Uchida,
K Ishizaka,
P. Hansmann,
X. Yang,
M. Sakano,
J. Miyawaki,
R. Arita,
Y Kaneko,
Y Takata,
M Oura,
A. Toschi,
K. Held,
A. Chainani, O. K. Andersen,
S Shin,
Y Tokura
[show abstract]
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ABSTRACT: The three-dimensional Fermi surface structure of hole-doped metallic layered
nickelate Eu2-xSrxNiO4 (x=1.1), an important counterpart to the isostructural
superconducting cuprate La2-xSrxCuO4, is investigated by energy-dependent
soft-x-ray angle-resolved photoemission spectroscopy. In addition to a large
cylindrical hole Fermi surface analogous to the cuprates, we observe a
Gamma-centered 3z2-r2-derived small electron pocket. This finding demonstrates
that in the layered nickelate the 3z2-r2 band resides close to the x2-y2 one in
energy. The resultant multi-band feature with varying orbital character as
revealed may strongly work against the emergence of the high-temperature
superconductivity.
12/2011;
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ABSTRACT: Reduced dimensionality and strong electronic correlations, which are among
the most important ingredients for cupratelike high-Tc superconductivity,
characterize also the physics of nickelate-based heterostructures. Starting
from the local-density approximation we arrive at a simple two-band model for
quasi-two-dimensional 2D LaNiO3 /LaAlO3 heterostructures and extend it by
introducing an appropriate hopping in the z direction to describe the
dimensional crossover to three dimensions 3D. Using dynamical mean-field
theory, we study the effects of electronic correlations with increasing
interaction strength along the crossover from 2D to 3D. Qualitatively, the
effects of electronic correlations are surprisingly similar, albeit
quantitatively larger interaction strengths are required in three dimensions
for getting a Mott-Hubbard insulating state. The exchange parameters of an
effective Kugel-Khomskii-type spin-orbital model are also derived and reveal
strong antiferromagnetic tendencies.
11/2011;
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Annalen der Physik 01/2011; 523(1‐2):8 - 50. · 0.84 Impact Factor
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M Uchida,
K Ishizaka,
P Hansmann,
Y Kaneko,
Y Ishida,
X Yang,
R Kumai,
A Toschi,
Y Onose,
R Arita,
K Held, O K Andersen,
S Shin,
Y Tokura
[show abstract]
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ABSTRACT: We have investigated charge dynamics and electronic structures for single crystals of metallic layered nickelates, R(2-x)Sr(x)NiO4 (R = Nd, Eu), isostructural to La(2-x)Sr(x)CuO4. Angle-resolved photoemission spectroscopy on the barely metallic Eu(0.9)Sr(1.1)NiO4 (R = Eu, x = 1.1) has revealed a large hole surface of x2-y2 character with a high-energy pseudogap of the same symmetry and comparable magnitude with those of underdoped (x<0.1) cuprates, although the antiferromagnetic interactions are 1 order of magnitude smaller. This finding strongly indicates that the momentum-dependent pseudogap feature in the layered nickelate arises from the real-space charge correlation.
Physical Review Letters 01/2011; 106(2):027001. · 7.37 Impact Factor
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M Uchida,
K Ishizaka,
P. Hansmann,
Y Kaneko,
Y Ishida,
X. Yang,
R Kumai,
A. Toschi,
Y Onose,
R. Arita,
K. Held, O. K. Andersen,
S Shin,
Y Tokura
[show abstract]
[hide abstract]
ABSTRACT: We have investigated charge dynamics and electronic structures for single
crystals of metallic layered nickelates, R2-xSrxNiO4 (R=Nd, Eu), isostructural
to La2-xSrxCuO4. Angle-resolved photoemission spectroscopy on the
barely-metallic Eu0.9Sr1.1NiO4 (R=Eu, x=1.1) has revealed a large hole surface
of x2-y2 character with a high-energy pseudogap of the same symmetry and
comparable magnitude with those of underdoped (x<0.1) cuprates, although the
antiferromagnetic interactions are one order of magnitude smaller. This finding
strongly indicates that the momentum-dependent pseudogap feature in the layered
nickelate arises from the real-space charge correlation.
12/2010;
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ABSTRACT: BiOCuS is a band insulator that becomes metallic upon hole doping. Superconductivity was recently reported in doped BiOCu$_{1-x}$S and attributed to spin fluctuations as a pairing mechanism. Based on first principles calculations of the electron-phonon coupling, we argue that the latter is very strong in this material, and probably drives superconductivity, which is however strongly depressed by the proximity to magnetism. We find however that BiOCu$_{1-x}$S is a quite unique compound where both a conventional phonon-driven and an unconventional triplet superconductivity are possible, and compete with each other. We argue that, in this material, it should be possible to switch from conventional to unconventional superconductivity by varying such parameters as doping or pressure.
12/2010;
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S. Lupi,
L. Baldassarre,
B. Mansart,
A. Perucchi,
A Barinov,
P Dudin,
E. Papalazarou,
F. Rodolakis,
J. P. Rueff,
J P Itié, [......],
D. Nicoletti,
P Postorino,
P. Hansmann,
N. Parragh,
A. Toschi,
T. Saha-Dasgupta, O. K. Andersen,
G. Sangiovanni,
K. Held,
M. Marsi
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ABSTRACT: V2O3 is the prototype system for the Mott transition, one of the most fundamental phenomena of electronic correlation. Temperature, doping or pressure induce a metal to insulator transition (MIT) between a paramagnetic metal (PM) and a paramagnetic insulator (PI). This or related MITs have a high technological potential, among others for intelligent windows and field effect transistors. However the spatial scale on which such transitions develop is not known in spite of their importance for research and applications. Here we unveil for the first time the MIT in Cr-doped V2O3 with submicron lateral resolution: with decreasing temperature, microscopic domains become metallic and coexist with an insulating background. This explains why the associated PM phase is actually a poor metal. The phase separation can be associated with a thermodynamic instability near the transition. This instability is reduced by pressure which drives a genuine Mott transition to an eventually homogeneous metallic state. Comment: Paper plus supplementary material
11/2010;
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S Lupi,
L Baldassarre,
B Mansart,
A Perucchi,
A Barinov,
P Dudin,
E Papalazarou,
F Rodolakis,
J-P Rueff,
J-P Itié, [......],
D Nicoletti,
P Postorino,
P Hansmann,
N Parragh,
A Toschi,
T Saha-Dasgupta, O K Andersen,
G Sangiovanni,
K Held,
M Marsi
[show abstract]
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ABSTRACT: V(2)O(3) is the prototype system for the Mott transition, one of the most fundamental phenomena of electronic correlation. Temperature, doping or pressure induce a metal-to-insulator transition (MIT) between a paramagnetic metal (PM) and a paramagnetic insulator. This or related MITs have a high technological potential, among others, for intelligent windows and field effect transistors. However the spatial scale on which such transitions develop is not known in spite of their importance for research and applications. Here we unveil for the first time the MIT in Cr-doped V(2)O(3) with submicron lateral resolution: with decreasing temperature, microscopic domains become metallic and coexist with an insulating background. This explains why the associated PM phase is actually a poor metal. The phase separation can be associated with a thermodynamic instability near the transition. This instability is reduced by pressure, that promotes a genuine Mott transition to an eventually homogeneous metallic state.
Nature Communications 11/2010; 1:105. · 7.40 Impact Factor
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A. P. Petrović,
R. Lortz,
G. Santi,
M. Decroux,
H. Monnard,
L. Boeri, O. K. Andersen,
J. Kortus,
D. Salloum,
P. Gougeon,
M. Potel,
Ø. Fischer
[show abstract]
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ABSTRACT: We present electronic structure calculations, electrical resistivity data and
the first specific heat measurements in the normal and superconducting states
of quasi-one-dimensional M2Mo6Se6 (M = Tl, In, Rb). Rb2Mo6Se6 undergoes a
metal-insulator transition at ~170K: electronic structure calculations indicate
that this is likely to be driven by the formation of a dynamical charge density
wave. However, Tl2Mo6Se6 and In2Mo6Se6 remain metallic down to low temperature,
with superconducting transitions at Tc = 4.2K and 2.85K respectively. The
absence of any metal-insulator transition in these materials is due to a larger
in-plane bandwidth, leading to increased inter-chain hopping which suppresses
the density wave instability. Electronic heat capacity data for the
superconducting compounds reveal an exceptionally low density of states DEF =
0.055 states eV^-1 atom^-1, with BCS fits showing 2Delta/kBTc >= 5 for
Tl2Mo6Se6 and 3.5 for In2Mo6Se6. Modelling the lattice specific heat with a set
of Einstein modes, we obtain the approximate phonon density of states F(w).
Deconvolving the resistivity for the two superconductors then yields their
electron-phonon transport coupling function a^2F(w). In Tl2Mo6Se6 and
In2Mo6Se6, F(w) is dominated by an optical "guest ion" mode at ~5meV and a set
of acoustic modes from ~10-30meV. Rb2Mo6Se6 exhibits a similar spectrum;
however, the optical phonon has a lower intensity and is shifted to ~8meV.
Electrons in Tl2Mo6Se6 couple strongly to both sets of modes, whereas In2Mo6Se6
only displays significant coupling in the 10-18meV range. Although pairing is
clearly not mediated by the guest ion phonon, we believe it has a beneficial
effect on superconductivity in Tl2Mo6Se6, given its extraordinarily large
coupling strength and higher Tc compared to In2Mo6Se6.
07/2010;
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ABSTRACT: Significant progress in the theoretical description of Mott-Hubbard metal-to-insulator transitions has been made in the last years, especially thanks to the LDA+DMFT approach (local density approximation + dynamical mean field theory). Obviously the main attention has been focused on the transition itself, as, for example, in the textbook case of the Cr-doped V2O3. As we discuss here, however, also the study of the insulating phase, characterized by the opening of a visible Mott-Hubbard gap in the spectral functions is far from being trivial: Strong-correlation effects make this phase strongly sensitive to small changes of external parameters, much more than one would expect for an insulator. In this situation, requiring a full consistency of the theoretical calculations with data from different spectroscopies may provide the most precise estimate for the local Coulomb interaction U in the LDA+DMFT approach.
Journal of Physics Conference Series 02/2010; 200(1):012208.
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F Rodolakis,
P Hansmann,
J-P Rueff,
A Toschi,
M W Haverkort,
G Sangiovanni,
A Tanaka,
T Saha-Dasgupta, O K Andersen,
K Held,
M Sikora,
I Alliot,
J-P Itié,
F Baudelet,
P Wzietek,
P Metcalf,
M Marsi
[show abstract]
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ABSTRACT: The changes in the electronic structure of V2O3 across the metal-insulator transition induced by temperature, doping, and pressure are identified using high resolution x-ray absorption spectroscopy at the V pre-K edge. Contrary to what has been taken for granted so far, the metallic phase reached under pressure is shown to differ from the one obtained by changing doping or temperature. Using a novel computational scheme, we relate this effect to the role and occupancy of the a{1g} orbitals. This finding unveils the inequivalence of different routes across the Mott transition in V2O3.
Physical Review Letters 01/2010; 104(4):047401. · 7.37 Impact Factor
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ABSTRACT: Using the local density approximation and its combination with dynamical mean-field theory, we show that electronic correlations induce a single-sheet, cupratelike Fermi surface for hole-doped 1/1 LaNiO3/LaAlO3 heterostructures, even though both eg orbitals contribute to it. The Ni 3d3z(2)-1} orbital plays the role of the axial Cu 4s-like orbital in the cuprates. These two results indicate that "orbital engineering" by means of heterostructuring should be possible. As we also find strong antiferromagnetic correlations, the low-energy electronic and spin excitations in nickelate heterostructures resemble those of high-temperature cuprate superconductors.
Physical Review Letters 08/2009; 103(1):016401. · 7.37 Impact Factor
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ABSTRACT: Using muffin-tin orbital (MTO) based NMTO-downfolding procedure within the framework of local density approximation, we construct the Wannier orbitals for the $t_{2g}$ manifold of bands in V2O3 in the paramagnetic phase. The real space representation of the one-electron Hamiltonian in the constructed Wannier function basis shows that, contrary to the popular belief, the in-plane hopping interactions are as important as the vertical pair hopping. Following the language of Di Matteo {\it et.al.} [Phys. Rev. B 65, 054413 (2002)], this implies, the problem of V2O3 falls in the atomic regime rather than in the molecular regime. We have also repeated our construction procedure in the low temperature monoclinic phase, for which the changes in hopping interactions are found not to be dramatic. Comment: 22 pages, 15 figures, 6 Tables
07/2009;
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[show abstract]
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ABSTRACT: Using a combined local density functional theory (LDA-DFT) and quantum Monte Carlo (QMC) dynamic cluster approximation approach, the parameter dependence of the superconducting transition temperature Tc of several single-layer hole-doped cuprate superconductors with experimentally very different Tcmax is investigated. The parameters of two different three-band Hubbard models are obtained using the LDA and the downfolding Nth-order muffin-tin orbital technique with N=0 and 1 respectively. QMC calculations on 4-site clusters show that the d-wave transition temperature Tc depends sensitively on the parameters. While the N=1 MTO basis set which reproduces all three $pd\sigma$ bands leads to a d-wave transition, the N=0 set which merely reproduces the LDA Fermi surface and velocities does not.
07/2008;
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ABSTRACT: Ab initio calculation of the electronic properties of materials is a major challenge for solid-state theory. Whereas 40 years' experience has proven density-functional theory (DFT) in a suitable form, e.g. local approximation (LDA), to give a satisfactory description when electronic correlations are weak, materials with strongly correlated electrons, say d- or f-electrons, remain a challenge. Such materials often exhibit 'colossal' responses to small changes of external parameters such as pressure, temperature, and magnetic field, and are therefore most interesting for technical applications. Encouraged by the success of dynamical mean-field theory (DMFT) in dealing with model Hamiltonians for strongly correlated electron systems, physicists from the bandstructure and many-body communities have joined forces and developed a combined LDA+DMFT method for treating materials with strongly correlated electrons ab initio. As a function of increasing Coulomb correlations, this new approach yields a weakly correlated metal, a strongly correlated metal, or a Mott insulator. In this paper, we introduce the LDA+DMFT method by means of an example, LaMnO(3). Results for this material, including the 'colossal' magnetoresistance of doped manganites, are presented. We also discuss the advantages and disadvantages of the LDA+DMFT approach.
Journal of Physics Condensed Matter 02/2008; 20(6):064202. · 2.55 Impact Factor
