arXiv subjects

Sergej Y. Savrasov

Publications and source records attributed to Sergej Y. Savrasov.

8 recordsLinked to original sources

arXiv2010

Electronic Structure Calculations of Magnetic Exchange Interactions in Europium Monochalcogenides

Using a combination of local spin density and Hubbard 1 approximations we study the mechansim of exchange interacion in EuX (X=O, S, Se and Te). We reproduce known experimental results about bulk modulus, critical pressure for structural phase transition, magnetic ordering temperature, spin--wave dispersions as well as momentum-- and tempearuture--dependent band shift. Our numerical results show pressure induced competition between the hybirization enhanced exchange interaction and Kondo--like coupling in EuO. Possible ways to enhance T_{c} are discussed.

cond-mat.mtrl-sci↗

arXiv2009

Calculated Magnetic Exchange Interactions in High-Temeprature Superconductors

Using a first principles linear response approach, we study the magnetic exchange interactions J for a series of superconducting cuprates. We reproduce the observed spin-wave dispersions together with other experimental trends, and show that different cuprates have similar J's regardless their T$_{c}$. The nearest neighbor J is not sensitive to the hole-doping, which agrees with recent experiments. For the undoped cuprates, the second nearest neighbor J is ferromagnetic, but changes its sign with hole-doping. We also find that, in contrast to the hopping integral, the exchange interaction is not sensitive to the position of apical oxygen. To see the effect of the long--range nature of the exchange on the superconducting T$_{c}$, we study the dynamical spin susceptibility $χ(q,ω)$ within the t--J model using a dynamical cluster approximation.

cond-mat.str-el↗

arXiv2006

Calculations of Magnetic Exchange Interactions in Mott--Hubbard Systems

An efficient method to compute magnetic exchange interactions in systems with strong correlations is introduced. It is based on a magnetic force theorem which evaluates linear response due to rotations of magnetic moments and uses a novel spectral density functional framework combining our exact diagonalization based dynamical mean field and local density functional theories. Applications to spin waves and magnetic transition temperatures of 3d metal mono--oxides as well as high--T_{c} superconductors are in good agreement with experiment.

cond-mat.str-el↗

arXiv2005

Many-Body Electronic Structure of Americium metal

We report computer based simulations of energetics, spectroscopy and electron-phonon interaction of americium using a novel spectral density functional method. This approach gives rise to a new concept of a many-body electronic structure and reveals the unexpected mixed valence regime of Am 5f6 electrons which under pressure acquire the 5f7 valence state. This explains unique properties of Am and addresses the fundamental issue of how the localization delocalization edge is approached from the localized side in a closed shell system.

cond-mat.str-el↗

arXiv2004

The alpha to gamma transition in Ce: a theoretical view from optical spectroscopy

Using a novel approach to calculate optical properties of strongly correlated systems, we address the old question of the physical origin of the alpha to gamma transition in Ce. We find that the Kondo collapse model describes the optical data better than the Mott transition picture. Our results compare well with existing thin--film experiments. We predict the full temperature dependence of the optical spectra and find the development of a pseudogap around 0.6 eV in the vicinity of the alpha to gamma phase transition.

cond-mat.str-el↗

arXiv2001

Importance of Correlation Effects on Magnetic Anisotropy in Fe and Ni

We calculate magnetic anisotropy energy of Fe and Ni by taking into account the effects of strong electronic correlations, spin-orbit coupling, and non-collinearity of intra--atomic magnetization. The LDA+U method is used and its equivalence to dynamical mean--field theory in the static limit is emphasized. Both experimental magnitude of MAE and direction of magnetization are predicted correctly near U=1.9 eV, J=1.2 eV for Ni and U=1.2 eV, J=0.8 eV for Fe. Correlations modify the one--electron spectra which are now in better agreement with experiments.

cond-mat.str-el↗

arXiv2000

Cellular Dynamical Mean Field Approach to Strongly Correlated Systems

We propose a cellular version of dynamical-mean field theory which gives a natural generalization of its original single-site construction and is formulated in different sets of variables. We show how non-orthogonality of the tight-binding basis sets enters the problem and prove that the resulting equations lead to manifestly causal self energies.

cond-mat.str-el↗

arXiv2000

Importance of Correlation Effects on Magnetic Anisotropy in Fe and Ni

We calculate magnetic anisotropy energy of Fe and Ni by taking into account the effects of strong electronic correlations, spin-orbit coupling, and non-collinearity of intra-atomic magnetization. The LDA+U method is used and its equivalence to dynamical mean-field theory in the static limit is emphasized. Both experimental magnitude of MAE and direction of magnetization are predicted correctly near U=4 eV for Ni and U=3.5 eV for Fe. Correlations modify one-electron spectra which are now in better agreement with experiments.

cond-mat.str-el↗