Plenarvorträge - DPG-Tagungen

Tiefe Temperaturen Donnerstag
A current route to describing the physical properties of real materials
with strongly correlated electrons, is to derive a low-energy Hubbard
Hamiltonian using Wannier-functions obtained by a density-functional
calculation, and to solve it using the dynamical mean-field approximation.
As an example, we consider the series of 3d 1 orthorhombic perovskites
SrVO3, CaVO3, LaTiO3, and YTiO3, in which an increasing tilting and
rotation of the oxygen octahedron is accompanied by an increasing localization
of the t2g electron; the vanadates are mass-enhanced metals
and the titanates Mott insulators. We show that cation covalency, rather
than ion-sizes and JT-distortions, is the controlling mechanism.
Hauptvortrag TT 28.4 Do 15:15 H20
Wannier functions formalism and DMFT — •V. I. Anisimov —
Institute of Metal Physics, Russian Academy of Science - Ural Division,
620219 Ekaterinburg, GSP-170, Russia
The Hubbard model is expressed in a site-centered, atomic-like orbital
basis set which is usually not explicitly defined. We propose a method for
calculating the explicit form of the Wannier functions and also a procedure
of projecting the full-orbital Hamiltonian on the Wannier function
subspace defined for the partially filled bands of interest. The few (Wannier)
orbital Hamiltonian calculated in this way is used for DMFT(QMC)
calculations. The self-energy operator defined in Wannier function basis
obtained in such calculations is converted back into the full-orbital Hilbert
space and is used for the calculation of the total and partial densities
of states of real materials. Results obtained by this method for SrVO3
and V2O3 are reported.
Fachvortrag TT 28.5 Do 15:40 H20
Multi-Band Gutzwiller Method for Transition metals and Compounds:
Magnetism, Fermi Surfaces and Spin-Orbit Coupling —
•Werner Weber1 , Jörg Bünemann2 , and Florian Gebhard2 — 1Institu für Physik, Universität Dortmund — 2Fachbereich Physik,
Philipps Universität Marburg
The multi-band Gutzwiller method is used to calculate ground state
properties and quasi-particle energy bands of magnetic transition metals
and compounds. Our scheme utilizes single-particle model Hamiltonians
with an s, p, and d spin orbital basis, obtained from density functional
theory studies. For cubic, ferromagnetic Nickel our results even correctly
reproduce details of the quasi particle bands near the Fermi surface. In
the case of low crystal symmetry and/or of a large orbital basis, the hopping
reduction factors q(σ, σ ′
)of the effective single particle Hamiltonian
have a matrix form in the space of the spin orbitals σ. Furthermore,
additional variational parameters appear, which act on the eigenvectors
of the atomic multiplet states. Incorporation of spin-orbit coupling for
Nickel results, via the off-diagonal q(σ, σ ′
), in spin-flip hopping terms of
the effective Hamiltonian. These terms considerably enhance the value of
the orbital magnetic moment over the Hartree-Fock limit, so that good
agreement with experiment is achieved.
16:05 Pause
Fachvortrag TT 28.6 Do 16:30 H20
Partial localization, dual nature of 5f electrons and heavy fermions
in U compounds — •G. Zwicknagl — Institut fuer Mathematische
Physik, TU Braunschweig, D-38106 Braunschweig
There is growing evidence that actinide ions may have localized as well
as delocalized 5f electrons. These observations form the basis of the dual
model which provides a microscopic theory for the heavy quasiparticles
in U compounds. In the present talk, I shall present results for the Fermi
surface and effective masses in U-based heavy fermion compounds.
In addition, I shall show how the dual character of the 5f electrons may
arise from the interplay between (effective) hopping and Hund’s rule correlations.
Fachvortrag TT 28.7 Do 16:55 H20
Realistic Description of Strongly Correlated Materials — •A. I.
Lichtenstein — University of Nijmegen, The Netherlands
Local density approximation (LDA) of density functional theory has
been highly successful for electronic structure calculations of different
non-correlated ystems. The LDA scheme quite often failed for strongly
correlated materials containing transition metals and rare-earth elements
with complicated charge, spin and orbital fluctuations. Dynamical
mean field theory (DMFT) in combination with the first-principle LDA
scheme can be a starting point for a realistic description of various correlated
electron materials. We discuss a competition between the local
Coulomb interaction and chemical bonding as well as effects of of nonlocal
Coulomb interactions for transiton metal oxides within a cluster
LDA+DMFT scheme.
Fachvortrag TT 28.8 Do 17:20 H20
The orbital state and magnetic properties of LiV2O4: Recent insight
from LDA+DMFT — •Th. Pruschke — Institute for Theoretical
Physics, University of Goettingen, D-37077 Goettingen
LiV2O4 is considered to be the first system showing heavy fermion
physics without f electrons. This behaviour is even more surprising if one
takes into account that the average occupancy of the Vanadium d-states
is 1.5 electrons/V, i.e. the system seems to be rather in the mixed-valence
than in the classical Kondo regime typically required for heavy-fermions.
Within the framework of DMFT+LDA we show that this part of the
puzzle can be resolved in a rather surprising manner, namely by localizing
one of the d-electrons in the non-degenerate A1g level of the t2g
manifold, while 0.5 electrons/V in the twofold degenerate Eg level remain
itinerant. The existence of precisley one localized and 0.5 delocalized electrons
per Vanadium leads to very specific theoretical predictions about
the magnetic properties of LiV2O4, which can be compared to experiment.
In particular, the effective magnetic moment deduced from the
high-temperature Curie behavior and inelastic, spin-polarized neutron
scattering support our conjecture.
Fachvortrag TT 28.9 Do 17:45 H20
Coulomb Correlations in Multi-Orbital Materials — •A. Liebsch
— Forschungszentrum Juelich, D-52425 Juelich
The influence of local Coulomb interactions on the electronic properties
of transition metal oxides is investigated within the Dynamical Mean
Field Theory and multi-orbital Quantum Monte Carlo method. In materials
such as VO2, SrVO3, and Sr2RuO4 the quasi-particle spectra exhibit
correlation features which cannot be understood within density functional
theory. In particular, we discuss the enhancement of correlation effects
due to orbital polarization induced by Peierls distortion, the enhancement
of correlations at surfaces due to band narrowing, and the possibility of
observing multi-gapped Mott insulators.
TT 29 Quantenkohärenz und Quanteninformationssysteme II
Zeit: Donnerstag 14:30–18:00 Raum: H19
TT 29.1 Do 14:30 H19
Experimental investigations of superconducting qubits using a
resonant tank circuit. — •Il’ichev Evgeni — IPHT, A. Einstein
Str. 9, 07745 Jena, Germany
On-chip LC tank circuits with a high quality factor 2000 can be effective
probes of superconducting qubits, to which they are coupled inductively.
Resonant properties of the circuits are strongly dependent on the
qubit’s effective susceptibility that allows to measure the qubit’s tunneling
amplitude and decoherence rate. This setup trades off time control
for sensitivity at the LC-resonance frequency. As a result, a weak coupling
to the qubit suffices, which helps to reduce measurement-induced
decoherence in the system. Weak continuous measurements of Rabi os-
cillations and a detection of Landau-Zener transitions will be discussed
together with low-frequency measurements of the energy splitting in the
flux qubit.
TT 29.2 Do 14:45 H19
Quantum dissociation of a vortex-antivortex pair in a long
Josephson junction — •M.V. Fistul 1 , A. Wallraff 2 , Y. Koval
1 , A. Lukashenko 1 , B.A. Malomed 3 , and A.V. Ustinov 1 —
1 Physikalisches Institut III, Universität Erlangen-Nürnberg, 91058 Erlangen,
Germany — 2 Dept. Applied Physics, Yale University, New Haven,
CT 06520 USA — 3 Tel Aviv University, Tel-Aviv, 69978 Israel
Thermal and quantum dissociation of a single vortex-antivortex (VAV)