114 research outputs found
Lifshitz transitions and quasiparticle de-renormalization in YbRhSi
We study the effect of magnetic fields up to 15 T on the heavy fermion state
of YbRhSi via Hall effect and magnetoresistance measurements down to 50
mK. Our data show anomalies at three different characteristic fields. We
compare our data to renormalized band structure calculations through which we
identify Lifshitz transitions associated with the heavy fermion bands. The Hall
measurements indicate that the de-renormalization of the quasiparticles, {\it
i.e} the destruction of the local Kondo singlets, occurs smoothly while the
Lifshitz transitions occur within rather confined regions of the magnetic
field.Comment: 7 pages, 5 figure
Interplay between Kondo suppression and Lifshitz transitions in YbRhSi at high magnetic fields
We investigate the magnetic field dependent thermopower, thermal
conductivity, resistivity and Hall effect in the heavy fermion metal YbRh2Si2.
In contrast to reports on thermodynamic measurements, we find in total three
transitions at high fields, rather than a single one at 10 T. Using the Mott
formula together with renormalized band calculations, we identify Lifshitz
transitions as their origin. The predictions of the calculations show that all
experimental results rely on an interplay of a smooth suppression of the Kondo
effect and the spin splitting of the flat hybridized bands.Comment: 5 pages, 4 figure
Spectral functions for strongly correlated 5f-electrons
We calculate the spectral functions of model systems describing 5f-compounds
adopting Cluster Perturbation Theory. The method allows for an accurate
treatment of the short-range correlations. The calculated excitation spectra
exhibit coherent 5f bands coexisting with features associated with local
intra-atomic transitions. The findings provide a microscopic basis for partial
localization. Results are presented for linear chains.Comment: 10 Page
Quantum Resistive Transition in Type II Superconductors under Magnetic Field
It is shown that, within a Ginzburg-Landau (GL) formalism, the
superconducting fluctuation is insulating at zero temperature even if the
fluctuation dynamics is metallic (dissipative). Based on this fact, the low
temperature behavior of the -line and the resistivity curves near a
zero temperature transition are discussed. In particular, it is pointed out
that the neglect of quantum fluctuations in data analysis of the dc resistivity
may lead to an under-estimation of the values near zero temperature.Comment: 7 page
Electronic structure of spinel-type LiV_2O_4
The band structure of the cubic spinel compound LiV_2O_4, which has been
reported recently to show heavy Fermion behavior, has been calculated within
the local-density approximation using a full-potential version of the linear
augmented-plane-wave method. The results show that partially-filled V 3d bands
are located about 1.9 eV above the O 2p bands and the V 3d bands are split into
a lower partially-filled t_{2g} complex and an upper unoccupied e_{g} manifold.
The fact that the conduction electrons originate solely from the t_{2g} bands
suggests that the mechanism for the mass enhancement in this system is
different from that in the 4f heavy Fermion systems, where these effects are
attributed to the hybridization between the localized 4f levels and itinerant
spd bands.Comment: 5 pages, revte
Shubnikov-de Haas measurements on LuRh2Si2
We present Shubnikov-de Haas measurements on LuRh2Si2, the non-magnetic
reference compound to the prototypical heavy-fermion system YbRh2Si2. We find
an extensive set of orbits with clear angular dependences. Surprisingly, the
agreement with non-correlated band structure calculations is limited. This may
be related to an uncertainty in the calculations arising from a lack of
knowledge about the exact Si atom position in the unit cell. The data on
LuRh2Si2 provide an extensive basis for the interpretation of measurements on
YbRh2Si2 indicative of discrepancies between the high-field Fermi surface of
YbRh2Si2 and the "small" Fermi surface configuration.Comment: 5 page
Kondo Effect in a Metal with Correlated Conduction Electrons: Diagrammatic Approach
We study the low-temperature behavior of a magnetic impurity which is weakly
coupled to correlated conduction electrons. To account for conduction electron
interactions a diagrammatic approach in the frame of the 1/N expansion is
developed. The method allows us to study various consequences of the conduction
electron correlations for the ground state and the low-energy excitations. We
analyse the characteristic energy scale in the limit of weak conduction
electron interactions. Results are reported for static properties (impurity
valence, charge susceptibility, magnetic susceptibility, and specific heat) in
the low-temperature limit.Comment: 16 pages, 9 figure
Quasiparticle Interactions for f-Impurity Anderson Model with Crystalline-Electric-Field: Numerical Renormalization Group Study
The aspect of the quasiparticle interaction of a local Fermi liquid, the
impurity version of f-based heavy fermions, is studied by the Wilson
numerical renormalization group method. In particular, the case of the
f-singlet crystalline-electric-field ground state is investigated assuming
the case of UPt with the hexagonal symmetry. It is found that the
interorbital interaction becomes larger than the intraorbital one in contrast
to the case of the bare Coulomb interaction for the parameters relevant to
UPt. This result offers us a basis to construct a microscopic theory of the
superconductivity of UPt where the interorbital interactions are expected
to play important roles.Comment: 9 pages, 5 figure
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