58 research outputs found
Theoretical approach to resonant inelastic x-ray scattering in iron-based superconductors at the energy scale of the superconducting gap
We develop a phenomenological theory to predict the characteristic features
of the momentum-dependent scattering amplitude in resonant inelastic x-ray
scattering (RIXS) at the energy scale of the superconducting gap in iron-based
superconductors. Taking into account all relevant orbital states as well as
their specific content along the Fermi surface we evaluate the charge and spin
dynamical structure factors for the compounds LaOFeAs and LiFeAs, based on
tight-binding models which are fully consistent with recent angle-resolved
photoemission spectroscopy (ARPES) data. We find a characteristic intensity
redistribution between charge and spin dynamical structure factors which
discriminates between sign-reversing and sign-preserving quasiparticle
excitations. Consequently, our results show that RIXS spectra can distinguish
between and wave gap functions in the singlet pairing case. In
addition, we find that an analogous intensity redistribution at small momenta
can reveal the presence of a chiral -wave triplet pairing.Comment: 12 pages, 5 figure
Heavy fermion properties of the Kondo Lattice model
We study the S = 1/2 Kondo lattice model which is widely used to describe heavy fermion behavior. In conventional treatments of the model the Kondo interaction is decoupled in favour of a hybridization of conduction and localized f electrons. However, such an approximation breaks the local gauge symmetry and implicates that the local f-occupation is no longer conserved. To avoid these problems, we use in this work an alternative approach to the model based on the Projective Renormalization Method (PRM). Thereby, within the conduction electron spectral function we identify the lattice Kondo resonance as an almost flat excitation near the Fermi surface which is composed of conduction electron creation operators combined with localized spin fluctuations. This leads to an alternative description of the Kondo resonance without having to resort to an artificial symmetry breaking
Unconventional superconductivity and interaction induced Fermi surface reconstruction in the two-dimensional Edwards model
We study the competition between unconventional superconducting pairing and
charge density wave (CDW) formation for the two-dimensional Edwards Hamiltonian
at half filling, a very general two-dimensional transport model in which
fermionic charge carriers couple to a correlated background medium. Using the
projective renormalization method we find that a strong renormalization of the
original fermionic band causes a new hole-like Fermi surface to emerge near the
center of the Brillouin zone, before it eventually gives rise to the formation
of a charge density wave. On the new, disconnected parts of the Fermi surface
superconductivity is induced with a sign-changing order parameter. We discuss
these findings in the light of recent experiments on iron-based oxypnictide
superconductors.Comment: 13 pages, 2 figure
Berry curvature unravelled by the Nernst effect in MnGe
The discovery of topological quantum materials represents a striking
innovation in modern condensed matter physics with remarkable fundamental and
technological implications. Their classification has been recently extended to
topological Weyl semimetals, i.e., solid state systems which exhibit the
elusive Weyl fermions as low-energy excitations. Here we show that the Nernst
effect can be exploited as a sensitive probe for determining key parameters of
the Weyl physics, applying it to the non-collinear antiferromagnet MnGe.
This compound exhibits anomalous thermoelectric transport due to enhanced Berry
curvature from Weyl points located extremely close to the Fermi level. We
establish from our data a direct measure of the Berry curvature at the Fermi
level and, using a minimal model of a Weyl semimetal, extract for the first
time the Weyl point energy and their distance in momentum-space
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Disorder-induced coupling of Weyl nodes in WTe2
The finite coupling between Weyl nodes due to residual disorder is investigated by magnetotransport studies in WTe2. The anisotropic scattering of quasiparticles is evidenced from classical and quantum transport measurements. A theoretical approach using the real band structure is developed in order to calculate the dependence of the scattering anisotropy with the correlation length of the disorder. A comparison between theory and experiments reveals a short correlation length in WTe2 (ξ∼5 nm). This result implies a significant coupling between Weyl nodes and other bands. Our study thus shows that a finite intercone scattering rate always exists in weakly disordered type-II Weyl semimetals, such as WTe2, which strongly suppresses topologically nontrivial properties
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