26 research outputs found
Extraordinary low-energy charge excitations in high- cuprate superconductors
Despite decades of intensive experimental and theoretical efforts, the
physics of cuprate high-temperature superconductors in general and, in
particular, the nature of the normal state, is still under debate. Numerous
collective excitations arising from the proximity to two other phases, magnetic
and charge density waves, make it difficult to elucidate their origin.
Here, we report our investigation of low-energy charge excitations in the
normal state. We find that the peculiarities of the electronic band structure
at low energies have a profound impact on the nature of the intraband
collective modes. We show that it gives rise to a new kind of modes with huge
intensity and non-Lorentzian spectral function in addition to well-known
collective excitations like conventional plasmons and spin-fluctuation. We
predict the existence of two such modes with maximal spectral weight in the
nodal and antinodal directions. Additionally, we found a long-living
quasi-one-dimensional plasmon becoming an intense soft mode over an extended
momentum range along the antinodal direction. These modes might explain some of
the RIXS data and might also contribute to the strong renormalization of
quasiparticles in high- cuprates in these regions.Comment: 9 pages, 5 figure
Influence of the van Hove singularity on the specific heat jump in BCS superconductors
Within the weak-coupling BCS scheme we derive a general form of the
coefficients in the Ginzburg-Landau expansion of the free energy of a
superconductor for the case of a Fermi level close to a van Hove singularity
(VHS). A simple expression for the influence of the VHS on the specific heat
jump is then obtained for the case where gaps for different bands are distinct
but nearly constant at the corresponding sheets of the Fermi surface.Comment: 8 pages, 2 figures, LaTeX2
The strength of frustration and quantum fluctuations in LiVCuO4
For the 1D-frustrated ferromagnetic J_1-J_2 model with interchain coupling
added, we analyze the dynamical and static structure factor S(k,omega), the
pitch angle phi of the magnetic structure, the magnetization curve of
edge-shared chain cuprates, and focus on LiCuVO4 for which neither a perturbed
spinon nor a spin wave approach can be applied. phi is found to be most
sensitive to the interplay of frustration and quantum fluctuations. For LiVCuO4
the obtained exchange parameters J are in accord with the results for a
realistic 5-band extended Hubbard model and LSDA + U predictions yielding
alpha=J_2/|J_1| about 0.75 in contrast to 5.5 > alpha > 1.42 suggested in the
literature. The alpha-regime of the empirical phi-values in NaCu2O2 and
linarite are considered, too.Comment: 7 pages, 7 figures, (1 figure added), improved text including also
the abstract (the present second version has been submitted to EPL
26.10.2011, so far with one missing first referee report
Electron-lattice interactions strongly renormalize the charge transfer energy in the spin-chain cuprate LiCuO
Strongly correlated insulators are broadly divided into two classes:
Mott-Hubbard insulators, where the insulating gap is driven by the Coulomb
repulsion on the transition-metal cation, and charge-transfer insulators,
where the gap is driven by the charge transfer energy between the
cation and the ligand anions. The relative magnitudes of and
determine which class a material belongs to, and subsequently the nature of its
low-energy excitations. These energy scales are typically understood through
the local chemistry of the active ions. Here we show that the situation is more
complex in the low-dimensional charge transfer insulator
LiCuO, where has a large non-electronic
component. Combining resonant inelastic x-ray scattering with detailed
modeling, we determine how the elementary lattice, charge, spin, and orbital
excitations are entangled in this material. This results in a large
lattice-driven renormalization of , which significantly reshapes the
fundamental electronic properties of LiCuO.Comment: Nature Communications, in pres
Determining the Short-Range Spin Correlations in Cuprate Chain Materials with Resonant Inelastic X-ray Scattering
We report a high-resolution resonant inelastic soft x-ray scattering study of
the quantum magnetic spin-chain materials Li2CuO2 and CuGeO3. By tuning the
incoming photon energy to the oxygen K-edge, a strong excitation around 3.5 eV
energy loss is clearly resolved for both materials. Comparing the experimental
data to many-body calculations, we identify this excitation as a Zhang-Rice
singlet exciton on neighboring CuO4-plaquettes. We demonstrate that the strong
temperature dependence of the inelastic scattering related to this high-energy
exciton enables to probe short-range spin correlations on the 1 meV scale with
outstanding sensitivity.Comment: 5 pages, 4 figure