180 research outputs found
Magnetic response of nonmagnetic impurities in cuprates
A theory of the local magnetic response of a nonmagnetic impurity in a doped
antiferromagnet, as relevant to the normal state in cuprates, is presented. It
is based on the assumption of the overdamped collective mode in the bulk system
and on the evidence, that equal-time spin correlations are only weakly
renormalized in the vicinity of the impurity. The theory relates the Kondo-like
behavior of the local susceptibility to the anomalous temperature dependence of
the bulk magnetic susceptibility, where the observed increase of the Kondo
temperature with doping reflects the crossover to the Fermi liquid regime and
the spatial distribution of the magnetization is given by bulk
antiferromagnetic correlations.Comment: 5 pages, 3 figure
Freezing of spin dynamics in underdoped cuprates
The Mori's memory function approach to spin dynamics in doped
antiferromagnetic insulator combined with the assumption of temperature
independent static spin correlations and constant collective mode damping leads
to w/T scaling in a broad range. The theory involving a nonuniversal scaling
parameter is used to analyze recent inelastic neutron scattering results for
underdoped cuprates. Adopting modified damping function also the emerging
central peak in low-doped cuprates at low temperatures can be explained within
the same framework.Comment: 5 pages, 3 figure
Crossover to non-Fermi-liquid spin dynamics in cuprates
The antiferromagnetic spin correlation function , the staggered
spin susceptibility and the energy scale are studied numerically within the t-J model and the Hubbard
model, as relevant to cuprates. It is shown that , related to the
onset of the non-Fermi-liquid spin response at , is very low in
the regime below the 'optimum' hole doping , while it
shows a steep increase in the overdoped regime. A quantitative analysis of NMR
spin-spin relaxation-rate for various cuprates reveals a similar
behavior, indicating on a sharp, but continuous, crossover between a
Fermi-liquid and a non-Fermi-liquid behavior as a function of doping.Comment: 4 pages, 4 figures. Submitted to PR
Entanglement of two delocalised electrons
Several convenient formulae for the entanglement of two indistinguishable
delocalised spin-1/2 particles are introduced. This generalizes the standard
formula for concurrence, valid only in the limit of localised or
distinguishable particles. Several illustrative examples are given.Comment: 4 page
Double dispersion of the magnetic resonant mode in cuprates
The magnetic excitation spectra in the vicinity of the resonant peak, as
observed by inelastic neutron scattering in cuprates, are studied within the
memory-function approach. It is shown that at intermediate doping the
superconducting gap induces a double dispersion of the peak, with an anisotropy
rotated between the downward and upward branch. Similar behavior, but with a
spin-wave dispersion at higher energies, is obtained for the low-doping case
assuming a large pairing pseudogap.Comment: 4 LaTeX pages, 4 figure
Electron Spin Resonance of SrCu2(BO3)2 at High Magnetic Field
We calculate the electron spin resonance (ESR) spectra of the
quasi-two-dimensional dimer spin liquid SrCu2(BO3)2 as a function of magnetic
field B. Using the standard Lanczos method, we solve a Shastry-Sutherland
Hamiltonian with additional Dzyaloshinsky-Moriya (DM) terms which are crucial
to explain different qualitative aspects of the ESR spectra. In particular, a
nearest-neighbor DM interaction with a non-zero D_z component is required to
explain the low frequency ESR lines for B || c. This suggests that crystal
symmetry is lowered at low temperatures due to a structural phase transition.Comment: 4 pages, 4 b&w figure
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