arXiv subjects

P. Horsch

Publications and source records attributed to P. Horsch.

25 records · Page 2Linked to original sources

arXiv1999

On the electron-energy loss spectra and plasmon resonance in cuprates

The consequences of the non-Drude charge response in the normal state of cuprates and the effect of the layered structure on electron-energy loss spectra are investigated, both for experiments in the transmission and the reflection mode. It is shown that in the intermediate doping regime the plasmon resonance has to be nearly critically damped as a result of the anomalous frequency dependence of the relaxation rate. This also implies an unusual low-energy dependence of the loss function. Both facts are consistent with experiments in cuprates. Our study based on the t-J model shows good agreement with measured plasmon frequencies.

cond-mat.str-el↗

arXiv1998

A new view of the electronic structure of the spin-Peierls compound alpha'-NaV2O5

The present understanding of the electronic and magnetic properties of $α'$-NaV$_2$O$_5$ is based on the hypothesis of strong charge disproportionation into V$^{4+}$ and V$^{5+}$, which is assumed to lead to a spin-1/2 Heisenberg chain system. A recent structure analysis shows, however, that the V-ions are in a mixed valence state and indistiguishable. We propose an explanation for the insulating state, which is not based on charge modulation, and show that strong correlations together with the Heitler-London character of the relevant intermediate states naturally lead to antiferromagnetic Heisenberg chains. The interchain coupling is weak and frustrated, and its effect on the uniform susceptibility is found to be small.

cond-mat.str-el↗

arXiv1997

Spatial Structure of Spin Polarons in the t-J Model

The deformation of the quantum Neel state induced by a spin polaron is analyzed in a slave fermion approach. Our method is based on the selfconsistent Born approximation for Green's and the wave function for the quasiparticle. The results of various spin-correlation functions relative to the position of the moving hole are discussed and shown to agree with those available from small cluster calculations. Antiferromagnetic correlations in the direct neighborhood of the hole are reduced, but they remain antiferromagnetic even for J as small as 0.1 t. These correlation functions exhibit dipolar distortions in the spin structure, which sensitively depend on the momentum of the quasiparticle. Their asymptotic decay with the distance from the hole is governed by power laws, yet the spectral weight of the quasiparticles does not vanish.

cond-mat.str-el↗

arXiv1996

Theory of the density fluctuation spectrum of strongly correlated electrons

The density response function $N(q,ω)$ of the two-dimensional $t-J$ model is studied starting from a mixed gauge formulation of the slave boson approach. Our results for $N(q, ω)$ are in remarkable agreement with exact diagonalization studies, and provide a natural explanation of the anomalous features in the density response in terms of the spin polaron nature of the charge carriers. In particular we have identified unexplained low energy structures in the diagonalization data as arising from the coherent polaron motion of holes in a spin liquid.

cond-mat↗

arXiv1996

Critical behavior of the S=3/2 antiferromagnetic Heisenberg chain

Using the density-matrix renormalization-group technique we study the long-wavelength properties of the spin S=3/2 nearest-neighbor Heisenberg chain. We obtain an accurate value for the spin velocity v=3.8+- 0.02, in agreement with experiment. Our results show conclusively that the model belongs to the same universality class as the S=1/2 Heisenberg chain, with a conformal central charge c=1 and critical exponent eta=1

cond-mat↗

arXiv1995

Superconducting pairing of spin polarons in the t-J model

The pairing of quasiparticles in a CuO$_2$ plane is studied within a spin polaron formulation of the $t$-$t^{'}$-$J$ model. Our numerical solution of the Eliashberg equations unambiguously shows d-wave pairing between spin polarons on different sublattices mediated by the exchange of spin-fluctuations, and a strong doping dependence of the quasiparticle bandwidth. The transition temperature $T_c$ is an increasing function of $J/t$ and crosses a maximum at an optimal doping concentration $δ_{opt}$. For the t-J model with $J/t=0.4$ we obtain $T_c\simeq 0.013 t$ at $δ_{opt}\simeq 0.2$.

cond-mat↗

arXiv1995

Numerical renormalization group study of the correlation functions of the antiferromagnetic spin-$\frac{1}{2}$ Heisenberg chain

We use the density-matrix renormalization group technique developed by White \cite{white} to calculate the spin correlation functions $<{S}_{n+l}^z{S}_n^z>=(-1)^l ω(l,N)$ for isotropic Heisenberg rings up to $N=70$ sites. The correlation functions for large $l$ and $N$ are found to obey the scaling relation $ω(l,N)=ω(l,\infty)f_{XY}^α (l/N)$ proposed by Kaplan et al. \cite{horsch} , which is used to determine $ω(l,\infty)$. The asymptotic correlation function $ω(l,\infty)$ and the magnetic structure factor $S(q=π)$ show logarithmic corrections consistent with $ω(l,\infty)\sim a\sqrt{\ln{cl}}/l$, where $c$ is related to the cut-off dependent coupling constant $g_{eff}(l_0)=1/\ln(cl_0)$, as predicted by field theoretical treatments.

cond-mat↗