Michael Holicki | Searcharxiv

arXiv2000

Magneto-elastic excitations in spin-Peierls systems

Within the random phase approximation to the spin-Peierls transition two parameter regimes of phonon softening and hardening are present. Magneto-elastic excitations are discussed in detail for phonons coupled to the exactly solvable model of XY spin chains for both regimes, leading to a modified interpretation of the 30 cm$^{-1}$ mode in CuGeO$_3$. Frustrated Heisenberg chains coupled to phonons satisfactory describe the pre-transitional quasi-elastic scattering in CuGeO$_3$. A real space interpretation of the quasi-elastic scattering is given justifying effective Ising model approaches.

cond-mat.str-el↗

arXiv2000

Lattice dynamical effects on the Peierls transition in one-dimensional metals and spin chains

The interplay of charge, spin and lattice degrees of freedom is studied for quasi-one-dimensional electron and spin systems coupled to quantum phonons. Special emphasis is put on the influence of the lattice dynamics on the Peierls transition. Using exact diagonalization techniques the ground-state and spectral properties of the Holstein model of spinless fermions and of a frustrated Heisenberg model with magneto-elastic coupling are analyzed on finite chains. In the non-adiabatic regime a (T=0) quantum phase transition from a gapless Luttinger-liquid/spin-fluid state to a gapped dimerized phase occurs at a nonzero critical value of the electron/spin-phonon interaction. To study the nature of the spin-Peierls transition at finite temperatures for the infinite system, an alternative Green's function approach is applied to the magnetostrictive XY model. With increasing phonon frequency the structure factor shows a remarkable crossover from soft-mode to central-peak behaviour. The results are discussed in relation to recent experiments on $\rm CuGeO_3$.

cond-mat.str-el↗