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H. Büttner

Publications and source records attributed to H. Büttner.

10 recordsLinked to original sources
arXiv2006

The effects of the symmetric and antisymmetric anisotropies on the dynamics of the spin-1/2 XY chain

The dynamic properties of the spin-1/2 anisotropic XY chain with the Dzyaloshinskii-Moriya (DM) interaction in a transverse field are investigated. Using the Jordan-Wigner transformation, the dynamic structure factors of the model are evaluated rigorously (partially analytically and partially numerically). The effects of the DM interaction on the frequency shapes of the dynamic structure factors are discussed.

cond-mat.str-el↗
arXiv2002

Ground state and excitation of an asymmetric spin ladder model

We perform a systematic investigation of an asymmetric zig-zag spin ladder with inter-leg exchange $J_1$ and different exchange integrals $J_2 \pm δ$ on both legs. In the weak limit of frustration, the spin model can be mapped to a revised double frequency Sine-Gorden model by using bosonization. Renormalization group analysis shows that the Heisenberg critical point flows to an intermediate-coupling fixed point with gapless excitations and a vanishing spin velocity. When the frustration is large, a spin gap opens and a dimer liquid is realized. Fixing $J_2 = J_1 /2$, we find, as a function of $δ$, a continuous manifold of Hamiltonians with dimer product ground states, interpolating between the Majumdar-Ghosh and sawtooth spin-chain model. While the ground state is independent of the alternating next-nearest-neighbor exchange $δ$, the gap size of excitations is found to decrease with increasing $δ$. We also extend our study to a two-dimensional double layer model with an exactly known ground state.

cond-mat.str-el↗
arXiv2001

Peierls-insulator Mott-insulator transition in 1D

In an attempt to clarify the nature of the crossover from a Peierls band insulator to a Mott Hubbard insulator, we analyze ground-state and spectral properties of the one-dimensional half-filled Holstein Hubbard model using exact diagonalization techniques.

cond-mat.str-el↗
arXiv2000

Spin correlation functions and susceptibilities in the easy-plane XXZ chain

We present a Green's-function theory of magnetic short-range order in the $S=1/2$ easy-plane XXZ chain based on the projection method for the dynamic spin susceptibility and a decoupling of three-spin operator products introducing vertex parameters. The longitudinal and transverse static susceptibilities and two-point correlation functions of arbitrary range are calculated self-consistently for all wavenumbers, temperatures, and anisotropy parameters $ -1\leq Δ\leq 1$. In the easy-plane ferromagnetic region $(Δ< 0)$, the longitudinal correlators of spins at distance $n$ change sign at a finite temperature $T_0(n,Δ)$, in reasonable agreement with recent data obtained by finite-chain diagonalizations. The temperature dependence of the uniform static susceptibilities exhibits a maximum which is explained as an effect of magnetic short-range order which decreases with increasing temperature.

cond-mat.str-el↗
arXiv2000

Quantum to classical crossover in the 2D easy-plane XXZ model

Ground-state and thermodynamical properties of the spin-1/2 two-dimensional easy-plane XXZ model are investigated by both a Green's-function approach and by Lanczos diagonalizations on lattices with up to 36 sites. We calculate the spatial and temperature dependences of various spin correlation functions, as well as the wave-vector dependence of the spin susceptibility for all anisotropy parameters $Δ$. In the easy--plane ferromagnetic region $(-1< Δ< 0)$, the longitudinal correlators of spins at distance $r$ change sign at a finite temperature $T_0(Δ, {\bf r})$. This transition, observed in the 2D case for the first time, can be interpreted as a quantum to classical crossover.

cond-mat.str-el↗
arXiv2000

Effects of spin-elastic interactions in frustrated Heisenberg antiferromagnets

The Heisenberg antiferromagnet on a compressible triangular lattice in the spin- wave approximation is considered. It is shown that the interaction between quantum fluctuations and elastic degrees of freedom stabilizes the low symmetric L-phase with a collinear Neel magnetic ordering. Multi-stability in the dependence of the on-site magnetization on an unaxial pressure is found.

cond-mat↗
arXiv1999

Local mode behaviour in quasi-1D CDW systems

We analyze numerically the ground-state and spectral properties of the three-quarter filled Peierls-Hubbard Hamiltonian. Various charge- and spin-ordered states are identified. In the strong-coupling regime, we find clear signatures of local lattice distortions accompanied by intrinsic multi-phonon localization. The results are discussed in relation to recent experiments on MX chain [-PtCl-] complexes. In particular we are able to reproduce the observed red shift of the overtone resonance Raman spectrum.

cond-mat.str-el↗
arXiv1996

On the stability of polaronic superlattices in strongly coupled electron-phonon systems

We investigate the interplay of electron-phonon (EP) coupling and strong electronic correlations in the frame of the two-dimensional (2D) Holstein t-J model (HtJM), focusing on polaronic ordering phenomena for the quarter-filled band case. The use of direct Lanczos diagonalization on finite lattices allows us to include the effects of quantum phonon fluctuations in the calculation of spin/charge structure factors and hole-phonon correlation functions. In the adiabatic strong coupling regime we found evidence for ``self-localization'' of polaronic carriers in a $(π,π)$ charge-modulated structure, a type of superlattice solidification reminiscent of those observed in the nickel perovskites $La_{2-x}Sr_{x}NiO_{4+y}$.

cond-mat.str-el↗
arXiv1996

Polaronic effects in strongly coupled electron-phonon systems: Exact diagonalization results for the 2D Holstein t-J model

Ground-state and dynamical properties of the 2D Holstein t-J model are examined by means of direct Lanczos diagonalization, using a truncation method of the phononic Hilbert space. The single-hole spectral function shows the formation of a narrow hole-polaron band as the electron-phonon coupling increases, where the polaronic band collapse is favoured by strong Coulomb correlations. In the two-hole sector, the hole-hole correlations unambiguously indicate the existence of inter-site bipolaronic states. At quarter-filling, a polaronic superlattice is formed in the adiabatic strong-coupling regime.

cond-mat↗