Regensburg 1998 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 24: Metall-Isolator-Übergang und Spin-Peierls-Systeme

TT 24.6: Vortrag

Freitag, 27. März 1998, 10:45–11:00, H 19

Molecular-field approach to the spin-Peierls transition in CuGeO₃ — •R. Werner and C. Gros — Universit"at Dortmund, Institut f"ur Physik, D-44221 Dortmund

We present a theory for the spin-Peierls transition in CuGeO₃. We map the elementary excitations of the dimerized chain (solitons) on an effective Ising model. Inter-chain coupling (or phonons) then introduces a linear binding potential between a pair of soliton and anti-soliton, leading to a finite transition temperature. We evaluate, as a function of temperature, the order parameter, the singlet-triplet gap, the specific heat, and the susceptibility and compare with experimental data on CuGeO₃. We find that CuGeO₃ is close to a first-order phase transition. We point out, that the famous scaling law ∼δ^2/3 of the triplet gap is a simple consequence of the linear binding potential between pairs of solitons and anti-solitons in dimerized spin chains.