Anomalous thermal expansion of high-temperature superconductors at low temperatures

The origins of the anomalous (negative) thermal expansion of high-temperature superconductors (HTSCs) and of the anomalously strong effect of a magnetic field on the thermal expansion coefficient at low temperatures are discussed. A physical model is proposed based on the stabilizing influence of a charge density wave (CDW) arising in the oxygen sublattice in addition to the antiferromagnetic and spin-Peierls ordering in the copper ion sublattice of an HTSC compound. The effects of temperature, magnetic field, and doping on the interaction of such a CDW with the ionic subsystem of an HTSC compound are studied. The conclusions derived from the model are in agreement with experimental data.