Anomalous thermal expansion of high-temperature superconductors Bi2Sr2−x LaxCuO6 at low temperatures

The low-temperature thermal expansion of Bi₂Sr_2?x La_xCuO₆ single crystals with different doping levels is measured. The effect of a magnetic field on the thermal expansion of Bi₂Sr_2?x La_xCuO₆ is studied. Anomalous (negative) thermal expansion whose characteristics depend on the doping level of the sample is revealed at T ≤ 10–20 K. It is found that these characteristics are significantly affected by moderately strong magnetic fields (2–4 T). The experimental results can be interpreted within a model relating the anomalous thermal expansion in high-temperature superconductors at low temperatures and the strong effect of the magnetic field on this expansion to the change in the stabilizing role of the charge-density waves in the oxygen sublattice.