Structural phase transition at low temperature in La_2-xSr_xCuO₄ around x =0.12 under magnetic fields

The effect of magnetic field on the structural phase transitions at low temperature in La_2-xSr_xCuO₄ has been investigated using the ultrasonic sound velocity experiment. An increase in the sound velocity V_s is observed below ~10K around x =0.12, which seems to be a precursor of thestructural phase transition. This increase of V_s is drastically enhanced by applying a magnetic field. In case of x =0.120, the temperature where V_s shows the upturn shifts from 5K(H:0T) to 12K(H:15T), whereas,in x =0.160, V_s is not affected by magnetic fields up to 15T. These results suggest that the structure at low temperatur e (P₄₂/ncm or Pccn) in La_2-xSr_xCuO₄ around x =0.12 is stabilized in magnetic fields.