An anomaly has been observed in the ultrasonic attenuation and thermal properties of the $A-15\mathrm{}$ compound ${\mathrm{V}}_3$Si in the superconducting mixed state. The anomalous behavior has been successfully explained in terms of the reorientation of the tetragonal domains, with their $c$-axis perpendicular to the magnetic field. This mechanism of domain instability is based on a model, proposed by Tachiki, one of the present authors, in which an anisotropic mixed state is induced by the band Jahn-Teller effect for the structural (martensitic) transformation just above the superconducting transition temperature. Anisotropic behavior of the ultrasonic anomaly with respect to the direction of an applied magnetic field was studied in order to examine the mechanism. It is found that, although the experimental results are rather complicated due to the demagnetization effect of sample geometry and the irreversible mechanism in nonideal type-II superconductors, they are not contradictory to but qualitatively in agreement with predictions of the model.

• Received 29 May 1979

DOI:https://doi.org/10.1103/PhysRevB.21.1827