Ultrasonic study of La-based high-T_c superconductor under high magnetic field

Lanthanum based cuprate superconductors are highly correlated electrons systems well-know for their structural, magnetic, charge and superconducting instabilities. In underdoped compound (i.e. for doping less than optimal for superconductivity) a dip in the onset temperature for superconductivity T_c, centered at p∼0.125, occurs. While the origin of this dip is still under debate, most of the experimental evidence in La_2-xSr_xCuO₄ (LSCO) seems to point toward a competition with frozen magnetism¹.

In order to further investigate the relationship between magnetism and superconductivity we have performed measurements of ultrasonic velocity and attenuation in LSCO. Around p=1/8, several anomalies are observed in the sound velocity and attenuation, associated with superconductivity and magnetic freezing. The competition between the two orders parameters is tuned with a magnetic field which enhances magnetic correlations at the expense of superconductivity².

[1] M. H. Julien, Physica B 329-333 (2000) 693.
[2] J. Chang et al., Phys. Rev. B 78 (2008) 104525.