Electronic nematic softening in cuprate superconductors probed by resonant ultrasound spectroscopy

Electronic-nematic order has been shown to be the driver of the structural and magnetic transitions in the
Ba-pnictide superconductors. For cuprate superconductors, the determination of the existence of long-range
electronic-nematic order and fluctuations is not as clearly established as for the pnictides. In this talk I will present
Resonant Ultrasound Spectroscopy (RUS) measurements in single crystals of La2-xSrxCuO4 of different Sr
compositions, through which we have determined the temperature dependence of all elastic moduli in the tetragonal
phase of this compound. A strong softening of the C66 elastic shear moduli, associated with the B2g symmetry channel,
is observed as temperature is decreased, even for the compositions for which the tetragonal to orthorhombic structural
transition is not seen. The temperature dependence of this softening is consistent with a Curie-like temperature
dependence, 1/(T-T0). The B2g softening is truncated by the opening of the superconducting gap at Tc>T0, evidenced by
the stiffening of C66 below Tc. These observations suggest an electronic nematic origin for this softening.