Divergent Nematic Susceptibility Near The Pseudogap Critical Point In A Cuprate Superconductor

In strongly correlated materials, superconductivity is often found near a magnetic quantum critical point (QCP) where a magnetic phase vanishes and its fluctuations proliferate, suggesting unconventional superconductivity mechanisms driven by spin fluctuations. In cuprate superconductors, however, the superconducting transition temperature attains its maximum not at the antiferromagnetic vanishing point, but near the verge of enigmatic pseudogap state that appears below doping-dependent temperature T*. Thus a key question is what kind of fluctuations are associated with the pseudogap. Here we report elastoresistance measurements of nematic susceptibility in (Bi,Pb)(2)Sr2CaCu2O8+delta, which is sensitive to an electronic order with twofold in-plane anisotropy. The nematic susceptibility shows an anomaly at T*. evidencing a phase transition with broken rotational symmetry. Near the pseudogap end point, nematic susceptibility becomes singular and divergent. This signifies the presence of a nematic QCP, which has emerging links to the high-T-c superconductivity and strange metallic behaviors in cuprates.