Divergent nematic susceptibility near the pseudogap critical point in Bi-cuprate superconductors*

In strongly correlated materials, superconductivity is often found near a magnetic quantum critical point (QCP) where a magnetic phase vanishes in the zero-temperature limit. Moreover, the maximum of superconducting transition temperature T_c frequently locates near the magnetic QCP, suggesting that the proliferation of critical spin fluctuations emanating from the QCP plays an important role in Cooper pairing. In cuprate superconductors, however, the superconducting dome is usually separated from the antiferromagnetic phase and T_c attains its maximum value near the verge of enigmatic pseudogap state that appears below doping-dependent temperature T^*. Thus a clue to the pairing mechanism resides in the pseudogap and associated anomalous transport properties. Recent experiments suggested a phase transition at T^* but the key question is what kind of fluctuations are associated with the pseudogap. Here we report elastoresistance measurements of nematic susceptibility in (Bi,Pb)₂Sr₂CaCu₂O_8+δ, 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 behaviours in cuprates.

This work has been done in collaboration with K. Ishida, S. Hosoi, Y. Teramoto, T. Usui, Y. Mizukami, K. Itaka, Y. Matsuda, and T. Watanabe.