Spontaneous nemaitc transition within the pseudogap state in cuprates
Overshadowing the superconducting dome in hole-doped cuprates, the pseudogap state is still one of the mysteries that no consensus can be achieved. It has been shown that the rotational symmetry is broken in this state and may result in a nematic phase transition, whose temperature seems to coincide with the onset temperature of the pseudogap state $T^*$ around optimal doping level, raising the question whether the pseudogap is resulted from the establishment of the nematic order. Here we report results of resistivity measurements under uniaxial pressure on several hole-doped cuprates, where the normalized slope of the elastoresisvity $\zeta$ can be obtained as illustrated in iron-based superconductors. The temperature dependence of $\zeta$ along particular lattice axes exhibits kink feature at $T_{k}$ and shows Curie-Weiss-like behavior above it, which suggests a spontaneous nematic transition. While $T_{k}$ seems to be the same as $T^*$ around optimal doping level, they become different in very underdoped La$_{2-x}$Sr$_{x}$CuO$_4$. Our results suggest that the nematic order is an electronic phase within the pseudogap state.