The pseudogap phenomenon in the cuprates is arguably the most mysterious puzzle in the field of high-temperature superconductivity. The tetragonal cuprate HgBa2CuO4+δ, with only one CuO2 layer per primitive cell, is an ideal system to tackle this puzzle. Here, we measure the magnetic susceptibility anisotropy within the CuO2 plane with exceptionally high-precision magnetic torque experiments. Our key finding is that a distinct two-fold in-plane anisotropy sets in below the pseudogap temperature T*, which provides thermodynamic evidence for a nematic phase transition with broken four-fold symmetry. Surprisingly, the nematic director orients along the diagonal direction of the CuO2 square lattice, in sharp contrast to the bond nematicity along the Cu-O-Cu direction. Another remarkable feature is that the enhancement of the diagonal nematicity with decreasing temperature is suppressed around the temperature at which short-range charge-density-wave formation occurs. Our result suggests a competing relationship between diagonal nematic and charge-density-wave order in HgBa2CuO4+δ.
Bibliographical noteFunding Information:
We thank A. Fujimori, T. Hanaguri, S. Kivelson, H. Kontani, P.A. Lee, D. Pelc, S. Sachdev, L. Taillefer, T. Tohyama, C. Varma, H. Yamase, Y. Yanase and G. Yu for fruitful discussions. This work was supported by Grants-in-Aid for Scientific Research (KAKENHI) (Nos. JP25220710, JP15H02106, JP15H03688, JP16K13837, JP18H01177 and JP18H05227) and on Innovative Areas “Topological Material Science” (No. JP15H05852) and “Quantum Liquid Crystals” (No. JP19H05824) from Japan Society for the Promotion of Science (JSPS). This work was partly performed using facilities of the Institute for Solid State Physics, the University of Tokyo. H.U. thanks Alfred Baron for making the work possible in Materials Dynamics laboratory, RIKEN SPring-8 Center. The work at the University of Minnesota was funded by the Department of Energy through the University of Minnesota Center for Quantum Materials under DE-SC-0016371. E.-G.M. acknowledges the financial supports from the POSCO Science Fellowship of POSCO TJ Park Foundation and NRF of Korea under Grant no. 2017R1C1B2009176.
© 2019, The Author(s).