A long-standing controversial issue in the quest to understand the superconductivity in cuprates is the nature of the enigmatic pseudogap region of the phase diagram 1 . Especially important is whether the pseudogap state is a distinct thermodynamic phase characterized by broken symmetries below the onset temperature T * . Here we report torque-magnetometry measurements of anisotropic susceptibility within the ab planes in orthorhombic YBa 2 Cu 3 O y with exceptionally high precision. The in-plane anisotropy displays a significant increase with a distinct kink at the pseudogap onset temperature T * , showing a remarkable scaling behaviour with respect to T/T * in a wide doping range. Our systematic analysis reveals that the rotational symmetry breaking sets in at T * in the limit where the e ect of orthorhombicity is eliminated. These results provide thermodynamic evidence that the pseudogap onset is associated with a second-order nematic phase transition, which di ers from the recently reported charge-density-wave transition that accompanies translational symmetry breaking [2][3][4][5][6][7][8][9][10] . The pseudogap state harbours anomalous electronic states such as Fermi arcs, charge density waves (CDW), and d-wave superconductivity 1 . Electronic nematicity, a four-fold (C 4 ) rotational symmetry breaking, has emerged as a key feature inside the pseudogap regime 11-14 , but the presence or absence of a nematic phase transition and its relationship to the pseudogap remain unresolved. Nematicity has been widely discussed in cuprates, and one of its mechanism is the onset of a stripe-type CDW order parameter which generally breaks rotation symmetry as well as translation symmetry with a nonzero wavenumber Q = 0 (refs 2-10,15-18). In Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO), scanning tunnelling microscopy experiments at low temperatures report an electronic state, consisting of short-range CDW of unidirectional (one-dimensional, 1D) type with a period of ∼4a 0 , where a 0 is the Cu-O-Cu distance 19,20 . This nano-stripe structure persists even well above the superconducting transition temperature T c (ref. 21). In YBa 2 Cu 3 O y (YBCO), the short-range CDW order forms a dome-shaped boundary inside the pseudogap regime 6,7 . Resonant X-ray scattering (RXS) experiments in YBCO report that the CDW is of unidirectional type with a periodicity of ∼3a 0 (ref. 4).In both BSCCO and YBCO, the CDW forms domains with a size of ∼3 nm in zero field, inside which the C 4 symmetry of the unit cell is strongly broken. In contrast to such CDW orders, the nematicity may also be caused by an instability without breaking translational symmetry, characterized by Q = 0.The measurement of the magnetic torque has a very high sensitivity for detecting magnetic anisotropy. The torque τ = µ 0 V M × H is a thermodynamic quantity, a differential of the free energy with respect to angular displacement. Here µ 0 is the permeability of vacuum, V is the sample volume, and M is the magnetization induced by the external magnetic field H. When H is rotated ...
Magnetization measurements on untwinned YBa 2 Cu 3 O y are performed in magnetic fields up to 27 T using the Hall probe magnetometry and the anomalous second peak is found near the multicritical point. Below the second peak, the vortex pinning force shows a steep increase at a characteristic field H*(T), which is connected both with the first-order vortex lattice melting line T m (H) and with the second-order vortex glass transition line T g (H) at the multicritical point. The field-driven transition from the ordered Bragg glass to the disordered vortex glass phase is discussed as a possible origin of H*(T). ͓S0163-1829͑98͒00841-8͔
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.