Magnetic Anisotropy of Quantum Critical Fluctuation in YBa_2Cu_3O_7 at High Magnetic Fields of up to 100 T

The investigation of high-temperature superconductors under high magnetic fields is one of the most important topics in condensed matter physics. For YBa_2Cu_3O_7 (YBCO), the measurements of magnetoresistance under a high magnetic field are technically challenging because the required magnetic field (B) is 100 T class. The low temperature (from 52 to 150 K) magnetoresistance is measured in optimally-doped YBCO thin films under the condition B∥CuO_2-plane up to 103 T by employing the single-turn coil technique and a radio frequency reflection method. The electrical resistivity ρ exhibits B-linear behavior in the normal phase in the high magnetic field region. The field slope coefficient β (=dρ/dB) becomes converged at low temperatures. The convergency of β below T_c indicates the field-induced strange metal phase, which is determined by the quantum critical fluctuation at high magnetic fields. The β value difference under the different directions of the magnetic field suggests the strong anisotropy in quantum critical fluctuations in the strange metal phase of YBCO.