Revisiting Cu-63 NMR evidence for charge order in superconducting La1.885Sr0.115CuO

Article

关键词: SPIN-LATTICE RELAXATION;    TEMPERATURE STRUCTURAL TRANSITION;    STRIPE-PHASE ORDER;    MAGNETIC-SUSCEPTIBILITY;    NEUTRON-SCATTERING;    NORMAL-STATE;    NQR;    CU;    RESONANCE;    SR;   

DOI  :  10.1103/PhysRevB.96.224508

来源: SCIE

【 摘 要 】

The presence of charge and spin stripe order in the La2CuO4-based family of superconductors continues to lead to new insight on the unusual ground-state properties of high-T-c cuprates. Soon after the discovery of charge stripe order at T-charge similar or equal to 65 K in Nd3+ co-doped La1.48Nd0.4Sr 0.12CuO4(T-c similar or equal to 6 K) [Tranquada et al., Nature (London) 375, 561 (1995)], Hunt et al. demonstrated that La1.48Nd0.4Sr0.12CuO4 and superconducting La2-xSrxCuO4 with x similar to 1/8 (T-c similar or equal to 30 K) share nearly identical NMR anomalies near T-charge of the former [Phys. Rev. Lett. 82, 4300 (1999)]. Their inevitable conclusion that La1.885Sr0.115CuO4 also undergoes charge order at a comparable temperature became controversial, because diffraction measurements at the time were unable to detect Bragg peaks associated with charge order. Recent advances in x-ray diffraction techniques finally led to definitive confirmations of the charge order Bragg peaks in La1.885Sr0.115CuO4 with an onset at as high as T-charge similar or equal to 80 K. Meanwhile, improved instrumental technology has enabled routine NMR measurements that were not feasible two decades ago. Motivated by these new developments, we revisit the charge order transition of a La1.885Sr0.115CuO4 single crystal based on Cu-63 NMR techniques. We demonstrate that Cu-63 NMR properties of the nuclear spin I-z= -1/2 to +1/2 central transition below T-charge exhibit unprecedentedly strong dependence on the measurement time scale set by the separation time tau between the 90 degrees and 180 degrees radio-frequency pulses; a new kind of anomalous, very broad winglike Cu-63 NMR signals gradually emerge below T-charge only for extremely short tau less than or similar to 4 mu s, while the spectral weight I-Normal of the normal NMR signals is progressively wiped out. The NMR linewidth and relaxation rates depend strongly on tau below T-charge, and their enhancement in the charge ordered state indicates that charge order turns on strong but inhomogeneous growth of Cu spin-spin correlations.

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