Absence of Broken Time-Reversal Symmetry in the Pseudogap State of the High TemperatureLa2−xSrxCuO4Superconductor from Muon-Spin-Relaxation Measurements

Abstract

We have performed zero-field muon-spin-relaxation measurements on single crystals of La(2-x)SrxCuO4 to search for spontaneous currents in the pseudogap state. By comparing measurements on materials across the phase diagram, we put strict upper limits on any possible time-reversal symmetry breaking fields that could be associated with the pseudogap. Comparison between experimental limits and the proposed circulating current states effectively eliminates the possibility that such states exist in this family of materials.

Absence of Static Loop-Current Magnetism at the Apical Oxygen Site inHgBa2CuO4+δfrom NMR

“…[14] show the appearance of broken time reversal symmetry that correlates with the onset of the pseudogap phase with a magnetic moment tilted away from the crystalline c-axis. A muon spin relaxation (µSR) experiment in zero field was unable to detect this magnetism [15] although screening effects may account for muon insensitivity. [16] To account for neutron data, extensions of 2D orbital currents to 3D models have been proposed which include the apical oxygen[17] as well as a quantum mechanical calculation [18] which has an out-of-plane component with a tilted local field.…”

“…For example antiferromagnetic ordering has been observed by neutron scattering in UPt 3 [46] but not detected in NMR measurements which was suggested to be a consequence of the effects of thermal fluctuations and different time scales for these experiments. [47,48] Roughly speaking these are 10 −11 s for neutrons,[8] 10 −8 s for µSR, [15] and 10 −6 for NMR frequency shifts. In the context of Hg1201 this was noted by Li et al [12] In summary, we have measured the temperature, field, and angular dependence of the narrow planar and apical 17 O NMR spectra in an underdoped Hg1201 single crystal.…”

Direct search for a ferromagnetic phase in a heavily overdoped nonsuperconducting copper oxide

“…Furthermore, μSR exploits muon beams possessing a naturally created ∼100% spin polarization, and hence unlike NMR does not require constant or time-varying external magnetic fields. Zero-field (ZF) μSR experiments on La 2−x Sr x CuO 4 (LSCO) above 2 K show the absence of static electronic moments for p > 0.12 (16,17), which we have confirmed by measurements on LSCO single crystals with Sr content x ¼ 0.15, 0.166, 0.176, 0.196, 0.216, 0.24, and 0.33, with corresponding doping concentrations p ¼ 0.15, 0.166, …, 0.33 (henceforth referred to as LSCO15, LSCO166, …, LSCO33). However, the onset of static FM order is expected to occur at a very low temperature, determined by the weak interlayer coupling of the CuO 2 planes (8).…”

X-ray natural dichroism and chiral order in underdoped cuprates

“…This has now been seen in a variety of cuprates 7 . Interestingly, this symmetry breaking has not been seen by µSR 8 , implying that the observed order is actually fluctuating in nature.…”