Muon spin relaxation and fluctuating magnetism in the pseudogap phase of YBa2Cu3Oy

Abstract

We report the results of a muon spin relaxation study of slow magnetic fluctuations in the pseudogap phase of underdoped single-crystalline YBa 2 Cu 3 O y , y = 6.77 and 6.83. The dependence of the dynamic muon spin relaxation rate on applied magnetic field yields the rms magnitude B rms loc and correlation time τ c of fluctuating local fields at muon sites. The observed relaxation rates do not decrease with decreasing temperature below the pseudogap onset at T * , as would be expected for a conventional magnetic transition; both B rms loc and τ c are roughly constant between T * and the superconducting transition. NMR relaxation rates due to putative loop-current fluctuations are estimated and found to be too small to be observed. Our results put strong constraints on the theories of the anomalous pseudogap magnetism in YBa 2 Cu 3 O y .

Superconductivity due to fluctuating loop currents

“…Nuclear magnetic resonance (NMR) measurements also failed to observe LC order ( 16 , 17 ) of a magnitude comparable to that predicted theoretically ( 18 ). Furthermore, recent muon spin relaxation measurements ( 19 , 20 ) found no evidence for LC order in the pseudogap state and were used to argue that the effects of LCs on NMR relaxation rates are too small to be observable ( 20 ).…”