Plausible loop currents in the GdBCO pseudogap phase

For the cuprate pseudogap phase, Varma [1] predicts loop currents above T$_{c}$. We search for fields near 100 Oe, created by such currents in GdBa$_{2}$Cu$_{3}$O$_{7-\delta }$ (GdBCO). Using MaxEnt-Burg (ME) we analyze zero-field (ZF) muon-spin-rotation ($\mu $SR) data of underdoped ($\delta $1; T$_{c }$= 81 K) and optimal doped ($\delta $0; T$_{c }$= 93 K) GdBCO. [2] ME-$\mu $SR applied to ZF-GdBCO data yields T-dependent signals at 0-MHz (f0) and 0.3-MHz (f1) and hints of 1.4-MHz signals. To cancel any systematic (f1) effect, we analyze DS(t,T) = S(t,T$>$T$_{c})$ - S(t,T'$<<$T$_{c})$. This ME-Burg analysis of GdBCO($\delta $0 {\&} $\delta $1) indicates weak signals near 1.4 MHz above T$_{c}$ (and f1 disappears). These ME-peaks occur at $\sim $1.3 MHz (95 Oe) for GdBCO($\delta $1) and $\sim $1.5 MHz (110 Oe) for GdBCO($\delta $0). These $\mu $SR signals, plausibly due to fields created by loop currents, appear only above T$_{c}$. Below T$_{c}$, only ME background noise exist in DS(t,T) transforms.~The $\sim $1.4-MHz peak intensity to background ratio at its maximum is $\sim $5 for GdBCO($\delta $1) and $\sim $4 for GdBCO($\delta $0) at $\sim $10 degrees above T$_{c}$. Validating predicted loop currents is essential for understanding the pseudogap phase. Research supported by REU NSF {\&} DOE LANL. [1] CM Varma, Phys Rev Lett 83 (1999) 3538; [2] T Songatikamas et al, J Supercond {\&} Novel Magn 23 (2010) 793.