Muon Spin Relaxation and fluctuating magnetism in the pseudogap phase of YBa$_{2}$Cu$_{3}$O$_{y}$

TL;DR

This study uses muon spin relaxation to investigate slow magnetic fluctuations in the pseudogap phase of underdoped YBa₂Cu₃O₆.77 and 6.83, revealing constant magnetic dynamics that challenge conventional magnetic transition models.

Contribution

It provides new experimental constraints on theories of pseudogap magnetism by measuring magnetic fluctuation parameters in underdoped YBa₂Cu₃O₆.77 and 6.83 using muon spin relaxation.

Findings

Magnetic fluctuations remain roughly constant below pseudogap temperature.

Observed relaxation rates do not decrease with temperature as expected.

Results challenge conventional magnetic transition models in pseudogap phase.

Abstract

We report 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~$B\mathrm{_{loc}^{rms}}$ and correlation time~$\tau_c$ of fluctuating local fields at muon sites. The observed relaxation rates do not decrease with decreasing temperature~$T$ below the pseudogap onset at $T^\ast$, as would be expected for a conventional magnetic transition; both $B\mathrm{_{loc}^{rms}}$ and $\tau_c$ are roughly constant in the pseudogap phase down to the superconducting transition. Corresponding NMR relaxation rates are estimated to be too small to be observable. Our results put strong constraints on theories of the anomalous pseudogap magnetism in YBa$_{2}$Cu$_{3}$O$_{y}$.