Anomaly in YBa2Cu4O8 charge distribution below Tc: a zero-field muSR study

Abstract

Zero-field $\mu$SR measurements in ${}^{63}$Cu isotope enriched and natural YBa${}_2$Cu${}_4$O${}_8$ powders are presented. The temperature dependence of the ${\mu }^{+}$ relaxation rate is characterized by a sizeable enhancement below T${}_c$. The comparison of the asymmetry decay in the two samples reveals that the ${\mu }^{+}$ relaxation is driven by nuclear dipole interaction from 300 K down to 4.2 K. It is argued that the increase in the relaxation below T${}_c$ originates from a change in ${\mu }^{+}$ site, possibly due to a modification in the charge distribution within CuO chains.

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