On the monotonicity of weighted power means of matrices

Let ${\mu }_p(A,B,t)=(t{A}^p+(1-t)B^p{)}^{1\mathrm{/}p}$ denote the weighted power mean between positive operators $A$ and $B$. We show that the function $t\to |A-\mu_p(A,B,t)|_2$ismonotonicallydecreasingwhenever$1/2 \leq p \leq 1$. Hence showing that the weighted power means satisfy Audenaert’s “in-betweenness” property for positive operators for power satisfying $1/2 \leq p \leq 1$\mathrm{.}Wealsoshowthatwhen$p>2$ there exist operators for which the weighted power mean does not satisfy this “in-betweenness” property with respect to the Euclidean metric.