  We focus on the metric sorter unit of successive cancellation list decoders
for polar codes, which lies on the critical path in all current hardware
implementations of the decoder. We review existing metric sorter architectures
and we propose two new architectures that exploit the structure of the path
metrics in a log-likelihood ratio based formulation of successive cancellation
list decoding. Our synthesis results show that, for the list size of $L=32$,
our first proposed sorter is $14\%$ faster and $45\%$ smaller than existing
sorters, while for smaller list sizes, our second sorter has a higher delay in
return for up to $36\%$ reduction in the area.
