  The discovery of suitable automorphisms of polar codes gained a lot of
attention by applying them in Automorphism Ensemble Decoding (AED) to improve
the error-correction performance, especially for short block lengths. This
paper introduces Successive Cancellation Automorphism List (SCAL) decoding of
polar codes as a novel application of automorphisms in advanced Successive
Cancellation List (SCL) decoding. Initialized with L permutations sampled from
the automorphism group, a superposition of different noise realizations and
path splitting takes place inside the decoder. In this way, the SCAL decoder
automatically adapts to the channel conditions and outperforms the
error-correction performance of conventional SCL decoding and AED. For a polar
code of length 128, SCAL performs near Maximum Likelihood (ML) decoding with
L=8, in contrast to M=16 needed decoder cores in AED. Application-Specific
Integrated Circuit (ASIC) implementations in a 12 nm technology show that
high-throughput, pipelined SCAL decoders outperform AED in terms of energy
efficiency and power density, and SCL decoders additionally in area efficiency.
