We (Arm's Support and Content Services teams) have been working on creating a Developer Guide for AArch64. They're aimed at anyone wanting a bare-metal focused introduction to the Armv8-A architecture. The first few chapters are now live, with more planed to appear over the next few months.
https://developer.arm.com/architectures/learn-the-architecture
We'd love to know what you like, and don't like, about the guides we've written so far.
PDF looks nice. Later, linking between PDFs would be a nice feature and of course a "download all PDFs". BTW: Downloading the complete guide for off-line browsing would be nice as well. (Xilinx does this for example with the Zynq US+ TRM).