Han's $O(n \log\log n)$ time, linear space, integer sorting algorithm
I was just wondering the same thing.

Fortunately, I was able to find a journal-article published in 2011 which explains this very thing; whats more, you don't need a subscription to view it: Implementation and Performance Analysis of Exponential Tree Sorting

I recommend reading the entire article to learn how it can be implemented and to better understand its underlying theory. It also shows how Exponential Trees stack up against Quick-Sort and Binary Trees. Here's the relevant excerpt related to Han's $\bf O(n \log\log n)$ time, linear space, integer sorting algorithm:


  Yijie Han has given an idea which reduces the complexity to expected
  time in linear space.[6] The technique used by him is coordinated pass
  down of integers on the Andersson’s exponential search tree[8] and the
  linear time multi-dividing of the bits of integers. Instead of
  inserting integer one at a time into the exponential search tree, he
  passed down all integers one level of the exponential search tree at a
  time. Such coordinated passing down provides the chance of performing
  multi-dividing in linear time and therefore speeding up the algorithm.
  This idea may provide speed up, but in practical implementation it is
  very difficult to handle integers in batches.


[6]  Y.  Han,  Deterministic  sorting  in  O(n  log  log n)  time  and linear space, 34th STOC, 2002.

[8]  A.  Andersson,  Fast deterministic  sorting  and  searching  in linear  space,  IEEE  Symposium  on  Foundations  of Computer Science, 1996.