Ground Cover Herbs in Shade and Poor Soil

We have an area in our back yard (Atlanta, GA) under big trees we want to keep (oak and hickory) that is rocky, sloped, lots of big nearly exposed roots and moderate shade. We have found no variety of grass that will grow there. Is there anything in perennial herbs that might work as a ground cover? We have considered creeping thyme (but does that not want more sun?). We considered Yarrow, but I seem to be sensitive to it, and it's an area I have to work in occasionally.

None of the thymes will do well in shade. Wild thyme will do well in poor, sandy soils, but not if the exposure is shaded.
Have you tried sweet woodruff? It is listed on our online catalogue under "W Herbs". It is a very hardy perennial that forms dense mats that choke out most weeds. It produces a white blanket of flowers in spring and the whorled leaves are attractive.