On 1/2-BPS Wilson-'t Hooft loops
  We investigate the 1/2-BPS Wilson-'t Hooft loops in ${\cal N}=4$ Super-Yang-Mills theory. We use the bulk D-brane with both electric and magnetic charges to calculate the all genus contribution of the circular loops. The expectation value of Wilson-'t Hooft loops are in perfect agreement with the result through supersymmetric condition and duality transformation in the gauge theory. 
Bin Chen and Wei He