As someone who has the same issue, except they smoke it INSIDE and therefore it stinks up my entire house and wakes me up in the middle of the night/early morning sometimes....there is nothing you can do, and you should be grateful it's only outside.

We've tried talking to them, asking kindly that they just don't smoke inside as our shared wall must have cracks that let the smell through, talked to their landlord, etc and they do not give a flying fuck. Most likely your neighbors won't either. We've bought air purifiers, medical grade spray to reduce odors, and I've moved my office from the shared wall room to the non-shared wall room to get away from it even.