Visa needed for a Scientific Conference in Xian

Dear Chinese Embassy in Vienna,

I am a British citizen working in Vienna. I have been invited to give a presentation at a scientific conference in Xi'An in October. Which is the correct visa for me? Do i need to provide an invitation letter from the conference organizers?

Furthermore, my wife would like to accompany me, but she will only be visiting as a tourist. From what I have read, she will require the L-visa. Is this correct?