Recent content by psi*psi

I am trying to understand Wen and Zee's article on topological quantum numbers of Hall fluid on curved space: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.69.953 They passingly mentiond the fact that a spinning particle with orbital angular momentum $s$ moving on a manifold with...

Thanks again and sorry about the unclear question in my last post. My actual question is: just looking at the hopping term in the Hubbard Model on an extended lattice (say a square lattice) \hat H_t = \displaystyle\sum_{\langle i j \rangle} a^{\dagger}_{i \sigma} a_{j \sigma}, since the...

Thank you for your answer. I am having trouble to see why the hopping term only involves two sites. Vaguely I have a feeling that this has to do with the fact that we are only considering the perturbation to second order, but I don't know how to draw the connections.

This is a question from Altland and Simons book "Condensed Matter Field Theory". In the second exercise on page 64, the book claims that if we define \hat P_s, \hat P_d to be the operators that project onto the singly and doubly occupied subspaces respectively, then at half-filling the...