Tamm–Hubbard surface states in the continuum

In the framework of the Bose–Hubbard model, we show that two-particle surface bound states embedded in the continuum (BIC) can be sustained at the edge of a semi-infinite one-dimensional tight-binding lattice for any infinitesimally-small impurity potential V at the lattice boundary. Such thresholdless surface states, which can be referred to as Tamm–Hubbard BIC states, exist provided that the impurity potential V is attractive (repulsive) and the particle–particle Hubbard interaction U is repulsive (attractive), i.e. for UV < 0. (paper)