Spin-1/2 Heisenberg antiferromagnet on the pyrochlore lattice: An exact diagonalization study

We present exact diagonalization calculations for the spin-1/2 nearest-neighbor antiferromagnet on the pyrochlore lattice. We study a section of the lattice in the [111] direction and analyze the Hamiltonian of the breathing pyrochlore system with two coupling constants J(1) and J(2) for tetrahedra of different orientations and investigate the evolution of the system from the limit of disconnected tetrahedra (J(2) = 0) to a correlated state at J(1) = J(2). We evaluate the low-energy spectrum, two and four spin correlations, and spin chirality correlations for a system size of up to 36 sites. The model shows a fast decay of spin correlations and we confirm the presence of several singlet excitations below the lowest magnetic excitation. We find chirality correlations near J(1) = J(2) to be small at the length scales available at this system size. Evaluation of dimer-dimer correlations and analysis of the nature of the entanglement of the tetrahedral unit shows that the triplet sector of the tetrahedron contributes significantly to the ground-state entanglement at J(1) = J(2).