We study electronic structures of two-dimensional quantum dots in strong magnetic fields using mean-field density-functional theory and exact diagonalization. Our numerically accurate mean-field solutions show a reconstruction of the uniform-density electron droplet when the magnetic field flux quanta enter one by one the dot in stronger fields. These quanta correspond to repelling vortices for...

The level of current understanding of the physics of time-dependent strongly correlated quantum systems is far from complete, principally due to the lack of effective controlled approaches. Recently, there has been progress in the development of approaches for one-dimensional systems. We describe recent developments in the construction of numerical schemes for general (one-dimensional) Hamilton...

Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/J< or =0.025 for H=0 and H=8.7 T, where the system is approximately 30% magnetized. At H=0, the results are in agreement with exact calculations of the dyna...

Highly frustrated lattices yield a completely flat lowest single-electron band. Remarkably, exact many-body ground states can be constructed for the repulsive Hubbard model and the t − J model by filling this flat band with localized electron states. This construction leads to a macroscopic ground-state degeneracy. We discuss how to compute these ground-state degeneracies for a certain class of...

We study the excitation spectrum and ground-state properties of the two-leg S5 1 2 quantum spin ladder with staggered dimerization. Two massive phases separated by a critical line are found, as predicted by previous analysis, based on the nonlinear sigma model. We have used dimer series expansions, exact diagonalization of small clusters, and diagrammatic analysis of an effective interacting Bo...

A new, recursive method of calculating matrix elements of polynomial hamiltonians is proposed. It is particularly suitable for the recent algebraic studies of the supersymmetric Yang-Mills quantum mechanics in any dimensions. For the D = 2 system with the SU(2) gauge group, considered here, the technique gives exact, closed expressions for arbitrary matrix elements of the hamiltonian and of the...

We study the excitation spectrum and ground state properties of the two-leg S = 1 2 quantum spin ladder with staggered dimerization. Two massive phases, separated by a critical line are found, as predicted by previous analysis , based on the non-linear sigma model (NLSM). We have used dimer series expansions, exact diagonalization of small clusters and diagrammatic analysis of an effective inte...

We present numerical exact results for the polaronic band structure of the Holstein molecular crystal model in one and two dimensions. The use of direct Lanczos diagonalization technique, preserving the full dynamics and quantum nature of phonons, allows us to analyze in detail the renormalization of both quasiparticle bandwidth and dispersion by the electron–phonon interaction. For the two–dim...

The interacting phase diagram of a non-Hermitian one-dimensional model featuring topologically different phases is demonstrated. Furthermore, the exact solution in integrable regime, which has been extended to nonintegrable regime by employing diagonalization and matrix product state methods, presented. present results are expected pave new pathway toward characterizing topology realistic quant...

We present an effective Hamiltonian for a bilayer quantum Hall system at filling factor ν = 1 neglecting charge fluctuations. Our model is formulated in terms of spin and pseudospin operators and is an exact representation of the system within the above approximation. We analyze its low-lying excitations in terms of spin-wave theory. Moreover we add to previous first-principle exact-diagonaliza...