No abstract

Recently, the field of strongly correlated electrons has begun an intense search for a correlation induced topological insulating phase. An example is the quadratic band touching point which arises in a checkerboard lattice at half-filling, and in the presence of interactions gives rise to topological Mott insulators. In this work, we perform a mean-field theory computation to show that such a system shows instability to topological insulating phases even away from half-filling (chemical potential µ = 0). The interaction parameters consist of on-site repulsion (U), nearest-neighbour repulsion (V ), and a next-nearest-neighbour correlated hopping (t c ). The t c interaction originates from strong Coulomb repulsion. By tuning the values of these parameters, we obtain a desired topological phase that spans the area around (V = 0, µ = 0), extending to regions with (V > 0, µ = 0) and (V > 0, µ > 0). This extends the realm of current experimental efforts to find these topological phases.

We study non-equilibrium order parameter dynamics of the non-linear sigma model in the large N limit, using Keldysh formalism. We provide a scheme for obtaining stable numerical solution of the Keldysh saddle point equations and use them to study order parameter dynamics of the model either following a ramp, or in the presence of a periodic drive. We find that the transient dynamics of the order parameter in the presence of a periodic drive is controlled by the drive frequency displaying the phenomenon of synchronization. We also study the approach of the order parameter to its steady state value following a ramp and find out the effective temperature of the steady state. We chart out the steady state temperature of the ordered phase as a function of ramp time and amplitude, and discuss the relation of our results to experimentally realizable spin models. CONTENTS

We present analytically and numerically the spectrum of high harmonic emission generated by twisted electrons in the presence of linearly polarized light. Ensuing transitions from electronic continuum states with orbital angular momentum to bound states give rise to circularly polarized attosecond pulses. For central collisions with twisted wavepackets continuum-bound transitions are subject to dipole selection rules. For non-central collisions a crossover from circularly to linearly polarized emission occurs for increasing impact parameter, due to the transverse topology of twisted wavepackets.