Defects in low dimensional quantum magnets

Adam Iaizzi

Masamichi Nishino

Low dimensional strongly correlated systems have great potential for new quantum devices. Among them, quantum wires are actively investigated with development of new methods based on self-organized formation. For magnetic wires (chains), impurity doping, which causes inhomogeneity of magnetic interaction, can bring new magnetic properties to the systems. In the present study, the effect of inhomogeneity (defect) on magnetic chains with bond alternation is focused on. Defects induce local moments in the magnetic chains at low temperatures. However, depending on the relation of the distance between the defects, the magnetic profile is found to be drastically changed.

Hyejin Ju

Massimo Campostrini B, Andrea Pelissetto C, Ettore Vicari

We investigate quantum scaling phenomena driven by lower-dimensional defects in quantum Ising-like models. We consider quantum Ising rings in the presence of a bond defect. In the ordered phase, the system undergoes a quantum transition driven by the bond defect between a magnet phase, in which the gap decreases exponentially with increasing size, and a kink phase, in which the gap decreases instead with a power of the size. Close to the transition, the system shows a universal scaling behavior, which we characterize by computing, either analytically or numerically, scaling functions for the low-level energy differences and the two-point correlation function. We discuss the implications of these results for the nonequilibrium dynamics in the presence of a slowly varying parallel magnetic field h, when going across the first-order quantum transition at h=0.

Wolfgang Lechner, Fabio Cinti, Guido Pupillo

Point defects in self-assembled crystals, such as vacancies and interstitials, attract each other and form stable clusters. This leads to a phase separation between perfect crystalline structures and defect conglomerates at low temperatures. We propose a method that allows one to tune the effective interactions between point defects from attractive to repulsive by means of external periodic fields. In the quantum regime, this allows one to engineer strongly-correlated many-body phases. We exemplify the microscopic mechanism by considering dipolar quantum gases of ground state polar molecules and weakly bound molecules of strongly magnetic atoms trapped in a weak optical lattice in a two-dimensional configuration. By tuning the lattice depth, defect interactions turn repulsive, which allows us to deterministically design a novel supersolid phase in the continuum limit.

Gang Su