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Magnetic-charge ordering and corresponding magnetic/monopole phase transitions in spin ices are the emergent topics of condensed matter physics. In this work, we investigate a series of magnetic-charge (monopole) phase transitions in artificial square spin ice model using the conserved monopole density algorithm. It is revealed that the dynamics of low monopole density lattices is controlled by the effective Coulomb interaction and the Dirac string tension, leading to the monopole dimerization which is quite different from the dynamics of three-dimensional pyrochlore spin ice. The condensation of the monopole dimers into monopole crystals with staggered magnetic-charge order can be predicted clearly. For the high monopole density cases, the lattice undergoes two consecutive phase transitions from high-temperature paramagnetic/charge-disordered phase into staggered charge-ordered phase before eventually toward the long-range magnetically-ordered phase as the ground state which is of staggered charge order too. A phase diagram over the whole temperature-monopole density space, which exhibits a series of emergent spin and monopole ordered states, is presented.

We report the ferroelectric aging effect of dense BaTi 0.995 Mn 0.005 O 3 ceramics with grain size varying from 2000 nm to 150 nm. Given the identical aging process, it is revealed that the significant aging effect with clear doublehysteresis loop, observed in coarse-grain sample, is substantially suppressed with decreasing grain size. This suppression can be attributed to the reduction of tetragonal distortion and the grain boundary barrier effect in fine-grain sample. Consequently, the weak thermodynamic driving force and the limited kinetic migration are unfavorable to a reversible domain switching, resulting in a normal hysteresis loop in small grained samples.

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We apply the Wigner-Yanase skew information approach to analyze two typical models that exhibit a topological quantum phase transition. Based on the exact solutions of the ground states, the Wigner-Yanase skew information between two nearest sites for each of the two models is obtained. For the one-dimensional Kitaev chain model, the first-order derivative of the Wigner-Yanase skew information is non-analytical around the critical point. The scaling behavior and the universality are verified numerically. In particular, the skew information can also detect the factorization transition in such a model. For the two-dimensional Kitaev honeycomb model, the first-order derivative of the Wigner-Yanase skew information shows some singularities at the critical points where the system transits from the gapless phase to the gapped one. Our results suggest that the Wigner-Yanase skew information can serve as a good indicator of the topological phase transitions in these models and shed considerable light on the relationships between topological quantum phase transition and information theory.

The concept of quantum Fisher information (QFI) is used to characterize the localization transitions in three representative one-dimensional models. It is found that the localization transition in each model can be distinctively illustrated by the evolution of QFI. For the Aubry-André model, the QFI exhibits an inflexion at the boundary between the extended states and localized ones. In the t 1 − t 2 model, the QFI has a transition point separating the extended states from the localized states, while the mobility edge of the QFI is energy dependent. Furthermore, nine energy bands in the Soukoulis-Economou (S-E) model can be clearly revealed by the QFI with global mobility edges and local mobility edges. The present work demonstrates the implication of the QFI as a general fingerprint to characterize the localization transitions.