Localization of electrons in ordered and disordered systems II. Bound bands

Localization of Dirac Fermions in Finite-Temperature Gauge Theory

It is by now well established that Dirac fermions coupled to non-Abelian gauge theories can undergo an Anderson-type localization transition. This transition affects eigenmodes in the lowest part of the Dirac spectrum, the ones most relevant to the low-energy physics of these models. Here we review several aspects of this phenomenon, mostly using the tools of lattice gauge theory. In particular, we discuss how the transition is related to the finite-temperature transitions leading to the deconfinement of fermions, as well as to the restoration of chiral symmetry that is spontaneously broken at low temperature. Other topics we touch upon are the universality of the transition, and its connection to topological excitations (instantons) of the gauge field and the associated fermionic zero modes. While the main focus is on Quantum Chromodynamics, we also discuss how the localization transition appears in other related models with different fermionic contents (including the quenched approximation), gauge groups, and in different space-time dimensions. Finally, we offer some speculations about the physical relevance of the localization transition in these models.

A High-Capacity Negative Electrode for Asymmetric Supercapacitors Based on a PMo12 Coordination Polymer with Novel Water-Assisted Proton Channels

The development of a negative electrode for supercapacitors is a critical challenge for the next-generation of energy-storage devices. Herein, two new electrodes formed by the coordination polymers [Ni(itmb)₄ (HPMo₁₂ O₄₀ )]·2H₂ O (1) and [Zn(itmb)₃ (H₂ O)(HPMo₁₂ O₄₀ )]·4H₂ O (2) (itmb = 1-(imidazo-1-ly)-4-(1,2,4-triazol-1-ylmethyl)benzene), synthesized by a simple hydrothermal method, are described. Compounds 1 and 2 show high capacitances of 477.9 and 890.2 F g^-1 , respectively. An asymmetric supercapacitor device assembled using 2 which has novel water-assisted proton channels as negative electrode and active carbon as positive electrode shows ultrahigh energy density and power density of 23.4 W h kg^-1 and 3864.4 W kg^-1 , respectively. Moreover, the ability to feed a red light emitting diode (LED) also demonstrates the feasibility for practical use. The results allow a better elucidation of the storage mechanism in polyoxometalate-based coordination polymers and provide a promising direction for exploring novel negative materials for new-generation high-performance supercapacitors.

A coordination polymer based on dinuclear (pyrazinyl tetrazolate) copper(ii) cations and Wells–Dawson anions for high-performance supercapacitor electrodes

A new POM-based coordination polymer was used as supercapacitor electrode showing excellent performance, which can effectively solve the water solubility and low conductivity of traditional POM electrodes.

dc electric field effect on the anomalous exponent of the hopping conduction in the one-dimensional disorder model

The dc electric field effect on the anomalous exponent of the hopping conduction in the disorder model is investigated. First, we explain the model and derive an analytical expression of the effective waiting time for the general case. We show that the exponent depends on the external field. Then we focus on a one-dimensional system in order to illustrate the features of the anomalous exponent. We derive approximate expressions of the anomalous exponent of the system analytically. For the case of a weak field, the anomalous exponent is consistent with that of diffusive systems. This is consistent with the treatments of Barkai et al. [Phys. Rev. E 63, 046118 (2001)] and our result supports their theory. On the other hand, for the case of a strong field and a strong disorder, the time evolution of the exponent clearly differs from that in the weak field. The exponent is consistent with the well-known expression of the anomalous exponent in the multiple trapping model at mesoscopic time scales. In the long-time limit, a transition of the anomalous exponent to the same value of the weak field occurs. These findings are verified by the Monte Carlo simulation.

The electronic structure of liquid silver chalcogenides: a tight-binding approach

We present a computational study of the electronic structure of the stoichiometric liquid zero-gap semiconductors [Formula: see text], [Formula: see text] and [Formula: see text]. The geometry of the fluids is described by the primitive model of charged hard spheres; the electronic structure is modelled using a tight-binding Hamiltonian. The density of states is computed considering the Madelung potential fluctuations and the topological disorder characteristic of an ionic fluid. Only the introduction of nonzero tight-binding hopping matrix elements - equivalent to the formation of chemical bonds - induces a pseudogap between the chalcogenide conduction band and the silver valence band. The Fermi level can be located in a region of a small density of states; eigenstates at [Formula: see text] are likely to exhibit disorder-induced localization.