Electronic states of the icosahedral quasiperiodic systems in magnetic fields

The electronic properties of the icosahedral quasiperiodic system in a tile-dependent or uniform magnetic field is studied by quasi-Bloch scheme and the general solutions are obtained for the electronic states. The behavior of the three-dimensional (3D) non-interacting electrons in an icosahedral quasiperiodic system may be treated as the projection of that of the non-interacting pseudo-electrons in 6D. In the presence of the tile-dependent magnetic field, the non-interacting electrons are quasi-Bloch electrons, while they are partial quasi-Bloch electrons when the magnetic field is uniform.     

Bound states in the continuum in quasiperiodic systems

We first propose the existence of bound states in the continuums (BICs) in quasiperiodic systems. Owing to long-range correlation, destructive interference may occur in quasiperiodic systems with higher generation order. Occurrences of BICs in Fibonacci quantum wells studied by localization analysis and gap map method are proposed.     

Controlled delocalization of electronic states in a multi-strand quasiperiodic lattice

Finite strips, composed of a periodic stacking of infinite quasiperiodic Fibonacci chains, have been investigated in terms of their electronic properties. The system is described by a tight binding Hamiltonian. The eigenvalue spectrum of such a multi-strand quasiperiodic network is found to be sensitive on the mutual values of the intra-strand and inter-strand tunnel hoppings, whose distribution displays a unique three-subband self-similar pattern in a parameter subspace. In addition, it is observed that special numerical correlations between the nearest and the next-nearest neighbor hopping integrals can render a substantial part of the energy spectrum absolutely continuous. Extended, Bloch like functions populate the above continuous zones, signalling a complete delocalization of single particle states even in such a non-translationally invariant system, and more importantly, a phenomenon that can be engineered by tuning the relative strengths of the hopping parameters. A commutation relation between the potential and the hopping matrices enables us to work out the precise correlation which helps to engineer the extended eigenfunctions and determine the band positions at will.     

Stable heavy pentaquark states

If the Θ⁺(1540) is interpreted as a bound state of a quark and two (ud) diquarks in a relative P-wave, then it is very likely that there exist pentaquark states with a heavy antiquark, or , and two “light” diquarks in a relative S-wave which are stable against strong decays. We make a mass estimate for exotic states of this type and discuss their weak decays. Isospin relations are constructed which test their flavor quantum numbers.     

Suppression of the singularly localized states in dimer quasiperiodic Fibonacci superlattices

Using the transfer-matrix technique, we have numerically investigated the effect of introducing the dimer on the nature of the states across Dimer Fibonacci semiconductor superlattices on the miniband structure of the GaAs/Al_xGa_1?xAs superlattices. By the introduction of the dimer model, the transmission spectra reveal the appearance of a miniband structure with a concomitant disappearance of the singularly localized states. This behavior is due to the interaction between the states of the dimer wells inside the potential and, therefore, the system is seen by the particle as two overlapped ordered structures.     

The continuum gauge field-theory model for low-energy electronic states of icosahedral fullerenes

The low-energy electronic structure of icosahedral fullerenes is studied within the field-theory model. In the field model, the pentagonal rings in the fullerene are simulated by two kinds of gauge fields. The first one, non-abelian field, follows from so-called K spin rotation invariance for the spinor field while the second one describes the elastic flow due to pentagonal apical disclinations. For fullerene molecule, these fluxes are taken into account by introducing an effective field due to magnetic monopole placed at the center of a sphere. Additionally, the spherical geometry of the fullerene is incorporated via the spin connection term. The exact analytical solution of the problem (both for the eigenfunctions and the energy spectrum) is found.     

Engineering bands of extended electronic states in a class of topologically disordered and quasiperiodic lattices

We show that a discrete tight-binding model representing either a random or a quasiperiodic array of bonds can have the entire energy spectrum or a substantial part of it absolutely continuous, populated by extended eigenfunctions only, when atomic sites are coupled to the lattice locally, or non-locally from one side. The event can be fine-tuned by controlling only the host–adatom coupling in one case, while in two other cases cited here an additional external magnetic field is necessary. The delocalization of electronic states for the group of systems presented here is sensitive to a subtle correlation between the numerical values of the Hamiltonian parameters – a fact that is not common in the conventional cases of Anderson localization. Our results are analytically exact, and supported by numerical evaluation of the density of states and electronic transmission coefficient.     

Comparative study of the heat capacity of icosahedral quasicrystals in solid and liquid states

The heat capacity of icosahedral quasicrystals Al₆₃Cu₂₅Fe₁₂ and Al₆₂Cu_25.5Fe_12.5 has been studied at high temperatures up to 1700 K, which is by almost 400 K higher than the melting point of the material. It has been shown that the melt exhibits an excess heat capacity with respect to that determined by the Dulong-Petit law and that is a direct extension of the excess heat capacity of the solid state. It has been concluded that the excess heat capacity is related, as a whole, to the short-range order in the quasicrystal structure. This circumstance allows the identification of the orbital hybridization as the most probable mechanism of formation of the pseudogap in the electronic structure of the quasicrystals.     

光学超晶格中级联参量过程制备纠缠光子对

探索制备纠缠光子对的新途径是量子光学领域的一个研究热点.从理论上证明在准周期极化 的光学超晶格晶体中的级联参量过程能够产生纠缠光子对.分别利用脉冲和连续的532nm抽运 光在一块准周期极化的 LiTaO3晶体中同时实现非简并参量下转换（产生信号光与闲置光 ）与和频（闲置光与抽运光和频生成和频光）的级联参量过程，获得630nm的信号光与460nm 的和频光.指出信号光与和频光之间存在纠缠关联性质.该方案的优点是可产生短波长的纠缠 光子对. 关键词： 准相位匹配 级联参量过程 光量子纠缠态     

Many-body ground state localization and coexistence of localized and extended states in an interacting quasiperiodic system

We study the localization problem of one-dimensional interacting spinless fermions in anincommensurate optical lattice, which changes from an extended phase to a non-ergoicmany-body localized phase by increasing the strength of the incommensurate potential. Weidentify that there exists an intermediate regime before the system enters the many-bodylocalized phase, in which both the localized and extended many-body states coexist, thusthe system is divided into three different phases, which can be characterized bynormalized participation ratios of the many-body eigenstates and distributions of naturalorbitals of the corresponding one-particle density matrix. This is very different from itsnoninteracting limit, in which all eigenstates undergo a delocalization-localizationtransition when the strength of the incommensurate potential exceeds a critical value.