The European Physical Journal B最新文献

Blending ordering within an uncorrelated disorder potential in families of 3D Lieb lattices preserves the macroscopic degeneracy of compact localized states and yields unconventional combinations of localized and delocalized phases—as shown in Liu et al. (Phys Rev B 106:214204, 2022). We proceed to reintroduce translation invariance in the system by further ordering the disorder, and discuss the spectral structure and eigenstates features of the resulting perturbed lattices. We restore order in steps by first (i) rendering the disorder binary—i.e., yielding a randomized checkerboard potential, then (ii) reordering the randomized checkerboard into an ordered one, and at last (iii) realigning all the checkerboard values yielding a constant potential shift, but only on a sub-lattice. Along this path, we test the influence of additional random impurities on the order restoration. We find that in each of these steps, about half of the dispersive states are projected upon the unperturbed sites hosting the degenerate compact states, while the remaining ones are localized in the perturbed sites with energy determined by the strength of checkerboard. This strategy, herewith implemented in the 3D Lieb lattice, highlights order restoration as experimental pathway to engineer spectral and states features in disordered lattice structures in the pursuit of quantum storage and memory applications.

The mesoscopic transport through double-quantum-dot (DQD) Aharonov–Bohm (AB) interferometer coupled with Majorana bound states (MBSs), as well as normal and superconductive terminals has been investigated. The current, shot noise and Fano factor have been calculated versus AB phase and source-drain bias (eV). The calculated Fano factor F displays explicit features of MBSs through its AB oscillations and source-drain bias characteristics. The sinusoid and multi-peak (4pi )-periodic oscillations are exhibited versus AB phase due to modifying the DQD levels and coupling constants. Significant peak-valley structures of Fano factor contributed by Andreev reflections and MBSs exhibit in small source-drain bias region. The Fano factor is suppressed by increasing the coupling strengths (lambda _i) (( i=1,2)) of MBSs with DQD, while it is enhanced by increasing the coupling energy ((varepsilon _{M})) between two MBSs. For the case as (varepsilon _{M}ne 0), a specific value around (Fapprox 2) is reached for different (lambda _i) as (eVrightarrow 0). While for the case as (varepsilon _{M}=0), small values around (Fapprox 0) are presented due to setting different coupling constants (lambda _i) as (eVrightarrow 0).

Using the mean field approximation based on the Bogoliubov inequality for free energy, we investigate the effects of the biquadratic exchange interaction on the critical behavior and phase diagram of the mixed spin (1,2) Blume–Emery–Griffiths model. We first focus on a specific case of the model: when the interaction parameter (K=0), corresponding to the Blume–Capel model. For the attractive Blume–Emery–Griffiths model, we present the phase diagram in the temperature-crystal field plane. The phase diagram is significantly influenced by the value of the biquadratic exchange interaction K. For small values of K, similar to the Blume–Capel model, the phase diagram exhibits first and second order phase transition lines separating ordered and disordered phases, with a tricritical point marking the boundary between these regions. As K increases, the phase diagram changes significantly, with the appearance of reentrant and double reentrant phenomena.

We have studied theoretically the magnetization M and the band gap energy (E_g) in dependence on temperature, size and ion doping concentration in the double perovskite La(_2)NiMnO(_6) (LNMO)—bulk and nanoparticles. LNMO is a ferromagnetic semiconductor. Therefore, it is appropriate to use for describing its properties the (s-d(f)) model. The method for the calculation of M and (E_g) is the Green’s function theory within we are able to make a finite temperature analysis of the excitation spectrum and of all physical quantities. The temperature-dependent Matsubara Green’s function formalism can be used for describing the temperature-dependent behavior of realistic systems in thermal equilibrium. M increases with decreasing the nanoparticle size. (E_g) decreases with increasing temperature. For nanoparticles, it is smaller than that of bulk LNMO. Doping with Sr ions at the La site reduces M and enhances (E_g). The band gap decreases by Sc ion doping at the La site. The substitution with different ions at the Ni site can also tune (E_g). For example, doping with Fe or Sc ion increases (E_g), whereas by Co, doping (E_g) decreases. Substitution by the same ion at different sites, A or B (La or Ni) leads to different behavior of the band gap. It is shown that Sr-, Ba-, Ca-, and Y-doped LNMO NPs with a band gap of (sim ) 1.4 eV are appropriate for application in solar cells. Comparison to the existing experimental data is made.

We study the dynamics of a single spin coupled to a bosonic bath at zero temperature driven by a ramp of the bias field. A single spin coupled to a bosonic sub-Ohmic bath exhibits a quantum phase transition at a certain strength of spin-boson coupling. When the bias field is ramped from a large value to zero at this critical coupling strength, the system initialized at the ground state ends up with a finite magnetization due to the critical slowing down near the transition. On the basis of the pulse-impulse approximation, we derive a scaling law between the residual magnetization and the ramp speed. The obtained scaling relation is examined using a numerical simulation based on the tensor network. The data are in favor of the scaling law to hold. We discuss the demonstration of our theoretical results by means of quantum simulation using the quantum annealer.

We propose two new kinds of infinite resistor networks based on the Fibonacci sequence: a serial association of resistor sets connected in parallel (type 1) or a parallel association of resistor sets connected in series (type 2). We show that the sequence of the network’s equivalent resistance converges uniformly in the parameter (alpha =frac{r_2}{r_1} in [0,+infty )), where (r_1) and (r_2) are the first and second resistors in the network. We also show that these networks exhibit self-similarity and scale invariance, which mimics a self-similar fractal. We also provide some generalizations, including resistor networks based on high-order Fibonacci sequences and other recursive combinatorial sequences.

Polling all the participants to find a time when everyone is available is the ubiquitous method of scheduling meetings nowadays. We examine the probability of a poll with m participants and (ell ) possible meeting times succeeding, where each participant rejects r of the (ell ) options. For large (ell ) and fixed (r/ell ,) we can carry out a saddle-point expansion and obtain analytical results for the probability of success. Despite the thermodynamic limit of large (ell ,) the ‘microcanonical’ version of the problem where each participant rejects exactly r possible meeting times, and the ‘canonical’ version where each participant has a probability (p = r/ell ) of rejecting any meeting time, only agree with each other if (mrightarrow infty .) For (mrightarrow infty ,) (ell ) has to be (O(p^{-m})) for the poll to succeed, i.e., the number of meeting times that have to be polled increases exponentially with m. Equivalently, as a function of p, there is a discontinuous transition in the probability of success at (p sim 1/ell ^{1/m}). If the participants’ availability is approximated as being unchanging from one week to another, i.e., (ell ) is limited, a realistic example discussed in the text of the paper shows that the probability of success drops sharply if the number of participants is greater than approximately 4.

Exact ground states (GS) are deduced for conducting polymers possessing pentagon type of unit cell. The study is done in the presence of many-body spin–orbit interaction (SOI), local and nearest-neighbor Coulomb repulsion (CR), and presence of external E electric and B magnetic fields (EF). The simultaneous presence of SOI, CR, and EF in the exact conducting polymer GS is a novelty, so the development of the technique for the treatment possibility of such strongly correlated cases is presented in detail. The deduced GS show a broad spectrum of physical characteristics ranging from charge density waves doubling the system periodicity, metal–insulator transitions, to interesting external field-driven effects as, e.g., modification possibility of a static charge distribution by a static EF.