The European Physical Journal B最新文献

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.

We present a review of the Non-additive Stochastic Model (NSM) for supercooled liquids, an efficient approach for diffusive processes that provide a suitable interpretation for the non-Arrhenius dynamics in these materials. Based on a class of non-homogeneous continuity equations, the NSM provides functions to model the thermal behavior of the viscosity and diffusivity in fragile liquids. The model defines a rigorous physical criterion that distinguishes super-Arrhenius from sub-Arrhenius processes, establishes a robust scale of fragility, describes fragile-to-strong curves in Angell’s plot, and provides an accurate fitting equation for experimental viscosity data as effective as others viscosity classic models.

 Multiferroics are materials where a single cell of a magnetically ordered crystal forms an electric dipole moment. In this work, we derive an equation for the evolution of the macroscopic density of the electric dipole moment (polarization of the system). For this purpose, we employ the quantum hydrodynamic method, which allows us to derive equations for the evolution of the macroscopic functions of quantum systems starting with the microscopic description. Here, we do not consider the microscopic level of individual electrons and ions; rather, we start our analysis from the combination of ions in the cells of the crystal. We present an effective Hamiltonian for the evolution of such intermediate-scale objects. We also apply the equation for the electric dipole moment of the single cell, which is re-contracted in the corresponding operator. Using this operator and the wave function of the combination of ions in the cell, we define the macroscopic density of the electric dipole moment. Finally, we apply the nonstationary Schrodinger equation with the chosen Hamiltonian in order to derive the equation for the evolution of the polarization which describes the dipole formed by the exchange-striction mechanism in type II multiferroic materials. The interaction-defined term in the polarization evolution equation is found to be proportional to the fourth space derivative of a mixed product (triple scalar product) of three spin-density vectors. Conditions are discussed for the regime where the interaction appears in a smaller order on the space derivatives.

We document the ground state phase diagram of the one-dimensional Kitaev chain with quasi-periodic disorder in the presence of two-body interactions. Our data were obtained for systems of (L=1000) sites using large-scale density-matrix renormalization group numerics and is benchmarked against known results for the clean system. We demonstrate that moderate quasi-periodic disorder stabilizes the topological phase both for repulsive and attractive interactions. For larger disorder strengths, the system features re-entrance behavior and multiple phase transitions.

Phase diagram as a function of the chemical potential and the disorder strength for repulsive interactions