We study the phase diagram and transport properties of arbitrarily doped quantum wires functionalized by magnetic adatoms. The appropriate theoretical model for these systems is a dense ...one-dimensional Kondo lattice (KL) which consists of itinerant electrons interacting with localized quantum magnetic moments. We discover the novel phase of the locally helical metal where transport is protected from a destructive influence of material imperfections. Paradoxically, such a protection emerges without a need of the global helicity, which is inherent in all previously studied helical systems and requires breaking the spin-rotation symmetry. We explain the physics of this protection of the new type, find conditions, under which it emerges, and discuss possible experimental tests. Our results pave the way to the straightforward realization of the protected ballistic transport in quantum wires made of various materials.
We study the Kondo chain in the regime of high spin concentration where the low energy physics is dominated by the Ruderman-Kittel-Kasuya-Yosida interaction. As has been recently shown (Tsvelik and ...Yevtushenko 2015 Phys. Rev. Lett. 115 216402), this model has two phases with drastically different transport properties depending on the anisotropy of the exchange interaction. In particular, the helical symmetry of the fermions is spontaneously broken when the anisotropy is of the easy plane type. This leads to a parametrical suppression of the localization effects. In the present paper we substantially extend the previous theory, in particular, by analyzing a competition of forward- and backward- scattering, including into the theory short range electron interactions and calculating spin correlation functions. We discuss applicability of our theory and possible experiments which could support the theoretical findings.
We study the phase diagram and transport properties of arbitrarily doped quantum wires functionalized by magnetic adatoms. The appropriate theoretical model for these systems is a dense ...one-dimensional Kondo lattice (KL) which consists of itinerant electrons interacting with localized quantum magnetic moments. We discover the novel phase of the locally helical metal where transport is protected from a destructive influence of material imperfections. Paradoxically, such a protection emerges without a need of the global helicity, which is inherent in all previously studied helical systems and requires breaking the spin-rotation symmetry. We explain the physics of this protection of the new type, find conditions, under which it emerges, and discuss possible experimental tests. Our results pave the way to the straightforward realization of the protected ballistic transport in quantum wires made of various materials.
Vaccination against COVID-19 is the main global preventive measure in the fight against SARS-CoV-2. As the COVID-19 vaccine will be administered to billions of individuals worldwide during the ...pandemic, there exists a reasonable fear of severe adverse reactions requiring constant vigilance and careful treatment, particularly in individuals with a history of severe allergy. The aim of our study was to develop and implement an algorithm for the safe vaccination against COVID-19 in patients with pathology associated with hypersensitivity reactions. From January to June 2022, after signing the informed consent, 126 adult patients with relevant diseases in remission were included in a prospective single-center study. Complaints and case histories were collected from all patients, including comorbidity and medications received, anthropometric data were studied, a standard clinical examination was performed, tryptase in venous blood was measured, the level of control was additionally assessed in patients with asthma using the asthma control test and spirography. According to the results of the study, it was proven that vaccination against COVID-19 in patients with pathology associated with hypersensitivity reactions is safe, on condition of prior consultation with an allergist and performing vaccination in a medical institution. The algorithm developed for preparing for vaccination in the mentioned above persons consists of a careful collection of case history; assessment and, in case of absence – achieving control of the underlying disease; analysis and correction of therapy with temporary replacement of medications that are potential cofactors of anaphylaxis; determination of blood tryptase level. For safe vaccination in patients with severe allergic anamnesis, administration of 20 mg of desloratadine before each dose of the vaccine with observation after vaccination within 30 minutes is suggested.
Optomechanical systems attract a lot of attention because they provide a novel platform for quantum measurements, transduction, hybrid systems, and fundamental studies of quantum physics. Their ...classical nonlinear dynamics is surprisingly rich and so far remains underexplored. Works devoted to this subject have typically focussed on dissipation constants which are substantially larger than those encountered in current experiments, such that the nonlinear dynamics of weakly dissipative optomechanical systems is almost uncharted waters. In this work, we fill this gap and investigate the regular and chaotic dynamics in this important regime. To analyze the dynamical attractors, we have extended the 'generalized alignment index' method to dissipative systems. We show that, even when chaotic motion is absent, the dynamics in the weakly dissipative regime is extremely sensitive to initial conditions. We argue that reducing dissipation allows chaotic dynamics to appear at a substantially smaller driving strength and enables various routes to chaos. We identify three generic features in weakly dissipative classical optomechanical nonlinear dynamics: the Neimark-Sacker bifurcation between limit cycles and limit tori (leading to a comb of sidebands in the spectrum), the quasiperiodic route to chaos, and the existence of transient chaos.
Abstract
Understanding possible mechanisms, which can lead to suppression of helical edge transport in quantum spin Hall (QSH) systems, attracted huge attention right after the first experiments ...revealing the fragility of the ballistic conductance. Despite the very intensive research and the abundance of theoretical models, the fully consistent explanation of the experimental results is still lacking. We systematize various theories of helical transport with the help of the spin conservation analysis which allows one to single out setups with the ballistic conductance being robustly protected regardless of the electron backscattering. First, we briefly review different theories of edge transport in the QSH samples with and without the spin axial symmetry of the electrons including those theoretical predictions which are not consistent with the spin conservation analysis and, thus, call for a deeper study. Next, we illustrate the general approach by a detailed study of representative examples. One of them addresses the helical edge coupled to an array of Heisenberg-interacting magnetic impurities (MIs) and demonstrates that the conductance remains ballistic even if the time-reversal symmetry on the edge is (locally) broken but the total spin is conserved. Another example focuses on the effects of the space-fluctuating spin–orbit interaction on the QSH edge. It reveals weakness of the protection in several cases, including, e.g. the presence of either the U(1)-symmetric, though not fully isotropic, MIs or generic electron–electron interactions.
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