The expectation value of the edge Majorana operator is calculated for the one-dimensional model of spinless fermions with nearest-neighbor interactions and with open boundary conditions. The ...consideration is performed for the regime of the topological insulator (gapped bulk excitations and edge modes inside the gap), and for the normal metal regime (gapless bulk excitations). We show that the expectation value of the edge Majorana operator can be formed by two contributions, from the bulk states, and from the localized edge modes.
Nitrogen-vacancy colour centres in diamond can undergo strong, spin-sensitive optical transitions under ambient conditions, which makes them attractive for applications in quantum optics, nanoscale ...magnetometry and biolabelling. Although nitrogen-vacancy centres have been observed in aggregated detonation nanodiamonds and milled nanodiamonds, they have not been observed in very small isolated nanodiamonds. Here, we report the first direct observation of nitrogen-vacancy centres in discrete 5-nm nanodiamonds at room temperature, including evidence for intermittency in the luminescence (blinking) from the nanodiamonds. We also show that it is possible to control this blinking by modifying the surface of the nanodiamonds.
Abstract
Quantum triangular-lattice antiferromagnets are important prototype systems to investigate numerous phenomena of the geometrical frustration in condensed matter. Apart from highly unusual ...magnetic properties, they possess a rich phase diagram (ranging from an unfrustrated square lattice to a quantum spin liquid), yet to be confirmed experimentally. One major obstacle in this area of research is the lack of materials with appropriate (ideally tuned) magnetic parameters. Using Cs
2
CuCl
4
as a model system, we demonstrate an alternative approach, where, instead of the chemical composition, the spin Hamiltonian is altered by hydrostatic pressure. The approach combines high-pressure electron spin resonance and r.f. susceptibility measurements, allowing us not only to quasi-continuously tune the exchange parameters, but also to accurately monitor them. Our experiments indicate a substantial increase of the exchange coupling ratio from 0.3 to 0.42 at a pressure of 1.8 GPa, revealing a number of emergent field-induced phases.
The effect of the modulation of a high-frequency ac magnetic field parallel to the dc one (longitudinal pumping) by the lower-frequency ac field acting on quantum spin systems is considered for ...closed and open systems. For most magnetically ordered spin systems, the modulation causes the oscillation of the threshold of the parametric instability of spin waves as a function of the amplitude and the frequency of the modulation. On the other hand, our results for quantum spin systems with fermionic eigenstates imply that the modulating field causes the combined resonance and the modulation of the magnitude of time-dependent oscillations of the magnetization and the absorbed by the system power of the ac field for the closed system and for the open system in the dynamical and the steady-state regimes.
Existence of uniform trajectory and uniform global attractors for an incompressible non-Newtonian fluid (namely, for the mathematical model of nonlinearly viscous fluid motion) in 2D and 3D bounded ...domains is studied in this paper. For this aim the topological approximation method is effectively combined with the theory of attractors of trajectory spaces.
Several scenarios for the realization of edge Majorana modes in quantum chain systems, spin chains, chains of Josephson junctions, and chains of coupled cavities in quantum optics, are considered. ...For all these systems excitations can be presented as superpositions of a spinless fermion and a hole, characteristic of a Majorana fermion. We discuss the features of our exact solution with respect to possible experiments, in which edge Majorana fermions can be directly observed when studying magnetic, superconducting, and optical characteristics of such systems.
This paper is devoted to studying the solvability of one initial boundary value problem describing the motion of aqueous solutions of polymers. This model considers a nonlinearly viscous fluid. The ...existence of weak solutions for the considered problem is considered on the basis of a topological approximation approach. In addition, the problem of optimal feedback control is considered for the studied mathematical model. The existence of the optimal solution providing a minimum for the specified bounded and semicontinuous quality functional is proven.
On the basis of the trajectory pullback attractors theory, this paper studies the dynamics of weak solutions for a nonautonomous model of the polymer solutions motion (with the rheological relation ...satisfying the objectivity principle). For this model, we establish the existence of weak solutions, determine a family of trajectory spaces, introduce the concepts of trajectory and minimal pullback attractors, and prove the existence of these attractors.
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