We report on a theoretical study on the tunneling anomalous Hall effect (TAHE) in a ferroelectric tunnel junction (FTJ), resulting from spin-orbit coupling (SOC) in the ferroelectric barrier. For ferroelectric barriers with large SOC, such as orthorhombic HfO2 and BiInO3, we predict values of the tunneling anomalous Hall conductivity (TAHC) measurable experimentally. We demonstrate strong anisotropy in TAHC depending on the type of SOC. For the SOC with equal Rashba and Dresselhaus parameters, we predict the perfect anisotropy with zero TAHC for certain magnetization orientations. The TAHC changes sign with ferroelectric polarization reversal providing a new functionality of FTJs. Conversely, measuring the TAHC as a function of magnetization orientation offers an efficient way to quantify the type of SOC in the insulating barrier. Our results provide a new insight into the TAHE and open avenues for potential device applications.
Using a simple quantum-mechanical model, we explore a tunneling anisotropic magnetoresistance (TAMR) effect in ferroelectric tunnel junctions (FTJs) with a ferromagnetic electrode and a ferroelectric barrier layer, which spontaneous polarization gives rise to the Rashba and Dresselhaus spin-orbit coupling (SOC). For realistic parameters of the model, we predict sizable TAMR measurable experimentally. For asymmetric FTJs, which electrodes have different work functions, the built-in electric field affects the SOC parameters and leads to TAMR dependent on ferroelectric polarization direction. The SOC change with polarization switching affects tunneling conductance, revealing a new mechanism of tunneling electroresistance (TER). These results demonstrate new functionalities of FTJs which can be explored experimentally and used in electronic devices.
We consider the notion of zilch current that was recently discussed in the literature as an alternative helicity measure for photons. Developing this idea, we suggest the generalization of the zilch for the systems of fermions. We start with the definition of the photonic zilch current in chiral kinetic theory framework and work out field-theoretical definition of the fermionic zilch using the Wigner function formalism. This object has similar properties to the photonic zilch and is conserved in the non-interacting theory. We also show that, in full analogy with a case of photons, the fermionic zilch acquires a non-trivial contribution due to the medium rotation - zilch vortical effect (ZVE) for fermions. Combined with a previously studied ZVE for photons, these results form a wider set of chiral effects parameterized by the spin of the particles and the spin of the current. We briefly discuss the origin of the ZVE, its possible relation to the anomalies in the underlying microscopic theory and possible application for studying the spin polarization in chiral media.
We discuss the aspects of synchronization on inhomogeneous star-like graphs with long rays in the Kuramoto model framework. We assume the positive correlation between internal frequencies and degrees for all nodes which supports the abrupt first-order synchronization phase transition. It is found that different ingredients of the graph get synchronized at different critical couplings. Combining numerical and analytic tools, we evaluate all critical couplings for the long star graph. Surprisingly, it is found that at strong coupling there are discrete values of coupling constant that support the synchronized states with emerging $\mathbb{Z}_{p}$ symmetries. The stability of the synchronized phase is discussed, and the interpretation of the phase with emerging $\mathbb{Z}_{p}$ symmetry for the Josephson array on a long star graph is mentioned.
Spin accumulation and spin current are phenomena that enhanced the functionality of the devices operating with charge and spin. We calculated them for the system consisting of a ferroelectric barrier and a thin ferromagnetic layer when the current flows parallel to the interface. We assume Dresselhaus and Rashba spin-orbit coupling linear in electron wave number. We demonstrate that spin accumulation and spin current can be manipulated by changing the direction of the magnetization of the FM layer with respect to the crystallographic axes of the ferroelectric barrier.
Here, classical and quantum field theory of dipolar, axisymmetric quadrupolar and octupolar Bose gases is considered within a general approach. Dipole, axisymmetric quadrupole and octupole interaction potentials in the momentum representation are calculated. These results clearly demonstrate attraction and repulsion areas in corresponding gases. Then the Gross–Pitaevskii (GP) equation, which plays a key role in the present paper, is derived from the corresponding functional. The zoology of the form factors appearing in the GP equation is studied in details. The proper classes for the description of spatially non-uniform condensates form factors are chosen. In the Thomas–Fermi approximation a general solution of the GP equation with a quasilocal form factor is obtained. This solution has an interesting form in terms of a double rapidly converging series that universally includes all the interactions considered. Plots of condensate density functions for the exponential-trigonometric form factor are given. For the sake of completeness, in this paper we consider the GP equation with an optical lattice potential in the limit of small condensate densities. This limit does not distinguish between dipolar, quadrupolar and octupolar gases. An important analysis of the condensate stability, in other words the study of condensate excitations, is also performed in this paper. In the Gaussian approximation (from the Gross–Pitaevskii functional), a functional describing the perturbations of the condensate is derived in detail. This problem is an analog of the Bogolubov transformation used in the study of quantum Bose gases in operator formalism. For a probe wave function in the form of a plane wave, a spectrum of (Bogoliubov) excitations was obtained, from which an equation describing the threshold momentum for the emergence of instability was derived. An important result of this paper is the dependence of the threshold on the momentum of a stationary condensate. For completeness of the presentation, the approximating expression in the form of a rapidly converging series is obtained for the corresponding dependence, and plots of the corresponding series for the exponential-trigonometric form factor are given. Finally, in the conclusion a quantum hydrodynamic theory for dipolar, axisymmetric quadrupolar and octupolar gases is briefly presented, giving a clue to the experimental determination of the form factors.
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