Presence Of Magnetic Flux Research Articles

Interplay between hopping dimerization and quasi-periodicity on flux-driven circular current in an incommensurate Su–Schrieffer–Heeger ring

We report for the first time the phenomenon of flux-driven circular current in an isolated Su–Schrieffer–Heeger (SSH) quantum ring in presence of cosine modulation in the form of the Aubry–André–Harper (AAH) model. The quantum ring is described within a tight-binding framework, where the effect of magnetic flux is incorporated through Peierls substitution. Depending on the arrangements of AAH site potentials we have two different kinds of ring systems that are referred to as staggered and non-staggered AAH SSH rings. The interplay between the hopping dimerization and quasiperiodic modulation leads to several new features in the energy band spectrum and persistent current which we investigate critically. An atypical enhancement of current with increasing AAH modulation strength is obtained that gives a clear signature of transition from a low conducting phase to a high conducting one. The specific roles of AAH phase, magnetic flux, electron filling, intra- and inter-cell hopping integrals, and ring size are discussed thoroughly. We also study the effect of random disorder on persistent current with hopping dimerization to compare the results with the uncorrelated ones. Our analysis can be extended further in studying magnetic responses of similar kinds of other hybrid systems in presence of magnetic flux.

Electron Propagation in Molybdenum Disulfide Quantum Dot in the Presence of Magnetic Flux

Electron Propagation in Molybdenum Disulfide Quantum Dot in the Presence of Magnetic Flux

Higher-Order Weyl Semimetals.

We investigate higher-order Weyl semimetals (HOWSMs) having bulk Weyl nodes attached to both surface and hinge Fermi arcs. We identify a new type of Weyl node, which we dub a 2nd-order Weyl node, that can be identified as a transition in momentum space in which both the Chern number and a higher order topological invariant change. As a proof of concept we use a model of stacked higher order quadrupole insulators (QI) to identify three types of WSM phases: 1st order, 2nd order, and hybrid order. The model can also realize type-II and hybrid-tilt WSMs with various surface and hinge arcs. After a comprehensive analysis of the topological properties of various HOWSMs, we turn to their physical implications that show the very distinct behavior of 2nd-order Weyl nodes when they are gapped out. We obtain three remarkable results: (i)the coupling of a 2nd-order Weyl phase with a conventional 1st-order one can lead to a hybrid-order topological insulator having coexisting surface cones and flat hinge arcs that are independent and not attached to each other. (ii)A nested 2nd-order inversion-symmetric WSM by a charge-density wave (CDW) order generates an insulating phase having coexisting flatband surface and hinge states all over the Brillouin zone. (iii)A CDW order in a time-reversal symmetric higher-order WSM gaps out a 2nd-order node with a 1st-order node and generates an insulating phase having coexisting surface Dirac cone and hinge arcs. Moreover, we show that a measurement of charge density in the presence of magnetic flux can help to identify some classes of 2nd-order WSMs. Finally, we show that periodic driving can be utilized as a way for generating HOWSMs. Our results are relevant to metamaterials as well as various phases of Cd_{3}As_{2}, KMgBi, and rutile-structure PtO_{2} that have been predicted to realize higher order Dirac semimetals.

Rashba-controlled two-electron spin-charge qubits as building blocks of a quantum computer

The spin-sensitive charge oscillation, controlled by an external magnetic field, was recently proposed as a mechanism of transformations of qubits, defined as two-electron spin-charge Wannier molecules in a square quantum dot.1 The paper expands this idea by including the effects of Rashba-type spin-orbit coupling. The problem is studied theoretically by mapping the system to an analytic effective Hamiltonian for 8 low-energy states, comprising singlet and triplet on each dot diagonal. The validity of mapping is confirmed by comparing the energy and spin of full and mapped system, and also by the reproduction of charge-oscillation dynamics in the presence of magnetic flux. The newly introduced Rashba coupling significantly enriches the system dynamics, affecting the magnitude of charge oscillations and allowing the controlled transitions between singlet and triplet states due to the spin rotations, induced by spin-orbit coupling. The results indicate the possibility for use of the studied system for quantum information processing, while possible extensions of the system to serve as a qubit in a universal quantum computer, fulfilling all five Di Vincenzo criteria, is also discussed.

Radiative heat transfer in Homann stagnation-point flow of hybrid nanofluid

In this paper, we study the heat transfer for $$({\text {Al}}_{{2}}{\text {O}}_{{3}} -{\text {Cu}}/{\text {water}})$$ hybrid nanofluid in non-axisymmetric Homann stagnation region by adopting the Tiwari and Das model in the presence of magnetic flux. The importance of nanoparticle shape factor, i.e., cylinder, blades, bricks, and platelets has been studied under the time-independent free stream. Further, the impact of non-linear thermal radiations on the heat transfer process is investigated. The resulting equations representing the physical problem are transformed by adopting the proper variables. Through asymptotic approach, the resultant problem is scrutinized for large- $$\gamma$$ (shear-to-strain-rate ratio) through bvp4c technique in MATLAB. The impression of significant parameters for both single nanoparticle and hybrid nanofluid on the flow field, temperature, skin friction and local Nusselt number is reported through tabular and graphical depictions. It is noted that the fluid temperature in the hybrid phase has always been greater than the nanophase.

Many-Body Chiral Edge Currents and Sliding Phases of Atomic Spin Waves in Momentum-Space Lattice.

Collective excitations (spin waves) of long-lived atomic hyperfine states can be synthesized into a Bose-Hubbard model in momentum space. We explore many-body ground states and dynamics of a two-leg momentum-space lattice formed by two coupled hyperfine states. Essential ingredients of this setting are a staggered artificial magnetic field engineered by lasers that couple the spin wave states and a state-dependent long-range interaction, which is induced by laser dressing a hyperfine state to a Rydberg state. The Rydberg dressed two-body interaction gives rise to a state-dependent blockade in momentum space and can amplify staggered flux-induced antichiral edge currents in the many-body ground state in the presence of magnetic flux. When the Rydberg dressing is applied to both hyperfine states, exotic sliding insulating and superfluid (supersolid) phases emerge. Because of the Rydberg dressed long-range interaction, spin waves slide along a leg of the momentum-space lattice without costing energy. Our study paves a route to the quantum simulation of topological phases and exotic dynamics with interacting spin waves of atomic hyperfine states in momentum-space lattice.

Thermal analysis for radiative flow of magnetized Maxwell fluid over a vertically moving rotating disk

In the current framework, we study the chemically reactive Maxwell fluid flow over a vertically moving upward/downward rotating disk during the unsteady motion in the presence of magnetic flux. The problem formulation is made in a manner that governing equations of the physical phenomenon ultimately reduce to classical von Karman viscous pumping problem in the absence of vertical motion. Additionally, the aspects of chemical reaction and nonlinear radiations on heat and mass transfer analysis are studied. For the analysis, we use the similarity transformations that convert the governing system of partial differential equations into ordinary ones. The solution of the transformed system is obtained numerically using bvp4c in MATLAB. The numerical outcomes are demonstrated through graphical and tabular depictions. The results of velocity, temperature and concentration fields are discussed in the presence of upward/downward motion of the disk, magnetic parameter, Deborah number, Schmidt number and chemical reaction parameter. Significant outcomes reveal that the impact of disk upward motion parameter boosts the radial and angular flows. It is further noted that the heat transfer rate grows considerably with the disk rotation and radiation parameters. Moreover, Schmidt and chemical reaction parameters play a vital role in enhancing the Sherwood number.

Unconventional localization phenomena in a spatially non-uniform disordered material

A completely opposite behavior of electronic localization is revealed in a spatially non-uniform disordered material compared to the traditional spatially uniform disordered one. This fact is substantiated by considering an order-disorder separated (ODS) nanotube and studying the response of non-interacting electrons in presence of magnetic flux. We critically examine the behavior of flux induced energy spectra and circular current for different band fillings, and it is observed that maximum current amplitude (MCA) gradually decreases with disorder strength for weak disorder regime, while surprisingly it (MCA) increases in the limit of strong disorder suppressing the effect of disorder, resulting higher conductivity. This is further confirmed by investigating Drude weight and exactly same anomalous feature is noticed. It clearly gives a hint that localization-to-delocalization transition (LTD) is expected upon the variation of disorder strength which is justified by analyzing the nature of different eigenstates. Our analysis may give some significant inputs in analyzing conducting properties of different doped materials.

Spin-charge separation in an Aharonov-Bohm interferometer

We study manifestations of spin-charge separation (SCS) in transport through a tunnel-coupled interacting single-channel quantum ring. We focus on the high-temperature case (temperature $T$ larger than the level spacing $\Delta$) and discuss both the classical (flux-independent) and interference contributions to the tunneling conductance of the ring in the presence of magnetic flux. We demonstrate that the SCS effects, which arise solely from the electron-electron interaction, lead to the appearance of a peculiar fine structure of the electron spectrum in the ring. Specifically, each level splits into a series of sublevels, with their spacing governed by the interaction strength. In the high-$T$ limit, the envelope of the series contains of the order of $T/\Delta$ sublevels. At the same time, SCS suppresses the tunneling width of the sublevels by a factor of $\Delta/T$. As a consequence, the classical transmission through the ring remains unchanged compared to the noninteracting case: the suppression of tunneling is compensated by the increase of the number of tunneling channels. On the other hand, the flux-dependent contribution to the conductance depends on the interaction-induced dephasing rate which is known to be parametrically increased by SCS in an infinite system. We show, however, that SCS is not effective for dephasing in the limit of weak tunneling. Moreover, generically, in the almost closed ring, the dephasing rate does not depend on the interaction strength and is determined by the tunneling coupling to the leads. In certain special symmetric cases, dephasing is further suppressed. Similar to the spinless case, the high-$T$ conductance shows, as a function of magnetic flux, a sequence of interaction-induced sharp negative peaks on top of the classical contribution.

Monopole operators from the 4 − ϵ expansion

Three-dimensional quantum electrodynamics with $N$ charged fermions contains monopole operators that have been studied perturbatively at large $N$. Here, we initiate the study of these monopole operators in the $4-\epsilon$ expansion by generalizing them to codimension-3 defect operators in $d = 4-\epsilon$ spacetime dimensions. Assuming the infrared dynamics is described by an interacting CFT, we define the "conformal weight" of these operators in terms of the free energy density on $S^2 \times \mathbb{H}^{2-\epsilon}$ in the presence of magnetic flux through the $S^2$, and calculate this quantity to next-to-leading order in $\epsilon$. Extrapolating the conformal weight to $\epsilon = 1$ gives an estimate of the scaling dimension of the monopole operators in $d=3$ that does not rely on the $1/N$ expansion. We also perform the computation of the conformal weight in the large $N$ expansion for any $d$ and find agreement between the large $N$ and the small $\epsilon$ expansions in their overlapping regime of validity.

Characteristics of persistent spin current components in a quasi-periodic Fibonacci ring with spin–orbit interactions: Prediction of spin–orbit coupling and on-site energy

In the present work we investigate the behavior of all three components of persistent spin current in a quasi-periodic Fibonacci ring subjected to Rashba and Dresselhaus spin–orbit interactions. Analogous to persistent charge current in a conducting ring where electrons gain a Berry phase in presence of magnetic flux, spin Berry phase is associated during the motion of electrons in presence of a spin–orbit field which is responsible for the generation of spin current. The interplay between two spin–orbit fields along with quasi-periodic Fibonacci sequence on persistent spin current is described elaborately, and from our analysis, we can estimate the strength of any one of two spin–orbit couplings together with on-site energy, provided the other is known.

Yukawa couplings in 6D gauge–Higgs unification onT2/ZNwith magnetic fluxes

We discuss the Yukawa couplings in 6D gauge-Higgs unification models on $T^2/Z_N$ in the presence of magnetic fluxes. We provide general formulae for them, and numerically evaluate their magnitude in a specific model on $T^2/Z_3$. Thanks to the nontrivial profiles of the zero-mode wave functions, the top quark Yukawa coupling can be reproduced without introducing a large representation of the gauge group for matter fields. However, it is difficult to realize small Yukawa couplings only by the magnetic fluxes and the Wilson-line phases because of the complicated structure of the mode functions on $T^2/Z_N$ ($N=3,4,6$).

Conformation dependent magnetotransport in a single handed helical geometry

Conformation dependent circular current is investigated in a single handed helical geometry in presence of magnetic flux ϕ within a Hartree–Fock mean field approach. The helical model is approximated as a set of non-planar rings connected by some bonds describing the proximity effect between two nearby sites of the two successive rings. By stretching and compressing the geometry, circular current can be regulated significantly and thus the system can be exploited to design current controlled device at the nano-scale level. The proximity effect between the sites is also discussed in detail which exhibits interesting results.

Collapse and revival of entanglement of two-qubit in superconducting quantum dot lattice with magnetic flux and inhomogeneous gate voltage

We study the entanglement of a two-qubit system in a superconducting quantum dot (SQD) lattice in the presence of magnetic flux and gate voltage. The ground state is always in a maximally entangled Bell state for homogeneous gate voltage. In the presence of inhomogeneous gate voltage, the half-integer magnetic flux quantum, completely washes out the entanglement of the system at zero temperature. The entanglement is much higher for the Mott insulating phase. At finite temperature, collapse of entanglement occurs for wider region of magnetic flux.

The impact of quantum dots magnetization on spin separation and spin current in a multiple quantum-dot ring in the presence of Rashba spin-orbit coupling

The influence of quantum dot magnetization on electronic spin-dependent transport is investigated through a triple-quantum-dot ring structure in which one of the quantum dots is non-magnetic subjected to the Rashba spin-orbit interaction and the two other ones possess magnetic structure. Evaluated results, based on single particle Green’s function formalism, indicate that the presence of magnetic moment on the quantum dots leads to additional spin-dependent phase factor which affects electronic transport through the system. For both antiferromagnetic and ferromagnetic quantum dots, the system can operate as a spin-splitter but differently; by tuning Rashba spin-orbit strength and in the presence of magnetic flux, respectively. Besides, in the absence of one of the outgoing leads, spin current in the output is calculated and demonstrated that magnetization of quantum dots leads to spin current even in the absence of Rashba spin-orbit effect. Moreover, it is shown that in the presence of Rashba spin orbit interaction, magnetic quantum dots, and magnetic flux, the two terminal system produces a completely tunable spin current.

NONUNIVERSAL TUNNELING RESISTANCE AT THE QUANTUM CRITICAL POINT OF MESOSCOPIC SQUIDS ARRAY

We calculate the tunneling resistance at the quantum critical point of a mesoscopic SQUIDs array in the presence of magnetic flux. We observe nonuniversal bahaviour of tunneling resistance. We find the analytical relation between the magnetic flux induced dissipation strength and the Luttinger liquid parameter of the system. We also predict the evidence of length scale independent metallic state. This study also emphasizes the importance of co-tunneling effect.

Nonlinear optical properties in a nanoring: quantum size and magnetic field effect

We have studied the nonlinear optical absorption and the nonlinear optical rectification of an exciton in a nanoring in the presence of magnetic flux. The calculation results show that one can control the properties of nonlinear optical absorption and nonlinear optical rectification of a nanoring by tuning the outer and inner radius. Moreover, we find that the nonlinear optical properties of a nanoring can be modulated by the magnetic flux through the nanoring.

Interacting spinless fermions in a diamond chain

We study spinless fermions in a flux threaded AB$_2$ chain taking into account nearest-neighbor Coulomb interactions. The exact diagonalization of the spinless AB$_2$ chain is presented in the limiting cases of infinite or zero nearest-neighbor Coulomb repulsion for any filling. Without interactions, the AB$_2$ chain has a flat band even in the presence of magnetic flux. We show that the respective localized states can be written in the most compact form as standing waves in one or two consecutive plaquettes. We show that this result is easily generalized to other frustrated lattices such as the Lieb lattice. A restricted Hartree-Fock study of the $V/t$ versus filling phase diagram of the AB$_2$ chain has also been carried out. The validity of the mean-field approach is discussed taking into account the exact results in the case of infinite repulsion. The ground-state energy as a function of filling and interaction $V$ is determined using the mean-field approach and exactly for infinite or zero $V$. In the strong-coupling limit, two kinds of localized states occur: one-particle localized states due to geometry and two-particle localized states due to interaction and geometry. These localized fermions create open boundary regions for itinerant carriers. At filling $\rho=2/9$ and in order to avoid the existence of itinerant fermions with positive kinetic energy, phase separation occurs between a high-density phase ($\rho=2/3$) and a low-density phase ($\rho=2/9$) leading to a metal-insulator transition. The ground-state energy reflects such phase separation by becoming linear on filling above 2/9. We argue that for filling near or larger than 2/9, the spectrum of the t-V AB$_2$ chain can be viewed as a mix of the spectra of Luttinger liquids (LL) with different fillings, boundary conditions, and LL velocities.

Electronic energy levels of nanorings with impurities and Aharonov–Bohm effects

By modeling impurities along a nanoring as general potential forms the Schrödinger equation for ballistic electrons is shown to separate in cylindrical coordinates. We find an analytical eigenvalue equation for N delta-function-barrier impurities in the presence of magnetic flux. Previous calculations of the electronic states of a one-dimensional (1D) and two-dimensional (2D) nanoring for only one or two impurities modeled by equal square barriers is explicitly extended to three and four different or equal impurities modeled as delta-barrier, square-barrier, or delta-well potential forms. This is shown to be generalizable to any number N. Effects on the energy spectra due to magnetic flux and different kinds and numbers of impurities are compared in 1D and 2D nanorings.

Edged topological disordered quantum ring in the presence of magnetic flux

The effects of edged topological disorder on persistent current and magnetic susceptibility are investigated in a two-dimensional quantum ring enclosed within a magnetic flux in tight binding model. In an ordered quantum ring, persistent current shows kink-like variation, while in an edged topological disordered quantum ring, disorder-averaged current gets continuous variation due to appearance of energy gaps in energy spectra. Magnetic susceptibility has delta-like paramagnetic peaks in an ordered quantum ring, while in the edged topological disordered one; the delta-like peaks become wider and begin to overlap. In addition magnetic susceptibility versus magnetic flux shows a sign reversal, which depends on the disordered configuration. In the ordered quantum ring, the temperature-averaged current decreases when the temperature increases, while in the edged topological disordered one, at first temperature-averaged current raises somewhat and then reduces in a general thermal behavior manner. At absolute zero temperature, in strong regime; the disorder-averaged current versus magnetic flux is periodic with the period of Φ 0 / 2 ; whereas, this period is Φ 0 in weak regime or in an ordered one ( Φ 0 is magnetic flux quantum). Within higher temperatures, the period of Φ 0 is achieved only in the ordered ring and Φ 0 / 2 in either weak or strong regime, wide or narrow ring.