Nonzero Orbital Momentum Research Articles

Optomechanical effects caused by non-zero field quantities in multiple evanescent waves.

Evanescent waves, with their high energy density, intricate local momentum, and spatial distribution of spins, have been the subject of extensive recent study. These waves offer promising applications in near-field particle manipulation. Consequently, it becomes imperative to gain a deeper understanding of the impacts of scattering and gradient forces on particles in evanescent waves to enhance and refine the manipulation capabilities. In this study, we employ the multipole expansion theory to present analytical expressions for the scattering and gradient forces exerted on an isotropic sphere of any size and composition in multiple evanescent waves. The investigation of these forces reveals several unusual optomechanical phenomena. It is well known that the scattering force does not exist in counter-propagating homogeneous plane waves. Surprisingly, in multiple pairs of counter-propagating evanescent waves, the scattering force can arise due to the nonzero orbital momentum (OM) density and/or the curl part of the imaginary Poynting momentum (IPM) density. More importantly, it is found that the optical scattering force can be switched on and off by simply tuning the polarization. Furthermore, optical forces typically vary with spatial position in an interference field. However, in the interference field generated by evanescent waves, the gradient force becomes a spatial constant in the propagating plane as the particle's radius increases. This is attributed to the decisive role of the non-interference term of the electromagnetic energy density gradient. Our study establishes a comprehensive and rigorous theoretical foundation, propelling the advancement and optimization of optical manipulation techniques harnessed through multiple evanescent waves. Specifically, these insights hold promise in elevating trapping efficiency through precise control and manipulation of optical scattering and gradient forces, stimulating further explorations.

Role of spin-orbit coupling in canted ferromagnetism and spin-wave dynamics of SrRuO3

A canted ferromagnetic arrangement with a long-range-ordered antiferromagnetic component is predicted for the metallic ${\mathrm{SrRuO}}_{3}$ orthoperovskite based on local-density-approximation-type electronic-structure calculation including on-site Coulomb repulsion $U$ and spin-orbit coupling. The electronic state of ${\mathrm{Ru}}^{4+}$ ions and the nature of nonzero orbital momentum are analyzed in detail. With regard to the density of states at the Fermi level, the value of the magnetic moment, and the easy axis along the $a$-axis in a Pbnm setting, a good agreement with the experimental data is achieved for $U=1$ eV. The calculated parameters of magnetic exchange, including the anisotropic and antisymmetric terms, are used to determine the magnon spectra. It is shown that notable anisotropic exchange in ${\mathrm{SrRuO}}_{3}$ is responsible for a gap of 1.7 meV at the $\mathrm{\ensuremath{\Gamma}}$ point of the magnon spectra, found previously by inelastic neutron diffraction. The origin of the spin canting that is confined within the $ab$-plane follows from the presence of the Dzyaloshinskii-Moriya interaction associated with the antisymmetric exchange.

Optomechanical circulator with a polaritonic microcavity

We study theoretically optomechanical interactions in a semiconductor microcavity with embedded quantum well under the optical pumping by a Bessel beam, carrying a non-zero orbital momentum. Due to the transfer of orbital momentum from light to phonons, the microcavity can act as an acoustic circulator: it rotates the propagation direction of the incident phonon by a certain angle clockwise or anticlockwise. Due to the optomechanical heating and cooling effects, the circulator can also function as an acoustic laser emitting sound with nonzero angular momentum. Our calculations demonstrate the potential of semiconductor microcavities for compact integrable optomechanical devices.

Isospin triplet A=12: search for states with enhanced radii

Two independent methods: Asymptotic Normalization Coefficients (ANC) and Modified Diffraction Model (MDM) were applied to new and existing experimental data to search for states with enhanced radii in isobaric analogue states (IAS) of 12B and 12N. The ANC analysis of the 11B(d,p)12B reaction at Ed = 21.5 MeV has confirmed neutron halo existence for two states of 12B: 2−, 1.67 MeV and 1−, 2.62 MeV [1]. Some new results were obtained for higher excited states: halo-like states were observed for 0+, 2.72 MeV and 3−, 3.39 MeV states. It should be mentioned that the last one is unbound state, which is 19 keV above the neutron emission threshold and in both states last neutron has a non-zero orbital momentum (ln=1 and ln=2 correspondingly). We propose to use MDM to study isobaric analogue states of 12B in the mirror 12N nucleus and apply it to analyze the (3He,t) reaction data. The existing in the literature data are not completed enough to make definite conclusion about halo in the 2− and 1− states of 12N. This fact simulated us to carry out a new experiment on the 12C(3He,t)12N reaction at the end of 2018. The measurements were conducted at the University of Jyväskylä (Finland) using the K130 cyclotron to produce a 3He beam at E(3He)=40 MeV. The differential cross sections of the 12C(3He,t)12N reaction were measured in the c.m. angular range 8°–70°. Preliminary results for angular distributions are obtained. MDM analysis of preliminary (3He,t) experimental data is done.

High-field anomalies of equilibrium and ultrafast magnetism in rare-earth–transition-metal ferrimagnets

Magneto-optical spectroscopy in fields up to 30 Tesla reveals anomalies in the equilibrium and ultrafast magnetic properties of the ferrimagnetic rare-earth-transition metal alloy TbFeCo. In particular, in the vicinity of the magnetization compensation temperature, each of the magnetizations of the antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis loops. Contrary to state-of-the-art theory, which explains such loops by sample inhomogeneities, here we show that they are an intrinsic property of the rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and have a non-zero orbital momentum in the ground state and, therefore, a large magnetic anisotropy, we are able to reproduce the experimentally observed behavior in equilibrium. The same theory is also able to describe the experimentally observed critical slowdown of the spin dynamics in the vicinity of the magnetization compensation temperature, emphasizing the role played by the orbital momentum in static and ultrafast magnetism of ferrimagnets.

Virtual Delbrück scattering and the Lamb shift in light hydrogenlike atoms

We return to the problem of evaluation of the light-by-light contribution to the energy levels of the hydrogen atom. We find an additional contribution directly related to the Delbr\"uck scattering amplitude. The new correction is larger than the previously included light-by-light terms at order~$\alpha^2 (Z\alpha)^6\ln(Z\alpha)\, m_e$. We consider the effective potential in position space using an effective field theory approach and evaluate light-by-light corrections to the energy levels of states with non-zero orbital momentum as well as to the weighted difference of $s$ states. We also determine the large distance asymptotic behaviour of the effective potential induced by the light-by-light scattering in muonic atoms.

Three-neutron resonance study using transition operators

Existing bound-state type calculations of three-neutron resonances yield contradicting results. A direct study of the three-neutron continuum using rigorous scattering equations with realistic potentials and search for possible resonances is aimed. Faddeev-type integral equations for three-neutron transition operators are solved in the momentum-space partial-wave framework. The evolution of resonances is studied by enhancing the strength of the two-neutron interaction in partial waves with nonzero orbital momentum. Calculated three-neutron transition operators exhibit resonant behavior for sufficiently large enhancement factors; pole trajectories in the complex-energy energy plane are extracted from their energy dependence. However, the resonant behavior completely disappears for the physical interaction strength. There are no physically observable three-neutron resonant states consistent with presently accepted interaction models.

Q-factor of spherical optical silicon dioxide nanoresonators

The Q-factor of the bound optical modes of silicon dioxide spheres with a radius smaller than one micron has been studied in the visible spectrum, showing that local photonic states with a nonzero orbital momentum yield a thin structure in glow spectra, whose maxima positions depend on the diameters of SiO2 nanospheres. A theoretical model to calculate the Q-factor of nanoresonators depending on the wavelengths of bound modes and the radius value of spheres has been proposed. It has been shown that the quality of an optical resonator increases as its diameter grows. The Q-factor values have been calculated for the visible light of the order of 10 for spheres smaller than 1 μm in diameter and 106 for spheres of more than 7 μm in diameter. A dependence of bound modes’ radiation propagation outside of the sphere on their wavelengths and orbital momenta has been detected.

Hopping Magnetotransport via Nonzero Orbital Momentum States and Organic Magnetoresistance

In hopping magnetoresistance of doped insulators, an applied magnetic field shrinks the electron (hole) s-wave function of a donor or an acceptor and this reduces the overlap between hopping sites resulting in the positive magnetoresistance quadratic in a weak magnetic field, B. We extend the theory of hopping magnetoresistance to states with nonzero orbital momenta. Different from s states, a weak magnetic field expands the electron (hole) wave functions with positive magnetic quantum numbers, m>0, and shrinks the states with negative m in a wide region outside the point defect. This together with a magnetic-field dependence of injection/ionization rates results in a negative weak-field magnetoresistance, which is linear in B when the orbital degeneracy is lifted. The theory provides a possible explanation of a large low-field magnetoresistance in disordered π-conjugated organic materials.

Gfactors and diamagnetic coefficients of electrons, holes, and excitons in InAs/InP quantum dots

The electron, hole, and exciton $g$ factors and diamagnetic coefficients have been calculated using envelope-function theory for cylindrical InAs/InP quantum dots in the presence of a magnetic field parallel to the dot symmetry axis. A clear connection is established between the electron $g$ factor and the amplitude of those valence-state envelope functions that possess nonzero orbital momentum associated with the envelope function. The dependence of the exciton diamagnetic coefficients on the quantum dot height is found to correlate with the energy dependence of the effective mass. Calculated exciton $g$ factor and diamagnetic coefficients, constructed from the values associated with the electron and hole constituents of the exciton, match experimental data well, however including the Coulomb interaction between the electron and hole states improves the agreement. Remote-band contributions to the valence-band electronic structure, included perturbatively, reduce the agreement between theory and experiment.

Scattering phases for particles with nonzero orbital momenta and resonance regimes in the Pais approximation

The functional Pais equation for scattering phases with nonzero orbital momenta is solved in the case of low-energy particles. For short-range screened potentials, in particular, Yukawa or Thomas-Fermi potentials, the Pais equation is shown to reduce to transcendental equations. For the potentials varying , , simple algebraic equations are obtained for determining the phases , . Possible applications of the Pais approximation to the problem of finding resonance regimes in the scattering of low-energy particles with nonzero orbital momenta are discussed.

Фазы рассеяния частиц с ненулевыми орбитальными моментами и резонансные ситуации в приближении Пайса

Фазы рассеяния частиц с ненулевыми орбитальными моментами и резонансные ситуации в приближении Пайса, Брук Ю.М., Волощук А.Н.

Partial cancellation of correlations in the nonrelativistic high-energy asymptotics of the photoeffect

We investigate the total effect of correlations on photoionization of atomic states with nonzero orbital momentum in the nonrelativistic high-energy asymptotic limit, considering the exclusive case of the dominant final state of an initial neutral atom. We find that the substantial cancellation of the dominant intrashell correlations, which had been reported earlier, can be understood utilizing the closure properties satisfied by the eigenfunctions of the nonrelativistic Hamiltonian. Considering the sum of correlations with all states, occupied or not, we show that complete sum is equal to the contribution of the high-energy part of the continuum. Consequently there is a total cancellation between the contributions of the bound states (occupied and unoccupied) and the low-energy part of the continuum states. This means that the real correlations in the physical atom due to the sum rule over the occupied states can be also obtained as the negative of the sum of contributions of low-energy bound and continuum unoccupied states. We calculate this in the framework of the quantum-defect model. As we would expect, the results are close to those obtained earlier in particular cases by direct summation over the occupied states. However this approach also allows us to see that the summore » of correlations over the occupied states is smaller than the dominant intrashell correlation. Hence, there is a partial cancellation between correlations with the occupied states. We can also obtain some limits on the correlation effects by considering calculations with the screened Coulomb functions. The role of correlations in the exclusive photoionization processes, also the modification of correlations in the case of atomic ions, is discussed.« less

Unconventional Pairs Glued by Conventional Phonons in Cuprate Superconductors

It has gone almost unquestioned that superexchange in the t−J (or Hubbard) model, and not phonons, is responsible for the unconventional (“d-wave”) pairing symmetry of cuprate superconductors. However, a number of advanced numerical studies have not found superconductivity in the Hubbard (or t−J) model. On the other hand, compelling experimental evidence for a strong electron–phonon interaction (EPI) has currently arrived. Here I briefly review some phonon-mediated unconventional pairing mechanisms. In particular the anisotropy of sound velocity makes the phonon-mediated attraction of electrons non-local in space providing unconventional Cooper pairs with a non-zero orbital momentum already in the framework of the conventional BCS theory with weak EPI. In the opposite limit of strong EPI rotational symmetry breaking appears as a result of a reduced Coulomb repulsion between unconventional bipolarons. Using the variational Monte Carlo method we have found that a relatively weak finite-range EPI induces a d-wave BCS state also in doped Mott–Hubbard insulators or strongly-correlated metals. These results tell us that poorly screened EPI with conventional phonons is responsible for the unconventional pairing in cuprate superconductors.

Unconventional pairing symmetry of layered superconductors caused by acoustic phonons

An inevitable anisotropy of sound velocity in crystals makes the phonon-mediated attraction of electrons nonlocal in space providing unconventional Cooper pairs with a nonzero orbital momentum. As a result of this anisotropy, quasi-two-dimensional charge carriers weakly coupled with acoustic phonons undergo a quantum phase transition from a conventional $s$-wave to an unconventional $d$-wave superconducting state with less carriers per unit cell. In the opposite strong-coupling regime, rotational symmetry breaking appears as a result of a reduced Coulomb repulsion between unconventional bipolarons dismissing thereby some constraints on unconventional pairing in the Bose-Einstein condensation limit. The conventional acoustic phonons, and not superexchange, are shown to be responsible for the $d$-wave symmetry of cuprate superconductors, where the on-site Coulomb repulsion is large.

Zerogfactors and nonzero orbital momenta in self-assembled quantum dots

We point out using an empirical tight-binding approach that the ground state of holes in $\mathrm{InAs}∕\mathrm{GaAs}$ self-assembled quantum dots carries nonzero orbital momentum. The spin and orbital motions of the hole state are found to have opposite contributions to the hole $g$ factor, leading to zero $g$ factors of holes and then excitons in dots of high aspect ratio. The nonzero envelope orbital momenta of the holes are also shown to account for anisotropic circular polarization of exciton emission and nonlinear Zeeman splittings in high magnetic fields. Our theory well explains recent experiments and indicates the possibility of engineering magnetic splitting by tuning the electric confinement in nanostructures.

Unconventional Strongly Interacting Bose-Einstein Condensates in Optical Lattices

Feschbach resonances in a non-s-wave channel of two-component bosonic mixtures can induce atomic Bose-Einstein condensates with a nonzero orbital momentum in the optical lattice, if one component is in the Mott insulator state and the other is not. Such non-s-wave condensates break the symmetry of the lattice and, in some cases, time-reversal symmetry. They can be revealed in specific absorption imaging patterns.

Interaction of a spin-1/2 particle with an electromagnetic field

An equation for the action of a spin-1/2 particle is proposed. The proposed action results in a second-order differential equation for the bispinor wavefunction of the particle. The obtained equation is compared with the Dirac equation. It is shown that all of the solutions of the Dirac equation satisfy the obtained equation. However, among the solutions of the second-order differential equation are solutions not satisfying the Dirac equation. The equation for the current density four-vector is derived. It is shown that the CPT transformation properties of the obtained current density four-vector are qualitatively different from that derived from those of the Dirac equation. The solution of the proposed equation for the problem of electron motion in the Coulomb field is found in analytically tractable form. The calculated spectrum is different from that described by the well-known Sommerfeld formula of the Dirac theory. The predicted spectrum includes the hyperfine structure which is doublet for the levels with the zero angular momentum and triplet for the levels with the non-zero orbital momentum. Analytically tractable solutions of the proposed equation are also found for the problems of electron motion in a uniform magnetic field, and in a superposition of Coulomb and uniform magnetic fields.

Asymptotic theory of s-->p charge exchange: Extended Demkov model.

The asymptotic theory is developed for the calculation of the charge-exchange amplitudes for large impact parameters \ensuremath{\rho}. The case of the small energy defect is considered which corresponds to the Demkov model (nonadiabatic transitions induced by the switching of the wave functions from the atomic states to the molecular-orbital regime). The effect of electron momentum transfer is included. The initial and final states with nonzero orbital momentum are considered with a special emphasis on the simplest case of s\ensuremath{\rightarrow}p charge exchange. The large-\ensuremath{\rho} asymptote of the charge-exchange amplitude is calculated both for the transitions induced by radial and rotational couplings. One-center depolarization transitions (changing the projection of the angular momentum) are also incorporated in the general theory. The orientation and alignment parameters characterizing the asymmetry created in the s\ensuremath{\rightarrow}p process are obtained in a simple analytical form for large \ensuremath{\rho} (or small scattering angles). They include contributions both from the one-center depolarization and from the competition of the charge exchange induced by radial and rotational coupling. The relative role of both mechanisms is analyzed and a strong dependence of the asymmetry parameters on the sign of the process energy defect is predicted. The theory is applied to the process Na(3p)+${\mathrm{H}}^{+}$\ensuremath{\rightarrow}${\mathrm{Na}}^{+}$+H(n=2).

Fractional-quantum-Hall scenario for two-dimensional spin systems and pairing due to statistical gauge forces.

We emphasize that the global SU(2) symmetry generated by total spin is broken in the thermodynamic limit in the fractional quantum Hall state proposed for two-dimensional spin systems. A scenario of superconductivity in this state is presented, based on the existence of fractional statistics particles with opposite values of statistical charge. We perform a self-consistent treatment of the pairing potential and obtain BCS-like pairing with nonzero orbital momentum.