Spin Precession Frequency Research Articles

Direct evidence for the all-in/all-out magnetic structure in the pyrochlore iridates from muon spin relaxation

In the pyrochlore iridates R${}_{2}$Ir${}_{2}$O${}_{7}$ (R = lanthanide, Y) determination of the magnetic structure of the iridium moments remains an outstanding problem despite the role this is expected to play in the formation of novel band structures and topologies in these materials. In this work, an analysis of the experimentally measured spontaneous muon spin precession frequency is presented which incorporates both probabilistic and ab initio modeling techniques to determine the ground state magnetic structure. It is shown that the experimentally observed results are consistent only with a magnetically ordered Ir${}^{4+}$ sublattice with the so-called ``all-in/all-out'' magnetic structure, and that the electronic state of the Ir${}^{4+}$ is best described by the ${J}_{\mathrm{eff}}=\frac{1}{2}$ model in several member compounds. Through this approach it is also demonstrated that such a simple structure is not likely to be present on the rare-earth sublattice which contains much larger localized moments.

Search for electric dipole moment in129Xe atom using active nuclear spin maser

An experimental search for an electric dipole moment in the diamagnetic atom 129 Xe is in progress through the precision measurement of spin precession frequency using an active nuclear spin maser. A 3 He comagnetometer has been incorporated into the active spin maser system in order to cancel out the long-term drifts in the external magnetic field. Also, a double-cell geometry has been adopted in order to suppress the frequency shifts due to interaction with polarized Rb atoms. The first EDM measurement with the 129 Xe active spin maser and the 3 He comagnetometer has been conducted.

Rf Wien filter in an electric dipole moment storage ring: The “partially frozen spin” effect

An rf Wien filter (WF) can be used in a storage ring to measure a particle's electric dipole moment (EDM). If the WF frequency equals the spin precession frequency without WF, and the oscillating WF fields are chosen so that the corresponding transverse Lorentz force equals zero, then a large source of systematic errors is canceled but the EDM signal is not. This effect, discovered by simulation, can be called the ``partially frozen spin'' effect.

Fermions with Lorentz-violating operators of arbitrary dimension

The theoretical description of fermions in the presence of Lorentz and $CPT$ violation is developed. We classify all Lorentz- and $CPT$-violating and invariant terms in the quadratic Lagrange density for a Dirac fermion, including operators of arbitrary mass dimension. The exact dispersion relation is obtained in closed and compact form, and projection operators for the spinors are derived. The Pauli Hamiltonians for particles and antiparticles are extracted, and observable combinations of operators are identified. We characterize and enumerate the coefficients for Lorentz violation for any operator mass dimension via a decomposition using spin-weighted spherical harmonics. The restriction of the general theory to various special cases is presented, including isotropic models, the nonrelativistic and ultrarelativistic limits, and the minimal Standard-Model Extension. Expressions are derived in several limits for the fermion dispersion relation, the associated fermion group velocity, and the fermion spin-precession frequency. We connect the analysis to some other formalisms and use the results to extract constraints from astrophysical observations on isotropic ultrarelativistic spherical coefficients for Lorentz violation.

Spin-precession-induced currents through ferromagnet/nanomagnet/superconductor junctions

The spin-precession-induced current through ferromagnet/nanomagnet/superconductor junctions is investigated by using the nonequilibrium Green’s function method. It is found that the charge current I c for the spin precession frequency ω less than the energy gap Δ only arises from the equal-spin Andreev reflection, which is independent of the spin polarization p of the ferromagnetic lead, while that for ω > Δ mainly originates from the quasiparticle’s contribution. Both equal-spin AR and quasiparticle scattering processes contribute to the spin current I s and the quasiparticle scattering process plays a dominant role. While I c for ω < Δ can be enhanced by the spin polarization p, I s decreases with p. These features may be of interest for ongoing experiments in the field of molecular spintronics.

Periastron advance in spinning black hole binaries: comparing effective-one-body and numerical relativity

We compute the periastron advance using the effective-one-body formalism for binary black holes moving on quasi-circular orbits and having spins collinear with the orbital angular momentum. We compare the predictions with the periastron advance recently computed in accurate numerical-relativity simulations and find remarkable agreement for a wide range of spins and mass ratios. These results do not use any numerical-relativity calibration of the effective-one-body model, and stem from two key ingredients in the effective-one-body Hamiltonian: (i) the mapping of the two-body dynamics of spinning particles onto the dynamics of an effective spinning particle in a (deformed) Kerr spacetime, fully symmetrized with respect to the two-body masses and spins, and (ii) the resummation, in the test-particle limit, of all post-Newtonian (PN) corrections linear in the spin of the particle. In fact, even when only the leading spin PN corrections are included in the effective-one-body spinning Hamiltonian but all the test-particle corrections linear in the spin of the particle are resummed we find very good agreement with the numerical results (within the numerical error for equal-mass binaries and discrepancies of at most 1% for larger mass ratios). Furthermore, we specialize to the extreme mass-ratio limit and derive, using the equations of motion in the gravitational skeleton approach, analytical expressions for the periastron advance, the meridional Lense-Thirring precession and spin precession frequency in the case of a spinning particle on a nearly circular equatorial orbit in Kerr spacetime, including also terms quadratic in the spin.

Muon-spin-rotation study of muon polarization losses in plastic scintillators and quartz

Muon polarization losses in plastic scintillators of two types and in fused quartz have been studied by the μSR method. The muon and muonium spin precession spectra have been measured on the μSR setup placed at the output of the muon channel of the Gatchina synchrocyclotron. It has been shown that a significant fraction of stopped muons participate in the formation of the muonium. As a result, these muons lose their polarization completely. The magnitude of muon depolarization depends considerably on the type of plastic. It has been found that the muon spin precession frequency in fused quartz in an external magnetic field (FQ, μ = 0.116 ± 0.002 MHz) is shifted with respect to that in plastic scintillators (F1, μ = 0.101 ± 0.005 MHz and F2, μ = 0.101 ± 0.002 MHz).

A dual‐isotope rubidium comagnetometer to search for anomalous long‐range spin‐mass (spin‐gravity) couplings of the proton

AbstractThe experimental concept of a search for a long‐range coupling between rubidium (Rb) nuclear spins and the mass of the Earth is described. The experiment is based on simultaneous measurement of the spin precession frequencies for overlapping ensembles of 85Rb and 87Rb atoms contained within an evacuated, antirelaxation‐coated vapor cell. Rubidium atoms are spin‐polarized in the presence of an applied magnetic field by synchronous optical pumping with circularly polarized laser light. Spin precession is probed by measuring optical rotation of far‐off‐resonant, linearly polarized laser light. Simultaneous measurement of 85Rb and 87Rb spin precession frequencies enables suppression of magnetic‐field‐related systematic effects. The nuclear structure of the Rb isotopes makes the experiment particularly sensitive to anomalous spin‐dependent interactions of the proton. Experimental sensitivity and a variety of systematic effects are discussed, and initial data are presented.

Magneto-intersubband oscillations of the kinetic coefficients of a two-dimensional system with a spin-orbit interaction

The temperature dependence of the Shubnikov–de Haas oscillations of longitudinal magnetoresistance of a two-dimensional electron system with the Rashba spin-orbit interaction is analyzed by using the expression for conductivity derived by S. G. Novokshonov and A. G. Groshev, Phys. Rev. B 74, 245333 (2006). It is shown that in the above system there exist magneto-intersubband oscillations of the kinetic coefficients characteristic for multisubband conductors. The period of these oscillations is determined by the spin precession frequency at the Fermi level ΩBF. In the case under consideration, the intersubband spin splitting depends on electron energy. This results in a weak temperature dependence of the magneto-intersubband oscillation amplitude, which is determined by Λ* = (2π2kBT/ℏωc)ℏ ΩBF / εF. This dependence is considerably weaker in comparison to the temperature smoothing of the Shubnikov–de Haas oscillation amplitude due to a small parameter (ℏ ΩBF /εF ≪ 1).

Localized States Influence Spin Transport in Epitaxial Graphene

We developed a spin transport model for a diffusive channel with coupled localized states that result in an effective increase of spin precession frequencies and a reduction of spin relaxation times in the system. We apply this model to Hanle spin precession measurements obtained on monolayer epitaxial graphene on SiC(0001). Combined with newly performed measurements on quasi-free-standing monolayer epitaxial graphene on SiC(0001) our analysis shows that the different values for the diffusion coefficient measured in charge and spin transport measurements on monolayer epitaxial graphene on SiC(0001) and the high values for the spin relaxation time can be explained by the influence of localized states arising from the buffer layer at the interface between the graphene and the SiC surface.

Zitterbewegungof neutral relativistic particles in static longitudinal fields

Zitterbewegung of neutral relativistic particles propagating along a constant magnetic and/or electric field is studied. It is shown that spin Zitterbewegung, when superimposed on the Larmor precession frequency, leads to a beating pattern. The existence of a forbidden frequency of spin precession is predicted. Modifications of position and velocity Zitterbewegung due to lifted spin degeneracy manifested in the appearance of longitudinal and transversal Zitterbewegung, each with two Zitterbewegung frequencies and resulting beating patterns, are reported.

Gas samples with a mixture of hydrogen isotopes and 3He for NMR spectroscopy and estimation of the magnetic moment of the 3He nucleus

We describe the technique for preparing high-pressure glass ampoules for NMR spectroscopy, which contain hydrogen isotopes (deuterium and protium) as well as the light helium isotope (3He). Using these ampoules, we succeeded in measuring the spin precession frequencies for 3He nuclei and the molecular deuterium nuclei and in calculating one of the fundamental physical constants, viz., the ratio of the magnetic moments of the helion and the proton μh/μp = −0.761 812 215(3).

Electron paramagnetic resonance study of spin centers related to charge transport in metallic polyaniline

Film-like conducting form of polyaniline (PANI), doped with 10-camphorsulfonic acid (CSA) and 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPSA) has been studied by multifrequency EPR spectroscopy at wide temperature range. Two types of paramagnetic centers with different magnetic resonance and mobility parameters were detected to be stabilized in metal-like domains and amorphous matrix of the samples. Sum spin susceptibility of the samples was shown to consist of the terms originated from paramagnetic centers localized in amorphous polymer backbone as well as spin charge carriers delocalized in embedded metal-like domains. The part of electron spins strongly interacts in the samples that resulting antiferromagnetic term in paramagnetic susceptibility. The delocalized paramagnetic centers characterizing by a stronger Pauli component in spin susceptibility are directly involved in the charge transfer, as compared to the localized ones. Their linewidth is governed by spin precession frequency and dipole–dipole interaction modulated by macromolecular torsional oscillations. The charge was described to be transferred in terms of the Mott quasi-one-dimensional variable range hopping of localized carriers through amorphous bridges between crystalline metal-like domains with mobile carriers interacting with the lattice phonons. The latter process is shown to be accelerated as AMPSA counterion is replaced by CSA one. The activation energy of spin dynamics in crystalline phase inversely correlates with the effective energy separation between localized states. This indicates a major role of dopant structure in local molecular-scale ordering and charge transport properties in doped PANI.

Growth of nuclear spin precession frequency of antiprotons (negative hyperons) under deceleration in matter with polarized nuclei

The Coulomb interaction leads to an increase of the real part of the amplitude of scattering of negatively charged particles (antiprotons, hyperons) by nuclei. In consequence, when antiprotons (negative hyperons) are decelerated in a medium with polarized nuclei, their effective energy of interaction with the medium and the nuclear spin precession frequency in a pseudomagnetic field grow as the particles decelerate. As a result, spin rotation of negatively charged particles becomes observable despite their rapid deceleration. This provides information about the spin-dependent part of the amplitude of coherent elastic zero-angle scattering in the range of low energies, where scattering experiments are practically impossible to perform.

Coherent spin dynamics of electrons and holes in semiconductor quantum wells and quantum dots under periodical optical excitation: Resonant spin amplification versus spin mode locking

The coherent spin dynamics of resident carriers, electrons and holes, in semiconductor quantum structures is studied by periodical optical excitation using short laser pulses and in an external magnetic field. The generation and dephasing of spin polarization in an ensemble of carrier spins, for which the relaxation time of individual spins exceeds the repetition period of the laser pulses, are analyzed theoretically. Spin polarization accumulation is manifested either as resonant spin amplification or as mode-locking of carrier spin coherences. It is shown that both regimes have the same origin, while their appearance is determined by the optical pump power and the spread of spin precession frequencies in the ensemble.

Electron spin synchronization induced by optical nuclear magnetic resonance feedback

We predict a new physical mechanism explaining the electron spin precession frequency focusing effect observed recently in singly charged quantum dots exposed to a periodic train of resonant circularly polarized short optical pulses [A. Greilich et al, Science 317, 1896 (2007), Ref. 1]. We show that electron spin precession in an external magnetic field and a field of nuclei creates a Knight field oscillating at the frequency of nuclear spin resonance. This field drives the projection of the nuclear spin onto magnetic field to the value that makes the electron spin precession frequency a multiple of the train cyclic repetition frequency, which is the condition at which the Knight field vanishes.

Microscopic Evidence for Long-Range Magnetic Ordering in the Γ8Ground Quartet Systems SmTr2Al20(Tr: Ti, V, Cr)

We report on muon spin relaxation (µSR) studies of Sm Tr 2 Al 20 ( Tr : Ti, V, Cr) with a cubic Γ 8 crystalline-electric-field ground state. A coherent muon spin precession was observed below the phase transition temperature in a zero applied field for each compound, manifesting long-range magnetic ordering from a microscopic point of view. The muon spin precession frequency distribution is qualitatively different among the three compounds, indicating differences in the magnetic structure and/or the muon stopping site.

Spin relaxation due to polar optical phonon scattering

Spin relaxation due to polar optical phonon scattering in semiconductors was investigated. The relaxation of the electron spin was found to increase with increasing the strength of the electric field. However, a high field completely depolarized the electron spin due to an increase of the spin precession frequency of the hot electrons, suggesting that high field transport conditions might not be desirable for spin-based technology with these semiconductors. It was also found that spin relaxation decreases with increasing moderately n-doping density or decreasing temperature. The results were discussed in comparison with the data available in the literature.

Dresselhaus field-induced anisotropic spin propagation in ZnSe/BeTe type-II quantum wells

The dynamics of photo-injected electrons and the propagation of photo-created spins in nondoped ZnSe/BeTe type-II quantum wells were investigated by time-resolved photo-induced circular dichroism microscopy at room temperature. Spin propagation from the pump spot presents a directionally dependent spin precession frequency in a magnetic field in Voigt configuration. This anisotropic spin propagation is ascribed to the Dresselhaus effect (G. Dresselhaus, Phys. Rev. 100, 580, 1955) on the radially diffusing photo-injected electrons, since the anisotropy depends on both the directions of crystallographic axis and magnetic field.

First-order nature of the ferromagnetism in CeIn2investigated using muon spin rotation and by systematic substitution of La for Ce

The nature of the first-order ferromagnetic transition in binary CeIn${}_{2}$ alloy is investigated by muon spin rotation ($\ensuremath{\mu}$SR) measurements and chemical substitution of Ce by La in the La${}_{1\ensuremath{-}x}$Ce${}_{x}$In${}_{2}$ ($0.9\ensuremath{\leqslant}x\ensuremath{\leqslant}1.0$) series of alloys. Below 22 K, the analysis of $\ensuremath{\mu}$SR spectra shows two spin precession frequencies associated with the local field at the muon site created by the surrounding ferromagnetic ordered magnetic moments. These frequencies abruptly disappear above ${T}_{C}$, indicating the first-order character of this transition, as previously reported. For temperatures between 22 and 24 K, the shape of the $\ensuremath{\mu}$SR spectra indicates the existence of an additional magnetic phase with features of an incommensurate magnetic structure. The presence of this magnetic phase is supported by dc(ac)-magnetic susceptibility and specific-heat results obtained on chemical diluted samples, which also show a magnetic contribution above the ferromagnetic transition. The combined analysis of these results clarifies the first-order character of the ferromagnetic transition in CeIn${}_{2}$, based on the existence of an intermediate magnetic phase between the paramagnetic and ferromagnetic states.