Spin-rotation Coupling Research Articles

Measurement of the spin–rotation coupling in neutron polarimetry

The effect of spin–rotation coupling is measured for the first time with neutrons. The coupling of spin with the angular velocity of a rotating spin turner can be observed as a phase shift in a neutron polarimeter set-up. After the neutron’s spin is rotated by 2π through a rotating magnetic field, different phase shifts are induced for ‘up’ and ‘down’ spin eigenstates. This phase difference results in the rotation of the neutron’s spin-vector, which turns out to depend solely on the frequency of the rotation of the magnetic field. The experimental results agree well with the solutions acquired by the Pauli–Schrödinger equation.

Relativistic theory of nuclear spin-rotation tensor with kinetically balanced rotational London orbitals.

Both kinetically balanced (KB) and kinetically unbalanced (KU) rotational London orbitals (RLO) are proposed to resolve the slow basis set convergence in relativistic calculations of nuclear spin-rotation (NSR) coupling tensors of molecules containing heavy elements [Y. Xiao and W. Liu, J. Chem. Phys. 138, 134104 (2013)]. While they perform rather similarly, the KB-RLO Ansatz is clearly preferred as it ensures the correct nonrelativistic limit even with a finite basis. Moreover, it gives rise to the same "direct relativistic mapping" between nuclear magnetic resonance shielding and NSR coupling tensors as that without using the London orbitals [Y. Xiao, Y. Zhang, and W. Liu, J. Chem. Theory Comput. 10, 600 (2014)].

Coherent spin–rotational dynamics of oxygen superrotors

We use state- and time-resolved coherent Raman spectroscopy to study the rotational dynamics of oxygen molecules in ultra-high rotational states. While it is possible to reach rotational quantum numbers up to by increasing the gas temperature to 1500 K, low population levels and gas densities result in correspondingly weak optical response. By spinning molecules with an optical centrifuge, we efficiently excite extreme rotational states with in high-density room temperature ensembles. Fast molecular rotation results in the enhanced robustness of the created rotational wave packets against collisions, enabling us to observe the effects of weak spin–rotation coupling in the coherent rotational dynamics of oxygen. The decay rate of spin–rotational coherence due to collisions is measured as a function of the molecular angular momentum and its dependence on the collisional adiabaticity parameter is discussed. We find that at high values of N, the rotational decoherence of oxygen is much faster than that of the previously studied non-magnetic nitrogen molecules, pointing at the effects of spin relaxation in paramagnetic gases.

Terahertz spectroscopy of methanimine and its isotopologs

Context. Methanimine (CH2NH) is a simple molecule composed of methylene and imine. The molecule has been detected toward the Galactic center, star-forming regions, circumstellar envelopes, and other galaxies since 1973. In previous studies, the rest frequency of methanimine has been measured for normal species up to the 650-GHz region, but its 13 CH2NH, CH2 15 NH, and CH2ND isotopologs were limited to the 100-GHz region. Aims. If a rotational temperature of 100 K is assumed for methanimine, the highest intensity falls at approximately 1.5 THz. In addition to normal methanimine, the 13 CH2NH, CH2 15 NH, and CH2ND isotopologs in their ground-vibrational states were observed in the frequency range of 120–1600 GHz to provide accurate rest frequency information. Based on this study, the calculated rest frequencies below 2 THz should be sufficiently precise and support observations using all ALMA and Herschel/HIFI observational bands. Methods. Methanimine was generated by pyrolysis of diaminoethane (DAE) vapor at 850 ◦ C. 13 CH2NH and CH2 15 NH isotopologs were measured with their natural abundance, and deuterization of DAE was performed by mixing normal DAE with deuterated water, D2O, and then pyrolyzed. This gives the deuterated isotopolog of methanimine, CH2ND. Spectral measurements were performed by using the 23 kHz source-frequency modulated terahertz spectrometer at Toho University. Results. Both a -a ndb-type transitions up to 1.6 THz for the three isotopologs and the normal species were measured. Rotational and centrifugal distortion constants for the three isotopologs were accurately determined. For normal species (CH2NH), both electric quadrupole and nuclear spin-rotation coupling constants for nitrogen nucleus were determined, while for the 13 CH2NH and CH2ND species, only electric quadrupole-coupling constants for nitrogen nucleus were determined. Conclusions. Our spectral line frequencies are suitable for a future astronomical search for these isotopologs of methanimine. The 1σ frequency accuracy up to 2 THz is lower than 100 kHz.

Fourier-transform microwave spectroscopy of the H2–H2O complex

Fourier-transform microwave spectroscopy was applied to observe the J=1–0 rotational transition of the ortho-H2–H2O complex and isotopologues in the ground Σ0 state (H2 in the jH2=1 state and H2O in the ground 000 state) to obtain precise molecular constants. Observed spectra were split into three hyperfine components, confirming the complexes are the ortho-H2/para-D2 species. The determined nuclear spin–spin coupling constant indicates H2 is rotating almost freely in the complex; the Σ0 state is nearly of jH2=1 and kH2=0. For the ortho-H2 species, the nuclear spin–rotation coupling constant was also determined.

Spin transport in non-inertial frame

The influence of acceleration and rotation on spintronic applications is theoretically investigated. In our formulation, considering a Dirac particle in a non-inertial frame, different spin related aspects are studied. The spin current appearing due to the inertial spin–orbit coupling (SOC) is enhanced by the interband mixing of the conduction and valence band states. Importantly, one can achieve a large spin current through the k→.p→ method in this non-inertial frame. Furthermore, apart from the inertial SOC term due to acceleration, for a particular choice of the rotation frequency, a new kind of SOC term can be obtained from the spin rotation coupling (SRC). This new kind of SOC is of Dresselhaus type and controllable through the rotation frequency. In the field of spintronic applications, utilizing the inertial SOC and SRC induced SOC term, theoretical proposals for the inertial spin filter, inertial spin galvanic effect are demonstrated. Finally, one can tune the spin relaxation time in semiconductors by tuning the non-inertial parameters.

Theory of mechanical spin current generation via spin–rotation coupling

The spin–rotation coupling (SRC) is responsible for angular momentum conversion between the electron spin and rotational deformations of elastic media, whereby spin current generation from mechanical motions is theoretically predicted. Here a surface acoustic wave (SAW) is considered as an example of such elastic deformations. We formulate the spin diffusion equation that is extended to include the influence of the SRC, and from the solution we find that larger spin currents can be obtained in materials with longer spin lifetimes. This distinct feature arises from the fact that the present method is of “purely” mechanical origin, i.e., it relies on neither equilibrium magnetization nor spin–orbit coupling, offering a new route to building the so-called “rare-metal-free” spintronics devices.

Synchrotron Based FT-FIR Pure Rotational Spectroscopy of the NH2 Radical in Its Two Lowest Vibrational States

Six Fourier-transform FIR spectra of the NH2 radical have been recorded at high resolution (0.001 cm(-1)) using synchrotron radiation on the AILES beamline at SOLEIL Synchrotron. Three different experimental discharge setups have been used to observe, in absorption, 1009 pure rotational transitions of NH2 in the vibrational ground state (000) and 170 pure rotational transitions within the first excited vibrational state (010). These results constitute a significant extension of the observed quantum numbers for these two states. The spectra permitted several couplings to be resolved (asymmetric coupling, spin-rotation coupling, hyperfine structure) for relatively highly excited energy levels. An effective fit has been realized using both standard Watson-S and -A reductions despite an abnormal centrifugal distortion effect for this light hydride.

New Experimental NMR Shielding Scales Mapped Relativistically from NSR: Theory and Application.

The recently proposed relativistic mapping between nuclear magnetic resonance (NMR) shielding and nuclear spin-rotation (NSR) coupling tensors [J. Chem. Phys. 2013, 138, 134104] is employed to establish new experimental (more precisely, experimentally derived) absolute shielding constants for H and X in HX (X = F, Cl, Br, and I). The results are much more accurate than the old "experimental" values that were based on the well-known nonrelativistic mapping. The relativistic mapping is very robust in the sense that it is rather insensitive to the quality of one-particle basis sets and the treatment of electron correlation. Relativistic effects in the NSR coupling constants are also elucidated in depth.

Should There Be a Spin-Rotation Coupling for a Dirac Particle?

It was argued by Mashhoon that a spin-rotation coupling term should add to the Hamiltonian operator in a rotating frame, as compared with the one in an inertial frame. For a Dirac particle, the Hamiltonian and energy operators H and E were recently proved to depend on the tetrad field. We argue that this non-uniqueness of H and E really is a physical problem. We compute the energy operator in the inertial and the rotating frame, using three tetrad fields: one for each of two frameworks proposed to select the tetrad field so as to solve this non-uniqueness problem, and one proposed by Ryder. We find that Mashhoon's term is there if the tetrad rotates as does the reference frame --- but then it is also there in the energy operator for the inertial frame. In fact, the Dirac Hamiltonian operators in two reference frames in relative rotation, but corresponding to the same tetrad field, differ only by the angular momentum term. If the Mashhoon effect is to exist for a Dirac particle, the tetrad field must be selected in a specific way for each reference frame.

Effect of spin rotation coupling on spin transport

We have studied the spin rotation coupling (SRC) as an ingredient to explain different spin-related issues. This special kind of coupling can play the role of a Dresselhaus like coupling in certain conditions. Consequently, one can control the spin splitting, induced by the Dresselhaus like term, which is unusual in a semiconductor heterostructure. Within this framework, we also study the renormalization of the spin-dependent electric field and spin current due to the k→⋅p→ perturbation, by taking into account the interband mixing in the rotating system. In this paper we predict the enhancement of the spin-dependent electric field resulting from the renormalized spin rotation coupling. The renormalization factor of the spin electric field is different from that of the SRC or Zeeman coupling. The effect of renormalized SRC on spin current and Berry curvature is also studied. Interestingly, in the presence of this SRC-induced SOC it is possible to describe spin splitting as well as spin galvanic effect in semiconductors.

Rotationally resolved ${\tilde{B}} \leftarrow {\tilde{X}}$B̃←X̃ electronic spectra of the isopropoxy radical: A comparative study

The B̃-X̃ laser-induced-fluorescence spectrum of jet-cooled isopropoxy radical (i-C3H7O[middle dot]) has been recorded. Using an isolated state model the observed rotational and fine structure of the origin band has been well simulated to determine rotational constants for both the X̃ and B̃ states and the electron spin-rotation constants of the X̃ state. The line intensities are well simulated with a parallel transition type, requiring the same symmetry for the levels involved of each the X̃ and B̃ state, which confirms the previous suggestion that going from ethoxy (C2H5O[middle dot]) to isopropoxy, the energy ordering of the electron configurations with in- and out-of-plane half-filled p-orbitals of the oxygen atom is reversed and the ground vibronic symmetry changes from a" to a'. However, the observed spin-rotation coupling constants are not consistent with their predication from either semi-empirical theory or quantum chemical calculations. Additionally, the lack of observed transitions involving the out-of-plane transition moment component is not consistent with high level electronic structure calculations suggesting mixing of vibronic levels by strong spin-orbit coupling. A new twofold model has been developed that explicitly includes Coriolis and spin-orbit coupling between different vibronic levels. This model renders the discrepancy between theoretical and experimental spin-rotation constants moot. Moreover, it determines independently the contributions to the observed splitting between the lowest two levels, resulting from non-relativistic kinetic and Coulombic effects, and that due to the relativistic spin-orbit interaction. The experimental values show that these effects are comparable, but that the vibronic one is slightly more important. This result is at variance with state-of-the-art electronic structure calculations which otherwise do a remarkably good job of describing the ground state of isopropoxy.

On the Non-uniqueness Problem of the Covariant Dirac Theory and the Spin-Rotation Coupling

Gorbatenko & Neznamov [arXiv:1301.7599] recently claimed the absence of the title problem. In this paper, the reason for that problem is reexplained by using the notions of a unitary transformation and of the mean value of an operator, invoked by them. Their arguments actually aim at proving the uniqueness of a particular prescription for solving this problem. But that prescription is again shown non-unique. Two Hamiltonians in the same reference frame in a Minkowski spacetime, only one of them including the spin-rotation coupling term, are proved to be physically non-equivalent. This confirms that the reality of that coupling should be checked experimentally.

Hawking radiation of Kerr-Newman black hole in different tortoise coordinate transformations

Hawking radiation effect of Maxwell’s electromagnetic fields in the Kerr-Newman black hole space-time is investigated using two different tortoise coordinate transformations. It has been shown that the new tortoise coordinate transformation produces constant term ξ in the expression of surface gravity and Hawking temperature. If ξ is set to zero, the surface gravity and Hawking temperature will be equal to those obtained from the old tortoise coordinate transformation. This indicates that new transformation is more reliable and accurate. The black body radiant spectrum of photon displays a new spin-rotation coupling effect.

Spin-rotation coupling and Thomas precession of ionsin a storage ring

We discuss the role of spin-rotation coupling and Thomas precession in the decayof hydrogen-like heavy ions that are injected in a storage ring. We find that the decay curve hasa time modulation that vanishes if the magnetic field also disappears. The results can be appliedto the recently reported modulation in the decay of the hydrogen-like ions 140Pr58+, 142Pm60+and 122I52+, where rotation couples to the spins of electron and nucleus. Spin-rotation couplingand Thomas precession also generate oscillations in the decay of a muon bound to a nucleusrotating in a storage ring.

Mechanical generation of spin current by spin-rotation coupling

Spin-rotation coupling, which is responsible for angular momentum conversion between the electron spin and rotational deformations of elastic media, is exploited for generating spin current. This method requires neither magnetic moments nor spin-orbit interaction. The spin current generated in nonmagnets is calculated in presence of surface acoustic waves. We solve the spin diffusion equation, extended to include spin-rotation coupling, and find that larger spin currents can be obtained in materials with longer spin lifetimes. Spin accumulation induced on the surface is predicted to be detectable by time-resolved Kerr spectroscopy.

Anomalous EPR Intensity Distribution of the Methyl Radical Quartet Adsorbed on the Surface of Porous Materials. Comparison with Solid Gas Matrix Isolation

The two inner lines of the EPR quartet of methyl radicals trapped in cryogenic gas matrices are superpositions of the inner transitions of an A-proton-spin quartet and an E-proton-spin doublet. Their intensity relative to the outer lines provides information on the population of the methyl-rotation quantum states. The above intensity ratio for the CH3 in solids is a challenging problem of the quantum dynamics and statistical thermodynamics. The influence of the quantum-mechanical/inertial rotation on the intensity distribution of the hf components of methyl radical on the surface of porous materials, e.g., silica gel, is investigated by EPR line shape simulations and compared with spectra of the radical isolated in the bulk of solid gas samples. The experimental part of this study includes the first in literature EPR observation of methyl radical in the bulk of N2O solid and provides new essential information on CH3 in CO2 and Ar matrices, thus, covering both strongly hindered and almost free rotation of the radical. We verify the observation of nonrotating methyl radicals in a N2O matrix, discovered earlier in cold CO2, give a thorough account of their EPR characteristics, and explore their formation at the inner surface of porous materials. Combination of a classical spin-Hamiltonian with employment of quantum effects due to nuclear spin-rotation coupling and the radical symmetry were used to interpret the experimental spectral observations. The cause of experimentally found unexpected contribution of the excited degenerate E-doublets to the EPR spectrum down to 4.2 K and A/E transition amplitude ratios sometimes as high as ca. 1:8 at liquid-N2 temperature is sought. The validity of Bose-Einstein quantum (BEq-) statistics of the spin rotation states in addition to the classical Maxwell-Boltzmann (Boltzmann) statistics was also assessed against experimental population A/E-ratio data. The BEq-statistics were not previously applied to similar systems. Furthermore, detailed consideration of the laboratory/free space rotational degeneracy and the planarity of methyl radical was also included in this work.

Renormalization of spin-rotation coupling

We predict the enhancement of the spin-rotation coupling due to the interband mixing. The Bloch wavefunctions in the presence of mechanical rotation are constructed with the generalized crystal momentum which includes a gauge potential arising from the rotation. Using the eight- band Kane model, the renormalized spin-rotation coupling is explicitly obtained. As a result of the renormalization, the rotational Doppler shift in electron spin resonance and the mechanical torque on an electron spin will be strongly modulated.

Spin-rotation coupling in compound spin objects

We generalize spin-rotation coupling to compound spin systems. In the case of muons bound to nuclei in a storage ring the decay process acquires a modulation. Typical frequencies for $Z/A\sim 1/2$ are $\sim 3\times 10^6$Hz, a factor 10 higher than the modulation observed in $g-2$ experiments.

High-resolution spectroscopic study of the C 0+ and D 1 Rydberg states of KrXe and of the X 1/2 and A1 3/2 states of KrXe+

The electronic spectrum of the C 0+, D 1←X 0+ transitions of KrXe has been studied at high resolution in the vicinity of the Kr(1S0)+Xe 6p[5/2]2 dissociation limit by resonance-enhanced (1+1′) two-photon ionization spectroscopy. The rotational structure of 13 bands, 5 and 8 of which correspond to transitions to levels of 0+ and 1 symmetry, respectively, were observed in the spectra of several isotopomers. The hyperfine structure in the spectrum of the Ω=1 levels of 84Kr129Xe was determined. The five transitions to levels of 0+ symmetry form a regular progression of bands characterized by a regular rotational structure and corresponding to high vibrational levels (with v=16–20) of the C 0+ state. The C 0+ state is found to possess significant X 1/2, A1 3/2 and A2 1/2 ion-core character in combination with an excited electron of 6pσ, 6pπ and 6sσ character, respectively, and to correlate adiabatically to the Kr(1S0)+Xe6s[1/2]1o dissociation limit. The transition to the eight levels of Ω=1 symmetry form a very irregular progression both as far as spectral positions and intensities are concerned. Rotational levels of f-symmetry, accessed via Q-branch transitions, are weakly predissociated by a repulsive level associated with the Kr(1S0)+Xe6s[1/2]0o limit. A local perturbation in the rotational structure of the fourth level of Ω=1 symmetry enabled the identification of a so far unobserved predissociative level of Ω=1 or Ω=2 symmetry with band center near 77318.5cm−1. The determination of the band centers, rotational constants and isotopic shifts of the Ω=1 levels led to the conclusion that the level structure is affected by homogeneous perturbations and that at least two electronic states of Ω=1 symmetry contribute to the spectrum of KrXe in this spectral region. Modelling the observed rovibronic structure using a coupling model involving low vibrational levels of a weakly bound Ω=1 state associated with the Kr(1S0)+Xe6s[1/2]1o dissociation limit and high vibrational levels of a more strongly bound state associated with the Kr(1S0)+Xe 6p[5/2]2 dissociation limit enabled us to reproduce the observed values of the rotational constants, vibronic positions and intensity distribution in a qualitatively satisfactory manner. However, the model failed to account for the observed isotopic shifts. Rotationally resolved photoelectron spectra of the KrXe+ X 1/2←KrXe C 0+ and KrXe+ A1 3/2←KrXe C 0+ ionizing transitions were recorded from selected rotational levels of selected isotopomers of KrXe. The rotational levels of the X 1/2 state of KrXe+ group as pairs of levels of opposite parity and have a spin-rotation coupling constant γ of approximately −2B, as a consequence of pure precession. The rotational level structure of the low-lying electronic states of KrXe+ thus appears to form the same patterns as the corresponding states of ArXe+.