Acoustic Paramagnetic Resonance Research Articles

Spin–phonon interactions in silicon carbide addressed by Gaussian acoustics

Hybrid spin-mechanical systems provide a platform for integrating quantum registers and transducers. Efficient creation and control of such systems require a comprehensive understanding of the individual spin and mechanical components as well as their mutual interactions. Point defects in silicon carbide (SiC) offer long-lived, optically addressable spin registers in a wafer-scale material with low acoustic losses, making them natural candidates for integration with high quality factor mechanical resonators. Here, we show Gaussian focusing of a surface acoustic wave in SiC, characterized by a novel stroboscopic X-ray diffraction imaging technique, which delivers direct, strain amplitude information at nanoscale spatial resolution. Using ab initio calculations, we provide a more complete picture of spin-strain coupling for various defects in SiC with C3v symmetry. This reveals the importance of shear for future device engineering and enhanced spin-mechanical coupling. We demonstrate all-optical detection of acoustic paramagnetic resonance without microwave magnetic fields, relevant to sensing applications. Finally, we show mechanically driven Autler-Townes splittings and magnetically forbidden Rabi oscillations. These results offer a basis for full strain control of three-level spin systems.

Semen A Altshuler: scientist, mentor, teacher

International Conference `Resonances in Condensed Matter' is devoted to 100 years of the birthday of the Corresponding member of Academy of Sciences of the USSR, Professor of the Kazan University Semen Alexandrovich Altshuler (1911–1983). He is well known by pioneer works on EPR, the prediction and grounds for an existence of the neutron magnetic moment, the prediction and the theory of the acoustic paramagnetic resonance, and as a founder of the Kazan scientific school `Magnetic radiospectroscopy of condensed matter' (with E K Zavoiskii and B M Kozyrev)

Mechanism of stratification of turbulent heat transfer in a sound field in the presence of rotational anisotropy of the flow

It is established that the stratification of the heat transfer intensity coefficients into n discrete levels, as discovered previously in the turbulent flow accompanying rotation of a supersonic flow, is described by the formula αn2/α12=2n−1, n=1,2,3,.... It is found that the ratio of the measured amplitudes of the discrete components of the pressure-pulsation spectrum is of a similar form and corresponds to the pressure field from multipole sources. As expected, similarly to the case of acoustic paramagnetic resonance, the selection of discrete frequencies of intense acoustic radiation from the external flow occurs under the influence of resonances with the radiation of multipoles of turbulent vortices oriented in the rotational anisotropy field.

The ground states of trigonal Cr2+(II):GaAs. Refinements in the model from low-frequency phonon scattering

A theoretical analysis of low-frequency acoustic paramagnetic resonance (APR) data is presented for trigonal Cr2+(II) ions. This together with previous APR measurements at a higher frequency is used to predict more accurate values for the parameters appearing in the split 5T2 ground-state Hamiltonian. It is also shown how the model can account for at least some of the frequency-crossing resonances seen in semi-insulating, chromium-doped GaAs crystals.

Acoustic paramagnetic resonance of vanadium in semi-insulating GaAs

The authors report strong acoustic paramagnetic resonances (APR) from LEC-grown semi-insulating GaAs:V. The results obtained are consistent with observations made on similar samples by other workers using thermally detected electron paramagnetic resonance (TDEPR). The results can be interpreted as being due to a V2+-X centre producing phonon scattering where X is some other lattice defect or impurity associated with the vanadium. In one sample the APR is only observed after illumination of the sample while another sample that contained fewer impurities apart from vanadium showed the APR in the dark and enhancement after illumination. They suggest that illumination converts V3+-X centres into V2+-X by capturing an excited electron in the former case whereas in the second case illumination converts V+-X centres into V2+-X centres and the electron released is trapped at another site with a very long life at low temperature.

The strong APR spectrum from trigonal Cr2+in GaAs

The authors report a study of the intense acoustic paramagnetic resonance spectra observed in semi-insulating or illuminated n-type chromium-doped gallium arsenide. The experimental data are compared with a Jahn-Teller model for Cr2- ions occupying substitutional sites but subject to a large trigonal distortion as well as to random lattice strains (Cr2-II). Despite the lack of a detailed knowledge of this lattice strain distribution, a satisfactory fit to the major experimental features is obtained after noting that the four equivalent directions for the trigonal strain are not magnetically equivalent for an arbitrary magnetic field direction. The origin of this large trigonal distortion present at a small fraction of the Cr sites is, however, unexplained.

Ultrasonic Investigation of the Acceptor Ground State of Si(B) II. The Distribution of Splittings

AbstractThe splitting distribution of the acceptor ground state of Si(B) is determined from the frequency dependence of the ultrasonic resonance attenuation and from acoustic paramagnetic resonance. In the purest crystals a residual distribution is found of unknown origin. In crystals containing carbon or oxygen at concentrations above about 1022 m−3 the distribution is broadened in rough accordance with statistical estimates.

Intermediate Jahn-Teller effect within an orbital triplet - II — Application to the acoustic paramagnetic resonance of V3+ in CaO

Experimental results of Acoustic Paramagnetic Resonance of V3+ in CaO are presented. The spectra cannot be interpreted as due to the well known static or dynamic Jahn-Teller effect. On the other hand, they are well explained by the intermediate situation described in the preceding paper. Thus, V3+ : CaO appears as the first system representing the intermediate case of Jahn-Teller coupling for an orbital triplet. In addition, a general analysis of the hyperfine coupling for d2 systems submitted to Jahn-Teller coupling is presented. It explains satisfactorily why the hyperfine structure is not observed for the intermediate V3+ : CaO system. However, when applied to the dynamic V3+ : MgO system previously studied, it leads to an unacceptable contact term value.

The Cr2+:CaO Jahn-Teller system

Acoustic paramagnetic resonance from Cr2+ ions in CaO has been observed at frequencies close to 9 GHz and detailed results have been obtained with the magnetic field H directed along the (111) direction. With this direction for H, the peaks in the APR spectrum are expected to arise from those Cr2+ ions occupying zero-strain sites as the Hamiltonian displays C3i symmetry. An analysis of the data obtained is given and it is shown that the results can be fitted to a multimode Jahn-Teller model. Values for the basic crystal-field parameters and an energy-level diagram for zero-strain sites are obtained.

Further possibilities of APR and attenuation studies by means of transverse hypersonic waves at 9.4 GHz

New developments for the study of acoustic paramagnetic resonance (APR) and hypersonic attenuation in solids at 9.4 GHz are presented. Efficient electro-acoustic conversion for the transverse mode was achieved together with the generation of longitudinal waves in a high-quality CdS thin film placed parallel to the electric field in the re-entrant cavity. An electron bombardment set up was used for the preparation of the thin films which have a typical thickness of about 3000 AA. Reflection electron diffraction studies showed that the orientation of the layers is little influenced by the substrate so that it will easily be possible to use this method to the APR and attenuation studies in different crystals.

The effect of acoustic paramagnetic resonance on the reflection of sound at the solid-Paramagnetic liquid interface

The effect of an external magnetic field on the propagation of sound in a paramagnetic liquid is considered. It is shown that because of the interaction of molecular spins with the magnetic field and the interaction of the spins with the molecular orientation the resonant singularity appears in the spectra of the molecular orientation fluctuations. Due to this and to the coupling between orientational fluctuations and high-frequency shear waves in the liquid a number of peculiarities in the sound propagation arise. In particular, the reflection of sound is followed by rotation of the polarization plane and by changes of reflection coefficient.

Dynamic Jahn-Teller effect forCr2+in MgO: Acoustic paramagnetic resonance

An empirical evaluation of the parameters defining the dynamic Jahn-Teller effect for ${\mathrm{Cr}}^{2+}$ in MgO is made using the temperature dependence of the acoustic-paramagnetic-resonance (APR) spectra. The molecular-cluster model for the tightly bound ${\mathrm{Cr}}^{2+}$ and its nearest neighbours is applied to the experimental results to determine the tunneling splitting and spin-orbit splitting. The magnitude of the tunneling splitting ($\ensuremath{\delta}\ensuremath{\sim}19$ ${\mathrm{cm}}^{\ensuremath{-}1}$) and spin-orbit splitting ($D\ensuremath{\sim}2.3$ ${\mathrm{cm}}^{\ensuremath{-}1}$) indicates the ${\mathrm{Cr}}^{2+}$ impurity is in a more extreme dynamic limit of the Jahn-Teller effect than previously assumed ($\frac{\ensuremath{\delta}}{D}\ensuremath{\sim}8$). The gyromagnetic ratio for the paramagnetic triplet levels of ${\mathrm{Cr}}^{2+}$ ions exhibits a significant anisotropy resulting from local distortions of the cubic site due to internal strains. The anisotropy depends on the acoustic mode used to observe the spectra. For longitudinal waves the observed anisotropy of the $g$ factor can be explained as due to induced transitions in ions in a primarily tetragonal environment. The magnitude of the internal strain is found to be approximately ${10}^{\ensuremath{-}5}$. Only doublet transitions are observed for the triplet even though the strain splitting (singlet-doublet) is found to be approximately 0.2 ${\mathrm{cm}}^{\ensuremath{-}1}$ which would allow $\ensuremath{\Delta}m=1$ transitions for the acoustic frequencies used in this investigation. The slow transverse mode couples more strongly to the chromous ion and exhibits an APR spectrum which is more complex than the longitudinal wave under similar conditions. The anisotropy of the $g$ factor is due to the same sets of ions as the longitudinal mode but the magnitude of the APR peaks depends on the direction of the magnetic field in the crystal.

A hypersonic attenuation study of V3+in magnesium oxide

The authors measured the hypersonic attenuation at 580 MHz and 1 GHz and as a function of temperature. Two peaks are found in the attenuation of longitudinal waves propagating in the (100) direction, which are attributed to V3+. Both peaks have the typical characteristics of relaxation phenomena. The attenuation measurements have been interpreted using the current model of V3+ which assumes cubic site symmetry and a dynamic Jahn-Teller effect, but the results are not entirely consistent with those obtained from acoustic paramagnetic resonance by previous workers.

Acoustic paramagnetic resonance of Ti2+ in CaO

Experimental results of acoustic paramagnetic resonance of Ti2+ in CaO are reported. The spectra are interpreted as due to Ti2+ ions in cubic sites distorted by random strains. The anisotropy comes from the fact that the effect of these strains is of the same order of magnitude as the Zeeman effect. The results are compared to those obtained with V3+ in MgO.

Strongly coupled impurities in MgO: Acoustic paramagnetic resonance ofFe2+andCr2+

Strongly coupled impurities in MgO: Acoustic paramagnetic resonance of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Fe</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Cr</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>

The acoustic paramagnetic resonance of rare-earth-doped calcium fluoride

Acoustic paramagnetic resonance experiments have been made on calcium fluoride crystals doped with cerium, neodymium and samarium using longitudinal ultrasonic waves at about 9.4 GHz. Strong resonances have been observed for each of these three ions and are attributed to transitions within the Gamma 8 ground state of the trivalent ions. In the case of Ce3+ the cubic crystal-field interaction must be taken to second order to account for the resonance. For Nd3+ a first-order crystal-field calculation will explain the resonance while for Sm3+ the crystal-field calculation must be taken to second order and the Jahn-Teller effect invoked to explain the resonance.

A study of a Jahn-Teller orbital doublet: Ni3+in Al2O3

Acoustic paramagnetic resonance and thermally detected, electric-field-induced electron paramagnetic resonance experiments have been carried out at liquid helium temperatures on the Ni3+ ion in Al2O3. Five features in the spectra are identified and it is shown that dependence on the angle between the magnetic field and the c axis can be explained by an effective Hamiltonian operating within the 2E ground state only but including the effects of the trigonal field and spin-orbit coupling by perturbation theory. The same hamiltonian also gives a complete explanation of the original electron paramagnetic resonance measurements of Geschwind and Remeika (1962) and of recent thermal-conductivity scattering experiments.

Thermal detection of paramagnetic resonance

Abstract

Optically detected acoustic paramagnetic resonance in molecular crystals

The optically detected acoustic paramagnetic resonance of the metastable triplet state of 1,2,4,5-tetrachlorobenzene (TCB) in zero field is reported. The spin-phonon interaction in molecular crystals is discussed in terms of the direct process single phonon absorption by the paramagnetic spin system. t is estimated that in many molecular solids, sufficient acoustic power densities may be produced to observe acoustic paramagnetic resonance by optical detection methods.

Effect of rotational diffusion on acoustic paramagnetic resonance in liquids

It is shown that a mechanism exists which gives rise to narrow lines of paramagnetic resonance absorption of longitudinal sound waves, transverse sound waves and temperature waves in a liquid in spite of the rotational diffusion. The observation conditions for these resonances are discussed. The interaction of the molecular orientation with the fluctuations of shear stresses has been found to affect significantly the spin-lattice relaxation rate in a liquid.