Longitudinal Spin Relaxation Research Articles

Longitudinal spin-relaxation in nitrogen-vacancy centers in electron irradiated diamond

We present systematic measurements of longitudinal relaxation rates (1/T1) of spin polarization in the ground state of the nitrogen-vacancy (NV–) color center in synthetic diamond as a function of NV– concentration and magnetic field B. NV– centers were created by irradiating a Type 1b single-crystal diamond along the [100] axis with 200 keV electrons from a transmission electron microscope with varying doses to achieve spots of different NV– center concentrations. Values of (1/T1) were measured for each spot as a function of B.

Branch-Induced Heterogeneous Chain Motion in Precision Polyolefins

The effect of branching on the chain dynamics of model branched polyethylene was studied by solid state 2H and 13C NMR. Methyl branched polyethylene models with branches at every 15th (PE15) and 21st (PE21) chain carbon were synthesized with deuterons placed either at the carbon alpha to the branching point or in the middle of the chain between branches. Line shape analysis of the temperature-dependent 2H spectra revealed that the distribution of motional amplitudes in the solid state is homogeneous along the crystalline chain but heterogeneous in the less constrained amorphous phase. The 13C and 2H longitudinal spin relaxation data obtained at different positions along the chain are explained in terms of the segmental dynamics as a function of branch incorporation into the crystals. A detailed analysis of the chain dynamics in the conformationally disordered phase exhibited in PE15 is also provided.

Spin Relaxation Times of Donor Centers Associated with Lithium in Monoisotopic <sup>28</sup> Si

We report a detailed study of electron longitudinal and transverse spin relaxation times for Li donors in monoisotopic 28Si over the temperature range 4–20 K using continuous wave and pulsed electron paramagnetic resonance. Comparison of the obtained spin-lattice relaxation times for the states of the isolated donor center and lithium complex LiO showed that due to the presence of orbital degeneracy, relaxation is faster for single lithium than for the LiO complexes with the nondegenerate ground state. For the isolated lithium center in silicon the relaxation is well described by Blume-Orbach process, with the parameters of the spin-orbit coupling ~ 1·10-6 meV compare to Orbach process for LiO complex with spin-orbit coupling parameter ~ 1.5·10-2 meV.

Anisotropic spin relaxation inn-GaAs from strong inhomogeneous hyperfine fields produced by the dynamical polarization of nuclei

The hyperfine field from dynamically polarized nuclei in n-GaAs is very spatially inhomogeneous, as the nu- clear polarization process is most efficient near the randomly-distributed donors. Electrons with polarized spins traversing the bulk semiconductor will experience this inhomogeneous hyperfine field as an effective fluctuating spin precession rate, and thus the spin polarization of an electron ensemble will relax. A theory of spin relaxation based on the theory of random walks is applied to such an ensemble precessing in an oblique magnetic field, and the precise form of the (unequal) longitudinal and transverse spin relaxation analytically derived. To investigate this mechanism, electrical three-terminal Hanle measurements were performed on epitaxially grown Co$_2$MnSi/$n$-GaAs heterostructures fabricated into electrical spin injection devices. The proposed anisotropic spin relaxation mechanism is required to satisfactorily describe the Hanle lineshapes when the applied field is oriented at large oblique angles.

Optimizing a dynamical decoupling protocol for solid-state electronic spin ensembles in diamond

We demonstrate significant improvements of the spin coherence time of a dense ensemble of nitrogen-vacancy (NV) centers in diamond through optimized dynamical decoupling (DD). Cooling the sample down to $77$ K suppresses longitudinal spin relaxation $T_1$ effects and DD microwave pulses are used to increase the transverse coherence time $T_2$ from $\sim 0.7$ ms up to $\sim 30$ ms. We extend previous work of single-axis (CPMG) DD towards the preservation of arbitrary spin states. Following a theoretical and experimental characterization of pulse and detuning errors, we compare the performance of various DD protocols. We identify that the optimal control scheme for preserving an arbitrary spin state is a recursive protocol, the concatenated version of the XY8 pulse sequence. The improved spin coherence might have an immediate impact on improvements of the sensitivities of AC magnetometry. Moreover, the protocol can be used on denser diamond samples to increase coherence times up to NV-NV interaction time scales, a major step towards the creation of quantum collective NV spin states.

Longitudinal and transverse spin dynamics of donor-bound electrons in fluorine-doped ZnSe: Spin inertia versus Hanle effect

The spin dynamics of strongly localized donor-bound electrons in fluorine-doped ZnSe epilayers is studied using pump-probe Kerr rotation techniques. A method exploiting the spin inertia is developed and used to measure the longitudinal spin relaxation time ${T}_{1}$ in a wide range of magnetic fields, temperatures, and pump densities. The ${T}_{1}$ time of the donor-bound electron spin of about $1.6 \ensuremath{\mu}\mathrm{s}$ remains nearly constant for external magnetic fields varied from zero up to 2.5 T (Faraday geometry) and in a temperature range 1.8--45 K. These findings impose severe restrictions on possible spin relaxation mechanisms. In our opinion they allow us to rule out scattering between free and donor-bound electrons, jumping of electrons between different donor centers, scattering between phonons and donor-bound electrons, and with less certainty charge fluctuations in the environment of the donors caused by the 1.5 ps pulsed laser excitation.

Development of high-homogeneity magnetic field coil for 129Xe EDM experiment

We search for 129Xe EDM by using an active nuclear spin maser. In this experiment, the amplitude of the maser oscillation signal is one of the most important parameters that eventually determine the frequency precision. The amplitude is proportional to the ratio of the transverse spin relaxation time T 2 to the effective longitudinal spin relaxation time $T_{1}^{\ast }$ . In particular, for a spin maser of 3He (a co-magnetometer) for which $T_{1}^{\ast }$ typically reaches ∼50 h, a long T 2 is needed. T 2 depends on the homogeneity of the magnetic field which is applied with coils in order to keep the spins under precession. In the present report, we discuss on the design and construction of a new coil which provided a root-mean square (rms) field gradient of less than 5.0 μG/cm. The result of the field measurement has shown that the field gradient in the cell fulfills the target condition $\sqrt {\langle {(\nabla B_{z})^{2}} \rangle } <5\; \mu \text {G/cm}$ , and in fact T 2 of 3He has been measured to be as long as 11,000 s.

NMR Study on the Ru-dimer System with Valence Fluctuation

Substituting effect of CF3 to the Ru-based binuclear complex [{RuIII(acac)2}2(μ-OEt)2], in which S = 1/2 spin dimer takes the singlet ground state have been investigated by means of the magnetic susceptibility χ and the longitudinal nuclear spin relaxation rate T1-1 of 1H/19F-NMR. In CF3-substituted complex [{RuIII(fhma)2}2(μ-OMe)2], we have observed the prominent magnetic response both in χ and T1−1. This behavior is attributed to the slight change in the Ru valence state due to the substitution.

Rotation-induced recovery and bleaching in magnetic resonance.

Thurber and Tycko recently described a 'bleaching effect' that occurs in magnetic resonance when solid samples that are doped with paramagnetic agents are subjected to rotation by magic angle spinning (MAS) in a static magnetic field with a rotation period comparable to the longitudinal relaxation time T1e of the electron spins. The bleaching effect has been investigated by Thurber and Tycko in samples spinning at temperatures near 20 K in a field of 9.4 T and by Corzilius et al. near 80 K in a field of 4.9 T. In our experience, the bleaching effect is not very severe at temperatures near 100 K in a field of 9.4 T at spinning frequencies up to 12 kHz. Bleaching can partly cancel DNP enhancements that are normally evaluated by comparing signal intensities with and without microwave irradiation. The signal attenuation due to doping and sample rotation is usually not taken into consideration when defining enhancement factors. In this paper, we describe a novel observation that the rotation of glassy samples doped with lanthanides spinning at frequencies as low as 0.1 kHz can lead to a significant reduction of the spin-lattice relaxation times T1((1)H) of protons. This effect, which bears similarities with the so-called spin refrigerators, may contribute to the success of 'brute force polarization' at sample temperatures in the mK range. The acceleration of longitudinal proton relaxation also allows one to improve the signal-to-noise ratio per unit time.

Molecular Dynamics of Transient Radicals in Solution Probed by Longitudinal-Field Muon Spin Relaxation

Longitudinal field muon spin relaxation (LF-μSR) has been used to measure the magnetic field dependence of the longitudinal field muon spin relaxation rates (λμ = 1/Tμ1) of two muoniated radicals, 2-muoxyprop-2-yl radical (formed by Mu addition to acetone) and the muoniated 1,2-dicarboxyvinyl radical dianion (formed by Mu addition to the 1,2- dicarboxyacetylene dianion), in aqueous solution. The rotational correlations time of the radicals in solution at 298 K were determined from the magnetic field dependence of λμ and were found to be 32±2 ps for the 2-muoxyprop-2-yl radical and 55±3 ps for the muoniated 1,2-dicarboxyvinyl radical dianion.

NMR study on kagome-lattice antiferromagnet Cs2Mn3LiF12

133Cs/7Li-NMR study was performed on a quasi-two-dimensional spin system Cs2Mn3LiF12, in which S = 2 Mn atoms form undistorted Kagome lattice. We have observed a clear splitting in the Li-NMR resonance line for a single crystal at low temperatures below TN = 3.6 K. The longitudinal nuclear spin relaxation rate T−11 of both Cs and Li-NMR showed a critical divergence at the same temperature. These observations are considered to be a microscopic evidence for an occurrence of long range magnetic order due to a weak inter-plane spin interactions.

Limiting factor of defect-engineered spin-filtering effect at room temperature

We identify hyperfine-induced electron and nuclear spin cross-relaxation as the dominant physical mechanism for the longitudinal electron spin relaxation time $\left({T}_{1}\right)$ of the spin-filtering $G{a}_{i}^{2+}$ defects in GaNAs alloys. This conclusion is based on our experimental findings that ${T}_{1}$ is insensitive to temperature over 4--300 K, and its exact value is directly correlated with the hyperfine coupling strength of the defects that varies between different configurations of the $G{a}_{i}^{2+}$ defects present in the alloys. These results thus provide a guideline for further improvements of the spin-filtering efficiency by optimizing growth and processing conditions to preferably incorporate the $G{a}_{i}^{2+}$ defects with a weak hyperfine interaction and by searching for new spin-filtering defects with zero nuclear spin.

Spatially selective heteronuclear multiple-quantum coherence spectroscopy for biomolecular NMR studies.

Spatially selective heteronuclear multiple-quantum coherence (SS HMQC) NMR spectroscopy is developed for solution studies of proteins. Due to "time-staggered" acquisitioning of free induction decays (FIDs) in different slices, SS HMQC allows one to use long delays for longitudinal nuclear spin relaxation at high repetition rates. To also achieve high intrinsic sensitivity, SS HMQC is implemented by combining a single spatially selective (1)H excitation pulse with nonselective (1) H 180° pulses. High-quality spectra were obtained within 66 s for a 7.6 kDa uniformly (13) C,(15) N-labeled protein, and within 45 and 90 s for, respectively, two proteins with molecular weights of 7.5 and 43 kDa, which were uniformly (2)H,(13) C,(15) N-labeled, except for having protonated methyl groups of isoleucine, leucine and valine residues.

Optical spin noise of a single hole spin localized in an (InGa)As quantum dot.

We advance spin noise spectroscopy to the ultimate limit of single spin detection. This technique enables the measurement of the spin dynamic of a single heavy hole localized in a flat (InGa)As quantum dot. Magnetic field and light intensity dependent studies reveal even at low magnetic fields a strong magnetic field dependence of the longitudinal heavy hole spin relaxation time with an extremely long T1 of ≥180 μs at 31mT and 5K. The wavelength dependence of the spin noise power discloses for finite light intensities an inhomogeneous single quantum dot spin noise spectrum which is explained by charge fluctuations in the direct neighborhood of the quantum dot. The charge fluctuations are corroborated by the distinct intensity dependence of the effective spin relaxation rate.

Muon spin spectroscopy of ferrocene: characterization of muoniated ferrocenyl radicals.

Radicals formed by the reaction of muonium (Mu), a light isotope of hydrogen, with ferrocene and ferrocene-d10 have been studied with the avoided level crossing muon spin resonance (ALC-μSR) and longitudinal field muon spin relaxation (LF-μSR) techniques between 10 and 100 K. A single type of radical was observed in each compound and the muon hyperfine coupling constants (hfcc) and the muon spin relaxation rates were measured as a function of temperature. A previous report concerning the observation of Mu adducts of ferrocene (U. A. Jayasooriya et al. Chem. - Eur. J., 2007, 13, 2266-2276) appears to be incorrect. DFT calculations were performed to aid in the assignment of the ALC-μSR spectra. A tentative assignment is that the observed radicals were formed by Mu addition to the exterior of the cyclopentadienyl rings and that the structures are distorted due to interactions with neighbouring molecules. The temperature dependence of the muon hfcc can be explained assuming the population of two levels with different muon hfccs separated by 1.4 ± 0.1 kJ mol(-1). The temperature dependence of the width and amplitude of the Δ1 resonance and the muon spin relaxation rate suggests that the electron spin relaxation rate increase with temperature, but the relaxation mechanism is unknown.

Spin relaxation in an ultracold spin-orbit-coupled40K gas

We report the anomalous D'yakonov-Perel' spin relaxation in ultracold spin-orbit-coupled ${}^{40}$K gas when the coupling between $|9/2,9/2\ensuremath{\rangle}$ and $|9/2,7/2\ensuremath{\rangle}$ states, acting as an effective Zeeman magnetic field, is much stronger than the spin-orbit coupled field. Both the transverse and longitudinal spin relaxations are investigated with small and large spin polarizations. It is found that with small spin polarization, the transverse (longitudinal) spin relaxation is divided into four (two) regimes: the normal weak scattering regime, the anomalous D'yakonov-Perel'-like regime, the anomalous Elliott-Yafet-like regime, and the normal strong scattering regime (the anomalous Elliott-Yafet-like regime and the normal strong scattering regime). With large spin polarization, we find that the Hartree-Fock self-energy, which acts as an effective magnetic field, can markedly suppress the transverse spin relaxation in both weak and strong scattering limits. Moreover, by noting that as both the momentum relaxation time and the Hartree-Fock effective magnetic field vary with the scattering length in cold atoms, the anomalous D'yakonov-Perel'-like regime is suppressed and the transverse spin relaxation is hence divided into three regimes in the scattering length dependence: the normal weak scattering regime, the anomalous Elliott-Yafet-like regime, and the strong scattering regime. On the other hand, the longitudinal spin relaxation is again divided into the anomalous Elliott-Yafet-like and normal strong scattering regimes. Furthermore, it is found that the longitudinal spin relaxation can be either enhanced or suppressed by the Hartree-Fock effective magnetic field if the spin polarization is parallel or antiparallel to the effective Zeeman magnetic field.

β2‐Adrenergic Receptor Activation by Agonists Studied with 19F NMR Spectroscopy

β₂‐Adrenergic Receptor Activation by Agonists Studied with ¹⁹F NMR Spectroscopy

Low temperature ballistic spin transport in the S = 1/2 antiferromagnetic Heisenberg chain compound SrCuO2

We report zero and longitudinal magnetic field muon spin relaxation (μSR) measurements of the spin S = 1/2 antiferromagnetic Heisenberg chain material SrCuO2. We find that in a weak applied magnetic field B0 the spin–lattice relaxation rate λ follows a power law with n = 0.9(3). This result is temperature independent for 5 K ≤ T ≤ 300 K. Within conformal field theory and using the Müller ansatz we conclude ballistic spin transport in SrCuO2.

Spin qubit relaxation in a moving quantum dot

Long-range quantum communication for spin qubits is an important open problem. Here we study decoherence of an electron spin qubit that is being transported in a moving quantum dot. We focus on spin decoherence due to spin-orbit interaction and a random electric potential. We find that at the lowest order, the motion induces longitudinal spin relaxation, with a rate linear in the dot velocity. Our calculated spin relaxation time ranges from sub $\mu$s in GaAs to above ms in Si, making this relaxation a significant decoherence channel. Our results also give clear indications on how to reduce the decoherence effect of electron motion.

Anomalous D’yakonov-Perel’ spin relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration

We report an anomalous scaling of the D'yakonov-Perel' spin relaxation with the momentum relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration. We focus on the case that the external magnetic field is perpendicular to the spin-orbit-coupling--induced effective magnetic field and its magnitude is much larger than the later one. It is found that the longitudinal spin relaxation time is proportional to the momentum relaxation time even in the strong scattering limit, indicating that the D'yakonov-Perel' spin relaxation shows the Elliott-Yafet-like behaviour. Moreover, the transverse spin relaxation time is inversely proportional (proportional) to the momentum relaxation time in the weak (strong) scattering limit, both in the opposite trends against the well-established conventional D'yakonov-Perel' spin relaxation behaviours. We further demonstrate that all the above anomalous scaling relations come from the unique form of the effective inhomogeneous broadening.