Spin Relaxation Time Measurements Research Articles

Rapid measurement of longitudinal nuclear spin relaxation time based on the in-situ longitudinal magnetometer in Rb–Xe comagnetometers

The longitudinal relaxation time T1 of Xe nuclear spins is an important parameter to determine the performance of Rb–Xe comagnetometers. The industry standard delayed pulse method is time-consuming, and requires multiple π pulses and π/2 pulses. In this work, a direct measurement method for obtaining T1 based on the in-situ longitudinal magnetometer is introduced with the measurement period shortened to 3-5 T1. The proposed method requires only a single π pulse, reducing the measurement time by approximately more than 90%. By solving the Bloch equation, the working principle of the longitudinal magnetometer and the measurement method is demonstrated. The experiment shows that the longitudinal magnetometer achieves a linear working range greater than 60 nT, and the difference in measurement results of T1 through different methods at different temperatures and pump beam power is less than 3%. In addition, the longitudinal magnetometer introduced in this method has broad prospects for measuring the basic physical quantities in comagnetometers.

Measurement of muon spin relaxation time in various scintillating materials

A new experimental method to search for T-violating transverse muon polarization (PT ) in the K+ → π 0 μ + ν decay was recently proposed. In this new experiment, the measurements of the μ + momentum vector, the π 0 momentum vector, and the μ + polarization will be performed by the same segmented calorimeter. One of key issues is the choice of a scintillation material which can maintain the μ + spin polarization for several μ + lifetimes. A test experiment to measure the μ + spin relaxation time in various scintillating materials was carried out at J-PARC Material and Life Science Facility (MLF). It was concluded that the residual μ + polarization in CeF3 is high enough to perform the proposed T-violation experiment.

Measurement of longitudinal nuclear spin relaxation time in NMR gyroscope by real-time monitoring

In the atomic cell of a nuclear magnetic resonance gyroscope, a transverse bias field is applied to enable the in situ alkali magnetometer to sense the variations in the longitudinal magnetic field. During a single relaxation process of the noble gas, the longitudinal relaxation time is obtained by monitoring and fitting the signal of the magnetometer in real-time. The relaxation times measured using our method are nearly identical to those obtained using the conventional delayed pulse method, but in contrast, our method saves ∼90% of the time. By using the new method, fast and accurate batch testing for a large number of atomic cells can be achieved to optimize the manufacturing of the cells, which is helpful in speeding up the development of gyroscopes.

Measurement of muon spin relaxation time in scintillating materials

Measurement of muon spin relaxation time in scintillating materials

Measurement of nuclear spin relaxation time in lanthanum aluminate for development of polarized lanthanum target

The nuclear spin–lattice relaxation time (T1) of lanthanum and aluminum nuclei in a single crystal of lanthanum aluminate doped with neodymium ions is studied to estimate the feasibility of the dynamically polarized lanthanum target applicable to beam experiments. The application of our interest is the study of fundamental discrete symmetries in the spin optics of epithermal neutrons. This study requires a highly flexible choice of the applied magnetic field for neutron spin control and favors longer T1 under lower magnetic field and at higher temperature. The T1 of 139La and 27Al was measured under magnetic fields of 0.5–2.5 T and at temperatures of 0.1–1.5 K and found widely distributed up to 100 h. The result suggests that the T1 can be as long as T1∼ 1 h at 0.1 K with a magnetic field of 0.1 T, which partially fulfills the requirement of the neutron beam experiment. Possible improvements to achieve a longer T1 are discussed.

Spin relaxation in diluted magnetic semiconductors: GaMnAs as example

The paper deals with a study of the magnetic impurities spin relaxation in the diluted magnetic semiconductors above the Curie temperature. Systems with a high concentration of magnetic impurities where magnetic correlations take place were studied. The proposed theory assumes the main channel of the spin relaxation being the mobile carriers, which provide the indirect interactions of the magnetic impurities. This theoretical model is supported by the experimental measurements of the manganese spin relaxation time in the GaMnAs by means of spin-flip Raman scattering. As has been found with a temperature increase the spin relaxation rate of the ferromagnetic samples grows, tending to that measured in a paramagnetic sample.

Spin relaxation of holes in In0.53Ga0.47As/InP quantum wells

Polarization-resolved photoluminescence was used to study spin relaxation of photoexcited holes in In0.53Ga0.47As/InP quantum wells in a quantizing magnetic field as a function of temperature. At a temperature below 10 K, the circular polarization of the photoluminescence due to the spin-split valence band Landau levels was found temperature-independent. In this temperature range fast hole spin relaxation as compared to their lifetime leads to the photoluminescence circular polarization determined by the ratio of these times. Increasing temperature resulted in efficient hole spin thermalization in the Zeeman split valence band Landau levels and as a consequence, in vanishing photoluminescence polarization. Fits of the experimental data by the theory allowed a determination of the hole spin relaxation times related to different Landau levels and the corresponding hole effective g-factor. Direct measurements of the hole spin relaxation times prove the obtained results.

Rapid relaxation NMR measurements to predict rate coefficients in ionic liquid mixtures. An examination of reaction outcome changes in a homologous series of ionic liquids

A series of ionic liquids based on the 1-alkyl-3-methylimidazolium cations were examined as components of the solvent mixture for a bimolecular substitution process. The effects on both the rate coefficient of the process and the NMR spin-spin relaxation of the solvent components of changing either the alkyl chain length or the amount of ionic liquid in the reaction mixture were determined. At a constant mole fraction, a shorter alkyl chain length resulted in a greater rate coefficient enhancement and a longer relaxation time, with the opposite effects for a longer alkyl chain length. For a given ionic liquid, increasing the proportion of salt in the reaction mixture resulted in a greater rate coefficient and a shorter relaxation time. The microscopic origins of the rate coefficient enhancement were determined and a step change found in the activation parameters on increasing the alkyl chain length from hexyl to octyl, suggesting notable structuring in solution. Across a range of ionic liquids and solvent compositions, the relaxation time from NMR measurements was shown to relate to the reaction rate coefficient. The approach of using fast and simple NMR relaxation measurements to predict reaction outcomes was exemplified using a morpholinium-based ionic liquid.

Study of Electron Spin Diffusion and Relaxation Dynamics by Diffraction of transient spin grating in an Intrinsic GaAs/AlGaAs Quantum Well

In this paper, the transient spin grating method was used to measure the attenuation rate of the diffraction signals of the intrinsic spin gratings of the intrinsic GaAs/AlGaAs quantum wells in different periods at room temperature, and the electron spin diffusion coefficient Ds = 121±6cm2/s was obtained. The electron spin diffusion coefficients of GaAs/AlGaAs quantum well were in good agreement with that of p-type GaAs/AlGaAs quantum well, indicating that the doping type for GaAs/AlGaAs quantum well has no significant effect on the diffusion rate of spin-polarized electrons. In this paper, the widely used formula of transient spin grating diffraction signal attenuation rate was used to fit the diffraction experimental results of the transient spin grating in the intrinsic GaAs/AlGaAs quantum well. The measured electron spin relaxation time was much shorter than that measured by the saturation absorption method. The reason for the deviation in the measured spin relaxation time was analyzed. The dynamic law of transient spin grating modulation attenuation over time was derived. The decay rate formula was modified, and the modified formula was used to fit the experimental data in the transient spin grating diffraction to obtain the spin relaxation time τs = 123 ps. The result was consistent with the measured electron spin relaxation time by the saturation absorption method.

1 H NMR tests on damaged and undamaged XLPE and SiR samples

Cross-linked polyethylene (XLPE) and silicone rubber (SiR) samples were subjected to a high-voltage AC stress plane–plane configuration and inclined plane test, respectively. The voltage was applied such that discharge was observed across the surface of the XLPE test sample for several hours and for visible damage to occur on SiR samples also after several hours. Selected stressed samples together with virgin samples from the same manufactured batch were tested using nuclear magnetic resonance (NMR) spectroscopy. Specifically, 1 H NMR spin–lattice ( T 1 ) and spin–spin ( T 2 ) relaxation time measurements were employed to examine potential changes in the chemical bonding of undamaged and damaged XLPE and SiR samples. Preliminary results show that there may be a moderate increase in the T 1 and T 2 values of the damaged samples in comparison with the undamaged ones. This raises the possibility that NMR can be a useful additional experimental tool in characterising material degradation.

Impact of Polylactide Fluorinated End-Group Lengths and Their Dynamics on Perfluorohexane Microcapsule Morphology

We have synthesized polylactide (PLA) polymers containing five distinct lengths of fluorinated end-groups (from C3F7 to C13F27). The influence of fluorinated end-group lengths and their dynamics in chlorinated solvents (chloroform and dichloromethane) was investigated as a function of the presence of perfluorohexane (PFH) and related to the morphology of capsules of PFH obtained using these fluorinated polylactides. 19F spin–spin relaxation time (T2) measurements revealed a reduced mobility of the fluorinated units with dependency on fluorinated chain length in the order C3F7 > C8F17 > C13F27. The presence of PFH led to a further decrease on the segmental mobility, indicating the existence of fluorous interactions. The T2 relaxation time of the CF3 resonance of PLA-C3F7 decreased from 540 ± 50 ms in CDCl3 to 81 ± 15 ms after the addition of PFH. Because of these fluorous interactions, PLA polymers containing short fluorinated groups (C3F7 and C6F13) led to microcapsules with core–shell morphologies, whereas those formulated with long F units (C8F17, C11F23, and C13F27) favored the formation of multinucleated capsules as observed by confocal microscopy.

(Keynote) Physics, Materials and Applications of High-Mobility Organic Transistor Circuits

Development of functional materials and understanding of the microscopic mechanisms mutually benefit through their close interaction. To accelerate development of organic semiconductor devices for industrial application to flexible and printed electronics, it has been essential to understand the mechanism of charge transport in conjunction with molecular-scale charge transfer. We examine the idea that high-mobility charge transport in newly developed solution-crystalized organic transistors is caused by band-like charge transport, using several different methods to probe coherence in the electronic charge. These materials, being essentially different from conventional organic semiconductors with basically incoherent hopping-like transport, often show high values of mobility exceeding 10 cm2/Vs so that high-speed organic transistor circuits are realized. We first employ Hall-effect measurement which differentiates the coherent band transport from site-to-site hopping. Rubrene single crystal transistors were the first to show the Hall voltage obviously indicating the band transport with the mobility exceeding 10 cm2/Vs, whereas the result of pentacene single crystal transistors with the mobility around 1 cm2/Vs suggested somewhat intermediate between coherent and incoherent charge transport. An interesting crossover from hopping-like to band-like transport is also found by gradually changing temperature and external pressure, clearly indicating involvement of intermolecular phonons. Stimulated by the experiments in the early stage, such materials as decyldinaphthobenzo-dithiophene derivatives (Cn-DNBDT) are newly synthesized to stabilize the molecular position in the crystal form by introducing steric hindrance in their p-conjugated cores. With the development of solution-crystallization method, arrays of the single crystal transistors are formed to the size of wafer scale on plastic substrates. The mobility is as high as 20 cm2/Vs for p-type compound and 4 cm2/Vs for an n-type compound. We measured spin relaxation time of the electric-field induced carriers down to 4.2 K using the large-area ultra-thin single-crystal transistors, so that electron-spin relaxiation is precisely investigated. We found that the spin-relaxation follows the Elliott-Yafet mechanism so that the spin life time is consistently elongated at low temperatures due to reduced phonon scattering via spin-orbit coupling. The result suggest that charge carrier mobility can as high as 650 cm2/Vs with minimized phonon scattering at the low temperature. This presentation also focuses on recent development of key technologies for printed LSIs which can provide future low-cost platforms for RFID tags, AD converters, data processors, and sensing circuitries. Such prospect bears increasing reality because of recent research innovations in the field of material chemistry, charge transport physics, and solution processes of printable organic semiconductors. With excellent chemical and thermal stability in recently developed new materials, we are developing simple integrated devices based on CMOS using p-type and n-type printed organic FETs. Particularly important are new processing technologies for continuous growth of the organic single-crystalline semiconductor “wafers” from solution and for lithographical patterning of semiconductors and metal electrodes. Successful rectification and identification are demonstrated at 13.56 MHz with printed organic CMOS circuits.

All-electrical measurement of the triplet-singlet spin relaxation time in self-assembled quantum dots

We have measured the spin relaxation time of an excited two-electron spin-triplet state into its singlet ground state in self-assembled InAs/GaAs quantum dots. We use a time-resolved measurement scheme that combines transconductance spectroscopy with spin-to-charge conversion to address the |s↑,p↑〉 triplet state, where one electron is in the quantum dot s-shell and a second one in the p-shell. The evaluation of the state-selective tunneling times from the dots into a nearby two-dimensional electron gas allows us to determine the s- and p-shell occupation and extract the relaxation time from a rate equation model. A comparably long triplet-to-singlet spin relaxation time of 25 μs is found.

Effect of doping symmetry on electron spin relaxation dynamics in (110) GaAs/AlGaAs quantum wells

Considerable interest has been aroused in the study of the spin dynamics in semiconductors due to its potential applications in spintronics and quantum computation. In this paper, time-resolved circularly polarized pump-probe spectroscopy is used to study the carrier density dependences on the electron spin relaxation in approximately symmetrical and completely asymmetrical doping (110) GaAs/AlGaAs quantum wells. With the increase of the carrier density, the spin relaxation time first increases and then decrease obviously in both of the quantum wells, and the measured spin relaxation time of the approximately symmetrical doping quantum wells is always longer than that of the asymmetrical doping one. By analysis, we find that the spin relaxation is not dominated only by the Bir-Aronov-Pikus (BAP) mechanism in (110) GaAs quantum wells, that though the Dresselhaus spin-orbit coupling does not lead to any spin relaxation, the asymmetry of the doping position contributes to the asymmetry of potential energy structure, thus the built-in electric field which can induce the Rashba spin-orbit coupling to appear, and that the effective magnetic field induced by the Rashba spin-orbit coupling normal to the growth direction can lead to spin relaxation along the growth direction. Therefore, the Dyakonov-Perel (DP) mechanism plays an important role in asymmetrical doping (110) GaAs/AlGaAs quantum wells. In the approximately symmetrical and completely asymmetrical doping (110) GaAs/AlGaAs quantum wells, the DP mechanism dominates the spin relaxation at low carrier density, thus the spin relaxation time increases with carrier density increasing due to the strengthening of the electron-electron scattering and the decreasing of the momentum relaxation time. However, at high carrier density, BAP mechanism plays an important role, thus the spin relaxation time decreases obviously with carrier density increrasing, but the decay rates in both of the quantum wells are slower than that in the casethat only BAP mechanism dominates, because both the DP and BAP mechanism play an important role. The strength of the Rashba spin-orbit coupling depends on the symmetry of the quantum well. The DP mechanism in a completely asymmetrical doping quantum well is stronger than that in an approximately symmetrical doping quantum wells, thus the decay rate in a completely asymmetrical doping quantum wells is always slower than that in an approximately symmetrical doping quantum wells, and the spin relaxation time in a completely asymmetrical doping quantum wells is shorter than that in an approximately symmetrical doping quantum wells.

Charge and spin diffusion on the metallic side of the metal-insulator transition: A self-consistent approach

We develop a self-consistent theory describing the spin and spatial electron diffusion in the impurity band of doped semiconductors under the effect of a weak spin-orbit coupling. The resulting low-temperature spin-relaxation time and diffusion coefficient are calculated within different schemes of the self-consistent framework. The simplest of these schemes qualitatively reproduces previous phenomenological developments, while more elaborate calculations provide corrections that approach the values obtained in numerical simulations. The results are universal for zinc-blende semiconductors with electron conductance in the impurity band, and thus they are able to account for the measured spin-relaxation times of materials with very different physical parameters. From a general point of view, our theory opens a new perspective for describing the hopping dynamics in random quantum networks.

Spin-Relaxation Dynamics ofE′Centers at High Density inSiO2Thin Films for Single-Spin Tunneling Force Microscopy

Methods for the creation of thin amorphous silicon dioxide (aSiO2) layers on crystalline silicon substrates with very high densities of silicon dangling bonds (so called E' centers) have been explored and volume densities of [E']> 5x10^18 cm-3 throughout a 60nm thick film have been demonstrated by exposure of a thermal oxide layer to a low pressure Argon radio frequency plasma. While the generated high E' center densities can be annealed completely at 300C, they are comparatively stable at room temperature with a half life of about one month. Spin relaxation time measurements of these states between T = 5K and T = 70K show that the phase relaxation time T2 does not strongly depend on temperature and compared to SiO2 films of lower E' density, is significantly shortened. The longitudinal relaxation time T1 ~195(5)us at room temperature is in agreement with low-density SiO2. In contrast, T1 ~625(51)us at T = 5K is much shorter than in films of lower E' density. These results are discussed in the context of E' centers being used as probe spins for spin-selection rules based single spin-readout.

Fluorinated Microgels in Star Polymers: From In-Core Dynamics to Fluorous Encapsulation

The dynamics of in-core perfluorinated alkyl pendants in microgel star polymers were investigated by 19F nuclear magnetic resonance spectroscopy and 19F spin–spin relaxation time (T2) measurements, to elucidate the origin of the efficient encapsulation of perfluorinated guests into the fluorous microgel cores. Fluorinated microgel star polymers were prepared by the linking reaction of chlorine-capped poly(methyl methacrylate) arms with dimethacrylate linking agents and a perfluorinated methacrylate via ruthenium-catalyzed living radical polymerization. Temperature-dependent T2 measurements revealed the reduced thermodynamic mobility of the perfluorinated pendants indicative of their accumulation and thus aggregation in the core network. Fluorinated microgel star polymers accordingly provide stable “fluorous compartments” where the encapsulation of perfluoromethylcyclohexane (PFMCH) in DMF is better attained and more efficient than that in the corresponding block copolymer micelles.

Nonlinear optical spectroscopy of indirect excitons in coupled quantum wells

Indirect excitons in coupled quantum wells are long-living quasi-particles, explored in the studies of collective quantum states. We demonstrate, that despite the extremely low oscillator strength, their spin and population dynamics can by addressed by time-resolved pump-probe spectroscopy. Our experiments make it possible to unravel and compare spin dynamics of direct excitons, indirect excitons and residual free electrons in coupled quantum wells. Measured spin relaxation time of indirect excitons exceeds not only one of direct excitons, but also one of free electrons by two orders of magnitude.

Lattice Relaxation of 4He with 3He Impurities: NMR Studies

Measurements of the 3He nuclear spin relaxation times of dilute 3He impurities in solid 4He have been used to explore the unusual dynamics of solid 4He at low temperatures. The 3He impurities move through the lattice by quantum mechanical exchange with neighboring 4He atoms. Because of the larger zero point motion of the 3He atoms, there is an appreciable lattice distortion that accompanies the tunneling 3 He atom and the tunneling motion depends on the elastic properties of the 4He lattice. This motion modulates the 3He-3He nuclear dipole- dipole interactions and thus determines the NMR relaxation rates. We compare the observed temperature dependence of the NMR relaxation rates with that expected from the measurements of the shear modulus by Syshchenko et al. [Phys. Rev. Lett. 104, 195301 (2009)].

Pseudospin-driven spin relaxation mechanism in graphene

The prospect of transporting spin information over long distances in graphene, possible because of its small intrinsic spin–orbit coupling (SOC) and vanishing hyperfine interaction, has stimulated intense research exploring spintronics applications. However, measured spin relaxation times are orders of magnitude smaller than initially predicted, while the main physical process for spin dephasing and its charge-density and disorder dependences remain unconvincingly described by conventional mechanisms. Here, we unravel a spin relaxation mechanism for non-magnetic samples that follows from an entanglement between spin and pseudospin driven by random SOC, unique to graphene. The mixing between spin and pseudospin-related Berry’s phases results in fast spin dephasing even when approaching the ballistic limit, with increasing relaxation times away from the Dirac point, as observed experimentally. The SOC can be caused by adatoms, ripples or even the substrate, suggesting novel spin manipulation strategies based on the pseudospin degree of freedom. Spin relaxation in graphene is much faster than theoretically expected. Now, a scenario based on a mixing of spin and pseudospin degrees of freedom and defect-induced spatial spin–orbit coupling variations predicts longer spin relaxation times.