Spin Relaxation Time T2 Research Articles

Coherent Spin Dynamics of Electrons in CdSe Colloidal Nanoplatelets

Coherent spin dynamics of electrons in CdSe colloidal nanoplatelets are investigated by time-resolved pump–probe Faraday rotation at room and cryogenic temperatures. We measure electron spin precession in a magnetic field and determine g-factors of 1.83 and 1.72 at low temperatures for nanoplatelets with a thickness of 3 and 4 monolayers, respectively. The dephasing time of spin precession T2* amounts to a few nanoseconds and has a weak dependence on temperature, while the longitudinal spin relaxation time T1 exceeds 10 ns even at room temperature. Observations of single and double electron spin–flips confirm that the nanoplatelets are negatively charged. The spin–flip Raman scattering technique reveals g-factor anisotropy by up to 10% in nanoplatelets with thicknesses of 3, 4, and 5 monolayers. In the ensemble with a random orientation of nanoplatelets, our theoretical analysis shows that the measured Larmor precession frequency corresponds to the in-plane electron g-factor. We conclude that the experimentally observed electron spin dephasing and its acceleration in the magnetic field are not provided by the electron g-factor anisotropy and can be related to the localization of the resident electrons and fluctuations of the localization potential.

Indistinguishable telecom band photons from a single Er ion in the solid state.

Atomic defects in the solid state are a key component of quantum repeater networks for long-distance quantum communication1. Recently, there has been significant interest in rare earth ions2-4, in particular Er3+ for its telecom band optical transition5-7 that allows long-distance transmission in optical fibres. However, the development of repeater nodes based on rare earth ions has been hampered by optical spectral diffusion, precluding indistinguishable single-photon generation. Here, we implant Er3+ into CaWO4, a material that combines a non-polar site symmetry, low decoherence from nuclear spins8 and is free of background rare earth ions, to realize significantly reduced optical spectral diffusion. For shallow implanted ions coupled to nanophotonic cavities with large Purcell factor, we observe single-scan optical linewidths of 150 kHz and long-term spectral diffusion of 63 kHz, both close to the Purcell-enhanced radiative linewidth of 21 kHz. This enables the observation of Hong-Ou-Mandel interference9 between successively emitted photons with a visibility of V = 80(4)%, measured after a 36 km delay line. We also observe spin relaxation times T1,s = 3.7 s and T2,s > 200 μs, with the latter limited by paramagnetic impurities in the crystal instead of nuclear spins. This represents a notable step towards the construction of telecom band quantum repeater networks with single Er3+ ions.

Relaxational signal attenuation during soft refocusing pulses

Quantitative NMR is widely used, but the systematic errors introduced when signals are excited by anything other than a single hard pulse are not always well understood. One important source of error in experiments using soft pulses is the spin relaxation that takes place during pulses, which contains contributions from both spin–spin and spin–lattice relaxation. Here it is shown that relaxation on resonance during shaped soft 180° refocusing pulses in practical experiments can be well represented by biexponential decay, with rate constants R2 and a shape-dependent linear combination of R1 and R2, where R1 and R2 are the inverses of the spin–lattice and spin–spin relaxation times T1 and T2. In principle this would allow correction for relaxational losses in experiments using on-resonance selective refocusing pulses.

External Stimuli-Responsive Characteristics of Poly(N,N'-diethylacrylamide) Hydrogels: Effect of Double Network Structure.

Swelling experiments and NMR spectroscopy were combined to study effect of various stimuli on the behavior of hydrogels with a single- and double-network (DN) structure composed of poly(N,N′-diethylacrylamide) and polyacrylamide (PAAm). The sensitivity to stimuli in the DN hydrogel was found to be significantly affected by the introduction of the second component and the formation of the double network. The interpenetrating structure in the DN hydrogel causes the units of the component, which is insensitive to the given stimulus in the form of the single network (SN) hydrogel, to be partially formed as globular structures in DN hydrogel. Due to the hydrophilic PAAm groups, temperature- and salt-induced changes in the deswelling of the DN hydrogel are less intensive and gradual compared to those of the SN hydrogel. The swelling ratio of the DN hydrogel shows a significant decrease in the dependence on the acetone content in acetone–water mixtures. A certain portion of the solvent molecules bound in the globular structures was established from the measurements of the 1H NMR spin–spin relaxation times T2 for the studied DN hydrogel. The time-dependent deswelling and reswelling kinetics showed a two-step profile, corresponding to the solvent molecules being released and absorbed during two processes with different characteristic times.

Dipolar spin relaxation of divacancy qubits in silicon carbide

Divacancy spins implement qubits with outstanding characteristics and capabilities in an industrial semiconductor host. On the other hand, there are still numerous open questions about the physics of these important defects, for instance, spin relaxation has not been thoroughly studied yet. Here, we carry out a theoretical study on environmental spin-induced spin relaxation processes of divacancy qubits in the 4H polytype of silicon carbide (4H-SiC). We reveal all the relevant magnetic field values where the longitudinal spin relaxation time T1 drops resonantly due to the coupling to either nuclear spins or electron spins. We quantitatively analyze the dependence of the T1 time on the concentration of point defect spins and the applied magnetic field and provide an analytical expression. We demonstrate that dipolar spin relaxation plays a significant role both in as-grown and ion-implanted samples and it often limits the coherence time of divacancy qubits in 4H-SiC.

Measurement of a129Xe transverse relaxation rate without the influence of Rb polarization-induced magnetic gradient.

We demonstrate the measurement of the transverse spin relaxation rate of Xe without the influence of the Rb polarization-induced magnetic field gradient. The optical pumping beam and probe beam turn on and off repeatedly during the measurement to reduce the relaxation originating from the Rb polarization-induced magnetic field gradient. During the absence of the optical pumping beam, the nuclear spin of the noble gas atom does not experience the alkali-polarization-induced magnetic field gradient so that the transverse spin relaxation rate (1/T2) decreases. When the duty cycle reaches zero, the measured transverse relaxation time T2 approaches the longitudinal spin relaxation time T1. Our method helps in roughly estimating the longitudinal spin relaxation time with a single measurement of the free induction decay.

An Integrated Petrophysical Workflow for Fluid Characterization and Contacts Identification Using NMR Continuous and Stationary Measurements in a High-Porosity Sandstone Formation, Offshore Norway

The Alvheim Field in the Norwegian North Sea was discovered in 1998. Two wells were drilled in 2018 in the Gekko structure to confirm oil column height and to evaluate reservoir quality in the Heimdal Formation. A comprehensive wireline logging program, including NMR and formation testing, was optimized to reduce formation evaluation uncertainty. Evaluating fluid properties, oil column height, and reservoir quality were primary objectives. Well A was first drilled on the south of the structure, followed by Well B on the north of the structure. Reservoir quality encountered in both wells was very good, and a project to develop these resources is currently in the selection phase. Formation evaluation uncertainty encompassing pore geometry distribution, permeability, reservoir quality, and hydrocarbon identification are mitigated by studying the nuclear magnetic resonance (NMR) log response. NMR fluid typing has been widely used in the oil industry since the 1990s. NMR fluid typing today is a combination of the contrast of spin relaxation time T1, the spin-spin relaxation time T2 (T1T2), and the diffusivity (T2D) of formation fluids (Chen et al., 2016). NMR fluid typing can be obtained from a continuous log and/or stationary log measurements. This paper showcases excellent, textbook-quality NMR data, as well as the integration of NMR data in the petrophysical workflow. High-confidence fluid properties and fluid contacts are determined. This paper also highlights a comparison of NMR data acquired in stationary vs. continuous depth-based log modes in both wells. The continuous log data quality is equivalent to stationary data, implying continuous log data quality is sufficient for reliable NMR fluid properties evaluation without depending on time-consuming stationary NMR measurements. Reducing logging operations rig time is very advantageous in the North Sea, where drilling rig operations cost is high, and enhanced rig time management is constantly required.

A scanning tunneling microscope capable of electron spin resonance and pump-probe spectroscopy at mK temperature and in vector magnetic field.

In the last decade, detecting spin dynamics at the atomic scale has been enabled by combining techniques such as electron spin resonance (ESR) or pump-probe spectroscopy with scanning tunneling microscopy (STM). Here, we demonstrate an ultra-high vacuum STM operational at milliKelvin (mK) temperatures and in a vector magnetic field capable of both ESR and pump-probe spectroscopy. By implementing GHz compatible cabling, we achieve appreciable RF amplitudes at the junction while maintaining the mK base temperature and high energy resolution. We demonstrate the successful operation of our setup by utilizing two experimental ESR modes (frequency sweep and magnetic field sweep) on an individual TiH molecule on MgO/Ag(100) and extract the effective g-factor. We trace the ESR transitions down to MHz into an unprecedented low frequency band enabled by the mK base temperature. We also implement an all-electrical pump-probe scheme based on waveform sequencing suited for studying dynamics down to the nanoseconds range. We benchmark our system by detecting the spin relaxation time T1 of individual Fe atoms on MgO/Ag(100) and note a field strength and orientation dependent relaxation time.

Spin Dynamics of the Radicals Produced from Methane Sulfonic Acid and Acetic Acid by Hydroxyl Radicals in Aqueous Solution Studied by Means of Time-Resolved Electron Spin Resonance Spectroscopy.

Fundamental information on the reactions of ·OH radical with alkyl sulfonic acid and carboxylic acid is important for understanding the degradation of the polymer electrolytes for fuel cells. In the present research, the spin dynamics of the organic radicals generated by the ·OH radical was investigated by means of a time-resolved electron spin resonance (TR-ESR) method with the pulsed laser irradiation on H2O2 in aqueous solution. The time profiles of the ESR signals of ·SO3-, ·CH2SO3-, ·CH2COOH, and ·CH2COO- have been analyzed along with the evaluation of characteristics of electron spins such as the g factor, hyperfine coupling constant A, lifetime of radicals, and electron spin relaxation time T1. The effects of the laser repetition frequency on the TR-ESR spectra, the pH dependence on the kinetic parameters, and the mechanism of chemically induced dynamic electron polarization (CIDEP) were discussed. The radical pair mechanism was suggested for the CIDEP, where the electron spins of these radicals are polarized by forming a free radical pair with another radical or the·OH radical, which have remained in the vicinity of photon absorption.

Electron Spin Resonance in Heterostructures with Ring Molecules of GeSi Quantum Dots

Heterostructures with annular groups of GeSi quantum dots grown on Si(001) substrates with GeSi nanodisks embedded beneath the surface are investigated by the electron spin resonance technique. It is demonstrated that electrons in annular groups can be localized at the apexes of quantum dots in the annular groups. Narrowing of the electron spin resonance line of the annular electron states localized at the nanodisks is observed. The width of this line decreases when the magnetic field deviates from the structure growth direction, which confirms experimentally the earlier prediction that the spin relaxation time T2 should increase in this case.

Manipulation of Molecular Qubits by Isotope Effect on Spin Dynamics

Controlling spin behavior via external stimuli is a key route to develop molecular spintronics devices. Photons, temperature, pressure, chemicals, and electric field are the possible stimuli. Herei...

Electron Spin Relaxation of Tb3+ and Tm3+ Ions.

Electron spin relaxation times T1 and Tm of Tb3+ and Tm3+ in 1:1 water:ethanol and of Tb3+ doped (2%) in crystalline La2(oxalate)3 decahydrate were measured between about 4.2 and 10 K. Both cations are non-Kramers ions and have J = 6 ground states. Echo-detected spectra are compared with CW spectra and with field-stepped direct-detected EPR spectra. Due to the strong temperature dependence of T1, measurements were not made above 10 K. Between about 4.2 and 6 K T1 is strongly concentration dependent between 1 and ~50 mM. T1 values at 4.2 K are in the μs range which is orders of magnitude faster than for 3d transition metals. Phase memory times, Tm, are less than 500 ns, which is short relative to values observed for 3d transition metals and organic radicals at 4 K. Tm is longer in the oxalate lattice which is attributed to the lower proton concentration in oxalate than in the organic solvent, which decreases nuclear spin diffusion. The rigidity of the crystalline lattice also may contribute to longer Tm.

Nuclear Magnetic Relaxation Mapping of Spin Relaxation in Electrically Stressed Glycerol.

This work discusses nuclear magnetic relaxation effects in glycerol subject to a strong electric field. The methods used are 1.5 T magnetic resonance imaging (MRI), referenced by 9.4 T nuclear magnetic resonance (NMR). While MRI allows a glycerol probe to be sampled with a high voltage (HV) of 16 kV applied to the probe, NMR provides precise molecular data from the sample, but the sample cannot be tested under HV. Using MRI, the recording of magnetic relaxation times was possible while HV was applied to the glycerol. NMR spectroscopy was used to confirm that MRI provides a reasonably accurate estimation of temperature. The applied HV was observed to have a negligible effect on the spin–lattice relaxation time T1, which represents the energy release to the thermal bath or system enthalpy. In contrast to that, the spin–spin relaxation time T2, which does represent the local entropy of the system, shows a lower response to temperature while the liquid is electrically stressed. These observations point toward a proton population in electrically stressed glycerol that is more mobile than that found in the bulk, an observation that is in agreement with previously published results for water.

Temperature Behavior of Aqueous Solutions of Poly(2-oxazoline) Homopolymer and Block Copolymers Investigated by NMR Spectroscopy and Dynamic Light Scattering.

1H NMR methods in combination with dynamic light scattering were applied to study temperature behavior of poly(2-isopropyl-2-oxazoline) (PIPOx) homopolymer as well as PIPOx-b-poly(2-methyl-2-oxazoline) (PMeOx) and poly(2-ethyl-2-oxazoline) (PEtOx)-b-PMeOx diblock copolymers in aqueous solutions. 1H NMR spectra showed a different way of phase transition for the main and side chains in PIPOx-based solutions. Additionally, the phase transition is irreversible for PIPOx homopolymer and partially reversible for PIPOx-b-PMeOx copolymer. As revealed by NMR, the phase transition in PEtOx-based copolymers solutions exists despite the absence of solution turbidity. It is very broad, virtually independent of the copolymer composition and reversible with some hysteresis. Two types of water molecules were detected in solutions of the diblock copolymers above the phase transition—“free” with long and “bound” with short spin–spin relaxation times T2. NOESY spectra revealed information about conformational changes observed already in the pre-transition region of PIPOx-b-PMeOx copolymer solution.

New Approach to Analyze 2D Map T1–T2

Based on the method of two-dimensional (2D) nuclear magnetic resonance (NMR) relaxometry, a technique was developed for determining the joint distribution of the correlation time $$ \tau_{c} $$ and the Van Vleck second moments $$ \Delta \omega^{2} $$. The field of application is the study of slow molecular motions corresponding to the condition of the ratio of nuclear magnetic relaxation times T1/T2 > 1.05 (the relation of spin–lattice relaxation time T1 to spin–spin relaxation time T2). The technique is based on the use of a priori information about the mechanism of nuclear magnetic relaxation in a system. The technique has used this information in the regularization solution of an inverse problem. In contrast to the known method for calculating 2D maps of the joint distribution P2 (T1, T2), the proposed method for constructing a 2D map of the joint distribution $$ Q_{2} \left( {\tau_{c} ,\Delta \omega^{2} } \right) $$ does not depend on the main characteristic of the NMR relaxometer—the resonance frequency $$ \omega_{0} $$. The technique was used to analyze the characteristics of sorbed water in clay rocks–argillite.

Fast Proton Magnetic Resonance Relaxometry Methods for Determining Viscosity and Concentration of Asphaltenes in Crude Oils

We have used proton magnetic resonance relaxometry to study the dependences of the spin–lattice and spin–spin relaxation times T1,2 on viscosity and concentration of asphaltenes + resins in crude oils, in particular from the Bach Ho field (Vietsovpetro joint venture), and we have derived equations relating them. We have refined the correlation ηT1,2 = const/T. The viscosity ν = η/ρ in these crude oils is exponentially proportional to the concentration of asphaltenes + resins.

Nuclear magnetic resonance biosensor for rapid detection of Vibrio parahaemolyticus

BackgroundVibrio parahaemolyticus is a Gram-negative bacterium widely distributed in marine environments and a well-recognized invertebrate pathogen frequently isolated from seafood. V. parahaemolyticus may also spread into humans, via contaminated, raw, or undercooked seafood, causing gastroenteritis and diarrhea. MethodsA Nuclear Magnetic Resonance (NMR)-based detection system was used to detect pathogenic levels of this microorganism (105 CFU/ml) with Molecular Mirroring using iron nanoparticles coated with target-specific biomarkers capable of binding to DNA of the target microorganism. The NMR system generates a signal (in milliseconds) by measuring NMR spin–spin relaxation time T2, which correlates with the amount of microorganism DNA. ResultsCompared with conventional microbiology techniques such as real-time PCR (qPCR), the NMR biosensor showed similar limits of detection (LOD) at different concentrations (105–108 CFU/ml) using two DNA extraction methods. In addition, the NMR biosensor system can detect a wide range of microorganism DNAs in different matrices within a short period of time. ConclusionNMR biosensor represents a potential tool for diagnostic and quality control to ensure microbial pathogens such as V. parahaemolyticus are not the cause of infection. The “hybrid” technology (NMR and nanoparticle application) opens a new platform for detecting other microbial pathogens that have impacted human health, animal health and food safety.

Single hole spin relaxation probed by fast single-shot latched charge sensing

Hole spins have recently emerged as attractive candidates for solid-state qubits for quantum computing. Their state can be manipulated electrically by taking advantage of the strong spin-orbit interaction (SOI). Crucially, these systems promise longer spin coherence lifetimes owing to their weak interactions with nuclear spins as compared to electron spin qubits. Here we measure the spin relaxation time T1 of a single hole in a GaAs gated lateral double quantum dot device. We propose a protocol converting the spin state into long-lived charge configurations by the SOI-assisted spin-flip tunneling between dots. By interrogating the system with a charge detector we extract the magnetic-field dependence of T1 ∝ B−5 for fields larger than B = 0.5 T, suggesting the phonon-assisted Dresselhaus SOI as the relaxation channel. This coupling limits the measured values of T1 from ~400 ns at B = 1.5 T up to ~60 μs at B = 0.5 T.

Hyperfine-phonon spin relaxation in a single-electron GaAs quantum dot

Understanding and control of the spin relaxation time T1 is among the key challenges for spin-based qubits. A larger T1 is generally favored, setting the fundamental upper limit to the qubit coherence and spin readout fidelity. In GaAs quantum dots at low temperatures and high in-plane magnetic fields B, the spin relaxation relies on phonon emission and spin–orbit coupling. The characteristic dependence T1 ∝ B−5 and pronounced B-field anisotropy were already confirmed experimentally. However, it has also been predicted 15 years ago that at low enough fields, the spin–orbit interaction is replaced by the coupling to the nuclear spins, where the relaxation becomes isotropic, and the scaling changes to T1 ∝ B−3. Here, we establish these predictions experimentally, by measuring T1 over an unprecedented range of magnetic fields—made possible by lower temperature—and report a maximum T1 = 57 ± 15 s at the lowest fields, setting a record electron spin lifetime in a nanostructure.

Thermoresponsive poly(2-oxazoline) homopolymers and copolymers in aqueous solutions studied by NMR spectroscopy and dynamic light scattering

Structural changes during temperature-induced phase transition in D2O solutions of poly(2-ethyl-2-oxazoline) (PEOx) and P(EOx-grad-2-methyl-2-oxazoline (MOx)) copolymers were investigated by 1H NMR methods in combination with dynamic light scattering. NMR spectra showed that in PEOx solutions on molecular level structures formed during gradual heating are preserved during subsequent cooling. Phase transition in solutions of P(EOx-grad-MOx) copolymers as revealed by NMR exists irrespective the solution is turbid or nonturbid at higher temperatures. In contrast to PEOx homopolymers it is very broad, virtually independent of the copolymer composition and molecular weight, and reversible with some hysteresis. Reduced intensities of cross-peaks in NOESY spectra of copolymer solutions at elevated temperatures are mainly due to the changed mobility of copolymer segments. In all investigated solutions two types of water, “free” and “bound” with long and very short spin–spin relaxation times T2, respectively, were detected in the transition region and above the transition. The existence of two T2 components shows that exchange between “bound” and “free” water is slow regarding T2 values.