Temperature Dependence Of T1 Research Articles

Characterization of low sodium type II silicon clathrate film spin dynamics

Type II Si clathrate is a Si-based, crystalline alternative to diamond silicon with interesting optoelectronic properties. Here, a pulsed electron paramagnetic resonance study of the spin dynamics of sodium-doped, type II NaxSi136 silicon clathrate films is reported. Focusing on the hyperfine lines of isolated Na atoms, the temperature dependence of the electron spin dynamics is examined from 6 to 25 K. The measurements exhibit multi-exponential decay, indicating multiple spin relaxation rates in the system. As expected, spin relaxation time (T1) increases rapidly with decreasing temperature, reaching ∼300 μs at 6.4 K. The phase memory (TM) shows less temperature dependence with a value of ∼3 μs at the same temperature. The temperature dependence of T1 exhibits Arrhenius behavior in the measurement range consistent with an Orbach pathway. There are strong similarities to the spin behavior of other defect donors in diamond silicon. The results provide insights into the potential of Si clathrates for spin-based applications.

Spin-lattice relaxation with non-linear couplings: Comparison between Fermi's golden rule and extended dissipaton equation of motion.

Fermi's golden rule (FGR) offers an empirical framework for understanding the dynamics of spin-lattice relaxation in magnetic molecules, encompassing mechanisms like direct (one-phonon) and Raman (two-phonon) processes. These principles effectively model experimental longitudinal relaxation rates, denoted as T1-1. However, under scenarios of increased coupling strength and nonlinear spin-lattice interactions, FGR's applicability may diminish. This paper numerically evaluates the exact spin-lattice relaxation rate kernels, employing the extended dissipaton equation of motion formalism. Our calculations reveal that when quadratic spin-lattice coupling is considered, the rate kernels exhibit a free induction decay-like feature, and the damping rates depend on the interaction strength. We observe that the temperature dependence predicted by FGR significantly deviates from the exact results since FGR ignores the higher order effects and the non-Markovian nature of spin-lattice relaxation. Our methods can be easily extended to study other systems with nonlinear spin-lattice interactions and provide valuable insights into the temperature dependence of T1 in molecular qubits when the coupling is strong.

Quantifying the effects of peripheral substituents on the spin-lattice relaxation of a vanadyl molecular quantum bit

Electron spin superpositions represent a critical component of emergent quantum technologies in computation, sensing, encryption, and communication. However, spin relaxation (T1) and decoherence (Tm) represent major obstacles to the implementation of molecular quantum bits (qubits). Synthetic strategies have made substantial progress in enhancing spin coherence times by minimizing contributions from surrounding electron and nuclear spins. For room-temperature operation, however, the lifetime of spin coherence becomes limited by coupling with vibrational modes of the lattice. Using pulse electron paramagnetic resonance (EPR) spectroscopy, we measure the spin-lattice relaxation of a vanadyl tetrapyrazinoporphyrazine complex appended with eight peripheral 2,6-diisopropylphenol groups (VOPyzPz-DIPP) and compare it to the relaxation of the archetypical vanadyl phthalocyanine molecular qubit (VOPc). The added peripheral groups lead to distinctly different spin relaxation behavior. While similar relaxation times are observed at low temperatures and ambient conditions, significant changes are observed for the orientation dependence of T1 at 100 K, as well as the temperature dependence of T1 over the intermediate temperature range spanning [Formula: see text]10–150 K. These results can be tentatively interpreted as arising from loosened spin-phonon coupling selection rules and a greater number of accessible acoustic and optical modes contributing to the spin relaxation behavior of VOPyzPz-DIPP relative to VOPc.

Investigation of Dynamic Behavior of Confined Ionic Liquid [BMIM]+[TCM]- in Silica Material SBA-15 Using NMR.

The molecular dynamics of 1-butyl-3-methyl imidazolium tricyanomethanide ionic liquid [BMIM]+[TCM]- confined in SBA-15 mesoporous silica were examined using 1H NMR spin-lattice (T1) relaxation and diffusion measurements. An extensive temperature range (100 K-400 K) was considered in order to study both the liquid and glassy states. The hydrogen dynamics in the two states and the self-diffusion coefficients of the cation [BMIM]+ above the glass transition temperature were extracted from the experimental data. The results were then compared to the corresponding bulk substance. The effects of confinement on the dynamic properties of the ionic liquid clearly manifest themselves in both temperature regimes. In the high-temperature liquid state, the mobility of the confined cations reduces significantly compared to the bulk; interestingly, confinement drives the ionic liquid to the glassy state at a higher temperature Tg than the bulk ionic liquid, whereas an unusual T1 temperature dependence is observed in the high-temperature regime, assigned to the interaction of the ionic liquid with the silica-OH species.

Electronic Spin Qubit Candidates Arrayed within Layered Two-Dimensional Polymers

Molecular electronic spin qubits are promising candidates for quantum information science applications because they can be reliably produced and engineered via chemical design. Embedding electronic spin qubits within two-dimensional polymers (2DPs) offers the possibility to systematically engineer inter-qubit interactions while maintaining long coherence times, both of which are prerequisites to their technological utility. Here, we introduce electronic spin qubits into a diamagnetic 2DP by n-doping naphthalene diimide subunits with varying amounts of CoCp2 and analyze their spin densities by quantitative electronic paramagnetic resonance spectroscopy. Low spin densities (e.g., 6.0 × 1012 spins mm-3) enable lengthy spin-lattice (T1) and spin-spin relaxation (T2) times across a range of temperatures, ranging from T1 values of 164 ms at 10 K to 30.2 μs at 296 K and T2 values of 2.36 μs at 10 K to 0.49 μs at 296 K for the lowest spin density sample examined. Higher spin densities and temperatures were both found to diminish T1 times, which we attribute to detrimental cross-relaxation from spin-spin dipolar interactions and spin-phonon coupling, respectively. Higher spin densities decreased T2 times and modulated the T2 temperature dependence. We attribute these differences to the competition between hyperfine and dipolar interactions for electron spin decoherence, with the dominant interaction transitioning from the former to the latter as spin density and temperature increase. Overall, this investigation demonstrates that dispersing electronic spin qubits within layered 2DPs enables chemical control of their inter-qubit interactions and spin decoherence times.

On the Origin and the Amplitude of T‐Square Resistivity in Fermi Liquids

AbstractIn 1937, Baber, Landau, and Pomeranchuk postulated that collisions between electrons generates a contribution to the electric resistivity of metals with a distinct T2 temperature dependence. The amplitude of this term is small in common metals, but dominant in metals hosting either heavy carriers or a low concentration of them. The temperature dependence is set by the size of the scattering phase, but the microscopic source of dissipation is not straightforward. To explain how electron–electron collisions lead to momentum leak, Umklapp events or multiple electron reservoirs have been invoked. This interpretation is challenged by several experimental observations: the persistence of T‐square resistivity in dilute metals (in which the two mechanisms are irrelevant), the successful extension of Kadowaki–Woods scaling to dilute metals, and the observation of a size‐dependent T‐square thermal resistivity () and its WiedemannFranz correlation with T‐square electrical resistivity. This paper argues that much insight is provided by the case of normal liquid 3He where the T‐square temperature dependence of energy and momentum diffusivity is driven by fermionfermion collisions. The amplitude of T‐square resistivity in 3He and in metals share a common scaling. Thus, the ubiquitous T‐square electrical resistivity ultimately stems from the Fermi‐liquid temperature dependence of momentum diffusivity.

Temperature dependence, accuracy, and repeatability of T1 and T2 relaxation times for the ISMRM/NIST system phantom measured using MR fingerprinting.

Before MR fingerprinting (MRF) can be adopted clinically, the derived quantitative values must be proven accurate and repeatable over a range of T1 and T2 values and temperatures. Correct assessment of accuracy and precision as well as comparison between measurements can only be performed when temperature is either controlled or corrected for. The purpose of this study was to investigate the temperature dependence of T1 and T2 MRF values and evaluate the accuracy and repeatability of temperature-corrected relaxation values derived from a B1 -corrected MRF-fast imaging with steady-state precession implementation using 2 different dictionary sizes. The International Society of MR in Medicine/National Institute of Standards and Technology phantom was scanned using an MRF sequence of 2 different lengths, a variable flip angle T1 , and a multi-echo spin echo T2 at 14 temperatures ranging from 15°C to 28°C and investigated with a linear regression model. Temperature-corrected accuracy was evaluated by correlating T1 and T2 times from each MRF dictionary with reference values. Repeatability was assessed using the coefficient of variation, with measurements taken over 30 separate sessions. There was a statistically significant fit of the model for MRF-derived T1 and T2 and temperature (p < 0.05) for all the spheres with a T1 > 500 ms. Both MRF methods showed a strong linear correlation with reference values for T1 (R2 = 0.996) and T2 (R2 = 0.982). MRF repeatability for T1 values was ≤1.4% and for T2 values was ≤3.4%. MRF demonstrated relaxation times with a temperature dependence similar to that of conventional mapping methods. Temperature-corrected T1 and T2 values from both dictionaries showed adequate accuracy and excellent repeatability in this phantom study.

Measurement of sub-zero temperatures in MRI using T1 temperature sensitive soft silicone materials: Applications for MRI-guided cryosurgery.

One standard method, proton resonance frequency shift, for measuring temperature using magnetic resonance imaging (MRI), in MRI-guided surgeries, fails completely below the freezing point of water. Because of this, we have developed a new methodology for monitoring temperature with MRI below freezing. The purpose of this paper is to show that a strong temperature dependence of the nuclear relaxation time T1 in soft silicone polymers can lead to temperature-dependent changes of MRI intensity acquired with T1 weighting. We propose the use of silicone filaments inserted in tissue for measuring temperature during MRI-guided cryoablations. The temperature dependence of T1 in bio-compatible soft silicone polymers was measured using nuclear magnetic resonance spectroscopy and MRI. Phantoms, made of bulk silicone materials and put in an MRI-compatible thermal container with dry ice, allowed temperature measurements ranging from -60°C to + 20°C. T1 -weighted gradient echo images of the phantoms were acquired at spatially uniform temperatures and with a gradient in temperature to determine the efficacy of using these materials as temperature indicators in MRI. Ex vivo experiments on silicone rods, 4mm in diameter, inserted in animal tissue were conducted to assess the practical feasibility of the method. Measurements of nuclear relaxation times of protons in soft silicone polymers show a monotonic, nearly linear, change with temperature (R2 >0.98) and have a significant correlation with temperature (Pearson's r>0.99, p<0.01). Similarly, the intensity of the MR images in these materials, taken with a gradient echo sequence, are also temperature dependent. There is again a monotonic change in MRI intensity that correlates well with the measured temperature (Pearson's r<-0.98 and p<0.01). The MRI experiments show that a temperature change of 3°C can be resolved in a distance of about 2.5mm. Based on MRI images and external sensor calibrations for a sample with a gradient in temperature, temperature maps with 3°C isotherms are created for a bulk phantom. Experiments demonstrate that these changes in MRI intensity with temperature can also be seen in 4mm silicone rods embedded in ex vivo animal tissue. We have developed a new method for measuring temperature in MRI that potentially could be used during MRI-guided cryoablation operations, reducing both procedure time and cost, and making these surgeries safer.

Impact of Chlorine Substitution on Electron Spin Relaxation of a Trityl Radical.

A perchlorotriarylmethyl tricarboxylic acid radical 99% enriched in 13C at the central carbon (13C1-PTMTC) was characterized in phosphate buffered saline solution (pH = 7.2) (PBS) at ambient temperature. Samples immobilized in 1:1 PBS:glycerol or in 9:1 trehalose:sucrose were studied as a function of temperature. Isotope enrichment at C1 creates a trityl that can be used to accurately measure microscopic viscosity. Understanding of the impact of the 13C hyperfine interaction on electron spin relaxation is important for application of this trityl in oximetry and distance measurements. The anisotropic 13C1 hyperfine couplings (Ax = Ay = 24 ± 2 MHz, Az = 200 ± 1 MHz) are larger than for the related 13C1-perdeuterated Finland trityl (13C1-dFT) and the g anisotropy (gx = 2.0013, gy = 2.0016, gz = 2.0042) is slightly larger than for 13C1-dFT. The tumbling correlation times (τR) for 13C1-PTMTC are 0.20 ± 0.02 ns in PBS and 0.40 ± 0.05 ns in 3:1 PBS:glycerol, which are shorter than for 13C1-dFT in the same solutions. T1 for 13C1-PTMTC is 3.5 ± 0.5 μs in PBS and 5.3 ± 0.4 μs in 3:1 PBS:glycerol, which are shorter than for 13C1-dFT due to faster tumbling, larger anisotropy of the 13C1 hyperfine, and about 30% larger contribution from the local mode. In immobilized samples T1 for 13C1-PTMTC is similar to that for 13C1-dFT and other trityls without chlorine or 13C1 substituents, indicating that the 13C1 and Cl substituents on the phenyl rings have little impact on T1. The temperature dependence of T1 was modeled with contributions from the direct, Raman, and local mode processes. Broadening of CW linewidths of about 0.6 G in fluid solution and about 2 G in rigid lattice is attributed to unresolved 35,37Cl hyperfine couplings.

Nodeless superconductivity in the kagome metal CsV3Sb5

The recently discovered kagome metal series AV3Sb5 (A=K, Rb, Cs) exhibits topologically nontrivial band structures, chiral charge order and superconductivity, presenting a unique platform for realizing exotic electronic states. The nature of the superconducting state and the corresponding pairing symmetry are key questions that demand experimental clarification. Here, using a technique based on the tunneling diode oscillator, the magnetic penetration depth Δλ(T) of CsV3Sb5 was measured down to 0.07 K. A clear exponential behavior in Δλ(T) with marked deviations from a T or T2 temperature dependence was observed at low temperatures, indicating an absence of nodal quasiparticles. Temperature dependence of the superfluid density and electronic specific heat can be described by two-gap s-wave superconductivity, consistent with the presence of multiple Fermi surfaces in CsV3Sb5. These results evidence nodeless superconductivity in CsV3Sb5 under ambient pressure, and constrain the allowed pairing symmetry.

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.

Correlation of Physicochemical Properties of Bach Ho Oils with Proton NMR Relaxation Parameters and Their Temperature Dependence

The physicochemical properties of crude oils (density, viscosity, asphaltene concentrations) from the Bach Ho oilfield (Vietnam) have been correlated with 1H NMR relaxation parameters (spin–lattice and spin–spin relaxation times T1i and T2i, respectively), and their temperature dependence has been studied. The results are discussed in terms of the concept of the formation of structural units (SU) in oils. The standard “alkane line”—the conventional correlation ηТ1,2 = const/Т for viscous oils—has been refined. The temperature dependences of T1,2i have been obtained, which manifest ordering processes in the test oils.

Temperature dependent transport spin-polarization in the low Curie temperature complex itinerant ferromagnet EuTi1−xNbxO3

The physical systems with ferromagnetism and ‘bad’ metallicity hosting unusual transport properties are playgrounds of novel quantum phenomena. Recently EuTi1−xNbxO3 emerged as a ferromagnetic system where non-trivial temperature dependent transport properties are observed due to coexistence and competition of various magnetic and non-magnetic scattering processes. In the ferromagnetic state, the resistivity shows a T2 temperature dependence possibly due to electron–magnon scattering and above the Curie temperature , the dependence changes to T3/2 behaviour indicating a correlation between transport and magnetic properties. In this paper, we show that the transport spin-polarization () in EuTi1−xNbxO3, a low Curie temperature ferromagnet, is as high (∼40%) as that in some of the metallic ferromagnets with high Curie temperatures. In addition, owing to the low Curie temperature of EuTi1−xNbxO3, the temperature (T) dependence of could be measured systematically up to which revealed a proportionate relationship with magnetization versus T. This indicates that such proportionality is far more universally valid than the ferromagnets with ideal parabolic bands. Furthermore, our band structure calculations not only helped to understand the origin of such high spin polarization in EuTi1−xNbxO3 but also provided a route to estimate the Hubbard U parameter in complex metallic ferromagnets in general using experimental inputs.

Phase transitions in (C7 H12 N2 )2 [SnCl6 ]Cl2 ·1.5H2 O crystal, studied by NMR and infrared spectroscopy.

The (C7 H12 N2 )2 [SnCl6 ]Cl2 ·1.5H2 O complex is a new member of the family of hybrid organic-inorganic perovskite compounds. It exhibits two order-disorder phase transitions with changes in the conformation of aromatic cations at the two transition temperatures 360 and 412K. Differential scanning calorimetry, nuclear magnetic resonance (NMR), and Fourier-transform infrared (FT-IR) spectroscopy were used to investigate these phase transitions. These transition mechanisms were investigated in terms of the spin-lattice relaxation times T1 for 1 H static NMR and the chemical shifts for 13 C CP-MAS. The temperature dependence of T1(1 H) and 13 C chemical shifts are changed near TC1 and TC2 . Furthermore, the splitting for 13 C NMR signals in Phases (II) and (III) indicated a ferroelastic characteristic of the compound. In addition, FT-IR results indicate that the ordered conformational structure of aromatic cations undergoes a remarkable disorder with increasing temperature. The NMR and FT-IR studies suggest that the phase transition mechanisms are related to the reorientational motion of [C7 H12 N2 ]2+ cations as a whole. Phase transition was examined in light of the interesting optical properties of this material.

Determination of limiting values of 1H spin-spin relaxation time to assess lifetime of thermally aged acrylonitrile butadiene rubber

We propose a method to determine the limiting value of 1H spin–spin relaxation time (T2) for assessing the lifetime of thermally aged acrylonitrile butadiene rubber (NBR) parts. So far, it has been difficult to determine the limiting values of T2 without performing other experiments such as mechanical property measurements and air tightness tests. We exposed two types of NBR diaphragm sheets to air at 100 °C for up to 7540 h and 6000 h, respectively. After that, we tested their air-tightness and we measured T2 of the virgin and aged diaphragms. To evaluate the temperature dependence of T2, T2 measurements were performed at 20, 40, and 60 °C. Additionally, we observed the 13C Nuclear Magnetic Resonance (NMR) spectra, toluene swelling ratio, acetone soluble fraction, and glass transition temperature for only one type of the diaphragm sheets. The diaphragm aged for 7540 h had lost sealability, and all the results indicated that this was caused by the degradation of NBR. The 13C NMR spectra clearly revealed that the degradation of NBR proceeded in three stages: self-cross-linking reactions in the initial stage, concurrent reactions of cross-linking and molecular chain scission in the second stage, and an increased number of reactions of cross-linking and molecular chain scission in the final stage. The results of the T2 measurements showed that T2 is useful not only to evaluate the complicated degradation behavior quantitatively, but also to determine the different limiting values of T2 itself corresponding to large and small safety margins. Finally, we demonstrated that the temperature dependence of T2 is an effective parameter for quantitatively predicting the ultimate lifetime at each aging temperature with no safety margin for various thermally aged NBR rubber sheets.

Phonon diffraction and dimensionality crossover in phonon-interface scattering

Thermal resistance at interfaces and grain boundaries is important in a range of fields from microelectronics to energy materials. Standard models treat interfaces as structureless even though at the nanoscale they are often better described as arrays of linear defects. Here, we examine several characteristics of heat transport that arise when considering such a structure at the interface. When heat carrying phonons scatter off linear defect arrays, diffraction of phonons occurs. Furthermore, a dimensionality crossover is observed in diffusive transport. Phonons transition from seeing a structureless planar defect when their wavelength is longer than the defect spacing, lambda gtrsim D, to seeing the interface as a collection of independently scattering linear defects when lambda lesssim D. By applying this theory to grain boundary strain-field scattering, we show that this dimensionality crossover can explain the frequency dependence of grain boundary scattering and transmissivity, which results in the T2 temperature dependence observed in the low-T thermal conductivity of poly/nanocrystalline materials.

Elastic properties of the charge density wave system HoTe3

We present ultrasonic measurements on the rare earth tritelluride HoTe3 compound. Different anomalies are observed at the upper and lower charge density wave phase transition T[Formula: see text] = 284 K and T[Formula: see text] = 120 K. A striking T2 temperature dependence of the velocities of the longitudinal C[Formula: see text], C[Formula: see text] and shear C[Formula: see text] modes is observed in the ordered phase below the lower CDW phase transition T[Formula: see text]. Such a behavior is related to the temperature dependence of the CDW order parameter.

Nuclear quadrupolar spin-lattice relaxation with realistic phonon density of states in alkali halides

The nuclear quadrupolar spin-lattice relaxation times T1 have been calculated in alkali halides, whereby the phonon densities of states have been extracted from the shell model lattice dynamics. The calculations at room temperature were performed on 79Br in KBr, NaBr, and RbBr; 23Na in NaI, NaCl, and NaBr; 35Cl in NaCl and KCl; and 127I in NaI and KI. The obtained values of relaxation time T1 are an order of magnitude smaller than those calculated with the Debye-model phonon density of states and agree well with experiments. The temperature dependence of acoustic and optical phonon contributions to the nuclear relaxation rate (first-order Raman phonon process) are carried out in the temperature range 20 to 300 K for 23Na and 127I in NaI. The role of optical phonons becomes important from 77 K on; the temperature dependence of T1 agrees with experimental data throughout most of the temperature range studied (77–300 K), while differing quantitatively from the predictions obtained on the basis of the Debye model.

Disorder versus two transport lifetimes in a strongly correlated electron liquid

We report on angle-dependent measurements of the sheet resistances and Hall coefficients of electron liquids in SmTiO3/SrTiO3/SmTiO3 quantum well structures, which were grown by molecular beam epitaxy on (001) DyScO3. We compare their transport properties with those of similar structures grown on LSAT [(La0.3Sr0.7)(Al0.65Ta0.35)O3]. On DyScO3, planar defects normal to the quantum wells lead to a strong in-plane anisotropy in the transport properties. This allows for quantifying the role of defects in transport. In particular, we investigate differences in the longitudinal and Hall scattering rates, which is a non-Fermi liquid phenomenon known as lifetime separation. The residuals in both the longitudinal resistance and Hall angle were found to depend on the relative orientations of the transport direction to the planar defects. The Hall angle exhibited a robust T2 temperature dependence along all directions, whereas no simple power law could describe the temperature dependence of the longitudinal resistances. Remarkably, the degree of the carrier lifetime separation, as manifested in the distinctly different temperature dependences and diverging residuals near a critical quantum well thickness, was completely insensitive to disorder. The results allow for a clear distinction between disorder-induced contributions to the transport and intrinsic, non-Fermi liquid phenomena, which includes the lifetime separation.