Showing papers on "Relaxation (NMR) published in 2019"

Bad metallic transport in a cold atom Fermi-Hubbard system

Abstract: Strong interactions in many-body quantum systems complicate the interpretation of charge transport in such materials. To shed light on this problem, we study transport in a clean quantum system: ultracold lithium-6 in a two-dimensional optical lattice, a testing ground for strong interaction physics in the Fermi-Hubbard model. We determine the diffusion constant by measuring the relaxation of an imposed density modulation and modeling its decay hydrodynamically. The diffusion constant is converted to a resistivity by using the Nernst-Einstein relation. That resistivity exhibits a linear temperature dependence and shows no evidence of saturation, two characteristic signatures of a bad metal. The techniques we developed in this study may be applied to measurements of other transport quantities, including the optical conductivity and thermopower.

A comparative study on the structural, dielectric and multiferroic properties of Co0.6Cu0.3Zn0.1Fe2O4/Ba0.9Sr0.1Zr0.1Ti0.9O3 composite ceramics

Abstract: High performance multiferroic composites have attracted great attentions because they are more beneficial to increasing magnetoelectric coupling effect. We report the effects of molar ratio (4:1, 2:1, 1:1, 1:2 and 1:4) on the structural, dielectric and multiferroic properties of Co0.6Cu0.3Zn0.1Fe2O4/Ba0.9Sr0.1Zr0.1Ti0.9O3 (CCZFO/BSZTO) composite ceramics prepared by sol-gel method. The XRD results confirm successful formation of the CCZFO/BSZTO composites without presence of any impurity phase. The mean grain size is about 1.5 mm and it shows double dispersing behavior, the larger grains belong to CCZFO while the smaller ones are ascribed to BSZTO. The maximum dielectric constant and loss appear with the molar ratio is 1:1 due to its more grain boundaries. Two peaks appear in the e∼T curves, the peak corresponding to the lower temperature corresponds to the Curie temperature of BSZTO, while the other one is resulted by the relaxation polarization. The height of the relaxation peak decreases and the position shifts to higher temperature range with the increase of molar ratio. The maximal remanent polarization is 3.76 μC/cm2, obtained at 1 kHz when the molar ratio is 1:1. An enhanced magnetic properties are observed when the molar ratio is 1:1 due to the stronger interface interaction effect between the two phases. Strong direct magnetoelectric coupling coefficient of 1.53 V/(cm.Oe) is obtained at the field of 8000 Oe for the sample 1:4. These results may provide valuable information for improving the multiferroic properties of composite multiferroic materials.

Characterization of Néel and Brownian Relaxations Isolated from Complex Dynamics Influenced by Dipole Interactions in Magnetic Nanoparticles

Abstract: The magnetization dynamics involved in applying an alternating field are composed of a superposition of Neel and Brownian relaxations. To evaluate the mechanisms of magnetic relaxations, it is necessary to individually evaluate the Neel and Brownian regimes. In this study, by applying a fast responding pulse field, the two-step magnetization response of magnetic nanoparticles dispersed in a fluid in the Brownian regime occurred after the Neel regime. We isolated Neel and Brownian relaxations from an experimentally observed superposition relaxation system by fitting the theoretical calculation to the measured time evolution response of the magnetization, which was in agreement with the susceptibility that was measured through applying an alternating magnetic field. The dependence of Neel and Brownian relaxation’s dominance in the superposition system on relaxation times was clearly observed. In particular, the effect of dipole interactions on Neel and Brownian relaxation times were confirmed by changing th...

Aromatic 19F-13C TROSY: a background-free approach to probe biomolecular structure, function, and dynamics

Abstract: Atomic-level information about the structure and dynamics of biomolecules is critical for an understanding of their function. Nuclear magnetic resonance (NMR) spectroscopy provides unique insights into the dynamic nature of biomolecules and their interactions, capturing transient conformers and their features. However, relaxation-induced line broadening and signal overlap make it challenging to apply NMR spectroscopy to large biological systems. Here we took advantage of the high sensitivity and broad chemical shift range of 19F nuclei and leveraged the remarkable relaxation properties of the aromatic 19F-13C spin pair to disperse 19F resonances in a two-dimensional transverse relaxation-optimized spectroscopy spectrum. We demonstrate the application of 19F-13C transverse relaxation-optimized spectroscopy to investigate proteins and nucleic acids. This experiment expands the scope of 19F NMR in the study of the structure, dynamics, and function of large and complex biological systems and provides a powerful background-free NMR probe.

Spin Selectivity in Photoinduced Charge-Transfer Mediated by Chiral Molecules.

Abstract: Optical control and readout of electron spin and spin currents in thin films and nanostructures have remained attractive yet challenging goals for emerging technologies designed for applications in information processing and storage. Recent advances in room-temperature spin polarization using nanometric chiral molecular assemblies suggest that chemically modified surfaces or interfaces can be used for optical spin conversion by exploiting photoinduced charge separation and injection from well-coupled organic chromophores or quantum dots. Using light to drive photoexcited charge-transfer processes mediated by molecules with central or helical chirality enables indirect measurements of spin polarization attributed to the chiral-induced spin selectivity effect and of the efficiency of spin-dependent electron transfer relative to competitive relaxation pathways. Herein, we highlight recent approaches used to detect and to analyze spin selectivity in photoinduced charge transfer including spin-transfer torque for local magnetization, nanoscale charge separation and polarization, and soft ferromagnetic substrate magnetization- and chirality-dependent photoluminescence. Building on these methods through systematic investigation of molecular and environmental parameters that influence spin filtering should elucidate means to manipulate electron spins and photoexcited states for room-temperature optoelectronic and photospintronic applications.

High-resolution spectroscopy of single nuclear spins via sequential weak measurements

Abstract: Nuclear magnetic resonance (NMR) of single spins have recently been detected by quantum sensors. However, the spectral resolution has been limited by the sensor’s relaxation to a few kHz at room temperature. This can be improved by using quantum memories, at the expense of sensitivity. In contrast, classical signals can be measured with exceptional spectral resolution by using continuous measurement techniques, without compromising sensitivity. When applied to single-spin NMR, it is critical to overcome the impact of back action inherent of quantum measurement. Here we report sequential weak measurements on a single 13C nuclear spin. The back-action causes the spin to undergo a quantum dynamics phase transition from coherent trapping to coherent oscillation. Single-spin NMR at room-temperature with a spectral resolution of 3.8 Hz is achieved. These results enable the use of measurement-correlation schemes for the detection of very weakly coupled single spins. Quantum sensors can have exceptional properties but the limits on their performance involve nonclassical effects such as quantum backaction. Here the authors show how to mitigate the effects of backaction on the spectral resolution of an NV centre nuclear spin sensor by controlling the measurement strength.

Synthesis, structures and magnetic properties of [(η 9 -C 9 H 9 )Ln(η 8 -C 8 H 8 )] super sandwich complexes

Abstract: Sandwich complexes are an indispensable part of organometallic chemistry, which is becoming increasingly important in the field of lanthanide-based single molecule magnets. Herein, a fundamental class of pure sandwich complexes, [(η9-C9H9)Ln(η8-C8H8)] (Ln=Nd, Sm, Dy, Er), is reported. These neutral and sandwiched lanthanide compounds exclusively contain fully π-coordinated coplanar eight and nine membered CH rings. The magnetic properties of these compounds are investigated, leading to the observation of slow relaxation of the magnetization, including open hysteresis loops up to 10 K for the Er(III) analogue. Fast relaxation of the magnetization is likewise observed near zero field, a highly important characteristic for quantum information processing schemes. Our synthetic strategy is straightforward and utilizes the reaction of [(η8-C8H8)LnI(thf)n] complexes with [K(C9H9)]. Although all compounds are fully characterized, structural details of the title compounds can also be deduced by Raman spectroscopy only. Lanthanide sandwich complexes represent both a fundamental class of organometallic compounds and promising molecular magnets for information storage. Here the authors unveil a class of lanthanide sandwich complexes containing fully π-coordinated 8- and 9-membered rings, and show their slow relaxation of the magnetization.

Phase field modeling of domain dynamics and polarization accumulation in ferroelectric HZO

Abstract: In this work, we investigate the accumulative polarization (P) switching characteristics in ferroelectric (FE) thin films under the influence of sequential sub-coercive electric-field pulses. Performing the dynamic phase-field simulation (based on time-dependent Landau-Ginzburg model) and experimental measurement on Hf0.4Zr0.6O2 (HZO), we analyze the electric field induced domain-wall (DW) motion and the resultant P accumulation process in FE. According to our analysis, even in the absence of an applied electric field, the DW can potentially undergo spontaneous motion. Such a DW instability leads to spontaneous P-excitation and relaxation processes, which play a pivotal role in accumulative P-switching in an FE grain. We show that the extent of such P accumulation increases with the increase in the applied electric field, increase in excitation time and decrease in relaxation time. Finally, by considering an ensemble of grains with local and global coercive field distributions, we model the P-accumulation process in a large area HZO sample. In such a multi-grain scenario, the dependency of P accumulation on the applied electric field pulse attributes follows similar features as that of a single-grain, although the spontaneous processes (excitation/relaxation) are less prominent in large area sample.

A Series of Lanthanide-Based Metal-Organic Frameworks Derived from Furan-2,5-dicarboxylate and Glutarate: Structure-Corroborated Density Functional Theory Study, Magnetocaloric Effect, Slow Relaxation of Magnetization, and Luminescent Properties.

Abstract: Herein, through a dual-ligand strategy, we report eight isorecticular lanthanide(III) furan-2,5-dicarboxylic acid metal-organic frameworks (Ln-MOFs) with the general formula {[Ln(2,5-FDA)0.5(Glu)(H2O)2]· xH2O} n [Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7), and Yb (8); 2,5-FDA2- = furan-2,5-dicarboxylate and Glu2- = glutarate; x = 0.5 for 1, 2, and 4 and x = 0 for 3 and 5-8], synthesized under solvothermal conditions by using an N, N'-dimethylformamide/H2O mixed solvent system. Crystallographic data reveal that all eight Ln-MOFs 1-8 crystallize in the orthorhombic Pnma space group. All of the MOFs are isostructural as well as isomorphous with distorted monocapped square-antiprismatic geometry around the Ln1 metal center. In Ln-MOFs 1-8, the 2,5-FDA2- and Glu2- ligands exhibit μ2-κ4,η1:η1:η1:η1 and μ3-κ5,η2:η1:η1:η1 coordination modes, respectively. Topologically, assembled Ln-MOFs 1-8 consist of the 2D cem topological type. The designed Ln-MOFs 1-8 are further explored for structure-corroborated density functional theory study. Meanwhile, room temperature photoluminescence properties of Ln-MOFs 2 and 4 and magnetic properties of Ln-MOFs 3 and 5 have been explored in detail. A highly intense, ligand-sensitized, Ln3+ f-f photoluminescence emission is exhibited by Ln-MOFs 2 [Eu3+ (red emission)] and 4 [Tb3+ (green emission)]. Magnetic studies suggest weak antiferro- and ferromagnetic interactions between adjacent GdIII ions in Ln-MOF 3, thereby displaying a large magnetocaloric effect. The magnetic data measured at T = 2 K and Δ H = 30 kOe depict that the -Δ Sm value per unit mass reaches 32.1 J kg-1 K-1, which is larger than most of the GdIII-based complexes reported. The alternating-current susceptibility measurements on Ln-MOF 5 revealed that out-of-phase signals are frequency- and temperature-dependent under both 0 and 2 kOe direct-current fields, thereby suggesting a typical slow magnetic relaxation behavior with two relaxation processes. This is further supported by the Cole-Cole plots at 2.4-6 K.

Engineering electronic structure to prolong relaxation times in molecular qubits by minimising orbital angular momentum.

Abstract: The proposal that paramagnetic transition metal complexes could be used as qubits for quantum information processing (QIP) requires that the molecules retain the spin information for a sufficient length of time to allow computation and error correction. Therefore, understanding how the electron spin-lattice relaxation time (T1) and phase memory time (Tm) relate to structure is important. Previous studies have focused on the ligand shell surrounding the paramagnetic centre, seeking to increase rigidity or remove elements with nuclear spins or both. Here we have studied a family of early 3d or 4f metals in the +2 oxidation states where the ground state is effectively a 2S state. This leads to a highly isotropic spin and hence makes the putative qubit insensitive to its environment. We have studied how this influences T1 and Tm and show unusually long relaxation times given that the ligand shell is rich in nuclear spins and non-rigid.

Lanthanide(III) Hexanuclear Circular Helicates: Slow Magnetic Relaxation, Toroidal Arrangement of Magnetic Moments, and Magnetocaloric Effects.

Abstract: Four hexanuclear circular helicates, {[Dy6L6(DMF)12]·6CF3SO3·12DMF}2 (1Dy), {[Gd6L6(DMF)12]·6CF3SO3·12DMF}2 (1Gd), [Dy6L6(DMF)10(H2O)2]·6ClO4·4H2O·10DMF (2Dy), and [Gd6L6(DMF)12]·6ClO4·2H2O·10DMF (2Gd), where DMF = N,N-dimethylformamide, were synthesized by employing a glutaratedihydrazide-bridged bis(3-methoxysalicylaldehyde) ligand (H2L) and characterized structurally and magnetically. Direct-current magnetic susceptibility studies indicated predominant weak antiferromagnetic exchange interactions among gadolinium analogues, which were quantified using the PHI software, giving J = -0.003 cm-1 with g = 2.00 for 1Gd and J = -0.001 cm-1 with g = 2.02 for 2Gd. Alternating-current magnetic susceptibility measurements indicated that complexes 1Dy and 2Dy show slow relaxation of magnetization behavior, further supported by theoretical calculations that also highlighted the toroidal arrangement of the magnetic moments.

High Blocking Temperature of Magnetization and Giant Coercivity in the Azafullerene Tb2@C79N with a Single‐Electron Terbium–Terbium Bond

Abstract: The azafullerene Tb2 @C79 N is found to be a single-molecule magnet with a high 100-s blocking temperature of magnetization of 24 K and large coercivity. Tb magnetic moments with an easy-axis single-ion magnetic anisotropy are strongly coupled by the unpaired spin of the single-electron Tb-Tb bond. Relaxation of magnetization in Tb2 @C79 N below 15 K proceeds via quantum tunneling of magnetization with the characteristic time τQTM =16 462±1230 s. At higher temperature, relaxation follows the Orbach mechanism with a barrier of 757±4 K, corresponding to the excited states, in which one of the Tb spins is flipped.

Quantum tunnelling of the magnetisation in single-molecule magnet isotopologue dimers.

Abstract: Quantum tunnelling of the magnetisation plays a major role in the magnetic properties of lanthanide Single-Molecule Magnets: while it is considered a problem for data storage device applications since it leads to information loss, it is an essential pre-requisite for the read-out and manipulation of the nuclear states in Quantum Information Processing schemes. Here we describe two isotopologue dysprosium dimers, i.e. [(163Dy(tmhd)3)2(bpym)] and [(164Dy(tmhd)3)2(bpym)] (tmd = tris(tetramethylheptanedionato) and bpym = bipyrimidine), where the nuclear spin presence or absence clearly affects the magnetic properties of the systems. Through μ-SQUID studies at milli-Kelvin temperatures and alternating current magnetic measurements, we find significant differences in the magnetic behaviour of both complexes. While simulation of the hysteresis loops at 30 mK reveals that the presence of nuclear spin does not influence the tunnelling rate, we find that it facilitates the coupling to the phonon bath enhancing the direct relaxation process; an observation reflected in the temperature and field dependence of the relaxation rates.

Ultrafast photocarrier dynamics in a 3D Dirac semimetal Cd3As2 film studied with terahertz spectroscopy

Abstract: By employing optical pump Terahertz (THz) probe spectroscopy, a three dimensional (3D) Dirac semimetal, Cd3As2 film, was investigated systematically at room temperature. After photoexcitation at 400/800 nm, the rise time of photoenhanced THz photoconductivity (PC) is about ∼1.0 ps, increasing slightly with the pump fluence, in which time scale, photoexcited electrons and holes establish separate Fermi distribution with electrons in the conduction band and holes in the valence band via fast carrier-carrier scattering and carrier-phonon coupling. The subsequent THz PC relaxation shows single exponential decay with a time constant of ∼6.0 ps that is independent of pump fluence. The relaxation process is dominated by the electron-hole recombination via a radiative and nonradiative way, which is mediated by the phonon-phonon scattering. The optically induced THz complex PC can be well fitted with the Drude-Smith model. Our experimental results shed light on understanding the photocarrier dynamics of the 3D Dirac semimetal materials at THz frequency.

Controlling the dominant magnetic relaxation mechanisms for magnetic hyperthermia in bimagnetic core–shell nanoparticles

Abstract: We report a simple and effective way to control the heat generation of a magnetic colloid under alternate magnetic fields by changing the shell composition of bimagnetic core-shell Fe3O4/ZnxCo1-xFe2O4 nanoparticles. The core-shell structure constitutes a magnetically-coupled biphase system, with an effective anisotropy that can be tuned by the substitution of Co2+ by Zn2+ ions in the shell. Magnetic hyperthermia experiments of nanoparticles dispersed in hexane and butter oil showed that the magnetic relaxation is dominated by Brown relaxation mechanism in samples with higher anisotropy (i.e., larger concentration of Co within the shell) yielding high specific power absorption values in low viscosity media as hexane. Increasing the Zn concentration of the shell, diminishes the magnetic anisotropy, which results in a change to a Neel relaxation that dominates the process when the nanoparticles are dispersed in a high-viscosity medium. We demonstrate that tuning the Zn contents at the shell of these exchange-coupled core/shell nanoparticles provides a way to control the magnetic anisotropy without loss of saturation magnetization. This ability is an essential prerequisite for most biomedical applications, where high viscosities and capturing mechanisms are present.

Linear and nonlinear rheology and structural relaxation in dense glassy and jammed soft repulsive pNIPAM microgel suspensions.

Abstract: We present an integrated experimental and quantitative theoretical study of the mechanics of self-crosslinked, slightly charged, repulsive pNIPAM microgel suspensions over a very wide range of concentrations (c) that span the fluid, glassy and putative “soft jammed” regimes. In the glassy regime we measure a linear elastic dynamic shear modulus over 3 decades which follows an apparent power law concentration dependence G′ ∼ c5.64, a variation that appears distinct from prior studies of crosslinked ionic microgel suspensions. At very high concentrations there is a sharp crossover to a nearly linear growth of the modulus. To theoretically understand these observations, we formulate an approach to address all three regimes within a single conceptual Brownian dynamics framework. A minimalist single particle description is constructed that allows microgel size to vary with concentration due to steric de-swelling effects. Using a Hertzian repulsion interparticle potential and a suite of statistical mechanical theories, quantitative predictions under quiescent conditions of microgel collective structure, dynamic localization length, elastic modulus, and the structural relaxation time are made. Based on a constant inter-particle repulsion strength parameter which is determined by requiring the theory to reproduce the linear elastic shear modulus over the entire concentration regime, we demonstrate good agreement between theory and experiment. Testable predictions are then made. We also measured nonlinear rheological properties with a focus on the yield stress and strain. A theoretical analysis with no adjustable parameters predicts how the quiescent structural relaxation time changes under deformation, and how the yield stress and strain change as a function of concentration. Reasonable agreement with our observations is obtained. To the best of our knowledge, this is the first attempt to quantitatively understand structure, quiescent relaxation and shear elasticity, and nonlinear yielding of dense microgel suspensions using microscopic force based theoretical methods that include activated hopping processes. We expect our approach will be useful for other soft polymeric particle suspensions in the core–shell family.

Metal-Ligand Covalency Enables Room Temperature Molecular Qubit Candidates

Abstract: Harnessing synthetic chemistry to design electronic spin-based qubits, the smallest unit of a quantum information system, enables us to probe fundamental questions regarding spin relaxation dynamics. We sought to probe the influence of metal–ligand covalency on spin–lattice relaxation, which comprises the upper limit of coherence time. Specifically, we studied the impact of the first coordination sphere on spin–lattice relaxation through a series of four molecules featuring V–S, V–Se, Cu–S, and Cu–Se bonds, the Ph4P+ salts of the complexes [V(C6H4S2)3]2− (1), [Cu(C6H4S2)2]2− (2), [V(C6H4Se2)3]2− (3), and [Cu(C6H4Se2)2]2− (4). The combined results of pulse electron paramagnetic resonance spectroscopy and ac magnetic susceptibility studies demonstrate the influence of greater M–L covalency, and consequently spin-delocalization onto the ligand, on elongating spin–lattice relaxation times. Notably, we observe the longest spin–lattice relaxation times in 2, and spin echos that survive until room temperature in both copper complexes (2 and 4).

Stability of the lattice kinetic scheme and choice of the free relaxation parameter.

Abstract: The lattice kinetic scheme (LKS), a modified version of the classical single relaxation time (SRT) lattice Boltzmann (LB) method, was initially developed as a suitable numerical approach for non-Newtonian flow simulations and a way to reduce memory consumption of the original SRT approach. The better performances observed for non-Newtonian flows are mainly due to the additional degree of freedom allowing an independent control over the relaxation of higher-order moments, independently from the fluid viscosity. Although widely applied to fluid flow simulations, yet no theoretical analysis of LKS has been performed. The present work focuses on a systematic von Neumann analysis of the linearized collision operator. Thanks to this analysis, the effect of the modified collision operator on the stability domain and spectral behavior of the scheme are clarified. Results obtained in this study show that correct choices of the "second relaxation coefficient" lead, to a certain extent, to more consistent dispersion and dissipation for large values of the first relaxation coefficient. Furthermore, appropriate values of this parameter can lead to a larger linear stability domain. At moderate and low values of the viscosity, larger values of the free parameter are observed to increase dissipation of kinetic modes, while leaving the acoustic modes untouched and having a less pronounced effect on the convective mode. This increased dissipation leads in general to less pronounced sources of non-linear instability, thus improving the stability of the LKS.

Thermal conductivity and phonon hydrodynamics in transition metal dichalcogenides from first-principles

Abstract: We carry out a systematic study of the thermal conductivity of four single-layer transition metal dichalcogenides, MX$_2$ (M = Mo, W; X = S, Se) from first-principles by solving the Boltzmann Transport Equation (BTE). We compare three different theoretical frameworks to solve the BTE beyond the Relaxation Time Approximation (RTA), using the same set of interatomic force constants computed within density functional theory (DFT), finding that the RTA severely underpredicts the thermal conductivity of MS$_2$ materials. Calculations of the different phonon scattering relaxation times of the main collision mechanisms and their corresponding mean free paths (MFP) allow evaluating the expected hydrodynamic behaviour in the heat transport of such monolayers. These calculations indicate that despite of their low thermal conductivity, the present TMDs can exhibit large hydrodynamic effects, being comparable to those of graphene, especially for WSe$_2$ at high temperatures.

Gd(III)-Grafted Detonation Nanodiamonds for MRI Contrast Enhancement

Abstract: We report on the first 1H NMR relaxation and magnetic resonance imaging (MRI) study of aqueous suspensions of detonation nanodiamond (DND) grafted by Gd(III) ions. In contrast to Gd(III)–ND conjuga...

Solvent-dependent segmental dynamics in intrinsically disordered proteins

Abstract: Protein and water dynamics have a synergistic relationship, which is particularly important for intrinsically disordered proteins (IDPs), although the details of this coupling remain poorly understood. Here, we combine temperature-dependent molecular dynamics simulations using different water models with extensive nuclear magnetic resonance (NMR) relaxation to examine the importance of distinct modes of solvent and solute motion for the accurate reproduction of site-specific dynamics in IDPs. We find that water dynamics play a key role in motional processes internal to "segments" of IDPs, stretches of primary sequence that share dynamic properties and behave as discrete dynamic units. We identify a relationship between the time scales of intrasegment dynamics and the lifetime of hydrogen bonds in bulk water. Correct description of these motions is essential for accurate reproduction of protein relaxation. Our findings open important perspectives for understanding the role of hydration water on the behavior and function of IDPs in solution.

Analysis on the Magnetic Field Response for Nuclear Spin Co-Magnetometer Operated in Spin-Exchange Relaxation-Free Regime

Abstract: A nuclear spin co-magnetometer operated in the spin-exchange relaxation-free (SERF) regime is a promising tool for long-term navigation application for its abilities to sense inertial rotation and to suppress environmental magnetic field disturbance. The magnetic field response model of a K-Rb- 21 Ne nuclear spin co-magnetometer is derived based on the state space method and the model is experimentally validated on a tabletop SERF co-magnetometer. The theoretical and experimental results indicate that the relaxation rate of the nuclear spins limits the field-suppression ability. The results here not only give insight into the nature of self-compensate characteristic but also provide a precise model for the estimation of the magnetic noise-induced rotation measurement error in a SERF co-magnetometer.

Field-Induced Slow Magnetic Relaxation in a Mononuclear Manganese(II) Complex

Abstract: A mononuclear manganese(II) complex, [Mn(4-bzpy)4Cl2] (4-bzpy = 4-benzylpyridine), exhibits a slow magnetic relaxation with three relaxation modes that is supported by the external magnetic field. The low-frequency mode shows an exceptionally slow relaxation time: τ = 798 ms at T = 1.9 K and BDC = 0.35 T. The high-frequency domain exhibits unusual acceleration of the relaxation time upon cooling below 3.5 K.

Holographic plasmon relaxation with and without broken translations

Abstract: We study the dynamics and the relaxation of bulk plasmons in strongly coupled and quantum critical systems using the holographic framework. We analyze the dispersion relation of the plasmonic modes in detail for an illustrative class of holographic bottom-up models. Comparing to a simple hydrodynamic formula, we entangle the complicated interplay between the three least damped modes and shed light on the underlying physical processes. Such as the dependence of the plasma frequency and the effective relaxation time in terms of the electromagnetic coupling, the charge and the temperature of the system. Introducing momentum dissipation, we then identify its additional contribution to the damping. Finally, we consider the spontaneous symmetry breaking (SSB) of translational invariance. Upon dialing the strength of the SSB, we observe an increase of the longitudinal sound speed controlled by the elastic moduli and a decrease in the plasma frequency of the gapped plasmon. We comment on the condensed matter interpretation of this mechanism.