Korringa relaxation rates of Mn ion in noble metal hosts

Neutron scattering measurements of the paramagnetic spectral function in dilute alloys of Mn in the noble metal hosts Ag and Au are reported. The spectral width is found to have the characteristic q-dependence due to Mn-Mn couplings for moderately concentrated alloys (?3 at% Mn) but is q-independent in the measured q-range (>0.3Å^-1) for Mn concentrations around 1 at% as found earlier in $\text{Cu}$-Mn alloys also. The dilute limit spectral width which is proportional to the Korringa relaxation rate decreases down the column of the periodic table following roughly the ration $\text{3: 1}\text{1}\text{2}\text{: 1}$ for Cu, Ag and Au, respectively. Assuming that the direct exchange constants are roughly the same in the three hosts, it would appear that the s-d mixing term decreases progressively with increasing “nobility” of the host.     

Incomplete phonon relaxation in X-ray emission

We calculate the phonon broadening in x-ray emission for Li, Na, Al, and K, treating the excitation and the subsequent emission as one quantum process. When the core-hole lifetime width is of the same order as the Debye energy, incomplete phonon relaxation gives a partial quenching of the Stokes shift and an additional width. This effect has previously not been seriously investigated; we find here that it gives a likely explanation of the broad Li emission edge.     

Korringa relaxation time of magnetic ion system near a two-dimensional electron gas

Spin relaxation of Mn ions in a (Cd,Mn)Te quantum well with quasi-two-dimensional carriers (Q2DEG) is investigated. The mechanism of energy transfer is spin-flip scattering of Mn spin with electrons making transitions between spin subbands accompanied by a change in the Mn spin. A calculation of the spin-flip scattering rate shows that the Mn spin relaxation rate is proportional to the coupling constant squared, the density of states squared, and the electron temperature, the so called Korringa relaxation rate. It was found that for small Mn ion concentration, the relaxation time ≈10−7-10−6s is in a good agreement with experimental results. Moreover, the relaxation rate scales with L⁻², L being the well width, and it can be enhanced over its value in bulk.     

Calculations of anharmonic phonon relaxation times

Anharmonic phonon relaxation times in Ge are calculated using (i) an isotropic continuum model, and (ii) a dispersive model. A complete spectrum of calculated results is presented. Frequency-averaged values for normal- and umklapp-three-phonon relaxation times are also calculated. A comparison is made between our findings and some earlier works, and disagreements are discussed. The results are applied in calculating some results in the theory of lattice thermal conductivity. From February 1976: Department of Theoretical Physics, The University, Newcastle-Upon-Tyne, NE1 7RU U.K.     

Quasiparticle relaxation and phonon emission in superconducting tunnel junctions

Using SnISn tunnel junctions as generators and detectors of high frequency phonons, the temperature dependence (down to 0.3°K) of the derivative of the detected signal as a function of generator bias is reported. For T?1°K we have observed the expected BCS singularity in the signal at a generator bias of 4Δ. An additional singularity has been observed at a bias of 2Δ when the number of injected particles greatly exceeds the number thermally excited. Unlike the 4Δ peak, the temperature of occurrence of the 2Δ peak depends markedly on generator impedance, (injection rate) as expected. The data provide strong evidence that Tewordt's model (strictly valid for T = 0°K), in which an excited quasiparticle relaxes predominantly in a single step to the gap edge before recombination, is correct in the temperature range $\text{T}\text{T}{}_{\mathrm{c}}\text{< 0.3}$ and for low injection rates.     

Fano lineshape and phonon softening in single isolated metallic carbon nanotubes

Evolution of G-band modes of single metallic carbon nanotubes with the Fermi level shift is examined by simultaneous Raman and electron transport studies. Narrow Lorentzian line shape and upshifted frequencies are observed near the van Hove singularities. However, all G modes soften and broaden at the band crossing point. The concurrent appearance of an asymmetric Fano line shape at this point indicates that phonon-continuum coupling is intrinsic to single metallic tubes. The apparent Lorentzian line shapes of as-synthesized metallic tubes are induced by O2 adsorption causing the Fermi level shift.     

Observation of phonon bottleneck in quantum dot electronic relaxation

Time-resolved differential transmission measurements of self-assembled In0.4Ga0.6As quantum dots clearly indicate a phonon bottleneck between the n = 2 and n = 1 electronic levels. The key to this observation is the generation of electrons in dots where there are no holes so that electron-hole scattering does not mask the bottleneck. We use a simple carrier capture model consisting of two capture configurations to explain the bottleneck signal and offer arguments to rule out other possible sources of the signal.     

Correlating dynamic relaxation and viscoelasticity in metallic glasses

Relaxation dynamics,essential for the structural evolution of non-equilibrium systems like glassy materials,remain enigmatic.Here,we explore relaxation dynamics and viscoelastic properties in three types of metallic glasses with distinct β relaxation behavior.In systems with significant β relaxation,stress relaxation and creep experiments reveal a transition from two-step to one-step relaxation with rising temperature.However,such a phenomenon is absent in systems with weaker β relaxation.We mod...     

Spin relaxation due to polar optical phonon scattering

Spin relaxation due to polar optical phonon scattering in semiconductors was investigated. The relaxation of the electron spin was found to increase with increasing the strength of the electric field. However, a high field completely depolarized the electron spin due to an increase of the spin precession frequency of the hot electrons, suggesting that high field transport conditions might not be desirable for spin-based technology with these semiconductors. It was also found that spin relaxation decreases with increasing moderately n-doping density or decreasing temperature. The results were discussed in comparison with the data available in the literature.     

Influence of phonon dimensionality on electron energy relaxation

We studied experimentally the role of phonon dimensionality on electron-phonon (e-p) interaction in thin copper wires evaporated either on suspended silicon nitride membranes or on bulk substrates, at sub-Kelvin temperatures. The power emitted from electrons to phonons was measured using sensitive normal metal-insulator-superconductor tunnel junction thermometers. Membrane thicknesses ranging from 30 to 750 nm were used to clearly see the onset of the effects of two-dimensional (2D) phonon system. We observed for the first time that a 2D phonon spectrum clearly changes the temperature dependence and strength of the e-p scattering rate, with the interaction becoming stronger at the lowest temperatures below approximately 0.5 K for the 30 nm membranes.     

High-energy phonon branches of an individual metallic carbon nanotube

We present excitation-energy dependent Raman measurements between 2.05 and 2.41 eV on the same individual carbon nanotube. We find a change in the Raman frequencies of both the D mode (63 cm(-1)/eV) and the high-energy modes. The observed frequencies of the modes at approximately 1600 cm(-1) as a function of laser-energy map the phonon dispersion relation of a metallic tube near the Gamma point of the Brillouin zone. Our results prove the entire first-order Raman spectrum in single-wall carbon nanotubes to originate from double-resonant scattering. Moreover, we confirm experimentally the phonon softening in metallic tubes by a Peierls-like mechanism.     

NMR relaxation rate in metallic carbon nanotubes

NMR relaxation rate, T₁⁻¹, of the metallic carbon nanotube is discussed based on Tomonaga–Luttinger-liquid theory. It is found that the Coulomb interaction leads to increase of (T₁T)⁻¹ by a power law with decreasing temperature, T. The dependence on temperature of (T₁T)⁻¹ in the multi-wall nanotube (MWNT) is shown to be strongly suppressed by existence of the metallic shells in the MWNTs.     

Hole-interface optical phonon relaxation rates with valence band-mixing effects

We theoretically investigate the hole-interface optical phonon scattering rates for a InGaAs-AlGaAs quantum well structure, taking into account the valence-band mixing. The dispersion relation and the electrostatic potentials for interface optical phonon modes are obtained based on the macroscopic dielectric continuum model. For the hole dispersion relation, the Luttinger-Kohn Hamiltonian is used. The hole-interface optical phonon interaction is evaluated by the Fermi's golden rule taking into account the Bloch overlap factor.Our results show that the hole-interface phonon scattering rates within the parabolic band approximation are different from those including valence band mixing effects. Especially, in the low energy region, the hole-interface phonon scattering rates within the parabolic band approximation are overestimated very significantly.     

Microscopic origin of reversible relaxation in metallic glasses

Mössbauer spectroscopy has been used to measure changes associated with structural relaxation in the glass Pd₄₀Ni₄₀P₂₀. When taken with data from X-ray diffraction, the results characterize the differences between irreversible and reversible relaxation, and show that the latter involves at least two distinct processes.     

Intrinsic nonlinear ferromagnetic relaxation in thin metallic films

We propose an intrinsic mechanism for ferromagnetic relaxation in thin films that can dominate competing linear mechanisms even for rapidly relaxing metals. In particular, we use an analytic theory of four-magnon scattering to demonstrate rapid decay for technologically important systems involving high moment materials subject to large rotations. A micromagnetic simulation is used to verify the results.     

Electron and phonon relaxation in metal films perturbed by a femtosecond laser pulse

A theoretical investigation of the electron and phonon time-dependent distributions in an Ag film subjected to a femtosecond laser pulse has been carried out. A system of two coupled time-dependent Boltzmann equations, describing electron and phonon dynamics, has been numerically solved. In the electron Boltzmann equation, electron–electron and electron–phonon collision integrals are considered together with a source term for laser perturbation. In the phonon Boltzmann equation, only electron–phonon collisions are considered, neglecting laser perturbation and phonon–phonon collisions. Screening of the interactions has been accounted for in both the electron–electron and the electron–phonon collisions. The results show the simultaneous electron and phonon time-dependent distributions from the initial non-equilibrium behaviour up to the establishment of a new final equilibrium condition. PACS 72.10.-d; 71.10.Ca; 63.20.Kr     

Alternating-current relaxation of a rotating metallic particle

Based on a first-principles approach,we establish an alternating-current(AC) relaxation theory for a rotating metallic particle with complex dielectric constant ε_α=ε_α-iσ_α/ω_0.Here εα is the real part,σ_α the conductivity,ω_0 the angular frequency of an AC electric field,and i=-1~(1/2).Our theory yields an accurate interparticle force,which is in good agreement with the existing experiment.The agreement helps to show that the relaxations of two kinds of charges,namely,surface polarized charges(described by ε_α) and free charges(corresponding to σ_α),contribute to the unusually large reduction in the attracting interparticle force.This theory can be adopted to determine the relaxation time of dynamic particles in various fields.     

Structural relaxation of metallic glass forming melts

The fragility of superheated melts, M, for 13 kinds of metallic alloys has been evaluated from the data of the dynamic viscosity above their liquidus temperatures. The authors find that the glass forming ability of metallic melts depends on the fragility of superheated melts rather than on the value of viscosity. In the present work the value of fragility is less than 1 for good glass-forming melts but more than 1 for the other melts. The variation rate of atomic coordination number with temperature indicat...