No abstract

We have studied the effect of thermal annealing on electron dephasing times τ φ in three-dimensional polycrystalline metals. Measurements are performed on as-sputtered and annealed AuPd and Sb thick films, using weak-localization method. In all samples, we find that τ φ possesses an extremely weak temperature dependence as T → 0. Our results show that the effect of annealing is non-universal, and it depends strongly on the amount of disorder quenched in the microstructures during deposition. The observed "saturation" behavior of τ φ cannot be easily explained by magnetic scattering. We suggest that the issue of saturation can be better addressed in three-dimensional, rather than lowerdimensional, structures.

To identify and investigate the mechanisms of electron-phonon (e-ph) relaxation in weakly disordered metallic conductors, we measure the electron dephasing rate in a series of suspended and supported 15-nm thick AuPd wires. In a wide temperature range, from ∼8  K to above 20 K, the e-ph interaction dominates in the dephasing processes. The corresponding relaxation rate reveals a quadratic temperature dependence, τ(e-ph)(-1)=A(ep)T2, where A(ep)≈5×10(9)  K(-2)  s(-1) is essentially the same for all samples studied. Our observations are shown to be in good agreement with the theory which predicts that, even in weakly disordered metallic structures at moderately low temperatures, the major mechanism of the e-ph relaxation is the electron scattering from vibrating defects and impurities.

We theoretically investigate the exciton formed with two massive Dirac particles in monolayer [Formula: see text] and other transition metal dichalcogenides as well as two layers separated by a dielectric layer. In the low-energy limit, the separation of the center-of-mass and relative motions is obtained. Analytical solutions for the exciton wave function and energy dispersion are obtained including the Coulomb interaction between electron and hole, the exciton Bohr radius, binding energy and its effective mass are obtained in monolayer transition metal dichalcogenides. In the case of two monolayers separated by a dielectric layer, we find that the exciton effective mass can be continuously tuned by the interlayer separation.

Using the weak-localization method, we have measured the electron-phonon scattering times τep in Pd60Ag40 thick films prepared by DC-and RF-sputtering deposition techniques. In both series of samples, we find an anomalous 1/τep ∝ T 2 ℓ temperature and disorder dependence, where ℓ is the electron elastic mean free path. This anomalous behavior cannot be explained in terms of the current concepts for the electron-phonon interaction in impure conductors. Our result also reveals that the strength of the electron-phonon coupling is much stronger in the DC than RF sputtered films, suggesting that the electron-phonon interaction not only is sensitive to the total level of disorder but also is sensitive to the microscopic quality of the disorder.