Nonadiabatic coupling of the dynamical structure to the superconductivity in YSr2Cu2.75Mo0.25O7.54 and Sr2CuO3.3

A crucial issue in cuprates is the extent and mechanism of the coupling of the lattice to the electrons and the superconductivity. Here we report Cu K edge extended X-ray absorption fine structure measurements elucidating the internal quantum tunneling polaron (iqtp) component of the dynamical structure in two heavily overdoped superconducting cuprate compounds, tetragonal YSr2Cu2.75Mo0.25O7.54 with superconducting critical temperature, Tc = 84 K and hole density p = 0.3 to 0.5 per planar Cu, and the tetragonal phase of Sr2CuO3.3 with Tc = 95 K and p = 0.6. In YSr2Cu2.75Mo0.25O7.54 changes in the Cu-apical O two-site distribution reflect a sequential renormalization of the double-well potential of this site beginning at Tc, with the energy difference between the two minima increasing by ∼6 meV between Tc and 52 K. Sr2CuO3.3 undergoes a radically larger transformation at Tc, >1-Å displacements of the apical O atoms. The principal feature of the dynamical structure underlying these transformations is the strongly anharmonic oscillation of the apical O atoms in a double-well potential that results in the observation of two distinct O sites whose Cu–O distances indicate different bonding modes and valence-charge distributions. The coupling of the superconductivity to the iqtp that originates in this nonadiabatic coupling between the electrons and lattice demonstrates an important role for the dynamical structure whereby pairing occurs even in a system where displacements of the atoms that are part of the transition are sufficiently large to alter the Fermi surface. The synchronization and dynamic coherence of the iqtps resulting from the strong interactions within a crystal would be expected to influence this process.

Synthesis of Fe-Doped Tetrahedrites Cu12-xFexSb4S13 and Characterization of Their Thermoelectric Properties

Tetrahedrite (C₁₂Sb₄S₁₃) has attracted attention as a p-type thermoeletric material with very low thermal conductivity induced by the anharmonic oscillation of Cu due to the lone-pair electrons of Sb. Many studies have been conducted to improve its thermoelectric performance by partially substituting the transition elements for the Cu sites. In this study, Fe-doped tetrahedrites Cu_12-xFe_xSb₄S₁₃ (x = 0.1-0.4) were prepared by mechanical alloying and hot pressing. The tetrahedrite phase was successfully synthesized by mechanical alloying without post-annealing and exhibited stability even without phase transition after hot pressing. Moreover, the Fe content was observed to be directly proportional to the lattice constant, which confirmed the Fe substitutions on the Cu sites. The electrical conductivity was observed to decrease with the increase in the Seebeck coefficient due to the charge compensation caused by Fe doping (electron donation). The highest power factor was 0.84 mWm^-1K^-2 at 723 K for the specimen with x = 0.1; however, it decreased with an increase in Fe content. In addition, as the Fe content increased, the electronic thermal conductivity decreased. Thus, the lowest thermal conductivity value was obtained for the specimen with x = 0.4 (0.45–0.64 Wm^-1K^-1) in the temperature range of 323–723 K. As a result, the maximum value of the dimensionless figure of merit (ZT = 0.80) was achieved at 723 K for the specimen with x = 0.2.

Artificial Generation of High Harmonics via Nonrelativistic Thomson Scattering in Metamaterial

High harmonic generation allows one to extend the frequency of laser to a much broader regime and to study the electron dynamics of matters. However, severely limited by the vague high-order process in natural material and the unfriendly state of the commonly applied gas and plasma media, the ambitious goal of custom-design high harmonics remains exceptionally challenging. Here, we demonstrate that high harmonics can be artificially designed and tailored based on a metamaterial route. With the localized reconstruction of magnetic field in a metamaterial, the nonlinear Thomson scattering, a ubiquitous electromagnetic process which people used to believe that it only occurs with the relativistic velocity, can be stimulated in a nonrelativistic limit, which drives anharmonic oscillation of free electrons and generates high harmonics. An explicit physical model and the numerical simulations perfectly demonstrate the artificial generation and tailoring of the high harmonics. This novel mechanism is entirely dominated by the artificial structure instead of the natural nonlinear compositions. It not only provides unprecedented design freedom to the high harmonic generation but breaks the rigorous prerequisite of the relativistic velocity of the nonlinear Thomson scattering process, which offers fascinating possibilities to the development of new light source and ultrafast optics, and opens up exciting opportunities for the advanced understanding of electrodynamics in condensed matters.

Artificial Generation of High Harmonics via Nonrelativistic Thomson Scattering in Metamaterial

High harmonic generation allows one to extend the frequency of laser to a much broader regime and to study the electron dynamics of matters. However, severely limited by the vague high-order process in natural material and the unfriendly state of the commonly applied gas and plasma media, the ambitious goal of custom-design high harmonics remains exceptionally challenging. Here, we demonstrate that high harmonics can be artificially designed and tailored based on a metamaterial route. With the localized reconstruction of magnetic field in a metamaterial, the nonlinear Thomson scattering, a ubiquitous electromagnetic process which people used to believe that it only occurs with the relativistic velocity, can be stimulated in a nonrelativistic limit, which drives anharmonic oscillation of free electrons and generates high harmonics. An explicit physical model and the numerical simulations perfectly demonstrate the artificial generation and tailoring of the high harmonics. This novel mechanism is entirely dominated by the artificial structure instead of the natural nonlinear compositions. It not only provides unprecedented design freedom to the high harmonic generation but breaks the rigorous prerequisite of the relativistic velocity of the nonlinear Thomson scattering process, which offers fascinating possibilities to the development of new light source and ultrafast optics, and opens up exciting opportunities for the advanced understanding of electrodynamics in condensed matters.

High Molecular Weight Polyethylene Nanospheres: Synthesis, Physical and Mechanical Properties—Second Harmonic Generation

The weak second harmonic light generating from carbon nanotubes are detected. The signal intensity closely related to the density of π-bonds attributed to the defects in the rolled graphene sheets, which is stimulated to have anharmonic oscillation as strongly affected by the environment. The intensities of SHG are diminished in order of well-aligned multi-wall carbon nanotubes (MWCNTs), randomly-aligned MWCNTs, and then to single-wall CNTs.

GIANT THIRD-ORDER NONLINEARITIES IN ANHARMONIC QUANTUM WELLS

Third-harmonic generation (THG) and its origin are investigated in an anharmonic quantum well by the perturbation theory. The calculated results show that the nonlinear effect roots in an anharmonic oscillation of electrons deviate asymmetrically or symmetrically from an ideal harmonic oscillation, and the more the deviation is, the larger the nonlinearities will be. In addition, the nonlinear coefficient is also relative to the anharmonic-oscillation frequency in the model. The most important point is that the THG coefficient may be obtained over 10-10 (m/V)2, about ten orders of magnitude greater than those in bulk GaAs.