Attosecond nanoplasmonic streaking of localized fields near metal nanospheres

Collective electron dynamics in plasmonic nanosystems can unfold on timescales in the attosec- ond regime and the direct measurements of plasmonic near-field oscillations is highly desirable. We report on numerical studies on the application of attosecond nanoplasmonic streaking spectroscopy to the measurement of collective electron dynamics in isolated Au nanospheres. The plasmonic field oscillations are induced by a few-cycle NIR driving field and are mapped by the energy of photoemitted electrons using a synchronized, time-delayed attosecond XUV pulse. By a detailed analysis of the amplitudes and phase shifts, we identify the different regimes of nanoplasmonic streaking and study the dependence on particle size, XUV photoelectron energy and emission position. The simulations indicate that the near-fields around the nanoparticles can be spatio-temporally reconstructed and may give detailed insight into the build-up and decay of collective electron motion.Comment: Revised versio

On the Experimental Estimation of Surface Enhanced Raman Scattering (SERS) Cross Sections by Vibrational Pumping

We present an in-depth analysis of the experimental estimation of cross sections in Surface Enhanced Raman Scattering (SERS) by vibrational pumping. The paper highlights the advantages and disadvantages of the technique, pinpoints the main aspects and limitations, and provides the underlying physical concepts to interpret the experimental results. Examples for several commonly used SERS probes are given, and a discussion on future possible developments is also presented.Comment: To be submitted to J. Phys. Chem.

Ab initio Studies of the Possible Magnetism in BN Sheet by Non-magnetic Impurities and Vacancies

We performed first-principles calculations to investigate the possible magnetism induced by the different concentrations of non-magnetic impurities and vacancies in BN sheet. The atoms of Be, B, C, N, O, Al and Si are used to replace either B or N in the systems as impurities. We discussed the changes in density of states as well as the extent of the spatial distributions of the defect states, the possible formation of magnetic moments, the magnitude of the magnetization energies and finally the exchange energies due to the presence of these defects. It is shown that the magnetization energies tend to increase as the concentrations of the defects decreases in most of the defect systems which implies a definite preference of finite magnetic moments. The calculated exchange energies are in general tiny but not completely insignificant for two of the studied defect systems, i.e. one with O impurities for N and the other with B vacancies.Comment: 8 pages, 10 figures, submitted to Phys. Rev.

Effects of isospin and momentum dependent interactions on thermal properties of asymmetric nuclear matter

Thermal properties of asymmetric nuclear matter are studied within a self-consistent thermal model using an isospin and momentum dependent interaction (MDI) constrained by the isospin diffusion data in heavy-ion collisions, a momentum-independent interaction (MID), and an isoscalar momentum-dependent interaction (eMDYI). In particular, we study the temperature dependence of the isospin-dependent bulk and single-particle properties, the mechanical and chemical instabilities, and liquid-gas phase transition in hot asymmetric nuclear matter. Our results indicate that the temperature dependence of the equation of state and the symmetry energy are not so sensitive to the momentum dependence of the interaction. The symmetry energy at fixed density is found to generally decrease with temperature and for the MDI interaction the decrement is essentially due to the potential part. It is further shown that only the low momentum part of the single-particle potential and the nucleon effective mass increases significantly with temperature for the momentum-dependent interactions. For the MDI interaction, the low momentum part of the symmetry potential is significantly reduced with increasing temperature. For the mechanical and chemical instabilities as well as the liquid-gas phase transition in hot asymmetric nuclear matter, our results indicate that the boundary of these instabilities and the phase-coexistence region generally shrink with increasing temperature and is sensitive to the density dependence of the symmetry energy and the isospin and momentum dependence of the nuclear interaction, especially at higher temperatures.Comment: 21 pages, 29 figure

Surface plasmon lifetime in metal nanoshells

The lifetime of localized surface plasmon plays an important role in many aspects of plasmonics and its applications. In small metal nanostructures, the dominant mechanism restricting plasmon lifetime is size-dependent Landau damping. We performed quantum-mechanical calculations of Landau damping for the bright surface plasmon mode in a metal nanoshell. In contrast to the conventional model based on the electron surface scattering, we found that the damping rate decreases as the nanoshell thickness is reduced. The origin of this behavior is traced to the spatial distribution of plasmon local field inside the metal shell. We also found that, due to interference of electron scattering amplitudes from nanoshell's two metal surfaces, the damping rate exhibits pronounced quantum beats with changing shell thickness.Comment: 9 pages, 4 Figure

Pressure dependence of the charge-density-wave gap in rare-earth tri-tellurides

We investigate the pressure dependence of the optical properties of CeTe$_3$, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of $R$Te$_3$.Comment: 5 pages, 4 figure

Is it possible to formulate least action principle for dissipative systems?

A longstanding open question in classical mechanics is to formulate the least action principle for dissipative systems. In this work, we give a general formulation of this principle by considering a whole conservative system including the damped moving body and its environment receiving the dissipated energy. This composite system has the conservative Hamiltonian $H=K_1+V_1+H_2$ where $K_1$ is the kinetic energy of the moving body, $V_1$ its potential energy and $H_2$ the energy of the environment. The Lagrangian can be derived by using the usual Legendre transformation $L=2K_1+2K_2-H$ where $K_2$ is the total kinetic energy of the environment. An equivalent expression of this Lagrangian is $L=K_1-V_1-E_d$ where $E_d$ is the energy dissipated by the friction from the moving body into the environment from the beginning of the motion. The usual variation calculus of least action leads to the correct equation of the damped motion. We also show that this general formulation is a natural consequence of the virtual work principle.Comment: 11 pages, no figur