123 research outputs found
Diffractive parton distributions from the saturation model
We review diffractive deep inelastic scattering (DIS) in the light of the
collinear factorization theorem. This theorem allows to define diffractive
parton distributions in the leading twist approach. Due to its selective final
states, diffractive DIS offers interesting insight into the form of the
diffractive parton distributions which we explore with the help of the
saturation model. We find Regge-like factorization with the correct energy
dependence measured at HERA. A remarkable feature of diffractive DIS is the
dominance of the twist-4 contribution for small diffractive masses. We quantify
this effect and make a comparison with the data.Comment: 18 pages, 6 figures, latex, Q_0^2 corrected in comparison to the
journal versio
Femtosecond manipulation of spins, charges, and ions in nanostructures, thin films, and surfaces
Modern ultrafast techniques provide new insights into the dynamics of ions, charges, and spins in photoexcited nanostructures. In this review, we describe the use of time-resolved electron-based methods to address specific questions such as the ordering properties of self-assembled nanoparticles supracrystals, the interplay between electronic and structural dynamics in surfaces and adsorbate layers, the light-induced control of collective electronic modes in nanowires and thin films, and the real-space/real-time evolution of the skyrmion lattice in topological magnets
Energy-dependent photoemission delays from noble metal surfaces by attosecond interferometry
How quanta of energy and charge are transported on both atomic spatial and
ultrafast time scales is at the heart of modern technology. Recent progress in
ultrafast spectroscopy has allowed us to directly study the dynamical response
of an electronic system to interaction with an electromagnetic field. Here, we
present energy-dependent photoemission delays from the noble metal surfaces
Ag(111) and Au(111). An interferometric technique based on attosecond pulse
trains is applied simultaneously in a gas phase and a solid state target to
derive surface-specific photoemission delays. Experimental delays on the order
of 100 as are in the same time range as those obtained from simulations. The
strong variation of measured delays with excitation energy in Ag(111), which
cannot be consistently explained invoking solely electron transport or initial
state localization as supposed in previous work, indicates that final state
effects play a key role in photoemission from solids
Renormalization of spectral lineshape and dispersion below Tc in Bi2Sr2CaCu2O8+d
Angle-resolved photoemission (ARPES) data in the superconducting state of
Bi2Sr2CaCu2O8+d show a kink in the dispersion along the zone diagonal, which is
related via a Kramers-Kronig analysis to a drop in the low-energy scattering
rate. As one moves towards (pi,0), this kink evolves into a spectral dip. The
occurrence of these anomalies in the dispersion and lineshape throughout the
zone indicate the presence of a new energy scale in the superconducting state.Comment: New Figure 3 with expanded discussio
Robustness of the charge-ordered phases in IrTe against photoexcitation
We present a time-resolved angle-resolved photoelectron spectroscopy study of
IrTe, which undergoes two first-order structural and charge-ordered phase
transitions on cooling below 270 K and below 180 K. The possibility of inducing
a phase transition by photoexcitation with near-infrared femtosecond pulses is
investigated in the charge-ordered phases. We observe changes of the spectral
function occuring within a few hundreds of femtoseconds and persisting up to
several picoseconds, which we interpret as a partial photoinduced phase
transition (PIPT). The necessary time for photoinducing these spectral changes
increases with increasing photoexcitation density and reaches timescales longer
than the rise time of the transient electronic temperature. We conclude that
the PIPT is driven by a transient increase of the lattice temperature following
the energy transfer from the electrons. However, the photoinduced changes of
the spectral function are small, which indicates that the low temperature phase
is particularly robust against photoexcitation. We suggest that the system
might be trapped in an out-of-equilibrium state, for which only a partial
structural transition is achieved.Comment: 8 pages, 5 figures, accepted for publication in Phys. Rev.
Robustness of the charge-ordered phases in against photoexcitation
We present a time-resolved angle-resolved photoelectron spectroscopy study of IrTe2, which undergoes two first-order structural and charge-ordered phase transitions on cooling below 270 K and below 180 K. The possibility of inducing a phase transition by photoexcitation with near-infrared femtosecond pulses is investigated in the charge-ordered phases. We observe changes of the spectral function occurring within a few hundreds of femtoseconds and persisting up to several picoseconds, which we interpret as a partial photoinduced phase transition (PIPT). The necessary time for photoinducing these spectral changes increases with increasing photoexcitation density and reaches time scales longer than the rise time of the transient electronic temperature. We conclude that the PIPT is driven by a transient increase of the lattice temperature following the energy transfer from the electrons. However, the photoinduced changes of the spectral function are small, which indicates that the low- temperature phase is particularly robust against photoexcitation. We suggest that the system might be trapped in an out-of-equilibrium state, for which only a partial structural transition is achieved
Delayed electron emission in strong-field driven tun-nelling from a metallic nanotip in the multi-electronregime
Illuminating a nano-sized metallic tip with ultrashort laser pulses leads to the emission of electrons due to multiphoton excitations. As optical fields become stronger, tunnelling emission directly from the Fermi level becomes prevalent. This can generate coherent electron waves in vacuum leading to a variety of attosecond phenomena. Working at high emission currents where multi-electron effects are significant, we were able to characterize the transition from one regime to the other. Specifically, we found that the onset of laser-driven tunnelling emission is heralded by the appearance of a peculiar delayed emission channel. In this channel, the electrons emitted via laser-driven tunnelling emission are driven back into the metal, and some of the electrons reappear in the vacuum with some delay time after undergoing inelastic scattering and cascading processes inside the metal. Our understanding of these processes gives insights on attosecond tunnelling emission from solids and should prove useful in designing new types of pulsed electron sources.111410Ysciescopu
Electron-phonon renormalization in small Fermi energy systems
The puzzling features of recent photoemission data in cuprates have been
object of several analysis in order to identity the nature of the underlying
electron-boson interaction. In this paper we point out that many basilar
assumptions of the conventional analysis as expected to fail in small Fermi
energy systems when, as the cuprates, the Fermi energy is
comparable with the boson energy scale. We discuss in details the novel
features appearing in the self-energy of small Fermi energy systems and the
possible implications on the ARPES data in cuprates.Comment: 4 pages, 5 eps figures include
Ferrule-top nanoindenter: An optomechanical fiber sensor for nanoindentation
Ferrule-top probes are self-aligned all-optical devices obtained by fabricating a cantilever on the top of a ferruled optical fiber. This approach has been proven to provide a new platform for the realization of small footprint atomic force microscopes (AFMs) that adapt well to utilization outside specialized laboratories [D. Chavan, Rev. Sci. Instrum. 81, 123702 (2010)10.1063/1.3516044; D. Chavan, Rev. Sci. Instrum. 82, 046107 (2011)10.1063/1.3579496]. In this paper we now show that ferrule-top cantilevers can be also used to develop nanoindenters. Our instrument combines the sensitivity of commercial AFM-based indentation with the ease-of-use of more macroscopic instrumented indenters available today on the market. Furthermore, the all-optical design allows smooth operations also in liquids, where other devices are much more limited and often provide data that are difficult to interpret. This study may pave the way to the implementation of a new generation user-friendly nanoindenters for the measurement of the stiffness of samples in material sciences and medical research. © 2012 American Institute of Physics
- âŠ