Daniel Sánchez-Portal

Direct observation of electron dynamics in the attosecond domain

Dynamical processes are commonly investigated using laser pump–probe experiments, with a pump pulse exciting the system of interest and a second probe pulse tracking its temporal evolution as a function of the delay between the pulses. Because the time resolution attainable in such experiments depends on the temporal definition of the laser pulses, pulse compression to 200 attoseconds (1 as = 10-18 s) is a promising recent development. These ultrafast pulses have been fully characterized, and used to directly measure light waves and electronic relaxation in free atoms. But attosecond pulses can only be realized in the extreme ultraviolet and X-ray regime; in contrast, the optical laser pulses typically used for experiments on complex systems last several femtoseconds (1 fs = 10-15 s). Here we monitor the dynamics of ultrafast electron transfer—a process important in photo- and electrochemistry and used in solid-state solar cells, molecular electronics and single-electron devices—on attosecond timescales using core-hole spectroscopy. We push the method, which uses the lifetime of a core electron hole as an internal reference clock for following dynamic processes, into the attosecond regime by focusing on short-lived holes with initial and final states in the same electronic shell. This allows us to show that electron transfer from an adsorbed sulphur atom to a ruthenium surface proceeds in about 320 as.

First-principles study of substitutional metal impurities in graphene: structural, electronic and magnetic properties

We present a theoretical study using density functional calculations of the structural, electronic and magnetic properties of 3d transition metal, noble metal and Zn atoms interacting with carbon monovacancies in graphene. We pay special attention to the electronic and magnetic properties of these substitutional impurities and find that they can be fully understood using a simple model based on the hybridization between the states of the metal atom, particularly the d shell, and the defect levels associated with an unreconstructed D3h carbon vacancy. We identify three different regimes associated with the occupation of different carbon–metal hybridized electronic levels: (i) bonding states are completely filled for Sc and Ti, and these impurities are non-magnetic; (ii) the non-bonding d shell is partially occupied for V, Cr and Mn and, correspondingly, these impurities present large and localized spin moments; (iii) antibonding states with increasing carbon character are progressively filled for Co, Ni, the noble metals and Zn. The spin moments of these impurities oscillate between 0 and 1μB and are increasingly delocalized. The substitutional Zn suffers a Jahn–Teller-like distortion from the C3v symmetry and, as a consequence, has a zero spin moment. Fe occupies a distinct position at the border between regimes (ii) and (iii) and shows a more complex behavior: while it is non-magnetic at the level of generalized gradient approximation (GGA) calculations, its spin moment can be switched on using GGA+U calculations with moderate values of the U parameter.

Magnetism of substitutional Co impurities in graphene: Realization of single π vacancies

We report ab initio calculations of the structural, electronic, and magnetic properties of a graphene monolayer substitutionally doped with

Atomistic Near-Field Nanoplasmonics: Reaching Atomic-Scale Resolution in Nanooptics

\text{Co}\text{ }({\text{Co}}_{sub})

Atomic-orbital-based approximate self-interaction correction scheme for molecules and solids

atoms. These calculations are done within density-functional theory using the generalized gradient approximation. We focus in Co because among traditional ferromagnetic elements (Fe, Co, and Ni), only

Potential energy landscape for hot electrons in periodically nanostructured graphene.

{\text{Co}}_{sub}

Tunable Molecular Plasmons in Polycyclic Aromatic Hydrocarbons

atoms induce spin polarization in graphene. Our results show the complex magnetism of Co substitutional impurities in graphene, which is mapped into simple models such as the

Different origins of the ferromagnetic order in (Ga,Mn)As and (Ga,Mn)N

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Electronic Stopping Power in LiF from First Principles

-vacancy and Heisenberg model. The links established in our work can be used to bring into contact the engineering of nanostructures with the results of

An O(N3) implementation of Hedin's GW approximation for molecules

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