An article published in Nature Communications (see Nat. Comm. 2018, 9, 955, DOI: 10.1038/s41467-018-03009-1) has identified the role of autoionizing resonances in photoemission time delays, a clear manifestation of electron correlation effects on photoionization processes. The work results from an international cooperation among researchers led by U. Keller (ETH-Zurich), F. Martín (Universidad Autonoma de Madrid, IFIMAC Condensed Matter Center and IMDEA-Nanoscience), and A. L’Hullier (Lund University).
Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. The process of autoionization, induced by resonant excitation of electrons into discrete states present in the continuum spectrum of atomic and molecular targets, is mediated by electron correlation. The paper investigates the attosecond photoemission dynamics in argon in the 20–40 eV spectral range, in the vicinity of the 3s−1np autoionizing resonances. Measurements of the differential photoionization cross section are reported, from which energy and angle-dependent atomic time delays are extracted with an attosecond interferometric method. With the support of a theoretical model, a large part of the measured time delay anisotropy is attributed to the presence of autoionizing resonances, which not only distort the phase of the emitted photoelectron wave packet but also introduce an angular dependence.
Figure: Anisotropic photoemission time delays close to a Fano resonance.
Angular-resolved time delays. (a) and (b) show the measured atomic time delay as a function of electron emission angle in the absence and the presence of an autoionizing state, respectively (red and blue symbols). The delays are referenced to the value retrieved for electrons departing within an opening angle of up to 30 degrees. The green lines show the calculated delays in resonant (solid) and nonresonant (dashed) conditions. The error bars indicate the standard deviation as extracted by a series of independent measurements. Source: Nat. Comm. 2018, 9, 955, DOI: 10.1038/s41467-018-03009-1
The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are manybody systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far.
Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H2 two-electron wave function in which electron–electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources.
CampuS theoretical group offers mentorship in four different research topics to international students who wish to develop a research project, oriented to obtain a PhD diploma, at the Condensed Matter Physics Center (IFIMAC-UAM) and at IMDEA-Nanoscience(Fundación IMDEA-Nanociencia).
The PhD positions are funded by the doctoral fellowship programme INPhINIT, which is devoted to attract international Early-Stage Researchers (ESR) to top Spanish excellent research centres. INPhINIT is promoted by the “la Caixa” Foundation and relies on the European Commission’s support through the Horizon 2020 Marie Skłodowska-Curie Actions – COFUND programme.
The fellowship shall cover a 3-year doctoral employment contract, a top up contribution for other training expenses, and complementary training on transversal skills. In addition, phd candidates may opt to a price amounting to 7.500 € if they got the diploma earlier than 6 months after the finalization of the contract.
For more information on the fellowship programme, please visit: www.inphinitlacaixa.org. Deadline for application is February 1st, 2018.
For more information on the research topics, check the documents below:
Theoretical Attosecond Electron Dynamics: from biomolecules to solids (IMDEA-Nanociencia) – Description
Ultrafast molecular dynamics induced by attosecond pulses (IFIMAC-UAM) – Description
Chemical-physics properties of new 2D materials (IMDEA-Nanociencia) – Description
Graphene-based materials: Exploring new physical properties based on theoretical simulations (IFIMAC-UAM) – Description
In case you are interested in this fellowship, you should check the fullfillment of the excellence criteria and other specific call requirements (research experience, training, language and mobility requirements) here.
Students with spanish nationality not fullfilling the mobility requirements can apply to a fellowship to carry out a doctorate at a Spanish University. The deadline to apply is February 27, 2018. Mor information here.
For any question on the research projects or if you became selected for the face-to-face evaluation stage, please, do not doubt to contact the group projects manager beatriz..
Fernando Martín, Professor of the Department of Chemistry of the Faculty of Sciences of the UAM, received on October 30 the King Jaime I Prize for Basic Research in a ceremony held in Valencia, in the Hall of Columns of the Lonja of Merchants.
The event was chaired by His Majesty Queen Letizia and was attended by the President of the Generalitat Valenciana, the Mayor of Valencia and the President of the Valencian Foundation for Advanced Studies. The ceremony was attended on behalf of the UAM by its Rector, Rafael Garesse, the dean of the Faculty of Sciences, José Mª Carrascosa, the Director of the Department of Chemistry, Otilia Mó, and Professor Manuel Yáñez who was the Director of the Doctoral thesis by Fernando Martín.
The jury, chaired by Roger Kornberg, Nobel Prize in Chemistry 2006, recognized the merits of Fernando Martín in “the foundation of the field of theoretical attochemistry, which makes it possible to calculate the movement of electrons and, therefore, the prediction of chemical reactions”. This discipline, consolidated during the last years, has opened the way to a new chemistry in which the obtaining of new compounds would be possible from reactions that do not follow the conventional patterns. The research of Professor Fernando Martín has a strong multidisciplinary character, which has led him to relevant discoveries in various areas: lasers physics, physical chemistry, quantum chemistry, atomic and molecular physics, surface physics, computational modelling, organic and inorganic chemistry , physics of accelerators and biophysics.
With more than 400 international publications, Professor Fernando Martín has been invited as a lecturer in the main forums of his research area, and has attracted important funding from the European Union, among others, an ERC Advanced Grant project. This award is added to others previously obtained as the King Juan Carlos I Research Prize (2001), or the Spanish Society of Chemistry in Physical Chemistry Prize (2010).
Spanish and Italian scientists have laid down the foundations of a new scientific discipline that pursues to control the movement of electrons in molecules using attosecond methodologies and may open the door to a new way of doing chemistry.
Figure. Evolution of the charge density induced by an attosecond pulse on the aminoacid phenylalanine (purple: charge excess; yellow: charge default).
Source: UAM Gazette (July 6, 2017)
An article published in the journal Chemical Reviews, led by Fernando Martín (Universidad Autónoma de Madrid, IMDEA Nanoscience, IFIMAC Condensed Matter Center) and by Mauro Nisoli (Polytenico de Milano) details the bases and the most important milestones of a new scientific discipline: attochemistry.
In general, this discipline seeks to control and manipulate the movement of electrons that form chemical bonds in molecules, using attosecond light pulses (1 attosecond is equivalent to 10-18 seconds). According to the authors, since the structure and reactivity of matter arises from the properties of chemical bonds, attochemistry may enable new reactions and have a direct impact on the development of new substances and materials, making possible a better understanding of the electronic processes that occur in chemical and biological systems.
The study documents the first real-time observation of charge migration processes on molecules of biological interest (as the amino acid phenylalanine, see figure 1), with unprecedented temporal resolution. It also shows the first signs of control of charge migration processes. These observations were made by first irradiating the molecules with a pulse (or pulses) of attosecond light, followed by a second pulse of equal or greater duration, which captures an image of the electronic motion at a particular instant. The variation of the elapsed time between the first and second pulses provides a sequence of images of the electronic motion, which allows the selection of the precise instant in which the localization of the charge may favour (or prevent) a certain chemical reaction .
From femtochemistry to attochemistry
Chemical reactions are the result of bond-formation and bond-breakage and, during this process, atoms in molecules may arrange to form a new substance. Reactivity, the essence of chemistry, is a dynamic process that results from the movement of electrons and atomic nuclei. These movements occur in an ultrafast time scale, ranging from femtoseconds (10-15 seconds), typical of nuclear movement, to attoseconds, typical of electronic movement.
In this sense, all the chemistry could be understood as femtochemistry or attochemistry. Femtochemistry, born in the second half of the last century, is now a well-established scientific discipline whose main objective is to control a chemical reaction by directing the movement of the nuclei of the involved molecules using femtosecond pulses of light. Today, femtosecond lasers are widely used in most areas of the chemical sciences and in many laboratories.
The 21st century has brought remarkable advances in the manufacture of coherent light sources that allow the generation of even shorter pulses of light, with durations that reach the few tens of attoseconds, in the extreme ultraviolet frequency region.
These advances have led to a substantial evolution of laser technology in recent years, enabling for the first time a direct control of the ultra-rapid movement of electrons within a molecule and, consequently, the nuclear dynamics induced by such electronic movement, which occurs at longer time scales.
Since the distribution of electrons in the molecule, or electronic density, is ultimately responsible for the formation and breaking of bonds, the control of this movement has opened the door to a new way of doing chemistry.
This research has received funds from the European Research Council, under the ERC Advanced Grant nº 290853, and the principal investigator of this project, Fernando Martín, has been awarded with the prize King Jaime I 2017, in the category of Basic Research.
——————————————-
Reference: Attosecond electron dynamics in molecules. M. Nisoli, P. Decleva, F. Calegari, A. Palacios and F. Martín, Chem. Rev., 2017, 117 (16), pp 10760–10825, DOI: 10.1021/acs.chemrev.6b00453
Fernando Martín, Full Professor at the Chemistry Department of the Universidad Autónoma de Madrid and researcher at IMDEA-Nanociencia and IFIMAC Condensed Matter Physics Center, has been awarded the King Jaime I Prize in Basic Research in its 2017 edition. The jury has recognized his role in the establishment of the theoretical foundations of attochemistry. This emerging scientific field aims at observing and manipulating the electronic motion in atoms and molecules in their natural time scale, the attosecond (10-18 seconds), so as to control the chemical properties of substances and modify their natural behaviour. Although the first steps in this new scientific field date back only a decade ago, it is expected to become a multidisciplinary tool with numerous applications in chemistry, physics or biology, for example, to control the evolution of a chemical reaction, obtain images of charge transfer processes in individual molecules or influence the biological response to radiation, whether desired or undesired.
The demonstration that attosecond science can have a large impact in chemistry came in 2014, when, with the help of sophisticated computational modelling, it was shown (Science346, 336) that experiments in which the amino acid phenylalanine is irradiated with attosecond laser pulses are indeed able to monitor the movement of electrons, and hence to modify the properties and chemical behaviour of the molecule.
According to the award-winning, the next steps in this field point to the use of attosecond techniques to prevent undesired chemical reactions, as those biological processes leading to adverse effects or, conversely, to induce chemical reactions that are currently impossible, which could lead to the production of new substances or materials. According to a recent article (Chemical Reviews, DOI: 10.1021/acs.chemrev.6b00453), the measurement and control of electronic motion in complex molecular structures is a formidable challenge that must be tackled in a multidisciplinary way, including intensive theoretical modelling in supercomputers, and may have a strong impact In chemistry for years to come.
King Jaime I Prizes
The Rey Jaime I Award recognizes researchers whose work is highly significant and has been developed for the most part in Spain. Throughout its 28 editions, it has been awarded to more than 100 researchers, the most important figures of the scientific, technological and entrepreneurial world of Spain. Many of the winners have received, during their careers, other relevant national and international awards.
Fernando Martín was born in Madrid, Spain, in 1961. He graduated in Chemistry in 1984 and Physics in 1986 at the Universidad Autónoma de Madrid. He received his Ph.D. at the same university in 1986. He completed his postdoctoral studies at the University of Bordeaux (1988), the Université de Paris VI (1989–1990), and the Univesity of Chicago (1995–1996). He has been Full Profesor at the Universidad Autónoma de Madrid since 2005. He obtained the national research price Rey Juan Carlos I on 2000 and the prize of the Spanish Royal Society of Chemistry in 2010. He is currently Chair of the “Cátedra UAM-Fujitsu” on Scientific Computing and Big Data.
His research focuses on the theoretical modelling of photoexcitation and photoionization of atomic and molecular systems induced by synchrotron radiation and ultrashort laser pulses, as well as that of complex molecular systems, isolated or deposited on surfaces. He has published almost 400 articles, and since 2011, he has been the recipient of an Advanced Grant of the European Research Council to lead a project focused on the development of computational tools for the study of processes that occur in the femto- and atto-second timescales (XCHEM).
In the last years, his research group (https://campusys.qui.uam.es/) has attracted significant funding from the European Union (projects ERC-AdG- 290853 XCHEM, COST Action CM0702, MCA-ITN- 264951 CORINF y MSCA-EJD-642294 TCCM, MCA-RIG- 268284 ATTOTREND) and national programs funded through MICINN, MINECO and the AEI (projects FIS-2016-77889-R, FIS-2013-42002-R, FIS-2010-15127 and PIM2010EEC-00751-ERA-Chemistry), which has allowed him to establish what is perhaps the reference research group in Europe in the area of “Theoretical Attochemistry”.
We offer the possibility to develop a research project on Theoretical Attosecond Electron Dynamics, oriented to obtain a PhD diploma, to theoretically investigate the coupled electron and nuclear dynamics induced by attosecond laser pulses and strong electromagnetic fields on small and mid-size molecules, as well as in solids.
The position shall be funded by the doctoral fellowship programme INPhINIT, which is devoted to attract international Early-Stage Researchers (ESR) to top Spanish research centres. INPhINIT is promoted by the “la Caixa” Foundation and relies on the European Commission’s support through the Horizon 2020 Marie Skłodowska-Curie Actions – COFUND programme.
The fellowship shall cover a 3-year doctoral employment contract with good remuneration conditions (gross salary 26.000 € per year) in comparison with the standard of living in Spain, and a top up contribution for training and networking activities. Researchers shall complement their training with a variety of transnational, intersectoral and interdisciplinary activities.
In addition, phd candidates may opt to a price amounting to 7.500 € if they got the diploma earlier than 6 months after the finalization of the contract.
More information on the PhD position on Theoretical Attosecond Electron Dynamics can be found here: phd-position-descrption. If selected, researchers should join the Condensed Matter Physics Center (IFIMAC) by September 2017.
In case you are interested in this fellowship position and consider you fulfil the excellence criteria and other specific call requirements (research experience, training, language and mobility requirements), please, do not doubt to submit you application here: https://www.lacaixafellowships.org/index.aspx, before February 2, 2017.
For any question on the research project or if you became selected for the face-to-face interview stage, please, do not doubt to contact beatriz.
A group of Spanish and French researchers has described in the journal Science the first real-time observation of the birth and subsequent evolution of an electronic wave packet.
In addition to providing the first ‘movie’ of the electron wave packet dynamics, and of the interferences that such dynamics implies, the high degree of control and high temporal resolution achieved by the study opens the door to the design of electronic wave packets in atomic and molecular systems, hence to control the electronic properties of such systems systems, which could have a direct impact on nanotechnology by allowing the design of materials with unusual electronic properties.
The advent of attosecond physics (i.e., physics at the natural time scale of electronic motion) has opened the possibility of making ‘movies’ which explicitly show the wave behavior of particles and the interference phenomena associated with it.
To measure the dynamics of the electronic wave packet (EWP) the researchers bombarded a helium atom with a train of attosecond light pulses, which induces ionization by two different paths, one direct (direct ionization) and one delayed (autoionization).
Just as a wave interferes with itself as it travels along two different paths leading to the same destination (as in the famous Young Double Slit experiment, for example), the superposition of EWP generated by direct ionization and autoionization also leads to interferences, which show up in the form of peaks with an asymmetric Fano profile.
To visualize the birth of such interference (the characteristic Fano profile), a second reference light pulse was used in time intervals of the order of 200 attoseconds.
In this way, scientists were able to determine the amplitude and phase of the wave packet produced by the attosecond pulse train, and hence reconstruct the movie showing the birth of of the EWP and the subsequent establishment of the interference.
As the figure shows, the interference between the two processes leading to helium ionization takes about 5 femtoseconds (5,000 attoseconds).
Fig. 3. Dynamics of the EWP resulting from helium ionization. The evolution of the envelope of the wave packet with time is shown: time zero, the wave packet has a symmetric envelope with respect to its central position (36.7 eV). Approximately 5 femtoseconds later, the wave packet divides into two, giving rise to two asymmetric components whose shape evolves until it stabilizes at 20 femtoseconds. The splitting of the wave packet is due to interference between the direct ionization process, which occurs at time zero, and autoionization, which takes approximately 5 femtoseconds to occur.
The research leading to these results has been directed by Fernando Martín Universidad Autónoma de Madrid, IMDEA Nanoscience, and IFIMAC Institute) and by Pascal Salières (Paris-Saclay University), and has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° 290853 (XChem project)
Reference: Attosecond dynamics through a Fano resonance: Monitoring the birth of a photoelectron V. Gruson, L. Barreau, A. Jiménez-Galán, F. Risoud, J. Caillat, A. Maquet, B. Carré, F. Lepetit, J-F. Hergott, T. Ruchon, L. Argenti, R. Taïeb, F. Martín, and P. Salières Science 354 , 734-738 (2016). DOI: 10.1126/science.aah5188
Isotropic gases irradiated by long pulses of intense IR light can generate very high harmonics of the incident field. It is generally accepted that, due to the symmetry of the generating medium, be it an atomic or an isotropic molecular gas, only odd harmonics of the driving field can be produced. In a recent article, the authors show how the interplay of electronic and nuclear dynamics can lead to a marked breakdown of this
standard picture: a substantial part of the harmonic spectrum can consist of even rather than odd harmonics. They demonstrate the effect using ab-initio solutions of the time-dependent Schrödinger equation for ionized molecular hydrogen and its isotopes in full dimensionality. By means of a simple analytical model, they identify its physical origin, which is the appearance of a permanent dipole moment in dissociating homonuclear molecules, caused by light-induced localization of the electric charge during dissociation.
The effect arises for sufficiently long laser pulses and the region of the spectrum where even harmonics are produced is controlled by pulse duration. The results (i) show how the interplay of femtosecond nuclear and attosecond electronic dynamics, which affects the charge flow inside the dissociating molecule, is reflected in the nonlinear response, and (ii) force one to augment standard selection rules found in nonlinear optics textbooks by considering light-induced modifications of the medium during the generation process.
Reference:
Even harmonic generation in isotropic media of dissociating homonuclear molecules
R. E. F. Silva and P. Rivière and F. Morales and O. Smirnova and M. Ivanov and F. Martín
Scientific Reports, 6, 32653, 2016 (September 6, 2016)
DOI: 10.1038/srep32653
Ionizing radiation can bring an atom to a super-excited state that survives for an infinitesimal time before emitting one electron. Using advanced attosecond interferometric techniques, several researchers from Lund, Madrid, Paris, and Stockholm have now resolved the collapse of such state in time, finally confirming a theoretical prediction formalized more than 50 years ago that has its roots at the very beginning of the quantum revolution.
When irradiated with light with sufficiently high frequency, such as extreme ultraviolet rays or x rays, matter emits electrons; this is the celebrated photoelectric effect. To explain this effect, in 1905 Einstein suggested that light was composed of photons, small packets of energy that provide individual electrons with enough momentum to escape the Coulomb attraction of atomic nuclei. Some twenty years later, quantum theory finally provided the theoretical framework necessary to formalize Einstein’s intuition: matter does exchange energy by quanta, and, in the simplest scenario, the absorption of an ionizing photon is accompanied by the instantaneous emission of an electron wave packet.
In 1933, H. Beutler [Z. Physik 86, 495], an experimental physicist, showed that things were not as simple after all. He found that the absorption spectra of rare-gas atoms above the ionization threshold exhibit wide peaks with anomalously asymmetric profiles. These peaks indicated that the atom, instead of being instantaneously ionized, could be temporarily excited to some unstable state, hence the finite width. The meaning of the peak asymmetry, however, remained obscure. The following year, Enrico Fermi, then a professor in Rome, assigned this puzzle to Ugo Fano, a 22 years old post-doctoral collaborator, who published the provisional results of his investigations in 1935 in an Italian journal. According to Fano, the asymmetry of photoelectron absorption peaks arise from the interplay between the direct-ionization wave front, predicted since the beginning, and the trailing emission from the collapsing excited atom. Due to the dispersive character of electron waves (more energetic electrons move faster than less energetic ones), the latter component catches up with the direct wave front, carving a trough where the two waves interfere destructively. It is this interference that skews the spectrum of the electrons from the decaying atom, which would otherwise be a perfectly symmetric Lorentzian peak.
Fano had to interrupt his studies of atomic photoionization due to the precipitating historical conditions that eventually lead to the outbreak of WWII. For more than 25 years, his 1935 paper, which was written in Italian, was all but forgotten. In 1961, Fano managed to resume his studies, publishing a second more refined English version of his work which soon became one of the most cited physics papers of all times. Since then, the characteristic asymmetric photoelectron energy distribution predicted by Fano’s theory has been confirmed for countless systems. One inherent aspect of the phenomenology modeled by Fano, however, that is how the direct and resonant wave packets come together in time to give rise to the final spectral asymmetry, had eluded any direct experimental confirmation for all this time.
In a paper published on February 18th in Nature Communication, researches from Lund University, XChem project/Universidad Autónoma de Madrid (UAM), Université Pierre et Marie Curie in Paris, and Stockholm University have announced that they have finally closed this long-standing gap. Using a novel attosecond interferometric laser technique developed in Lund by the experimental group of Professor Anne L’Huillier, the authors were able to compare in detail the structured wave front generated by the resonant ionization of the argon atom with the simpler direct-ionization wave obtained at energies where no metastable state is excited. Their finding closely matches the prediction of the Fano model, which researchers from XChem project have extended to the multiphoton regime entailed in the experiment. This finding, which is the first “observation” of the collapse of an autoionizing atomic state, opens the way to the detailed study of the ultrafast photoelectron dynamics, which plays a fundamental role in many processes triggered by energetic light in matter, from radiation damage of biological tissues to charge emission in photoelectric cells.
Reference: Spectral phase measurement of a Fano resonance using tunable attosecond pulses M. Kotur, D. Guénot, A. Jiménez-Galán, D. Kroon, E.W. Larsen, M. Louisy, S. Bengtsson, M. Miranda, J. Mauritsson, C.L. Arnold, S.E. Canton, M. Gisselbrecht, T. Carette, J.M. Dahlström, E. Lindroth, A. Maquet, L. Argenti, F. Martín & A. L’Huillier Nature Communications, 7, 10566. 18 de febrero de 2016.
DOI: 10.1038/ncomms10566
Figure: Anisotropic photoemission time delays close to a Fano resonance.
