Fabrizio Carbone

January 2011

Grant-recipient Professor, ICMP - Institute of Condensed Matter Physics - , LUMES - Laboratory for ultrafast microscopy and electron scattering - , School of Basic Sciences (SB), EPFL Lausanne. He is working on the spectroscopic diffraction of quantum solids.

In this project, we propose to investigate the temporal evolution of structures and chemical bonds across quantum phase transitions, and phase transformations, in low-dimensional solids, and superconductors. A novel technique will be developed, ultrafast spectroscopic electron diffraction (USED). A train of fs light pulses is used in order to excite a specimen (pump), and generate electrons packets for probing the specimen. The lattice and electronic structure are probed simultaneously by energy filtering different electron-diffraction peaks with a position sensitive spectrometer. USED yields simultaneous and time-resolved information on the structure and orbitals properties of monolayers and solids, even made of light elements, thanks to the cross section for electron-matter interaction, 106 times higher than X-rays.

We will investigate:

• the dynamical properties of low-dimensional films, graphene and related materials: the way relativistic electrons couple to lattice motions in two 2D will be observed investigating graphene by USED. Fundamental parameters like the electron phonon coupling and its symmetry will be obtained, relevant for the material`s description as well as its applications. Diamondoids monolayers exhibit extraordinary physical and mechanical properties, useful for nanomachines and thanks to their inherent bio-compatibility for drug delivery purposes and other pharmaceutical applications. The dynamics of orbitals, their orientation, and electronic population govern their functionality, and will be imaged directly with fs-time resolution in our experiments.
• crystallization and melting of helium films on graphite/grahene surfaces: when helium films are deposited on a graphitic surface, crystallization and melting phenomena can occur. Melting of bulk helium can be induced either by changing the film coverage, quantum phase transition, or the temperature, classical phase transition, providing an ideal system for the investigation of the difference between quantum and classical melting. The possibility to use string theory`s formalism to describe the fermionic many-body system associated to a quantum critical state has been recently proposed. Besides its relevance for fundamental physics, quantum critical theories are among the most accredited candidates for describing the physics of high-tempertaure superconductors and heavy fermions systems. We will observe the dynamics of the structure and chemical bonds in real time during quantum and conventional melting of helium films, providing new and direct insights on quantum criticality
• the fs structural and carriers dynamics of superconductors: a peculiar type of dynamical structure-anisotropy has been suggested by recent ultrafast electron diffraction experiments. The possibility to observe the motion of ions and the changes in orbitals simultaneously, offered by spectroscopic diffraction, provides a unique opportunity to clarify the interplay between such structural phenomena and the superconducting condensate in these materials.

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