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By generating ultrashort and intense light pulses, we can create, manipulate and eventually control new quasiparticle modes to create emergent collective states and change material topology.
Optically Driven Materials
Accessing materials physics on the smallest dimensions of time is of fundamental importance, since the natural events in the microscopic quantum world of solids typically proceed on ultrashort (femtosecond or picosecond) time scales, being this the time scale of fundamental quantum excitations and collective interactions in solids. Ultrashort light pulses can therefore act as a tool to unravel the intrinsic forces that drive correlated ground states, as well as to generate novel phases that have no equivalent in thermal equilibrium. Our goal is to exploits advanced ways in which ultrashort and intense light pulses can be used to create, manipulate and eventually control new quasiparticle distributions and topologies in materials; and how we can tailored vibrational and electronic excitations to influence fundamental interactions and create new emergent collective states.
Generation of ultrafast photo-induced electric field
We discover a new way to generate ultrafast back-gating with speed as fast as 10GHZ, never achieved before. We apply this method to Rashba quantum wells, demonstrating, through a modulation of the density of states, an ultrafast control of Rashba splitting and energy level spacing.
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Manipulating surface photocurrents with light
Persistent topological states and currents can be tuned by optically using femotosecond pulses.
Vibrational Symmetry Breaking in a Charge Ordered Nickelate
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Excitonic states
The ability of light pulses to create new transient quasiparticles such as excitons, bi-excitons and trions, together with the discovery of topological materials and 2D heterostructures where a much richer excitonic landscape can be engineered, has opened up new frontiers in fundamental science and applications. In this relatively new field, some of the open questions that our group is trying to address are, what individual contributions from the electron and hole part of the many-body states and what is their distribution in momentum space; how does excitons or trions formation affects the underlying’ materials band structure; what is the mechanism under which excitons condensation or exciton driven CDW states can be achieved; and ultimately what is the role of topology on exciton formation.
See below for some of our contributions to the field.
Exciton driven effective mass renormalization
HHG tr-ARPES reveals an unexpected renormalization of the effective mass, and anomalous increase of the bandgap following exciton formation.
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Discovery of an Indirect Topological excitonic states
Tr ARPES revealed the emergence of an indirect excitonic state in a topological insulator, where the holes reside in the bulk and the electrons on the surface state. The non-zero spin polarization of this state is revealed by tr spin ARPES.
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Optical Control of TI Surface State Photoelectrons
Polarized laser-ARPES photoemission from a topological insulator provides control of ejected electron spin.