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Coherent many-body dynamics in electronic insulators
viewed on extreme timescales

In conventional solids, the interaction between electrons is considered negligible, and the macroscopic properties can be understood in terms of band theory. Such theory has been enormously successful and has guided us through, among other things, the development of semiconductor technology and the electronic revolution. When electrons feel the charge of other electrons, the mobility is determined by complex interactions within the electron gas, and the electronic structure is very sensitive to doping. Understanding doping of the Mott insulator is one of the grand challenges of modern condensed matter physics. In one dimension Fermi liquid theory is no longer valid, and the relevant quantum statistics is to be cast in the language of Luttinger theory, with many non-intuitive effects, such as the separation of spin and charge transport. Photo-excitation, which re-distributes charge between sites, can control many-body processes in Mott insulators on the ultrafast timescale.

By using near-IR pulses of extreme duration (<10 fs), we have measured coherent electronic excitations in the organic salt ET-F2TCNQ [1]. In this way, we have singled out coherent oscillations in the conductivity, occurring at high frequencies and associated with electronic correlations. These oscillations reflect the nature of charge excitations in Mott insulators when the onsite and interasite interaction is present. Quantum interference between different excitation paths, those between bound and free holons and doubloon states are revealed in his spectroscopy.

Close interaction with theorists (Jacksch group – University of Oxford) and application T-DMRG (Time Dependent Matrix Renormalization Group) methodologies has made it possible to simulate with predictive accuracies the coherent ultrafast physics. This work is combined to extreme timescale spectroscopies in complex oxides, in which orbital excitations and lattice motions at high frequencies have been measured in the time domain [2],[3]. Collaborations with theoretical work done at the University of Hamburg (Lichtenstein group), seeks to describe similar phenomena with time dependent DMFT (Dynamical Mean Field Theory).

Figure: Simulated probabilities for doublons (blue) and holon (red), decreasing upward with time [1].

Left: The electron which overcame the Mott gap (strong top position) can not move freely, there is a certain probability for being pulled back to the holon (red) and making a double step to build the next doublon (light top position) [1].

Related publications:

[1] Quantum interference between charge excitation paths in a solid state Mott insulator

S.Wall, D. Brida, S. R. Clark, H. P. Ehrke, D. Jaksch, A. Ardavan, S. Bonora, H. Uemura, Y. Takahashi, T. Hasegawa, H. Okamoto, G. Cerullo and A. Cavalleri

Nature Physics 7, 114 (2011)

[2] Control of the electronic phase of a manganite by mode-selective vibrational excitation

M. Rini, R. Tobey, N. Dean, J. Itatani, Y. Tomioka, Y. Tokura, R. W. Schoenlein & A. Cavalleri

Nature 449, 72-74 (6 September 2007)

→ more

[3] Ultrafast Coupling between Light, Coherent Lattice Vibrations, and the Magnetic Structure of Semicovalent LaMnO3

S. Wall, R. Prabakharan, A.T.J. Boothroyd and A. Cavalleri

Phys. Rev. Lett. 103, 097402 (2009)

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