LEE Laboratory
<Major Research Areas>condensed matter theory; dynamics, spectroscopy, ultrafast phenomena

Toward theoretical understanding of photoinduced ultrafast dynamics of correlated electron systems and their application

Research activity

　　Photoinduced ultrafast dynamics of the matter driven by the ultrashort laser pulse is a new fascinating field because it implies the exploration of new science, that is, “science of small world on the time-axis”, and the unlimited potential application of new functionality of the material and its controlled operation. The usual time scale for the “ultrafast” phenomena would be picoseconds (10-12 second) or femtoseconds (10-15 second). In Lee laboratory, a reliable and general theoretical platform for the photoinduced ultrafast dynamics of material is developed and applied, for theoretical understanding and optimized operation in a controlled fashion.

1Development of theoretical platform for the photoinduced ultrafast dynamics

　　The proper theoretical formulation for microscopic quantum mechanical description of the ultrafast dynamics of the correlated systems is still lacking. Due to that reason, recently, we suggested a new theoretical formulation called many-body time-dependent diagonalization (MTD). The MTD has shown remarkable success for pure electronic systems or electronic systems weakly coupled to phonons (see FIG.1). Nevertheless, within the present version of MTD, it is formidable to treat complex cooperative ultrafast dynamics where several kinds of degrees of freedom are coupled to each other. It is one of our immediate goals to improve MTD in order to cover such complicated systems.

2Theoretical understanding of photoinduced dynamics

　　Many fascinating functionalities of materials can be realized by controlling microscopic degrees of freedom by use of the ultrashort laser pulse. One of our motivations for these photoinduced phenomena is to investigate the ultrafast switching phenomena and underlying fundamental physics, for example, (i) the switching of the insulating-metallic phase in a Br-bridged Ni-chain (see FIG.2(a)), (ii) the on-off switching of the spin-Pierls phase in KTCNQ, (iii) the switching of the neutral-ionic phase in TTF-CA, and so on.

3Control of coherence

　　First, the real-time quantum manipulation of the microscopic phase coherence of qubits coupled to a suitable host is explored. Here we try to find and control the possible gate operation of a given system in a form of Rabi oscillation (see FIG.2(b)). Second, the macroscopic coherence of the fundamental excitation of the material and its transients are studied (see FIG.1). Currently, we perform the study in order to find the possibility of positive feedback of such macroscopic coherences to electron transport or other basic characteristics, and its control.

4Theory of novel types of optical spectroscopies

　　Recently, by advancement of laser technology and sample fabrication technology, many novel spectroscopies have shown up to deliver deeper and wider understanding of the fundamental properties of matter. In particular, we have interests in novel types of photoemission, for example, illuminated photoemission (see FIG.2(c)), time-resolved photoemission, and the extrinsic loss of the photoemission, which make it possible for us to have deeper and clearer understanding of the electronic structure of material.

Equipment

IBM IntelliStation, IBM xServer cluster (5 nodes and 10 CPUs), and other JAIST computing resources

The main research achievements in the past five years

1. J.D. Lee and S. Maenosono, Field-induced control of universal fluorescence intermittency of a quantum dot light emitter, J. Chem. Phys., 133, 074703 (2010).
2. J.D. Lee, S.W. Han, N. Miyawaki, and H. Gomi, Comment on "Temperature-dependent localized excitations of doped carriers in superconducting diamond", Phys. Rev. Lett. 102, 199701 (2009).
3. J.D. Lee and Muneaki Hase, Coherent optical control of the ultrafast dephasing of phonon-plasmon coupling in a polar semiconductor using pulse train of below-band-gap excitation, Phys. Rev. Lett. 101, 235501 (2008).
4. J.D. Lee, S.W. Han, and J. Inoue, Sharp contrasts in low-energy quasiparticle dynamics of graphite between Brillouin zone K and H points, Phys. Rev. Lett. 100, 216801 (2008).
5. J.D. Lee, J. Inoue, and Muneaki Hase, Ultrafast Fano resonance between optical phonons and electron-hole pairs at the onset of quasiparticle generation in a semiconductor, Phys. Rev. Lett. 97, 157405 (2006).