Periodic Reporting for period 2 - DynaQuanta (Nonequilibrium Terahertz Dynamics of Interacting Quantum Spins: from Novel Driven States towards Coherent Controls)
Période du rapport: 2023-01-01 au 2024-06-30
Electrons have not only a negative elementary charge but also an intrisic magnetic moment - spin. In a solid which is characterized by a regular arrangement of many atoms, the quantum-mechanical interactions between the electron spins and between spins and other degrees of freedom (such as lattice, orbital, and charge) can lead to fascinating quantum magnetic phenomena. By using time-resolved terahertz spectroscopy especially with intense teraherz laser pulses, we explore the characteristic spin dynamics of exotic quantum magnetic phases, and aim to identify the governing quantum-mechanical principles of the observed spin dynamics and to provide guidance towards a deterministic control of spins for possible applications.
We have established a femtosecond amplifier laser system and realized a variety of time-resolved pump-probe spectroscopies, especially terahertz pump-probe spectroscopy and terahertz high-harmonic-generation spectroscopy for the investigations of nonequilibrium terahertz dynamics and nonlinear terahertz responses, and complimentary spectroscopic techniques such as optical-pump terahertz-probe spectroscopy. We have installed cryogenic magneto-optic system which allows to perform the optical spectroscopic measurements down to liquid helium temperature and in a tunable high magnetic field.
We have carried out studies of linear terahertz spin dynamics in selected one-dimensional and two-dimensional quantum magnetic systems as a function of temperature and magnetic fields, and revealed exotic properties such as many-body magnon bound states and possible signatures of fractional excitations for a quantum spin liquid. We have also studied terahertz third-harmonic generation and found an approach to control the efficiency and ellipticity of the third-harmonic radiation. The nonlinear terahertz response has been found to exhibit characteristics of exotic states of matter governed by strong electron correlations. Moreover, we have been able to reveal linear and nonlinear responses of optically driven nonequilibrium states in magnetic and nonmagnetic systems.
We have carried out studies of linear terahertz spin dynamics in selected one-dimensional and two-dimensional quantum magnetic systems as a function of temperature and magnetic fields, and revealed exotic properties such as many-body magnon bound states and possible signatures of fractional excitations for a quantum spin liquid. We have also studied terahertz third-harmonic generation and found an approach to control the efficiency and ellipticity of the third-harmonic radiation. The nonlinear terahertz response has been found to exhibit characteristics of exotic states of matter governed by strong electron correlations. Moreover, we have been able to reveal linear and nonlinear responses of optically driven nonequilibrium states in magnetic and nonmagnetic systems.
Our progress made beyond the state of the art and what we continue to persue towards the end of the project is on two major research directions. One is on the study and understanding of high-energy quantum spin dynamics, the other on the terahertz nonlinear dynamics of highly nonthermal states far from equilibrium. For the former, our studies have revealed that the high-energy quantum spin dynamics can exhibit new characteristic features which are very different from the rather well-known low-energy properties. For the latter, we found extremely nonlinear responses of optically excited nonequilibrium states. In both of the two research directions we are excited by these achievements to explore rich new physics and expect to obtain important knowledge.