Physics

Dr. Shovon Pal
Department of Materials, ETH Zurich, Switzerland

Abstract:

Quantum critical phase transition has remained an intriguing topic of fundamental research over decades. It describes a second-order phase transition in the ground state of a many-body system resulting solely from quantum fluctuations. Crystalline rareearth heavy-fermion systems such as CeCu6-xAux and YbRh2Si2 are well-known compounds that show a quantum phase transition (QPT) between a fully Kondoscreened paramagnetic Fermi-liquid phase and an anti-ferromagnetically ordered phase. When excited by coherent low energy terahertz pulses, heavy-fermions are susceptible to disintegration near the QPT because of heavy effective electronic mass and low characteristic energies. Depending on the lattice Kondo temperature, the system would then coherently recover on timescales that are in the order of picoseconds. In my talk I will demonstrate how terahertz time domain spectroscopy can serve as a versatile tool for near resonant probing of such collapse and resurgence of Kondo quasiparticles. The Kondo spectral weight and the characteristic energy (or time) scales of the heavy-fermion state can be accessed directly in a single timeresolved experiment, unveiling the physics of such strongly correlated systems.