Regensburg 2022 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 6: Kondo Physics, f-Electron Systems and Heavy Fermions

TT 6.4: Vortrag

Montag, 5. September 2022, 15:45–16:00, H22

Quasiparticle critical slowing down in a heavy-fermion system — •Chia-Jung Yang¹, Kristin Kliemt², Cornelius Krellner², Johann Kroha³, Manfred Fiebig¹, and Shovon Pal^1,4 — ¹Department of Materials, ETH Zurich, 8093 Zurich, Switzerland — ²Physikalisches Institut, Goethe-Universität Frankfurt, 60438 Frankfurt, Germany — ³Physikalisches Institut and Bethe Center for Theoretical Physics, Universität Bonn, 53115 Bonn, Germany — ⁴School of Physical Sciences, National Institute of Science Education and Research, HBNI, Jatni, 752 050 Odisha, India

Critical slowing down (CSD) is a universal phenomenon in phase transitions. A system, after suffering an initial perturbation, takes a very long time to return to its equilibrium state. While CSD is universally observed in the dynamics of bosonic excitations, it is not observed to occur for fermionic excitations. This is because of the half-integer nature of the fermionic spin. In this contribution, we show a fermionic CSD in the heavy-fermion (HF) compound YbRh₂Si₂ (YRS) by using phase-sensitive terahertz time-domain spectroscopy (THz-TDS). THz-TDS has recently been introduced as a novel tool to investigate the quasiparticle dynamics across quantum phase transition (QPT) in HF compounds [1–3]. We see that near the QPT in YRS, the build-up of spectral weight towards the Kondo temperature T_K^* = 25 K is followed by a logarithmic rise of the quasiparticle excitation rate on the heavy-Fermi-liquid side below 10 K. A critical two-band HF liquid theory shows that this is indicative of fermionic CSD, the softening of the HF quasiparticle dispersion.