Berlin 2018 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

TT: Fachverband Tiefe Temperaturen

TT 65: Quantum-Critical Phenomena II

TT 65.12: Vortrag

Mittwoch, 14. März 2018, 18:00–18:15, HFT-FT 131

Coherent low energy resonant excitation of heavy-fermion systems — •Shovon Pal¹, Christoph Wetli¹, Johann Kroha², Cornelius Krellner³, Kristin Kliemt³, Oliver Stockert⁴, Hilbert v. Loehneysen⁵, and Manfred Fiebig¹ — ¹ETH Zurich — ²Bonn University, Germany. — ³Goethe University Frankfurt, Germany. — ⁴MPI Dresden, Germany. — ⁵KIT, Germany.

Quantum phase transitions (QPT) describe a change between two ground states of a many-body system resulting from quantum fluctuations. Rare-earth heavy-fermion systems such as CeCu_6−xAu_x show a QPT between a fully Kondo-screened paramagnetic Fermi-liquid phase and an antiferromagnetically (AFM) ordered phase. When excited by THz pulses, the system disintegrates near the QPT and coherently recovers on timescales in the order of picoseconds, characteristic to the Kondo temperature. We use THz time-domain spectroscopy to probe Kondo quasi-particle spectral weight at such ultrafast timescales. Temperature-dependent examination of samples with different Au concentrations reveals that in the heavy fermion (CeCu₆) and the quantum critical (CeCu_5.9Au_0.1) samples, the Kondo weight first shows a logarithmic increase by lowering the temperature until 30 K, followed by a decrease as we enter the quantum critical regime below the Kondo temperature. While in CeCu_5.9Au_0.1 the Kondo weight is destroyed below 5 K, CeCu₆ shows a drop of about 40%. The CeCu₅Au sample being deep in the AFM phase does not exhibit visible Kondo weight at any temperatures despite the fact that low-temperature specific heat measurements reveal a sizeable Fermi-liquid-like contribution.