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TT: Fachverband Tiefe Temperaturen
TT 65: Quantum-Critical Phenomena II
TT 65.12: Talk
Wednesday, March 14, 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 CeCu6−xAux 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 (CeCu5.9Au0.1) 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 CeCu5.9Au0.1 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.