Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 35: Correlated Electrons: Quantum-Critical Phenomena - Experiment I

TT 35.1: Talk

Tuesday, April 1, 2014, 09:30–09:45, HSZ 204

Optical non-Fermi-liquid behavior in CeCoIn₅ — •Marc Scheffler¹, Uwe S. Pracht¹, Martin Dressel¹, Masaaki Shimozawa², Ryota Endo², Takahito Terashima³, Takasada Shibauchi², and Yuji Matsuda² — ¹1. Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany — ²Department of Physics, Kyoto University, Kyoto, Japan — ³Research Center for Low Temperature and Materials Science, Kyoto University, Kyoto, Japan

The non-Fermi-liquid metallic state of the heavy-fermion superconductor CeCoIn₅ is interpreted as a consequence of a nearby quantum-critical point. Spectroscopic studies of quantum-critical heavy fermions have yielded valuable information, but are experimentally challenging. This also holds for optical techniques: the required low energies, both in temperature and frequency, are hard to reach. We overcome these difficulties by combining high-quality thin films of CeCoIn₅ with THz transmission spectroscopy. We cover frequencies 0.2-1.1 THz at temperatures down to 3 K, i.e. matching energy scales.

The THz spectra of CeCoIn₅ indicate metallic behavior with unconventional features. Upon cooling, the transport relaxation rate decreases through our frequency window, but we never find a simple Drude response. Instead, at low temperatures we observe a strongly frequency-dependent relaxation rate which is clearly inconsistent with Fermi-liquid predictions and which we attribute to electronic correlations in this non-Fermi-liquid phase. We further address the frequency- and temperature-dependent effective mass, and we discuss possible scaling behavior in the quantum-critical regime.