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Jeudi 21 Novmebre 2013, 14h
Amphi Holweck, Esc C, 1ème etage
Temperature-magnetic phase diagram of the cubic compound Ce3Pd20Si6
Valentina Martelli
Technische Universität Wien
A quantum phase transition (QPT) is a phase transition at zero temperature between two quantum mechanical ground states, driven by a non-thermal parameter.
The ground state of a heavy fermion system (HF) is determined by the competition between the Ruderman-Kittel-Kasuya-Yosida (RKKY) and the Kondo interactions. When the RKKY interaction dominates a magnetic ground state sets in. The application of an external tuning control parameter (like magnetic field, pressure or chemical composition) can suppress the magnetic order to zero. If this suppression is continuously driven to zero, the system approaches a quantum critical point (QCP). At the QCP, new states of matter have been observed in many physical properties which are a topic of intensive investigation.
The heavy fermion cubic compound Ce3Pd20Si6 has a cubic crystal structure with two inequivalent Ce sites. Its crystal structure places it in the barely-explored three-dimensional part of the global phase diagram of quantum critical heavy fermion system [1], giving the possibility to explore the role of the dimensionality in quantum criticality.
Previous investigations in polycrystalline samples show two phase transitions, at TN = 0.31 K and at TQ = 0.5 K, attributed respectively to antiferromagnetic (AF) and, tentatively, to antiferroquadrupolar (AFQ) order. The suppression of TN to zero at around 0.9 T points out a field-induced quantum critical point (QCP) with Kondo destruction [2]. Magnetization and ultrasound investigations on single crystals have revealed an anisotropic evolution of TQ with respect to the direction of an external magnetic field. More recently, we have investigated the electrical resistivity at low temperatures and under magnetic field in single crystalline samples of Ce3Pd20Si6 in order to elucidate the temperature-magnetic field phase diagram, with focus on putative additional QCPs above 1 T. In this seminar I will discuss our experimental findings comparing the results with the previous reported phase diagram..
[1] Q. Si, Phys. Status Solidi B 247 (2010) 484.
[2] J. Custers, K-A. Lorenzer, M. Müller, A. Prokofiev, A. Sidorenko, H. Winkler, A. M. Strydom, Y. Shimura, T. Sakakibara, R. Yu, Q. Si, and S. Paschen : Nature Mater. 11 2012 189.