Seminar TRR80

2.5.2017 16:00, Raum: S-288
Dr. Igor I. Mazin (U.S. Naval Research Laboratory, Washington D.C.)
Molecular orbitals vs. relativistic orbitals in t2g honeycomb lattices: SrRu2O6 as compared to Na2IrO3, RuCl3, and LiRuO3
30.5.2017 16:00, Raum: S-288
Prof. Dr. Takahiro Onimaru (Hiroshima University, Japan)
Exotic Quadrupolar Phenomena in Non-Kramers Doublets of Pr 1-2-20 Systems

A variety of exotic phenomena arising from active quadrupoles in non-Kramers doublet of 4f2 systems, PrT2X20 (T: transition metal, X: Al, Zn, and Cd), are briefly presented. PrT2X20 crystallizes in the cubic CeCr2Al20-type structure, where the Pr3+ ion is encapsulated in a symmetric cage formed by sixteen X atoms.[1] The cubic point group of Td at the Pr site may bring about a degenerated 4f2 crystalline electric field (CEF) ground state. Furthermore, the s-p orbitals of cage atoms would hybridize with the 4f2 state. In fact, the CEF ground states of Pr3+ in PrT2X20 are the non-Kramers doublet. Since the non-Kramers doublets have no mag-netic dipole but quadrupolar degrees of freedom, the transport, thermodynamic and magnetic properties are governed by the purely active quadrupoles of the doublet in a low temperature range below a few K, being lower than a few tens K of the CEF splitting energy. At the low temperature range, the quadrupoles play a key role to induce the phenomena such as long-range quadrupole order, superconductivity, non-Fermi liquid behavior, and magnetic-field induced heavy fermion state.[2-4] In this talk, I would like to present the systematic under-stand ing on the quadrupole-induced phenomena and progress of the recent researches on them.

[1] T. Nasch et al, Z. Naturforsch. B 52, 1023 (1997). [2] T. Onimaru et al., Phys. Rev. Lett. 106, 177001 (2011). [3] A. Sakai and S. Nakatsuji, J. Phys. Soc. Jpn. 80, 063701 (2011). [4] T. Onimaru and H. Kusunose, J. Phys. Soc. Jpn. 85, 082002 (2016).

20.6.2017 16:00, Raum: S-288
Dr. Kamran Behnia (ESPCI, Paris)
Superconductivity and ferroelectricity in strontium titanate