Center for Correlated Electron Systems

Seminar

Spin-orbit coupling driven magnetism in transition metal oxides

July 18, 2017l Hit 754
Date : July 12, 2017 14:00 ~ 15:30
Speaker : Abhishek Nag(Indian Association for the Cultivation of Science)
Location : Bldg. 19, Rm. 210

In the last decade many Sd comp unds having for instance Iridium, have been reported which went against the expectations of a wide-band metallic state [1]. This insulating state was shown to be an outcome of increased spin-orbit coupling (SO ( 0.5 ev) in these elements [2]. lridates therefore, with several competing energy scales: the Hubbard Hunds exchange JH, SOC, crystal field (CF and electron hopping energy t, are predicted to show a rich phase diagram of exciting physical properties [1 ].
A unique situation develops if the Ir ions are in 5+ (Sd") oxidati
n state, where ideally str ng SOC should lead to a non-magnetic 1=0 ground state. Our results on a 6H hexag nal comp und Ba3Znlr209 with lr5+ ions and strong SOC arrives very cl se to the J = 0 state but each Ir ions still possess a weak moment [3]. The spins within structural lr209 dimers are expected to form a spin- rbit singlet state (SOS) with no resultant moment, but substantial frustration arising from inter-dimer exchange interactions induce quantum fluctuati ns in these possible SOS states favoring a spin- rbital liquid phase down t at least 100 mK.
Unable to obtain J = 0 state in the comp
unds having Ir p9 dimers, we decided t see the effect of separating the Ir ions by non-magnetic ions in double perovskite Ba2Ylr06. Although we observe the J = 0 state to be largely separated from the higher magnetic states in Resonant Inelastic X:-Ray Scattering experiments, which could be explained using an atomic model, magnetic moments were still bserved from magnetic measurements suggesting that a minute amount of hopping still exists between the Ir ions. These m ments that are generated, also do no order till 60 mK [4].
A question thus remains, w
uld it be ever possible to observe atomic like spin-orbit coupled states in a solid?

 

Hos t : Prof. Changyoung Kim