题　目：Azurite, herbertsmithite and hexagonal iridates: Understanding the physics by working out the relevant Hamiltonian description

报告人： Harald O. Jeschke (Junior Group leader, Institute for Theoretical Physics, Goethe-University Frankfurt)

时　间： 10月9日（周三），下午3：30-4：30

地　点： 南校区第一实验楼406会议室

报告摘要：
The natural mineral azurite Cu3(CO3)2(OH)2 is a frustrated magnet displaying unusual and controversially discussed magnetic behavior. We perform a theoretical study based on density functional theory as well as state-of-the-art numerical many-body calculations. We propose an effective generalized spin-1/2 diamond chain model which provides a consistent description of experiments: low-temperature magnetization, inelastic neutron scattering, nuclear magnetic resonance measurements, magnetic susceptibility as well as new specific heat measurements. With this study we demonstrate that the balanced combination of first principles with powerful many-body methods successfully describes the behavior of this frustrated material.
Herbertsmithite (ZnCu3(OH)6Cl2) is often discussed as the best realization of the highly frustrated antiferromagnetic kagome lattice known so far. We employ density functional theory calculations to determine the underlying Heisenberg Hamiltonian. We find the nearest neighbour coupling J1 to exceed all other couplings by far. However, some additional couplings slightly modify the perfect antiferromagnetic kagome Hamiltonian. In addition, we validate our DFT approach by applying it to kapellasite, a polymorph of herbertsmithite which is known experimentally to exhibit competing exchange interactions.
Contrary to previous studies that classify the hexagonal iridate Na2IrO3 as a realization of the Heisenberg-Kitaev model with dominant spin-orbit coupling, we show that this system represents a highly unusual case in which the electronic structure is dominated by the formation of quasi-molecular orbitals (QMOs), with substantial quenching of the orbital moments. The QMOs consist of six atomic orbitals on an Ir hexagon, but each Ir atom belongs to three different QMOs. The concept of such QMOs in solids invokes very different physics compared to the models considered previously.

报告人简介：
Dr. Harald O. Jescke received his Ph.D. degree from Freie University Berlin in June 2000. From Jan. 2002 to Feb.2004, he was a Emmy Noether fellow and postdoctoral associate in department of physics & astronomy, Rutgers university. From Mar. 2004, he became a Junior group leader in Institute for Theoretical Physics, JohannWolfgang Goethe-University, Frankfurt am Main. Dr. Jeschke has published over 70 papers in international research journals, including 1 Nature Materials, 11 Physical Review Letters, 1 JACS.