発表者名 |
大村 哲士 |
指導教員名 |
森本 高裕 准教授 |
発表題目(英語) |
Exploration of ground states in spin-orbit coupled systems |
要旨(英語) |
An orbital order is a phenomenon where the orbital degrees of freedom of electrons are aligned in solids. The orbital orders have not been fully investigated compared to magnetic orders where the spins of electrons are aligned, since it is difficult to measure orbital degrees of freedom directly. However, the orbital order plays a crucial role in some systems. For example, in the perovskite manganese oxides, which is a representative strongly correlated electron system, many tantalizing phenomena have been observed like colossal magnetoresistance (CMR) due to the orbital effect [1]. In this presentation, I will discuss ground states of the spin-orbit coupled system in LaMnO3 using a simple Monte Carlo method.
First, I will derive Kugel-Khomskii model in LaMnO3 where electrons split into localized and itinerant ones. Under crystal field effects, manganese ions host one electron in eg orbitals, which results in orbital degrees of freedom. In the strongly correlated limit, electrons can move nowhere, and an effective spin-orbit Hamiltonian can be derived. Due to the Hund coupling to the localized magnetic moments, the degeneracy of the energy of the virtual states is lifted, which makes spins and orbitals inequivalent.
Next, I will introduce Markov chain Monte Carlo method (MCMC) as a simple and powerful tool to explore classical ground states without a preferable ansatz. Unlike simple mean-field analyses, MCMC can provide probability distributions around ground states, corresponding to a given Hamiltonian. As an exercise of MCMC, I will confirm that the previous result [2] of the ground states of Kugel-Khomskii model in LaMnO3 holds true. If time allows, I would like to touch on my recent calculation about a spin-orbit coupled bilayer system.
[1] Y. Tokura, Rep. Prog. Phys. 69, 797 (2006).
[2] R. Shiina, T. Nishitani, and H. Shiba, J. Phys. Soc. Jpn. 66, 3159 (1997). |
発表言語 |
英語 |