II Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany.
J Phys Condens Matter. 2010 Apr 28;22(16):164209. doi: 10.1088/0953-8984/22/16/164209. Epub 2010 Mar 30.
The standard point of view is that at low energies Mott insulators exhibit only magnetic properties, while charge degrees of freedom are frozen out because electrons are localized. We demonstrate (Bulaevskii et al 2008 Phys. Rev. B 78 024402) that in general this is not true: for certain spin textures there exist quite nontrivial charge effects in the ground and lowest excited states. We show that in frustrated systems spontaneous orbital currents may exist in the ground state, proportional to the scalar spin chirality. For other spin structures spontaneous charge redistribution may exist, so that the average charge at a site is different from 1. This can lead to the appearance of dipole moments and possibly of the net spontaneous polarization. This is a novel, purely electronic mechanism of multiferroic behaviour. We also discuss some dynamic consequences, such as dipole-active 'ESR' transitions. Also, the possibility of using chirality instead of spin in memory applications is briefly discussed.
标准观点认为，在低能下，莫特绝缘体仅表现出磁性性质，而电荷自由度被冻结，因为电子被局域化。我们证明（Bulaevskii 等人，2008 年，物理评论 B78，024402），一般来说，事实并非如此：对于某些自旋结构，在基态和最低激发态中存在相当复杂的电荷效应。我们表明，在受挫系统中，在基态中可能存在自发轨道电流，与标量自旋手性成正比。对于其他自旋结构，可能存在自发电荷再分布，使得一个位置的平均电荷不同于 1。这可能导致偶极矩的出现，并且可能导致净自发极化的出现。这是多铁行为的一种新颖的、纯粹的电子机制。我们还讨论了一些动态后果，例如偶极活性“ESR”跃迁。此外，简要讨论了在记忆应用中使用手性而不是自旋的可能性。
