Like so many goals of scientific investigation, the material class called Kagome Magnet has proven to be a source of both frustration and wonder. The further discovery of the quantum properties of the Kagome magnet is considered to be one of the main challenges of fundamental physics ̵
An unusual underlying geometry of atomic organization is central to the value of these materials. Kagome lattices are described as intersecting nets of "angular triangles" and are valued for their unique behavior of the passing electrons as a fertile soil for studying quantum electronic states that are described as frustrated, correlated, and topological.
A recent study by an international group of researchers published in the journal Nature found that the kagome ferromagnet Fe3Sn2 has an electronic state that is unusually strong in coupling with an applied magnetic field that can be rotated to show in any direction of a 3-dimensional direction space, which in quantum scale reveals a "huge" magnetization-driven electronic energy shift within the material.
This shift in energy sheds new light on the existence of spin-orbit coupling and topological spin textures in Kagome lattices, in which magnetic and magnetic structures are present. Electronic structures interlock and produce unusual – often previously unknown – spin orbit interactions. Activities, said the Boston College Professor of Physics Ziqiang W ang, a co-author of the report entitled "Huge and Anisotropic Spinorbite Tuning in a Highly Correlated Kagome Magnet."
"We found two things, the first being that the electronic state of Fe3Sn2 is nematic, a state that spontaneously interrupts the rotational symmetry, and the electrons behave like a liquid crystal within this magnet, presumably because of the strong electron electrons "The second thing we found is that you can manipulate the electron energy structure by adjusting the magnetic structure and making big changes to it using a magnetic field."
Wang, a theoretical physicist and PhD student Kun Jiang, who has studied novel quantum electronic states that result from the interplay of electron-electron interaction, geometric frustration, and topological bonds, together with experimental colleagues who first noticed the unusual electronic activity when they examined the material by scanning tunneling microscopy.
The team, which included researchers from BC, Princeton University, the Chinese Academy of Sciences, Renmin University, and Peking University, used STM and vector magnetic field tools to determine the spin orbit-coupled electronic properties of the Kagome ferromagnets and the study of e xotic phenomena, while modeling and calculations are performed to theoretically interpret and understand the observed phenomena.
"What our colleagues found was that when they changed the direction of the magnetic field they saw changes in the electronic states that are abnormally large," Wang said. "The shifts in the bands – there are band gaps, forbidden areas in quantum mechanics, in which there can be no electrons – these areas can be set enormously by the applied magnetic field."
The "belt shift" is a change in the electronic band structure, Wang said. Depending on the magnetic field directions, the band gap is increased and narrowed. The Kagome ferromagnet showed about a 150-fold shift over ordinary materials.
Examination of the electron's quantum-wave wavefunctions showed a consistent spontaneous nematicity – an indication of an important electron correlation that causes the rotational symmetry break of the electronic state.
These spin-driven giant electronic reactions suggested the possibility of an underlying correlated magneto-topological phase, the researchers reported. The tunability of the Kagome magnet demonstrated a strong interaction between an externally applied magnetic field and the nematic, providing new opportunities for controlling spin orbit properties and investigating emerging phenomena in topological or quantum materials of electrical properties may one day become potential applications in electronic devices such as storage and information storage and sensor technologies, Wang said.
"What's exciting about these results is the potential to do something useful," Wang said. "This comes from a very fundamental physics, but it may one day connect to applications, we do not understand everything, but we now know that this is a material that contains all of these important ingredients."
Scientists create an atomic 2-D electronic Kagomegitter
Jia-Xin Yin et al., Giant and Anisotropic Multibody Spin-Orbit Tunability in a Highly Correlated Kagome Magnet, Nature (2018). DOI: 10.1038 / s41586-018-0502-7