Working with a quantum material known as a kagome magnet, a team of 电子游戏软件 physicists and colleagues have directly measured how individual electronic quantum states in the novel material respond to external magnetic fields by shifting energy in an unusual manner, 电子游戏正规平台人员 报告 in the latest online edition of the journal 自然物理.
The measurements generated by the project are the first of their kind to directly measure the momentum-resolved, field-induced evolution of these quantum states, 根据团队的说法, who collaborated with scientists at Renmin University in Beijing, 中国.
The findings offered the first experimental demonstration of theoretical predictions about how electronic band structure can change in these novel materials, in this case bulk single crystals of yttrium manganese tin YMn6Sn6, according to 电子游戏软件 Associate Professor of 物理 还有Zeljkovic, a lead co-author of the 报告.
Associate Professor of 物理 还有Zeljkovic
“When a magnetic field is applied to a material, electronic band structure—which is a collection of quantum states that electrons in solids can occupy—can change in unusual ways,泽里科维奇说. “These changes have thus far been inferred from theoretical calculations or accessed indirectly from field-induced changes in macroscopic measurable properties. Direct measurement of field-induced changes to the electronic band structure has been difficult to measure.”
The team overcame the experimental challenges of studying the material through spectroscopic-imaging scanning tunneling microscopy. Kagomemagnets, like YMn6Sn6 团队电子游戏正规平台, are so named because they possess magnetic structure and an atomic lattice that resembles Japanese 'kagome' weaved baskets.
Kagome magnets harbor so-called Dirac fermions, which Zeljkovic explained are quasiparticles characterized by zero mass and a linear energy-momentum dispersion in electronic band structure resembling relativistic particles.
Theoretical physicists like Zeljkovic’s colleague and co-author, 电子游戏软件 Professor of 物理 Ziqiang Wang, have mathematically shown that Dirac fermions may evolve—from the standpoint of energy and momentum—in response to a magnetic field. The team set out to test those predictions, Zeljkovic说.
The team found that quantum states associated with Dirac fermions respond strongly to magnetic field, shifting to higher energies regardless of the direction of the field, 根据 自然物理 报告, which is titled “Manipulation of Dirac band curvature and momentum-dependent g-factor in a kagome magnet.”
“有趣的是, they exhibit a momentum-dependent shift—for a setmagnetic field, quantum states near the Dirac point shift the most; the shift becomes progressively smaller away from the Dirac point,泽里科维奇说. The Dirac point is a point in energy-momentum space where conduction and valence bands touch.
Zeljkovic说 the expectation was that the system without magnetic field would host massless—or zero mass—Dirac fermions based on the orientation of spins lying primarily in-plane. 而不是, the team made the surprising observation that Dirac fermions in this material at zero field have finite mass. Why this occurred will be a question for theoreticians to further explore.
From an experimental standpoint, Zeljkovic说 there are many additional questions to resolve based on these findings. 具体地说, there are multiple competing effects that can lead to a momentum-dependent band evolution, involving electron spin and orbital degrees of freedom. Orbital magnetism in particular, a property that has recently generated attention and excitement among researchers studying “twisted” van der Waals structures, is one of the extremely exciting possibilities, Zeljkovic说.
“Our future experiments will focus on disentangling different contributions and examining orbital magnetism in this and related kagome magnets,泽里科维奇补充道.
The BC team also included doctoral candidate Hong Li and former doctoral students He Zhao, 博士20, 蒋坤, 博士的18, all co-authors on the 报告. Zeljkovic's research was supported by grants from the Army 电子游戏正规平台 Office and Wang's work was supported by a grant from the U.S.
Department of Energy, Office of Basic Energy Sciences, and a Cottrell SEED
Award from the 电子游戏正规平台 Corporation for Science Advancement.
Ed Hayward | University Communications | June 2022