arXivDaily arXiv每日学术速递 周一至周五更新
北美退伍军人节(Veterans Day),12 日无更新
arXiv 1507.01334cond-mat.str-el
收藏

石墨烯$n=1$朗道能级复合费米子的自发极化

Spontaneous polarization of composite fermions in the $n=1$ Landau level of graphene

Ajit C. Balram, Csaba Tőke, A. Wójs, J. K. Jain

摘要:

受最近实验的启发,这些实验揭示了$n=1$石墨烯朗道能级中的扩展分数量子霍尔态,并提出了自旋自由度的重要作用[Amet { \em et al.},纳特。普通。{ \bf 6},5838(2014)],我们对具有不同自旋极化的分数量子霍尔态之间的竞争进行了精确的定量研究。我们发现分数量子霍尔效应可以用复合费米子来描述,但自旋物理性质与$n=0$ Landau能级有本质的不同.特别地,对于填充因子为$n/(2n\pm 1)$的态,精确对角化和复合费米子理论都表明,基态是完全自旋极化的,并且即使在塞曼耦合消失的极限下也支持稳健的自旋波模式。因此,即使形成了复合费米子,将它们视为弱相互作用粒子的平均场描述也会失效,它们之间的交换相互作用足够强,可以通过诱导全自旋极化来引起行为的质的变化。我们还验证了完全自旋极化的复合费米海在$n=1$石墨烯朗道能级的相关半填充处具有比成对的Pfenan态更低的能量,表明在$n=1$石墨烯朗道能级的半填充处缺乏分数量子霍尔效应。

英文摘要:

Motivated by recent experiments that reveal expansive fractional quantum Hall states in the $n=1$ graphene Landau level and suggest a nontrivial role of the spin degree of freedom [Amet {\em et al.}, Nat. Common. {\bf 6}, 5838 (2014)], we perform accurate quantitative study of the the competition between fractional quantum Hall states with different spin polarizations. We find that the fractional quantum Hall effect is well described in terms of composite fermions, but the spin physics is qualitatively different from that in the $n=0$ Landau level. In particular, for the states at filling factors $n/(2n\pm 1)$, both exact diagonalization and the composite fermion theory show that the ground state is fully spin polarized and supports a robust spin wave mode even in the limit of vanishing Zeeman coupling. Thus, even though composite fermions are formed, a mean field description that treats them as weakly interacting particles breaks down, and the exchange interaction between them is strong enough to cause a qualitative change in the behavior by inducing full spin polarization. We also verify that the fully spin polarized composite fermion Fermi sea has lower energy than the paired Pfaffian state at the relevant half fillings in the $n=1$ graphene Landau level, indicating a lack of fractional quantum Hall effect at half filling in the $n=1$ graphene Landau level.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑