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arXiv 2011.12083cond-mat.str-elcond-mat.mes-hall
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${\ ext{C}}_{60}$ 富勒烯几何上的反铁磁 $S=1/2$ 海森堡模型

The antiferromagnetic $S=1/2$ Heisenberg model on the ${\text{C}}_{60}$ fullerene geometry

Roman Rausch, Cassian Plorin, Matthias Peschke

AI总结:

利用DMRG方法求解C$_{60}$富勒烯几何上的反铁磁海森堡模型,发现其最低激发态为三重态且阻挫减弱,揭示了富勒烯尺寸可调节阻挫的特性。

摘要:

我们使用密度矩阵重整化群(DMRG)求解了自旋位于截角二十面体顶点上的量子力学反铁磁海森堡模型。这描述了在强在位相互作用 $U$ 极限下,半填充时未掺杂 C$_{60}$ 富勒烯的磁性质。我们计算了所有可能距离的基态和关联函数、最低单态和三重态激发态,以及热力学性质,即比热和自旋磁化率。我们发现,与可通过精确对角化求解的较小 C$_{20}$ 或 C$_{32}$ 不同,其最低激发态是三重态而非单态,这表明由于存在许多六边形面以及五边形面的相互分离,阻挫有所减弱,这与截角四面体的情况类似。这意味着可以通过改变尺寸来调节富勒烯中的阻挫。自旋-自旋关联在六边形键上要强得多,并随距离呈指数衰减,因此该分子足够大,以至于不会在整个范围内产生关联。比热显示出高温峰和低温肩,让人联想到 kagome 晶格,而自旋磁化率则显示出单个宽峰,并且非常接近 C$_{20}$ 的自旋磁化率。

英文摘要:

We solve the quantum-mechanical antiferromagnetic Heisenberg model with spins positioned on vertices of the truncated icosahedron using the density-matrix renormalization group (DMRG). This describes magnetic properties of the undoped C$_{60}$ fullerene at half filling in the limit of strong on-site interaction $U$. We calculate the ground state and correlation functions for all possible distances, the lowest singlet and triplet excited states, as well as thermodynamic properties, namely the specific heat and spin susceptibility. We find that unlike smaller C$_{20}$ or C$_{32}$ that are solvable by exact diagonalization, the lowest excited state is a triplet rather than a singlet, indicating a reduced frustration due to the presence of many hexagon faces and the separation of the pentagonal faces, similar to what is found for the truncated tetrahedron. This implies that frustration may be tuneable within the fullerenes by changing their size. The spin-spin correlations are much stronger along the hexagon bonds and exponentially decrease with distance, so that the molecule is large enough not to be correlated across its whole extent. The specific heat shows a high-temperature peak and a low-temperature shoulder reminiscent of the kagome lattice, while the spin susceptibility shows a single broad peak and is very close to the one of C$_{20}$.

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。

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