LaPd $_3$ S $_4$中阴离子骨架的成键和电子性质
Bonding and Electronic Nature of the Anionic Framework in LaPd$_3$S$_4$
摘要：
双狄拉克材料是物质的一种拓扑相，其中非对称对称性使电子简并度比通常预期的高出八倍。立方钯青铜NaPd $_3$ O $_4$和LaPd $_3$ S $_4$是由Pd $_3$ X $_4$（X = O，S）阴离子骨架与A阳离子（A = Na，La）离子键合而成。这些材料最近被计算确定为含有八重费米子。本文报道了LaPd $_3$ S $_4$单晶的制备和电子性质。测量下至T = 0.45 K和磁场高达$μ$ 0 H = 65 T是符合正常费米液体物理的狄拉克金属在稀磁性杂质的存在下。这一解释进一步证实了比热分析，磁化测量和比较密度泛函理论（DFT）计算。通过对NaPd $_3$ O $_4$和LaPd $_3$ S $_4$的DFT电子结构的成键分析，我们确定了阴离子Pd $_3$ X $_4$骨架在比X = O更高的电子数下的稳定性的起源，并提出了化学调谐策略，以使8倍费米子点移动到费米能级。
英文摘要：
Double Dirac materials are a topological phase of matter in which a non-symmorphic symmetry enforces greater electronic degeneracy than normally expected up to eightfold. The cubic palladium bronzes NaPd$_3$O$_4$ and LaPd$_3$S$_4$ are built of Pd$_3$X$_4$ (X = O, S) anionic frameworks that are ionically bonded to A cations (A = Na, La). These materials were recently identified computationally as harboring eightfold fermions. Here we report the preparation of single crystals and electronic properties of LaPd$_3$S$_4$. Measurements down to T = 0.45 K and in magnetic fields up to $μ$0H = 65 T are consistent with normal Fermi liquid physics of a Dirac metal in the presence of dilute magnetic impurities. This interpretation is further confirmed by analysis of specific heat, magnetization measurements and comparison to density functional theory (DFT) calculations. Through a bonding analysis of the DFT electronic structure of NaPd$_3$O$_4$ and LaPd$_3$S$_4$, we identify the origin of the stability of the anionic Pd$_3$X$_4$ framework at higher electron counts for X = S than X = O, and propose chemical tuning strategies to enable shifting the 8-fold fermion points to the Fermi level.
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