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arXiv 2104.09173cond-mat.supr-concond-mat.str-el
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可果美超导体CsV3Sb5中的轨道有序和涨落

Orbital ordering and fluctuations in a kagome superconductor CsV3Sb5

D. W. Song, L. X. Zheng, F. H. Yu, J. Li, L. P. Nie, M. Shan, D. Zhao, S. J. Li, B. L. Kang, Z. M. Wu, Y. B. Zhou, K. L. Sun, K. Liu, X. G. Luo, Z. Y. Wang, J. … 展开作者

D. W. Song, L. X. Zheng, F. H. Yu, J. Li, L. P. Nie, M. Shan, D. Zhao, S. J. Li, B. L. Kang, Z. M. Wu, Y. B. Zhou, K. L. Sun, K. Liu, X. G. Luo, Z. Y. Wang, J. J. Ying, X. G. Wan, T. Wu, X. H. Chen

摘要:

最近,在具有非平凡能带拓扑结构的钒基可果美金属AV 3Sb 5(A = K,Rb,Cs)中发现了竞争性电子不稳定性,包括超导性和密度波状有序。这一发现激发了人们广泛的兴趣,研究这些竞争的电子秩序和可能的奇异激发超导状态的相互作用。在此,为了进一步明确这些可果美超导体中的密度波状转变的性质,我们对CsV 3Sb 5单晶进行了51 V和133 Cs核磁共振(NMR)测量。在结构转变温度Ts ~ 94 K,51 V NMR谱中观察到轨道位移的突然分裂,揭示了与轨道有序化有关的一级相变。相比之下,在51 V NMR谱上,电荷密度波(CDW)级的四极分裂仅在Ts以下逐渐出现,具有典型的二级跃迁行为,表明CDW级是二级电子级。结合~(133)Cs核磁共振谱,进一步证实了该化合物具有周期为2x 2x 2c的三维结构调制。在Ts以上,随温度变化的Knight位移和核自旋-晶格弛豫速率(1/T1)进一步表明存在来自钒3d轨道的显著的磁涨落,而在Ts以下,由于轨道有序化,这些磁涨落被抑制。目前的结果强烈支持,除了CDW有序之外,之前声称的类似密度波的转变还涉及主导轨道有序,这表明这些可果美超导体中存在丰富的轨道物理。

英文摘要:

Recently, competing electronic instabilities, including superconductivity and density-wave-like order, have been discovered in vanadium-based kagome metals AV3Sb5 (A = K, Rb, Cs) with a nontrivial band topology. This finding stimulates wide interests to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state. Here, in order to further clarify the nature of density-wave-like transition in these kagome superconductors, we performed 51V and 133Cs nuclear magnetic resonance (NMR) measurements on the CsV3Sb5 single crystal. A first-order phase transition associated with orbital ordering is revealed by observing a sudden splitting of orbital shift in 51V NMR spectrum at the structural transition temperature Ts ~ 94 K. In contrast, the quadrupole splitting from a charge-density-wave (CDW) order on 51V NMR spectrum only appears gradually below Ts with a typical second-order transition behavior, suggesting that the CDW order is a secondary electronic order. Moreover, combined with 133Cs NMR spectrum, the present result also confirms a three-dimensional structural modulation with a 2ax2ax2c period. Above Ts, the temperature-dependent Knight shift and nuclear spin-lattice relaxation rate (1/T1) further indicate the existence of remarkable magnetic fluctuations from vanadium 3d orbitals, which are suppressed due to orbital ordering below Ts. The present results strongly support that, besides CDW order, the previously claimed density-wave-like transition also involves a dominant orbital order, suggesting a rich orbital physics in these kagome superconductors.

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