Browsing by Author "Si, Q."

Now showing 1 - 6 of 6
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    Direct visualization of coexisting channels of interaction in CeSb
    (AAAS, 2019) Jang, Sooyoung; Kealhofer, Robert; John, Caolan; Doyle, Spencer; Hong, Ji-Sook; Shim, Ji Hoon; Si, Q.; Erten, O.; Denlinger, Jonathan D.; Analytis, James G.
    Our understanding of correlated electron systems is vexed by the complexity of their interactions. Heavy fermion compounds are archetypal examples of this physics, leading to exotic properties that weave magnetism, superconductivity and strange metal behavior together. The Kondo semimetal CeSb is an unusual example where different channels of interaction not only coexist, but have coincident physical signatures, leading to decades of debate about the microscopic picture describing the interactions between the f moments and the itinerant electron sea. Using angle-resolved photoemission spectroscopy, we resonantly enhance the response of the Ce f electrons across the magnetic transitions of CeSb and find there are two distinct modes of interaction that are simultaneously active, but on different kinds of carriers. This study reveals how correlated systems can reconcile the coexistence of different modes on interaction—by separating their action in momentum space, they allow their coexistence in real space.
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    Evolution of the Kondo lattice and non-Fermi liquid excitations in a heavy-fermion metal
    (Springer Nature, 2018) Seiro, S.; Jiao, L.; Kirchner, S.; Hartmann, S.; Friedemann, S.; Krellner, C.; Geibel, C.; Si, Q.; Steglich, F.; Wirth, S.
    Strong electron correlations can give rise to extraordinary properties of metals with renormalized Landau quasiparticles. Near a quantum critical point, these quasiparticles can be destroyed and non-Fermi liquid behavior ensues. YbRh2Si2 is a prototypical correlated metal exhibiting the formation of quasiparticle and Kondo lattice coherence, as well as quasiparticle destruction at a field-induced quantum critical point. Here we show how, upon lowering the temperature, Kondo lattice coherence develops at zero field and finally gives way to non-Fermi liquid electronic excitations. By measuring the single-particle excitations through scanning tunneling spectroscopy, we find the Kondo lattice peak displays a non-trivial temperature dependence with a strong increase around 3.3 K. At 0.3 K and with applied magnetic field, the width of this peak is minimized in the quantum critical regime. Our results demonstrate that the lattice Kondo correlations have to be sufficiently developed before quantum criticality can set in.
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    Experimental observation of incoherent-coherent crossover and orbital-dependent band renormalization in iron chalcogenide superconductors
    (American Physical Society, 2015) Liu, Z.K.; Yi, M.; Zhang, Y.; Hu, J.; Yu, R.; Zhu, J.-X.; He, R.-H.; Chen, Y.L.; Hashimoto, M.; Moore, R.G.; Mo, S.-K.; Hussain, Z.; Si, Q.; Mao, Z.Q.; Lu, D.H.; Shen, Z.-X.
    The level of electronic correlation has been one of the key questions in understanding the nature of superconductivity. Among the iron-based superconductors, the iron chalcogenide family exhibits the strongest electron correlations. To gauge the correlation strength, we performed a systematic angle-resolved photoemission spectroscopy study on the iron chalcogenide series Fe1+ySexTe1−x (0
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    Kondo Insulator to Semimetal Transformation Tuned by Spin-Orbit Coupling
    (American Physical Society, 2017) Dzsaber, S.; Prochaska, L.; Sidorenko, A.; Eguchi, G.; Svagera, R.; Waas, M.; Prokofiev, A.; Si, Q.; Paschen, S.
    Recent theoretical studies of topologically nontrivial electronic states in Kondo insulators have pointed to the importance of spin-orbit coupling (SOC) for stabilizing these states. However, systematic experimental studies that tune the SOC parameter λ SOC in Kondo insulators remain elusive. The main reason is that variations of (chemical) pressure or doping strongly influence the Kondo coupling J K and the chemical potential μ —both essential parameters determining the ground state of the material—and thus possible λ SOC tuning effects have remained unnoticed. Here, we present the successful growth of the substitution series Ce 3 Bi 4 ( Pt 1 − x Pd x ) 3 ( 0 ≤ x ≤ 1 ) of the archetypal (noncentrosymmetric) Kondo insulator Ce 3 Bi 4 Pt 3 . The Pt-Pd substitution is isostructural, isoelectronic, and isosize, and it therefore is likely to leave J K and μ essentially unchanged. By contrast, the large mass difference between the 5 d element Pt and the 4 d element Pd leads to a large difference in λ SOC , which thus is the dominating tuning parameter in the series. Surprisingly, with increasing x (decreasing λ SOC ), we observe a Kondo insulator to semimetal transition, demonstrating an unprecedented drastic influence of the SOC. The fully substituted end compound Ce 3 Bi 4 Pd 3 shows thermodynamic signatures of a recently predicted Weyl-Kondo semimetal.
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    Low-carrier density and fragile magnetism in a Kondo lattice system
    (American Physical Society, 2019) Rai, Binod K.; Oswald, Iain W.H.; Ban, Wenjing; Huang, C.-L.; Loganathan, V.; Hallas, A.M.; Wilson, M.N.; Luke, G.M.; Harriger, L.; Huang, Q.; Li, Y.; Dzsaber, Sami; Chan, Julia Y.; Wang, N.L.; Paschen, Silke; Lynn, J.W.; Nevidomskyy, Andriy H.; Dai, Pengcheng; Si, Q.; Morosan, E.; Rice Center for Quantum Materials
    Kondo-based semimetals and semiconductors are of extensive current interest as a viable platform for strongly correlated states in the dilute carrier limit. It is thus important to explore the routes to understand such systems. One established pathway is through the Kondo effect in metallic nonmagnetic analogs, in the so called half-filling case of one conduction electron and oneﾠ4fﾠelectron per site. Here, we demonstrate that Kondo-based semimetals develop out of conduction electrons with a low-carrier density in the presence of an even number of rare-earth sites. We do so by studying the Kondo materialﾠYb3Ir4Ge13ﾠalong with its closed-4f-shell counterpart,ﾠLu3Ir4Ge13. Through magnetotransport, optical conductivity, and thermodynamic measurements, we establish that the correlated semimetallic state ofﾠYb3Ir4Ge13ﾠbelow its Kondo temperature originates from the Kondo effect of a low-carrier conduction-electron background. In addition, it displays fragile magnetism at very low temperatures, which in turn, can be tuned to a Griffiths-phase-like regime through Lu-for-Yb substitution. These findings are connected with recent theoretical studies in simplified models. Our results can pave the way to exploring strong correlation physics in a semimetallic environment.
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    Nematic Energy Scale and the Missing Electron Pocket in FeSe
    (American Physical Society, 2019) Yi, M.; Pfau, H.; Zhang, Y.; He, Y.; Wu, H.; Chen, T.; Ye, Z.R.; Hashimoto, M.; Yu, R.; Si, Q.; Lee, D.-H.; Dai, Pengcheng; Shen, Z.-X.; Lu, D.H.; Birgeneau, R.J.
    Superconductivity emerges in proximity to a nematic phase in most iron-based superconductors. It is therefore important to understand the impact of nematicity on the electronic structure. Orbital assignment and tracking across the nematic phase transition prove to be challenging due to the multiband nature of iron-based superconductors and twinning effects. Here, we report a detailed study of the electronic structure of fully detwinned FeSe across the nematic phase transition using angle-resolved photoemission spectroscopy. We clearly observe a nematicity-driven band reconstruction involving dxz, dyz, and dxy orbitals. The nematic energy scale between dxz and dyz bands reaches a maximum of 50 meV at the Brillouin zone corner. We are also able to track the dxz electron pocket across the nematic transition and explain its absence in the nematic state. Our comprehensive data of the electronic structure provide an accurate basis for theoretical models of the superconducting pairing in FeSe.