Browsing by Author "Chen, T."

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    Anomalous Metamagnetism in the Low Carrier Density Kondo Lattice YbRh3Si7
    (American Physical Society, 2018) Rai, Binod K.; Chikara, S.; Ding, Xiaxin; Oswald, Iain W.H.; Schönemann, R.; Loganathan, V.; Hallas, A.M.; Cao, H.B.; Stavinoha, Macy; Chen, T.; Man, Haoran; Carr, Scott; Singleton, John; Zapf, Vivien; Benavides, Katherine A.; Chan, Julia Y.; Zhang, Q.R.; Rhodes, D.; Chiu, Y.C.; Balicas, Luis; Aczel, A.A.; Huang, Q.; Lynn, Jeffrey W.; Gaudet, J.; Sokolov, D.A.; Walker, H.C.; Adroja, D.T.; Dai, Pengcheng; Nevidomskyy, Andriy H.; Huang, C.-L.; Morosan, E.
    We report complex metamagnetic transitions in single crystals of the new low carrier Kondo antiferromagnet YbRh3Si7. Electrical transport, magnetization, and specific heat measurements reveal antiferromagnetic order at TN=7.5 K. Neutron diffraction measurements show that the magnetic ground state of YbRh3Si7 is a collinear antiferromagnet, where the moments are aligned in the ab plane. With such an ordered state, no metamagnetic transitions are expected when a magnetic field is applied along the c axis. It is therefore surprising that high-field magnetization, torque, and resistivity measurements with H∥c reveal two metamagnetic transitions at μ0H1=6.7 T and μ0H2=21 T. When the field is tilted away from the c axis, towards the ab plane, both metamagnetic transitions are shifted to higher fields. The first metamagnetic transition leads to an abrupt increase in the electrical resistivity, while the second transition is accompanied by a dramatic reduction in the electrical resistivity. Thus, the magnetic and electronic degrees of freedom in YbRh3Si7 are strongly coupled. We discuss the origin of the anomalous metamagnetism and conclude that it is related to competition between crystal electric-field anisotropy and anisotropic exchange interactions.
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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.
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    Orbital Ingredients and Persistent Dirac Surface State for the Topological Band Structure in ${\mathrm{FeTe}}_{0.55}{\mathrm{Se}}_{0.45}$
    (American Physical Society, 2024) Li, Y.-F.; Chen, S.-D.; García-Díez, M.; Iraola, M. I.; Pfau, H.; Zhu, Y.-L.; Mao, Z.-Q.; Chen, T.; Yi, M.; Dai, P.-C.; Sobota, J. A.; Hashimoto, M.; Vergniory, M. G.; Lu, D.-H.; Shen, Z.-X.
    FeTe0.55⁢Se0.45 (FTS) occupies a special spot in modern condensed matter physics at the intersections of electron correlation, topology, and unconventional superconductivity. The bulk electronic structure of FTS is predicted to be topologically nontrivial due to the band inversion between the 𝑑𝑥⁢𝑧 and 𝑝𝑧 bands along Γ−𝑍. However, there remain debates in both the authenticity of the Dirac surface states (DSSs) and the experimental deviations of band structure from the theoretical band inversion picture. Here we resolve these debates through a comprehensive angle-resolved photoemission spectroscopy investigation. We first observe a persistent DSS independent of 𝑘𝑧. Then, by comparing FTS with FeSe, which has no band inversion along Γ−𝑍, we identify the spectral weight fingerprint of both the presence of the 𝑝𝑧 band and the inversion between the 𝑑𝑥⁢𝑧 and 𝑝𝑧 bands. Furthermore, we propose a renormalization scheme for the band structure under the framework of a tight-binding model preserving crystal symmetry. Our results highlight the significant influence of correlation on modifying the band structure and make a strong case for the existence of topological band structure in this unconventional superconductor.