Browsing by Author "Dai, P.-C."

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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.
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    Raman scattering study of NaFe0.53Cu0.47As
    (American Physical Society, 2018) Zhang, W.-L.; Song, Y.; Wang, W.-Y.; Cao, C.-D.; Dai, P.-C.; Jin, C.-Q.; Blumberg, G.
    We use polarization-resolved Raman scattering to study lattice dynamics in NaFe0.53Cu0.47As single crystals. We identify four A1g phonon modes, at 126, 172, 183, and 197 cm−1, and four B3g phonon modes at 101, 139, 173, and 226 cm−1(D4h point group). The phonon spectra are consistent with the Ibam space group, which confirms that the Cu and Fe atoms form a stripe order. The temperature dependence of the phonon spectra suggests weak electron-phonon and magnetoelastic interactions.
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    Reduced electronic correlation effects in half substituted Ba(Fe1−xCox)2As2
    (AIP Publishing, 2018) Liu, Z.-H.; Yaresko, A.N.; Li, Y.; Evtushinsky, D.V.; Dai, P.-C.; Borisenko, S.V.
    We report a comprehensive study of the tridimensional nature and orbital character of the low-energy electronic structure in 50% Cobalt doped Ba(Fe1−xCox)2As2 (d6.5), by using polarization- and photon energy-dependent angle-resolved photoemission spectroscopy. An extra electron-like Fermi surface is observed around the Brillouin zone boundary compared with isoelectronic KyFe2−xSe2 (d6.5). The bands near the Fermi level (EF) are mainly derived from Fe/Co 3d t2g orbitals, revealing visible dispersions along the kz direction. In combination with the local density approximation and the dynamical mean-field theory calculations, we find that the As 4p bands are non-renormalized and the whole 3d band needs to be renormalized by a “single” factor of ∟1.6, indicating moderate electronic correlation effects. The “single” factor description of the correlation strength among the different 3d orbitals is also in sharp contrast to orbital-dependent correlation effects in BaFe2As2. Our findings indicate a remarkable reduction of correlation effects with little difference among 3d orbitals in BaFeCoAs2, due to the increased filling of the electronic 3dshell in the presence of significant Hund's coupling. The results support that the electronic correlation effects and multiple orbital physics play an important role in the superconductivity of the 122 system and in other ferropnictides.