Browsing by Author "Yu, R."

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    Evolution of Magnetic Double Helix and Quantum Criticality near a Dome of Superconductivity in CrAs
    (American Physical Society, 2018) Matsuda, M.; Lin, F.K.; Yu, R.; Cheng, J.-G.; Wu, W.; Sun, J.P.; Zhang, J.H.; Sun, P.J.; Matsubayashi, K.; Miyake, T.; Kato, T.; Yan, J.-Q.; Stone, M.B.; Si, Qimiao; Luo, J.L.; Uwatoko, Y.
    At ambient pressure, CrAs undergoes a first-order transition into a double-helical magnetic state at TN=265  K, which is accompanied by a structural transition. The recent discovery of pressure-induced superconductivity in CrAs makes it important to clarify the nature of quantum phase transitions out of the coupled structural/helimagnetic order in this system. Here, we show, via neutron diffraction on the single-crystal CrAs under hydrostatic pressure (P), that the combined order is suppressed at Pc≈10  kbar, near which bulk superconductivity develops with a maximal transition temperature Tc≈2  K. We further show that the coupled order is also completely suppressed by phosphorus doping in CrAs1−xPx at a critical xc≈0.05, above which inelastic neutron scattering evidenced persistent antiferromagnetic correlations, providing a possible link between magnetism and superconductivity. In line with the presence of antiferromagnetic fluctuations near Pc(xc), the A coefficient of the quadratic temperature dependence of resistivity exhibits a dramatic enhancement as P (x) approaches Pc(xc), around which ρ(T) has a non-Fermi-liquid form. Accordingly, the electronic specific-heat coefficient of CrAs1−xPx peaks around xc. These properties provide clear evidence for quantum criticality, which we interpret as originating from a nearly second-order helimagnetic quantum phase transition that is concomitant with a first-order structural transition. Our findings in CrAs highlight the distinct characteristics of quantum criticality in bad metals, thereby bringing out new insights into the physics of unconventional superconductivity such as those occurring in the high-Tc iron pnictides.
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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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    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.