Browsing by Author "Chen, Justin S."

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    A Mott insulator continuously connected to iron pnictide superconductors
    (Springer Nature, 2016) Song, Yu; Yamani, Zahra; Cao, Chongde; Li, Yu; Zhang, Chenglin; Chen, Justin S.; Huang, Qingzhen; Wu, Hui; Tao, Jing; Zhu, Yimei; Tian, Wei; Chi, Songxue; Cao, Huibo; Huang, Yao-Bo; Dantz, Marcus; Schmitt, Thorsten; Yu, Rong; Nevidomskyy, Andriy H.; Morosan, Emilia; Si, Qimiao; Dai, Pengcheng; Rice Center for Quantum Materials
    Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe1−xCuxAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5, the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ∼x=0.05. Our discovery of a Mott-insulating state in NaFe1−xCuxAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-Tc superconductivity.
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    Chemical tuning of electrical transport in Ti1−xPtxSe2−y
    (American Physical Society, 2015) Chen, Justin S.; Wang, Jiakui K.; Carr, Scott V.; Vogel, Sven C.; Gourdon, Olivier; Dai, Pengcheng; Morosan, E.
    The structural and transport properties of polycrystalline Ti1−xPtxSe2−y(x≤0.13,y≤0.2) are studied, revealing highly tunable electrical properties, spanning nearly ten orders of magnitude in scaled resistivity. Using x-ray and neutron diffraction, Pt is found to dope on the Ti site. In the absence of Pt doping (for x=0), Se deficiency (y>0) increases the metallic character of TiSe2, while a large increase of the low-temperature resistivity is favored by a lack of Se deficiency (y=0) and increasing amounts of doped Pt (x>0). The chemical tuning of the resistivity in Ti1−xPtxSe2−y with Se deficiency and Pt doping results in a metal-to-insulator transition. Simultaneous Pt doping and Se deficiency (x,y>0) confirms the competition between the two opposing trends in electrical transport, with the main outcome being the suppression of the charge density wave transition below 2 K for y=2x=0.18. Band structure calculations on a subset of Ti1−xPtxSe2−y compositions are in line with the experimental observations.
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    Electronic nematic correlations in the stress-free tetragonal state of BaFe2−xNixAs2
    (American Physical Society, 2015) Man, Haoran; Lu, Xingye; Chen, Justin S.; Zhang, Rui; Zhang, Wenliang; Luo, Huiqian; Kulda, J.; Ivanov, A.; Keller, T.; Morosan, Emilia; Si, Qimiao; Dai, Pengcheng
    We use transport and neutron scattering to study electronic, structural, and magnetic properties of the electron-doped BaFe2−xNixAs2 iron pnictides in uniaxial-strained and external-stress-free detwinned states. Using a specially designed in situ mechanical detwinning device, we demonstrate that the in-plane resistivity anisotropy observed in the uniaxial-strained tetragonal state of BaFe2−xNixAs2 below a temperature T∗, previously identified as a signature of the electronic nematic phase, is also present in the stress-free tetragonal phase below T**(
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    Point-contact tunneling spectroscopy measurement of CuxTiSe2: Disorder-enhanced Coulomb effects
    (American Physical Society, 2015) Luna, Katherine; Wu, Phillip M.; Chen, Justin S.; Morosan, Emilia; Beasley, Malcolm R.
    We performed point-contact spectroscopy tunneling measurements on CuxTiSe2 bulk with x=0.02 and 0.06 at temperatures ranging from T=4−40 K and observe a suppression in the density of states around zero bias that we attribute to enhanced Coulomb interactions due to disorder. We find that the correlation gap associated with this suppression is related to the zero-temperature resistivity. We use our results to estimate the disorder-free transition temperature and find that the clean limit Tc0 is close to the experimentally observed Tc at optimal doping.
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    Point-contact tunneling spectroscopy measurement of CuxTiSe2: Disorder-enhanced Coulomb effects
    (American Physical Society, 2015) Luna, Katherine; Wu, Phillip M.; Chen, Justin S.; Morosan, Emilia; Beasley, Malcolm R.
    We performed point-contact spectroscopy tunneling measurements on CuxTiSe2 bulk with x=0.02 and 0.06 at temperatures ranging from T=4−40 K and observe a suppression in the density of states around zero bias that we attribute to enhanced Coulomb interactions due to disorder. We find that the correlation gap associated with this suppression is related to the zero-temperature resistivity. We use our results to estimate the disorder-free transition temperature and find that the clean limit Tc0 is close to the experimentally observed Tc at optimal doping.