Browsing by Author "Li, Wenhui"

Now showing 1 - 5 of 5
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    Deformation of a Trapped Fermi Gas with Unequal Spin Populations
    (American Physical Society, 2006) Partridge, G.B.; Li, Wenhui; Liao, Y.A.; Hulet, R.G.; Haque, M.; Stoof, H.T.C.; Rice Quantum Institute
    The real-space densities of a polarized strongly interacting two-component Fermi gas of Li6 atoms reveal two low-temperature regimes, both with a fully paired core. At the lowest temperatures, the unpolarized core deforms with increasing polarization. Sharp boundaries between the core and the excess unpaired atoms are consistent with a phase separation driven by a first-order phase transition. In contrast, at higher temperatures the core does not deform but remains unpolarized up to a critical polarization. The boundaries are not sharp in this case, indicating a partially polarized shell between the core and the unpaired atoms. The temperature dependence is consistent with a tricritical point in the phase diagram.
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    Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO2 hydrogenation
    (AAAS, 2022) Zhu, Jie; Wang, Peng; Zhang, Xiaoben; Zhang, Guanghui; Li, Rongtan; Li, Wenhui; Senftle, Thomas P.; Liu, Wei; Wang, Jianyang; Wang, Yanli; Zhang, Anfeng; Fu, Qiang; Song, Chunshan; Guo, Xinwen
    Identifying the dynamic structure of heterogeneous catalysts is crucial for the rational design of new ones. In this contribution, the structural evolution of Fe(0) catalysts during CO2 hydrogenation to hydrocarbons has been investigated by using several (quasi) in situ techniques. Upon initial reduction, Fe species are carburized to Fe3C and then to Fe5C2. The by-product of CO2 hydrogenation, H2O, oxidizes the iron carbide to Fe3O4. The formation of Fe3O4@(Fe5C2+Fe3O4) core-shell structure was observed at steady state, and the surface composition depends on the balance of oxidation and carburization, where water plays a key role in the oxidation. The performance of CO2 hydrogenation was also correlated with the dynamic surface structure. Theoretical calculations and controll experiments reveal the interdependence between the phase transition and reactive environment. We also suggest a practical way to tune the competitive reactions to maintain an Fe5C2-rich surface for a desired C2+ productivity.
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    Metastability in Spin-Polarized Fermi Gases
    (American Physical Society, 2011) Liao, Y.A.; Revelle, M.; Paprotta, T.; Rittner, A.S.C.; Li, Wenhui; Partridge, G.B.; Hulet, R.G.; Rice Quantum Institute
    We study the role of particle transport and evaporation on the phase separation of an ultracold, spin-polarized atomic Fermi gas. We show that the previously observed deformation of the superfluid paired core is a result of evaporative depolarization of the superfluid due to a combination of enhanced evaporation at the center of the trap and the inhibition of spin transport at the normal-superfluid phase boundary. These factors contribute to a nonequilibrium jump in the chemical potentials at the phase boundary. Once formed, the deformed state is highly metastable, persisting for times of up to 2ﾠs.
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    Pairing and Phase Separation in a Polarized Fermi Gas
    (American Association for the Advancement of Science, 2006) Partridge, Guthrie B.; Li, Wenhui; Kamar, Ramsey I.; Liao, Yean-an; Hulet, Randall G.
    We report the observation of pairing in a gas of atomic fermions with unequal numbers of two components. Beyond a critical polarization, the gas separates into a phase that is consistent with a superfluid paired core surrounded by a shell of normal unpaired fermions. The critical polarization diminishes with decreasing attractive interaction. For near-zero polarization, we measured the parameter β = –0.54 ± 0.05, describing the universal energy of a strongly interacting paired Fermi gas, and found good agreement with recent theory. These results are relevant to predictions of exotic new phases of quark matter and of strongly magnetized superconductors.
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    Spin-imbalance in a one-dimensional Fermi gas
    (Nature Publishing Group, 2010) Liao, Yean-an; Rittner, Ann Sophie C.; Paprotta, Tobias; Li, Wenhui; Partridge, Guthrie B.; Hulet, Randall G.; Baur, Stefan K.; Mueller, Erich J.; Rice Quantum Institute
    Superconductivity and magnetism generally do not coexist. Changing the relative number of up and down spin electrons disrupts the basic mechanism of superconductivity, where atoms of opposite momentum and spin form Cooper pairs. Nearly forty years ago Fulde and Ferrell [1] and Larkin and Ovchinnikov [2] (FFLO) proposed an exotic pairing mechanism in which magnetism is accommodated by the formation of pairs with finite momentum. Despite intense theoretical and experimental efforts, however, polarized superconductivity remains largely elusive [3]. Unlike the three-dimensional (3D) case, theories predict that in one dimension (1D) a state with FFLO correlations occupies a major part of the phase diagram [4, 5, 6, 7, 8, 9, 10, 11, 12]. Here we report experimental measurements of density profiles of a two-spin mixture of ultracold [6] Li atoms trapped in an array of 1D tubes (a system analogous to electrons in 1D wires). At finite spin imbalance, the system phase separates with an inverted phase profile, as compared to the 3D case. In 1D, we find a partially polarized core surrounded by wings which, depending on the degree of polarization, are composed of either a completely paired or a fully polarized Fermi gas. Our work paves the way to direct observation and characterization of FFLO pairing.