Tunable THz Surface Plasmon Polariton based on Topological Insulator-Layered Superconductor Hybrid Structure

We theoretically investigate the surface plasmon polariton (SPP) at the interface between 3D strong topological insulator (TI) and layered superconductor-magnetic insulator structure. The tunability of SPP through electronic doping can be enhanced when the magnetic permeability of the layered structure becomes higher. When the interface is gapped by superconductivity or perpendicular magnetism, SPP dispersion is further distorted, accompanied by a shift of group velocity and penetration depth. Such a shift of SPP reaches maximum when the magnitude of Fermi level approaches the gap value, and may lead to observable effects. The tunable SPP at the interface between layered superconductor and magnetism materials in proximity to TI surface may provide new insight in the detection of Majorana Fermions.Comment: 6 pages, 4 figure

Hydration-dependent dynamic crossover phenomenon in protein hydration water

The characteristic relaxation time τ of protein hydration water exhibits a strong hydration level h dependence. The dynamic crossover is observed when h is higher than the monolayer hydration level h[subscript c] =0.2–0.25 and becomes more visible as h increases. When h is lower than h[subscript c], τ only exhibits Arrhenius behavior in the measured temperature range. The activation energy of the Arrhenius behavior is insensitive to h, indicating a local-like motion. Moreover, the h dependence of the crossover temperature shows that the protein dynamic transition is not directly or solely induced by the dynamic crossover in the hydration water.United States. Dept. of Energy. Office of Basic Energy Sciences (Contract DE-FG02-90ER45429

Boson Peak in Deeply Cooled Confined Water: A Possible Way to Explore the Existence of the Liquid-to-Liquid Transition in Water

The boson peak in deeply cooled water confined in nanopores is studied with inelastic neutron scattering. We show that in the (P, T) plane, the locus of the emergence of the boson peak is nearly parallel to the Widom line below ∼1600  bar. Above 1600 bar, the situation is different and from this difference the end pressure of the Widom line is estimated. The frequency and width of the boson peak correlate with the density of water, which suggests a method to distinguish the hypothetical “low-density liquid” and “high-density liquid” phases in deeply cooled water.United States. Dept. of Energy (Grant DE-FG02-90ER45429

Studies on hydration water dynamics and microstructure of synthetic cement

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 75-79).The mechanical properties of cement pastes depend strongly on their porosities. In a wet paste, the porosity links to the free water volume after hydration. Structural water which presents in the solid phase, constrained water absorbed on the surface of the pores and free water in the center of the pores have different dynamical behavior. Hence, it should be possible to extract information on pore system by exploiting the water dynamics. We investigated the dynamics of hydration water confined in calcium- and magnesium-silicate-hydrate (C-S-H and M-S-H) gels using high-resolution quasi-elastic neutron scattering (QENS). C-S-H and M-S-H are the chemical binders present in calcium rich and magnesium rich cement. To analyze the cement QENS data, we developed a new global model which is numerically more stable than previous models for cement QENS analysis. With this model, we can correctly quantify the structural water index (SWI) and the confining radius. We also established the relation between the constrained to liquid water ratio and the temperature dependence of translational relaxation time. We analyzed two different sets of synthetic cement using this method: (1) C-S-H with different water to cement ratio (w/c) and (2) M-S-H with various additives. For the first set, SWI and confining radius are both controlled by w/c with a linear relation. For the second set, we show that by adding ASN-COOH additive, M-S-H becomes similar to C-S-H in all parameters. We also analyzed the small angle x-ray scattering data of M-S-H gel with a polydisperse cylinder model which fits better than previously published polydisperse sphere model and will be studied further in future work. The result indicates that C-SH and M-S-H have similar globule shape and fractal structure. The evidence from QENS and SAXS experiments suggest that the weak compressive strength of M-S-H compares to C-S-H is due to the high porosity rather than the globule shape.by Peisi Le.Ph. D