Compressibility and entropy of cold fermions in one dimensional optical lattices

We calculate several thermodynamic quantities for repulsively interacting one-dimensional fermions.We solve the Hubbard model at both zero and finite temperatures using the Bethe-ansatz method. For arbitrary values of the chemical potential, we calculate the particle number density, the double occupancy, various compressibilities, and the entropy as a function of temperature and interaction. We find that these thermodynamic quantities show a characteristic behavior so that measurements of these quantities can be used as a detection of temperature, the metal-insulator transition, and metallic and insulating phases in the trap environment. Further, we discuss an experimental scheme to extract these thermodynamic quantities from the column density profiles. The entropy and the compressibility of the entire trapped atomic cloud also reveal characteristic features indicating whether insulating and/or metallic phases coexist in the trap.Comment: 9 pages and 11 figures. The published versio

Electrical and material properties of hydrothermally grown single crystal (111) UO2

The semiconductor and optical properties of UO2 are investigated. The very long drift carrier lifetimes, obtained from current-voltage I(V) and capacitance-voltage C(V) measurements, along with the well-defined optical properties provide little evidence of an abundance of material defects away from the surface region. Schottky barrier formation may be possible, but very much dependent on the choice of contact and surface stoichiometry and we find that Ohmic contacts are in fact favored. Depth resolved photoemission provided evidence of a chemical shift at the surface. Density functional theory, with the Heyd-Scuseria-Ernzerhof (HSE) functional, indicates a band gap of a 2.19 eV and an anti-ferromagnetic ground state. Ellipsometry measurements indicates at UO2 is relatively isotropic with a band gap of approximately 2.0 eV band gap, consistent with theoretical expectations

The Electronic Structure of Two Dimensional Materials

This thesis details new insights into the electronic structure of various two-dimensional materials. Firstly, by means of magneto optical Kerr effect (MOKE) we compared the magnetic properties of two-dimensional samples on ferromagnetic substrates: trilayer graphene on top of Co3O4(111)/Co(0001), graphene on Co(0001), and multilayer hexagonal boron nitride, (h-BN)(0001), on Co(0001). While graphene on cobalt without Co3O4 interlayer and trilayer h-BN on cobalt showed ordinary Co ferromagnetic hysteresis loops, the trilayer heterostructures of graphene/Co3O4(111)/Co(0001) exhibited an unusual MOKE hysteresis loop, with lack of remanence, for temperature up to 400 K. Magnetic force microscopy measurements with the reference atomic force microscopy revealed that the complex domain state was formed on graphene imprinting the Co magnetic domain structures. Secondly, the valence band structure and spin-orbit splitting of bulk 2H-WSe2, monolayer WSe2 and multilayer WS2 were investigated by means of angle-resolved photoemission spectroscopy (ARPES). The bulk 2H-WSe2 revealed the significantly different band structures for states of even and odd reflection. The experimental and theoretical band structures, for the most part, showed agreement. The spin-orbit splitting at the top of the valence band at K was measured to be 513 ± 10 meV for monolayer WSe2, 490 ± 10 meV for bulk 2H-WSe2 and 420 ± 20 meV for multilayer WS2. The multilayer WS 2(0001), grown by chemical vapor deposition (CVD), showed n-type character as characterized by both ARPES and transistor measurements. Lastly, the influence of the metal adsorption on bulk 2H-MoS2(0001) and bulk 2H-WSe2(0001) were studied by various kinds of photoemission spectroscopy methods including ARPES and inverse photoemission spectroscopy (IPES). We observed rigid energy shifts of the occupied and unoccupied band structures upon Co or Na adsorption on the MoS2 and WSe2. Na adsorption enhanced the n-type character of MoS2 while Co adsorption enhanced the p-type character of WSe2. Interestingly, we detected only a negligible energy shift for Co adsorped MoS2 and Na adsorped WSe2. The binding energy shifts exhibited a positive correlation with the difference of the work function between the metallic adlayer and the TMDs

Spin-Orbit Coupling In The Band Structure Of Monolayer Wse2

We used angle-resolved photoemission spectroscopy (ARPES) to map out the band structure of single-layer WSe2. The splitting of the top of the valence band because of spin-orbit coupling is 513±10meV, in general agreement with theoretical predictions and in the same range as that of bulk WSe2. Overall, our density functional theory (DFT) calculations of the band structure are in excellent agreement with the ARPES results. We have verified that the few discrepancies between theory and experiment are not due to the effect of strain. The differences between the DFT-calculated band structure using local density approximation (LDA) and that using the generalized gradient approximation (GGA), for single-layer WSe2, are caused mainly by differences in the respective charge densities

Adsorbate Doping Of Mos2 And Wse2: The Influence Of Na And Co

We have investigated the influence of metal adsorbates (sodium and cobalt) on the occupied and unoccupied electronic structure of MoS2(0 0 0 1) and WSe2(0 0 0 1), through a combination of both photoemission and inverse photoemission. The electronic structure is rigidly shifted in both the WSe2 and MoS2 systems, with either Na or Co adsorption, generally as predicted by accompanying density functional theory based calculations. Na adsorption is found to behave as an electron donor (n-type) in MoS2, while Co adsorption acts as an electron acceptor (p-type) in WSe2. The n-type transition metal dichalcogenide (MoS2) is easily doped more n-type with Na deposition while the p-type transition metal dichalcogenide (WSe2) is easily doped more p-type with Co deposition. The binding energy shifts have some correlation with the work function differences between the metallic adlayer and the transition metal dichalcogenide substrate

The Symmetry-Resolved Electronic Structure Of 2H-Wse2(0 0 0 1)

The orbital symmetry of the band structure of 2H-WSe2(0 0 0 1) has been investigated by means of angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT). The WSe2(0 0 0 1) experimental band structure is found, by ARPES, to be significantly different for states of even and odd reflection parities along both Ω-K̄ and Ω-M the - and - lines, in good agreement with results obtained from DFT. The light polarization dependence of the photoemission intensities from the top of the valence band for bulk WSe2(0 0 0 1) is explained by the dominance of W 5dz2 states around the Ω-point and W 5dxy states around the Ω-point, thus dominated, respectively, by states of even and odd symmetry, with respect to the - line. The splitting of the topmost valence band at K̄, due to spin-orbit coupling, is measured to be 0.49 ± 0.01 eV, in agreement with the 0.48 eV value from DFT, and prior measurements for the bulk single crystal WSe2(0 0 0 1), albeit slightly smaller than the 0.513 ± 0.01 eV observed for monolayer WSe2

Band Structure Characterization Of Ws2 Grown By Chemical Vapor Deposition

Growth by chemical vapor deposition (CVD) leads to multilayer WS2 of very high quality, based on high-resolution angle-resolved photoemission spectroscopy. The experimental valence band electronic structure is considered to be in good agreement with that obtained from density functional theory calculations. We find the spin-orbit splitting at the K̄ point to be 420 ± 20 meV with a hole effective mass of -0.35 ± 0.02 me for the upper spin-orbit component (the branch closer to the Fermi level) and -0.43 ± 0.07 me for the lower spin-orbit component. As predicted by theory, a thickness-dependent increase of bandwidth is observed at the top of the valence band, in the region of the Brillouin zone center. The top of the valence band of the CVD-prepared films exhibits a substantial binding energy, consistent with n-type behavior, and in agreement with transistor characteristics acquired using devices incorporating the same WS2 material

EXAFS Determination of Clay Minerals in Martian Meteorite Allan Hills 84001 and Its Implication for the Noachian Aqueous Environment

The aqueous environment of ancient Mars is of significant interest because of evidence suggesting the presence of a large body of liquid water on the surface at ~4 Ga, which differs significantly from the modern dry and oxic Martian environment. In this study, we examined the Fe-bearing minerals in the 4 Ga Martian meteorite, Alan Hills (ALH) 84001, to reveal the ancient aqueous environment present during the formation of this meteorite. Extended X-ray absorption fine structure (EXAFS) analysis was conducted to determine the Fe species in ALH carbonate and silica glass with a high spatial resolution (~1–2 μm). The μ-EXAFS analysis of ALH carbonate showed that the Fe species in the carbonate were dominated by a magnesite-siderite solid solution. Our analysis suggests the presence of smectite group clay in the carbonate, which is consistent with the results of previous thermochemical modeling. We also found serpentine in the silica glass, indicating the decrease of water after the formation of carbonate, at least locally. The possible allochthonous origin of the hematite in the carbonate suggests a patchy redox environment on the ancient Martian surface

Electrical and material properties of hydrothermally grown single crystal (111) UO2

The semiconductor and optical properties of UO2 are investigated. The very long drift carrier lifetimes, obtained from current-voltage I(V) and capacitance-voltage C(V) measurements, along with the well-defined optical properties provide little evidence of an abundance of material defects away from the surface region. Schottky barrier formation may be possible, but very much dependent on the choice of contact and surface stoichiometry and we find that Ohmic contacts are in fact favored. Depth resolved photoemission provided evidence of a chemical shift at the surface. Density functional theory, with the Heyd-Scuseria-Ernzerhof (HSE) functional, indicates a band gap of a 2.19 eV and an anti-ferromagnetic ground state. Ellipsometry measurements indicates at UO2 is relatively isotropic with a band gap of approximately 2.0 eV band gap, consistent with theoretical expectations