This thesis has detailed the extensive analysis of the XAS and RIXS spectra of LiFePO4 and FePO4, with the primary focus on LiFePO4. One of the primary motivations for this study was to understand the electronic structure of the two compounds and, in particular, shed some light on the nature of electron correlation within the samples. Two classes of band structure calculations have come to light. One solution uses the Hubbard U parameter, and this solution exhibits a band gap of about 4 eV. Other solutions that use standard DFT electron correlation functionals yield band gaps between 0 and 1.0 eV. <p>The RIXS spectra of LiFePO4 and FePO4 were analyzed using Voigt function fitting, an uncommon practice for RIXS spectra. Each of the spectra was fit to a series of Voigt functions in an attempt to localize the peaks within the spectra. These peaks were determined to be RIXS events, and the energetic centers of these peaks were compared to a small band gap band structure calculation. The results of the RIXS analysis strongly indicate that the small gap solution is correct. This was a surprising result, given that LiFePO4 is an ionic, insulating transition metal oxide, showing all of the usual traits of a Mott-type insulator. <p>This contradiction was explained in terms of polaron formation. Polarons can severely distort the lattice, which changes the local charge density. This changes the local DOS such that the DOS probed by XAS or RIXS experiments is not necessarily in the ground state. In particular, polaron formation can reduce the band gap. Thus, the agreement between the small gap solution and experiment is false, in the sense that the physical assumptions that formed the basis of the small gap calculations do not reflect reality. Polaronic distortion was also tentatively put forward as an explanation for the discrepancy between partial fluorescence yield, total fluorescence yield, and total electron yield measurements of the XAS spectra of LiFePO4 and FePO4.

This thesis has detailed the extensive analysis of the XAS and RIXS spectra of LiFePO4 and FePO4, with the primary focus on LiFePO4. One of the primary motivations for this study was to understand the electronic structure of the two compounds and, in particular, shed some light on the nature of electron correlation within the samples. Two classes of band structure calculations have come to light. One solution uses the Hubbard U parameter, and this solution exhibits a band gap of about 4 eV. Other solutions that use standard DFT electron correlation functionals yield band gaps between 0 and 1.0 eV. <p>The RIXS spectra of LiFePO4 and FePO4 were analyzed using Voigt function fitting, an uncommon practice for RIXS spectra. Each of the spectra was fit to a series of Voigt functions in an attempt to localize the peaks within the spectra. These peaks were determined to be RIXS events, and the energetic centers of these peaks were compared to a small band gap band structure calculation. The results of the RIXS analysis strongly indicate that the small gap solution is correct. This was a surprising result, given that LiFePO4 is an ionic, insulating transition metal oxide, showing all of the usual traits of a Mott-type insulator. <p>This contradiction was explained in terms of polaron formation. Polarons can severely distort the lattice, which changes the local charge density. This changes the local DOS such that the DOS probed by XAS or RIXS experiments is not necessarily in the ground state. In particular, polaron formation can reduce the band gap. Thus, the agreement between the small gap solution and experiment is false, in the sense that the physical assumptions that formed the basis of the small gap calculations do not reflect reality. Polaronic distortion was also tentatively put forward as an explanation for the discrepancy between partial fluorescence yield, total fluorescence yield, and total electron yield measurements of the XAS spectra of LiFePO4 and FePO4.

No description available.

The inter-dimensional system of a three-dimensional bulk and a two-dimensional interface is analyzed for bosons with quasirelativistic dispersion relation. Using the energy-dependent Green's function, the inter-dimensional quasirelativistic density of states inside the interface is solved analytically. We find that in the low-energy limit the inter-dimensional quasirelativistic density of states shows three-dimensional behaviour, while in the high-energy limit the density of states shows two-dimensional behaviour. This work is the first step in a process that will lead to a fully-analytical model for fermions in topological materials.

The ruthenates are perhaps one of the most diverse group of materials known up to date. These compounds exhibit a wide array of behaviors ranging from the exotic pwave superconductivity in Sr2RuO4, to the itinerant ferromagnetism in SrRuO3, and the Mott-insulating behavior in Ca2RuO4. One of the most intriguing compounds belonging to this group is Ca3Ru2O7 which is known to undergo an antiferromagnetic ordering at 56K and an insulating transition at 48K. Most intriguing, however, is the behavior displayed by this compound in the presence of an external magnetic field. For fields parallel to the a-axis, the compound undergoes a metamagnetic transition into the ferromagnetic region at 6 T. If the external field direction is changed to the b-axis then the result will be different. colossal magnetoresistance occurs and a fall in reistivity of up to three orders of magnitude is recorded at fields of 15T. Most interesting, however, is the energy gap observed for this material. A number of groups have measured such gap with different methods and found conflicting results. For this reason it was of vital importance to perform measurements on this compound and try to resolve this issue. Tunneling spectroscopy is one of the most powerful techniques which can be used to probe the electronic properties of a material. The method is best suited to measure the density of states of a material and hence the nature of the strong correlations which dictate the properties of the compound. We performed a series of tunneling spectroscopy measurements by means of planar tunnel junctions. These types of junctions were chosen because of their stability over a large temperature range and their stability in the presence of an external field. The anisotropies which showed up in the resistivity and magnetization measurements manifested also in our data. For tunneling parallel to the a-axis, we observed a gap opening at 48K with a width a peak to peak width of 2Δa ~258±15meV. As the temperature was lowered, the gap size increased reaching a maximum width of 2Δa ~ 845±38meVat 4.2K. Tunneling parallel to the b-axis, the gap has a much smaller size than the a-axis gap. At 48K the gap width is about 2Δb ~ 201±13 meV and reaches a maximum width of 2Δb ~ 366±33 meV at 4.2K. For the c-axis, the situation is different since the gap opens at 56K instead of 48K. The gap width at 56K is about 2Δc ~ 102±6meV and reaches a maximum width of 2Δc ~ 179±14 meV at 4.2K. In the presence of an external field, we noticed that the overall behavior was always the same in the ab-plane but differed in c-axis direction. In our experiment, an external field was applied along the a-axis and measurements were made at 4.2K. For aaxis tunneling, the gap width decreased to a value of 2Δa ~ 587±27 meV at 4.2 K at 7T. On the other hand, the gap width in the b-axis direction decreased to a value of 2Δb ~ 308±25 meV for the same field. For the c-axis direction, the gap decreased to a value of 2Δc ~ 112±8 meV at 7T. The DOS of the c-axis differs for fields of 6T and above. A third peak emerges inside the gap on the valence side of the DOS. This third peak seems to be a direct consequence of the metamagnetic transition at 6T observed by other groups and may be attributable to a spin-filtering effect.

No description available.

This thesis describes a novel concept for a field-effect transistor based on metallic channels. Latest research demonstrates that the bulk (3D) properties of many materials begin to change when confined to 2D sheets, or 1D nanowires. Particularly, the bandgap increases and the density of states decreases. In this work, this effect is explored further to demonstrate its application to field-effect transistors. Certain metals such as Gold and Silver in these dimensions have extremely low density of states in particular energy regions and through gate modulation can be partially depleted from electrons thus creating conditions for field-effect. A simulation study of Gold channel FET demonstrates ION/IOFF of 30 and superior current driving capability compared to the state-of-the art 22nm SiGe ETSOI as well as 30nm nanotube transistors.

This thesis describes a novel concept for a field-effect transistor based on metallic channels. Latest research demonstrates that the bulk (3D) properties of many materials begin to change when confined to 2D sheets, or 1D nanowires. Particularly, the bandgap increases and the density of states decreases. In this work, this effect is explored further to demonstrate its application to field-effect transistors. Certain metals such as Gold and Silver in these dimensions have extremely low density of states in particular energy regions and through gate modulation can be partially depleted from electrons thus creating conditions for field-effect. A simulation study of Gold channel FET demonstrates ION/IOFF of 30 and superior current driving capability compared to the state-of-the art 22nm SiGe ETSOI as well as 30nm nanotube transistors.

The density of states of elastic waves in a porous amorphous “mesoglass” has been measured in the strong-scattering regime. Samples were constructed by sintering glass beads percolated on a random lattice. This structure was investigated via x-ray tomography, and fractal behaviour was observed with fractal dimension D = 2.6. Using sufficiently small samples, the individual modes of vibration could be resolved and counted in the Fourier transform of each transmitted ultrasonic pulse. A statistical treatment of the data, designed to account for the possibility of missing modes, was developed, yielding a robust method for measuring the density of states. In the strong-scattering regime, the data are in good agreement with a simple model based on mode conservation, though the density of states significantly exceeds the predictions of the Debye approximation at low frequencies. At intermediate frequencies, an average density of states of 47.1 ± 0.3 MHz⁻¹ mm⁻³ was found, with a frequency dependence of f^(0.01 ± 0.04).

The density of states of elastic waves in a porous amorphous “mesoglass” has been measured in the strong-scattering regime. Samples were constructed by sintering glass beads percolated on a random lattice. This structure was investigated via x-ray tomography, and fractal behaviour was observed with fractal dimension D = 2.6. Using sufficiently small samples, the individual modes of vibration could be resolved and counted in the Fourier transform of each transmitted ultrasonic pulse. A statistical treatment of the data, designed to account for the possibility of missing modes, was developed, yielding a robust method for measuring the density of states. In the strong-scattering regime, the data are in good agreement with a simple model based on mode conservation, though the density of states significantly exceeds the predictions of the Debye approximation at low frequencies. At intermediate frequencies, an average density of states of 47.1 ± 0.3 MHz⁻¹ mm⁻³ was found, with a frequency dependence of f^(0.01 ± 0.04).