Universität Stuttgart
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Item Open Access Ultrafast spectroscopy of single quantum dots(2012) Wolpert, Christian; Lippitz, Markus (Juniorprofessor Dr.)In this thesis, the coherent interaction of single semiconductor quantum dots and ultrafast optical pulses is studied. Under certain conditions, localized exciton transitions in quantum dots can be seen as semi-isolated two-level systems. While this description is sufficient for the explanation of some observations in coherent experiments, it is sometimes necessary to explicitly consider coupling of the discreet quantum states confined to the dot with the environment. We start out from simple, classical examples of coherent spectroscopy and then turn towards experiments where the interaction with the vicinity of the dot becomes an important factor. First, a novel method for transient differential reflectivity spectroscopy of single quantum systems is introduced. It is a pure far-field optical technique which does not require any sophisticated sample preparation steps which makes it applicable to a broad range of structures. Pump pulses excite the sample structure and probe pulses read out the pump-induced changes in the system after a variable delay time. In the case of a single dipole, the signal is given in the form of the spectral inteferogram between the backscattered wave from the particle and the probe light which is reflected at the sample surface. This form of homodyne detection amplifies the weak scattered wave from the particle and thus makes this kind of spectroscopy for single quantum dots feasible. In the remainder of this thesis our spectroscopic method is applied to either characterize the coherent properties of single quantum dots, to prepare and read-out a desired quantum state or to deliberately manipulate them. Coherence times and oscillator strengths are determined for localized exciton transitions. Arbitrary population states can be written by driving coherent population oscillations using resonant pulses, while entangled superpositions of two exciton states in a single dot are investigated by quantum beats on transient differential spectra. We finally exploit the interaction between the dot and a nearby absorbing layer to switch the dot's absorption spectrum on ultrafast timescales via light-induced transient electric fields.Item Open Access Role of disorder and interactions on the surface of topological superconductors(2015) Queiroz, Raquel; Metzner, Walter (Prof. Dr.)In this work we study the surface properties of topological systems, with a special focus on topological superconductors without inversion symmetry. These materials provide a rich playground for multiple topological phenomena, showing boundary modes with linear and (or) flat dispersion arising from complex nodal structures. A remarkable characteristic of topological phases is their robustness to local perturbations. In the present work, we explore the extent to which this robustness can be generalized to gapless topological phases. We numerically test the robustness of topological boundary modes against local disorder and explore the contrast between different disorder strengths and distributions. Additionally, we study the interplay between topology and electron-electron interactions at the surface of nodal superconductors, where the infinitely degenerate flat bands are susceptible to spontaneous symmetry breaking. Finally, we briefly look into possible symmetry preserving interactions that can lead to the destruction of the boundary modes.Item Open Access Phase transitions in single layer and bilayer quantum Hall ferromagnets(2004) Höppel, Lutz W.; Klitzing, Klaus von (Prof. Dr.)A remotely doped GaAs wide quantum well (WQW) of 77 nm width is used to explore ferromagnetic phase transitions (FPTs), which occur due to crossings of Landau levels (LLs), using magneto-transport at low temperatures. An in-situ grown back gate and an evaporated front gate allow to control the electron density confined to the WQW and its distribution. FPTs are indicated by the loss of the quantum Hall effect (QHE) of a particular filling factor (ff) over a critical density range. A theoretical description is developed which assigns a pseudospin to the two crossing LLs. The pseudospin anisotropy energy determines how the system evolves when passing an FPT. In the regime of the integer QHE (IQHE) the electron density is adjusted that high that the two lowest subbands (offset by BAB of the order of 1 meV) are occupied (bilayer regime) leading to two intersecting LL fan-charts. The two FPTs involving ff = 4 exhibit narrow critical density ranges in contrast to ff = 3 and ff =5 signaling easy-axis and easy-plane anisotropy, respectively. The critical densities or magnetic fields (BC) shift to higher values with imbalance s (defined as the normalized density difference between the two layers) in a quadratic manner due to the equivalent increase of BAB. The critical density ranges of ff = 4 widen with s most probably due to a gradual changeover to easy-plane anisotropy, as predicted. A quantitative analysis of the FPTs yields a six-fold enhancement (Z) of the Zeeman splitting (EZ). Substituting one electron and two flux quanta by one composite Fermion (CF) maps the regime of the fractional QHE (FQHE) to the one of the IQHE. The orbital energy splitting is quantified by the CF cyclotron energy (EC) which scales as the Coulomb energy. The ff = 2/3 with two fully occupied CF LL (CF-ff = 2) gives rise to two FPTs. One FPT involves a change from a spin unpolarized to a spin polarized system (spin FPT) and occurs as a competition between EC and EZ. The finite thickness l of a single electron layer is tuned by varying the tilt of the WQW potential thus influencing EC since EC depends inversely on the average inter-electron distance. The latter is a function of the magnetic length lB and l (measured as FWHM and deduced from self-consistent simulations). EZ depends linearly on the effective g factor (-0.44 for bulk GaAs) and the enhancement Z. BC is found to vary from 4.5 down to 2.5 T by changing the electron distribution from squeezed at one of the edges of the WQW to very broad when centered in the WQW. A fit of BC in dependence of l based on the equality EC = EZ yields Z = 6 as upper limit. In the case of narrow (< 22 nm) QWs the reduction of the absolute value of g due to confinement effects increases BC. Widely spreading BC values, as reported in the literature, thus arise from heterostructure design and sample specific properties affecting l and g. Spin flip-flop processes connecting electron and nuclear spin system via the hyperfine coupling become apparent at the spin FPT because the nuclear magnetic field (BN), which is a function of the nuclear spin polarization, exclusively affects EZ thus altering BC. BC is thus a probe for the electron-nuclear-spin interaction. The strength of the hyperfine coupling is controlled by changing the ff. The time scale t1 to equilibrium between the two spin systems is found to be 75 s at ff = 0.5 and less than 3 s at ff = 0.9. An as short t1 time at ff = 1 as at ff = 0.9 indicates that low energy excitations, which promote flip-flop processes are not only provided by Skyrmions. BN is 0.4 T at the lowest temperature (25 mK) and opposite to the external field and an increasing DC-current (up to 60 nA) reduces BN by up to 100 mT. The Curie-temperature of the spin FPT is determined to be 170 mK. The second FPT involves a mixing of CF LLs from different subbands and occurs as a competition between BAB and EC in the bilayer regime and leads to a loss of coherence between the electron layers, known as one-component to two-component phase transition, due to the layer separation which increases with density. BC is found to be 8.7 T when s = 0. A thermal activation study reveals that an excitation of the system close to the FPT is accompanied by up to eight pseudospin flips suggesting easy-axis anisotropy and the existence of bilayer Skyrmions as predicted. BC increases with s in a quadratic manner. The bilayer unique QHE at ff = 1/2 is investigated and found to be most pronounced at a density close to the 1C-2C phase transition supporting theory which attributes the stabilization of this QHE to comparable inter- (BAB) and intra-layer (EC) Coulomb correlation. The finite longitudinal resistance close to the spin FPT is accompanied by sudden jumps if explored in a 18 nm narrow QW at the lowest temperature and slow sweep rates (< 0.05 T/min). These jumps resemble similarity to Barkhausen jumps and may reflect discontinuous changes of electron spin domains.Item Open Access High pressure study of high-temperature superconductors(2014) Souliou, Sofia-Michaela; Keimer, Bernhard (Prof. Dr.)The current thesis studies experimentally the effect of high external pressure on high-Tc superconductors. The structure and lattice dynamics of several members of the high-Tc cuprate and Fe-based superconductors families were investigated by means of Raman spectroscopy and x-ray diffraction under well-controlled, hydrostatic high pressure and low temperature conditions. The lattice dynamics of the high-Tc superconductor YBa(2)Cu(3)O(6+x) have been investigated systematically by Raman spectroscopy as a function of doping (x = 0.95, 0.75, 0.60, 0.55, and 0.45) and external pressure. Under ambient pressure conditions, in addition to the Raman modes expected from group theory, we observe new Raman active phonons upon cooling the underdoped samples, at temperatures well above the superconducting transition temperature. The doping dependence and the onset temperatures of the new Raman features suggest that they are associated with the incommensurate charge density wave (CDW) state recently discovered in underdoped cuprates using synchrotron x-ray scattering techniques. Under high pressure conditions (from 2 to 12 GPa), our Raman measurements on highly ordered underdoped YBa(2)Cu(3)O(6.55) samples do not show any of the new Raman phonons seen at ambient pressure. High pressure and low temperature Raman measurements have been performed on the underdoped superconductor YBa(2)Cu(4)O(8). A clear renormalization of some of the Raman phonons is seen below Tc as a result of the changes in the phonon self-energy upon the opening of the superconducting gap, with the most prominent one being that of the B1g-like buckling phonon mode. The amplitude of this renormalization strongly increases with pressure, resembling the effect of hole doping in YBa(2)Cu(3)O(6+x). At 10 GPa, the system undergoes a reversible pressure-induced structural phase transition to a non-centrosymmmetric structure (space group Imm2). The structural transition is clearly reflected in the high pressure Raman data through the appearance of several new modes, allowing us to map in detail the (P,T) phase diagram and determine the transition line between the two phases. In the new phase, the renormalization of the buckling mode is completely suppressed, while no anomalies are observed in any of the other Raman active phonons. According to ab initio calculations, the coupling of the buckling mode to the electronic system is not significantly affected by the structural phase transition. The absence of phonon renormalizations in the presence of sizable electron-phonon coupling, indicate that, in contrast to earlier transport studies, YBa(2)Cu(4)O(8) is not superconducting anymore under hydrostatic pressures higher than 10 GPa. Finally we proceeded with the investigation of the high pressure structural and vibrational properties of SmFeAsO, a member of the "1111" family (space group P4/nmm) of the Fe-based superconductors, in which superconductivity is commonly induced either by substituting F/H for O or by applying high pressures on the parent magnetic compound. The magnetic transition of the undoped compound is accompanied with a tetragonal-to-orthorhombic structural distortion, both of which are commonly suppressed upon the emergence of superconductivity. In the SmFeAsO(x)F(1-x) system while the magnetic transition is totally suppressed already at low doping levels, structural studies have reported either the gradual suppression of the orthorhombic distortion or its retention over a wide regime of the superconducting phase. We addressed this controversy using high pressure as an alternative tuning parameter to suppress the magneto-structural transition and induce superconductivity in the parent compound. Our high pressure, low temperature x-ray diffraction measurements on single crystals of SmFeAsO have revealed that the tetragonal-to-orthorhombic transition survives with the application of high pressures up to 85 kbars. In addition, our Raman data reveal a linewidth renormalization of the c-axis polarized A1g and B1g Raman phonons through the magnetic transition, similar to the one previously observed in the "122" family and attributed to the opening of the spin density wave gap. The renormalization is gradually suppressed under high pressure, in line with an earlier high pressure magnetization study which reported the pressure-induced decrease of the magnetic transition temperature. The linewidth anomaly disappears at 8 GPa suggesting the complete suppression of the magnetic transition at this pressure.Item Open Access Interaction of superconductivity and ferromagnetism in YBCO/LCMO heterostructures(2005) Soltan, Soltan; Dressel, Martin (Prof. Dr.)It has been shown that bilayers grown out of spin-polarized LCMO and superconducting YBCO show a variety of new physical phenomena. The transition temperatures T_(c) and T_(Curie), the critical current density in the superconductor j_(c) and even the normal state resistance can be influenced by external parameters and/or the sample geometry. These bilayers might be good candidates for technical applications in the near future.Item Open Access Probing the liquid and solid phases in closely spaced two-dimensional systems(2014) Zhang, Ding; von Klitzing, Klaus (Prof. Dr.)Gas, liquid and solid phases are the most common states of matter in our daily encountered 3-dimensional space. The school example is the H2O molecule with its phases vapor, water and ice. Interestingly, electrons - with their point-like nature and negative charges - can also organize themselves under certain conditions to bear properties of these three common phases. At relatively high temperature, where Boltzmann statistics prevails, the ensemble of electrons without interactions can be treated as a gas of free particles. Cooling down the system, this electron gas condenses into a Fermi liquid. Finally, as a result of the repulsive Coulomb forces, electrons try to avoid each other by maximizing their distances. When the Coulomb interaction becomes sufficiently strong, a regular lattice emerges - an electron solid. The story however does not end here. Nature has much more in store for us. Electronic systems in fact exhibit a large variety of phases induced by spatial confinement, an external magnetic field, Coulomb interactions, or interactions involving degrees of freedom other than charge such as spin and valley. Here in this thesis, we restrict ourselves to the study of electrons in a 2-dimenisonal (2D) plane. Already in such a 2D electron system (2DES), several distinct states of matter appear: integer and fractional quantum Hall liquids, the 2D Wigner solid, stripe and bubble phases etc.. In 2DES it is sufficient to sweep the perpendicular magnetic field to pass from one of these phases into another. Experimentally, many of these phases can be revealed by simply measuring the resistance. For a quantum Hall state, the longitudinal resistance vanishes, while the Hall resistance exhibits a plateau. The quantum Hall plateau is a manifestation of localization induced by the inevitable sample disorder. Coulomb interaction can also play an important role to localize charges. Even in the disorder-free case, electrons - more precisely quasi-particles in the partially filled Landau levels - can crystallize into a Wigner crystal. The Wigner crystal is bound to get pinned and hence localizes electrons in the bulk. This may cause an increase of the quantum Hall plateau width. To unveil the existence of such a solid, one has to go beyond standard transport investigations. Both microwave and NMR experiments have shown strong evidences for Wigner crystal formation. In Part I of the thesis, we present measurements of a thermodynamic quantity - the chemical potential. We provide further insight into this solid phase by studying the B-field as well as temperature dependence of the electron crystallization. The sensitive technique that we employ to measure the chemical potential is developed on a GaAs heterostructure with two quantum wells. In fact, in the presence of a perpendicular magnetic field this bilayer system hosts a unique quantum Hall state when each layer has a half filled Landau level. An electron residing in one layer can pair up with an empty state in the opposite layer and excitons may form. These excitons are believed to form an exciton condensate under appropriate conditions. Part II of this thesis is devoted to the understanding of this correlated state. We employ a single electron transistor to probe the chemical potential - more directly its derivative with respect to density, the compressibility - around the νtot=1 quantum Hall state. We then compare excitation gap obtained from this approach with the gap determined from thermally activated transport studies. Our results help to clarify the nature of the excitations at νtot=1. Apart from the thermodynamic measurement, we also perform tunneling experiments on the bilayer. A systematic study of the interlayer tunneling on the distance between the two layers is carried out. Also, we investigate the tunneling on a bilayer with a constriction in the center. Interesting phenomena are observed such as an oscillating pattern in the tunneling current as we gradually open the constriction. While some of our results await further clarifications, one can safely conclude that the electronic bilayer offers intriguing physics, even two decades after its debut.Item Open Access Resonant X-ray scattering studies of ruthenium oxides and ruthenocuprates(2009) Bohnenbuck, Britta; Keimer, Bernhard (Prof. Dr.)The magnetic and orbital properties of the ruthenium oxides Ca3Ru2O7 and Mn doped Sr3Ru2O7 and the ruthenocuprate RuSr2GdCu2O8 were investigated using resonant and high-energy x-ray diffraction. Bilayered Ca3Ru2O7 is a paramagnetic metal at high temperatures and orders antiferromagnetically at T_N=56K. A second phase transition to a less conductive state is observed at T_MI=48K. This transition is accompanied by abrupt structural changes and a reorientation of the magnetic moment. In addition, there is experimental evidence for the existence of orbital order below T_MI. Our resonant x-ray diffraction studies at the Ru L-absorption edges were focused on the investigation of the magnetic reflections (001) and (110). The observation of a magnetic signal at these reciprocal space positions is in full agreement with an A-type antiferromagnetic structure, consisting of ferromagnetic bilayers coupled antiferromagnetically along the c-axis. Based on the azimuthal angle dependence of the signals, the direction of the magnetic moment was determined to lie along the b-axis below T_MI and along the $a$-axis between T_MI and T_N. The origin of the reorientation of the magnetic moment at T_MI is not yet completely understood. However, it might result from the strong spin-orbit coupling which presumably causes an unquenched orbital magnetization. The latter might then induce additional terms in the spin Hamiltonian that are responsible for the reorientation of the magnetic moment. Although various experiments have given indirect evidence of orbital order below T_MI, we did not detect any orbital signal within the experimental sensitivity. This indicates that the orbital ordering parameter is significantly weaker than in the single layered counterpart Ca2RuO4, which is presumably due to residual charge or orbital fluctuations in the insulating state. RuSr2GdCu2O8 exhibits long range magnetic order and superconductivity within a broad coexistence range. Only limited information about the magnetic structure has been available so far, as most studies were performed on powder samples due to the small size of available crystals. In this situation, resonant x-ray diffraction at the Ru L-absorption edges has turned out to be the ideal tool for the investigation of RuSr2GdCu2O8 since it is sensitive to magnetism, but does not depend on a large crystal mass. Our single crystal studies of the magnetic reflections (1/2 1/2 1/2) and (1/2 1/2 3/2) indicate a G-type antiferromagnetic structure, characterized by a doubling of the unit cell along all three crystallographic directions. From the azimuthal angle dependence of the magnetic signal, we deduced a magnetic moment direction along a low symmetry axis with substantial components parallel and perpendicular to the RuO2 planes. These findings are consistent with previous neutron powder diffraction results and magnetization data. A symmetry analysis in conjunction with a recent crystallographic study revealed that the experimentally observed G-type antiferromagnetic structure needs to be accompanied by an additional ferromagnetic in-plane component, which alternates between neighboring RuO2 layers. This ferromagnetic mode corresponds exactly to the one deduced from nuclear and ferromagnetic resonance experiments. Therefore, our resonant x-ray diffraction data reconcile a variety of apparently contradictory results on the magnetic structure of RuSr2GdCu2O8 and thus resolve a big controversy in the experimental literature. Bilayered Sr3Ru2O7 has attracted a lot of interest in the past years due to the observation of the quantum critical behavior which is related to a metamagnetic transition. In the ground state, the material is a paramagnetic metal and shows Fermi liquid behavior below 10K. Upon substituting Mn for Ru, an insulating antiferromagnetic state is induced; its transition temperature varies with the Mn concentration. Using resonant x-ray diffraction at the Ru L-absorption edges, we investigated the antiferromagnetic structure of 10 Mn substituted Sr3Ru2O7. Our studies of the superstructure reflections (1/4 1/4 0) and (3/4 3/4 0) indicate that the magnetic order is essentially two dimensional and that the magnetic moments are aligned along the c-axis. In combination with a previous neutron powder diffraction study, which was carried out on 5% Mn substituted Sr3Ru2O7, our results suggest an up-up-down-down spin arrangement in the RuO2 planes, which is independent of the Mn concentration. This implies that an antiferromagnetic instability is already present in the parent compound Sr3Ru2O7. Interestingly, the anisotropic resistivity behavior, observed in the nematic phase of Sr3Ru2O7, could be explained assuming the same up-up-down-down spin arrangement as in Mn substituted Sr3Ru2O7. If the two phases are in fact identical, has to be checked by a detailed single crystal neutron diffraction study including a complete structure refinement.Item Open Access 2-dimensionaler Ladungsträgertransport in Graphen und einkristallinen organischen Halbleitern(2008) Ulbricht, Gerhard; von Klitzing, Klaus (Prof. Dr.)Ziel dieser Arbeit war die Präparation und Untersuchung neuartiger 2-dimensionaler Systeme. Zu diesem Zweck wurden sowohl auf Einkristallen der organischen Halbleiter Tetracen und Perylen als auch auf Graphen-Mono- und Doppellagen Feldeffekttransistoren präpariert und untersucht. Wird die Oxidation der Tetracen-Kristalle erfolgreich verhindert, so kann bei Raumtemperatur in Lochleitung ein deutlicher Feldeffekt gemessen werden, Elektronenleitung jedoch konnten wir bei keiner Temperatur beobachten. SCLC-Messungen haben eine Trapkonzentration von minimal 5*10E14 pro cm³ gezeigt. Bei Raumtemperatur wiesen unsere Tetracen-FETs Lochbeweglichkeiten von bis zu 0,6 cm²/Vs auf, welche beim Abkühlen jedoch kontinuierlich schlechter wurden, Lochtransport konnte bis hinunter zu 21 K beobachtet werden. SCLC-Messungen an Perylen-Kristallen haben eine Reinheit von minimal 1,8*10E12 Traps pro cm³ für Elektronen und 2*10E13 Traps pro cm3 für Löcher ergeben. Dennoch konnte bei allen untersuchten Temperaturen nur Lochleitung beobachtet werden, was vermutlich auf mangelnde Elektroneninjektion zurückzuführen ist. Bei Raumtemperatur waren Lochbeweglichkeiten von bis zu 3*10E-3 cm²/Vs messbar. Auch in Perylen-FETs nahm der Strom beim Abkühlen stetig ab, so dass unter 120 K keine Transportmessungen mehr möglich waren. Sowohl die präparierten Graphen-Mono- als auch Doppellagen zeigten deutlich den QHE und SdH-Oszillationen. In Graphen-Monolagen ist die Energie der Ladungsträger proportional zu ihrem Impuls, was im QHE zu Plateaus bei den Füllfaktoren 2, 6, 10, ... führt, wodurch Graphen-Monolagen zweifelsfrei nachgewiesen werden können. Die Ladungsträgerbeweglichkeit erreichte in unseren Proben bis zu 6000 cm²/Vs, wobei kein nennenswerter Unterschied zwischen Elektronen & Löchern festgestellt werden konnte. Mit Hilfe eines Raster-SET-Mikroskops konnten wir in Zusammenarbeit mit der Gruppe von A. Yacoby zeigen, dass der Dirac-Punkt an unterschiedlichen Stellen der Monolage bei unterschiedlichen Gate-Spannungen erreicht wird, am Punkt des maximalen elektrischen Widerstands bilden sich demnach unregelmäßig geformte Bereiche mit Elektronen- bzw. Lochüberschuss.Item Open Access Investigation into the magnetic and the structural properties of two low-dimensional antiferromagnets TiPO4 and CrOCl(2014) Reuvekamp, Patrick Gerald; Keimer, Bernhard (Prof. Dr.)Titanium (III) phosphate TiPO4 (3d1 electronic configuration with S = 1/2) is a one-dimensional quantum antiferromagnet exhibiting non-conventional spin-Peierls behaviour at low temperatures. Chromium oxychloride CrOCl (3d3 electronic configuration with S = 3/2) is a two-dimensional antiferromagnet consisting of ferromagnetic spin chains interconnected by competing anti and ferromagnetic spin exchanges interactions. The magnetic and the structural properties of these compounds are intimately related via magnetoelastic coupling. Incommensurate and commensurate phases are observed at low temperatures in both compounds. These systems are investigated using various experimental techniques, i.e. magnetic susceptibility, heat capacity, dielectric, Raman scattering and electron paramagnetic resonance measurements. The mangetoelastic coupling in these compounds is explored using a thermal expansion cell commissioned and tested in the course of this dissertation work. TiPO4 consists of quasi one-dimensional Ti3+ spin S = 1/2 chains running along the c-axis with strong antiferromagnetic intrachain coupling (Jintra =-965 K, Jinter= -20 K). A two-stage spin-Peierls transition occurs in TiPO4 consisting of two successive phase transitions at Tc1 = ~74 K and Tc2 = ~110 K. The temperature dependence of the lattice parameters as well as the magnetic field and the pressure dependence of the two phase transitions are studied extensively. The results are analyzed and discussed in terms of the spin-Peierls theory and the crystallographic data. CrOCl is characterized by an intricate two-dimensional intrachain and interchain spin exchange scenario. A low temperature monoclinic distortion occurs at the onset of the commensurate antiferromangetic order at TN = ~13.5 K. The commensurate phase is preceded by an incommensurate antiferromagnetic phase starting below 27 K. Ferromagnetic spin exchange interactions are dominant in contrast to the low temperature antiferromagnetic ordering. In low temperature regime (T < 30 K), various measurement techniques are employed to construct extended (H, T) magnetic phase diagrams for H par c and H per c. The phase diagrams are very complex resulting from the magnetic frustration of the competing spin exchange interactions. The spin exchange interactions are investigated by employing spin polarized density functional theory calculations and classical mean-field/Monte Carlo simulations. Using the density functional theory results, the extended (H, T) magnetic phase diagrams are discussed in terms of the ANNNI model.Item Open Access Automated parametric Rietveld refinement and its application to two dimensional X-ray powder diffraction experiments(2011) Rajiv, Paneerselvam; Joswig, Manfred (Prof. Dr.)Parametric Rietveld refinement has opened new possibilities to simultaneously refine multiple powder diffraction patterns collected in in situ 2D experiments; in that way the models of crystallographic variables that changes with external variables can be introduced into the refinement. The substitution of a variable with its model during the refinement has several advantages, including the improved precision of variables, direct extraction/refinement of some parameters from powder data which is otherwise impractical (e.g., activation energy), etc. The basic requirement for the realization of sequential/parametric refinements (or Whole Powder Pattern Fit-WPPF) in 2D X-ray powder diffraction (XRPD) is a robust software that handles the data and performs fast WPPF. This concern has been primarily addressed in this thesis with the help of a software, in combination with the existing total pattern analysis software (Topas). The developed software could considerably speedup and automate the sequential/parametric quantitative analysis of large number of 2D powder data, which is in general a monotonous and time consuming task. The software also provides routines that automatically determines the reconstructive phase transitions of samples from the 2D powder data and facilitates the independent refinements (or WPPFs) of the determined phases. Two practical scientific applications of parametric Rietveld refinement method have been demonstrated with the assistance of the developed program. The first application concerns the kinetic analysis of several polymorphs and polymorphs-additives mixtures of copper phthalocyanine (CuPC). The reaction rate constant and the order of reactions involving the phase transitions of various forms of CuPC were directly extracted from the isothermal experimental data by introducing the Johnson-Mehl-Avrami-Kolmogorov relation as a model of the phase fraction during the multi phase parametric Rietveld refinement. Parametric refinements could be successfully performed for most of the CuPC data collected in the experiment, however the convergence of some of the refinements showed a strong dependence on the reaction rate. In many cases, the precision of the refined parameters could be improved considerably when the data collected between the optimal time steps alone were used in the refinement. The second application demonstrates the feasibility of the parameterization of crystallite size with respect to the annealing time/temperature. Some of the data samples used in the kinetic analysis (CuPC) and the temperature dependent nanocrystalline TiO2 data were used in this demonstration. The success of the parameterization of crystallite size depended strongly on the quality of the data used, on the uniformity of the variation of the crystallite size with time/temperature and also on the correctness of the model that describes the crystallite size variation with time/temperature. This application in its present form is general; as such it can be used for stabilizing other variables during parametric refinement.