14 Externe wissenschaftliche Einrichtungen
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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 Organic solar cells : correlation between molecular structure, morphology and device performance(2010) Bruder, Ingmar; Weis, Jürgen (Prof. Dr.)The development of efficient organic solar cells could be one approach to provide mankind with cheap, sustainable and ecofriendly energy. The introduction of bulk heterojunction and tandem device architectures led recently to devices with power conversion efficiencies close or even higher than n = 6%, showing the potential of organic photovoltaics. Nevertheless, to compete for the foreseeable future to inorganic solar cell technologies, the power conversion efficiencies of organic solar cells have to rise further in the range of 10 % into 15 %. Since the functioning of organic photovoltaics is based on a complex interplay of the electronic properties of its molecular components, it is desirable for an efficient evolution, to identify structural and energetical key characteristics of the molecular components that can lead to efficiency gains. Furthermore, there are virtually no limits for the synthesis of new photoactive materials for the use in organic photovoltaics. Therefore, it is crucial for the device fabrication as well as under a chemical point of view, to narrow potentially promissing classes of molecules and their derivatives under certain physical criteria. One aim of this study was to find and identify so far unknown design criteria for molecules providing high efficiencies in organic solar cells. Thus, the question was raised: What is the physical cause for the differing performance of various metal-phthalocyanines (MPc's with M = Zn, Cu, Ni, Fe) in organic solar cells. Therefore, MPc/C60 based bilayer heterojunction solar cells were fabricated showing a clear dependence of the optimal layer thickness and overall performance on the employed MPc material. Initially, the origin of these differences were explored through structural analysises by AFM and high resolution XRPD measurements on powder and evaporated thin films. The optical properties of the metal phthalocyanines were investigated by solidstate fluorescence and absorption measurements. The lowest excited states of the MPc series were explored by correlated multi-reference ab inito calculations. A high open circuit voltage Voc of a solar cell is a prerequisite for high efficiencies. Unfortunately, the Voc of small molecule based organic solar cells is usually considerably lower than the HOMO-LUMO offset of the device, which determines the theoretical maximum of the Voc in a first approximation. Thus, the question was investigated: What causes the difference between the possible open-circuit voltage and the actual measured voltage and how can this difference be reduced? To answer this question, heterojunction solar cells were produced containing ZnPc or one of the novel synthesized Phenyl-ZnPc, Naphtyl-ZnPc or Anthracenyl-ZnPc as p-conducting and C60 as n-conducting organic layers. By adding the respective aryl substituents to the ZnPc core, the polarizability of the molecules was successively increased. Concurrently, an increase of the Voc from 550 mV to 790 mV by using the highly polarizable Anthracenyl-ZnPc instead of ZnPc was achieved. Quantum mechanical calculations, simulating the charge separation mechanism at the DA-interface of Phenyl-ZnPc/C60 and Naphtyl-ZnPc/C60 showed, that the interplay between characteristic packing and polarization effects could lead to considerably different Coulomb interactions of the electron-hole pairs at the DA-interface. The control of the conduction type and Fermi-level of semiconductors is crucial for the realization of all optoelectronic devices. In inorganic as well as in organic devices this can be achieved by defined doping of appropriate areas within the device. Thus, it has been investigated, how the molecular structure of a dopant should be in order to reduce its diffusivity and increase the evaporation temperature to allow a more efficient processing of the compound. As a result, the novel p-dopant 2,3-di(N-phthalimido)-5,6-dicyano-1,4-benzoquinone (BAPD) was synthesized and compared to the state-of-the-art dopant F4TCNQ. In addition to basic and applied physical questions, I worked on the development of new, efficient solar cell architectures during my PhD thesis. In the course of this work it could be shown, that an efficient organic tandem cell can be prepared from a solid state dye-sensitized solar cell combined with a vacuum-deposited bulk heterojunction solar cell. The complementary absorption of the dyes, as well as an adequate serial connection of both subcells, leads to a high power conversion efficiency of n = (6.0±0.1)% under simulated 100 mW/cm2 AM 1.5 illumination.Item Open Access Spectroscopic study of CaMnO3/CaRuO3 superlattices and YTiO3 single crystals(2009) Yordanov, Petar; Keimer, Bernhard (Prof. Dr.)The first two sections of Chapter 1 give a general overview of the research topics and experimental methods discussed in the thesis. Further on, in Chapter 2, some of the most important characteristics and mechanisms underlying the physics of transition metal oxides are presented. As the experimental part of the thesis includes studies on manganites and titanates, these two classes of compounds are exemplified in the exposition of Chapter 2. Several recent works in the emerging research field of transition metal oxide interfaces and superlattices are also discussed along with a brief introduction in x-ray spectroscopic methods with synchrotron radiation. Chapter 3 introduces the principles of optical spectroscopy and the simplest models for dielectric function, i.e., Lorentz oscillator and Drude dielectric function. The following Chapter 4 introduces two of the experimental techniques in optical spectroscopy, reflectance and spectroscopic ellipsometry. Further on, we describe the design of a new home-built apparatus for near-normal reflectance with high magnetic fields. Several critical technical details and findings during the assembling process are also discussed. Chapter 5 represents a comprehensive experimental spectroscopic study of a prototypical superlattice system made from an antiferromagnetic insulator CaMnO3 and a paramagnetic metal CaRuO3. The resulting interface ferromagnetic state was closely investigated by means of optical spectroscopy as well as by soft x-ray scattering and absorption methods. This study led us to the conclusion that magnetic bound states, i.e. magnetic polarons, have to be considered in the description of this SL system. Chapter 6 describes a polarized far infrared reflectance study with high magnetic field on the ferromagnetic Mott insulator YTiO3, single crystals. All 25 infrared-active phonon modes were observed. The temperature and magnetic-field dependence of the phonon modes revealed a weak spin-phonon coupling in YTiO3 and largely extended temperature range (up to TM ~ 80 - 100K), for the field-induced effects on the oscillator parameters. This later observation, uncovered short-range magnetic order state which remains even at temperatures as high as three times the temperature of the actual ferromagnetic transition of Tc ~ 30K. While a quantitative theoretical description of these data is thus far not available, they point to a complex interplay between spin, orbital, and lattice degrees of freedom due to the near-degeneracy of the Ti t2g orbitals in YTiO3.Item Open Access Unconventional properties of non-centrosymmetric superconductors(2010) Klam, Ludwig; Metzner, Walter (Prof. Dr.)A kinetic theory for non-centrosymmetric superconductors (NCS) is formulated for low temperatures and in the clean limit. The transport equations are solved quite generally for any kind of antisymmetric spin-orbit coupling (ASOC) in an extended momentum and frequency range. The result is a particle-hole symmetric, gauge-invariant and charge conserving description, which is used to calculate the current response, the specific heat capacity, and the Raman response function. A detailed analysis of the gauge invariance and the associated phase fluctuations of the superconducting order parameter revealed two gauge modes: the Anderson-Bogoliubov mode on the one side and a new gauge mode on the other side, which strongly depends on the symmetry of the ASOC. As application of the kinetic theory, the polarization-dependence of the T=0 electronic Raman response in NCS is studied for two important classes of ASOC with the representative systems CePt3Si and Li2PdxPt3-xB. Analytical expressions for the Raman vertices are derived, and the frequency power laws and pair-breaking peaks are calculated. A characteristic two-peak structure is predicted for NCS and might serve as an indicator for the unknown relative magnitude of the singlet and triplet contributions to the superconducting order parameter. An efficient numerical method is introduced in order to calculate the dynamical spin and charge response of CePt3Si, using an itinerant description for the electrons. With a realistic parameterization of the band structure, the nesting function, inelastic neutron scattering cross sections, and Kohn anomalies are calculated for a selected band in the normal non-magnetic state. From the spin and charge susceptibility, a superconducting pairing interaction is constructed for the weak-coupling gap equation. A sign analysis of the decoupled gap equation supports the experimental evidence of a strong triplet contribution to the order parameter in CePt3Si. In particular for this compound, it can be shown that an increasing Rashba-type of spin-orbit coupling strengthens the triplet contribution.Item Open Access Adiabatic transport in the quantum Hall regime : comparison between transport and scanning force microscopy investigations(2008) Dahlem, Franck; Von Klitzing, KlausIn this PhD work, the local potential distribution has been measured in high mobility 2DES under quantum Hall conditions. The 2DES embedded in a GaAs-AlGaAs heterostructure designed in a small Hall bar geometry shows intrinsic adiabatic transport features. Usually presented in the literature with the edge state picture, these features are the disappearance of peaks in the Shubnikov-de Haas oscillations, the extension of quantum Hall plateaus to lower magnetic fields and the existence of non-local resistances. Our local potential measurement via cryogenic scanning force microscopy presents another microscopic explanation of such adiabatic transport. The new picture is based on compressible and incompressible strips. An incompressible strip is a region in which the Fermi energy is located inside the energy gap (the electron density is constant and the electrostatic potential is changing) whereas a compressible strip occurs if the Fermi energy is pinning inside a Landau level (the electron density is changing and the electrostatic potential is screening). In previous work, the compressible and incompressible strips model has been successfully used to describe the quantum Hall effect. The present work demonstrates that the strips distribution accounts also for the adiabatic transport features observed on high mobility samples in the quantum Hall regime. Our research shows that in adiabatic situations, compressible regions with an unusual difference of electrochemical potential are found to coexist along the same edge due to an insulator-like incompressible strip in between and due to the lack of impurities scattering. Due to the high mobility and small size of the Hall bar, such non equilibrium survives along the complete length of the sample and determines the transport features. The insulator properties of incompressible strips in front of the alloyed ohmic contacts are found to be anisotropic with a dependency on the orientation of the contact borderline with respect to the crystal direction. The incompressible strips are broader -so more insulating- if they are located close to contact with an interface perpendicular to the [01-1] direction than if they are in front of contact with an interface parallel to the [01-1] direction. This finding gives a physical meaning to the term "non ideal contact" in the case of low resistive and ohmic contacts. Finally our results advertise that every 2DES is inhomogeneous. A 2DES is never a flat distribution of electron but it owns border with gradient of electron density even in front of metal contacts. These "Regular inhomogeneities" at the edges of the mesa and in front of contacts determines the insulator properties of the incompressible strips in high magnetic field and therefore the transport.Item Open Access Exzitonen in gekoppelten 2d Elektronen- und 2d Lochgasen(2001) Pohlt, Michael; Klitzing, Klaus von (Prof. Dr.)Gegenstand der Arbeit ist die Herstellung und Untersuchung von gekoppelten 2d Elektronen- und Lochsystemen. Für solche Systeme werden bei ausreichend geringem Abstand zwischen der Elektronen- und der Lochschicht auf Grund der anziehenden Coulombwechselwirkung neuartige Zustände des Vielteilchensystems erwartet. Bei tiefen Temperaturen sollen sich räumlich indirekte Exzitonen bilden und einen Kosterlitz Thouless Phasenübergang zeigen. Es wurden Abstnde zwischen dem Elektronen- und dem Lochsystem bis herunter zu 15,3 nm realisiert. Zunächst wird eingehend beschrieben, wie im GaAs/AlGaAs Materialsystem ein Transistor aufgebaut werden kann, bei dem sich eine Elektronen- und eine Lochschicht in unmittelbarer Nähe zueinander befinden. Beide leitfähigen Schichten besitzen mehrere Kontakte; zu deren Herstellung wurde ein Verfahren aufgebaut und entwickelt, das auf der Kombination von Molekularstrahlepitaxie und fokussierter Ionenstrahlimplantation, die während einer Wachstumsunterbrechung durchgeführt wird, basiert. Im weiteren wird beschrieben, wie die Prozessierung der Probe durchgeführt werden muß und die Kontakte angeschlossen werden. Es werden Transportmessungen gezeigt und die grundsätzlichen Eigenschaften des neuartigen Doppellagentransistors demonstriert. Im zweiten Teil der Arbeit werden die thermodynamischen Eigenschaften des 2d Elektronen- und Lochsystems mit Hilfe von Kapazitätsmessungen untersucht. Die Magnetooszillationen der Kapazitätsmessungen lassen die unabhängige Bestimmung der Dichte des Ladungssystems zu und sind durch die magnetfeldabhängige Kompressibilität des Elektronensystems verständlich. Bei geringsten und identischen Dichten zwischen dem Elektronen- und dem Lochsystem zeigt sich bei tiefsten Temperaturen ein Peak in der Kapazität, der durch die Bildung von Exzitonen erklärt werden kann. Das Verhalten des Peaks in Abhängigkeit der Temperatur und dem Magnetfeld wird diskutiert.Item Open Access Raman scattering, magnetization and magnetotransport study of SrFeO3-delta, Sr3Fe2O7-delta and CaFeO3(2008) Damljanovic, Vladimir; Keimer, Bernhard (Prof. Dr.)In this thesis we have determined the Raman spectra as well as the magnetization, resistance and magnetoresistance of the compounds SrFeO3-delta, Sr3Fe2O7-delta and CaFeO3 as a function of temperature. These materials are interesting because they contain iron in the unusually high oxidation state +4, which has the same electroncic configuration as the Mn3+ ion in LaMnO3, a material that shows the giant magnetoresistance effect when doped with calcium or strontium. A novel aspect of the work described in this thesis is that it was performed on single crystals with controlled oxygen stoichiometry. In the compound SrFeO3-delta, delta can vary continuously in the range 0 to 0.5. The materialexhibits the following crystal structures due to oxygen vacancy ordering: cubic (delta=0), tetragonal (delta=0.125), orthorhombic (delta=0.25) or brownmillerite (delta=0.5). For other values of delta the material is a mixture of those phases. The cubic phase has the ideal cubic perovskite structure. In this thesis we describe the preparation of nearly stoichiometric SrFeO3-delta with delta<0.05. The Raman spectrum of a sample annealed under 5kbar of pure oxygen showed no phonon modes, as expected from a group-theoretical analysis of the ideal perovskite structure. The Mößbauer spectra on this sample shows that it contains 5.4% of the tetragonal phase. In another crystal annealed at oxygen pressure 40kbar Mößbauer spectra did not show any sign of additional phases, confirming that the sample is fully stoichiometric. In addition to the experiments we have performed lattice dynamics calculations for the ideal composition SrFeO3.00 in order to assign the phonon modes observed in infra-red experiments. The calculation accurately reproduces all frequencies observed. We have also measured the Raman spectra of the tetragonal phase in the temperature range 13K to 300K. While only three peaks can be resolved at room temperature, additional modes appear in the spectrum below the charge-ordering transition at 70K. This confirms that the crystal structure changes below this temperature. We have also measured the Raman spectra of the orthorhombic phase in the temperature range 6K to 475K. The paremeter delta in Sr3Fe2O7-delta can vary continuously between 0 and 1. We have measured the temperature dependence of the magnetization for the magnetic field along high symmetry axes of the crystal. We have also performed neutron diffraction measurements demonstrating that the magnetic moments are ordered in a helical structure. The resistivity and the magnetoresistance were measured in the range 10K to 300K. Finally we have measured the Raman spectra of the same sample in the temperature range 15K to 440K. In order to assign the observed modes, we have performed lattice dynamics calculations based on the published crystal structure of Sr3Fe2O7. The CaFeO3 compound has an orthorhombic crystal structure above 290K, which changes to monoclinic below this temperature. Here we describe the preparation of stoichiometric CaFeO3 single crystals by high pressure oxygenation of as-grown CaFeO2.5 samples, using KClO4 as an oxygen source. The powder X-ray diffraction pattern after annealing shows that the oxygen enrichment was successful. No magnetoresistance was observed within the experimental error up to magnetic fields of 9T. We have also measured Raman spectra of this material in the temperature range 15K to 300K. In contrast to tetragonal SrFeO2.875 these spectra are unaffected by the charge-ordering transition at 290K within the experimental sensitivity.Item Open Access Ultraschnelle Ladungsträgerdynamik in LTG-GaAs und ErAs:GaAs Übergittern : Grundlagen und Anwendungen(2002) Griebel, Martin; von Klitzing, Klaus (Prof. Dr.)Die Motivation für die Experimente dieser Arbeit entspringt dem Ziel, ultrahoch-zeitaufgelöste Transportmessungen an mesoskopischen Bauelementen durchzuführen. Derartige Messungen erfordern Zeitauflösungen weit unterhalb von 10 ps, gleichzeitig muss die verwendete Messmethode kompatibel zu tiefsten Temperaturen (T << 1 K) und hohen Magnetfeldern sein. Allein die geforderte Zeitauflösung schließt die Verwendung rein elektronischer Methoden zur Durchführung derartiger Experimente aus. In dieser Arbeit stellen wir ausgehend von der Methode des Photoleitungs-Samplings eine zu den Anforderungen mesoskopischer Bauelemente kompatible, integrierte Anordnung zur Durchführung hoch-zeitaufgelöster Transportexperimente vor, die sowohl die Erzeugung der hochfrequenten Signale als auch ihre Detektion und Konvertierung in quasi-DC Signale in unmittelbarer Nähe zum eigentlichen Untersuchungsobjekt innerhalb einer einzigen Probenstruktur ermöglicht. Da derartige Experimente zur Vermeidung übermäßiger Aufheizung durch Wärmestrahlung in fensterlosen Kryostaten betrieben werden sollten, wurde die Beleuchtung der Photoleitungs-Sampling Struktur durch kurze Laserpulse mithilfe optischer Fasern realisiert. Der Erfolg dieses Ansatzes hängt von der Verfügbarkeit photoleitender Materialien ab, die es einerseits erlauben, mithilfe kurzer optischer Pulse unter dem Einfluss tiefer Temperaturen und hoher Magnetfelder ultrakurze elektrische Pulse zu erzeugen und die andererseits zur monolithischen Integration mit den zur Herstellung mesoskopischer Bauelemente notwendigen Heterostrukturen geeignet sind. Der Schwerpunkt dieser Arbeit lag zunächst in der Untersuchung neuartiger photoleitender Materialien im Hinblick auf die Erfüllung dieser Kriterien. Besonderes Gewicht wurde auf die Aufklärung der für die Ladungsträgerdynamik relevanten physikalischen Mechanismen gelegt. Im Anschluss daran wurden die zur Erzeugung, Propagation und Detektion elektrischer Pulse mit Bandbreiten von einigen Terahertz notwendigen Methoden entwickelt und zur Verwendung unter dem Einfluss tiefer Temperaturen und hoher Magnetfelder optimiert. Ein Ausgangsmaterial für Photoleitungsschalter, das, wie wir zeigen konnten, den gestellten Anforderungen genügt, besteht aus einem Übergitter äquidistanter ErAs-Inselschichten in einer GaAs Matrix (ErAs:GaAs). Die Ladungsträgerdynamik in ErAs:GaAs wurde als Funktion der Übergitterperiode mithilfe von Autokorrelationsmessungen an Photoleitungsschaltern sowie mithilfe von Pulspropagationsexperimenten an koplanaren Streifenleitungen untersucht. Wir beobachten einen Anstieg der Elektronenlebensdauer um nahezu zwei Größenordnungen von 190 fs auf 17 ps bei einer Erhöhung der Übergitterperiode von 10 auf 400 nm. Dieses Verhalten kann im Rahmen eines Diffusionsmodells verstanden werden, das in Übereinstimmung mit den experimentellen Daten eine quadratische Abhängigkeit der Elektronenlebensdauer von der Übergitterperiode vorhersagt. ErAs:GaAs zeichnet sich nicht nur durch seine sehr kurze Elektronenlebensdauer aus, sondern besitzt darüber hinaus eine bislang in diesem Maße nicht beobachtete Abstimmbarkeit der Elektronenlebensdauer, eine hohe thermische Stabilität sowie zusätzliche, unabhängige Materialparameter zur Kontrolle des Dunkelstroms. Unter Verwendung dieses neuartigen Substratmaterials wurden Photoleitungssampling-Experimente durchgeführt, indem jeweils zwei Photoleitungsschalter in eine koplanare Wellenleiterstruktur integriert und über optische Monomodenfasern mit Subpikosekunden-Laserpulsen beleuchtet wurden. Für eine Propagationsdistanz von 1.5 mm konnten wir dabei eine Zeitauflösung von weniger als 2.0 ps erreichen. In Experimenten unter kryogenen Bedingungen erwies sich diese Zeitauflösung sowohl als temperatur- als auch als magnetfeldunabhängig. Ein numerisches Modell zur Beschreibung der Generation, Propagation und Detektion der elektrischen Pulse konnte die Dispersion der koplanaren Wellenleiter sowie die Kapazitäten der Photoleitungsschalter als limitierende Faktoren der Zeitauflösung identifizieren. Durch die Verringerung der Bandlücke des die ErAs-Inseln umgebenden Matrixmaterials können Photoleitungsschalter bei längeren Wellenlängen betrieben werden. Als besonders attraktiv erweist sich in diesem Zusammenhang InGaAs mit einer an InP Substrate angepassten Komposition. Dieses Material absorbiert bis zu Wellenlängen von 1.67 µm, so dass die für Kommunikationszwecke relevanten Wellenlängen abgedeckt werden können. In Photostrom-Autokorrelationsmessungen an Proben mit einer Übergitterperiode von 40 nm konnten wir eine Elektronenlebensdauer von 1.1 ps bei einer Wellenlänge von 800 nm erzielen. Eine Veränderung der Wellenlänge von 750 nm auf 1 µm ergab keine Veränderung der Ladungsträgerlebensdauer, so dass kurze Elektronenlebensdauern bis hin zu 1.67 µm erwartet werden können.Item Open Access A study of lattice dynamics in iron-based superconductors by inelastic light scattering(2013) Um, Youngje; Keimer, Bernhard (Prof. Dr.)After the discovery of high temperature (high Tc) superconductivity in copper oxide-based materials (cuprates) in 1986, this phenomenon was a unique property of the cuprates for more than 20 years. The origin of high Tc superconductivity is still under debate. In 2008, high Tc superconductivity was discovered in iron-based compounds. This discovery presents new opportunities for the development of a fundamental understanding of high Tc superconductivity. Density functional calculations indicate a weak electron-phonon coupling strength in iron-based superconductors and these suggest that superconductivity is not mediated by phonons. However, experimental report of a large isotope effect of the iron atoms on the superconductivity Tc suggests that phonons play an important role in iron-based superconductors. Motivated by these findings, this thesis presents a Raman scattering study of the lattice dynamics of the iron-based superconductors Fe1+yTe1-xSex, LiFeAs and NaFe1-xCoxAs as a function of chemical composition and temperature. In Fe1+yTe1-xSex, an unconventional linewidth broadening of the c-axis polarized Fe phonon of B1g symmetry is found with decreasing temperature, which indicates an unusual coupling between the phonon and iron excessinduced magnetic fluctuations in this compound. In LiFeAs, the Raman scattering data provide evidence for a weak electron-phonon coupling, which is consistent with non-phonon mediated Cooper pairing in this compound. In NaFe1-xCoxAs, upon cooling two features are observed: (i) an unconventional linewidth broadening of several phonons, which is indicative of spin fluctuation-phonon coupling, and (ii) a superconductivity-induced phonon lineshape renormalization, which can not be explained by standard model calculations.Item Open Access Proximity effects and Josephson currents in ferromagnet : spin-triplet superconductors junctions(2015) Terrade, Damien; Metzner, Walter (Prof. Dr.)Spin-triplet superconductivity, first attached to the description of He3, is now generally considered to also occur in heavy-fermions compounds and in perovskite ruthenium oxide Sr2RuO4. The latter material is especially interesting since many experiments show strong evidences for a unitary chiral spin-triplet state. Moreover, the recent fabrication of thin heterostructures made of ferromagnetic SrRuO3 on the top of Sr2RuO4 strongly encourages new theoretical studies on the interplay between spin-triplet superconductor and ferromagnet in similar fashion to spin-singlet superconductors. Using an extended tight-binding Hamiltonian to model the superconductor, we discuss in this thesis the specific proximity effects of such interface by solving self-consistently the Bogoliubov-De Gennes equations on two- and three-dimensional lattices in the ballistic limit. We obtain the spatial profile of the superconducting order parameters at the interface as well as the spin-polarisation and the current across the Josephson junctions. In contrast to heterostructures made of spin-singlet superconductor, we show that the physical properties at the interface are not only controlled by the strength of the magnetization inside the ferromagnet but also by its orientation due to the existence of a finite pair spin projection of the spin-triplet Cooper pairs. We analyse in the first part the spin-polarisation and the Gibbs free energy at the three-dimensional ferromagnet-chiral spin-triplet superconductor interface. Then, the second part of the thesis is dedicated to the study of the Josephson junctions made of a chiral spin-triplet superconductor and a ferromagnetic barrier. More precisely, we analyse the existence of 0-Pi state transitions in two- and three-dimensional junctions with respect to the strength and the orientation of the magnetization. Finally, we study the proximity effects at the interface of helical spin-triplet superconductors. They differ from the chiral superconductor by the direction of the pair spin polarisation of the Cooper pairs and by the properties of the edge states, present at the boundaries, which can sustain dissipationless spin-current.