Search

The impact of bismuth incorporation into the epitaxial layer of a (Ga,Mn)As dilute ferromagnetic semiconductor on its magnetic and electromagnetic properties is studied in very thin layers of quaternary (Ga,Mn)(Bi,As) compound grown on a GaAs substrate under a compressive misfit strain. An addition of a small atomic fraction of 1% Bi atoms, substituting As atoms in the layer, predominantly enhances the spin-orbit coupling strength in its valence band. The presence of bismuth results in a small decrease in the ferromagnetic Curie temperature and a distinct increase in the coercive fields. On the other hand, the Bi incorporation into the layer strongly enhances the magnitude of negative magnetoresistance without affecting the hole concentration in the layer. The negative magnetoresistance is interpreted in terms of the suppression of weak localization in a magnetic field. Application of the weak-localization theory for two-dimensional ferromagnets by Dugaev et al. to the experimental magnetoresistance results indicates that the decrease in spin-orbit scattering length accounts for the enhanced magnetoresistance in (Ga,Mn)(Bi,As).

In recent years, few-layer or even monolayer ferromagnetic materials have drawn a great deal of attention due to the promising integration of two-dimensional (2D) magnets into next-generation spintronic devices. The SrRuO3 monolayer is a rare example of stable 2D magnetism under ambient conditions, but only weak ferromagnetism or antiferromagnetism has been found. The bi-atomic layer SrRuO3 as another environmentally inert 2D magnetic system has been paid less attention heretofore. Here we study both the bi-atomic layer and monolayer SrRuO3 in (SrRuO3)n/(SrTiO3)m (n = 1, 2) superlattices in which the SrTiO3 serves as a non-magnetic and insulating space layer. Although the monolayer exhibits arguably weak ferromagnetism, we find that the bi-atomic layer exhibits exceedingly strong ferromagnetism with a Tc of 125 K and a saturation magnetization of 1.2 µB/Ru, demonstrated by both superconducting quantum interference device (SQUID) magnetometry and element-specific X-ray circular dichroism. Moreover, in the bi-atomic layer SrRuO3, we demonstrate that random fluctuations and orbital reconstructions inevitably occurring in the 2D limit are critical to the electrical transport, but are much less critical to the ferromagnetism. Our study demonstrates that the bi-atomic layer SrRuO3 is an exceedingly strong 2D ferromagnetic oxide which has great potentials for applications of ultracompact spintronic devices. [Figure not available: see fulltext.].

Resistivity saturation in Ti-Al alloys has been studied by fitting empirical functions of temperature, T, to 20 sets of literature data. By replacing the commonly used temperature-independent saturation term by a term in T−1/2, to model weak localization effects at high temperature, the quality of the fits improved significantly and physically acceptable values were obtained for the fitted parameters. A linear correlation was found between the fitted high-T weak localization parameters and experimental data for the corresponding low-T weak localization conduction terms. No such correlation could be detected when using constant saturation terms. The results suggest that weak localization is a possible cause for resistivity saturation in Ti-Al alloys.

The electronic structure of cerium oxide is investigated here using a combination of ab initio one-electron theory and elements from many-body physics, with emphasis on the nature of the 4f electron shell of cerium ions. We propose to use the hybridization function as a convenient measure for the degree of localization of the 4f shell of this material, and observe that changing the oxidation state is related to distinct changes in the hybridization between the 4f shell and ligand states. The theory reveals that CeO2 has essentially itinerant 4f states, and that in the least oxidized form of ceria, Ce2O3, the 4f states are almost (but not fully) localized. This conclusion is supported by additional calculations based on a combination of density functional theory and dynamical mean field theory. Most importantly, our model points to the fact that diffusion of oxygen vacancies in cerium oxide may be seen as polaron hopping, involving a correlated 4f electron cloud, which is located primarily on Ce ions of several atomic shells surrounding the vacancy.

This thesis presents an experimental work on electronic transport in two-dimensional (2D) van der Waals systems. The variety of the physics of the chapters reflects the exploratory character of the Ph.D. study and demonstrates the versatility and the unique properties of some of the members of the vast group of van der Waals materials. In the experiments we explore the fundamental properties of carriers and states in 2D materials via electrical transport. The first three chapters include experimental work on planar transport in multiterminal devices from transition metal dichalcogenides (2H-MoS2) and trichalogenides (TiS3). In the fist chapter, we study how intravalley spin relaxation and the phase coherence affects weak localization in boron nitride encapsulatedMoS2. In TiS3 we explore its electronic properties and in order to avoid disorder induced localization, we protect the devices with hexagonal boron nitride. An improvement in the quality of the transport and signatures of charge-density-wave transition are observed. Lastly, multi-terminal transport in 1T/1T0-MoS2 and its carrier transport mechanism are investigated, with special emphasis on how to establish low-temperature electrical contacts to 2H-MoS2. The next part of the thesis shifts to vertical transport in van der Waals heterostructures. Firstly, we use WS2 as tunneling barrier between monolayer graphene and metal contact. We observe sequential tunneling through localized states. By studying the ground and excited states, we gain information about their spatial sizes and the magnetic moments of these states. Lastly, we explore heterostructures of graphene on WSe2 and potential effects on the band structure due to the dielectric environment and the proximity induced spin-orbit coupling., QRD/Goswami Lab, QN/Steele Lab

We demonstrate that transport in metallic rare-earth nickelates can be engineered by directly tuning the electronic mean free path. Using irradiation as a tool to induce disorder, we drive this system from a metallic phase into an Anderson insulator. This proceeds via an intermediate regime which shows a thermal crossover from insulating to metallic behavior. We argue that this phase falls within the paradigm of weak localization in three dimensions. We develop a theoretical model for the temperature dependence of resistivity which shows good agreement with our data. The three-dimensional weak localization picture is supported by magnetoconductivity, which scales as ∼B2 up to several tesla. Interestingly, our data indicate that this phase lies in the Mott-Ioffe-Regel regime with the mean free path approaching the lattice constant. Upon further increasing disorder, the charge carriers are localized, leading to insulating behavior at all temperatures. Our results show that irradiation provides a “clean” tuning knob for the mean free path, without altering other system parameters. This suggests promising directions for studies of Anderson localization.

Topological qubits based on Majorana Fermions have the potential to revolutionize the emerging field of quantum computing by making information processing significantly more robust to decoherence. Nanowires are a promising medium for hosting these kinds of qubits, though branched nanowires are needed to perform qubit manipulations. Here we report a gold-free templated growth of III–V nanowires by molecular beam epitaxy using an approach that enables patternable and highly regular branched nanowire arrays on a far greater scale than what has been reported thus far. Our approach relies on the lattice-mismatched growth of InAs on top of defect-free GaAs nanomembranes yielding laterally oriented, low-defect InAs and InGaAs nanowires whose shapes are determined by surface and strain energy minimization. By controlling nanomembrane width and growth time, we demonstrate the formation of compositionally graded nanowires with cross-sections less than 50 nm. Scaling the nanowires below 20 nm leads to the formation of homogeneous InGaAs nanowires, which exhibit phase-coherent, quasi-1D quantum transport as shown by magnetoconductance measurements. These results are an important advance toward scalable topological quantum computing.

The study of quantum interference in solid-state systems yields insight in fundamental properties of mesoscopic systems. Electron quantum interference constitutes an important method to explore mesoscopic physics and quantum decoherence. This dissertation focuses on two-dimensional (2D) electron systems in $delta-$Si doped n-type In$_{0.64}$Ga$_{0.36}$As/In$_{0.45}$Al$_{0.55}$As, 2D hole systems in Si-doped p-type GaAs/Al$_{0.35}$Ga$_{0.65}$As and C-doped p-type GaAs/\Al$_{0.24}$Ga$_{0.76}$As heterostructures. The low temperature experiments study the magnetotransport of nano- and micro-scale lithographically defined devices fabricated on the heterostructures. These devices include a single ring interferometer and a ring interferometer array in 2D electron system, Hall bar geometries and narrow wires in 2D hole systems. The single ring interferometer yields pronounced Aharonov-Bohm (AB) oscillations with magnetic flux periodicity of h/e over a wide range of magnetic field. The periodicity was confirmed by Fourier transformation of the oscillations. The AB oscillation amplitude shows a quasi-periodic modulation over applied magnetic field due to local magnetic flux threading through the interferometer arms. Further study of current and temperature dependence of the amplitude of the oscillations indicates that the Thouless energy forms the measure of excitation energies giving quantum decoherence. An in-plane magnetic field was applied to the single ring interferometer to study the Berry's phase and the Aharonov-Casher effect. The ring interferometer array yields both AB oscillations and Altshuler-Aronov-Spivak (AAS) oscillations, the latter with magnetic flux periodicity of h/2e. The AAS oscillations require time-reversal symmetry and hence can be used to qualify time-reversal symmetry breaking. More importantly, the fundamental mesoscopic dephasing length associated with time-reversal symmetry breaking under applied magnetic field, an effective magnetic length, can

У черговій із серії оглядово-навчальних статей у рамках концепції «знизу – вгору» сучасної наноелектроніки розглядаються моделі пружного й спінового дефазування, врахування некогерентних процесів з використанням зонду Бюттекера, 1D провідник з двома й більше розсіювальними центрами, явище квантової інтерференції, режими сильної і слабкої локалізації, стрибок потенціалу на дефектах, квантові осциляції в методі нерівноважнох функцій Гріна (НРФГ) без урахування дефазування та з ним, ефекти деструктивної та конструктивної інтерференції, чотирикомпонентний опис спінового транспорту з урахуванням дефазування, формалізм псевдоспіну., В очередной из серии обзорно-учебных статей в рамках концепции «снизу – вверх» наноэлектроники рассматриваются модели упругой дефазировки и спиновой дефазировки, учет некогерентных процессов с использованием зонда Бюттекера, 1D проводник с двумя и более рассеивающими центрами, явление квантовой интерференции, режимы сильной и слабой локализации, скачок потенциала на дефектах, квантовые осцилляции в методе неравновесных функций Грина (НРФГ) без учета дефазировки и с ее учетом, эффекты деструктивной и конструктивной интерференции, четырехкомпонентное описание спинового транспорта с учетом дефазировки, формализм псевдоспина., Within the following in the series of the review and tutorial articles next topics are discussed in the frame of the «bottom – up» approach of modern nanoelectronics: elastic and spin dephasing modeling, account for non-coherent processes using Buttiker probe, 1D conductor with two and more scatterers, quantum interference, strong and weak localization, potential drop across scatterers, quantum oscillations in non-equilibrium Green’s functions (NEGF) method without dephasing and with it, destructive and constructive interference effects, four-component description of spin transport with account for dephasing, and pseudo-spin formalism.

We report transport studies on magnetically doped Bi 2Se 3 topological insulator ultrathin films grown by molecular beam epitaxy. The magnetotransport behavior exhibits a systematic crossover between weak antilocalization and weak localization with the change of magnetic impurity concentration, temperature, and magnetic field. We show that the localization property is closely related to the magnetization of the sample, and the complex crossover is due to the transformation of Bi 2Se 3 from a topological insulator to a topologically trivial dilute magnetic semiconductor driven by magnetic impurities. This work demonstrates an effective way to manipulate the quantum transport properties of the topological insulators by breaking time-reversal symmetry. © 2012 American Physical Society.

We study the weak antilocalization (WAL) effect in topological insulator Bi2Te3 thin films at low temperatures. The two-dimensional WAL effect associated with surface carriers is revealed in the tilted magnetic field dependence of magnetoconductance. Our data demonstrate that the observed WAL is robust against deposition of nonmagnetic Au impurities on the surface of the thin films, but it is quenched by the deposition of magnetic Fe impurities which destroy the π Berry phase of the topological surface states. The magnetoconductance data of a 5 nm Bi2Te3 film suggests that a crossover from symplectic to unitary classes is observed with the deposition of Fe impurities.

This thesis explores the physics of low-dimensional electronic conductors using two materials systems, carbon nanotubes (CNTs) and lithographically-defined silver nanowires. In order to understand the intrinsic electronic properties of CNTs, it is important to eliminate the contact effects from the measurements. Here, this is accomplished by using a conductive-tip atomic force microscope cantilever as a local electrode in order to obtain length dependent transport properties. The CNT-movable electrode contact is fully characterized, and is largely independent of voltage bias conditions, and independent of the contact force beyond a certain threshold. The contact is affected by the fine positioning of the cantilever relative to the CNT due to parasitic lateral motion of the cantilever during the loading cycle, which, if not controlled, can lead to non-monotonic behavior of contact resistance vs. force. Length dependent transport measurements are reported for several metallic and semiconducting CNTs. The resistance versus length R(L) of semiconducting CNTs is linear in the on state. For the depleted state R(L) is linear for long channel lengths, but non-linear for short channel lengths due to the long depletion lengths in one-dimensional semiconductors. Transport remains diffusive under all depletion conditions, due to both low disorder and high temperature. The study of quantum corrections to classical conductivity in mesoscopic conductors is an essential tool for understanding phase coherence in these systems. A long standing discrepancy between theory and experiment regards the phase coherence time, which is expected theoretically to grow as a power law at low temperatures, but is experimentally found to saturate. The origins of this saturation have been debated for the last decade, with the main contenders being intrinsic decoherence by zero-point fluctuations of the electrons, and decoherence by dilute magnetic impurities. Here, the phase coherence time in quasi

Series of Co-doped Al-codoped ZnO films with electron concentration at 5 K ranging from 8.31017 cm-3 to 9.91019 cm-3 were prepared by pulsed laser deposition under different O2 pressure and substrate temperature. The magnetoresistance (MR) effect was studied between 5 K and 290 K with fields up to 6 T, showing large electron concentration and temperature dependence. A large positive MR of 124 % has been observed in the film with the lowest electron concentration of 8.31017 cm-3, while only negative MR of –1.9 % was observed in the film with an electron concentration of 9.91019 cm-3 at 5 K. The positive MR is attributed to the quantum correction on the conductivity due to the s-d exchange interaction induced spin-splitting of the conduction band [1]. The negative MR is attributed to the magnetic field suppressed weak localization [1]. The modelled superimposed positive and negative MR agrees well with the experimentally observed MR and hints towards the physical origin of MR in Co-doped ZnO [2]. [1] P. A. Lee and T. V. Ramakrishnan, Rev. Mod. Phys. 57, 287 (1985) [2] Q. Xu, L. Hartmann, H. Schmidt, H. Hochmuth, M. Lorenz, D. Spemann, and M. Grundmann, Phys. Rev. B 76, 134417 (2007)

Carbon Nanotubes are molecules with exceptional physical properties that are most useful for applications in the growing field of nanotechnology. In addition, because of its special electrical properties, they are extremely useful for experiments on the fundamental properties of one-dimensional electronic systems. This thesis describes a series of experiments and a short numerical study aimed at a further understanding of the low-temperature electrical transport of single-walled carbon nanotubes. In this work we perform the first experimental study on the effect of quantum interference in single-wall nanotubes in the presence of disorder, leading to the observation of a weak localization effect and conductance fluctuations. Shifting the focus to systems with superconducting or ferromagnetic contacts, we first propose a phenomenological model to describe the experimental results from a former study with superconducting contacts. We also contact single-wall nanotubes with the large-gap superconductor NbTiN to study the rich interplay between Coulomb blockade, level quantization and superconductivity. And finally, the experimental study of nanotubes with highly transparent ferromagnetic contacts shows that the spin-dependent magnetoresistance is due to quantum interference., Applied Sciences

The low temperature electronic transport properties of delta-doped silicon are established here, in an effort to determine the technological limitations facing the construction of semiconductor wafers with monolayer doping profiles. Both phosphorous (Si:P) and boron (Si:B) delta-doped silicon wafers prepared by molecular beam epitaxy have been investigated. Devices fabricated from samples of these wafers were cooled to approximately 130 mK in a dilution refrigerator, where four wire resistance measurements were performed in the presence of magnetic fields both perpendicular and parallel to the plane of the devices. The data obtained was interpreted using the theory of weak localization. For Si:P samples, the effective thickness of the delta-doped region can be inferred by comparing the magnetoconductance signal in parallel magnetic fields to that of perpendicular fields. Using this technique on several different samples which were annealed at 850 C, an estimate of the diffusivity of phosphorus in silicon at this temperature is established. In addition, it is shown that the primary mechanism for the loss of quantum mechanical phase coherence in these samples at low temperatures is the electron-electron interaction, and provide evidence for lattice defects enhancing this dephasing. For Si:B samples, the spin-orbit interaction is shown to dominate the dephasing, and the temperature dependence of this interaction is found to be substantially different from that observed in Si:P devices. Based on these results, I conclude that specific epitaxial growth techniques must be followed if monolayer doping profiles are ever to be achieved in silicon. In addition, because this weak localization technique for measuring the thickness of delta-doped regions is highly sensitive and non-destructive, it may ultimately prove to be the most effective method yet established for probing ultra-thin doping profiles. Finally, several theoretical desiderata are established, which would enable

We show that the study of nonlinearity conductivity gives a possibility to determine the condition when the diffusion conductivity changes to the hopping one with increasing disorder. It is experimentally shown that the conductivity of single quantum well GaAs/InGaAs/GaAs heterostructures behaves like diffusive one down to the value approaching (2-3) × 10-2e2/h. © 2004 Elsevier B.V. All rights reserved.

A weak localization effect has been studied in macroscopically inhomogeneous 2D system. It is shown that although the real phase breaking length tends to infinity when the temperature tends to zero such a system can reveal a saturated behavior of the temperature dependence of that parameter which is obtained from the standard analysis of the negative magnetoresistance and usually identified by experimenters with the phase braking length., This article is from ADA408025 Nanostructures: Physics and Technology International Symposium (9th), St. Petersburg, Russia, June 18-22, 2001 Proceedings

The theory of weak localization is presented for quasi-2D systems where several sub- bands of size quantization are occupied. The weak-localization correction to conductivity is shown to depend strongly on the level concentration ratio and intersubband scattering intensity. Specifically at the comparable level occupations and equal relaxation times the conductivity correction of the m-subband system decreases in m times when transiting from the isolated levels to the high-intensive intersubband scattering case., This article is from ADA408025 Nanostructures: Physics and Technology International Symposium (9th), St. Petersburg, Russia, June 18-22, 2001 Proceedings

We have performed a calculation of the temperature dependence of the weak-localization correction to resistance in a AlGaAs/GaAs p-type quantum well. In such systems where the spin orbit coupling by far dominates the energy dispersion, we find that the spin relaxation time becomes comparable with the estimated value of the phase coherence time at sufficiently low temperatures and low hole densities. We wish to suggest this crossover between these different relaxation times as a possible explanation of the experimentally observed 'metal-insulator' transition in two- dimensional hole systems., This article is from ADA408025 Nanostructures: Physics and Technology International Symposium (9th), St. Petersburg, Russia, June 18-22, 2001 Proceedings

The pure rhombohedral phase of C60 polymer displays highly anisotropic electrical properties. Conductivity in the polymerized (001) planes exhibits a metal-insulator transition and shows the features of 2D weak localization. Anisotropy ratio is temperature-dependent and reaches 10_6. Dysonian ESR lineshape is consistent with the metallic nature of the samples., Editors: Günther Leising, Roland Resel, Helmut Neugebauer, N. Serdar Sariciftci and Hans Kuzmany

We present a proposal for a new type of quantum ratchets in application of weak-localization (WL) effect in mesoscopic chaotic dots. Coherent electrons transport through the dots under an applied ac voltage and a synchronized pulsating magnetic field. In the first half cycle of the voltage alternation with no magnetic field, the WL effect reduces the electron transmission on average, while the applied magnetic field breaks the time-reversal symmetry in the latter half cycle, suppressing the WL effect. As a result, nonvanishing amount of net electric current in one direction can be measured. We exactly calculate the net electric current which is found accessible in experiments. It is also suggested that the observation of this rectified current is a good quantitative measure of the WL effect in mesoscopic chaotic dots, in contrast with the WL lineshape measurement.

The weak localization correction to the conductivity in coupled double layer structures was studied both experimentally and theoretically. The statistics of the closed paths was determined from analysis of the magnetic field and temperature dependencies of the negative magnetoresistance for magnetic field perpendicular and parallel to the structure plane. The comparison of the results with the results of computer simulation of carrier motion at scattering shows that inter-layer tunneling plays decisive role in the weak localization., TPres: 8th Int Symp Nanostructures: Physics and Technology, St Petersburg, Russia, 19-23 Jun 2000, p66-69. This article is from ADA407315 Nanostructures: Physics and Technology International Symposium (8th) Held in St. Petersburg, Russia on June 19-23, 2000 Proceedings

Upon the occasion of the 10th ISIC conference, it seems appropriate to give a brief overview of some of the major advances made in our understanding of charge transport in intercalated graphite since the 1st Franco-American Conference on Graphite Intercalation Compounds held in 1977., Editors M. Endo, T. Enoki, H. Suematsu and S. Yamanaka; review

The results of computer simulation of particle motion over the plane with randomly distributed scatters are presented. They are used to analyse the influence of scattering anisotropy on the negative magnetoresistance due to weak localisation. It is shown that the magnetic field dependence of magnetoresistance in this case can be described by the well known expression. obtained in the diffusion limit for isotropic scattering. but with the prefactor less than unity and breaking-phase length which differs from the true value., Pres: 7th Int Symp Nanostructures: Physics and Technology, St Petersburg, Russia. 14-18 Jun 1999. p190-193. This article is from ADA407055 Nanostructures: Physics and Technology. 7th International Symposium. St. Petersburg, Russia, June 14-18, 1999 Proceedings

The magnetoresistance in weak localization regime was thoroughly investigated both for the classical and quantum two-dimensional (2D) electron systems., Pres: 6th Int Symp Nanostructures: Physics and Technology, St Petersburg, Russia. 22-26 Jun 1998. p135. This article is from ADA406591 Nanostructures: Physics and Technology International Symposium (6th) held in St. Petersburg, Russia on June 22-26, 1998 Proceedings

The logarithmic temperature dependence of resistivity, commonly observed in disordered films, has generally been interpreted as evidence for electron weak localization, with its slope indicative of the inelastic scattering mechanism. In this work, we show that the 2D quantum percolation (QP) model, pertaining to disordered metallic films, predicts a sample-size dependent ln L conductance correction that is three times larger than that for the Anderson model. Moreover, when the film has a finite thickness, the coefficient of ln L decreases to about 2/3 of its 2D value for both the QP and the Anderson models. Since for disordered metallic films the QP model is more realistic than the Anderson model, which pertains to doped metallic films, it follows that many prior experimental results on metallic films have to be re-interpreted in regard to their implications about the inelastic scattering mechanism(s). These results have direct implications for the interpretation of experimental data.

Functional structures as well as materials provided by nature have always been a great source of inspiration for new technologies. Adapting and improving the discovered concepts, however, demands a detailed understanding of their working principles, while employing natural materials for fabrication tasks requires suitable functionalization and modification. In this thesis, the white scales of the beetle Cyphochilus are examined in order to reveal unknown aspects of their light transport properties. In addition, the monomer of the material they are made of is utilized for 3D microfabrication. White beetle scales have been fascinating scientists for more than a decade because they display brilliant whiteness despite their small thickness and the low refractive index contrast. Their optical properties arise from highly efficient light scattering within the disordered intra-scale network structure. To gain a better understanding of the scattering properties, several previous studies have investigated the light transport and its connection to the structural anisotropy with the aid of diffusion theory. While this framework allows to relate the light scattering to macroscopic transport properties, an accurate determination of the effective refractive index of the structure is required. Due to its simplicity, the Maxwell-Garnett mixing rule is frequently used for this task, although its constraint to particle and feature sizes much smaller than the wavelength is clearly violated for the scales. To provide a correct calculation of the effective refractive index, here, finite-difference time-domain simulations are used to systematically examine the impact of size effects on the effective refractive index. Deploying this simulation approach, the Maxwell-Garnett mixing rule is shown to break down for large particles. In contrast, it is found that a quadratic polynomial function describes the effective refractive index in close approximation, while its coefficients can be obtain, In der Natur vorhandene funktionelle Strukturen sowie Materialien sind seit jeher eine Inspirationsquelle für die Entwicklung neuer Technologien gewesen. Die Adaption und Modifikation der gefundenen Konzepte erfordert jedoch ein genaues Verständnis der zugrundeliegenden Funktionsprinzipien, während natürliche Materialien oftmals funktionalisiert und modifiziert werden müssen, um sie für Fertigungszwecke einsetzen zu können. In der vorliegenden Dissertation werden die strahlend weißen Schuppen des Käfers Cyphochilus hinsichtlich bisher unbekannter Aspekte ihrer Lichttransporteigenschaften untersucht. Darüber hinaus wird die Monomereinheit des Materials, aus dem sie bestehen, funktionalisiert, um das Monomer für die 3D Mikrofabrikation nutzbar zu machen. Seit über einer Dekade faszinieren die weißen Käferschuppen Wissenschaftler, da sie trotz ihrer geringen Dicke und des kleinen Brechungsindexkontrasts eine strahlend weiße Färbung aufweisen. Diese optische Eigenschaft kommt durch die äußerst effiziente Streuung des Lichts in der ungeordneten Netzwerkstruktur im Inneren der Schuppen zustande. Um die Streueigenschaften besser zu verstehen, wurde in etlichen, bisherigen Veröffentlichungen der Lichttransport und seine Verbindung zu der strukturellen Anisotropie des Netzwerks mit Hilfe der Lichtdiffusionstheorie untersucht. Dieser Ansatz erlaubt es zwar die Streueigenschaften anhand makroskopischer Transporteigenschaften zu beschreiben, dafür wird aber eine genau Bestimmung des effektiven Brechungsindex der Schuppe benötigt. Für dessen Berechnung wird regelmäßig die Mischregel nach Maxwell-Garnett aufgrund ihrer Einfachheit verwendet. Die Gültigkeit dieser Regel ist allerdings beschränkt auf Partikel beziehungsweise Strukturdetails die viel kleiner als die Wellenlänge des Lichts sind, eine Bedingung, die von den Schuppen nicht erfüllt wird. Um eine korrekte Berechnung des effektiven Brechungsindex zu ermöglichen, werden in dieser Arbeit Simulationen genutzt, die auf der Me