Dissertations / Theses on the topic 'Systèmes quantiques désordonnés'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 31 dissertations / theses for your research on the topic 'Systèmes quantiques désordonnés.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
Couëdo, François. "Transitions de phase quantiques dans les systèmes désordonnés de basse dimension." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-00990782.
Hainaut, Clément. "Effets des symétries sur la localisation dans des systèmes quantiques désordonnés." Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10082/document.
In this thesis, we use the Kicked Rotor, paradigm of quantum chaos, to study new physical aspects of disordered systems.We thus present the first experimental observation with atomic matter wave of a phenomenon directly linked to weak localization which is the Enhanced Return to the Origin. We show that this effect can be used as a tool to measure accuratly the decoherence in the system. We present a novel, outstandingly simple, experimental method to control symmetry properties of the Kicked Rotor. This allows us to study a disordered system in presence of a non-trivial artificial Aharonov-Bohm flux in a synthetic dimension. This gives us the opportunity to break the time reversal symmetry and then to study the physics of Anderson localization in two different symmetry classes : the orthogonal class and the unitary class. We have investigated the effect of this symmetry breaking on physical properties of 1D disordered systems by looking two signatures of quantum transport. We observe thus experimentally, for the first time, the Coherent Forward Scattering effect, predicted recently and which represents a novel genuine signature of Anderson localization. We show its distinctive signatures and a good agreement with theoretical predictions. Finally, we realise the first experimental measurements of the (G) scaling function, characteristic of transport in disordered medium, in two symmetry classes and we demonstrate their universality
Hainaut, Clément. "Effets des symétries sur la localisation dans des systèmes quantiques désordonnés." Electronic Thesis or Diss., Lille 1, 2017. http://www.theses.fr/2017LIL10082.
In this thesis, we use the Kicked Rotor, paradigm of quantum chaos, to study new physical aspects of disordered systems.We thus present the first experimental observation with atomic matter wave of a phenomenon directly linked to weak localization which is the Enhanced Return to the Origin. We show that this effect can be used as a tool to measure accuratly the decoherence in the system. We present a novel, outstandingly simple, experimental method to control symmetry properties of the Kicked Rotor. This allows us to study a disordered system in presence of a non-trivial artificial Aharonov-Bohm flux in a synthetic dimension. This gives us the opportunity to break the time reversal symmetry and then to study the physics of Anderson localization in two different symmetry classes : the orthogonal class and the unitary class. We have investigated the effect of this symmetry breaking on physical properties of 1D disordered systems by looking two signatures of quantum transport. We observe thus experimentally, for the first time, the Coherent Forward Scattering effect, predicted recently and which represents a novel genuine signature of Anderson localization. We show its distinctive signatures and a good agreement with theoretical predictions. Finally, we realise the first experimental measurements of the (G) scaling function, characteristic of transport in disordered medium, in two symmetry classes and we demonstrate their universality
Van, Den Berg Tineke. "Conductivité de spin et effets magnétiques dans les systèmes quantiques désordonnés." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4812/document.
Spintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA)
Van, Den Berg Tineke. "Conductivité de spin et effets magnétiques dans les systèmes quantiques désordonnés." Electronic Thesis or Diss., Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4812.
Spintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA)
Sabri, Mostafa. "Etude de la localisation pour des systèmes désordonnés sur un graphe quantique." Paris 7, 2014. http://www.theses.fr/2014PA077022.
This work is devoted to the study of some spectral properties of random Schrödinger operators. It is divided into two parts : 1. A study of localization for multi-particle systems on quantum graphs. 2. An abstract formulation of some Wegner estimates, followed by a list of applications for concrete models. In Chapter 1 we try to introduce the problems and the results of this thesis in an elementary way. The first part occupies chapters 2 and 3. Chapter 2 essentially reproduces our article "Anderson Localization for a multi-particle quantum graph" [97] on this subject. In Chapter 3 we discuss some additional properties of our model, and we give alternative proofs to some results of Chapter 2. The second part occupies chapters 4 and 5. Chapter 4 essentially reproduces our article "Some abstract Wegner estimates with applications" [98]. In Chapter 5 we continue the study of Wegner estimates by giving more abstract theorems in Section 5. 2 and yet more applications in Section 5. 3. We conclude with two appendices A and B. In the first one we explain the theory of generalized eigenfunction expansions in great detail. In Appendix B, we prove some classical resutls usedin the text
Anfray, Valentin. "Étude numérique du point critique de systèmes quantiques de spin désordonnés en dimensions élevées." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0127.
Several random quantum spin models have been numerically studied in dimension D>1 by Strong Disorder Renormalisation Group (SDRG). We have implemented an efficient algorithm to be able to consider a system with up to a billion spins independently of its spatial dimension. Critical properties of the 2D and 3D random quantum Potts model with q=2,3,5,10,20 and 50 states are shown to be governed by an infinite disorder fixed point. We have computed the correlation-length exponent u, the magnetization exponent d_f and the energy gap exponent psi. Using finite-size scaling and taking into account finite-size corrections, critical properties of the Potts model are shown to be q-independent. Random quantum Clock models with q=2,3,5,8 and 10 states have been also studied in 2D and 3D. A minimum amount of initial disorder strength is required to flow to an infinite disorder fixed point. Despite large error bars on psi exponent, our estimates for the critical exponents u and psi for all q are compatible with those of the random transverse-field Ising model. Our estimates for the critical exponent d_f are incompatible within error bar but very close. Lastly, the tricritical point of the random quantum Ashkin-Teller model has been studied in dimension two and three. We have shown that the correlation-length exponent associated with one of the two unstable directions does not belong to the university class of the random transverse-field Ising model
Bocquet, Marc. "Chaînes de Spins, Fermions de Dirac, et Systèmes Désordonnés." Phd thesis, Ecole Polytechnique X, 2000. http://tel.archives-ouvertes.fr/tel-00001560.
Sabri, Mostafa. "Étude de la localisation pour des systèmes désordonnés sur un graphe quantique." Phd thesis, Université Paris-Diderot - Paris VII, 2014. http://tel.archives-ouvertes.fr/tel-01001715.
Bayo, Djénabou. "Détermination de phase par Deep Learning pour les systèmes désordonnés." Electronic Thesis or Diss., CY Cergy Paris Université, 2024. http://www.theses.fr/2024CYUN1280.
Our first model is the two-dimensional site percolation. In this paradigmatic model, sites are randomly occupied with probability «p»; a second-order phase transition from a non-percolating to a fully percolating phase appears at occupation density «p_c», called percolation threshold. Through supervised deep learning approaches like classification and regression, we explore the ability of convolutional neural networks (CNNs) to predict the density of occupation «p» of percolation states, the correlation length «xi», as well as the presence of a spanning cluster. We find that image recognition tools such as CNN, which are not naturally tailored for physics, successfully identify «p». However, when dealing with parameters like «xi» or the presence of a spanning cluster, these same techniques fail to provide quantitative results. The second model is the three-dimensional Anderson model of localisation. This model is characterised by a localisation of the wavefunctions above a critical disorder «W_c». We begin by reproducing previous work done on phase classification, and perform several new studies with classification and regression methods, to identify individual disorders in both phases. Throughout our investigation, multiple parameters such as the size of the system or the nature of the input are studied to observe their influence on the performance of the model. Via the study of these two models and the use of several ML methods, we will display the successes and limitations that one might be confronted with when using ML for phase recognition
Sciolla, Bruno. "Dynamique quantique hors-équilibre et systèmes désordonnés pour des atomes ultrafroids bosoniques." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00734641.
Voliotis, Dimitrios. "Contribution à l’étude des chaînes de spin quantique avec une perturbation aléatoire ou apériodique." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0253/document.
In the present thesis, the critical and off-critical behaviors of quantum spin chains in presence of a random or an aperiodic perturbation of the couplings is studied. The critical behavior of the Ising and Potts random quantum chains is known to be governed by the same Infinite-Disorder Fixed Point. We have implemented a numerical version of the Strong-Disorder Renormalization Group (SDRG) to test this prediction. We then studied the quantum random Ashkin-Teller chain by Density Matrix Renormalization Group. The phase diagram, previously obtained by SDRG, is confirmed by estimating the location of the peaks of the integrated autocorrelation times of both the spin-spin and polarization-polarization autocorrelation functions and of the disorder fluctuations of magnetization and polarization. Finally, the existence of a double-Griffiths phase is shown by a detailed study of the decay of the off-critical autocorrelation functions. As expected, a divergence of the dynamical exponent is observed along the two transition lines. In the aperiodic case, we studied both the Ising and Potts quantum chains. Using numerical SDRG, we confirmed the known analytical results for the Ising chains and proposed a new estimate of the magnetic scaling dimension.For the quantum q-state Potts chain, we estimated the magnetic scaling dimension for various aperiodic sequences and showed that it is independent of q for all sequences with a vanishing wandering exponent. However, we observed that the dynamical exponent is finite and increases with the number of states q. In contrast, for the Rudin-Shapiro sequence, the results are compatible with an Infinite-Disorder Fixed Point with a diverging dynamical exponent, equipe de renormalization
Grémaud, Benoît. "Transport quantique dans les systèmes complexes." Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00292696.
Coquand, Olivier. "Fluctuations dans la phase plate des membranes cristallines." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS096.
This works deals with the mechanical properties of crystalline membranes, which are two-dimensional materials with an underlying periodic lattice at the microscopic scale which provides them with elastic properties. It is one of the scarce examples of two-dimensional systems possessing a stable ordered phase at large distance in the presence of thermal fluctuations. In that phase, the vectors normal to the surface generated by the membrane are strongly correlated; it is thus called the flat phase. This manuscript presents a study of the properties of the flat phase with help of renormalisation group tools, and in particular the effective average action formalism. First, by studying the perturbation theory beyond lowest order, we confirm the stability of our effective average action ansatz used in the following, and unveil some pathologies of the perturbative development. Then we show how the non-perturbative renormalisation group flow can be used to compute various thermodynamic properties of crystalline membranes and draw their complete phase diagram in the space (volume, applied stress, temperature). Afterwards, we improve our model to account for the effect of quantum fluctuations, which allows to describe the low temperature regime. Finally, we examine the consequences of the presence of various defects in the material. In particular, we describe a new disorder driven phase transition which seems to be in good qualitative agreement with experimental observations
Dubouchet, Thomas. "Spectroscopie locale à basse température dans des systèmes supraconducteurs désordonnés." Phd thesis, Grenoble, 2010. http://www.theses.fr/2010GRENY036.
This thesis presents a study combining tunneling spectroscopy, point-contact Andreev spectroscopy and electronic transport on disordered superconducting indium oxide samples. Transport measurements reveal a diverging resistivity from room temperature shortcut by superconductivity at low temperature. This behavior shows that our samples are in the vicinity of the metal-insulator Anderson transition. Tunneling spectroscopy highlights a rather unusual superconducting state with a pseudogap regime above the critical temperature. It evolves at low temperature into an inhomogeneous system composed of both superconducting Cooper pairs and Cooper pairs without phase coherence, localized by the disorder. Comparison between different samples shows that incoherent Cooper pairs proliferate with increasing level of disorder, what indicates that superconductor-insulator transition in indium oxide is governed by the progressive localization of Cooper pairs. Besides, using our STM, we have continuously analyzed the local conductance between tunneling regime and contact regime. Andreev spectroscopy thus reveals a new energy scale related to the superconducting phase coherence and independent from spatial fluctuations of the density of states measured in tunneling regime. This shows that disorder induces a dichotomy between the pairing energy characterizing the binding of electrons into pairs and the coherence energy specific to macroscopic superconductivity
Dubouchet, Thomas. "Spectroscopie locale à basse température dans des systèmes supraconducteurs désordonnés." Phd thesis, Université de Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00576226.
Triozon, François. "Diffusion quantique et conductivité dans les systèmes apériodiques." Phd thesis, Université Joseph Fourier (Grenoble), 2002. http://tel.archives-ouvertes.fr/tel-00002292.
Forestier, Guillaume. "Transport quantique dans les verres de spins." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY023/document.
The experiments presented in this thesis associate two fields of condensed matter physic, on the one hand with the spin glass physic and the other hand with the mesoscopic physic. The spin glass state is one of the most emblematic of disordered and frustred system and at low temperature, it is caracterized by an unconventionel order where the magnetic disorder is quenched. Moroever, it is considered as a model system for glasses in general and thereby it has been extensively studied, both experimentally and theoreticlly. After extensive research efforts, the description of fundamental state of the system has lead towards two well different approaches. The first, given by the mean field solution, highlights a fundamental composed of mulitple states organised and hierarchical. The second, called droplet model is based on the off--equilibrium dynamic of a unique ground state. However, despite these contributions, the understanding ot this phase is far from being complete and the nature of the ground state still remains an open question. In a mesoscopic conductor, the transport of electron is coherent: electrons keep the memory of their phase, so that one can observe interference effects. The main motivation of this work is to use these interference effects in order to to probe the spin glass state. Indeed, as electronic interference depends of the position of the static disorder, coherent transport can be a useful tool to study the configuration of the microscopic disorder. Althought few coherent transport experiments exist to probe the spin glass, this field of research has very little explored. Nevertheless, this area has been a revival thanks to theoritical work, showing how coherent transport is sensitived to the quenched disorder and how it may provide informations of the nature of fundamental state of spin glass. So, this experimental work deals with the implementation of transport measurements in mesoscopic spin glasses. The first part of the study is focused on the general charateristics of classical and quatum transport of these system. We have examined the resistivity as a function of the temperature and magnetic field and we show that these mesoscopic systems have a spin glass-like behaviour. In a second part, we have focused on the low field magnetoresistivity. We show that it presents a strong hysteresis, whose the amplitude is strongly depends, both of the temperature in the glassy phase and sweeping rate of the magnetic field. We argue that this particular behaviour is related to the out off-equilibrium of the system and we show how the temperature and the sweeping rate control the deviation to the equilibrium. In this part, we also examine by transport measurements how the system relaxes towards the equilibrium just after its excitation. In addition, we present surprinsing transport propreties that we observed, resulting of experimental protocols more sophisticated in temperatures and magnetic fields
Zanon, Nathalie. "Théorie des matrices de transfert aléatoires : application à l'étude de la conductance d'un système désordonné en régime quantique cohérent." Paris 11, 1989. http://www.theses.fr/1989PA112350.
Capron, Thibaut. "Transport quantique dans les verres de spin." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00686330.
Crauste, Olivier. "Étude des transitions de phases quantiques supraconducteur -- isolant, métal -- isolant dans des matériaux amorphes désordonnés proches de la dimension 2." Phd thesis, Université Paris Sud - Paris XI, 2010. http://tel.archives-ouvertes.fr/tel-00579256.
Vermersch, Benoît. "Dynamique d'un gaz de bosons ultra-froids dans un milieu désordonné : Effets des interactions sur la localisation et sur la transition d'Anderson." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2013. http://tel.archives-ouvertes.fr/tel-00910405.
Gawiec, Pierre. "Propriétés statiques et dynamiques des états de basse énergie d'un système de spins bidimensionnel anisotrope désordonné." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10206.
Avriller, Rémi. "Contribution à la modélisation théorique et à l'étude du transport quantique dans les dispositifs à base de nanotubes de carbone." Phd thesis, Grenoble 1, 2008. http://www.theses.fr/2008GRE10100.
Carbon nanotubes are quasi-1D structures obtained by rolling a graphene sheet onto a cylinder surface. This determines the chirality and the complete electronic and vibrational band structure of carbon nanotubes. However, due to low dimensionnality of such systems and to the wave nature of electrons, this band structure is strongly modified by applying an external magnetic field, and broken by a random disordered potentiel(loss of translationnal invariance), or by excitation of an inelastic mechanism(electron-phonon interaction). The aim of the following thesis is to explore quantum transport properties in carbon nanotubes, due to the interplay between quantum interferences and interaction processes. We will focus ourselves on disordered carbon nanotubes doped by nitrogen or boron atoms, modelize the disordered hamiltonian and probe scaling laws of conductance. We will also consider the role of a uniform and static magnetic field on transport regimes at low bias(Landau level formation and Aharonov-Bohm oscillation). Inelastic collisions due to electron-optic phonon coupling will finally be considered. Due to the low dimensionnality of carbon nanotubes, the adiabatic approximation fails and a proper transport formalism in Fock space of electrons and phonons has to be considered. In the former studies, an effective microscopic hamiltonian is built and the problem of coherent quantum transport solved numerically or analytically
Avriller, Rémi. "Contribution à la modélisation théorique et à l'étude du transport quantique dans les dispositifs à base de nanotubes de carbone." Phd thesis, Université Joseph Fourier (Grenoble), 2008. http://tel.archives-ouvertes.fr/tel-00326421.
Dauzhenka, Taras. "Couches minces d'oxyde d'étain : la localisation faible et les effets de l'interaction." Phd thesis, Université Paul Sabatier - Toulouse III, 2011. http://tel.archives-ouvertes.fr/tel-00589730.
Dupont, Maxime. "Dynamics and disorder in quantum antiferromagnets." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30092/document.
Condensed matter physics, and especially strongly correlated systems provide some of the most challenging problems of modern physics. In these systems, the many-body interactions and correlations between quantum particles cannot be neglected; otherwise, the models would simply fail to capture the relevant physics at play and phenomena ensuing. In particular, the work presented in this manuscript deals with quantum magnetism and addresses several distinct questions through computational approaches and state-of-the-art numerical methods. The interplay between disorder (i.e. impurities) and interactions is studied regarding a specific magnetic compound, where instead of the expected many-body localized phase at high magnetic fields, a novel disorder-induced ordered state of matter is found, with a resurgence of quantum coherence. Furthermore, the dynamical response of quantum magnets to an external perturbation, such as it is accessed and measured in nuclear magnetic resonance and inelastic neutron scattering experiments is investigated
Semerjian, Guilhem. "Mean-field disordered systems : glasses and optimization problems, classical and quantum." Habilitation à diriger des recherches, Ecole Normale Supérieure de Paris - ENS Paris, 2013. http://tel.archives-ouvertes.fr/tel-00785924.
Solana, Mathias. "Electronic transport in spin-glasses and mesoscopic wires : correlations of universal conductance fluctuations in disordered conductors." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY020/document.
The experimental work developed during this PhD is situated at the interface of two fields of condensed matter physics, namely spin glasses and mesoscopic physics. Spin glasses have been widely studied and are one of the problem that has been the most discussed over the years, both on a theoretical and experimental point of view. This state is characterized by very peculiar properties that come to light as it exhibits a magnetic phase transition at low temperatures that is already unusual. Indeed, this transition is due to a mix of frustration and disorder in the magnetic structure of the system, making it an exceptional model system for glasses and frustrated systems in general. After many efforts, theoreticians managed to described the fundamental state of the system by the mean of two different and apparently incompatible approaches. The first one, called RSB theory, is based on a mean-field approximation and predicts a complex phase space with an unconventional hierarchical organization. The second is based on more phenomenological approach and is named Droplet theory. It points towards a unique ground state and explain all the observation by slow relaxation processes. However, the question of the true nature of the spin glass phase is still heavily debated. Mesoscopic physics, for its part, addresses the question of electronic transport for samples in which the electrons keep their phase coherence. If the electrons remains coherent, it is possible to see interference effects that are quantum signs of what happens at the atomic level. In this work, it is used to probe the magnetic and static disorder in spin glasses. Indeed, it is possible to interpret the change in those interferences as changes in the microscopic disorder configuration and to know exactly how the spin glass state evolves. Some work have already tried to use coherent transport in spin glasses but this remains an open field. This work has then be dedicated to the implementation of transport measurement in spin glasses and mesocopic conductors. The first part will be focused on a the experimental setup that was used to perform very precise transport measurements and on the processing of the data taken out of them. In a second part, we will present some general physical characteristics of our samples such as their resistance dependence to the temperature or magnetic field, before extracting the quantum signature in magnetoresistance measurements. Finally, we will discuss the results obtained. We show that strong changes in the microscopic disorder happen even at low temperatures, in opposition to what is believed. We argue that those observed changes are purely structural and come from systems that are widely distributed in energy
Adroguer, Pierre. "Propriétés de transport électronique des isolants topologiques." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2013. http://tel.archives-ouvertes.fr/tel-00832048.
Achille, Matteo d'. "Statistical properties of the Euclidean random assignment problem." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASQ003.
Given 2n points, n ``red'' and n ``blue'', in a Euclidean space,solving the associated Euclidean Assignment Problem consists infinding the bijection between red and blue points that minimizes afunctional of the point positions. In the stochastic version of this problem, the points are a Poisson Point Process, and some interest has developed over the years on the typical and average properties of thesolution in the limit n to ∞. This PhD thesis investigates this problem in a number of cases (many exact results in d=1, the derivation of some fine properties in d=2, in part still conjectural, an investigation on self-similar fractals with 1