Terahertz (THz) spectroscopy is an emerging technology with promising applications in imaging, homeland security, and material detection and quantification. Frequencies in the THz region can be generated by optical rectification of ultrafast near-infrared laser pulses in the presence of a nonlinear optical (NLO) materials such as organic crystals. Non-centrosymmetric organic THz generating crystals such as DAST, HMQ-TMS, and OH1 have received special attention due to the strong generated fields on the order of MV/cm. The cation of these organic salts is designed by connecting electron-donating with electron-accepting groups via a highly planar aromatic system. To improve the performance of organic crystals for THz generation, the molecular hyperpolarizability (β) can be optimized by introducing modifications in the architecture of these push-pull chromophores. However, the large dipole moments associated with molecules that have a large β promote the formation of NLO inactive centrosymmetric molecular alignments in the crystal state. This dissertation provides important insights into the design of new push-pull chromophores that feature a) higher β values compared with state-of-the-art organic crystals, and b) non-centrosymmetric molecular packing in the crystalline state. The first strategy presented on this dissertation relates to the introduction of a triple bond instead of a double bond in the cation of DAST to improve the β parameter. The newly designed 4DEP core was combined with different anions to promote non-centrosymmetric molecular packing with almost ideal arrangements for THz generation. However, large single crystals were difficult to obtain and high THz generation was not achieved. The second strategy presented in this dissertation raises the value of β by extending the π-conjugation length in different cations with dimethylamino and methoxy electron-donating groups. A new molecular cation, 6MNEP, was found to have large β value combined with ideal non-centrosymmetric molecular packing. Combining these two factors, a ~ 75% higher performance for THz generation is expected for 6MNEP compared with DAST. Currently, we are testing different crystallization techniques to grow large single crystals of 6MNEP. In addition to the strategies developed to increase the β parameter value, we also introduce a new molecular modification to induce non-centrosymmetric packing in organic salt THz generating crystals. This is achieved by substituting a methyl by an ethyl group in the quaternary nitrogen of hydrogen-bonded crystals. We showed the applicability of this method for changing molecular packing in the crystal state from centrosymmetric to non-centrosymmetric in two different molecular cations. We also demonstrated the generation of strong THz fields in the novel NLO crystal EHPSI-4NBS.

Recentemente, os compostos não-centrossimétricos têm sido intensamente estudados devido à grande variedade de comportamentos magnéticos, os quais são induzidos pela ausência de centro de simetria na sua estrutura cristalográfica. Esta assimetria induz uma modificação na estrutura de bandas, causando um acoplamento spin-orbita antissimétrico quem é responsável por mecanismos de interação magnética inusuais. A supercondutividade em este tipo de compostos apresenta propriedades que divergem do comportamento esperado pela teoria BCS. Neste trabalho será apresentado um estudo sobre a investigação de supercondutividade em dois sistemas ternários, Y-Co-C e Lu-Ni-C particularmente nos compostos YCo1-xC2 e Lu1-xThNiC2. Estes compostos cristalizam na estrutura CeNiC2 de simetria ortorrômbica é do grupo espacial 38 Amm2 que não possui centro de inversão. As técnicas de caracterização usadas neste trabalho incluem medidas de magnetização, resistividade e calor especifico como funções da temperatura, assim como magnetização como função do campo magnético aplicado. O composto YCo0.7C2 é supercondutor com Tc = 4 K e exibe um comportamento que diverge da teoria BCS. As medidas realizadas neste trabalho sugerem que este material é um forte candidato como supercondutor não convencional, onde poderia existir uma mistura de contribuições nos canais singleto e tripleto. No caso do sistema Lu1-xThxNiC2 os resultados preliminares indicam claramente supercondutividade nos compostos dopados com Th, onde a composição Lu0.6Th0.4NiC2 apresenta uma Tc= 8 K. / In recent years, non-centrosymmetric compounds have attracted a great interest because of their wealth variety of topical behaviors, induced by the lack of the inversion center on the crystallographic structure. This asymmetry leads to a strong modification in the band structures, causing an antisymmetric spin-orbit coupling which is responsible for unusual magnetic interaction mechanisms. Superconductivity in compounds whose crystal structure lacks inversion symmetry are known to display intriguing properties that deviate from conventional BCS superconducting behavior. Here we report the analysis of the ternary systems Y-Co-C and Lu-Ni-C, We focused our analysis in the intermetallic compounds YCo1-xC2 and Lu1-xThxNiC2. Magnetization, resistivity, and heat capacity measurements on polycrystalline samples of noncentrosymmetric YCo0.7C2, showing clear evidence of bulk superconductivity with a critical temperature of Tc =4 K. Interestingly the specific heat of the superconducting state deviates from conventional exponential temperature dependence, which is suggestive of possible unconventional superconducting behavior in YCo0.7C2, similar to that seen in the isostructural and isoelectronic superconductor LaNiC2. Besides, these results strongly suggest that this material is a strong candidate of multiband superconductivity. In the case of the system Lu1- xThxNiC2 our results showed a clear superconducting signal in the Th doped samples, where the composition Lu0.6Th0.4NiC2 has a Tc= 8 K.

Recentemente, os compostos não-centrossimétricos têm sido intensamente estudados devido à grande variedade de comportamentos magnéticos, os quais são induzidos pela ausência de centro de simetria na sua estrutura cristalográfica. Esta assimetria induz uma modificação na estrutura de bandas, causando um acoplamento spin-orbita antissimétrico quem é responsável por mecanismos de interação magnética inusuais. A supercondutividade em este tipo de compostos apresenta propriedades que divergem do comportamento esperado pela teoria BCS. Neste trabalho será apresentado um estudo sobre a investigação de supercondutividade em dois sistemas ternários, Y-Co-C e Lu-Ni-C particularmente nos compostos YCo1-xC2 e Lu1-xThNiC2. Estes compostos cristalizam na estrutura CeNiC2 de simetria ortorrômbica é do grupo espacial 38 Amm2 que não possui centro de inversão. As técnicas de caracterização usadas neste trabalho incluem medidas de magnetização, resistividade e calor especifico como funções da temperatura, assim como magnetização como função do campo magnético aplicado. O composto YCo0.7C2 é supercondutor com Tc = 4 K e exibe um comportamento que diverge da teoria BCS. As medidas realizadas neste trabalho sugerem que este material é um forte candidato como supercondutor não convencional, onde poderia existir uma mistura de contribuições nos canais singleto e tripleto. No caso do sistema Lu1-xThxNiC2 os resultados preliminares indicam claramente supercondutividade nos compostos dopados com Th, onde a composição Lu0.6Th0.4NiC2 apresenta uma Tc= 8 K. / In recent years, non-centrosymmetric compounds have attracted a great interest because of their wealth variety of topical behaviors, induced by the lack of the inversion center on the crystallographic structure. This asymmetry leads to a strong modification in the band structures, causing an antisymmetric spin-orbit coupling which is responsible for unusual magnetic interaction mechanisms. Superconductivity in compounds whose crystal structure lacks inversion symmetry are known to display intriguing properties that deviate from conventional BCS superconducting behavior. Here we report the analysis of the ternary systems Y-Co-C and Lu-Ni-C, We focused our analysis in the intermetallic compounds YCo1-xC2 and Lu1-xThxNiC2. Magnetization, resistivity, and heat capacity measurements on polycrystalline samples of noncentrosymmetric YCo0.7C2, showing clear evidence of bulk superconductivity with a critical temperature of Tc =4 K. Interestingly the specific heat of the superconducting state deviates from conventional exponential temperature dependence, which is suggestive of possible unconventional superconducting behavior in YCo0.7C2, similar to that seen in the isostructural and isoelectronic superconductor LaNiC2. Besides, these results strongly suggest that this material is a strong candidate of multiband superconductivity. In the case of the system Lu1- xThxNiC2 our results showed a clear superconducting signal in the Th doped samples, where the composition Lu0.6Th0.4NiC2 has a Tc= 8 K.

Title: Magnetism in the non-centrosymmetric uranium compound: UIrSi3 Author: RNDr. Jaroslav Valenta Department: Department of Condensed Matter Physics Supervisor of the doctoral thesis: RNDr. Jiří Prchal, Ph.D., DCMP Abstract: The study presented in this thesis is focused on UIrSi3 which is one of two known uranium compounds that crystallize in a non-centrosymmetric structure. This first study of UIrSi3 in single-crystalline form confirms antiferromagnetic order below TN = 41.7 K and reveals strong uniaxial anisotropy. The antiferromagnetic order is suppressed by application of a magnetic field along the c axis (0HC = 7.3 T at 2 K). In contrast, application of a magnetic field up to 14 T along the a axis gives paramagnetic response. The high TN, contrasting with the low 0HC, together with the opposite signs of the paramagnetic Curie temperatures of the a-axis and c-axis paramagnetic susceptibility indicate a competition between antiferromagnetic and ferromagnetic interactions. The first-order metamagnetic transition at HC shows asymmetric hysteresis which reflects a complex antiferromagnetic ground state. With increasing temperature, the hysteresis becomes gradually smaller and vanishes at 28 K where the first-order transition changes to second-order transition which remains up to TN. The point where the...

The experimental pieces of evidence for the existence of Majorana states in topo- logical superconductors have so far been inconclusive despite intense research in the past two decades [Zha+20; Kay+20]. Combined with promising applications in quantum computing [Nay+08; Ali+11] and the resulting technological development of society, the elusiveness of Majorana states keeps motivating theoretical and ex- perimental research to this day. Our analytical findings and numerical explorations in new topological superconducting platforms suggest several tools and solutions for their future realisation in condensed matter systems. The planar Josephson junction (pJJ) introduced in 2017 by F. Pientka et al. [Pie+17] and M. Hell et al. [HLF17] is a versatile platform for topological superconductivity. It harnesses the tunability of the superconducting phase difference across the Josephson junction as an external control parameter that switches the pJJ between the trivial and topological phases of matter. The junction between the (trivial) superconductors is quasi-one-dimensional and hosts one new Majorana zero mode at each of its ends following each topological phase transition. However, the creation of a second Majorana zero mode on one end triggers a return to the trivial regime as both zero modes hybridize into a regular non-topological fermion. It is then crucial to identify the model parameters that lead to topological phases with a single Majorana state per end. Our main result on the pJJ establishes the general constraint on its microscopic parameters—including the phase difference and a magnetic field—to cross the topo- logical phase transitions. The identification of sectors in parameter space leading to a single Majorana mode becomes then straightforward. In some limits the pJJ develops a topological sector at small magnetic field for a phase difference close to the value p while it remains trivial at the same field near zero phase difference. Since the phase is sufficient to turn on and off the topology, we call this feature “switchable topology”. Looking for switchable topology is experimentally relevant as it makes the topology easily tunable while keeping intact the proximitized su- perconductivity otherwise jeopardized by the applied field. Concretely, we found switchable topology in three configurations: in wide junctions with a transparent interface with the superconducting regions, in fine-tuned narrow junctions weakly coupled to the superconducting regions, and in junctions with a strong Zeeman energy when they are ultranarrow and transparent. Thanks to our exact analytical results, setups interpolating between these limits can adjust the desired properties at will. The other important finding about the pJJ concerns the stability of its topological phases, by which we mean the presence of a sizable spectral gap in the topological sector. We observed that the Rashba spin-orbit coupling is responsible for strongly decreasing the gap in the relevant topological sector at low Zeeman field, but sym- metry arguments justify that wide, transparent junctions are generically immune to this effect for large enough Rashba coupling. After 2017, other platforms started to use the Josephson superconducting phase difference as a knob to trigger topological superconductivity [Liu+19; JY21]. We introduce here the stacked Josephson junction (sJJ) as a new platform for topological superconductivity, which is made of two non-centrosymmetric superconductors sandwiching a two-dimensional magnet around which chiral Majorana edge modes propagate. Unlike the Majorana zero modes in the pJJ, chiral Majorana modes can add to each other if they propagate in the same direction, as indicated by the integer Chern number of their topological phase. The bulk-edge correspondence, however, only constrains the net number of topological edge states and allows room for other non-topological states to coexist with the chiral Majorana states without interacting with them. We found that the presence of trivial chiral edge modes in the sJJ restricts access to the Majorana states themselves. The symmetry protection of the trivial modes, fortunately, disappears with an in-plane magnetic field applied through the magnet or with superconducting leads different on the top and at the bottom of the stacked junction. The theoretical investigations of topological platforms have currently outnum- bered the experiments with convincing signatures of Majorana edge states. This imbalance calls for new ways to probe the agreement between topological models and laboratory setups. The critical current of a Josephson junction acts as a link between the microscopic description and macroscopic observables. Thermoelectric measurements, which distinguish between supercurrent and quasiparticle current, modify this model-dependent connection, and would provide an electrical probe to estimate the validity of a model like that of the pJJ. We computed the contribution to the thermoelectric coefficient of the bulk states of a uniform superconductor, that has a similar environment to that of the pJJ (i.e., Rashba coupling and in-plane Zeeman field). The results were not conclusive and motivated us to suggest new analytical and numerical approaches to obtain the thermoelectric response of the pJJ, in particular by including the contribution of the Andreev bound states and non-linear effects.:Foreword — how to read this thesis 1 Preamble A popular short story: pencils and lightbulbs 5 Basics and concepts 1 Introduction to Majorana physics 13 1.1 The electrons & their properties 13 1.1.1 Hamiltonian for the planar Josephson junction 17 1.2 The scattering matrix for bound states 19 1.3 Andreev bound states for topology 24 1.4 Topological superconductivity & Majorana edge states 28 1.5 Induced topological superconductivity 34 1.6 Summary 36 Appendices 37 1.A Microscopic dynamics 37 1.A.1 Origin of spin–orbit coupling 37 1.A.2 Bogoliubov-deGennes symmetrization 37 1.A.3 Andreev reflection below the coherence length 38 1.A.4 Proximity-induced superconductivity 40 1.A.5 From s- to p-wave superconductivity 41 1.B Scattering theory for bound states 44 1.B.1 Bound states as trapped waves 44 1.B.2 Scattering theory for an open region 45 1.B.3 Scattering theory for two open regions 46 1.B.4 Bound states recovered from an open region 47 1.B.5 Numerical scattering theory for bound states 48 2 Perspectives on electronic transport 53 2.1 Electric current in a metal 53 2.2 Quantum-mechanical current 54 2.2.1 Expression for the microscopic current 55 2.3 Thermoelectric current 57 2.3.1 The Boltzmann transport equation 61 2.4 Supercurrents and the superconducting coherence phase 64 2.4.1 Josephson currents 67 Appendices 71 2.A Electric current from a potential difference 71 2.B Scattering and current 71 2.C Hole-based current in metals 73 Introduction Introduction to the Research Projects 77 i Topological properties of Josephson junctions 3 Switchable topology in the planar Josephson junction 85 Motivation & Overview of the Study 85 3.1 The planar Josephson junction and the nanowire setup 87 3.1.1 Comparison with the nanowire setup. 89 3.2 Model 92 3.3 General formula for the phase transitions 94 3.3.1 Spin decoupling for the phase transitions 96 3.3.2 Exact reflection coefficients 97 3.3.3 Exact scattering formula and Andreev reflectivity 98 3.3.4 Andreev approximation 100 3.3.5 Dimensionless formulation 101 3.3.6 Numerical and analytical checks 103 3.4 Three regimes for switchable topology 105 3.4.1 Diamond-shape regime 108 3.4.2 V-shape regime 110 3.4.3 Nanowire regime 111 3.4.4 Summary: extent of the topological transitions 114 3.5 Avoiding regimes with a small topological gap 117 3.5.1 Gapless lines as BDI phase transitions 119 3.5.2 Opening the gap in f = p 120 3.5.3 Role of the Rashba coupling 121 3.6 Conclusion 125 Appendices 129 3.A Limiting cases of the pJJ 129 3.A.1 Andreev approximation 129 3.A.2 Small field limit 131 3.A.3 Delta-barrier junction 131 3.A.4 Semiconductor nanowire 132 3.B Normal reflection via surface impurity and surface refraction 134 3.C Symmetry-constrained gap closings 136 3.D Linear deviation of the gapless line near f = p 138 3.E Calculations for the scattering formula 141 3.E.1 Boundary conditions 141 3.E.2 Combinations of scattering coefficients 142 3.E.3 Andreev coefficients for the phase transitions 143 3.E.4 Formula for B > μ 145 4 Topological and trivial chiral states in the stacked Josephson junction 147 Motivation & Overview of the Study 147 4.1 The basics of the stacked Josephson junction 149 4.2 Continuous and lattice models 151 4.3 Topological index 155 4.3.1 Methodology for the Chern number 155 4.3.2 Interpretation of the results 156 4.4 Topological and trivial edge states 162 4.5 BDI phase transitions 167 4.5.1 Dimensional reduction 168 4.5.2 Link between topological invariants 170 4.5.3 Explaining the low-energy sector 171 4.6 Conclusion 174 Appendices 177 4.A Symmetries of the Hamiltonian 177 4.A.1 Class D 177 4.A.2 Class BDI 177 4.A.3 Gapless line in f = p 178 4.A.4 Symmetry around f = p 179 4.B The parity index in 2D TSC 180 ii Transport properties of the planar Josephson junction 5 An approach to thermoelectric effects in the planar Josephson junction 183 Motivation & Overview of the Study 183 5.1 From the Josephson junction to a homogeneous superconductor 185 5.2 Model and Phenomenology 187 5.2.1 Homogeneous superconductor 187 5.2.2 Analytical spectrum and two-surface approximation 188 5.2.3 Magnetoelectric supercurrent: phenomenology 191 5.3 Electric current in a spin–orbit coupled superconductor 194 5.3.1 Formula for the current 196 5.3.2 Zero-temperature current 198 5.3.3 Small perturbations at finite temperature 200 5.4 Thermoelectric current in a spin–orbit coupled superconductor 206 5.4.1 Distribution imbalance under temperature bias 208 5.4.2 Explicit formula for the thermoelectric current 209 5.5 Discussion and Outlook 213 Appendices 219 5.A The Boltzmann equation in temperature-biased superconductors 219 5.A.1 The linear approximation 220 5.A.2 The low-temperature approximation 220 5.A.3 Integral solution of the Boltzmann equation 223 5.B Diagonalisation of the planar superconductor 225 5.B.1 Eigenstates of spin–orbit coupled superconductor 225 5.B.2 Eigenstates with a small Zeeman field 227 Conclusion Majorana quasiparticles in Josephson junctions 233 Extra Material 6 Mathematical details of Scattering theory 241 6.1 Asymmetric quantum well 241 6.2 Scattering theory for an open region 243 6.2.1 Change in potential over a small region 243 6.2.2 Change in spin-orbit coupling over a small region 245 6.2.3 Change in mass over a small region 245 7 Numerical codes for chapter 4 247 7.1 BDI index 247 7.2 Chern number 255 7.3 Spectral gap 257 7.4 Localized edge states 258 8 Short courses 261 8.1 Two formulations of superconductivity 261 8.1.1 The BCS Hamiltonian 261 8.1.2 The Bogoliubov transformation 263 8.1.3 Bogoliubov-de Gennes symmetrization 264 8.1.4 Building the semiconductor representation 266 8.2 Topological band theory 270 8.3 Majorana physics in 1D 274 8.3.1 The SSH chain 275 8.3.2 The Kitaev chain 277 Bibliography 283

Η διφωτονική απορρόφηση (ΔΦΑ) είναι το μη γραμμικό-φαινόμενο κατά το οποίο δύο φωτόνια απορροφούνται ταυτόχρονα σε ένα υλικό μέσο. Τα τελευταία 20 χρόνια το φαινόμενο αυτό έχει προσελκύσει ιδιαίτερα το ενδιαφέρον της επιστημονικής κοινότητας για την ανακάλυψη νέων αποδοτικών ενώσεων λόγω και των εφαρμογών που έχει βρεθεί ότι μπορεί να προσφέρει. Η διφωτονική μικροσκοπία, ο διφωτονικός πολυμερισμός, η τρισδιάστατη αποθήκευση δεδομένων είναι μερικές από τις σημαντικές εφαρμογές που εκμεταλλεύονται τα πλεονεκτήματα της ΔΦΑ. Τη τελευταία δεκαετία η έρευνα επικεντρώνεται στη θεωρητική και πειραματική μελέτη της ΔΦΑ οργανικών ενώσεων με σκοπό την διασύνδεσης των χαρακτηριστικών της δομής των μορίων με την ΔΦΑ που παρέχουν και την εύρεση στρατηγικών σύνθεσης οργανικών ενώσεων υψηλής ΔΦΑ. Επίσης πολλές είναι οι επιστημονικές εργασίες που χρησιμοποιούν τις ενώσεις αυτές στην έρευνα για την ανάπτυξη και βελτίωση των διφωτονικών εφαρμογών. Στη διατριβή αυτή γίνεται μελέτη της ΔΦΑ συζυγιακών οργανικών ενώσεων αποτελούμενες από ένα κεντρικό τμήμα συνδεδεμένο αντιδιαμετρικά με δυο ίδιους υποκαταστάτες. Τα συμμετρικά αυτά μόρια έχουν ως κεντρικό τμήμα φλουορένιο ή αλκόξυ-φαινυλένιο ή καρβοξύλιο και διάφορους υποκαταστάτες στα άκρα. Η τεχνική μέτρησης διφωτονικά διεγερμένου φθορισμού με laser femtosecond χρησιμοποιήθηκε για τον υπολογισμό των τιμών της ενεργούς διατομής ΔΦΑ των μορίων στη φασματική περιοχή 750-840nm. Από τη συγκριτική μελέτη των ενώσεων προκύπτει ότι ο υποκαταστάτης φθαλιμίδιο προσφέρει την μεγαλύτερη ΔΦΑ και για τα τρία διαφορετικά κεντρικά τμήματα, ενώ όταν συνδέεται με το φλουορένιο έχει την υψηλότερη ενεργό διατομή ΔΦΑ φθάνοντας την τιμή των 1650GM στη φασματική περιοχή που μελετήθηκε. Επίσης παρατηρήθηκε ότι ο υποκαταστάτης ναφθαλιμίδιο προκαλεί μετατόπιση του μεγίστου ΔΦΑ σε αρκετά μεγαλύτερα μήκη κύματος. Παρόμοια μετατόπιση παρατηρείται και για τα μόρια με κεντρικό τμήμα το καρβαζόλιο. Η μετατόπιση αυτή του φάσματος ΔΦΑ δεν αντιστοιχεί σε μετατόπιση του φάσματος μονοφωτονικής απορρόφησης. Οφείλεται στην άρση της κεντροσυμμετρίας του μορίου, λόγω της διαμόρφωσης της δομής του, η οποία κάνει επιτρεπτή τη διφωτονική μετάβαση στην πρώτη μονοφωτονικά επιτρεπτή ενεργειακή κατάσταση που ειδάλλως είναι απαγορευμένη. Η επίδραση του διαλύτη στις διφωτονικές ιδιότητες των μορίων μελετάται επίσης στη διατριβή αυτή. Για τις τέσσερις πιο αποδοτικές ενώσεις, ως προς το διφωτονικά διεγερμένο φθορισμό, έγιναν μετρήσεις για τον υπολογισμό των φασμάτων ΔΦΑ τους σε πέντε διαλύτες διαφορετικής πολικότητας (διηλεκτρικής σταθεράς). Από τις μετρήσεις φάνηκε η σημαντική επίδραση του διαλύτη στη ΔΦΑ των τεσσάρων χρωστικών η οποία μεγιστοποιείται σε διαλύτη μεσαίας πολικότητας, ο τρεις στην ακετοφαινόνη και μια στο THF. Η χαμηλή κβαντική απόδοση φθορισμού που παρατηρείται στα διαλύματα με ακετοφαινόνης μειώνει αρκετά το διφωτονικά προκαλούμενο φθορισμό και κατατάσσει τo THF ως τον αποδοτικότερο διαλύτη για διφωτονικές εφαρμογές που εκμεταλλεύονται το φθορισμό. Επίσης και ο μη πολικός διαλύτης τολουόλιο προκαλεί έντονο φθορισμό λόγω της υψηλής κβαντικής απόδοσης παρόλο που επιφέρει δραστική μείωση της ΔΦΑ σε σύγκριση με τους άλλους διαλύτες που μελετήθηκαν. Δύο από τις χρωστικές που μελετήθηκαν ως προς τη ΔΦΑ τους χρησιμοποιήθηκαν ως φωτοεκκινητής πολυμερισμού ενός ακρυλικού μονομερούς και την μελέτη του πολυμερισμού συναρτήσει διαφόρων παραμέτρων ακτινοβόλησης της ρητίνης. Οι χρωστικές αυτές έχουν φλουορένιο ως κεντρικό τμήμα και υποκαταστάτες στα άκρα φθαλιμίδιο ή τριφαινυλαμίνη. Και οι δύο χρωστικές δύναται να προκαλέσουν τον πολυμερισμό του μονομερούς με ακτινοβόληση υπερβραχέων παλμών στα 800nm, αλλά η προσθήκη αμίνης ως συνεκκινητή μειώνει το κατώφλι ισχύος εκκίνησης του. Επίσης, σε υψηλές τιμές ισχύος ακτινοβόλησης στο ίδιο μήκος κύματος παρατηρήθηκε αυτο-πολυμερισμός του μονομερούς γεγονός το οποίο έχει επισημανθεί μία μόνο ακόμη φορά σε μια εργασία με ρητίνη μίξης τριών ακρυλικών μονομερών. Δύο ρητίνες που παρασκευάστηκαν στην παρούσα διατριβή αναμιγνύοντας το μονομερές με τη κάθε χρωστική και με προσθήκη του συνεκκινητή μελετήθηκαν για την εξάρτηση του πολυμερισμού από τον φακό εστίασης και από την ισχύ, την ταχύτητα σάρωσης και τη διάμετρο της δέσμης. Για το σκοπό αυτό κατασκευάστηκαν δοκίμια στα οποία εγγράφονταν πολυμερισμένες γραμμές μεταβάλλοντας κάποια από τις παραπάνω παραμέτρους και μετρώντας το πάχος και το ύψος των γραμμών αυτών από τις εικόνες μικροσκοπίου σάρωσης ηλεκτρονίων. Το γεγονός ότι ο μικρότερης ισχύος φακός παρατηρηθηκε ότι προκαλεί λεπτότερη γραμμή εξηγείται από το φαινόμενο κατωφλίου του πολυμερισμού. Ωστόσο η λεπτότερη γραμμή επιτυγχάνεται με τον ισχυρότερο φακό καθώς μπορεί να μειωθεί περισσότερο η ισχύς της δέσμης λόγω του χαμηλότερου κατωφλίου εκκίνησης του πολυμερισμού για το φακό αυτό. Η αύξηση της ταχύτητας σάρωσης ή η μείωση της ισχύος της δέσμης επιφέρουν μικρότερες διαστάσεις πάχους και ύψους της γραμμής που πολυμερίζεται. Επίσης η κατανομή της ισχύος ακτινοβόλησης σε ολόκληρο το πίσω άνοιγμα του φακού επιφέρει καλύτερη εστίαση και λεπτότερη πολυμερισμένη γραμμή. Ωστόσο η κατάλληλη χωρική διαμόρφωση της δέσμης μπορεί να μειώσει τις διαστάσεις των πολυμερισμένων δομών. / -

Ces travaux de thèse traitent de l’exploitation des nombreuses propriétés chimiques, physiques et structurales qu’offre le macrocycle porphyrinique.Le premier chapitre présente la sensibilisation de lanthanides émettant dans le proche-infrarouge par un chromophore porphyrinique. La synthèse d’une porphyrine substituée par deux 8-hydroxyquinoléines, sa métallation avec des lanthanides (La, Nd, Yb et Gd) ainsi que les propriétés photophysiques de ces complexes sont présentées. La synthèse de porphyrines fonctionnalisées par des oxamates orientés de façon convergente dans le but de diminuer les désactivations non radiatives du lanthanide par vibrations des liaisons est également étudiée. Le second chapitre décrit la synthèse de porphyrines substituées par deux groupements pyridyl et éthynylpyridyl en position méso-trans. La métallation du macrocyclique porphyrinique par du Zn(II) conduit à la formation de réseaux de coordination mono- ou bi-dimensionnels dont la topologie est dépendante de la nature de la porphyrine. Le troisième chapitre présente la fonctionnalisation de surface par chimi- ou par physi-sorption d’un réseau de coordination directionnel. Dans un premier temps la synthèse de porphyrines substituées par des pyridines et des terpyridines est présentée. Puis l’adsorption de ces tectons sur une surface de graphite est décrite. Enfin une dernière partie traite de la synthèse de porphyrines fonctionnalisées par deux ou quatre bras possédant des substituants soufrés, qui après chimisorption sur une surface d’or, pourraient servir de point d’ancrage à la construction d’un réseau de coordination directionnel perpendiculaire à la surface. / This thesis deals with the various chemical, physical and structural properties featured by the porphyrin macrocycle.The first chapter is related to the sensitization by a porphyrinic chromophore of the emission of lanthanide ions in the near-infrared. Synthesis of a porphyrin functionalized by two 8-hydroxyquinoline, its metallation with lanthanides (La, Nd, Yb and Gd) and its photophysical properties are described. In a second part, the synthesis of porphyrin functionalized by oxamates, in order to limit the non-radiative deactivation of lanthanides through vibrations of bounds, is also studied.The second chapter is focused on the synthesis of porphyrins substituted by two pyridyl or ethynylpyridyl groups in meso-trans positions. The metallation of the porphyrin core by Zn(II) leads to the formation a mono- or bi-dimensional coordination networks with different topologies depending on the nature of the porphyrin.The third chapter presents the surface functionnalisation by chemi- or physis-orption of a monodimensional polar network. The synthesis of porphyrin substituted with a pyridine and a terpyridine, necessary to the formation a non-centrosymmetric coordination network, is described. Thereafter the absorption of these compounds on graphite surface is studied. The second part of this chapter is related to the synthesis of porphyrin functionnalised by two or four arms with thiolate moiety that could be used as an anchor for the construction of a monodimensional network orthogonal to a gold surface.

Dans la première partie, nous présentons les résultats de l'étude du supraconducteur sans inversion de symétrie LaRhSi3 par spectroscopie muonique. En champ nul, nous n'avons pas détecté de champ interne. Ceci indique que la fonction d'onde de l'état supraconducteur n'est pas dominée par l'état triplet. Les mesures en champ transverse de 35G présentent une transition en accord avec la transition de phase attendue sous le champ critique Hc1. Nous avons répété ces mesures pour un champ entre Hc1 et Hc2, 150G. Le spectre obtenu pour ces mesures conserve l'asymétrie et relaxe rapidement à basse température tel que prédit pour un supraconducteur dans la phase d'Abrikosov. Néanmoins, les relaxations produites par ce balayage en température présentent une transition à près de 2 fois la température critique attendue. Dans la deuxième partie de ce mémoire, nous donnons l'interprétation des résultats de la diffraction neutronique inélastique par l'étude des champs électriques cristallins. Ces mesures ont été effectuées sur des aimants frustrés SrHo2O4 et SrDy2O4 sous la forme de poudre. L'étude des niveaux produits par les champs cristallins par la méthode des opérateurs de Stevens indique une perte du moment cinétique dans les deux matériaux. Pour le SrDy2O4, l'état fondamental serait constitué de quatre états dégénérés quasi accidentellement qui portent un moment magnétique total non-nul. Toute fois, nos mesures de susceptibilité magnétique ne montrent aucun ordre au-dessus de 50mK. Pour le SrHo2O4, le fondamental est formé d'une paire accidentelle. Nous obtenons un moment magnétique de 6.94(8)$\mu_B$ ce qui s'accorde avec les données expérimentales. / In the first part of this thesis, we present our muon spectroscopy results of the non-centrosymmetric superconductor LaRhSi3. Zero magnetic field measurements showed no internal field, suggesting at most a very small triplet component in the superconducting wave function. A temperature scan taken in 35G transverse-field geometry showed a phase transition at Hc1. The asymmetry of the muon relaxation spectrum measured at 20mK and field of 150G, which is between the lower and upper critical fields, shows a faster relaxation rate compared to the spectrum obtained at 4K, a behaviour expected in the presence of vortices in the type II superconductor. However, the temperature dependence of the relaxation rate begins to increase all the way to a temperature twice Tc of LaRhSi3 in a field of 150G. In the second part of this document, we present the interpretation of inelastic neutron scattering by crystalline electric fields. These measurements were carried out on powder samples of frustrated quantum magnets SrHo2O4 and SrDy2O4. Using Stevens operators method, we determined the level scheme du to crystalline electric field effects using a point charge model and fitted it to the experimental data. For the SrDy2O4 we found a ground state that appears to be composed of four quasi-accidental degenerate states that carry a non zero magnetic moment even though susceptibility measurements did not indicate magnetic order above 50mK. For the SrHo2O4, the ground state is a pair with a 6.98(8)$\mu_B$ magnetic moment. This lat value fots with experimental data.

Dans la première partie, nous présentons les résultats de l'étude du supraconducteur sans inversion de symétrie LaRhSi3 par spectroscopie muonique. En champ nul, nous n'avons pas détecté de champ interne. Ceci indique que la fonction d'onde de l'état supraconducteur n'est pas dominée par l'état triplet. Les mesures en champ transverse de 35G présentent une transition en accord avec la transition de phase attendue sous le champ critique Hc1. Nous avons répété ces mesures pour un champ entre Hc1 et Hc2, 150G. Le spectre obtenu pour ces mesures conserve l'asymétrie et relaxe rapidement à basse température tel que prédit pour un supraconducteur dans la phase d'Abrikosov. Néanmoins, les relaxations produites par ce balayage en température présentent une transition à près de 2 fois la température critique attendue. Dans la deuxième partie de ce mémoire, nous donnons l'interprétation des résultats de la diffraction neutronique inélastique par l'étude des champs électriques cristallins. Ces mesures ont été effectuées sur des aimants frustrés SrHo2O4 et SrDy2O4 sous la forme de poudre. L'étude des niveaux produits par les champs cristallins par la méthode des opérateurs de Stevens indique une perte du moment cinétique dans les deux matériaux. Pour le SrDy2O4, l'état fondamental serait constitué de quatre états dégénérés quasi accidentellement qui portent un moment magnétique total non-nul. Toute fois, nos mesures de susceptibilité magnétique ne montrent aucun ordre au-dessus de 50mK. Pour le SrHo2O4, le fondamental est formé d'une paire accidentelle. Nous obtenons un moment magnétique de 6.94(8)$\mu_B$ ce qui s'accorde avec les données expérimentales. / In the first part of this thesis, we present our muon spectroscopy results of the non-centrosymmetric superconductor LaRhSi3. Zero magnetic field measurements showed no internal field, suggesting at most a very small triplet component in the superconducting wave function. A temperature scan taken in 35G transverse-field geometry showed a phase transition at Hc1. The asymmetry of the muon relaxation spectrum measured at 20mK and field of 150G, which is between the lower and upper critical fields, shows a faster relaxation rate compared to the spectrum obtained at 4K, a behaviour expected in the presence of vortices in the type II superconductor. However, the temperature dependence of the relaxation rate begins to increase all the way to a temperature twice Tc of LaRhSi3 in a field of 150G. In the second part of this document, we present the interpretation of inelastic neutron scattering by crystalline electric fields. These measurements were carried out on powder samples of frustrated quantum magnets SrHo2O4 and SrDy2O4. Using Stevens operators method, we determined the level scheme du to crystalline electric field effects using a point charge model and fitted it to the experimental data. For the SrDy2O4 we found a ground state that appears to be composed of four quasi-accidental degenerate states that carry a non zero magnetic moment even though susceptibility measurements did not indicate magnetic order above 50mK. For the SrHo2O4, the ground state is a pair with a 6.98(8)$\mu_B$ magnetic moment. This lat value fots with experimental data.

Cette thèse est divisée en trois parties. Une première section présente les résultats de l'étude de la formation de polarons magnétiques liés (BMP) dans le ferroaimant EuB6 par diffusion de neutrons à petits angles (SANS). La nature magnétique du système ferromagnétique est observée sous une température critique de 15K. La signature des BMP n'apparaît pas dans la diffusion de neutrons, mais ces mesures permettent de confirmer une limite inférieure de 100\AA à la longueur de cohérence des BMP (xi_{Lower}). Dans un second temps, l'étude du LaRhSi3, un supraconducteur sans symétrie d'inversion, par muSR et ZF-muSR nous permet de sonder le comportement magnétique du système dans la phase supraconductrice. Aucun champ magnétique interne n'a été détecté en ZF-muSR sous la température critique (T_c = 2.2K). Cela indique que la phase supraconductrice ne porte pas de moment cinétique intrinsèque. L'analyse du spectre d'asymétrie sous l'application d'un champ magnétique externe nous apprend que le système est faiblement type II par l'apparition de la signature de domaines magnétiques typique d'un réseau de vortex entre H_{c1}(0) et H_{c2}(0), respectivement de 80+/- 5 et 169.0 +/- 0.5 G. Finalement, la troisième section porte sur l'étude du champ magnétique interne dans l'antiferroaimant organique NIT-2Py. L'observation d'une dépendance en température des champs magnétiques internes aux sites d'implantation muonique par ZF-muSR confirme la présence d'une interaction à longue portée entre les moments cinétiques moléculaires. Ces valeurs de champs internes, comparées aux calculs basés sur la densité de spins obtenue par calculs de la théorie de la fonctionnelle de la densité, indiquent que la moitié des molécules se dimérisent et ne contribuent pas à l'ordre antiferromagnétique. La fraction des molécules contribuant à l'ordre antiferromagnétique sous la température critique (T_c = 1.33 +/- 0.01K) forme des chaines uniformément polarisées selon l'axe (1 0 -2). Ces chaines interagissent antiferromagnétiquement entre elles le long de l'axe (0 1 0) et ferromagnétiquement entre les plan [-1 0 2]. / This thesis is divided in three sections. The first section presents the results from a small angle neutron scattering (SANS) investigation of the formation of bound magnetic polarons in the ferromagnet EuB6. While the magnetic nature of the system was observed below 15K, we could not resolve the q dependent signature of the polarons, thus putting a lower limit of 100\AA to the coherence length of the phenomenon (xi_{Lower}). Secondly, we investigated the non-centrosymmetric superconductor LaRhSi3 by muSR. The absence of an internal field below T_c = 2.2 K in ZF-muSR, indicates that the superconducting wave function does not carry an intrinsic magnetic moment. The asymmetry spectrum taken under external magnetic field shows the magnetic signature associated with vortices between H_{c1}(0) and H_{c2}(0), respectively 80 +/- 5 and 169.0 +/- 0.5 G, suggesting the system is weakly type-II. Finally, the third section presents the zero field muSR study of internal magnetic fields in the organic antiferromagnet NIT-2Py. The temperature dependent oscillating signal in the ZF-muSR spectrum confirms the presence of a long-range magnetic interaction between the molecules. By comparing the measured internal magnetic fields to calculated values based on density fonctional theory calculations, we confirm that half the molecules dimerizes while the other half forms the antiferromagnetic order under the critical temperature (T_c = 1.33 +/- 0.01K). In this antiferromagnetic order, the moments on the magnetic molecules are uniformly aligned along the (1 0 -2) axis. They interact antiferromagnetically along the (0 1 0) axis and ferromagnetically between the [-1 0 2] planes.