Mott transition, antiferromagnetism, and unconventional superconductivity in layered organic superconductors

The phase diagram of the layered organic superconductor $\kappa$-(ET)$_{2}$Cu[N(CN)$_{2}$]Cl has been accurately measured from a combination of $^{1}$H NMR and AC susceptibility techniques under helium gas pressure. The domains of stability of antiferromagnetic and superconducting long-range orders in the pressure {\it vs} temperature plane have been determined. Both phases overlap through a first-order boundary that separates two regions of inhomogeneous phase coexistence. The boundary curve is found to merge with another first order line related to the metal-insulator transition in the paramagnetic region. This transition is found to evolve into a crossover regime above a critical point at higher temperature. The whole phase diagram features a point-like region where metallic, insulating, antiferromagnetic and non s-wave superconducting phases all meet.Comment: 4 pages, 6 figures, Revte

Méthodes de calcul numérique pour la simulation thermique des circuits intégrés

RÉSUMÉ La simulation thermique des circuits intégrés est aujourd'hui incontournable afin de prévenir les problèmes de dissipation thermique. Les circuits intégrés modernes exhibent une densité de puissance très élevée, pouvant conduire à une température excessive, dégradant les performances du circuit et réduisant sa durée de vie. Depuis leur invention en 1958, les circuits intégrés ont subi une évolution spectaculaire. La miniaturisation des composants, l'émergence des technologies tridimensionnelles et l'introduction de systèmes de refroidissement à base de liquide nécessitent de résoudre des problèmes thermiques très complexes. Les méthodes numériques fournissent un outil de simulation puissant, mais aussi très coûteux en calcul. Les simulateurs thermiques existants basés sur les méthodes numériques requièrent un temps d'exécution très long et une consommation de mémoire très importante. Ces inconvénients majeurs ralentissent considérablement la conception des circuits intégrés ou contraint à choisir des solutions thermiques non optimales. Cette thèse propose deux méthodes de calcul numérique originales pour accélérer la simulation thermique des circuits intégrés. La première méthode est destinée à la simulation du régime transitoire, tandis que la deuxième méthode cible le régime permanent. Les méthodes de calcul proposées combinent des algorithmes puissants tels que la décomposition des opérateurs, les méthodes de projection et la décomposition de domaine. Les méthodes de calcul proposées sont évaluées sur des problèmes thermiques réalistes et variés, en étant comparés à des méthodes de calcul classiques bien éprouvées. La méthodologie utilisée pour modéliser le comportement thermique des circuits intégrés est validée en comparant les résultats obtenus par simulation à des mesures thermiques effectuées sur un circuit physique réel. Dans le cadre de cette thèse, un simulateur thermique pour circuits intégrés, appelé ICTherm a été développé. Ce logiciel implémente les méthodes de calcul proposées dans cette thèse pour simuler le régime transitoire et le régime permanent. Le logiciel ICTherm est actuellement utilisé en milieu universitaire pour des projets de recherche.---------- ABSTRACT Since their introduction in 1958, integrated circuits have gone through a spectacular evolution. The transistor miniaturization, the emergence of tridimensional technologies have caused an explosion in complexity. In addition, modern integrated circuits generate very high heat fluxes that can lead to a high temperature, degrading the performance and reducing the lifetime of the device. The thermal simulation of integrated circuits is extensively used to prevent this kind of heat dissipation issues, but its application is becoming increasingly difficult with the growing complexity of chip designs. Numerical methods offer a powerful tool for the thermal simulation of integrated circuits. However, their high computation cost leads to long simulation times and to a vast memory usage, slowing down the design process or constraining the designer to unoptimized solutions. This thesis presents two highly-efficient methods for the thermal simulation of integrated circuits, for both transient and steady-state thermal problems. The proposed methods combine powerful algorithms, such as operator splitting, sub-space projection, and domain decomposition. We evaluated the proposed techniques on a variety of representative thermal problems. Our results show up to an order of magnitude improvement in simulation speed when compared against well established methods for the same level of accuracy. We have also validated our approach by comparing simulation results with the temperature measured on a physical device via infrared thermography, achieving an error smaller than 6%. In addition, we developed a thermal simulator for integrated circuits called ICTherm, implementing the methods proposed in this thesis. ICTherm can be used to simulate the transient and steady-state behaviour of arbitrary integrated circuits, and it is currently used for research by several universities

Crystalline Bi4Ge3O12 fibers fabricated by micro-pulling down technique for optical high voltage sensing

AbstractCommonly optical high voltage sensors employ the Pockels effect in a bulk electro-optic crystal such as Bi4Ge3O12 (BGO). Typically, the maximum crystal length is 100-200mm and determined by the limits of the conventional growth technique (Czochralski). In this paper we report on the growth by a micro-pulling down technique of long single crystalline BGO fibers as an alternative to bulk crystals and their characterization for voltage sensing. The fiber thickness may range from a few 100μm to a few mm. The parameters needed for stable growth over the entire length of the crystal were analyzed and optimized. Thin rods with a length of up to 850mm were grown. Samples were characterized with respect to homogeneity of growth, residual birefringence (BGO is free of natural birefringence), crystal orientation, and performance under voltage

Thermal Aware Design Method for VCSEL-Based On-Chip Optical Interconnect

Optical Network-on-Chip (ONoC) is an emerging technology considered as one of the key solutions for future generation on-chip interconnects. However, silicon photonic devices in ONoC are highly sensitive to temperature variation, which leads to a lower efficiency of Vertical-Cavity Surface-Emitting Lasers (VCSELs), a resonant wavelength shift of Microring Resonators (MR), and results in a lower Signal to Noise Ratio (SNR). In this paper, we propose a methodology enabling thermal-aware design for optical interconnects relying on CMOS-compatible VCSEL. Thermal simulations allow designing ONoC interfaces with low gradient temperature and analytical models allow evaluating the SNR.Comment: IEEE International Conference on Design Automation and Test in Europe (DATE 2015), Mar 2015, Grenoble, France. 201

A sulfur-rich pi-electron acceptor derived from 5,5 '-bithiazolidinylidene: charge-transfer complex vs. charge-transfer salt

International audienceNovel pi-electron acceptors are still highly desirable for the formation of conducting salts or as n-dopable semiconductors. We describe here two synthetic approaches to substitute a dicyanovinylidene group, C=C(CN)(2) to a thioketone (C=S) in the recently described DEBTTT acceptor where DEBTTT stands for (E)-3,3'-diethyl-5,5'-bithiazolidinylidene-2,4,2',4'-tetrathione. These electron withdrawing groups enhance the electron accepting ability as demonstrated through electrochemical investigations, without hindering the formation of short intra-and intermolecular S center dot center dot center dot S contacts in the solid state. Association of this acceptor 1 with tetramethyltetrathiafulvalene (TMTTF) and decamethylferrocene (Fe(Cp*)(2)) afforded 1 : 1 adducts which were analyzed by single crystal X-ray diffraction. Combined with vibrational and magnetic properties, it appears that [TMTTF][1] behaves as a neutral charge-transfer complex while [Fe(Cp*)(2)][1] is an ionic salt. The concentration of the spin density on the exocyclic sulfur atoms in 1(-center dot) favors the setting of direct anti-ferromagnetic interactions in [Fe(Cp*)(2)][1

Growth and Characterization of Single Crystalline Bi 4

The micro-pulling-down technique for crystalline fiber growth is employed to grow fibers and thin rods of bismuth germanate, Bi4Ge3O12 (BGO), for use in electrooptic high voltage sensors. The motivation is the growth of fibers that are considerably longer than the typical lengths (100–250 mm) that are achieved by more conventional growth techniques like the Czochralski technique. At a given voltage (several hundred kilovolts in high voltage substation applications) longer sensors result in lower electric field strengths and therefore more compact and simpler electric insulation. BGO samples with lengths up to 850 mm and thicknesses from 300 μm to 3 mm were grown. Particular challenges in the growth of BGO fibers are addressed. The relevant optical properties of the fibers are characterized, and the electrooptic response is investigated at voltages up to

Anisotropic Charge Distribution and Anisotropic van der Waals Radius Leading to Intriguing Anisotropic Noncovalent Interactions

Although group (IV-VII) nonmetallic elements do not favor interacting with anionic species, there are counterexamples including the halogen bond. Such binding is known to be related to the charge deficiency because of the adjacent atom's electron withdrawing effect, which creates s/p-holes at the bond-ends. However, a completely opposite behavior is exhibited by N-2 and O-2, which have electrostatically positive/negative character around cylindrical-bond-surface/bond-ends. Inspired by this, here we elucidate the unusual features and origin of the anisotropic noncovalent interactions in the ground and excited states of the 2nd and 3rd row elements belonging to groups IV-VII. The anisotropy in charge distributions and van der Waals radii of atoms in such molecular systems are scrutinized. This provides an understanding of their unusual molecular configuration, binding and recognition modes involved in new types of molecular assembling and engineering. This work would lead to the design of intriguing molecular systems exploiting anisotropic noncovalent interactions.open

Metal Hydrides Form Halogen Bonds: Measurement of Energetics of Binding

The formation of halogen bonds from iodopentafluorobenzene and 1-iodoperfluorohexane to a series of bis(η5-cyclopentadienyl)metal hydrides (Cp2TaH3, 1; Cp2MH2, M = Mo, 2, M = W, 3; Cp2ReH, 4; Cp2Ta(H)CO, 5; Cp = η5-cyclopentadienyl) is demonstrated by 1H NMR spectroscopy. Interaction enthalpies and entropies for complex 1 with C6F5I and C6F13I are reported (ΔH° = −10.9 ± 0.4 and −11.8 ± 0.3 kJ/mol; ΔS° = −38 ± 2 and −34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ΔH° = −7.3 ± 0.1 kJ/mol, ΔS° = −24 ± 1 J/(mol·K)). For the more reactive complexes 2–5, measurements are limited to determination of their low-temperature (212 K) association constants with C6F5I as 2.9 ± 0.2, 2.5 ± 0.1, <1.5, and 12.5 ± 0.3 M–1, respectively