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Doped organic semiconductors are critical to emerging device applications, including thermoelectrics, bioelectronics, and neuromorphic computing devices. It is commonly assumed that low conductivities in these materials result primarily from charge trapping by the Coulomb potentials of the dopant counterions. Here, we present a combined experimental and theoretical study rebutting this belief. Using a newly developed doping technique based on ion exchange, we prepare highly doped films with several counterions of varying size and shape and characterize their carrier density, electrical conductivity, and paracrystalline disorder. In this uniquely large data set composed of several classes of high-mobility conjugated polymers, each doped with at least five different ions, we find electrical conductivity to be strongly correlated with paracrystalline disorder but poorly correlated with ionic size, suggesting that Coulomb traps do not limit transport. A general model for interacting electrons in highly doped polymers is proposed and carefully parametrized against atomistic calculations, enabling the calculation of electrical conductivity within the framework of transient localization theory. Theoretical calculations are in excellent agreement with experimental data, providing insights into the disorder-limited nature of charge transport and suggesting new strategies to further improve conductivities.

We study long-range interacting electrons on the triangular lattice using mixed quantum/classical simulations going beyond the usual classical descriptions of the lattice Coulomb fluid. Our results in the strong interaction limit indicate that the proliferation of quantum defects governs the low-temperature dynamics of this strongly frustrated system. The present theoretical findings explain the phenomenology observed in the \thetaθ-ET_22X materials as they fall out of equilibrium, including glassiness, resistive switching and a strong sensitivity to the electronic structure anisotropy. The method devised here can be easily generalized to address other systems and devices where itinerant and correlation-localized degrees of freedom are intertwined on short lengthscales.

In correlated electron systems the metallic character of a material can be strongly suppressed near an integer concentration of conduction electrons as Coulomb interactions forbid the double occupancy of local atomic orbitals. While the Mott-Hubbard physics arising from such on-site interactions has been largely studied, several unexplained phenomena observed in correlated materials challenge this description and call for the development of new ideas. Here we explore a general route for obtaining correlated behavior that is decidedly different from the spin-related Mott-Hubbard mechanism and instead relies on the presence of unscreened, long-range Coulomb interactions. We find a pseudogap metal phase characterized by a divergent quasiparticle mass and the opening of a Coulomb pseudogap in the electronic spectrum. The destruction of the Fermi-liquid state occurs because the electrons move in a nearly frozen, disordered charge background, as collective charge rearrangements are drastically slowed down by the frustrating nature of long-range potentials on discrete lattices. The present pseudogap metal realizes an early conjecture by Efros, that a soft Coulomb gap should appear for quantum lattice electrons with strong unscreened interactions due to self-generated randomness., 4 pages + 4 pages supplementary information

Conjugated polymers and molecular semiconductors are emerging as a viable semiconductor technology in industries such as displays, electronics, renewable energy, sensing and healthcare. A key enabling factor has been significant scientific progress in improving their charge transport properties and carrier mobilities, which has been made possible by a better understanding of the molecular structure–property relationships and the underpinning charge transport physics. Here we aim to present a coherent review of how we understand charge transport in these high-mobility van der Waals bonded semiconductors. Specific questions of interest include estimates for intrinsic limits to the carrier mobilities that might ultimately be achievable; a dis- cussion of the coupling between charge and structural dynamics; the importance of molecular conformations and mesoscale structural features; how the transport physics of conjugated polymers and small molecule semiconductors are related; and how the incorporation of counterions in doped films—as used, for example, in bioelectronics and thermoelectric devices—affects the electronic structure and charge transport properties., info:eu-repo/semantics/published

The control over material properties attainable through molecular doping is essential to many technological applications of organic semiconductors, such as organic light-emitting diodes or thermoelectrics. These excitonic semiconductors typically reach the degenerate limit only at impurity concentrations of 5-10%, a phenomenon that has been put in relation with the strong Coulomb binding between charge carriers and ionized dopants, and whose comprehension remained elusive so far. This study proposes a general mechanism for the release of carriers at finite doping in terms of collective screening phenomena. A multiscale model for the dielectric properties of doped organic semiconductor is set up by combining first principles and microelectrostatic calculations. The results predict a large nonlinear enhancement of the dielectric constant (tenfold at 8% load) as the system approaches a dielectric instability (catastrophe) upon increasing doping. This can be attributed to the presence of highly polarizable host-dopant complexes, plus a nontrivial leading contribution from dipolar interactions in the disordered and heterogeneous system. The enhanced screening in the material drastically reduces the (free) energy barriers for electron-hole separation, rationalizing the possibility for thermal charge release. The proposed mechanism is consistent with conductivity data and sets the basis for achieving higher conductivities at lower doping loads.

Molecular doping—the use of redox‐active small molecules as dopants for organic semiconductors—has seen a surge in research interest driven by emerging applications in sensing, bioelectronics, and thermoelectrics. However, molecular doping carries with it several intrinsic problems stemming directly from the redox‐active character of these materials. A recent breakthrough was a doping technique based on ion‐exchange, which separates the redox and charge compensation steps of the doping process. Here, the equilibrium and kinetics of ion exchange doping in a model system, poly(2,5‐bis(3‐alkylthiophen‐2‐yl)thieno(3,2‐b)thiophene) (PBTTT) doped with FeCl3 and an ionic liquid, is studied, reaching conductivities in excess of 1000 S cm−1 and ion exchange efficiencies above 99%. Several factors that enable such high performance, including the choice of acetonitrile as the doping solvent, which largely eliminates electrolyte association effects and dramatically increases the doping strength of FeCl3, are demonstrated. In this high ion exchange efficiency regime, a simple connection between electrochemical doping and ion exchange is illustrated, and it is shown that the performance and stability of highly doped PBTTT is ultimately limited by intrinsically poor stability at high redox potential.

Motivated by the potential for application of organic semiconductors in exible electronics, we present a theoretical study aiming at elucidating the interplay between mechanical strain and electronic, vibrational and charge transport properties of the prototypical high-mobility molecular semiconductor rubrene. Our study considers several factors that can play a role in the electro-mechanical response of a soft, van-der-Waals bonded, molecular crystal, such as intermolecular charge transfer integrals, lattice dynamics and electron phonon coupling. We find that compressive strain leads to an increase in magnitude of charge transfer integrals but also of the energetic disorder hampering the mobility. Charge transport simulations, based on the transient localization framework and fed with first-principles inputs, reveal a remarkably different response to strain applied along different crystal axes, in line with most recent experiments. The critical interplay between energetic disorder of intrinsic and extrinsic nature on the mobility-strain relationship is also discussed. The theoretical approach proposed in this work paves the way for the systematic study of the electro-mechanical response of different classes of high-mobility molecular semiconductors.

Molecular vibrations play a critical role in the charge transport properties of weakly van der Waals bonded organic semiconductors. To understand which specific phonon modes contribute most strongly to the electron – phonon coupling and ensuing thermal energetic disorder in some of the most widely studied high mobility molecular semiconductors, we have combined state-of-the-art quantum mechanical simulations of the vibrational modes and the ensuing electron phonon coupling constants with experimental measurements of the low-frequency vibrations using inelastic neutron scattering and terahertz time-domain spectroscopy. In this way we have been able to identify the long-axis sliding motion as a ‘killer’ phonon mode, which in some molecules contributes more than 80% to the total thermal disorder. Based on this insight, we propose a way to rationalize mobility trends between different materials and derive important molecular design guidelines for new high mobility molecular semiconductors., Royal Society German Research Foundation European Research Council Engineering and Physical Sciences Research Council ARCHER UK National Supercomputing Service Belgian National Fund for Scientific Research Leverhulme Trust Wiener-Anspach Foundation Belgian Walloon Region GENCI-CINES/IDRIS

International audience; The electrodynamic response of organic spin liquids with highly-frustrated triangular lattices has been measured in a wide energy range. While the overall optical spectra of these Mott insulators are governed by transitions between the Hubbard bands, distinct in-gap excitations can be identified at low temperatures and frequencies, which we attribute to the quantum-spin-liquid state. For the strongly correlated β ′-EtMe3Sb[Pd(dmit)2]2, we discover enhanced conductivity below 175 cm −1 , comparable to the energy of the magnetic coupling J ≈ 250 K. For ω → 0 these low-frequency excitations vanish faster than the charge-carrier response subject to Mott-Hubbard correlations, resulting in a dome-shape band peaked at 100 cm −1. Possible relations to spinons, magnons and disorder are discussed. PACS numbers: 75.10.Kt 71.30.+h, 74.25.Gz 78.30.Jw Quantum spin liquids are an intriguing state of matter [1-4]: although the spins interact strongly, the combination of geometrical frustration and quantum fluctuations prevents long-range magnetic order even in two and three dimensions. It took decades before clear experimental realizations of this theoretical concept [5, 6] became available, first in the organic compound κ-(BE-DT-TTF) 2 Cu 2 (CN) 3 , which crystallizes in a triangular pattern [7], and later in the kagome lattice of ZnCu 3-(OH) 6 Cl 2 [8-10]. Despite this progress, a smoking-gun experiment identifying its essential features is still lacking , and even a reliable theoretical description of real spin-liquid systems remains a subject of much dispute. At present, the fundamental nature of the spin-liquid state is far from being understood. The intensely studied quantum-spin-liquid candidate Herbertsmithite (ZnCu 3 (OH) 6 Cl 2) shows no magnetic order and no indications of a spin gap down to 0.1 meV, inferring that the spin excitations form a continuum [2]. This important issue, however, is far from being settled neither from the experimental nor from the theoretical side [11, 12]; the discussion on the nature of the quantum-spin-liquid state is rather controversial [13-19]. In this Letter we investigate the electrodynamic response of three organic quantum spin liquids. While close to the Mott transition the charge degrees of freedom dominate the conductivity, our optical experiments reveal considerable low-frequency absorption deep inside the Mott-insulating state. The observed dome-like feature is confined by the exchange energy J, suggesting a relation to the spin degrees of freedom and exotic spin-charge coupling. We study the charge-transfer salts κ-(BEDT-TTF) 2-Cu 2 (CN) 3 (abbreviated CuCN, BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene), κ-(BEDT-TTF) 2-Ag 2 (CN) 3 (called AgCN) and β ′-EtMe 3 Sb[Pd(dmit) 2 ] 2 (short EtMe, here EtMe 3 Sb stands for ethyltrimethylsti-bonium and dmit is 1,3-dithiole-2-thione-4,5-dithiolate), where the molecular dimers with spin-1 2 form a highly frustrated triangular lattice [7, 20-22]. At ambient pressure no indication of Néel order is observed at temperatures as low as 20 mK, despite the considerable antifer-romagnetic exchange of J ≈ 220 − 250 K. The origin of the spin-liquid phase is unresolved since the geometrical frustration introduced by a triangular lattice should not be sufficient to stabilize the quantum-spin-liquid state for ordinary Heisenberg exchange interactions [23-25]. Recently it was proposed that, alternatively, intrinsic disorder [26-28] or dynamical fluctuations [29] may play a crucial role for stabilizing the spin-liquid state in these molecular materials. In contrast to the completely insulating material Her-bertsmithite, where the on-site Coulomb repulsion U and bandwidth W are in the eV range (U = 8 eV [30]), the energy scales of these organic compounds are significantly smaller; here, k B T has a large effect on the Mott gap already for a few hundred Kelvins as evident in dc transport [22, 28, 31]. Moreover, the molecular conductors under study are closer to the metallic phase due to weaker correlations. With U/W ≈ 1.5, CuCN is almost at the metal-insulator transition; in fact it becomes supercon-ducting at T c = 3.6 K under hydrostatic pressure of only 4 kbar [7]. For AgCN the effective correlations are more pronounced, as U/W = 2, while EtMe is far on the Mott insulating side with U/W ≈ 2.4 [32]. Heat capacity measurements suggested gapless spin excitations for CuCN

Sufficiently disordered metals display systematic deviations from the behavior predicted by semi-classical Boltzmann transport theory. Here the scattering events from impurities or thermal excitations can no longer be considered as additive-independent processes, as asserted by Matthiessen’s rule following from this picture. In the intermediate region between the regime of good conduction and that of insulation, one typically finds a change of sign of the temperature coefficient of resistivity, even at elevated temperature spanning ambient conditions, a phenomenology that was first identified by Mooij in 1973. Traditional weak coupling approaches to identify relevant corrections to the Boltzmann picture focused on long-distance interference effects such as “weak localization”, which are especially important in low dimensions (1D and 2D) and close to the zero-temperature limit. Here we formulate a strong-coupling approach to tackle the interplay of strong disorder and lattice deformations (phonons) in bulk three-dimensional metals at high temperatures. We identify a polaronic mechanism of strong disorder renormalization, which describes how a lattice locally responds to the relevant impurity potential. This mechanism, which quantitatively captures the Mooij regime, is physically distinct and unrelated to Anderson localization, but realizes early seminal ideas of Anderson himself, concerning the interplay of disorder and lattice deformations. In conductive materials electronic transport is described by the Boltzmann theory, in which the scattering events giving rise to the finite resistivity are statistically independent. However, if disorder is increased, transport anomalies are consistently observed at high temperature and the Boltzmann theory does not apply. Simone Fratini at the Universite Grenoble Alpes and colleagues now propose a theory that captures these anomalies. One framework for the description of disordered metals involves Anderson localization, the formation of bound electronic states at impurity sites, but this model works only at low temperatures. The authors, who in a previous publication formulated a theory incorporating both Anderson localization and the interplay between disorder and phonons, find that a polaronic effect resulting from the lattice response to the impurity potential is dominant for strong disorder and can explain the high-temperature behavior.

The Widom line identifies the locus in the phase diagram where a supercritical gas crosses over from gas-like to a more liquid-like behavior. A similar transition exists in correlated electron liquids, where the interplay of Coulomb repulsion, bandwidth and temperature triggers between the Mott insulating state and an incoherent conduction regime. Here we explore the electrodynamic response of three organic quantum spin liquids with different degrees of effective correlation, where the absence of magnetic order enables unique insight into the nature of the genuine Mott state down to the most relevant low-temperature region. Combining optical spectroscopy with pressure-dependent dc transport and theoretical calculations, we succeeded to construct a phase diagram valid for all Mott insulators on a quantitative scale. In the vicinity of the low-temperature phase boundary, we discover metallic fluctuations within the Mott gap, exhibiting enhanced absorption upon cooling that is not present in antiferromagnetic Mott insulators. Our findings reveal the phase coexistence region and Pomeranchuk-like anomaly of the Mott transition, previously predicted but never observed., Comment: Supplementary information after Acknowledgements

International audience; have revealed the simultaneous presence of both high room temperature hole mobility above 10 cm 2 V −1 s −1[5] and, crucially , a negative temperature exponent for the mobility, i.e., mobility increases as temperature decreases down to about 180 K. [6] These observations and others, including mobility anisotropy [7,8] and a robust Hall effect, [9,10] are strong evidence for band-like transport in rubrene (band-width ≈0.5 eV), [11] where many features of classical band transport are observed. However, the estimated carrier mean free paths remain on the order of the unit cell dimension (≈1 nm), thus precluding the typical band picture in conventional semiconductors. The precise nature of band-like transport in organic semiconductor crystals is still being explored. [12] Currently, a consistent picture of charge transport in high mobility crystals is offered by the dynamic disorder model (DDM, also known as transient localization), in which the carrier transient localization length l loc and the propagation rate ω are determined by a competition between intermolecular electronic coupling and charge-phonon interaction ; in this scenario the carrier mobility μ can be evaluated as [13] µ ω = B loc 2 e k T l (1) Isotopic substitution is a useful method to study the influence of nuclear motion on the kinetics of charge transport in semiconductors. However, in organic semiconductors, no observable isotope effect on field-effect mobility has been reported. To understand the charge transport mechanism in rubrene, the benchmark organic semiconductor, crystals of fully isotopically substituted rubrene, 13 C-rubrene (13 C 42 H 28), are synthesized and characterized. Vapor-grown 13 C-rubrene single crystals have the same crystal structure and quality as native rubrene crystals (i.e., rubrene with a natural abundance of carbon isotopes). The characteristic transport signatures of rubrene, including room temperature hole mobility over 10 cm 2 V −1 s −1 , intrinsic band-like transport, and clear Hall behavior in the accumulation layer of air-gap transistors, are also observed for 13 C-rubrene crystals. The field-effect mobility distributions based on 74 rubrene and 13 C-rubrene devices, respectively, reveal that 13 C isotopic substitution produces a 13% reduction in the hole mobility of rubrene. The origin of the negative isotope effect is linked to the redshift of vibrational frequencies after 13 C-substitution, as demonstrated by computer simulations based on the transient localization (dynamic disorder) scenario. Overall, the data and analysis provide an important benchmark for ongoing efforts to understand transport in ordered organic semiconductors.

The introduction of more onboard autonomy in future single and multi-satellite missions is both a question of limited onboard resources and of how far can we actually thrust the autonomous functionalities deployed on board. In-flight experience with nasa's Deep Space 1 and Earth Observing 1 has shown how difficult it is to design, build and test reliable software for autonomy. The degree to which system-level onboard autonomy will be deployed in the single and multi satellite systems of tomorrow will depend, among other things, on the progress made in two key software technologies: autonomous onboard planning and robust execution. Parallel to the developments in these two areas, the actual integration of planning and execution engines is still nowadays a crucial issue in practical application. This paper presents an onboard autonomous model-based executive for execution of time-flexible plans. It describes its interface with an apsi-based timeline-based planner, its control approaches, architecture and its modelling language as an extension of apsl's ddl. In addition, it introduces a modified version of the classical blocks world toy planning problem which has been extended in scope and with a runtime environment for evaluation of integrated planning and executive engines.

International audience; The charge mobility of molecular semiconductors is limited by the large fluctuation of intermolecular transfer integrals, often referred to as oï¿¿-diagonal dynamic disorder, which causes transient localization of the carriers' eigenstates. Using a recently developed theoretical framework, we show here that the electronic structure of the molecular crystals determines its sensitivity to intermolecular fluctuations. We build a map of the transient localization lengths of high-mobility molecular semiconductors to identify what patterns of nearest-neighbour transfer integrals in the two-dimensional (2D) high-mobility plane protect the semiconductor from the eï¿¿ect of dynamic disorder and yield larger mobility. Such a map helps rationalizing the transport properties of the whole family of molecular semiconductors and is also used to demonstrate why common textbook approaches fail in describing this important class of materials. These results can be used to rapidly screen many compounds and design new ones with optimal transport characteristics. I n the comparison of the charge transport properties of families of materials it is very desirable to identify a few key parameters that can be used to rationalize the observed dierences in charge mobility. For example, eective masses and mean free paths can be used for wide-band semiconductors, hopping rates between nearest-neighbour sites would characterize molecular solids where molecular orbital overlaps are very weak, and relatively simple phe-nomenological theories are available to describe transport in highly disordered materials. Such a simple reduction is not yet established for the class of high-mobility molecular semiconductors-that is, those displaying mobilities exceeding ⇠1 cm 2 V 1 s 1 and the most interesting from the technological point of view. As noted many times in the past 1-4 , band transport models are unsatisfactory for these materials because of a too short mean free path and, similarly, hopping theories yield unphysically high hopping rates 5 alongside incorrect temperature dependences, even when they reproduce the absolute mobility. A number of authors have contributed over the years to develop a transport model that seems suitable for this class of materials and that has now reached a high level of predictive power 4,6. A starting point is the observation that the transfer integrals between nearest neighbouring molecules undergo large fluctuations 7 : due to the softness of the intermolecular interaction and the sensitivity of the transfer integrals to small nuclear displacements 8-10 , the amplitude of these fluctuations is comparable to the average value of the transfer integrals. Developing on this idea, the carrier dynamics has been studied in models that capture the essential physics, both numerically and analytically 7,11-18 , or performing non-adiabatic molecular dynamics simulations in models with atomistic detail 19,20. All these studies revealed a common microscopic origin for the unconventional charge transport of organic semiconductors: the dynamic disorder broadens the density of states (DOS) and causes a localization of the instantaneous eigenstates. This phenomenon, whose origin is genuinely quantum mechanical, is especially strong at the band edges where charge carriers reside 12 , and is intuitively associated with a suppressed mobility. As disorder fluctuates in time, however, one cannot speak of localization in the traditional sense 21. Based on extensive numerical evidence 6,7,11-14,16 it was proposed 13,14 that the eect of dynamic disorder is to cause a transient localization over a length L ⌧ within a fluctuation time given by the inverse of the typical intermolecular oscillation frequency, ⌧ ⇠ 1/! 0. The fact that this initial localization time must be overcome before charge diusion can actually take place is responsible for the long-known breakdown of semiclassical transport, causing the mobility to fall below the Mott-Ioe-Regel limit (apparent mean free paths shorter than the intermolecular distance) 3. The eects of transient localization were given a mathematical basis using a relaxation time argument 13,14 , resulting in the following analytical formula for the charge mobility: µ = e k B T L 2 ⌧ 2⌧ (1) with e the electron charge, k B the Boltzmann constant and T the temperature. The theory embodied in equation (1), which has been shown to agree quantitatively with the most accurate numerical studies presently available 4,15 , goes beyond the semiclassical band transport approaches (as it contains quantum localization corrections) and it is alternative to traditional hopping theories (which assume that the wavefunction coherence is lost at each hop, an assumption that does not hold in high-mobility materials). This allows us to reliably and eciently compute the mobility of actual semiconducting materials, treating all possible molecular structures of interest on the same footing and with an aordable numerical eort. As the transient localization length L ⌧ is what ultimately determines how a given material performs, regardless of the detail of the model it would be particularly useful to be able to assess this quantity-and, at once, make quantitative predictions for the charge mobility-without going each time through a complex quantum dynamics simulation. To this aim we proceed to study systematically an ensemble of models, encompassing in practice all the dierent physical situations that can be encountered in organic semiconductors. We start by observing that, with the exception of fullerene

International audience; We present an inhomogeneous dynamical mean field theory (I-DMFT) that is suitable to investigate electron-lattice interactions in non-translationally invariant and/or inhomogeneous systems. The presented approach, whose only assumption is that of a local, site-dependent self-energy, recovers both the exact solution of an electron for a generic random tight-binding Hamiltonian in the non-interacting limit and the DMFT solution for the small polaron problem in translationally invariant systems. To illustrate its full capabilities, we use I-DMFT to study the effects of defects embedded on a two-dimensional surface. The computed maps of the local density of states reveal Friedel oscillations, whose periodicity is determined by the polaron mass. This can be of direct relevance for the interpretation of scanning-tunneling microscopy (STM) experiments on systems with sizable electron-lattice interactions. Overall, the easy numerical implementation of the method, yet full self-consistency, allows one to study problems in real-space that were previously difficult to access.

We show that in presence of a deformable lattice potential, the nature of the disorder-driven metal-insulator transition (MIT) is fundamentally changed with respect to the non-interacting (Anderson) scenario. For strong disorder, even a modest electron-phonon interaction is found to dramatically renormalize the random potential, opening a mobility gap at the Fermi energy. This process, which reflects disorder-enhanced polaron formation, is here given a microscopic basis by treating the lattice deformations and Anderson localization effects on the same footing. We identify an intermediate "bad insulator" transport regime which displays resistivity values exceeding the Mott-Ioffe-Regel limit and with a negative temperature coefficient, as often observed in strongly disordered metals. Our calculations reveal that this behavior originates from significant temperature-induced rearrangements of electronic states due to enhanced interaction effects close to the disorder-driven MIT., 5 pages, 4 figures, revised version accepted in Phys. Rev. Lett

Charge transport in crystalline organic semiconductors is intrinsically limited by the presence of large thermal molecular motions, which are a direct consequence of the weak van der Waals inter-molecular interactions. These lead to an original regime of transport called \textit{transient localization}, sharing features of both localized and itinerant electron systems. After a brief review of experimental observations that pose a challenge to the theory, we concentrate on a commonly studied model which describes the interaction of the charge carriers with inter-molecular vibrations. We present different theoretical approaches that have been applied to the problem in the past, and then turn to more modern approaches that are able to capture the key microscopic phenomenon at the origin of the puzzling experimental observations, i.e. the quantum localization of the electronic wavefuntion at timescales shorter than the typical molecular motions. We describe in particular a relaxation time approximation which clarifies how the transient localization due to dynamical molecular motions relates to the Anderson localization realized for static disorder, and allows us to devise strategies to improve the mobility of actual compounds. The relevance of the transient localization scenario to other classes of systems is briefly discussed., Comment: Accepted for publication in Advanced Functional Materials - Special issue on Organic Single Crystals

The role of the multiorbital effects on the emergence of frustrated electronic orders on the triangular lattice at half filling is investigated through an extended spinless fermion Hubbard model. By using two complementary approaches, unrestricted Hartree-Fock and exact diagonalizations, we unravel a very rich phase diagram controlled by the strength of both local and off-site Coulomb interactions and by the interorbital hopping anisotropy ratio $t'/t$. Three robust unconventional electronic phases, a pinball liquid, an inverse pinball liquid, and a large-unit-cell $\sqrt{12} \times \sqrt{12}$ droplet phase, are found to be generic in the triangular geometry, being controlled by the band structure parameters. The latter are also stabilized in the isotropic limit of our microscopic model, which recovers the standard SU(2) spinful extended single-band Hubbard model., Comment: 10 pages, 6 figures

The interplay of non-local Coulomb repulsion and Hund's coupling in the d-orbital manifold in frustrated triangular lattices is analyzed by a mutliband extended Hubbard model. We find a rich phase diagram with several competing phases, including a robust pinball liquid phase, which is an unconventional metal characterized by threefold charge order, bad metallic behavior and the emergence of high spin local moments. Our results naturally explain the anomalous charge-ordered metallic state observed in the triangular layered compound AgNiO2. The potential relevance to other triangular transition metal oxides is discussed., Comment: 4 pages, 4 figures

In the absence of disorder, electrons can display glassy behavior through supercooling the liquid state, avoiding the solidification into a charge ordered state. Such supercooled electron liquids are experimentally found in organic $\theta$-$MM'$ compounds. We present theoretical results that qualitatively capture the experimental findings. At intermediate temperatures, the conducting state crosses over into a weakly insulating pseudogap phase. The stripe order phase transition is first order, so that the liquid phase is metastable below $T_s$. In the supercooled liquid phase the resistivity increases further and the density of states at the Fermi level is suppressed, indicating kinetic arrest and the formation of a glassy state. Our results are obtained using classical Extended Dynamical Mean Field Theory., Comment: 4 pages, 4 figures, submitted to the proceedings of "Superstripes 2015", Journal of Superconductivity and Novel Magnetism (2015)

We show that introducing long-range Coulomb interactions immediately lifts the massive ground state degeneracy induced by geometric frustration for electrons on quarter-filled triangular lattices in the classical limit. Important consequences include the stabilization of a stripe-ordered crystalline (global) ground state, but also the emergence of very many low-lying metastable states with amorphous "stripe-glass" spatial structures. Melting of the stripe order thus leads to a frustrated Coulomb liquid at intermediate temperatures, showing remarkably slow (viscous) dynamics, with very long relaxation times growing in Arrhenius fashion upon cooling, as typical of strong glass formers. On shorter time scales, the system falls out of equilibrium and displays the aging phenomena characteristic of supercooled liquids above the glass transition. Our results show remarkable similarity with the recent observations of charge-glass behavior in ultra-clean triangular organic materials of the $\theta$-(BEDT-TTF)$_2$ family., Comment: 5 pages,4 figures