Photoinduced Hund excitons in the breakdown of a two-orbital Mott insulator

We study the photoinduced breakdown of a two-orbital Mott insulator and resulting metallic state. Using time-dependent density matrix renormalization group, we scrutinize the real-time dynamics of the half-filled two-orbital Hubbard model interacting with a resonant radiation field pulse. The breakdown, caused by production of doublon-holon pairs, is enhanced by Hund's exchange, which dynamically activates large orbital fluctuations. The melting of the Mott insulator is accompanied by a high to low spin transition with a concomitant reduction of antiferromagnetic spin fluctuations. Most notably, the overall time response is driven by the photogeneration of excitons with orbital character that are stabilized by Hund's coupling. These unconventional "Hund excitons" correspond to bound spin-singlet orbital-triplet doublon-holon pairs. We study exciton properties such as bandwidth, binding potential, and size within a semiclassical approach. The photometallic state results from a coexistence of Hund excitons and doublon-holon plasma.Comment: 9 pages, 6 figure

Quantum phase transition between one-channel and two-channel Kondo polarons

For a mobile spin-1/2 impurity, coupled antiferromagnetically to a one-dimensional gas of fermions, perturbative ideas have been used to argue in favor of two-channel Kondo behavior of the impurity spin. Here we combine general considerations and extensive numerical simulations to show that the problem displays a novel quantum phase transition between two-channel and one-channel Kondo screening upon increasing the Kondo coupling. We construct a ground-state phase diagram and discuss the various non-trivial crossovers as well as possible experimental realizations.Comment: 5+4 pages, 5+3 fig

Wave packet dynamics in the one-dimensional extended Hubbard model

Using time-dependent density-matrix renormalization group, we study the time evolution of electronic wave packets in the one-dimensional extended Hubbard model with on-site and nearest neighbor repulsion, U and V, respectively. As expected, the wave packets separate into spin-only and charge-only excitations (spin-charge separation). Charge and spin velocities exhibit non-monotonic dependence on V. For small and intermediate values of V, both velocities increase with V. However, the charge velocity exhibits a stronger dependence than that of the spin, leading to a more pronounced spin-charge separation. Charge fractionalization, on the other hand, is weakly affected by V. The results are explained in terms of Luttinger liquid theory in the weak-coupling limit, and an effective model in the strong-coupling regime.Comment: 6 pages, 4 figure

Photoexcitation of electronic instabilities in one-dimensional charge-transfer systems

We investigate the real-time dynamics of photoexcited electronic instabilities in a charge-transfer system model, using the time-dependent density matrix renormalization group method. The model of choice was the quarter-filled one-dimensional extended Peierls-Hubbard Hamiltonian interacting with classical few-cycle electromagnetic radiation. The results show that only one electronic instability drives the main features of the photogenerated time-dependent behavior. Indeed, the photoresponse of the system shows a large enhancement of the $4k_F$ (bond and charge) instability whereas the $2k_F$ state remains largely unaffected. This conclusion holds regardless of the nature of the optical excitations and whether the system is perturbed resonantly or not. Our results suggest potential applications of charge-transfer systems with slow phononic dynamics as optoelectronic switching devices.Comment: 9 pages, 6 figures. Slightly modified; published versio

Emotions detection on an ambient intelligent system using wearable devices

In this paper we present an Ambient Intelligent System, the iGenda, and the integration of a wearable device. The aim is to detect emotional states through the wearable device and ultimately represent and manage the social emotion of a group of entities. The advantage of this action is that its usability is in line with retirement homes and similar places, where the community is extended and an harmonious environment is imperative. The iGenda serves has the visual interface and the information centre, receiving the information from the wearable device and managing the community emotion by sending information to the care-receivers, caregivers, or changing home parameters (like music or lighting) to achieve an specific emotion (such as calm or excitement). Thus the goal is to provide an affective system that directly interacts with humans by discreetly improving their lifestyle.FCT - Fuel Cell Technologies Program (UID/CEC/00319/2013)info:eu-repo/semantics/publishedVersio

A dynamic emotional model for agent societies

This paper presents a first approximation of a dynamic emotional model to be employed in agent societies. The proposed model is based on the PAD emotional model and allows the representation of the emotional contagion phenomena of a heterogeneous group of agents which are capable of express emotions. Moreover, the proposal allows the definition of the social emotion of this group of agents. The model is mainly based on three elements: personality, empathy and affinity. These elements allow the characterization of each individual, causing them susceptible to vary in some degre the emotions of other individuals

Using emotions in intelligent virtual environments: the EJaCalIVE framework

Nowadays, there is a need to provide new applications which allow the definition and implementation of safe environments that attends to the user needs and increases their wellbeing. In this sense, this paper introduces the EJaCalIVE framework which allows the creation of emotional virtual environments that incorporate agents, eHealth related devices, human actors, and emotions projecting them virtually and managing the interaction between all the elements. In this way, the proposed framework allows the design and programming of intelligent virtual environments, as well as the simulation and detection of human emotions which can be used for the improvement of the decision-making processes of the developed entities. The paper also shows a case study that enforces the need of this framework in common environments like nursing homes or assisted living facilities. Concretely, the case study proposes the simulation of a residence for the elderly. The main goal is to have an emotion-based simulation to train an assistance robot avoiding the complexity involved in working with the real elders. The main advantage of the proposed framework is to provide a safe environment, that is, an environment where users are able to interact safely with the system.This work is partially supported by the MINECO/FEDER TIN2015-65515-C4-1-R and the FPI Grant AP2013-01276 awarded to Jaime-Andres Rincon. This work is also supported by COMPETE: POCI-01-0145-FEDER-007043 and Fundacao para a Ciencia e Tecnologia (FCT) within the projects UID/CEC/00319/2013 and Post-Doc scholarship SFRH/BPD/102696/2014 (A. Costa).info:eu-repo/semantics/publishedVersio