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Every day we face numerous lifestyle decisions, some dictated by habits and some more conscious, which may or may not promote sustainable living. Aided by digital technology, sustainable behaviors can diffuse within social groups and inclusive communities. This paper outlines a longitudinal experimental study of social influence in behavioral changes toward sustainability, in the context of smart residential homes. Participants are residing in the housing on campus referred to as KTH Live-In Lab, whose behaviors are observed w.r.t. key lifestyle choices, such as food, resources, mobility, consumption, and environmental citizenship. The focus is on the preparatory phase of the case study and the challenges and limitations encountered during its setup. In particular, this work proposes a definition of sustainability indicators for environmentally significant behaviors, and hypothesizes that, through digitalization of a household into a social network of interacting tenants, sustainable living can be promoted. Preliminary results confirm the feasibility of the proposed experimental methodology., Comment: 7 pages, 4 figures, 1 table. Presented at the 2023 IFAC World Conference, Yokohama, Japan

We consider an extension of the Rescorla-Wagner model which bridges the gap between conditioning and learning on a neural-cognitive, individual psychological level, and the social population level. In this model, the interaction among individuals is captured by a Markov process. The resulting human-social behavior model is a recurrent iterated function systems which behaves differently from the classical Rescorla-Wagner model due to randomness. Convergence and ergodicity properties of the internal states of agents in the proposed model are studied.

Over the last decade, the rise of the mobile internet and the usage of mobile devices has enabled ubiquitous traffic information. With the increased adoption of specific smartphone applications, the number of users of routing applications has become large enough to disrupt traffic flow patterns in a significant manner. Similarly, but at a slightly slower pace, novel services for freight transportation and city logistics improve the efficiency of goods transportation and change the use of road infrastructure. The present article provides a general four-layer framework for modeling these new trends. The main motivation behind the development is to provide a unifying formal system description that can at the same time encompass system physics (flow and motion of vehicles) as well as coordination strategies under various information and cooperation structures. To showcase the framework, we apply it to the specific challenge of modeling and analyzing the integration of routing applications in today's transportation systems. In this framework, at the lowest layer (flow dynamics) we distinguish app users from non-app users. A distributed parameter model based on a non-local partial differential equation is introduced and analyzed. The second layer incorporates connected services (e.g., routing) and other applications used to optimize the local performance of the system. As inputs to those applications, we propose a third layer introducing the incentive design and global objectives, which are typically varying over the day depending on road and weather conditions, external events etc. The high-level planning is handled on the fourth layer taking social long-term objectives into account., Comment: 24 pages, 11 Figures

In this paper, we study neural cognition in social network. A stochastic model is introduced and shown to incorporate two well-known models in Pavlovian conditioning and social networks as special case, namely Rescorla-Wagner model and Friedkin-Johnsen model. The interpretation and comparison of these model are discussed. We consider two cases when the disturbance is independent identical distributed for all time and when the distribution of the random variable evolves according to a markov chain. We show that the systems for both cases are mean square stable and the expectation of the states converges to consensus., Comment: submitted to IEEE CCAT 2017

We present a self-contained review of the theory of dislocation-mediated quantum melting at zero temperature in two spatial dimensions. The theory describes the liquid-crystalline phases with spatial symmetries in between a quantum crystalline solid and an isotropic superfluid: quantum nematics and smectics. It is based on an Abelian-Higgs-type duality mapping of phonons onto gauge bosons ("stress photons"), which encode for the capacity of the crystal to propagate stresses. Dislocations and disclinations, the topological defects of the crystal, are sources for the gauge fields and the melting of the crystal can be understood as the proliferation (condensation) of these defects, giving rise to the Anderson-Higgs mechanism on the dual side. For the liquid crystal phases, the shear sector of the gauge bosons becomes massive signaling that shear rigidity is lost. Resting on symmetry principles, we derive the phenomenological imaginary time actions of quantum nematics and smectics and analyze the full spectrum of collective modes. The quantum nematic is a superfluid having a true rotational Goldstone mode due to rotational symmetry breaking, and the origin of this 'deconfined' mode is traced back to the crystalline phase. The two-dimensional quantum smectic turns out to be a dizzyingly anisotropic phase with the collective modes interpolating between the solid and nematic in a non-trivial way. We also consider electrically charged bosonic crystals and liquid crystals, and carefully analyze the electromagnetic response of the quantum liquid crystal phases. In particular, the quantum nematic is a real superconductor and shows the Meissner effect. Their special properties inherited from spatial symmetry breaking show up mostly at finite momentum, and should be accessible by momentum-sensitive spectroscopy., Comment: Review article, 137 pages, 32 figures. Accepted version

The Bogoliubov quasiparticles move in a practically uniform magnetic field in the vortex state of high temperature cuprate superconductors. Do the quasiparticles experience a Lorentz force when set in motion by an externally applied heat current ${\bf j}_Q$, bending their trajectories and causing the temperature gradient perpendicular to ${\bf j}_Q$ and the applied field ${\bf H}$, or is the thermal Hall effect a consequence of Berry phases as in an intrinsic anomalous Hall effect of a semiconductor/metal with spin-orbit coupling? Here we show that it is the latter, and for the first time, calculate the temperature, ${\bf H}$-field and the $d$-wave pairing gap $\Delta$ dependence of the intrinsic thermal Hall conductivity, $\kappa_{xy}$. We find that the intrinsic contribution to $\kappa_{xy}$ displays a rapid onset with increasing temperature, which compares favourably with existing experiments at high ${\bf H}$-fields on the highest purity samples. This finding may help to settle a much-debated question of the bulk value of the pairing strength in cuprate superconductors in magnetic field., Comment: 5 pages, 3 figures; Supplementary: 11 pages, 3 figures; v2: Figure 1 updated

Using a controlled weak-coupling renormalization group approach, we establish the mechanism of unconventional superconductivity in the vicinity of spin or charge ordered excitonic states for the case of electrons on the Bernal stacked bilayer honeycomb lattice. With one electron per site this system exhibits nearly parabolically touching conduction and valence bands. Such a state is unstable towards a spontaneous symmetry breaking, and repulsive interactions favor excitonic order, such as a charge nematic and/or a layer antiferromagnet. We find that upon adding charge carriers to the system, the excitonic order is suppressed, and unconventional superconductivity appears in its place, before it is replaced by a Fermi liquid. We focus on firmly establishing this phenomenon using the RG formalism within an idealized model with parabolic touching., Comment: 5+3 pages, 4 figures; typos corrected

We construct the symmetry adapted low energy effective Hamiltonian for the electronic states in the vicinity of the Fermi level in iron based superconductors. We use Luttinger's method of invariants, expanding about Gamma and M points in the Brillouin zone corresponding to two iron unit cell, and then matching the coefficients of the expansion to the 5- and 8-band models. We then use the method of invariants to study the effects of the spin-density wave order parameters on the electronic spectrum, with and without spin-orbit coupling included. Among the results of this analysis is the finding that the nodal spin-density wave is unstable once spin-orbit coupling is included. Similar analysis is performed for the A_{1g} spin singlet superconducting state. Without spin-orbit coupling there is one pairing invariant near the Gamma point, but two near the M point. This leads to an isotropic spectral gap at the hole Fermi surface near Gamma, but anisotropic near M. The relative values of these three parameters determine whether the superconducting state is s_{++}, s_{+-}, or nodal. Inclusion of spin-orbit coupling leads to additional mixing of spin triplet pairing, with one additional pairing parameter near Gamma and one near M. This leads to an anisotropic spectral gap near both hole and electron Fermi surfaces, the latter no longer cross, but rather split., Comment: 38 pages, 18 figures, 10 tables

The Goldstone theorem states that there should be a massless mode for each spontaneously broken symmetry generator. There is no such rotational mode in crystals, however superconducting quantum nematics should carry rotational Goldstone modes. By generalization of thermal 2D defect mediated melting theory into a 2+1D quantum duality, the emergence of the rotational mode at the quantum phase transition from the solid to the nematic arises as a deconfinement phenomenon, with the unusual property that the stiffness of the rotational mode originates entirely in the dual dislocation condensate., Comment: 5 pages

The effects of topology and electron-electron interactions on the phase diagram of ABC stacked trilayer graphene (TLG) at the neutrality point are investigated within a weak coupling renormalization group approach. We find that the leading instability of TLG with only a forward scattering density-density interaction is towards a mirror-breaking gapless state. Addition of a small, but finite back scattering favors gapped phases, allowing us to make connections to the existing experiments on TLG. We identify a fundamental symmetry difference between TLG and bilayer graphene (BLG) which is responsible for disfavoring nematic states in TLG under the same conditions that favor nematic states in BLG., Comment: 5 pages, 3 figures; Supplementary Material included (5 pages)

We map out the possible ordered states in bilayer graphene at the neutrality point by extending the previous renormalization group treatment of many-body instabilities to finite temperature, trigonal warping and externally applied perpendicular electric field. We were able to analytically determine all outcomes of the RG flow equations for the 9 four-fermion coupling constants. While the full phase diagram exhibits a rich structure, we confirm that when forward scattering dominates, the only ordering tendency with divergent susceptibility at finite temperature is the nematic. At finite temperature this result is stable with respect to small back and layer imbalance scattering; further increasing their strength leads to the layer antiferromagnet. We also determine conditions for other ordered states to appear and compare our results to the special cases of attractive and repulsive Hubbard models where exact results are available., Comment: 27 pages, 13 figures, 1 table (published version)

We consider the thermal expansion, change of sound velocity with pressure and temperature, and the Poisson ratio of lattices which have rigid units (polyhedra very large stiffness to change in bond-length and to bond-angle variations) connected to other such units through relatively compressible polyhedra. We show that in such a model, the potential energy for rotations of the rigid units can occur only as a function of the combination ${\boldsymbol \Theta}_i \equiv ({\boldsymbol \theta}_i - (\nabla \times {\bf u}_i)/2)$, where ${\boldsymbol \theta_i} $ are the orthogonal rotation angles of the rigid unit $i$ and ${\bf u}_i$ is its displacement. Given such new invariants in the theory of elasticity and the hierarchy of force constants of the model, a negative thermal expansion coefficient as well as a decrease in the elastic constants of the solid with temperature and pressure is shown to follow. These are consistent with the observations., Comment: 8 pages, 1 figure

The key feature of the Fe-based superconductors is their quasi 2D multiband Fermi surface. By relating the problem to a negative U Hubbard model and its superconducting ground state, we show that the defining instability of such a Fermi surface is the valley density-wave (VDW), a combined spin/charge density-wave at the wavevector connecting the electron and hole valleys. As the valley parameters change by doping or pressure, the fictitious superconductor experiences "Zeeman splitting", eventually going into a non-uniform "Fulde-Ferrell-Larkin-Ovchinikov" (FFLO) state, an itinerant and often incommensurate VDW of the real world, characterized by the metallic conductivity from the ungapped remnants of the Fermi surface. When "Zeeman splitting" exceeds the "Chandrasekhar-Clogston" limit, the "FFLO" state disappears, and the VDW is destabilized. Near this point, the VDW fluctuations and interband pair repulsion are essential ingredients of high-Tc superconductivity in Fe-pnictides., Comment: 8 pages, 2 figures; expanded version; extended discussion; additional references

Recent discovery of high T_c superconductivity in Fe-based compounds may have opened a new pathway to the room temperature superconductivity. The new materials feature FeAs layers instead of the signature CuO_2 planes of much-studied cuprates. A model Hamiltonian describing FeAs layers is introduced, highlighting the crucial role of puckering of As atoms in promoting d-electron itinerancy and warding off large local-moment magnetism of Fe ions, the main enemy of superconductivity. Quantum many-particle effects in charge, spin and multiband channels are explored and a nesting-induced spin density-wave order is found in the parent compund. We argue that this largely itinerant antiferromagnetism and high T_c itself are essentially tied to the multiband nature of the Fermi surface., Comment: 7 pages, 4 figures; typos corrected, updated Fig. 4, Fig. 1c added