We present reliable many-body calculations for the t-t(')-t('')-U Hubbard model that explain in detail the results of recent angle-resolved photoemission experiments on electron-doped high-temperature superconductors. The origin of the pseudogap is traced to two-dimensional antiferromagnetic spin fluctuations whose calculated temperature-dependent correlation length also agrees with recent neutron scattering measurements. We make specific predictions for photoemission, for neutron scattering, and for the phase diagram.

In the experimental context of cold-fermion optical lattices, we discuss the possibilities to approach the pseudogap or ordered phases by manipulating the scattering length or the strength of the laserinduced lattice potential. Using the Two-Particle Self-Consistent Approach as well as Quantum Monte Carlo simulations, we provide isentropic curves for the two-and three-dimensional Hubbard models at half-filling. These quantitative results are important for practical attempts to reach the ordered antiferromagnetic phase in experiments on optical lattices of two-component fermions. We find that adiabatically turning on the interaction in two dimensions to cool the system is not very effective. In three dimensions, adiabatic cooling to the antiferromagnetic phase can be achieved in such a manner although the cooling efficiency is not as high as initially suggested by Dynamical Mean-Field Theory. Adiabatic cooling by turning off the repulsion beginning at strong coupling is possible in certain cases.

The crossover from two-to three-dimensional critical behavior of nearly antiferromagnetic itinerant electrons is studied in a regime where the inter-plane single-particle motion of electrons is quantum-mechanically incoherent because of thermal fluctuations. This is a relevant regime for very anisotropic materials like the cuprates. The problem is studied within the Two-Particle SelfConsistent approach (TPSC), that has been previously shown to give a quantitative description of Monte Carlo data for the Hubbard model. It is shown that TPSC belongs to the n → ∞ limit of the O (n) universality class. However, contrary to the usual approaches, cutoffs appear naturally in the microscopic TPSC theory so that parameter-free calculations can be done for Hubbard models with arbitrary band structure. A general discussion of universality in the renormalized-classical crossover from d = 2 to d = 3 is also given.

We investigate a thermoelectric nano-engine whose properties are steered by Coulomb interaction. The device whose design decouples charge and energy currents is made up of two interacting quantum dots connected to three different reservoirs. We show that, by tailoring the tunnel couplings, this setup can be made very attractive for energy-harvesting prospects, due to a delivered power that can be of the order of the quantum bound [R. S. Whitney, Phys. Rev. Lett. 112, 130601 (2014); Entropy 18, 208 (2016)], with a concomitant fair efficiency. To unveil its properties beyond the sequential quantum master equation, we apply a nonequilibrium noncrossing approximation in the Keldysh Green's function formalism, and a quantum master equation that includes cotunneling processes. Both approaches are rather qualitatively similar in a large operating regime where sequential tunneling alone fails.Comment: Published version. (The discussion about the energy current in QME has been expanded