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We theoretically investigate the effects of criticality and multifractal states in a one-dimensional Aubry-Andre-Harper model coupled to electromagnetic cavities. We focus on two specific cases where the phonon frequencies are $\omega_{0}=1$ and $\omega_{0}=2$, respectively. Phase transitions are analyzed using both the average and minimum inverse participation ratio to identify metallic, fractal, and insulating states. We provide numerical evidence to show that the presence of the optical cavity induces a critical, intermediate phase in between the extended and localized phases, hence drastically modifying the traditional transport phase diagram of the Aubry-Andre-Harper model, in which critical states can only exist at the well-defined metal-insulator critical point. We also investigate the probability distribution of the inverse participation ratio and conduct a multifractal analysis to characterize the nature of the critical phase, in which we show that extended, localized, and fractal eigenstates coexist. Altogether our findings reveal the pivotal role that the coupling to electromagnetic cavities plays in tailoring critical transport phenomena at the microscopic level of the eigenstates., Comment: 10 pages, 10 Figures

In this study, we explore the impact of short-range antiferromagnetic correlations on the charge density wave (CDW) phase in strongly correlated electron systems exhibiting the pseudogap phenomenon. Our investigation employs a n-pole approximation to consider the repulsive Coulomb interaction $(U)$ and antiferromagnetic correlations. Utilizing a two-dimensional Hubbard model for the Coulomb interaction and a BCS-like model for the CDW order parameter, we observe that an increase in $U$ enhances antiferromagnetic fluctuations, resulting in a flattened re-normalized band around the anti-nodal point $(\pi,0)$. The pseudogap manifests in the band structure and density of states, prompting an exploration across various $U$ and occupation number values. Our findings indicate that antiferromagnetic correlations significantly influence the CDW state, as the Fermi surface is reconstructed within the ordered phase. Furthermore, we find a Lifhsitz transition inside both the CDW phase and the normal state, with the latter preceding the onset of the pseudogap., Comment: 19 pages, 10 figures

In this work, we investigate the influence of interlayer distance in a heterostructure containing both Kondo effects and short-range magnetic correlations. Our proposed heterostructure comprises three coupled square lattice layers. The first layer is governed by the Kondo-Heisenberg lattice model involving $f$- and $d$-electrons, which interact via Kondo and Heisenberg couplings, $J_{K}$ and $J_{H}$, respectively. The other two layers consist of non-interacting itinerant electrons, where coupling with the first layer is determined by two perpendicular hopping parameters. We find that varying the interlayer couplings induces electronic dynamics at the interface, altering the behavior of mean-field parameters describing the Kondo effect and short-range magnetic correlations. The system's temperature - interlayer hopping parameter phase diagram exhibits a sequence of discontinuous and continuous transitions. In the cases, $|J_{K}|<|J_{H}|$ and $|J_{K}|>|J_{H}|$ rich phase diagrams are found which include Kondo, ferromagnetic and antiferromagnetic correlations. Our work provides insights into hosting Kondo correlations in heterostructures., Comment: 11 pages. 9 figures

We investigate the onset and evolution of under the simultaneous application of pressure and magnetic field of distinct itinerant N\'eel states using the underscreened Anderson Lattice Model (UALM) which has been proposed to describe $5f$-electron systems. The model is composed by two narrow $f$-bands (of either $\alpha$ or $\beta$ character) that hybridize with a wide $d$-band and local $5f$-electron interactions. We consider both cubic and tetragonal lattices. The N\'eel order parameters $\phi^{\beta}$ and $\phi^{\alpha}$ are assumed to be fixed by an Ising anisotropy. The applied magnetic field $h_z$ is parallel to the anisotropy axis. It has been assumed that the variation of the band width $W$ is sensitive to pressure. In the absence of a magnetic field, the increase of $W$ takes the system from the phase AF$_1$ to another phase AF$_2$. The phase AF$_1$ occurs when $\phi^{\beta}>\phi^{\alpha}>0$ while in the AF$_2$ phase the gaps satisfy $\phi^{\alpha}>\phi^{\beta}>0$. In the presence of a magnetic field $h_z$, the phase AF$_2$ is quickly suppressed and reappears again at intermediate values of the magnetic field while it is predominant at higher magnetic fields. The analysis of the partial density of states close to the phase transition between the phases AF$_1$ and AF$_2$, allows a better understanding the mechanism responsible whereby the transition is induced by an increase in the magnetic field. As a important general result, we found that the magnetic field $h_z$ favours the phase AF$_2$ while the phase AF$_1$ is suppressed. For the tetragonal lattice, the phase AF$_2$ is even more favored when $h_z$ and $c/a$ increases concomitantly, where $c$ and $a$ are the lattice parameters.

In the present work, we will study the superconducting properties of a mesoscopic three-dimensional prism with square transversal section under an external magnetic field in both Zero-Field Cooling (ZFC) and Field-Cooling (FC) process. The studied sample is a three-band system (with three condensates $\psi_{1}$, $\psi_{2}$, $\psi_{3}$), in which we take a Josephson type inter-band coupling simulated via $\gamma$ parameter. We analyze the magnetization, superconducting electronic density and free Gibbs energy considering both processes. As results, we found an interesting tunneling of vortex and anti-vortex between the bands, and vortex cluster configuration in the sample. This behaviour is due to the non-monotonic interaction between the bands., Comment: 13 pages,14 figures

In this paper we investigate the electronic and superconducting properties in nickelate compounds of NiO2 through Perturbative Density Functional Theory (P-DFT) and multi-band BCS theory. We consider three different cases of study (i) the crystalline structure composed by two layers of NiO2, with a central single atom of Nd, Yb or Pr, which is subjected to mechanical compression and tension forces (pressure), (ii) the crystalline structure composed by three layers of NiO2 with central atom pairs of Nd-Nd, Nd-Sr or Sr-Sr, where the level doping x correspond to change between Nd/Sr and (iii) through multi-band theory we study the behaviour in a single-layer Nd1-xSrxNiO2} when $x$=0.5 through gaps $\Delta_{\chi,\textbf{p}}$, with $\chi$ (number of band or orbitals), only with the presence of inter-band coupling $V_{\chi\chi'}$. As results, for (i) and (ii) we present the electronic measures of the electronic band structures \textit{e-DOS}, \textit{p-DOS}. In (i) we show that under pressure there are a re-distribution of the band structures for \textit{e-DOS}, \textit{p-DOS}, allowing the destruction of van-\textit{Hove} near Fermi level $E_{F}$, thus in (ii) we show the presence of a single flat band when the doping level is $x$=0.5 and for (iii) the inter-band coupling between orbitals play a key role in the construction of a superconducting phase in nickelates compounds., Comment: there are problems in the numerical method used, therefore the results present serious errors

In the present work we studied the magnetization, vorticity, Cooper pairs density and the space distribution of the local magnetic field in a three-dimensional superconductor with a SQUID geometry (a square with a central hole connected to the outside vacuum through a very thin slit). Our investigation was carried out in both the Meissner-Oschenfeld and the Abrikosov state solving the two-band Ginzburg-Landau equations considering a Josephson coupling between the bands. We found a non-monotonic vortex behavior and the respective generation of vortex cluster due to the Josephson coupling used between condensates., Comment: 7 pages, 8 figures

Our study sample is a superconducting bi-dimensional octagon with different boundary conditions immersed in a magnetic external field H. The boundary conditions are simulated by considering different values of the deGennes extrapolation length b on different surfaces of the sample. Our investigation was carried out by solving the two-band time dependent Ginzburg-Landau equations (TB-TDGL). We analyzed the superconducting electron density and the magnetization curves as functions of H and temperature T in zero field cooling and in zero field cooling processes for different values of b and size of the sample. We found a strong dependence of the critical fields on b and size of the sample.