arXiv subjects

Pedro D. Sacramento

Publications and source records attributed to Pedro D. Sacramento.

14 recordsLinked to original sources

arXiv2026

Order parameters and ground-state phase diagram of the interacting topological Su-Schrieffer-Heeger model with extended-range hoppings

Topological insulators have attracted numerous attentions recent years, where the Su-Schrieffer-Heeger (SSH) model is one of the most studied models. While the interacting version of it has been explored recently, the interplay between interactions and long-range hoppings merit further investigations. In this work, we uncover a rich phase diagram of the interacting SSH model with extended-range hoppings, in which it consists of several topological phases, two novel superconducting-like (SC-like) phases and five distinct charge-density-wave (CDW) phases. We substantiate that the SC-like and two CDW phases are direct consequences of imbalanced interactions and extended-range hoppings. We derive the order parameters (OPs) for each of the phases and verify them in large-system simulations, finding consistency with the entanglement entropy and the fidelity in capturing the phase transitions. In contrast to the non-interacting case where the favored hoppings are unidirectional in the topological phases, the derived OPs suggest non-unidirectional hoppings are possible under the influence of interactions.

cond-mat.str-el↗

arXiv2026

Beyond Topological Invariants: Order Parameters from Dominant Fock-state Patterns

We introduce a general scheme for constructing order parameters (OPs) by extracting generic patterns from the dominant Fock states of many-body ground states. While topological phases are traditionally characterized by non-local invariants, we demonstrate that our real-space OPs provide a more refined classification. In the extended Su-Schrieffer-Heeger model, we show that the standard winding number is insufficient to fully distinguish all phases; our OPs reveal a hidden sub-structure where each topological sector splits into two distinct phases. Beyond identifying the phase boundaries, these OPs quantify the depth of a phase, and remain robust in characterizing transitions in disordered systems. Furthermore, our approach provides a practical finite-size diagnostic for the Berezinskii-Kosterlitz-Thouless transition in the interacting spin-1/2 XXZ model. The presented framework offers a broadly applicable tool for uncovering the phase diagrams of diverse interacting and non-interacting quantum many-body systems.

cond-mat.other↗

arXiv2025

Diffusive spin transport of the spin-1/2 XXZ chain in the Ising regime at zero magnetic field and finite temperature

The studies of this paper on the spin-1/2 XXZ chain at finite temperatures T>0 have two complementary goals. The first is to identify the spin carriers of all its Sq>0 energy eigenstates and to show that their spin elementary currents fully control the spin-transport quantities. Here Sq is the q-spin of the continuous SUq(2) symmetry of the model for anisotropy >1. To achieve this goal, our studies rely on a suitable exact physical-spin representation.Both the spin stiffness and the zero-field spin-diffusion constant are expressed in terms of thermal expectation values of the square of the elementary currents carried by the spin carriers. Our second goal is to confirm that the zero-field and finite-temperature spin transport is normal diffusive for anisotropy >1. We use two complementary methods that rely on an inequality for the T>0 spin stiffness and the above thermal expectation values, respectively, to show that the contributions to ballistic spin transport vanish. Complementarily, for T>0 and anisotropy >1, the spin-diffusion constant is found to be finite and enhanced upon lowering T, reaching its largest yet finite values at low temperatures. Evidence suggests that it diverges in the anisotropy limit to 1 for T>0, consistent with T>0 anomalous superdiffusive spin transport at anisotropy 1 and zero field.

cond-mat.str-el↗

arXiv2023

Multifractality and pre-thermalization in the quasi-periodically kicked Aubry-André-Harper model

In a class of periodically driven systems, multifractal states in non-equilibrium conditions and robustness of dynamical localization when the driving is made aperiodic have received considerable attention. In this paper, we explore a family of one-dimensional Aubry-André-Harper models that are quasi-periodically kicked with protocols following different binary quasi-periodic sequences, which can be realized in ultracold atom systems. The relationship between the systems' localization properties and the sequences' mathematical features is established utilizing the Floquet theorem and the Baker-Campbell-Hausdorff formula. We investigate the multifractality and pre-thermalization of the eigenstates of the unitary evolution operator combined with an analysis of the transport properties of initially localized wave packets. We further contend that the quasi-periodically kicked Aubry-André-Harper model provides a rich phase diagram as the periodic case but also brings the range of parameters to observe multifractal states and pre-thermalization to a regime more amenable to experiments.

cond-mat.dis-nn↗

arXiv2021

The role of q-spin singlet pairs of physical spins in the dynamical properties of the spin-1/2 Heisenberg-Ising XXZ chain

Dynamical correlation functions contain important physical information on correlated spin models. Here a dynamical theory suitable suitable to the isotropic spin-1/2 Heisenberg chain in a longitudinal magnetic field is extended to anisotropy larger than one . The aim of this paper is the study of the line shape of the spin dynamical structure factor components +-, -+ and zz of the spin-1/2 Heisenberg-Ising chain in a longitudinal magnetic field near their sharp peaks. To reach that goal, the nature of the specific type of elementary magnetic configurations both unbound and associated with real Bethe-ansatz rapidities and bound and described by complex Bethe strings is clarified: They are singlet q-spin pairs of physical spins 1/2. We derive analytical expressions for the line shapes of dynamical structure factor components +-, -+ and zz valid in the vicinity of lines of sharp peaks. Those are mostly located at and just above lower thresholds of continua associated with both real-rapidity states with only unbound q-spin singlet pairs and states with real and complex rapidities populated by such unbound pairs and a single 2-string or a single 3-string. The latter contain 2 and 3 bound q-spin singlet pairs, respectively. Our results provide physically interesting and important information on the microscopic processes that determine the dynamical properties of the non-perturbative spin-1/2 Heisenberg-Ising chain in a longitudinal magnetic field.

cond-mat.str-el↗

arXiv2021

One-particle spectral functions of the one-dimensional Fermionic Hubbard model with one fermion per site at zero and finite magnetic fields

Here the line shape of the up- and down-spin one-particle spectral functions at and in the (k,energy)-plane's vicinity of their cusp singularities is studied for the Mott-Hubbard insulator described by the 1D Hubbard model with one fermion per site at zero and finite magnetic fields. At zero field they can be accessed in terms of electrons by photoemission experiments. At finite field, such functions and corresponding interplay of correlations and magnetic-field effects refer to an involved non-perturbative many-particle problem that is poorly understood. The Mott-Hubbard gap that separates the addition and removal spectral functions is calculated for all spin densities and interaction values. The qualitative differences in the one-particle properties of the Mott-Hubbard insulator and corresponding doped insulator are also investigated. The relation of our theoretical results and predictions to both condensed-matter and ultracold spin-1/2 atom systems is discussed.

cond-mat.str-el↗

arXiv2019

Edge and bulk localization of Floquet topological superconductors

We study the bulk and edge properties of a driven Kitaev chain, where the driving is performed as instantaneous quenches of the on-site energies. We identify three periodic driving regimes: low period, which is equivalent to a static model, with renormalized parameters obtained from the Baker-Campbell-Hausdorff (BCH) expansion; intermediate period, where the first order BCH expansion breaks down; and high period when the quasienergy gap at $ω/2$ closes. We investigate the dynamical localization properties for the case of quasiperiodic potential driving as a function of its amplitude and the pairing strength, obtaining regimes with extended, critical and localized bulk states, if the driving is performed at high frequencies. In these, we characterize wave-packet propagation, obtaining ballistic, subdiffusive and absence of spreading, respectively. In the intermediate period regime, we find an additional region in the phase diagram with a mobility edge between critical and localized states. Further, we investigate the stability of these phases under time-aperiodicity on the drivings, observing that the system eventually thermalizes: It results in featureless random states which can be described by the symmetry of the Hamiltonian. In a system with open edges, we find that both Majorana and fermionic localized edge modes can be engineered with a spatially quasiperiodic potential. Besides, we demonstrate the possibility of creating multiple Majorana $0$ and $π$ modes in a driven setting, even if the underlying static Hamiltonian is in its trivial phase. Lastly, we study the robustness of the Majorana modes against the aperiodicity in the driving period, showing that the ones created via quasiperiodic potential are more robust to the decoherence. Moreover, we find an example where Majorana mode is robust, provided that it is chosen from a special point in the topological region.

cond-mat.supr-con↗

arXiv2016

Strain induced topological phase transition at zigzag edges of monolayer transition-metal dichalcogenides

The effect of strain in zigzag ribbons of monolayer transition-metal dichalcogenides with induced superconductivity is studied using a minimal 3-band tight-binding model. The unstrained system shows a topological phase with Majorana zero modes localized at the boundaries of the one-dimensional (1D) zigzag edges. By direct inspection of the spectrum and wave functions we examine the evolution of the topological phase as an in-plane, uniaxial deformation is imposed. It is found that strain shifts the energy of 1D edge states, thus causing a topological phase transition which eliminates the Majorana modes. For realistic parameter values, we show that the effect of strain can be changed from completely destructive -- in which case a small built in strain is enough to destroy the topological phase -- to a situation where strain becomes an effective tuning parameter which can be used to manipulate Majorana zero modes. These two regimes are accessible by increasing the value of the applied Zeeman field within realistic values. We also study how strain effects are affected by the chemical potential, showing in particular how unwanted effects can be minimized. Finally, as a cross-check of the obtained results, we reveal the connection between 1D Majorana zero modes in the zigzag edge and the multi-band Berry phase, which serves as a topological invariant of this system.

cond-mat.mes-hall↗

arXiv2015

Andreev spectroscopy of Majorana states in topological superconductors with multipocket Fermi surfaces

The topological properties of a multiband topological superconductor in two dimensions are studied, when the latter is obtained by introducing electron pairing in an otherwise topological insulator. The type of pairing, doping and Fermi surface topology play an essential role. Considering the Andreev reflection problem, we use a previously developed quantum waveguide theory for multiorbital systems and find that, when the Fermi surface has several pockets, this theory retrieves the correct number of Majorana fermion states as predicted by the topological index. By varying band structure parameters, the Fermi surface topology of the normal phase can be made to change, whereby the number of Majorana modes also varies. We calculate the effect of such transitions on the Andreev differential conductance.

cond-mat.supr-con↗

arXiv2013

Hall conductivity as bulk signature of topological transitions in superconductors

Topological superconductors may undergo transitions between phases with different topological numbers which, like the case of topological insulators, are related to the presence of gapless (Majorana) edge states. In $\mathbb{Z}$ topological insulators the charge Hall conductivity is quantized, being proportional to the number of gapless states running at the edge. In a superconductor, however, charge is not conserved and, therefore, $σ_{xy}$ is not quantized, even in the case of a $\mathbb{Z}$ topological superconductor. Here it is shown that while the $σ_{xy}$ evolves continuously between different topological phases of a $\mathbb{Z}$ topological superconductor, its derivatives display sharp features signaling the topological transitions. We consider in detail the case of a triplet superconductor with p-wave symmetry in the presence of Rashba spin-orbit (SO) coupling and externally applied Zeeman spin splitting. Generalization to the cases where the pairing vector is not aligned with that of the SO coupling is given. We generalize also to the cases where the normal system is already topologically non-trivial.

cond-mat.supr-con↗

arXiv2012

Change of an insulator's topological properties by a Hubbard interaction

We introduce two dimensional fermionic band models with two orbitals per lattice site, or one spinful orbital, and which have a non-zero topological Chern number that can be changed by varying the ratio of hopping parameters. A topologically non-trivial insulator is then realized if there is one fermion per site. When interactions in the framework of the Hubbard model are introduced, the effective hopping parameters are renormalized and the system's topological number can change at a certain interaction strength, $U=\bar U$, smaller than that for the Mott transition. Two different situations may then occur: either the anomalous Hall conductivity $σ_{xy}$ changes abruptly at $\bar U$, as the system undergoes a transition from one topologically non-trivial insulator to another, or the transition is through an anomalous Hall metal, and $σ_{xy}$ changes smoothly between two different quantized values as $U$ grows. Restoring time-reversal symmetry by adding spin to spinless models, the half-filled system becomes a $\mathbb{Z}_2$ topological insulator. The topological number $ν$ then changes at a critical coupling $\bar U$ and the quantized spin Hall response changes abruptly.

cond-mat.str-el↗

arXiv2006

Confinement of monopole field lines in a superconductor at T=/=0

We apply the Bogoliubov-de Gennes equations to the confinement of a monopole-antimonopole pair in a superconductor. This is related to the problem of a quark-antiquark pair bound by a confining string, consisting of a colour-electric flux tube, dual to the magnetic vortex of type-II superconductors. We study the confinement of the field lines due to the superconducting state and calculate the effective potential between the two monopoles. At short distances the potential is Coulombic and at large distances the potential is linear, as previously determined solving the Ginzburg-Landau equations. The magnetic field lines and the string tension are also studied as a function of the temperature $T$. Because we take into account the explicit fermionic degrees of freedom, this work may open new perspectives to the breaking of chiral symmetry or to colour superconductivity.

hep-ph↗

arXiv2006

Vorticity and magnetic shielding in a type-II superconductor

We study in detail, solving the Bogoliubov-de Gennes equations, the magnetic field, supercurrent and order parameter profiles originated by a solenoid or magnetic whisker inserted in a type-II superconductor. We consider solutions of different vorticities, n, in the various cases. The results confirm the connection between the vorticity, the internal currents and the boundstates in a self-consistent way. The number of boundstates is given by the vorticity of the phase of the gap function as in the case with no external solenoid. In the limiting case of an infinitely thin solenoid, like a Dirac string, the solution is qualitatively different. The quasiparticle spectrum and wave functions are a function of n-n_ext, where n_ext is the vorticity of the solenoid. The flux is in all cases determined by the vorticity of the gap function.

cond-mat.supr-con↗

arXiv1997

Landau Levels and Quasiparticle Spectrum of Extreme Type-II Superconductors

At high magnetic fields and low temperatures, numerous extreme type-II superconductors exhibit Landau quantization of electronic motion. We present an analytic construction of the quasiparticle spectrum in this regime, based on the high-field expansion. The spectrum is gapless and is separated from the familiar low-field regime by a quantum level-crossing transition. Such low energy excitations should lead to observable effects in thermodynamics and transport.

cond-mat.supr-con↗