arXiv subjects

P. D. Sacramento

Publications and source records attributed to P. D. Sacramento.

At least 19 recordsLinked to original sources

arXiv2026

Competition and coexistence of superconducting symmetries in $p$-wave magnets

We investigate the interplay between unconventional magnetism and superconductivity in a model of a $p$-wave magnet on a square lattice. Using a self-consistent Bogoliubov-de-Gennes approach, we analyze the pairing amplitudes, competition, and coexistence of spin-singlet $s$-wave and spin-triplet $p$-wave pairings in the presence of a magnetic texture with a helical structure along the $x$ direction that is repeated in the $y$ direction. We find that the magnetic helix selectively stabilizes different pairing symmetries depending on its orientation and strength. In particular, mixed-spin $p_x$-wave pairing is enhanced at intermediate magnetic couplings and equal-spin $p_y$-wave pairing is robust and insensitive to all coupling intensities. When the multiple order parameters are simultaneously considered, we find regimes of coexistence and competition. Increasing the magnetic coupling drives two quantum phase transitions. The first from dominant spin-singlet $s$-wave to mixed-spin triplet $p_x$-wave pairings in a regime of coexistence. The second from spin-singlet $s$-wave and mixed-spin triplet $p$-wave pairings with total spin projection $S_z=0$ to dominant equal-spin triplet $p_y$-wave pairings with $S_z=\pm1$ in a regime of mutually exclusive superconducting phases. Our results demonstrate that $p$-wave magnetic order does not merely diminish spin-singlet $s$-wave superconductivity but can actively promote and stabilize spin-triplet $p$-wave pairing, both intrinsically and in proximity to spin-singlet $s$-wave superconductors. These findings highlight unconventional magnets as promising materials for realizing robust triplet superconductivity.

cond-mat.supr-con↗

arXiv2025

Finite-temperature transport in the gapped spin-1/2 XXZ chain and one-dimensional lattice spinless fermion model

Here we consider a class of energy eigenstates of the spin-1/2 XXZ chain that exist both for anisotropies 1 and larger than 1. We show that at the isotropic point their contributions are behind the diffusion constant being infinite, spin transport being anomalous superdiffusive for temperatures T>0. That for anisotropy larger than 1 such states do not contribute to the diffusion constant is shown to imply it is finite, spin transport being normal diffusive for T>0. By combining the connection through a Jordan-Wigner transformation of the spin-1/2 XXZ chain to the one-dimensional (1D) lattice spinless fermion model at zero chemical potential for V/J larger or equal to 1 with its Bethe-ansatz solution, where V is the nearest-neighbor Coulomb repulsion and J is twice the hopping integrai, in this paper we also address the issue of the T>0 charge transport of that model at zero chemical potential. It is found to be anomalous superdiffusive for V/J=1 and normal diffusive for V/J>1.

cond-mat.str-el↗

arXiv2025

Diffusive charge transport in the gapped 1D Hubbard model at all finite temperatures

Studies relying on hydrodynamic theory and Kardar-Parisi-Zhang (KPZ) scaling have found that in the one-dimensional Hubbard model spin and charge transport are for all temperatures T > 0 anomalous superdiffusive at zero magnetic field, h = 0, and zero chemical potential, μ = 0, respectively. However, this contradicts recent exact results that at very low temperature charge transport rather is normal diffusive. In this Letter we identify the mechanisms that control the different types of temperature dependence of the h = 0 spin and μ = 0 charge transport and find that the latter is normal diffusive for all finite temperatures T > 0, in contrast to the hydrodynamic theory and KPZ scaling predictions.

cond-mat.str-el↗

arXiv2025

Ising spin-1/2 XXZ chain's quantum problems beyond the spinon paradigm

Spin chains are correlated quantum models of great interest in quantum systems and materials exhibiting quasi-one-dimensional magnetic properties. Here we review results on quantum problems associated with spin chains that are beyond the usual spinon paradigm. In this review we consider two quantum problems that are beyond the spinon representation: (a) Spin Bethe strings of length n that have no spinon representation, contribute to the dynamical properties of the spin-1/2 XXZ chain with anisotropy larger than 1 and for n=1,2,3 were experimentally identified and realized in the zigzag materials SrCo2V2O8 and BaCo2V2O8; (b) The spin stiffness associated with ballistic spin transport at arbitrary finite temperature, which involves a huge number of energy eigenstates, many of which are generated in the thermodynamic limit from ground states by an infinite number of elementary processes.

cond-mat.str-el↗

arXiv2024

Temperature dependence of charge transport in the half-filled 1D Hubbard model

The use of hydrodynamic transport theory seems to indicate that the charge diffusion constant D of the one-dimensional (1D) half-filled Hubbard model, whose Drude weight vanishes, diverges for temperature T>0, which would imply anomalous superdiffusive charge transport. Here the leading term of that constant is derived for low finite temperatures much smaller than the the Mott-Hubbard gap. It only diverges in the temperature infinite limit, being finite and decreasing upon increasing T within the low-temperature regime. Our exact results both provide valuable physical information ona complex quantum problem and bring about the interesting unsolved issue of how charge transport evolves from normal diffusive for low temperatures to anomalous superdiffusive in the infinite temperature limit.

cond-mat.str-el↗

arXiv2024

Entanglement in quenched extended Su-Schrieffer-Heeger model with anomalous dynamical quantum phase transitions

Research on topological models unveils fascinating physics, especially in the realm of dynamical quantum phase transitions (DQPTs). However, the understanding of entanglement structures and properties near DQPT in models with longer-range hoppings is far from complete. In this work, we study DQPTs in the quenched extended Su-Schrieffer-Heeger (SSH) model. Anomalous DQPTs, where the number of critical momenta exceeds the winding number differences between the pre-quench and post-quench phases, are observed. We find that the entanglement exhibits local maximum (minimum) around the anomalous DQPTs, in line with the level crossings (separations) around the middle of the correlation matrix spectrum. We further categorize the phases in the equilibrium model into two classes and distinctive features in the time evolution of the entanglement involving quenches within and across the two classes are identified. The findings pave the way to a better understanding of topological models with longer-range hoppings in the out-of-equilibrium regime.

cond-mat.str-el↗

arXiv2023

Zigzag materials: selective interchain couplings control the coexistence of one-dimensional physics and deviations from it

The coexistence in the low-temperature spin-conducting phases of the zigzag materials BaCo2V2O8 and SrCo2V2O8 of one-dimensional (1D) physics with important deviations from it is not well understood. The studies of this paper account for an important selection rule that follows from interchain spin states being coupled more strongly within the spin dynamical structure factor of such zigzag materials whenever they are connected by a specific symmetry operation of the underlying lattice. In the case of excited states, this symmetry operation is only a symmetry in spin-space ifno electronic spin flip is performed within the generation of such states. Our results on both the role of selective interchain couplings in protecting the 1D physics and being behind deviations from it and on the dynamical properties being controlled by scattering of singlet pairs of physical spins 1/2 open the door to a key advance in the understanding of the physics of the spin chains in BaCo2V2O8 and SrCo2V2O8.

cond-mat.str-el↗

arXiv2022

Quasidisorder Induced Topology

We study the effects of quasidisorder and Anderson disorder on a two dimensional topological superconductor with an applied external magnetic field. The cases of a $p$-wave superconductor and a noncentrosymmetric superconductor with mixed $p$ and $s$-wave pairings and Rashba spin-orbit coupling are studied. We show that, for a perpendicular magnetic field, the introduction of quasidisorder leads to the appearance of topological phases in new regions, characterised by an integer value of the Chern number. For a parallel magnetic field, we identify regimes with the appearance of new Majorana flat bands and also new unidirectional Majorana edge states, as quasidisorder is introduced. We show that the Majorana flat bands have a quantized Berry phase of $π$ and identify it as a topological invariant. Two topological transitions are identified and the values of the critical exponents $z$ and $ν$ are obtained. The fractal nature of the eigenstates is discussed both for Anderson disorder and Aubry-André disorder.

cond-mat.supr-con↗

arXiv2022

Topological states in chiral electronic chains

We consider the influence of topological phases, or their vicinity, on the spin density and spin polarization through a chiral chain. We show the quantization of the Berry phase in a one-dimensional polarization helix structure, under the presence of an external magnetic field, and show its influence on the spin density. The polar angle of the momentum space spin density becomes quantized in the regime that the Berry phase is quantized, as a result of the combined effect of the induced spin-orbit coupling and the external transverse magnetic field, while the edge states do not show the polar angle quantization, in contrast with the bulk states. Under appropriate conditions, the model can be generalized to have similarities with a chain with nonhomogeneous Rashba spin- orbit couplings, with zero- or low-energy edge states. Due to the breaking of time-reversal symmetry, we recover the effect of chiral-induced spin polarization and spin transport across the chiral chain, when coupling to external leads. Some consequences of the quantized spin polarization and low-energy states on the spin transport are discussed.

cond-mat.mes-hall↗

arXiv2021

Photoinduced anomalous Hall effect in the interacting Haldane model: targeting topological states with pump pulses

We investigate the nonequilibrium dynamics of the spinless Haldane model with nearest-neighbor interactions on the honeycomb lattice by employing an unbiased numerical method. In this system, a first-order transition from the Chern insulator (CI) at weak coupling to the charge-density-wave (CDW) phase at strong coupling can be characterized by a level crossing of the lowest energy levels. Here we show that adiabatically following the eigenstates across this level crossing, their Chern numbers are preserved, leading to the identification of a topologically-nontrivial low-energy excited state in the CDW regime. By promoting a resonant energy excitation via an ultrafast circularly polarized pump pulse, we find that the system acquires a non-vanishing Hall response as a result of the large overlap enhancement between the time-dependent wave-function and the topologically non-trivial excited state. This is suggestive of a photoinduced topological phase transition via unitary dynamics, despite a proper definition of the Chern number remaining elusive for an out-of-equilibrium interacting system. We contrast these results with more common quench protocols, where such features are largely absent in the dynamics even if the post-quench Hamiltonian displays a topologically nontrivial ground state.

cond-mat.str-el↗

arXiv2021

Correlations and dynamical quantum phase transitions in an interacting topological insulator

Dynamical quantum phase transitions (DQPTs), which refer to the criticality in time of a quantum many-body system, have attracted much theoretical and experimental research interest recently. Despite DQPTs are defined and signalled by the non-analyticities in the Loschmidt rate, its interrelation with various correlation measures such as the equilibrium order parameters of the system remains unclear. In this work, by considering the quench dynamics in an interacting topological model, we find that the equilibrium order parameters of the model in general exhibit signatures around the DQPT, in the short time regime. The first extrema of the equilibrium order parameters are connected to the first Loschmidt rate peak. By studying the unequal-time two-point correlation, we also find that the correlation between the nearest neighbors decays while that with neighbors further away builds up as time grows in the non-interacting case, and upon the addition of repulsive intra-cell interactions. On the other hand, the inter-cell interaction tends to suppress the two-site correlations. These findings could provide us insights into the characteristic of the system around DQPTs, and pave the way to a better understanding of the dynamics in non-equilibrium quantum many-body systems.

cond-mat.str-el↗

arXiv2020

Bethe strings in the dynamical structure factor of the spin-1/2 Heisenberg XXX chain

Recently there has been a renewed interest in the spectra and role in dynamical properties of excited states of the spin-1/2 Heisenberg antiferromagnetic chain in longitudinal magnetic fields associated with Bethe strings. The latter are bound states of elementary magnetic excitations described by Bethe-ansatz complex non-real rapidities. Previous studies on this problem referred to finite-size systems. Here we consider the thermodynamic limit and study it for the isotropic spin-1/2 Heisenberg XXX chain in a longitudinal magnetic field. We confirm that also in that limit the most significant spectral weight contribution from Bethe strings leads to gapped continua in the spectra of the spin +- and xx dynamical structure factors. The contribution of Bethe strings to the zz dynamical structure factor is found to be small at low spin densities and to become negligible upon increasing that density above 0.317. For the -+ dynamical structure factor, that contribution is found to be negligible at finite magnetic field. We derive analytical expressions for the line shapes of the +-, xx, and zz dynamical structure factors valid in the vicinity of singularities located at and just above the gapped lower thresholds of the Bethe-string states's spectra. As a side result and in order to provide an overall physical picture that includes the relative location of all spectra with a significant amount of spectral weight, we revisit the general problem of the line-shape of the transverse and longitudinal spin dynamical structure factors at finite magnetic field and excitation energies in the vicinity of other singularities. This includes those located at and just above the lower thresholds of the spectra that stem from excited states described by only real Bethe-ansatz rapidities.

cond-mat.other↗

arXiv2018

Detection of topological phases by quasi-local operators

It has been proposed recently by some of the authors that the quantum phase transition of a topological insulator like the SSH model may be detected by the eigenvalues and eigenvectors of the reduced density matrix. Here we further extend the scheme of identifying the order parameters by considering the SSH model with the addition of triplet superconductivity. This model has a rich phase diagram due to the competition of the SSH "order" and the Kitaev "order", which requires the introduction of four order parameters to describe the various topological phases. We show how these order parameters can be expressed simply as averages of projection operators on the ground state at certain points deep in each phase and how one can simply obtain the phase boundaries. A scaling analysis in the vicinity of the transition lines is consistent with the quantum Ising universality class.

cond-mat.str-el↗

arXiv2018

Vanishing k-space fidelity and phase diagram's bulk-edge-bulk correspondence

The fidelity between two infinitesimally close states or the fidelity susceptibility of a system are known to detect quantum phase transitions. Here we show that the k-space fidelity between two states far from each other and taken deep inside (bulk) of two phase s, generically vanishes at the k-points where there are gapless points in the energy spectrum that give origin to the lines (edges) separating the phases in the phase diagram. We consider a general case of two-band models and present a sufficient condition for the existence of gapless points, given there are pairs of parameter points for which the fidelity between the corresponding states is zero. By presenting an explicit counter-example, we showed that the sufficient condition is not necessary. Further, we showed that, unless the set of parameter points is suitably constrained, the existence of gapless points generically imply the accompanied pairs of parameter points with vanishing fidelity. Also, we showed the connection between the vanishing fidelity and gapless points on a number of concrete examples (topological triplet superconductor, topological insulator, 1d Kitaev model of spinless fermions, BCS superconductor, Ising model in a transverse field, graphene and Haldane Chern insulator), as well as for the more general case of Dirac-like Hamiltonians. We also briefly discuss the relation between the vanishing fidelity and gapless points at finite temperatures.

quant-ph↗

arXiv2018

Pseudoparticle approach to 1D integrable quantum models

Over the last three decades a large number of experimental studies on several quasi one-dimensional (1D) metals and quasi1D Mott-Hubbard insulators have produced evidence for distinct spectral features identified with charge-only and spin-only fractionalized particles. They can be also observed in ultra-cold atomic 1D optical lattices a nd quantum wires. 1D exactly solvable models provide nontrivial tests of the approaches for these systems relying on field theories. Different schemes such as the pseudofermion dynamical theory (PDT) and the mobile quantum impurity model (MQIM) have revealed that the 1D correlated models high-energy physics is qualitatively different from that of a low-energy Tomonaga-Luttinger liquid (TLL). This includes the momentum dependence of the exponents that control the one- and two-particle dynamical correlation functions near their spectra edges and in the vicinity of one-particle singular spectral features. On the one hand, the low-energy charge-only and spin-only fractionalized particles are usually identified with holons and spinons, respectively. On the other hand, `particle-like' representations in terms of {\it pseudoparticles}, related PDT {\it pseudofermions}, and MQIM particles are suitable for the description of both the low-energy TLL physics and high-energy spectral and dynamical properties of 1D correlated systems. The main goal of this review is to revisit the usefulness of pseudoparticle and PDT pseudofermion representations for the study of both static and high-energy spectral and dynamical properties of the 1D Lieb-Liniger Bose gas, spin-$1/2$ isotropic Heisenberg chain, and 1D Hubbard model. Moreover, the relation between the PDT and the MQIM is clarified.

cond-mat.str-el↗

arXiv2018

Duality and topology

Mappings between models may be obtained by unitary transformations with preservation of the spectra but in general a change in the states. Non- canonical transformations in general also change the statistics of the operators involved. In these cases one may expect a change of topological properties as a consequence of the mapping. Here we consider some dualities resulting from mappings, by systematically using a Majorana fermion representation of spin and fermionic problems. We focus on the change of topological invariants that results from unitary transformations taking as examples the mapping between a spin system and a topological superconductor, and between different fermionic systems.

cond-mat.str-el↗

arXiv2017

Dynamical localization and the effects of aperiodicity in Floquet systems

We study the localization aspects of a kicked non-interacting one-dimensional (1D) quantum system subject to either time-periodic or non-periodic pulses. These are reflected as sudden changes of the onsite energies in the lattice with different modulations in real space. When the modulation of the kick is incommensurate with the lattice spacing, and the kicks are periodic, a well known dynamical localization in real space is recovered for large kick amplitudes and frequencies. We explore the universality class of this transition and also test the robustness of localization under deviations from the perfect periodic case. We show that delocalization ultimately sets in and a diffusive spreading of an initial wave packet is obtained when the aperiodicity of the driving is introduced.

cond-mat.dis-nn↗

arXiv2017

Dynamics of quenched topological edge modes

A characteristic feature of topological systems is the presence of robust gapless edge states. In this work the effect of time-dependent perturbations on the edge states is considered. Specifically we consider perturbations that can be understood as changes of the parameters of the Hamiltonian. These changes may be sudden or carried out at a fixed rate. In general, the edge modes decay in the thermodynamic limit, but for finite systems a revival time is found that scales with the system size. The dynamics of fermionic edge modes and Majorana modes are compared. The effect of periodic perturbations is also referred allowing the appearance of edge modes out of a topologically trivial phase.

cond-mat.supr-con↗