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A. Ferraz

Publications and source records attributed to A. Ferraz.

At least 19 recordsLinked to original sources
arXiv2020

Physical pendulum model: Fractional differential equation and memory effects

A detailed analysis of three pendular motion models is presented. Inertial effects, self-oscillation, and memory, together with non-constant moment of inertia, hysteresis and negative damping are shown to be required for the comprehensive description of the free pendulum oscillatory regime. The effects of very high initial amplitudes, friction in the roller bearing axle, drag, and pendulum geometry are also analysed and discussed. The model that consists of a fractional differential equation provides both the best explanation of, and the best fits to, experimental high resolution and long-time data gathered from standard action-camera videos.

physics.class-ph↗
arXiv2017

Half-metal phases in a quantum wire with modulated spin-orbit interaction

We propose a spin valve device based on the interplay of a modulated spin-orbit interaction and a uniform external magnetic field acting on a quantum wire. Half-metal phases, where electrons with only a selected spin polarization exhibit ballistic conductance, can be tuned by varying the magnetic field. These half-metal phases are proven to be robust against electron-electron repulsive interactions. Our results arise from a combination of explicit band diagonalization, bosonization techniques and extensive DMRG computations.

cond-mat.str-el↗
arXiv2017

CP1|1 nonlinear sigma model vs strong electron correlations

The nonlinear sigma model targeted on the coset supermanifold $CP^{1|1}=SU(2|1)/U(1|1)$ is derived in an attempt to describe the quasiclassical low-energy effective action for the doped $t-J$ model at the SUSY point, $J=2t.$ In spite of the fact that the supermanifold $CP^{1|1}$ indeed appears as the phase space of the strongly correlated electrons, the canonical $CP^{1|1}$ nonlinear sigma model (NLSM) is unable to capture the physics of strong correlations displayed by the SUSY $t-J$ model at any finite doping. This is due to the fact that, in this regime, the doping itself cannot be self-consistently incorporated into the $CP^{1|1}$ NLSM. \end{abstract}

cond-mat.str-el↗
arXiv2015

Integrability of three dimensional models: cubic equations

We extend basic properties of two dimensional integrable models within the Algebraic Bethe Ansatz approach to 2+1 dimensions and formulate the sufficient conditions for the commutativity of transfer matrices of different spectral parameters, in analogy with Yang-Baxter or tetrahedron equations. The basic ingredient of our models is the R-matrix, which describes the scattering of a pair of particles over another pair of particles, the quark-anti-quark (meson) scattering on another quark-anti-quark state. We show that the Kitaev model belongs to this class of models and its R-matrix fulfills well-defined equations for integrability.

math-ph↗
arXiv2014

Ward Identities and chiral anomalies for coupled fermionic chains

Coupled fermionic chains are usually described by an effective model written in terms of bonding and anti-bonding spinless fields with linear dispersion in the vicinities of the respective Fermi points. We derive for the first time exact Ward Identities (WI) for this model, proving the existence of chiral anomalies which verify the Adler-Bardeen non-renormalization property. Such WI are expected to play a crucial role in the understanding of the thermodynamic properties of the system. Our results are non-perturbative and are obtained analyzing Grassmann functional integrals by means of Constructive Quantum Field Theory methods.

cond-mat.str-el↗
arXiv2013

Modulated Spin Liquid and Magnetic Order from a Kondo-Heisenberg model applied to $URu_{2}Si_{2}$

Within the framework of the Kondo-Heisenberg model, we analyse the effect of charge fluctuation on the modulated spin liquid (MSL) and antiferromagnetic (AF) orders which were established in a previous publication. We discuss the emergence of two quantum critical lines separating the coexisting Kondo-MSL and Kondo-MSL-AF phases. The various order parameters of the system possess a characteristic signature observable on the electronic band structure of each of the phases. We calculate that the MSL order is indeed a possible explanation of the hidden order phase of $URu_{2}Si_{2}$ heavy fermion compound. Our model produces results in qualitative agreement with the experimental (T,P) phase diagram and the two gap openings in the system and quantitative agreement with the entropy and Sommerfeld coefficient evolution.

cond-mat.str-el↗
arXiv2011

Effective action for strongly correlated electron systems

The su(2|1) coherent-state path-integral representation of the partition function of the t - J model of strongly correlated electrons is derived at finite doping. The emergent effective action is compared to the one proposed earlier on phenomenological grounds by Shankar to describe holes in an antiferromagnet (Nucl.Phys. B330 (1990) 433). The t - J model effective action is found to have an important "extra" factor with no analogue in Shankar's action. It represents the local constraint of no double electron occupancy and reflects the rearrangement of the underlying phase-space manifold due to the presence of strong electron correlation. This important ingredient is shown to be essential to describe the physics of strongly correlated electron systems. Keywords: t - J model of strongly correlated electrons; su(2|1) coherent-state path integral

cond-mat.str-el↗
arXiv2010

The modulated spin liquid: a new paradigm for URu$_2$Si$_2$

We argue that near a Kondo breakdown critical point, a spin liquid with spatial modulations can form. Unlike its uniform counterpart, we find that this occurs via a second order phase transition. The amount of entropy quenched when ordering is of the same magnitude as for an antiferromagnet. Moreover, the two states are competitive, and at low temperatures are separated by a first order phase transition. The modulated spin liquid we find breaks $Z_4$ symmetry, as recently seen in the hidden order phase of URu$_2$Si$_2$. Based on this, we suggest that the modulated spin liquid is a viable candidate for this unique phase of matter.

cond-mat.str-el↗
arXiv2008

Ising t-J model close to half filling: A Monte Carlo study

Within the recently proposed doped-carrier representation of the projected lattice electron operators we derive a full Ising version of the t-J model. This model possesses the global discrete Z_2 symmetry as a maximal spin symmetry of the Hamiltonian at any values of the coupling constants, t and J. In contrast, in the spin anisotropic limit of the t-J model, usually referred to as the t-J_z model, the global SU(2) invariance is fully restored at J_z=0, so that only the spin-spin interaction has in that model the true Ising form. We discuss a relationship between those two models and the standard isotropic t-J model. We show that the low-energy quasiparticles in all three models share the qualitatively similar properties at low doping and small values of J/t. The main advantage of the proposed Ising t-J model over the t-J_z one is that the former allows for the unbiased Monte Carlo calculations on large clusters of up to 10^3 sites. Within this model we discuss in detail the destruction of the antiferromagnetic order by doping as well as the interplay between the AF order and hole mobility. We also discuss the effect of the exchange interaction and that of the next nearest neighbour hoppings on the destruction of the AF order at finite doping. We show that the short-range AF order is observed in a wide range of temperatures and dopings, much beyond the boundaries of the AF phase. We explicitly demonstrate that the local no double occupancy constraint plays the dominant role in destroying the magnetic order at finite doping. Finally, a role of inhomogeneities is discussed.

cond-mat.str-el↗
arXiv2006

Field Theory Renormalization Group: The Tomonaga-Luttinger Model Revisited

We apply field theoretical renormalization group (RG) methods to describe the Tomonaga-Luttinger model as an important test ground to deal with spin-charge separation effects in higher spatial dimensions. We compute the anomalous dimension associated with the one-particle Green's functions $G_{(a)R}$. We calculate the RG equations for the renormalized forward couplings $g_{2R}$ and $g_{4R}$ up to two-loop order and demonstrate that they don't flow in the vicinities of the Fermi points (FPs). We solve the Callan-Symanzik equation for $G_{(a)R}$ in the neighborhood of the FPs. We calculate the related spectral function and the momentum distribution function at $p=k_{F},p_{0}=ω$. We compute the renormalized one-particle irreducible function $Γ_{(+)R}^{(2)}(p,p_{0}=0;Λ)$ and show it carries important spin-charge separation effects in agreement with well known results. Finally we discuss the implementation of the RG scheme taking into account the important simplifications produced by the Ward identities.

cond-mat.str-el↗
arXiv2005

Short-Range Order in a Flat Two-Dimensional Fermi Surface

We present the two-loop renormalization group (RG) calculations of all the susceptibilities associated with the two-dimensional flat Fermi surface with rounded corners (FS). Our approach follows our fermionic field theory RG method presented in detail earlier on. In one loop order our calculation reproduce the results obtained previously by other RG schemes. All susceptibilities diverge at some energy scale and the antiferromagnetic SDW correlations produce indeed the dominant instability in the physical system. In contrast, in two-loop order, for a given initial set of values of coupling constant regime only one of the susceptibilities at a time seems to diverge.

cond-mat.supr-con↗
arXiv2005

Field-theoretical renormalization group for a flat two-dimensional Fermi surface

We implement an explicit two-loop calculation of the coupling functions and the self-energy of interacting fermions with a two-dimensional flat Fermi surface in the framework of the field theoretical renormalization group (RG) approach. Throughout the calculation both the Fermi surface and the Fermi velocity are assumed to be fixed and unaffected by interactions. We show that in two dimensions, in a weak coupling regime, there is no significant change in the RG flow compared to the well-known one-loop results available in the literature. However, if we extrapolate the flow to a moderate coupling regime there are interesting new features associated with an anisotropic suppression of the quasiparticle weight Z along the Fermi surface, and the vanishing of the renormalized coupling functions for several choices of the external momenta.

cond-mat.str-el↗
arXiv2004

Limitations of the mean field slave-particle approximations

We show that the transformation properties of the mean field slave boson/fermion order parameters under an action of the global SU(2) group impose certain restrictions on their applications to describe the phase diagram of the t-J model.

cond-mat.str-el↗
arXiv2004

"Luttinger" and insulating spin liquids in two dimensions

In the present work, we implement an explicit two-loop renormalization of a two-dimensional flat Fermi surface (FS) in the framework of a field theoretical renormalization group approach (RG). In our scheme, we derive the RG equations for both the coupling functions and Fermi energy. In this way, we are able to probe the existence of spin-charge separation by showing that the low-energy sector of the system is in fact a non-Fermi liquid. In addition, associating the true interacting FS to the infrared stable (IR) fixed point of the Fermi energy, we demonstrate here that it either acquires a small curvature and behaves as a "Luttinger liquid" or it suffers a truncation in k-space depicting an insulating spin liquid.

cond-mat.str-el↗
arXiv2002

Fermi Surface Renormalization in Two Spatial Dimensions

We discuss the renormalization induced by interactions of a two-dimensional truncated Fermi surface (FS) model.Using a field theoretical renormalization group method we calculate the critical renormalized physical chemical potential. We show that it either vanishes or approaches a non-zero value. We argue that the vanishing of the chemical potential is indicative of a further truncation of the FS we started with and might well represent an insulating spin liquid phase.

cond-mat.str-el↗
arXiv2001

Non-Fermi Liquid in a Truncated Two-Dimensional Fermi Surface

Using perturbation theory and the field theoretical renormalization group approach we consider a two-dimensional anisotropic truncated Fermi Surface((FS) ) with both flat and curved sectors which approximately simulates the ``cold'' and ``hot'' spots in the cuprate superconductors. We calculate the one-particle two-loop irreducible functions (Γ^{(2)}) and (Γ^{(4)}) as well as the spin, the charge and pairing response functions up to one-loop order. We find non-trivial infrared stable fixed points and we show that there are important effects produced by the mixing of the existing scattering channels in higher order of perturbation theory. Our results indicate that the ``cold `` spots are turned into a non-Fermi liquid with divergents (\partial Σ_{0}/\partial p_{0}) and (\partial Σ_{0}/\partial \bar{p}), a vanishing (Z) and either a finite or zero ``Fermi velocity'' at (FS) when the effects produced by the flat portions are taken into account.

cond-mat.str-el↗
arXiv1999

Marginal Fermi Liquid with a Two-Dimensional Patched Fermi Surface

We consider a model composed of Landau quasiparticle states with patched Fermi surfaces (FS) sandwiched by states with flat FS to simulate the ``cold'' spot regions in cuprates. We calculate the one particle irreducible function and the self-energy up to two-loop order. Using renormalization group arguments we show that in the forward scattering channel the renormalized coupling constant is never infrared stable due to the flat FS sectors. Furthemore we show that the self-energy scales with energy as ${\rm Re} \Sigma \sim \omega \ln \omega $ as $\omega \to 0$, and thus the Fermi liquid state within each FS patch is turned into a marginal Fermi liquid.

cond-mat.supr-con↗