arXiv subjects

Marcello B. Silva Neto

Publications and source records attributed to Marcello B. Silva Neto.

17 recordsLinked to original sources

arXiv2026

Surface lone-pair polarization probed by quantum-geometric transport in tellurium

Stereochemically active lone pairs are ubiquitous microscopic sources of polarity in molecules and solids, but their collective behavior in crystals is often hidden by symmetry or confined to surfaces. Here we show that quantum-geometry transport provides a sensitive probe of surface lone-pair polarization in trigonal tellurium. This surface polarization appears microscopically as an inversion-odd dipolar component of the crystal potential, which shifts the center of mass of Bloch wavepackets and produces quantum-geometric corrections to their velocity. We describe this lone-pair polar texture through a minimal three-component lattice model, and we show that the resulting linear and nonlinear transport coefficients probe, respectively, the second and first moments of the net polarization field. Because rectified voltages in tellurium flakes are directly proportional to the surface lone-pair polarization, our results provide a microscopic route to understanding and engineering polarization-driven, quantum-geometric electronic devices based on tellurium allotropes.

cond-mat.mes-hall↗

arXiv2026

Polar unidirectional magnetotransport in $p-$type tellurene from quantum geometry

Unidirectional magnetoresistance, or electric magnetochiral anisotropy (eMChA), is a nonlinear magnetotransport phenomenon that arises in noncentrosymmetric conductors , where changes in resistance $R(B)$ are: (i) chiral, $ΔR(B)/R(0)=2\,χ\, {\bf I}\cdot{\bf B}$, or (ii) polar, $ΔR(B)/R(0)=2\,γ\, {\bf I}\cdot({\bf P}\times{\bf B})$, with eMChA coefficients $χ$ and $γ$. In [Phys. Rev. Lett. 135, 106602 (2025)], we showed that the eMChA in the conduction band of tellurene is polar ($χ=0$, $γ\neq 0$) and emerges from the quantum metric dipole due to its Weyl node and from the lone pair polarization ${\bf P}$. Here, we extend our work to the valence band of tellurene, where the eMChA is usually said to be chiral ($χ\neq 0, γ= 0$). We show that also a polar coefficient $γ\neq 0$ emerges naturally through a downfolding procedure, in which remote Weyl-node containing bands induce momentum-space gradients of the quantum metric in the low-energy levels, activating finite metric dipoles. Combining semiclassical Boltzmann transport with a ${\bf k}\cdot{\bf p}$ description of tellurene, our numerical calculations agree quantitatively with doping ($μ$) dependent second-harmonic measurements of the longitudinal voltage $V^{2ω}_\parallel(μ)$ in perpendicular field. The combined chiral and polar characters ($χ\neq0, γ\neq 0)$ of the eMChA in tellurene also explains the shift in the angular ($ϕ$) dependence of $V^{2ω}_\parallel(ϕ)$ for in plane fields. Our results demonstrate that the polar eMChA can arise in topologically trivial bands through multiband effects and establishes tellurene as a platform for quantum-geometric rectification in both electron and hole regimes.

cond-mat.mes-hall↗

arXiv2025

Gate-Tunable Giant Negative Magnetoresistance in Tellurene Driven by Quantum Geometry

Negative magnetoresistance in conventional two-dimensional electron gases is a well-known phenomenon, but its origin in complex and topological materials, especially those endowed with quantum geometry, remains largely elusive. Here, we report the discovery of a giant negative magnetoresistance, reaching a remarkable $- 90\%$ of the resistance at zero magnetic field, $R_0$, in $n$-type tellurene films. This record-breaking effect persists over a wide magnetic field range (measured up to $35$ T) at cryogenic temperatures and is suppressed when the chemical potential shifts away from the Weyl node in the conduction band, strongly suggesting a quantum geometric origin. We propose two novel mechanisms for this phenomenon: a quantum geometric enhancement of diffusion and a magnetoelectric spin interaction that locks the spin of a Weyl fermion, in cyclotron motion under crossed electric $\boldsymbol{\cal E}$ and magnetic ${\bf B}$ fields, to its guiding-center drift, $(\boldsymbol{\cal E}\times{\bf B})\cdotσ$. We show that the time integral of the velocity auto-correlations promoted by the quantum metric between the spin-split conduction bands enhance diffusion, thereby reducing the resistance. This mechanism is experimentally confirmed by its unique magnetoelectric dependence, $ΔR_{zz}(\boldsymbol{\cal E},{\bf B})/R_0=-β_{g}(\boldsymbol{\cal E}\times{\bf B})^2$, with $β_{g}$ determined by the quantum metric. Our findings establish a new, quantum geometric and non-Markovian memory effect in magnetotransport, paving the way for controlling electronic transport in complex and topological matter.

cond-mat.mes-hall↗

arXiv2025

Quantum geometry and the electric magnetochiral anisotropy in noncentrosymmetric polar media

The electric magnetochiral anisotropy is a nonreciprocal phenomenon accessible via second harmonic transport in noncentrosymmetric, time-reversal invariant materials, in which the rectification of current, ${\bf I}$, can be controlled by an external magnetic field, ${\bf B}$. Quantum geometry, which characterizes the topology of Bloch electrons in a Hilbert space, provides a powerful description of the nonlinear dynamics in topological materials. Here, we demonstrate that the electric magnetochiral anisotropy in noncentrosymmetric polar media owes its existence to the quantum metric, arising from the spin-orbit coupling, and to large Born effective charges. In this context, the reciprocal magnetoresistance $β{\bf B}^2$ is modified to $R( I,P,B)=R_0[1+βB^2 + γ^{\pm}{\bf I}\cdot({\bf P}\times{\bf B})]$, where the chirality dependent $γ^{\pm}$ is determined by the quantum metric dipole and the polarization ${\bf P}$. We predict a universal scaling $γ^{\pm}(V)\sim V^{-5/2}$ which we verified by phase sensitive, second harmonic transport measurements on hydrothermally grown 2D tellurium films under applied gate voltage, $V$. The control of rectification by varying ${\bf I}$, ${\bf P}$, ${\bf B}$, and $V$, demonstrated in this work, opens up new avenues for the building of ultra-scaled CMOS circuits.

cond-mat.mes-hall↗

arXiv2024

Magnetic control of Weyl nodes and wave packets in three-dimensional warped semimetals

We investigate the topological phase transitions driven by band warping and a transverse magnetic field, for three-dimensional Weyl semimetals. First, we use the Chern number as a mathematical tool to derive the topological phase diagram. Next, we associate each of the topological sectors to a given angular momentum state of a rotating wave packet. Then we show how the position of the Weyl nodes can be manipulated by a transverse external magnetic field that ultimately quenches the wave packet rotation, first partially and then completely, thus resulting in a sequence of field-induced topological phase transitions. Finally, we calculate the current-induced magnetization and the anomalous Hall conductivity of a prototypical warped Weyl material. Both observables reflect the topological transitions associated with the wave packet rotation and can help to identify the elusive 3D quantum anomalous Hall effect in three-dimensional, warped Weyl materials.

cond-mat.mes-hall↗

arXiv2023

Structure-driven phase transitions in paracrystalline topological insulators

We study phase transitions driven by structural disorder in noncrystalline topological insulators. We introduce a procedural generation algorithm, the Perlin noise, typically used in computer graphics, to incorporate disorder to a two-dimensional lattice, allowing a continuous interpolation between a pristine and a random gas system, going through all different intermediate structural regimes, such as the paracrystalline and the amorphous phases. We define a two-band model, including intraorbital and interorbital mixings, on the structures generated by the algorithm and we find a sequence of structure-driven topological phase transitions characterized by changes in the topological Bott index, at which the insulating gap dynamically closes while evolving from the Bragg planes of the Brillouin zone towards the center. We interpret our results within the framework of Hosemann's paracrystal theory, in which distortion is included in the lattice structure factor and renormalizes the band-splitting parameter. Based on these results, we ultimately demonstrate the phenomenon of topological protection at its extreme.

cond-mat.mes-hall↗

arXiv2023

Gap fluctuations, Cooper pairs with finite center-of-mass momentum, and suppression of superconductivity in inhomogeneous systems with dopant superpuddles agglomerates

Spatially extended aggregates of dopants are ubiquitous in a plethora of granular superconductors, forming a droplet network that is very important to their characterization and to the description of their superconducting properties. At the same time, one of the most studied classes of superconducting materials are the high-temperature superconductors, where special attention is given to the hole-doped cuprates, where the carrier concentration is controlled by the amount of interstitial oxygen dopants. In this context, the formation of spatially inhomogeneous aggregates of interstitial oxygen atoms, in the form of nanosized superpuddles, is not only relevant, but also a subject of intense recent experimental and theoretical surveys. Following these efforts, in this work we investigate the consequences of the presence of networks of inhomogeneously distributed dopant superpuddles on the superconducting state. Starting from the inhomogeneous extended disordered background brought by the network of superpuddles, we demonstrate, with the aid of an effective interaction between electrons mediated by the local vibrational degrees of freedom of each puddle, that the Cooper pairs arising from an attractive interaction in an inhomogeneous medium have a finite center-of-mass momentum, $\mathbf{p}$, that breaks up the Cooper channel. Furthermore, we derive an analytical expression for the amplitude of the superconducting gap, $Δ_{\mathbf{k}}$, in terms of disorder and finite center-of-mass momentum and show that amplitude fluctuations are induced in the superconducting state by the presence of the superpuddles, where both the gap and the critical temperature are reduced by disorder and finite momentum pairs. Finally, we discuss our findings in the context of synchronized networks of superconducting oxygen nano-puddles in cuprates and in other granular superconducting systems.

cond-mat.supr-con↗

arXiv2023

Kuramoto synchronization of quantum tunneling polarons for describing the dynamic structure in cuprate superconductors

A major open topic in cuprates is the interplay between the lattice and electronic dynamics and the importance of their coupling to the mechanism of high-temperature superconductivity (HTSC). As evidenced by Extended X-ray Absorption Fine Structure experiments (EXAFS), anharmonic structural effects are correlated with the charge dynamics and the transition to a superconducting phase in different HTSC compounds. Here we describe how structural anharmonic effects can be coupled to electronic and lattice dynamics in cuprate systems by performing the exact diagonalization of a prototype anharmonic many-body Hamiltonian on a relevant six-atom cluster and show that the EXAFS results can be understood as a Kuramoto synchronization between coupled internal quantum tunneling polarons associated with the two-site distribution of the copper-apical-oxygen ($Cu-O_{ap}$) pair in the dynamic structure. Furthermore, we find that this first order, anti-phase synchronization transition can be fine tuned by temperature and anharmonicity of the lattice vibrations, and promotes the pumping of charge, initially stored at the apical oxygen reservoirs, into the copper-oxide planes. Simultaneously, the internal quantum tunneling polaron extends to the copper-planar-oxygen ($Cu-O_{pl}$) pair. All these findings support an interpretation of the EXAFS data in terms of an effective, quantum mechanical triple-well-potential, which accurately represents the anti-phase synchronization of apical oxygens displacements and lattice-assisted charge transfer to the $CuO_2$ plane.

cond-mat.supr-con↗

arXiv2022

Correlation of strontium anharmonicity with charge-lattice dynamics of the apical oxygens and their coupling to cuprate superconductivity

Cu K edge X-ray absorption spectra of overdoped superconducting $YSr_2Cu_{2.75}Mo_{0.25}O_{7.54}$ and $Sr_2CuO_{3.3}$ show a remarkably strong correlation of their superconductivity with the local dynamics of their Cu-Sr and Cu-apical-O pairs. This finding that the entire alkaline earth cation-apical O "dielectric" layer has an active role in the unusual electronic properties of cuprates has not been previously considered and has far reaching implications. We develop this idea of a possible role for the apical oxygen charge dynamics via a soft mode of the Sr by applying Kuramoto's synchronization technique to exact diagonalization calculations of two neighboring Cu-apical O pairs bridged by Sr and a planar O atom. These calculations show a first order phase transition to a synchronized state of the Internal Quantum Tunneling Polarons (IQTPs) in which a fraction of the hole originally confined to the apical O atoms of the cluster is transferred onto the planar O. This combination of experimental results and theory demonstrates that the Sr-O dielectric layer of cuprates most likely plays an important role in high temperature superconductivity via its collective charge dynamics that extends into the $CuO_2$ conducting planes.

cond-mat.supr-con↗

arXiv2022

Hedgehog orbital texture in p-type tellurium and the antisymmetric nonreciprocal Hall response

Tellurium is a gyrotropic, p-type Weyl semiconductor with remarkable electronic, optical, and transport properties. It has been argued that some of these properties might stem from Weyl nodes at crossing points in the band structure, and their nontrivial topological textures. However, Weyl nodes in time-reversal invariant semiconductors are split up in energy, rather than in momentum, and located deep below (far above) the top (bottom) of the valence (conduction) band, challenging such an interpretation. Here, instead, we use a 4-band kp Hamiltonian for $p-$type tellurium to show how the k-dependent spin-orbit interaction mixes up the top two (Weyl node free) and bottom two (Weyl node containing) valence bands, generating a 3D hedgehog orbital magnetic texture at the uppermost valence band, accessible to transport already at the lowest doping. Hedgehog textures are important signatures of Weyl fermion physics in general and in the context of condensed matter physics arise form the carriers' wave packet rotation being locked to their propagation wavevector. For spatially dispersive media, such an induced hedgehog texture/carrier rotation stabilizes two novel, nonreciprocal and antisymmetric components to the Hall transport within different weak-localization (antilocalization) relaxation regimes: the anomalous and planar Hall effects, usually forbidden by time reversal symmetry. Our AC magnetotransport measurements on Sn-doped tellurium confirm the theoretical predictions and our work demonstrates how Weyl signatures generally appear in transport on enantiomorphic materials with natural optical activity.

cond-mat.mes-hall↗

arXiv2006

Charge stripe order from antiphase spin spirals in the spin-Fermion model

We revisit the ground state of the spin-Fermion model within a semiclassical approximation. We demonstrate that antiphase spin spirals, or pi-spirals, whose chirality alternates between consecutive rows (or columns) of local moments, have, for sufficiently high carrier concentration, lower energy than the traditional Shraiman and Siggia spirals. Furthermore, pi-spirals give rise to modulated hopping, anisotropic 1D transport, and charge density wave formation. Finally, we discuss the relevance of pi-spirals to the physics of charge stripe formation in cuprates, such as La(2-x)Sr(x)CuO4.

cond-mat.str-el↗

arXiv2003

Metallic Continuum Quantum Ferromagnets at Finite Temperature

We study via renormalization group (RG) and large N methods the problem of continuum SU(N) quantum Heisenberg ferromagnets (QHF) coupled to gapless electrons. We establish the phase diagram of the dissipative problem and investigate the changes in the Curie temperature, magnetization, and magnetic correlation length due to dissipation and both thermal and quantum fluctuations. We show that the interplay between the topological term (Berry's phase) and dissipation leads to non-trivial effects for the finite temperature critical behavior.

cond-mat.str-el↗

arXiv2001

Charge pairing, superconducting transition and supersymmetry in high-temperature cuprate superconductors

We propose a model for high-T$_{c}$ superconductors, valid for $0\leqδ\leqδ_{SC}$, that includes both the spin fluctuations of the Cu$^{++}$ magnetic ions and of the O$^{--}$ doped holes. Spin-charge separation is taken into account with the charge of the doped holes being associated to quantum skyrmion excitations (holons) of the Cu$^{++}$ spin background. The holon effective interaction potential is evaluated as a function of doping, indicating that Cooper pair formation is determined by the competition between the spin fluctuations of the Cu$^{++}$ background and of spins of the O$^{--}$ doped holes (spinons). The superconducting transition occurs when the spinon fluctuations dominate, thereby reversing the sign of the interaction. At this point ($δ= δ_{SC}$), the theory is supersymmetric at short distances and, as a consequence, the leading order results are not modified by radiative corrections. The critical doping parameter for the onset of superconductivity at T=0 is obtained and found to be a universal constant determined by the shape of the Fermi surface. Our theoretical values for $δ_{SC}$ are in good agreement with the experiment for both LSCO and YBCO.

cond-mat.supr-con↗

arXiv2000

Quantum skyrmions and the destruction of long-range antiferromagnetic order in the high-Tc superconductors La(2-x)Sr(x)CuO(4) and YBa(2)Cu(3)O(6+x)

We study the destruction of the antiferromagnetic order in the high-Tc superconductors La(2-x)Sr(x)CuO(4) and YBa(2)Cu(3)O(6+x) in the framework of the CP1-nonlinear sigma model formulation of the 2D quantum Heisenberg antiferromagnet. The dopants are introduced as independent fermions with appropriate dispersion relations determined by the shape of the Fermi surface. The energy of skyrmion topological defects, which are shown to be introduced by doping, is used as an order parameter for antiferromagnetic order. We obtain analytic expressions for this as a function of doping which allow us to plot the curves T_N(x_c)\times x_c and M(x)\times x, for both YBCO and LSCO, in good quantitative agreement with the experimental data.

cond-mat.str-el↗

arXiv2000

Effective Sublattice Magnetization and Neel Temperature in Quantum Antiferromagnets

We present an analytic expression for the finite temperature effective sublattice magnetization which would be detected by inelastic neutron scattering experiments performed on a two-dimensional square-lattice quantum Heisenberg antiferromagnets with short range Néel order. Our expression, which has no adjustable parameters, is able to reproduce both the qualitative behaviour of the phase diagram $M(T)xT$ and the experimental values of the Néel temperature $T_{N}$ for either doped YBa$_{2}$Cu$_{3}$O$_{6.15}$ and stoichiometric La$_{2}$CuO$_{4}$ compounds. Finally, we remark that by incorporating frustration and 3D effects as perturbations is sufficient to explain the deviation of the experimental data from our theoretical curves.

cond-mat.str-el↗

arXiv2000

From cool pions to the chiral phase transition

Using the ideas of effective field theory and dimensional reduction, we relate the parameters of two low energy models of QCD: the O(N) nonlinear sigma model in D=3+1, which describes the dynamics of cool pions, and the O(N) Heisenberg magnet in D=3+0, which is commonly argued to reproduce the correct critical behaviour of the chiral phase transition. As a result, we obtain a generalized expression for the finite temperature pion decay constant which reproduces, in certain limits, the available expressions in the literature.

hep-th↗

arXiv2000

Sublattice Magnetization and Néel Transition in the 2D Quantum Heisenberg Antiferromagnet

We present an analytic expression for the finite temperature sublattice magnetization, at the Josephson scale, in two dimensional quantum antiferromagnets with short range Néel order. Our expression is able to reproduce both the qualitative behaviour of the phase diagram $M(T)/M_{0}$ and the experimental values of the Néel temperature $T_{N}$ for either doped YBa$_{2}$Cu$_{3}$O$_{6.15}$ and stoichiometric La$_{2}$CuO$_{4}$.

cond-mat.str-el↗