arXiv subjects

A. C. Seridonio

Publications and source records attributed to A. C. Seridonio.

At least 19 recordsLinked to original sources

arXiv2026

Revisiting the Poor Man's Majoranas: The Spin-Exchange Induced Spillover Effect

We give a review on Poor Man's Majorana (PMM) modes, which are theoretically established in the minimal Kitaev chain implementation consisting of two grounded, spinless quantum dots (QDs) operating at the sweet spot condition, where electron cotunneling and crossed Andreev reflection amplitudes achieve precise balance. Particularly, we systematically review, within the Green's functions theoretical framework, the PMM hybridization dynamics under spin-exchange perturbations proposed by some of us in J. Phys.: Condens. Matter 37, 205601 (2025), which demonstrates a characteristic spatial delocalization when subjected to an exchange coupling $J$ mediated by a quantum spin $S$. This spin-exchange induced PMM spillover effect provides a spectroscopic protocol for determining the quantum statistics of $S$ through the emergent multi-level structure in the proximal QD's density of states. Our principal theoretical result establishes that the exchange interaction generates $2S+2$ ($2S+1$) satellite states symmetrically distributed about the zero-bias anomaly, serving as a definitive signature of bosonic (fermionic) spin statistics. As novelty, we demonstrate that multi-terminal environmental coupling induces significant suppression of the spin-exchange spillover mechanism. Under constrained variations of $J$, this effectively localizes the perturbed PMM within its host QD, preventing spatial hybridization with adjacent site. The absence of topological protection in this minimal Kitaev realization is strategically leveraged to: (i) Develop a novel spectroscopic technique for quantum spin characterization through PMM hybridization signatures; (ii) Propose the "environmentally induced protection", an engineered dissipative spectral stabilization for PMMs against exchange fluctuations in multi-terminal architectures.

cond-mat.mes-hall↗

arXiv2025

Impact of Broken Inversion Symmetry on Molecular States in multi-Weyl fermions

We study inversion-symmetry (IS) breaking in impurity dimers coupled to topological multi-Weyl systems in the low-energy dispersion domain. In the IS-preserved multi-Weyl semimetal phase, Hubbard bands split into symmetric and antisymmetric molecular-like subbands. Breaking IS induces a transition to a multi-Weyl metal, lifting the degeneracy of the Weyl node and closing the pseudogap. This causes opposite energy shifts: valence-band symmetric (antisymmetric) subbands red- (blue-) shift, reversing in the conduction band until a degeneracy point. Beyond this threshold, symmetric bands flatten near band cutoffs, whereas antisymmetric bands form quasi-zero energy modes asymptotically approaching -- yet never crossing -- the Fermi level. Crucially, identical molecular symmetries maintain nondegeneracy even as energy separation vanishes with stronger IS breaking. Our results demonstrate symmetry-selective mechanisms for topological molecular states in multi-Weyl systems.

cond-mat.mes-hall↗

arXiv2025

Spin-Exchange Induced Spillover on Poor Man's Majoranas in Minimal Kitaev Chains

The "Poor Man's Majoranas" (PMMs) [Phys. Rev. B 86, 134528 (2012)] devoid of topological protection can "spill over" from one edge into another of the minimal Kitaev chain when perturbed electrostatically. As aftermath, this leads to a delocalized Majorana fermion (MF) at both the edges. Additionally, according to recent differential conductance measurements in a pair of superconducting and spinless quantum dots (QDs), such a PMM picture was brought to reality [Nature 614, 445 (2023) and Nature 630, 329 (2024)]. Based on this scenario, we propose the spillover of the PMM when its QD is exchange coupled to a quantum spin $S$. We show that if this QD is perturbed by the exchange coupling $J$, solely the half $2S+1$ $(2S+2)$ of the fine structure stays explicit for a fermionic (bosonic) $S.$ Concurrently, the other half squeezes itself as the delocalized MF zero-mode. Particularly, turning-off the superconductivity the multiplicity $2S+1$ holds regardless the spin statistics. Meanwhile, the PMM spillover induced by $J$ becomes a statistics dependent effect. Hence, our findings contribute to the comprehension of spin-phenomena interplay with superconductivity in minimal Kitaev chains, offering insights for future quantum computing devices hosting PMMs.

cond-mat.mes-hall↗

arXiv2024

Squeezed state protection of fine structure in "Poor Man's Majorana" via quantum spin coupling

The "Poor Man's Majorana" [Phys. Rev. B 86, 134528 (2012)] devoid of topological protection has been theoretically predicted to rely on the minimal Kitaev chain. Afterward, a pair of superconducting and spinless quantum dots turned the proposal practicable and differential conductance pinpointed consistent fingerprints with such a scenario [Nature 614, 445 (2023) and Nature 630, 329 (2024)]. In this work, we propose a model wherein the "Poor Man's Majorana" presents protection when one of the dots is exchange coupled to a quantum spin. If this quantum dot is perturbed by tuning the exchange coupling, the well-known spill over-like behavior of this Majorana surprisingly remains unchanged, and solely half of the fine structure is unexpectedly viewed. As a matter of fact, the "Poor Man's Majorana" zero mode consists in squeezing of the other half at zero frequency, which imposes its pinning there and prevents the mixing of the mode with the explicit fine structure. We claim that if the supposed unavoidable split of the zero mode by the fine structure is unexpectedly absent, then the "Poor Man's Majorana" can be considered robust against the quantum spin. In this way, it becomes protected and the lack of topological protection paradigm of the "Poor Man's Majorana" has been revisited, pushing this seemingly well-established issue into a new direction.

cond-mat.mes-hall↗

arXiv2023

Fractionalization of Majorana-Ising-type quasiparticles

We theoretically investigate the spectral properties of a quantum impurity (QI) hosting the here proposed {Majorana-Ising-type quasiparticle (MIQ) excitation}. It arises from the coupling between a finite topological superconductor (TSC) based on a chain of magnetic adatoms-superconducting hybrid system and an integer large spin $S$ flanking the QI. Noteworthy, the spin $S$ couples to the QI via the Ising-type exchange interaction. As the Majorana zero-modes (MZMs) at the edges of the TSC chain are overlapped, we counterintuitively find a regime wherein the Ising term modulates the localization of a fractionalized and resonant MZM at the QI site. Interestingly enough, the fermionic nature of this state is revealed as purely of electron tunneling-type and most astonishingly, it has the Andreev conductance completely null in its birth. Therefore, we find that a resonant edge state appears as a zero-mode and discuss it in terms of a poor man's Majorana[Nature 614, 445 (2023)].

cond-mat.supr-con↗

arXiv2023

Analogue of atomic collapse for adatoms on rhombohedral multilayer graphene

We propose that a multi-graphene of ABC-type stacking yields virtual bound states lying within the Coulomb insulating gap of an Anderson-like adatom. Wondrously, a virtual state constitutes the counterpart of the atomic collapse phenomenon proposed in relativistic atomic Physics, while the second emerges as its particle-hole symmetric, analogous to a positron state. Thus, we introduce the effect as the adatomic collapse, which occurs due to a flat band with a dispersionless state and a divergent density of states $\sim|\varepsilon-\varepsilon_{F}|^{2/J-1}$ near the Fermi energy $\varepsilon_{F}$ for $J\geq3,$ where $Jπ$ is the Berry phase. We conclude this scenario based on the Kramers-Kronig transformation of the quasiparticle broadening, from where we observe that the aforementioned van Hove singularity induces virtual bound states. Counterintuitively, near the singularity, we find these states above and below the Fermi energy correlated to the existence of the bottom and top edges of the Coulomb insulating region, respectively. As such a behavior rises without a twist, the system is known as Moiréless and the phenomenon emerges also assisted by the adatom Coulomb correlations. Similarly to Science 340, 734 (2013) we find the effective critical atomic number $\mathcal{Z}_{c}\sim0.96$ in contrast to an ultra-heavy nucleus. Thus, we point out that multi-graphene is a proper playground for testing a predicted phenomenon of the relativistic atomic Physics in the domain of the condensed matter Physics.

cond-mat.str-el↗

arXiv2023

Spin-Polarized Majorana Zero Modes in Proximitized Superconducting Penta-Silicene Nanoribbons

We theoretically investigate the possibility of obtaining Majorana zero modes (MZMs) in penta-silicene nanoribbons (p-SiNRs) with induced \textit{p}-wave superconductivity. The model explicitly considers an external magnetic field perpendicularly applied to the nanoribbon plane, as well as an extrinsic Rashba spin-orbit coupling (RSOC), in addition to the first nearest neighbor hopping term and \textit{p}-wave superconducting pairing. By analyzing the dispersion relation profiles, we observe the successive closing and reopening of the induced superconducting gap with a single spin component, indicating a spin-polarized topological phase transition (TPT). Correspondingly, the plots of the energy spectrum versus the chemical potential reveal the existence of zero-energy states with a preferential spin orientation characterized by nonoverlapping wave functions localized at opposite ends of the superconducting p-SiNRs. These findings strongly suggest the emergence of topologically protected, spin-polarized MZMs at the ends of the p-SiNRs with induced \textit{p}-wave superconducting pairing, which can be realized by proximitizing the nanoribbon with an \textit{s}-wave superconductor, such as lead. The proposal paves the way for silicene-based Majorana devices hosting multiple MZMs with a well-defined spin orientation, with possible applications in fault-tolerant quantum computing platforms and Majorana spintronics.

cond-mat.mes-hall↗

arXiv2023

Reshaping the Jaynes-Cummings ladder with Majorana bound states

We study the optical properties of a hybrid device composed by a quantum dot (QD) resonantly coupled to a photonic mode of an optical microcavity and a Majorana nanowire: a topological superconducting segment hosting Majorana bound states (MBSs) at the opposite ends. In the regime of strong light-matter coupling, it is demonstrated that the leakage of the Majorana mode into the QD opens new optical transitions between polaritonic states formed due to hybridisation of material excitation with cavity photons, which leads to the reshaping of the Jaynes-Cummings ladder and can lead to the formation of a robust single-peak at cavity eigenfrequency in the emission spectrum. Moreover, weak satellite peaks in the low and high frequency regions are revealed for the distinct cases of highly isolated MBSs, overlapped MBSs and MBSs not well localized at the nanowire ends.

cond-mat.mes-hall↗

arXiv2022

Topological charge Fano effect in multi-Weyl semimetals

We theoretically analyze the Fano interference in a single impurity multi-Weyl semimetal hybrid system and show the emergence of the topological charge Fano effect in the bulk local density of states. In multi-Weyl semimetals, the number of Fermi arcs at the system boundaries is determined by the topological charge $J$, a direct consequence of the "bulk-boundary" correspondence principle. Analogously, we find that $J$ also modulates the bulk Fano profile of the system with an embedded quantum impurity. Thus, by increasing $J$, the Fano lineshape evolves from resonant, typical for $J=1$ (single Weyl), towards antiresonant, extrapolating to the so-called hyper Weyl semimetals with $J\gg1$. Specially for the maximum case protected by the rotational symmetry $C_{2J=6}$, namely the $J=3$ (triple Weyl), which acquires asymmetric Fano profile, the Fano parameter absolute value is predicted to be $\tan(C_{2J=6})$, where $C_{2J}\equiv(360^{\circ}/2J)$ defines the rotational angle. Hence, the Fano discretization in the $J$ term introduces the topological charge Fano effect in multi-Weyl semimetals. We also suggest a transport device where we expect that the proposed Fano effect could be detected.

cond-mat.mes-hall↗

arXiv2022

Accessing the degree of Majorana nonlocality in a quantum dot-optical microcavity system

We explore the tunneling transport properties of a quantum dot embedded in an optical microcavity and coupled to a semiconductor-superconductor one-dimensional nanowire (Majorana nanowire) hosting Majorana zero modes (MZMs) at their edges. Conductance profiles reveal that strong light-matter coupling can be employed to distinguish between the cases of highly nonlocal MZMs, overlapped MZMs and MZMs with less degree of nonlocal feature. Moreover, we show that it is possible to access the degree of Majorana nonlocality (topological quality factor) by changing the dot spectrum through photon-induced transitions tuned by an external pump applied to the microcavity.

cond-mat.mes-hall↗

arXiv2021

Atomic frustration-based twistronics

We theoretically investigate atomic frustrated states in diatomic molecules hosted by the bilayer graphene setup twisted by the first magic angle and with broken inversion symmetry in the Dirac cones of the system mini Brillouin zones. Such states show local spectral features typically from uncoupled atoms, but counterintuitively, they also exhibit nonlocal molecular correlations, which turn them into atomically frustrated. By considering a particle-hole symmetric molecule in the Moiré superlattice length-scale, we reveal distinctly from the metallic Weyl counterparts, a molecular zero mode atomically frustrated at the spectral densities of the dimer's atoms. To this end, a strong metallic phase with a plateau in the density of states established by the broken inversion symmetry, together with pronounced blue and red shifts in the molecular levels, due to the magic angle condition, should occur synergistically with atomic Coulomb correlations. Consequently, an entire collapse of these molecular peaks into a single one atomically frustrated, taking place exactly at the Fermi energy, becomes feasible just by tuning properly opposite gate voltages attached to the graphene monolayers. Therefore, we propose that unusual molecular bindings can be engineered via the twistronics of the bilayer graphene system, in particular, if its metallic phase is fully established.

cond-mat.str-el↗

arXiv2021

Spin-polarized Majorana zero-modes in double zigzag honeycomb nanoribbons

We study the emergence of Majorana zero modes (MZMs) at the ends of a finite double zigzag honeycomb nanoribbon (zHNR). We show that a double zHNR geometry can host spin-polarized MZMs at its ends. We considered a minimal model composed by first nearest neighbor hopping, Rashba spin-orbit coupling (RSOC), p-wave superconducting pairing, and an applied external magnetic field (EMF). The energy spectrum regions with either spin up or down MZMs belong to distinct topological phase transitions characterized by their corresponding winding numbers and can be accessed by tunning the chemical potential of the nanoribbons. Hybrid systems constituted by zHNRs deposited on conventional s-wave superconductors are potential candidates for experimentally realizing the proposal. The spin's discrimination of MZMs suggests a possible route for performing topological-conventional qubit operations using Majorana spintronics.

cond-mat.mes-hall↗

arXiv2020

Giant caloric effects close to $any$ critical end point

The electrocaloric effect (ECE), i.e., the reversible temperature change due to the adiabatic variation of the electric field, is of great interest due to its potential technological applications. Based on entropy arguments, we present a new framework to attain giant ECE. Our findings are fourfold: $i$) we employ the recently-proposed electric Grüneisen parameter $Γ_E$ to quantify the ECE and discuss its advantages over the existing so-called electrocaloric strength; $ii$) prediction of giant caloric effects $close$ to $any$ critical end point; $iii$) proposal of potential key-ingredients to enhance the ECE; $iv$) demonstration of $Γ_E$ as a proper parameter to probe quantum ferroelectricity in connection with the celebrated Barrett's formula. Our findings enable us to interpret the recently-reported large ECE at room-temperature in oxide multilayer capacitors [Nature 575, 468 (2019)], paving thus the way for new venues in the field.

cond-mat.mtrl-sci↗

arXiv2020

Atomic frustrated impurity states in Weyl metals

We theoretically analyze the effect of the inversion symmetry breaking on the structure of the impurity molecular states in Weyl metals. We show that for the case of a highly noncentrosymmetric Weyl metallic host, the standard picture of the alternating bonding and antibonding orbitals breaks down, and a qualitatively different frustrated atomic state emerges. This is a consequence of the pseudogap closing and related delicate Fano interplay between intra- and inter-impurity scattering channels.

cond-mat.str-el↗

arXiv2020

Majorana molecules and their spectral fingerprints

We introduce the concept of a Majorana molecule, a topological bound state appearing in the geometry of a double quantum dot (QD) structure flanking a topological superconducting nanowire. We demonstrate that, if the Majorana bound states (MBSs) at opposite edges are probed nonlocally in a two probe experiment, the spectral density of the system reveals the so-called half-bowtie profiles, while Andreev bound states (ABSs) become resolved into bonding and antibonding molecular configurations. We reveal that this effect is due to the Fano interference between pseudospin superconducting pairing channels and propose that it can be catched by a pseudospin resolved Scanning Tunneling Microscope (STM)-tip.

cond-mat.mes-hall↗

arXiv2020

Interaction induced hybridization of Majorana zero-modes in a coupled quantum-dot hybrid-nanowire system

We study the low-energy transport properties of a hybrid device composed by a native quantum dot coupled to both ends of a topological superconducting nanowire section hosting Majorana zero-modes. The account of the coupling between the dot and the farthest Majorana zero-mode allows to introduce the topological quality factor, characterizing the level of topological protection in the system. We demonstrate that Coulomb interaction between the dot and the topological superconducting section leads to the onset of the additional overlap of the wavefunctions describing the Majorana zero-modes, leading to the formation of trivial Andreev bound states even for spatially well-separated Majoranas. This leads to the spoiling of the quality factor and introduces a constraint for the braiding process required to perform topological quantum computing operations.

cond-mat.mes-hall↗

arXiv2020

Topological isoconductance signatures in Majorana nanowires

We consider transport properties of a hybrid device composed by a quantum dot placed between normal and superconducting reservoirs, and coupled to a Majorana nanowire: a topological superconducting segment hosting Majorana zero-modes at the opposite ends. It is demonstrated that if topologically protected (nonoverlapping) Majorana zero-modes are formed in the system, zero-bias Andreev conductance through the dot exhibits isoconductance profiles with the shape depending on the spin asymmetry of the coupling between a dot and a topological superconductor. Otherwise, for the topologically trivial situation corresponding to the formation of Andreev bound states, the conductance is insensitive to the spin polarization and the isoconductance signatures disappear. This allows to propose an experimental protocol for distinguishing between isolated Majorana zero-modes and Andreev bound states.

cond-mat.supr-con↗

arXiv2020

Unveiling the Physics of the Mutual Interactions in Paramagnets

In real paramagnets, there is always a subtle many-body contribution to the system's energy, which can be regarded as a small effective local magnetic field $B_{loc}$. Usually, it is neglected, since it is very small when compared with thermal fluctuations and/or external magnetic fields $B$. Nevertheless, as both the temperature $T \rightarrow$ 0K and $B \rightarrow$ 0T, such many-body contributions become ubiquitous. Here, employing the magnetic Grüneisen parameter $Γ_{mag}$ and entropy arguments, we report on the pivotal role played by the mutual interactions in the regime of ultra-low-$T$ and vanishing $B$. Our key results are: $i$) absence of a genuine zero-field quantum phase transition due to the presence of $B_{loc}$; $ii$) connection between the canonical definition of temperature and $Γ_{mag}$; and $iii$) possibility of performing adiabatic magnetization by only manipulating the mutual interactions. Our findings unveil unprecedented aspects emerging from the mutual interactions.

cond-mat.str-el↗