arXiv subjects

Paola Gentile

Publications and source records attributed to Paola Gentile.

At least 19 recordsLinked to original sources

arXiv2025

Topological spin multipolization and linear magnetoelectric coupling in two-dimensional antiferromagnets

In this paper we predict that the magnetoelectric response of two-dimensional (2D) antiferromagnets is determined by the topology of the ground state. This topological magnetoelectric response, encoded in the spin magnetoelectric polarizability and its closely related spin multipolization, occurs when the electronic structure of the antiferromagnetic insulator is described by massive 2D Dirac fermions, and is therefore native to 2D, unlike the topological magnetoelectric effect of three-dimensional topological insulators. To demonstrate the topological contribution to the (spin) magnetoelectric polarizability, we compute the magnetoelectric polarizability microscopically for two distinct minimal lattice models: a spin-orbit coupled Néel antiferromagnet and a spin-orbit-free noncollinear antiferromagnet with double-$Q$ spin order. We show that the topological origin of the revealed magnetoelectric effect can be traced back to the electromagnetic response of topological semimetals in two dimensions, and hence is ultimately governed by a strong topological invariant in one dimension. Given this dimensional hierarchy, we further consider two minimal lattice models in one dimension, both one-dimensional variants of the 2D lattice models, and show that the magnetoelectric polarizability exhibits a clear signature of nontrivial crystalline topology. Possible material realizations are discussed.

cond-mat.str-el↗

arXiv2025

Conditions for orbital selective altermagnetism in Sr$_2$RuO$_4$: tight binding model, similarities with cuprates and implications on superconductivity

The vibrational modes in Sr$_2$RuO$_4$ easily induce octahedral rotations without tilting. Being on the verge of a magnetic instability, such propensity of octahedral rotation may also produce magnetic fluctuations. In this work, we analyze the long-range magnetic phase diagram incorporating such octahedral rotations and demonstrate the possibility of an altermagnetic phase in Sr$_2$RuO$_4$. Using ab-initio calculations, we first study single layer Sr$_2$RuO$_4$ with octahedral rotations, obtaining an orbital-selective $g$-wave altermagnetic phase. We further provide an effective $t_{2g}$ tight-binding model, demonstrating that the $g$-wave altermagnetism is primarily a product of second and third nearest neighbor interorbital hybridizations between the $γz$ ($γ=x,y$) orbitals, but only a much longer range intraorbital hybridization in the $xy$ orbitals, establishing a strong orbital-selectiveness for the altermagnetism. Notably, by replacing the $xy$ orbital with the $x^2-y^2$ orbital, a similar tight-biding model may be used to investigate the hole-doped cuprate superconductors. We then study bulk Sr$_2$RuO$_4$, where we find the altermagnetic phase as the magnetic ground state for a range of finite octahedral rotations. In the bulk, interlayer hopping breaks some of the symmetries of the $g$-wave altermagnet, resulting in a $d_{xy}$-wave altermagnet, still with orbital selectiveness. We also include relativistic effects through spin-orbit coupling and obtain that an effective staggered Dzyaloshinskii-Moriya interaction generates weak ferromagnetism. Finally, we discuss the implications of the altermagnetic order on the intrinsic superconductivity of Sr$_2$RuO$_4$. Assuming in-plane and intraorbital pairing, the altermagnetism favors spin-singlet $d_{x^2-y^2}$-wave or $g$-wave pairing, or (nematic or chiral) combinations thereof.

cond-mat.supr-con↗

arXiv2023

Particle-hole spectral asymmetry at the edge of multiorbital noncentrosymmetric superconductors

Bogoliubov quasiparticles are a coherent electron-hole quantum superposition which typically, for time-reversal symmetric superconductors, exhibit a spectral distribution with particle-hole symmetry. Here, we demonstrate that in two-dimensional noncentrosymmetric superconductors with multiorbital spin-triplet pairing the energy profile of the density of states at the edge can violate this paradigm. We show that the structure of Andreev reflections generally leads to pairing states made of configurations that are orbitally split due to the low degree of crystalline symmetry at the edge. The resulting pairing state has a mixed parity character in the orbital sector that, in the presence of reduced crystal symmetry at the edge, sets out a particle-hole asymmetric profile for the spectral function. These findings indicate a path to design asymmetric spectral functions at the edge of superconductors with orbital degrees of freedom and time-reversal symmetry. The emerging signatures can be exploited for the detection of spin-triplet pairing equipped with internal degrees of freedom.

cond-mat.supr-con↗

arXiv2023

Anomalous Josephson Coupling and High-Harmonics in Non-Centrosymmetric Superconductors with $S$-wave Spin-Triplet Pairing

We study the Josephson effects arising in junctions made of non-centrosymmetric superconductors with spin-triplet pairing having $s$-wave orbital-singlet symmetry. We demonstrate that the orbital dependent character of the spin-triplet order parameter determines its non-trivial texture in the momentum space due to the inversion symmetry breaking and spin-orbit interactions. The emergence of this pattern is responsible for the occurrence of an anomalous Josephson coupling and a dominance of high-harmonics in the current phase relation. Remarkably, due to the spin-orbital couplings, variations in the electronic structure across the heterostructure can generally turn the ground state of the junction from 0- to a generic value of the Josephson phase, thus realizing the so-called $φ$-junction. Hallmarks of the resulting Josephson behavior, apart from non-standard current-phase relation, are provided by an unconventional temperature and magnetic field dependence of the critical current. These findings indicate the path for the design of superconducting orbitronics devices and account for several observed anomalies of the supercurrent in oxide interface superconductors.

cond-mat.supr-con↗

arXiv2022

Electronic materials with nanoscale curved geometries

Research into electronic nanomaterials has recently seen a growing focus into the synthesis of structures with unconventional curved geometries including bent wires in planar systems and three-dimensional architectures obtained by rolling up nanomembranes. The inclusion of these geometries has led to the prediction and observation of a series of novel effects that either result from shape-driven modifications of the electronic motion or from an intrinsic change of electronic and magnetic properties due to peculiar confinement effects. Moreover, local strains often generated by curvature also trigger the appearance of new phenomena due to the essential role played by electromechanical coupling in solids. Here we review the recent developments in the discovery of these shape-, confinement- and strain-induced curvature effects at the nanoscale, and discuss their potential use in electronic and spintronic devices.

cond-mat.mes-hall↗

arXiv2022

Nodal superconducting exchange coupling

The superconducting equivalent of giant magnetoresistance, involves placing a thin-film superconductor between two ferromagnetic layers. A change of magnetization-alignment in such a superconducting spin-valve from parallel (P) to antiparallel (AP) creates a positive shift in the superconducting transition temperature (ΔTc) due to an interplay of the magnetic exchange energy and the superconducting condensate. The magnitude of ΔTc scales inversely with the superconductor thickness (dS) and is zero when dS exceeds the superconducting coherence length (ξ) as predicted by de Gennes. Here, we report a superconducting spin-valve effect involving a different underlying mechanism that goes beyond de Gennes in which magnetization-alignment and ΔTc are determined by the nodal quasiparticle-excitation states on the Fermi surface of the d-wave superconductor YBa2Cu3O7-δ (YBCO) grown between insulating layers of ferromagnetic Pr0.8Ca0.2MnO3. We observe ΔTc values that approach 2 K with ΔTc oscillating with dS over a length scale exceeding 100 ξ and, for particular values of dS, we find that the superconducting state reinforces an antiparallel magnetization-alignment. These results pave the way for all-oxide superconducting memory in which superconductivity modulates the magnetic state.

cond-mat.supr-con↗

arXiv2022

Spin and charge transport in ferromagnet-superconductor-ferromagnet heterostructures: Stoner versus spin mass mismatch mechanism

We study transport phenomena through a ballistic ferromagnet-superconductor-ferromagnet (F/S/F) junction, comparing the case in which the ferromagnetic order in the two F layers is of the standard Stoner type with the case where it is driven by a spin mass mismatch (SMM). It is shown that the two mechanisms lead to a different behavior in the charge and the spin conductances, especially when compared to the corresponding non-superconducting ferromagnet-normal-ferromagnet (F/N/F) junctions. In particular, when the injected current is perpendicular to the barrier, for high barrier transparency and large magnetization of the F layers, the large mass mismatch gives rise to an enhancement of both low-bias charge and spin conductances of the F/S/F junction, which is not observed in the equal-mass case. When all the allowed injection directions are considered, the low bias enhancement of the charge conductance for SMM leads still holds for high barrier transparency and large magnetization of the F layers. However, in the case of non-transparent interfaces, spin transport with SMM ferromagnets exhibits an opposite sign response with respect to the Stoner case at high biases for all magnetization values, also manifesting a significant amplification induced by superconductivity at the gap edge. The above mentioned differences can be exploited to probe the nature of the electronic mechanism underlying the establishment of the ferromagnetic order in a given material.

cond-mat.supr-con↗

arXiv2020

Orbital tunable 0-$π$ transitions in Josephson junctions with noncentrosymmetric topological superconductors

We investigate the Josephson transport properties in a Josephson junction consisting of a conventional $s$-wave superconductor coupled to a multi-orbital noncentrosymmetric superconductor marked by an orbitally driven inversion asymmetry and isotropic interorbital spin-triplet pairing. Contrary to the canonical single band noncentrosymmetric superconductor, we demonstrate that the local interorbital spin-triplet pairing is tied to the occurrence of sign-changing spin-singlet pair amplitude on different bands with $d$-wave symmetry. Such multi-band $d^{\pm}$-wave state is a unique superconducting configuration that drives unexpected Josephson effects with 0-$π$ transitions displaying a high degree of electronic control. Remarkably, we find that the phase state of a noncentrosymmetric/$s$-wave Josephson junction can be toggled between 0 and $π$ in multiple ways through a variation of electron filling, strength of the spin-orbital coupling, amplitude of the inversion asymmetry interaction, and junction transparency. These results highlight an intrinsic orbital and electrical tunability of the Josephson response and provide unique paths to unveil the nature of unconventional multiorbital superconductivity as well as inspire innovative designs of Josephson quantum devices.

cond-mat.supr-con↗

arXiv2019

Magnetic field effects on electron transport in nanoring with orbital Rashba coupling

We study the effects of a Zeeman magnetic field on the electron transport of one-dimensional quantum rings which are marked by electronic states with $d-$orbital symmetry in the presence of spin-orbit and orbital Rashba couplings. By considering phase-coherent propagation, we analyse the geometric Aharonov-Anandan (AA) phase of the channels which is acquired in a closed path, by demonstrating that the orbital polarization can influence the electronic transport when amplitude and magnetic field directions are varied. We explore all the possible cases for the injection of electrons at various energies in the regime of low electron filling. The magnetic field can allow the selection of only one channel where the transmission is uniquely affected by the AA phase. Conversely, when more orbital channels are involved there is also a dynamical contribution that lead to oscillations in the transmission as the magnetic field is varied. In particular, the transmission is chiral when the energy states are close to the absolute minimum of the energy bands. Instead, when an interference between the channels occurs the orbital and spin contributions tend to balance each other with the increasing of the magnetic field amplitude resulting in a trivial AA phase. This saturation effect does not occur in the high magnetic field regime when orbital and spin properties of the channels exhibit sharp variations with direct consequences on the transport.

cond-mat.mes-hall↗

arXiv2019

Engineering Topological Nodal Line Semimetals in Rashba Spin-Orbit Coupled Atomic Chains

We study an atomic chain in the presence of modulated charge potential and modulated Rashba spin-orbit coupling (RSOC) of equal period. We show that for commensurate periodicities $λ=4 n$ with integer $n$, the three-dimensional synthetic space obtained by sliding the two phases of the charge potential and RSOC features a topological nodal line semimetal protected by an antiunitary particle-hole symmetry. The location and shape of the nodal lines strongly depend on the relative amplitude between the charge potential and RSOC.

cond-mat.mes-hall↗

arXiv2019

Topological superconducting phases and Josephson effect in curved time-reversal-invariant superconductors

We consider a Rashba spin-orbit coupled nanowire with anisotropic spin-singlet superconducting pairing and time-reversal-invariant symmetry. We explore the evolution of the topological superconducting phases of this system due to geometric deformations for the representative case of a wire bent in a semielliptical shape. We find that when the system is in its topological superconducting phase, strong inhomogeneities in the profile curvature can produce a pair of localized eigenmodes, which can be attributed to a nonuniform topological phase. The curved geometric profile also allows to tune the spin correlations of the superconducting state via the induced inhomogeneity of the spin-orbit coupling (SOC). The geometric control of the superconducting pair correlations allows to manipulate the critical current in Josephson junctions made up of two time reversal invariant topological superconductors separated by a spin-orbit coupled normal metal. In particular, we find that the curvature inhomogeneity can be exploited for amplifying the current intensity, but also to generate a $0-π$ transition, and a second harmonic contribution, which generates, for some specific geometric configurations, a $φ$-junction behavior.

cond-mat.supr-con↗

arXiv2019

Phase Diagram and Quench Dynamics in a Spinful Interacting Kitaev Chain

We consider an exact solvable interacting spinful Kitaev chain which is a generalization of the Mattis-Nam model. A nearest-neighbor dimerized interaction favoring the production of disjoint molecules drives the quantum phase into an insulating one. The phases are characterized statically and dynamically in terms of magnetization and spin-singlet correlations by using the exact solution. The model is shown to be exactly solvable also in the presence of boundary interactions which are originated from a spin-singlet superconducting pairing and a magnetic field. We exploit the exact solution to investigate the out-of-equilibrium dynamics as due to a quench at the boundary. The propagation of the disturbance in nearest-neighbor magnetic and spin-singlet pairing displays a ballistic behavior for long times with different velocities.

quant-ph↗

arXiv2019

Independent geometrical control of spin and charge resistances in curved spintronics

Spintronic devices operating with pure spin currents represent a new paradigm in nanoelectronics, with higher energy efficiency and lower dissipation as compared to charge currents. This technology, however, will be viable only if the amount of spin current diffusing in a nanochannel can be tuned on demand while guaranteeing electrical compatibility with other device elements, to which it should be integrated in high-density three-dimensional architectures. Here, we address these two crucial milestones and demonstrate that pure spin currents can effectively propagate in metallic nanochannels with a three-dimensional curved geometry. Remarkably, the geometric design of the nanochannels can be used to reach an independent tuning of spin transport and charge transport characteristics. These results put the foundation for the design of efficient pure spin current based electronics, which can be integrated in complex three-dimensional architectures.

cond-mat.mes-hall↗

arXiv2019

Spin-Orbital Hallmarks of Unconventional Superconductors Without Inversion Symmetry

The spin-orbital polarization of superconducting excitations in momentum space is shown to provide distinctive marks of unconventional pairing in the presence of inversion symmetry breaking.Taking the prototypical example of an electronic system with atomic spin-orbit and orbital-Rashba couplings, we provide a general description of the spin-orbital textures and their most striking changeover moving from the normal to the superconducting state. We find that the variation of the spin-texture is strongly imprinted by the combination of the misalignment of spin-triplet d-vector with the inversion asymmetry g-vector coupling and the occurrence of superconducting nodal excitations. Remarkably, the multi-orbital character of the superconducting state allows to unveil a unique type of topological transition for the spin-winding around the nodal points. This finding indicates the fundamental topological relation between chiral and spin-winding in nodal superconductors. By analogy between spin- and orbital-triplet pairing we point out how orbital polarization patterns can be also employed to assess the character of the superconducting state.

cond-mat.supr-con↗

arXiv2019

Geometric driving of two-level quantum systems

We investigate a class of cyclic evolutions for %the cyclic evolution of driven two-level quantum systems (effective spin-1/2) with a particular focus on the geometric characteristics of the driving and their specific imprints on the quantum dynamics. By introducing the concept of geometric field curvature for any field trajectory in the parameter space we are able to unveil underlying patterns in the overall quantum behavior: the knowledge of the field curvature provides a non-standard and fresh access to the interrelation between field and spin trajectories, and the corresponding quantum phases acquired in non-adiabatic cyclic evolutions. In this context, we single out setups in which the driving field curvature can be employed to demonstrate a pure geometric control of the quantum phases. Furthermore, the driving field curvature can be naturally exploited to introduce the geometrical torque and derive a general expression for the total quantum phase acquired in a cycle. Remarkably, such relation allows to access the mechanisms controlling the changeover of the quantum phase across a topological transition and to disentangle the role of the spin and field topological windings. As for implementations, we discuss a series of physical systems and platforms to demonstrate how the geometric control of the quantum phases can be realized for pendular field drivings. This includes setups based on superconducting islands coupled to a Josephson junction and inversion asymmetric nanochannels with suitably tailored geometric shapes.

cond-mat.mes-hall↗

arXiv2018

A topological quantum pump in serpentine-shaped semiconducting narrow channels

We propose and analyze theoretically a one-dimensional solid-state electronic setup that operates as a topological charge pump in the complete absence of superimposed oscillating local voltages. The system consists of a semiconducting narrow channel with strong Rashba spin-orbit interaction patterned in a mesoscale serpentine shape. A rotating planar magnetic field serves as the external ac perturbation, and cooperates with the Rashba spin-orbit interaction, which is modulated by the geometric curvature of the electronic channel to realize the topological pumping protocol originally introduced by Thouless in an entirely novel fashion. We expect the precise pumping of electric charges in our mesoscopic quantum device to be relevant for quantum metrology purposes.

cond-mat.mes-hall↗

arXiv2018

Inter-orbital topological superconductivity in spin-orbit coupled superconductors with inversion symmetry breaking

We study the superconducting state of multi-orbital spin-orbit coupled systems in the presence of an orbitally driven inversion asymmetry assuming that the inter-orbital attraction is the dominant pairing channel. Although the inversion symmetry is absent, we show that superconducting states that avoid mixing of spin-triplet and spin-singlet configurations are allowed, and remarkably, spin-triplet states that are topologically nontrivial can be stabilized in a large portion of the phase diagram. The orbital-dependent spin-triplet pairing generally leads to topological superconductivity with point nodes that are protected by a nonvanishing winding number. We demonstrate that the disclosed topological phase can exhibit Lifshitz-type transitions upon different driving mechanisms and interactions, e.g., by tuning the strength of the atomic spin-orbit and inversion asymmetry couplings or by varying the doping and the amplitude of order parameter. Such distinctive signatures of the nodal phase manifest through an extraordinary reconstruction of the low-energy excitation spectra both in the bulk and at the edge of the superconductor.

cond-mat.supr-con↗

arXiv2018

Josephson Current in Rashba-based Superconducting Nanowires with Geometric Misalignment

We investigate the properties of a weak link between two Rashba-based superconducting nanowires with geometric misalignment. By applying an external magnetic field the system can be driven into a topological non-trivial regime. We demonstrate that the Josephson current can be modulated in amplitude and sign through the variation of the applied field and, remarkably, via the angle controlling the spin-orbit locking mismatch at the interface of the nanowires. The proposed setup with misaligned coplanar nanowires provides the building block configuration for the manipulation of coherent transport via geometric-controlled mixing/splitting of interface states.

cond-mat.supr-con↗