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Mario Cuoco

Publications and source records attributed to Mario Cuoco.

At least 55 records · Page 3Linked to original sources
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↗
arXiv2023

Pattern Formation by Electric-field Quench in Mott Crystal

The control of Mott phase is intertwined with the spatial reorganization of the electronic states. Out-of-equilibrium driving forces typically lead to electronic patterns that are absent at equilibrium, whose nature is however often elusive. Here, we unveil a nanoscale pattern formation in the Ca$_2$RuO$_4$ Mott insulator. We demonstrate how an applied electric field spatially reconstructs the insulating phase that, uniquely after switching off the electric field, exhibits nanoscale stripe domains. The stripe pattern has regions with inequivalent octahedral distortions that we directly observe through high-resolution scanning transmission electron microscopy. The nanotexture depends on the orientation of the electric field, it is non-volatile and rewritable. We theoretically simulate the charge and orbital reconstruction induced by a quench dynamics of the applied electric field providing clear-cut mechanisms for the stripe phase formation. Our results open the path for the design of non-volatile electronics based on voltage-controlled nanometric phases.

cond-mat.str-el↗
arXiv2023

High orbital-moment Cooper pairs by crystalline symmetry breaking

The pairing structure of superconducting materials is regulated by the point group symmetries of the crystal. Here, we study spin-singlet multiorbital superconductivity in materials with unusually low crystalline symmetry content and unveil the the appearance of even-parity (s-wave) Cooper pairs with high orbital moment. We show that the lack of mirror and rotation symmetries makes pairing states with quintet orbital angular momentum symmetry-allowed. A remarkable fingerprint of this type of pairing state is provided by a nontrivial superconducting phase texture in momentum space with $π$-shifted domains and walls with anomalous phase winding. The pattern of the quintet pairing texture is shown to depend on the orientation of the orbital polarization and the strength of the mirror and/or rotation symmetry breaking terms. Such momentum dependent phase makes Cooper pairs with net orbital component suited to design orbitronic Josephson effects. We discuss how an intrinsic orbital dependent phase can set out anomalous Josephson couplings by employing superconducting leads with nonequivalent breaking of crystalline symmetry.

cond-mat.supr-con↗
arXiv2023

Materials challenges for SrRuO3: from conventional to quantum electronics

The need for faster and more miniaturised electronics is challenging scientists to develop novel forms of electronics based on quantum degrees of freedom different from electron charge. In this fast-developing field, often referred to as quantum electronics, the metal-oxide perovskite SrRuO3 can play an important role thanks to its diverse physical properties, which have been intensively investigated, mostly for conventional electronics. In addition to being chemically stable, easy to fabricate with high quality and to grow epitaxially onto many oxides - these are all desirable properties also for conventional electronics - SrRuO3 has interesting properties for quantum electronics like itinerant ferromagnetism and metallic behaviour, strong correlation between magnetic anisotropy and spin-orbit coupling, strain-tuneable magnetisation, anomalous Hall and Berry effects. In this Research Update, after describing the main phenomena emerging from the interplay between spin, orbital, lattice and topological quantum degrees of freedom in SrRuO3, we discuss the challenges still open to achieve control over these phenomena. We then provide our perspectives on the most promising applications of SrRuO3 for devices for conventional and quantum electronics. We suggest new device configurations and discuss the materials challenges for their realisation. For conventional electronics, we single out applications where SrRuO3 devices can bring competitive advantages over existing ones. For quantum electronics, we propose devices that can help gain a deeper understanding of quantum effects in SrRuO3 to exploit them for quantum technologies. We finally give an outlook about properties of SrRuO3 still waiting for discovery and applications that may stem from them.

cond-mat.mtrl-sci↗
arXiv2023

Spin-orbital mechanisms for negative thermal expansion in Ca2RuO$_4$

The phenomenon of negative thermal expansion (NTE) deals with the increase of the lattice parameters and the volume of the unit cell when the material is thermally cooled. The NTE is typically associated with thermal phonons and anomalous spin-lattice coupling at low temperatures. However, the underlying mechanisms in the presence of strong electron correlations in multi-orbital systems are not yet fully established. Here, we investigate the role of Coulomb interaction in the presence of lattice distortions in setting out the NTE effect, by focusing on the physical case of layered Ca$_2$RuO$_4$ with $d^4$ configuration at each Ru ion site. We employ the Slater-Koster parametrization to describe the electron-lattice coupling through the dependence of the $d-p$ hybridization on the Ru-O-Ru bond angle. The evaluation of the minimum of the free energy at finite temperature by fully solving the multi-orbital many-body problem on finite size cluster allows us to identify the regime for which the system is prone to exhibit NTE effects. The analysis shows that the nature of the spin-orbital correlations is relevant to drive the reduction of the bond angle by cooling, and in turn the tendency toward a NTE. This is confirmed by the fact that a changeover of the electronic and orbital configuration from $d^4$ to $d^3$ by transition metal substitution is shown to favor the occurrence of NTE in Ca$_2$RuO$_4$. This finding is in agreement with the experimental observations of a NTE effect which is significantly dependent on the transition metal substitution in the Ca$_2$RuO$_4$ compound.

cond-mat.str-el↗
arXiv2023

Current driven insulator-to-metal transition without Mott breakdown in Ca$_2$RuO$_4$

The electrical control of a material's conductivity is at the heart of modern electronics. Conventionally, this control is achieved by tuning the density of mobile charge carriers. A completely different approach is possible in Mott insulators such as Ca$_2$RuO$_4$, where an insulator-to-metal transition (IMT) can be induced by a weak electric field or current. This phenomenon has numerous potential applications in, e.g., neuromorphic computing. While the driving force of the IMT is poorly understood, it has been thought to be a breakdown of the Mott state. Using in operando angle-resolved photoemission spectroscopy, we show that this is not the case: The current-driven conductive phase arises with only a minor reorganisation of the Mott state. This can be explained by the co-existence of structurally different domains that emerge during the IMT. Electronic structure calculations show that the boundaries between domains of slightly different structure lead to a drastic reduction of the overall gap. This permits an increased conductivity, despite the persistent presence of the Mott state. This mechanism represents a paradigm shift in the understanding of IMTs, because it does not rely on the simultaneous presence of a metallic and an insulating phase, but rather on the combined effect of structurally inhomogeneous Mott phases.

cond-mat.str-el↗
arXiv2023

Multiple-q current states in a multicomponent superconducting channel

It is well-established that multicomponent superconductors can host different nonstandard phenomena such as broken-time reversal symmetry (BTRS) states, exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases, the fractional Josephson effect as well as plenty of topological defects like phase solitons, domain walls and unusual vortex structures. We show that in the case of a two-component superconducting quasi-one-dimensional channel this catalogue can be extended by a novel inhomogeneous current state, which we have termed as a multiple-momenta state or, in short, a multiple-q state, characterized by the coexistence of two different interpenetrating Cooper pair condensates with different total momenta. Within the Ginzburg-Landau formalism for a dirty two-band superconductor with sizable impurity scattering treated in the Born-approximation we reveal that under certain conditions, the occurrence of multiple-q states can induce a cascade of transitions involving switching between them and the homogeneous BTRS (non-BTRS) states and vice versa leading this way to a complex interplay of homogeneous and inhomogeneous current states. We find that hallmarks of such a multiple-q state within a thin wire or channel can be a saw-like dependence of the depairing current and the existence of two distinct stable branches on it (a bistable current state).

cond-mat.supr-con↗
arXiv2023

Designing spin and orbital sources of Berry curvature at oxide interfaces

Quantum materials can display physical phenomena rooted in the geometry of electronic wavefunctions. The corresponding geometric tensor is characterized by an emergent field known as Berry curvature (BC). Large BCs typically arise when electronic states with different spin, orbital or sublattice quantum numbers hybridize at finite crystal momentum. In all materials known to date, the BC is triggered by the hybridization of a single type of quantum number. Here, we report the discovery of the first material system having both spin and orbital-sourced BC: LaAlO$_3$/SrTiO$_3$ interfaces grown along the [111] direction. We detect independently these two sources and directly probe the BC associated to the spin quantum number through measurements of an anomalous planar Hall effect. The observation of a nonlinear Hall effect with time-reversal symmetry signals large orbital-mediated BC dipoles. The coexistence of different forms of BC enables the combination of spintronic and optoelectronic functionalities in a single material.

cond-mat.mes-hall↗
arXiv2023

Orbital design of Berry curvature: pinch points and giant dipoles induced by crystal fields

The Berry curvature (BC) - a quantity encoding the geometric properties of the electronic wavefunctions in a solid - is at the heart of different Hall-like transport phenomena, including the anomalous Hall and the non-linear Hall and Nernst effects. In non-magnetic quantum materials with acentric crystalline arrangements, local concentrations of BC are generally linked to single-particle wavefunctions that are a quantum superposition of electron and hole excitations. BC-mediated effects are consequently observed in two-dimensional systems with pairs of massive Dirac cones and three-dimensional bulk crystals with quartets of Weyl cones. Here, we demonstrate that in materials equipped with orbital degrees of freedom local BC concentrations can arise even in the complete absence of hole excitations. In these solids, the crystals fields appearing in very low-symmetric structures trigger BCs characterized by hot-spots and singular pinch points. These characteristics naturally yield giant BC dipoles and large non-linear transport responses in time-reversal symmetric conditions.

cond-mat.mes-hall↗
arXiv2022

Activating magnetoelectric optical properties by twisting antiferromagnetic bilayers

Twisting in bilayers introduces structural chirality with two enantiomers, i.e., left- and right-hand bilayers, depending on the oriented twist angle. The interplay between this global chirality and additional degrees of freedom, such as magnetic ordering and the local octahedral chirality arising from the geometry of the bonds, can yield striking phenomena. In this work, we focus on collinear antiferromagnetic CrI$_3$ twisted homo-bilayers, which are characterized by a staggered octahedral chirality in each monolayer. Using symmetry analysis, density functional theory and tight-binding model calculations we show that layers twisting can lower the structural and magnetic point-group symmetries, thus activating pyroelectricity and the magneto-optical Kerr effect, which would otherwise be absent in untwisted antiferromagnetic homo-bilayers. Interestingly, both electric polarization and Kerr angle are controllable by the twist angle and their sign is reversed when switching from left- to right-twisted bilayers. We further unveil the occurrence of unconventional vortices with spin textures that alternate opposite chiralities in momentum space. These findings demonstrate that the interplay between twisting and octahedral chirality in magnetic bilayers and related van der Waals heterostructures represents an extraordinary resource for tailoring their physical properties for spintronic and optoelectronic applications.

cond-mat.mes-hall↗
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

Magneto-topological transitions in multicomponent superconductors

Multi-component spin-singlet superconductors with competing 0- and $π$-pairing couplings, as in $s_{++}$ and $s_{\pm}$ phases, are close to instabilities with a spontaneous breaking of time-reversal symmetry. We demonstrate that the modification of the kinetic energy of superconducting electrons in a doubly connected superconducting cylinder, determined by the applied flux, generally drives transitions from chiral superconducting states to configurations that are time-reversal symmetric. This magneto-topological-induced changeover is investigated by means of a Ginzburg-Landau approach for a two-band superconductor with interband interactions and impurity scattering investigated for the case of a sample in the form of a mesoscopically thin-walled cylinder. We find that the application of a magnetic flux can convert a chiral $s_{\pm}+is_{++}$ state into a $s_{\pm}$ configuration and vice versa or tune the energy splitting of chiral states having inequivalent pairing amplitudes. We discuss signatures for the detection of these phases and of the corresponding transitions in mesoscopic superconducting loops.

cond-mat.supr-con↗
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↗
arXiv2022

Odd-frequency pairing in a nonunitary p-wave superconductor with multiple Majorana fermions

Odd-frequency Cooper pairs are gathering attention for the convenience of investigating the edge state of topological superconductors including Majorana fermions. Although a spinless p-wave superconductor has only one Majorana fermion in a topological phase, the system with magnetic fields can reach the topological phases with multiple Majorana fermions. To distinguish these multiple Majorana fermion phases, we correlate the energy spectrum with the odd-frequency pair amplitude as increasing the system size. The system size dependence tells us three pieces of information: the parity of the number of the Majorana fermions at the edge, the number of low-energy modes corresponding to the Majorana fermions with different localization lengths, and the fingerprints of the Majorana fermions. Also, we present the spatial dependence of the odd-frequency f vector that is created from odd-frequency pair amplitude and the spin structure of odd-frequency Cooper pairs. We find that the odd-frequency f vector is fixed in the same direction in any topological phase. Also, we show that the spin state of odd-frequency Cooper pairs tends to be oriented toward the direction of the magnetic fields. Our results highlight the odd-frequency Cooper pairs can be a good indicator for the detection of the multiple Majorana fermions and the distinction among the topological phases.

cond-mat.supr-con↗
arXiv2022

Frustration driven Josephson phase dynamics

The Josephson equations predict remarkable effects concerning the phase state of a superconducting junction with an oscillating current induced by a static voltage. Whether the paradigm can be twisted by yielding an oscillating voltage without making use of harmonic drives is a fundamentally relevant problem yet not fully settled. Here, we demonstrate that a dynamical regime with an oscillating phase evolution is a general hallmark of driven Josephson systems exhibiting sign competition in the Josephson couplings. We show that in frustrated Josephson systems an oscillating phase dynamics gets switched on by driving the changeover among different ground states, which can be induced by varying the parameters that set the phase state. Remarkably, the character of the transitions in the Josephson phase space allows different types of dynamics, with few or several harmonics. This result sets out a characteristic mark of any superconducting system with frustrated Josephson couplings and can be exploited to disentangle the complexity of the underlying phases.

cond-mat.supr-con↗
arXiv2021

Zero magnetic-field orbital vortices in s-wave spin-singlet superconductors

Breaking of time-reversal and point-group spatial symmetries can have a profound impact on superconductivity. One of the most extraordinary effects, due to the application of a magnetic field, is represented by the Abrikosov vortices with charged supercurrents circulating around their cores. Whether a similar phenomenon can be obtained by exploiting spatial symmetry breaking, e.g. through electric fields or mechanical strain, is a fundamentally relevant but not yet fully settled problem. Here, we show that in two-dimensional spin-singlet superconductors with unusually low degree of spatial symmetry content, vortices with supercurrents carrying angular momentum around the core can form and be energetically stable. The vortex has zero net magnetic flux since it is made up of counter-propagating Cooper pairs with opposite orbital moments. By solving self-consistently the Bogoliubov - de Gennes equations in real space, we demonstrate that the orbital vortex is stable and we unveil the spatial distribution of the superconducting order parameter around its core. The resulting amplitude has a characteristic pattern with a pronounced angular anisotropy that deviates from the profile of conventional magnetic vortices. These hallmarks guide predictions and proposals for the experimental detection.

cond-mat.supr-con↗