arXiv subjects

Manuel Bibes

Publications and source records attributed to Manuel Bibes.

At least 19 recordsLinked to original sources

arXiv2026

Orbital and Spin Edelstein Effects in KTaO$_3$(110) Two-Dimensional Electron Gases

The orbital Edelstein effect converts an electric field into a non-equilibrium orbital polarization, opening new opportunities for orbitronics. Although signatures of the orbital Edelstein effect have been reported, its microscopic mechanisms and quantitative validation remain underexplored. Here, by directly linking the atomic structure of KTaO$_3$(110) two-dimensional electron gases to both their calculated and measured electronic band dispersions, we predict and provide experimental evidence for an orbital Edelstein effect that largely counterbalances its spin counterpart. Scanning transmission electron microscopy and electron energy-loss spectroscopy resolve the interfacial atomic configuration, which is used as input for density-functional calculations. Angle-resolved photoemission spectroscopy then confirms the resulting band structure, which is fitted by a tight-binding model enabling computation of the spin and orbital Edelstein responses. Harmonic magnetotransport indicates that a $\sim$20 \% contribution from the orbital Edelstein response is necessary to describe the magnitude and anisotropy of the effect. Our results establish KTaO$_3$(110) as a model platform for orbitronics and demonstrate a pathway to generate and harness orbital polarization in quantum oxide systems while also offering new insights into pairing mechanisms in their superconducting state.

cond-mat.mtrl-sci↗

arXiv2026

Reprogrammable magnonic logic in a multiferroic heterostructure via magnetoelectric coupling

The realization of fully reconfigurable, voltage-controlled, and programmable on-chip magnonic devices is essential to fully harness the potential of spin waves for signal processing, logic and neuromorphic computing. Yet, existing demonstrations of electrical tuning of magnonic responses are either volatile, current-driven and thus energy-inefficient, or rely on local strain modification limiting their scalability for wafer-scale integration. Here, we address this challenge using a BiFeO3/La0.67Sr0.33MnO3 multiferroic thin film heterostructure. We show that ferroelectric domain engineering in BiFeO3 enables deterministic tuning of the magnon dispersion of La0.67Sr0.33MnO3, producing frequency shifts up to $\sim 150 MHz$ and allowing reconfigurable waveguiding. Micro-focused Brillouin light scattering directly images these effects, revealing electrically defined magnonic waveguides and spatially programmable dispersion. Compared to conventional approaches, this method provides non-volatile and reversible control. Furthermore, using an inverse-design simulation code, we demonstrate the capability of our platform to perform advanced magnonic functions such as frequency demultiplexing. Our results open a new avenue for using magnetoelectric heterostructures for magnonic logic, with further applicability to reservoir and neuromorphic computing and AI driven magnonic devices.

cond-mat.mes-hall↗

arXiv2026

Revealing the origin of XMCD in an altermagnet via three-dimensional control of spins

Altermagnets are an emerging class of collinear antiferromagnets that exhibit unconventional spin-polarised electronic bands, potentially unlocking new functionalities that do not rely on spin-orbit coupling (SOC). Experimental signatures traditionally associated with spin polarisation, like X-ray magnetic circular dichroism (XMCD), are thus being used as a validation of altermagnetism. However, unlike altermagnetic spin-splitting, these responses require SOC and are not invariant under spin-space rotations. This brings into question the extent to which they can be considered direct signatures of altermagnetism. Here, we exploit the g-wave altermagnet $\alpha$-Fe$_{2}$O$_{3}$ to demonstrate that XMCD is governed precisely by the spin-direction-induced symmetry breaking that altermagnetic spin groups are designed to ignore. Strikingly, the XMCD is highly anisotropic and is decoupled from the weak magnetic canting. We show that this anomalous XMCD can be described by on-site Faraday tensors capturing the locally uncompensated spin-orbital anisotropies - a scenario that can be applied to other altermagnets. Leveraging this, we reconstruct complete vectorial maps of nanoscale textures in $\alpha$-Fe$_{2}$O$_{3}$ thin films, including domain walls and topological solitons, which are promising for building future spintronics and magnonics devices.

cond-mat.mtrl-sci↗

arXiv2026

Spin Hall and Edelstein effects in a ballistic quantum dot with Rashba spin-orbit coupling

We study spin-resolved transport in a ballistic quantum dot with Rashba spin-orbit coupling, focusing on charge-to-spin conversion and spin Hall effect. In the regime where the dot size is comparable to the Fermi wavelength, we identify a clear crossover from weak localization to weak antilocalization as the Rashba coupling increases. This transition is accompanied by gate-tunable spin currents of Edelstein and spin Hall type, whose behavior reflects the underlying electron wavefunction interference. Notably, the Edelstein current shows an inflection point at the critical Rashba strength, signaling the crossover from weak localization to weak antilocalization. In the presence of an in-plane magnetic field we also report a transition in angular periodicity of the magnetoresistance -- from $\pi$ to $2\pi$ -- arising from the interplay between spin-orbit interaction and Zeeman coupling. These results establish a direct link between quantum coherence, charge-to-spin conversion, and geometric confinement in mesoscopic systems.

cond-mat.mes-hall↗

arXiv2026

Intrinsic Negative-U Centers in Freestanding LaAlO3/SrTiO3 Micro-membranes

The LaAlO3/SrTiO3 (LAO/STO) interface hosts a rich range of electronic phenomena, including unconventional electron pairing that in quantum dots gives rise to a negative effective charging energy U. Here, we show freestanding LAO/STO micro-membranes naturally hosting negative-U centers, where lateral confinement arises intrinsically, rather than from engineered nanostructures. These centers coexist with gate-tunable superconductivity and can remain stable upon thermal cycling from millikelvin temperatures to room temperature. Transport is in excellent agreement with calculations based on a negative-U Anderson model, and electrostatic simulations indicate characteristic center sizes of 20-80 nm. Our findings suggest that negative-U centers may arise from the intrinsic interfacial inhomogeneity typical of LAO/STO, and should therefore be considered a general feature of the LAO/STO interface. This could have important consequences for the microwave response of interfacial superconducting devices.

cond-mat.mtrl-sci↗

arXiv2026

Anisotropic magnon transport in an antiferromagnetic trilayer heterostructure: is BiFeO$_3$ an altermagnet?

Magnons provide a route to ultra-fast transport and non-destructive readout of spin-based information transfer. Here, we report magnon transport and its emergent anisotropic nature in BiFeO$_3$ layers confined between ultrathin layers of the antiferromagnet LaFeO$_3$. Due to the confined state, BiFeO$_3$ serves as an efficient magnon transmission channel as well as a magnetoelectric knob by which to control the stack by means of an electric field. We discuss the mechanism of the anisotropic spin transport based on the interaction between the antiferromagnetic order and the electric field. This allows us to manipulate and amplify the spin transport in such a confined geometry. Furthermore, lower crystal symmetric and suppression of the spin cycloid in ultrathin BiFeO$_3$ stabilizes a non-trivial antiferromagnetic state exhibiting symmetry-protected spin-split bands that provide the non-trivial sign inversion of the spin current, which is a characteristic of an altermagnet. This work provides an understanding of the anisotropic spin transport in complex antiferromagnetic heterostructures where ferroelectricity and altermagnetism coexist, paving the way for a new route to realize electric-field control of a novel state of magnetism.

cond-mat.mes-hall↗

arXiv2025

Spontaneous nonreciprocal transport in a gate-tunable ferromagnetic Rashba 2-dimensional electron gas

The broken inversion symmetry at interfaces of complex oxides gives rise to emergent phenomena, including ferromagnetism and Rashba spin-orbit coupling (SOC), which profoundly influence the electronic structure by entangling spin and momentum. While the interplay between Rashba SOC and ferromagnetism is theoretically intriguing, its experimental manifestations remain largely unexplored. Here, we demonstrate that ferromagnetic 2DEGs at SrTiO$_3$-based interfaces exhibit spontaneous nonreciprocal transport - a distinctive hallmark of Rashba ferromagnets - even in the absence of an external magnetic field. This nonreciprocal response, along with clear signatures of ferromagnetism such as anisotropic magnetoresistance and the anomalous Hall effect (AHE), is strongly tunable by gate voltage. Remarkably, the AHE not only varies in amplitude but even reverses sign, reflecting a subtle interplay between Fermi level position and Berry curvature distribution. These results establish SrTiO$_3$ 2DEGs as a model platform for studying Rashba ferromagnetism and demonstrate active control over transport phenomena in time- and inversion-symmetry-broken systems, paving the way for gate-tunable spintronic devices.

cond-mat.str-el↗

arXiv2025

Theory of charge-to-spin conversion under quantum confinement

The interplay between spin and charge degrees of freedom in low-dimensional systems is a cornerstone of modern spintronics, where achieving all-electrical control of spin currents is a major goal. Spin-orbit interactions provide a promising mechanism for such control, yet understanding how spin and charge transport emerge from microscopic principles remains a fundamental challenge. Here we develop a spin-dependent scattering matrix approach to describe spin and charge transport in a multiterminal system in the presence of Rashba spin-orbit interaction. Our framework generalizes the B\"uttiker formalism by offering explicit real-space expressions for spin and charge current densities, along with the corresponding linear response function. It simultaneously captures the effects of quantum confinement, the orbital response to external magnetic fields, and the intrinsic (geometric) properties of the electronic bands, offering a comprehensive description of the spin-charge interconversion mechanisms at play in a Hall bar, in agreement with experiments.

cond-mat.mes-hall↗

arXiv2025

Colossal enhancement of spin transmission through magnon confinement in an antiferromagnet

Since Felix Bloch's introduction of the concept of spin waves in 1930, magnons (the quanta of spin waves) have been extensively studied in a range of materials for spintronics, particularly for non-volatile logic-in-memory devices. Controlling magnons in conventional antiferromagnets and harnessing them in practical applications, however, remains a challenge. In this letter, we demonstrate highly efficient magnon transport in an LaFeO$_3$/BiFeO$_3$/LaFeO$_3$ all-antiferromagnetic system which can be controlled electrically, making it highly desirable for energy-efficient computation. Leveraging spin-orbit-driven spin-charge transduction, we demonstrate that this material architecture permits magnon confinement in ultrathin antiferromagnets, enhancing the output voltage generated by magnon transport by several orders of magnitude, which provides a pathway to enable magnetoelectric memory and logic functionalities. Additionally, its non-volatility enables ultralow-power logic-in-memory processing, where magnonic devices can be efficiently reconfigured via electrically controlled magnon spin currents within magnetoelectric channels.

cond-mat.mtrl-sci↗

arXiv2024

Achieving superconductivity in infinite-layer nickelate thin films by aluminum sputtering deposition

The recent discovery of superconductivity in infinite-layer (IL, ABO$_2$) nickelates has opened a new avenue to deepen the understanding of high-temperature superconductivity. However, progress in this field is slowed by significant challenges in material synthesis and the scarcity of research groups capable of producing high quality superconducting samples. IL nickelates are obtained from a reduction of the perovskite ABO$_3$ phase, typically achieved by annealing using CaH$_2$ as a reducing agent. Here, we present a new method to synthesize superconducting infinite-layer nickelate Pr$_{0.8}$Sr$_{0.2}$NiO$_2$ thin films using an aluminum overlayer deposited by sputtering as a reducing agent. We systematically optimized the aluminum deposition parameters and obtained superconducting samples reduced either in situ or ex situ (after air exposure of the precursor ABO$_3$ films). A comparison of their crystalline quality and transport properties shows that in situ Al reduction enhances the quality of the superconducting Pr$_{0.8}$Sr$_{0.2}$NiO$_2$ thin films, achieving a maximum superconducting transition temperature $T_{c}^{onset}$ of 17 K, in agreement with the optimum value reported for this compound. This simple synthesis route, much more accessible than existing methods, offers better control and reproducibility over the topotactic transformation, opening new opportunities to gain insights into the physics of superconductivity in nickelates.

cond-mat.supr-con↗

arXiv2024

Polarization boost and ferroelectricity down to one unit cell in layered Carpy-Galy La$_{2}$Ti$_{2}$O$_{7}$ thin films

Layered perovskite-based compounds offer a range of unconventional properties enabled by their naturally anisotropic structure. While most renowned for the superconductivity observed in the Ruddlesden-Popper phases, many of these layered compounds are also ferroelectric and exhibit a sizeable in-plane polarization. Among these, the Carpy-Galy phases (A${_n}$B${_n}$O$_{3n+2}$), characterized by 110-oriented perovskite planes interleaved with additional oxygen layers, have been debated as platforms for hosting not only a robust polarization but also multiferroicity and polar metallicity. However, the challenges associated with the synthesis of ultrathin Carpy-Galy films and understanding the impact of strain on their properties limit their integration into devices. Addressing this issue, our study focuses on La$_2$Ti$_2$O$_7$, an $n$=4 (A$_2$B$_2$O$_7$) representative of the Carpy-Galy family, exploring its growth and concurrent phase stability on various substrates under different strain conditions. Remarkably, we demonstrate that a 3% tensile strain from DyScO$_3$ (100) substrates promotes a controlled layer-by-layer growth mode, while SrTiO$_3$ (110) and LaAlO$_3$-Sr$_2$TaAlO$_6$ (110), that exert negligible and compressive strains respectively, require post-deposition annealing to achieve similar results. Using scanning probe microscopy, X-ray diffraction, scanning transmission electron microscopy, and polarization switching experiments, we confirm that these films possess exceptional ferroelectric properties, including a polarization of 18 $\mu$C/cm$^2$ - more than three times higher than previously reported - as well as persistence of ferroelectricity down to a single-unit-cell thickness. This study not only advances our understanding of Carpy-Galy phases in thin films but also lays a foundation for their application in advanced ferroelectric device architectures.

cond-mat.mtrl-sci↗

arXiv2024

Unraveling p-type and n-type interfaces in Superconducting Infinite-Layer Nickelate thin films

After decades of research, superconductivity was finally found in nickel-based analogs of superconducting cuprates, with infinite-layer (IL) structure. These results are so far restricted to thin films in the case of IL-nickelates. Therefore, the nature of the interface with the substrate, and how it couples with the thin film properties is still an open question. Here, using scanning transmission electron microscopy (STEM)- electron energy loss spectroscopy (EELS) and four-dimensional (4D)-STEM, a novel chemically sharp p-type interface is observed in a series of superconducting IL-praseodymium nickelate samples, and a comparative study is carried out with the previously reported n-type interface obtained in other samples. Both interfaces have strong differences, with the p-type interface being highly polar. In combination with ab-initio calculations, we find that the influence of the interface on the electronic structure is local, and does not extend beyond 2-3 unit cells into the thin film. This decouples the direct influence of the interface in driving the superconductivity, and indicates that the IL-nickelate thin films do not have a universal interface model. Insights into the spatial hole-distribution in SC samples, provided by monochromated EELS and total reflection-hard x-ray photoemission spectroscopy, suggest that this particular distribution might be directly influencing superconductivity.

cond-mat.supr-con↗

arXiv2024

Towards reliable synthesis of superconducting infinite layer nickelate thin films by topochemical reduction

Infinite layer nickelates provide a new route beyond copper oxides to address outstanding questions in the field of unconventional superconductivity. However, their synthesis poses considerable challenges, largely hindering experimental research on this new class of oxide superconductors. That synthesis is achieved in a two-step process that yields the most thermodynamically stable perovskite phase first, then the infinite-layer phase by topotactic reduction, the quality of the starting phase playing a crucial role. Here, we report on reliable synthesis of superconducting infinite-layer nickelate films after successive topochemical reductions of a parent perovskite phase with nearly optimal stoichiometry. Careful analysis of the transport properties of the incompletely reduced films reveals an improvement of the strange metal behaviour of their normal state resistivity over subsequent topochemical reductions, offering insight into the reduction process.

cond-mat.supr-con↗

arXiv2023

Electron-phonon mediated superconductivity in La$_6$Ni$_5$O$_{12}$ nickel oxides

Nickel oxide superconductors offer an alternative playground for understanding the formation of Cooper pairs in correlated materials such as the famous cuprates. By studying the La$_{n+1}$Ni$_n$O$_{2n+2}$ phase diagram on the basis of hybrid and spin-polarized density functional theory simulations, we reveal the existence of charge and bond ordered (CBO) insulating phases that are quenched by doping effects, ultimately resulting in a metallic phase at the n=5 member. Nevertheless, the phonons associated with the CBO identified in the phase diagram remain sufficiently large to mediate Cooper pairs in La$_6$Ni$_5$O$_{12}$, yielding a computed critical temperature between T$_c$=11-19K consistent with the 13K observed experimentally in Nd$_6$Ni$_5$O$_{12}$. Thus, in order to identify the superconducting mechanism, extracting the relevant instabilities in the doping phase diagram of superconductors appears critical.

cond-mat.supr-con↗

arXiv2023

Electrical control of magnetism by electric field and current-induced torques

While early magnetic memory designs relied on magnetization switching by locally generated magnetic fields, key insights in condensed matter physics later suggested the possibility to do it electrically. In the 1990s, Slonczewzki and Berger formulated the concept of current-induced spin torques in magnetic multilayers through which a spin-polarized current may switch the magnetization of a ferromagnet. This discovery drove the development of spin-transfer-torque magnetic random-access memories (STT-MRAMs). More recent research unveiled spin-orbit-torques (SOTs) and will lead to a new generation of devices including SOT-MRAMs. Parallel to these advances, multiferroics and their magnetoelectric coupling experienced a renaissance, leading to novel device concepts for information and communication technology such as the MESO transistor. The story of the electrical control of magnetization is that of a dance between fundamental research (in spintronics, condensed matter physics, and materials science) and technology (MRAMs, MESO, microwave emitters, spin-diodes, skyrmion-based devices, components for neuromorphics, etc). This pas de deux led to major breakthroughs over the last decades (pure spin currents, magnetic skyrmions, spin-charge interconversion, etc). As a result, this field has propelled MRAMs into consumer electronics products but also fueled discoveries in adjacent research areas such as ferroelectrics or magnonics. Here, we cover recent advances in the control of magnetism by electric fields and by current-induced torques. We first review fundamental concepts in these two directions, then discuss their combination, and finally present various families of devices harnessing the electrical control of magnetic properties for various application fields. We conclude by giving perspectives in terms of both emerging fundamental physics concepts and new directions in materials science.

physics.app-ph↗

arXiv2023

Electronic bandstructure of superconducting KTaO3 (111) interfaces

Two-dimensional electron gases(2DEGs)based on KTaO3 are emerging as a promising platform for spin-orbitronics due to their high Rashba spin-orbit coupling (SOC) and gate-voltage tunability. The recent discovery of a superconducting state in KTaO3 2DEGs now expands their potential towards topological superconductivity. Although the band structure of KTaO3 surfaces of various crystallographic orientations has already been mapped using angle-resolved photoemission spectroscopy(ARPES), this is not the case for superconducting KTaO3 2DEGs. Here, we reveal the electronic structure of superconducting 2DEGs based on KTaO3 (111) single crystals through ARPES measurements. We fit the data with a tight-binding model and compute the associated spin textures to bring insight into the SOC-driven physics of this fascinating system.

cond-mat.mtrl-sci↗

arXiv2023

Boosting the Edelstein effect of two-dimensional electron gases by ferromagnetic exchange

Strontium titanate (SrTiO$_3$) two-dimensional electron gases (2DEGs) have broken spatial inversion symmetry and possess a finite Rashba spin-orbit coupling. This enables the interconversion of charge and spin currents through the direct and inverse Edelstein effects, with record efficiencies at low temperature, but more modest effects at room temperature. Here, we show that making these 2DEGs ferromagnetic enhances the conversion efficiency by nearly one order of magnitude. Starting from the experimental band structure of non-magnetic SrTiO$_3$ 2DEGs, we mimic magnetic exchange coupling by introducing an out-of-plane Zeeman term in a tight-binding model. We then calculate the band structure and spin textures for increasing internal magnetic fields and compute the Edelstein effect using a semiclassical Boltzmann approach. We find that the conversion efficiency first increases strongly with increasing magnetic field, then shows a maximum and finally decreases. This field dependence is caused by the competition of the exchange coupling with the effective Rashba interaction. While enhancing the splitting of band pairs amplifies the Edelstein effect, weakening the in-plane Rashba-type spin texture reduces it.

cond-mat.mes-hall↗

arXiv2023

Gate-voltage switching of non-reciprocal transport in oxide-based Rashba interfaces

The linear magnetoelectric effect (ME) is the phenomenon by which an electric field produces a magnetization. Its observation requires both time-reversal and space-inversion symmetries to be broken, as in multiferroics. While the ME effect has only been studied in insulating materials, it can actually exist in non-centrosymmetric conductors such as two-dimensional electron gases (2DEGs) with Rashba spin-orbit coupling. It is then coined the Edelstein effect (EE), by which a bias voltage -- generating a charge current -- produces a transverse spin density, i.e. a magnetization. Interestingly, 2D systems are sensitive to voltage gating, which provides an extra handle to control the EE. Here, we show that the sign of the EE in a SrTiO$_3$ 2DEG can be controlled by a gate voltage. We propose various logic devices harnessing the dual control of the spin density by current and gate voltages and discuss the potential of our findings for gate-tunable non-reciprocal electronics.

cond-mat.mes-hall↗