arXiv subjects

Andrea D. Caviglia

Publications and source records attributed to Andrea D. Caviglia.

At least 19 recordsLinked to original sources

arXiv2026

Probing the quantum metric of 3D topological insulators

The surface states of 3D topological insulators possess geometric structures that imprint distinctive signatures on electronic transport. A prime example is the Berry curvature, which controls, for instance, electric frequency doubling via its higher order moments. In addition to the Berry curvature, topological surface states are expected to exhibit a nontrivial quantum metric, which plays a key role in governing nonlinear magnetotransport. However, its manifestation has yet to be experimentally observed and controlled in 3D topological insulators. Here, we provide evidence for a nonlinear response activated by the quantum metric of the topological surface states of Sb$_2$Te$_3$. We measure a time-reversal odd, nonlinear magnetoresistance that is independent from the temperature and the scattering time below 30 K, and is thus of intrinsic geometrical origin. This quantum metric magnetoresistance can be controlled by tuning the contributions of the top and bottom topological surface states by voltage gating. Our measurements thus demonstrate the existence and tunability of quantum geometry-induced transport in topological phases of matter and provide strategies for designing novel functionalities in topological devices.

cond-mat.mes-hall↗

arXiv2025

The quantum metric of electrons with spin-momentum locking

Quantum materials are characterized by electromagnetic responses intrinsically linked to the geometry and topology of electronic wavefunctions, encoded in the quantum metric and Berry curvature. Whereas Berry curvature-mediated transport effects have been identified in several magnetic and nonmagnetic systems, quantum metric-induced transport phenomena remain limited to topological antiferromagnets. Here we show that spin-momentum locking -- a general characteristic of the electronic states at surfaces and interfaces of spin-orbit coupled materials -- leads to a finite quantum metric. This metric activates a nonlinear in-plane magnetoresistance that we measure and electrically control in 111-oriented LaAlO$_3$/SrTiO$_3$ interfaces. These findings demonstrate the existence of quantum metric effects in a vast class of materials and enable previously unexplored strategies to design functionalities based on quantum geometry.

cond-mat.mes-hall↗

arXiv2025

Curvature-Controlled Polarization in Adaptive Ferroelectric Membranes

In this study, we explore the ferroelectric domain structure and mechanical properties of PbTiO$_3$-based membranes, which develops a well-ordered and crystallographic-oriented ripple pattern upon release from their growth substrate. The ferrolectric domain structure of the PbTiO$_3$ layer was examined at various length scales using optical second harmonic generation, piezoresponse force microscopy, and scanning transmission electron microscopy. These methods reveal the presence of purely in-plane domains organized into superdomains at the crest of the ripples, while an in-plane/out-of-plane domain structure was observed in the flat regions separating the ripples, in agreement with phase-field simulations. The mechanical properties of the membrane were assessed using contact resonance force microscopy, which identified distinct mechanical behaviors at the ripples compared to the flat regions. This study shows that the physical properties of the ferroelectric layer in membranes can be locally controlled within an ordered array of ripples, with well-defined geometric characteristics.

cond-mat.mtrl-sci↗

arXiv2025

Imaging orbital Rashba induced charge transport anisotropy

Identifying orbital textures and their effects on the electronic properties of quantum materials is a critical element in developing orbitronic devices. However, orbital effects are often entangled with the spin degree of freedom, making it difficult to uniquely identify them in charge transport phenomena. Here, we present a combination of scanning superconducting quantum interference device (SQUID) current imaging, global transport measurements, and theoretical analysis, that reveals a direct contribution of orbital textures to the linear charge transport of 2D systems. Specifically, we show that in the LaAlO$_3$/SrTiO$_3$ interface, which lacks both rotation and inversion symmetries, an anisotropic orbital Rashba coupling leads to conductivity anisotropy in zero magnetic field. We experimentally demonstrate this result by locally measuring the conductivity anisotropy, and correlating its appearance to the non-linear Hall effect, showing that the two phenomena have a common origin. Our results lay the foundations for an all--electrical probing of orbital currents in two-dimensional systems.

cond-mat.mes-hall↗

arXiv2024

High-field superconductivity from atomic-scale confinement and spin-orbit coupling at (111)$\mathrm{LaAlO_3/KTaO_3}$ interfaces

We study the superconducting critical fields of two-dimensional electron systems at (111)$\mathrm{LaAlO_3/KTaO_3}$ interfaces as a function of electrostatic back-gating. Our work reveals inplane critical fields of unprecedented magnitudes at oxide interfaces. By comparing the critical fields in-plane and out-of-plane we discover an extremely anisotropic superconductor with an effective thickness below 1 nm and a 12-fold violation of the Chandrasekhar-Clogston paramagnetic limit. The analysis of magneto-transport indicates that the enhancement of the critical fields is due to an exceptionally thin superconducting layer and to a paramagnetic susceptibility suppressed by spin-orbit scattering.

cond-mat.supr-con↗

arXiv2024

Electron-Beam Writing of Atomic-Scale Reconstructions at Oxide Interfaces

The epitaxial growth of complex oxides enables the production of high-quality films, yet substrate choice is restricted to certain symmetry and lattice parameters, thereby limiting the technological applications of epitaxial oxides. In comparison, the development of free-standing oxide membranes gives opportunities to create novel heterostructures by non-epitaxial stacking of membranes, opening new possibilities for materials design. Here, we introduce a method for writing, with atomic precision, ionically bonded crystalline material across the gap between an oxide membrane and a carrier substrate. The process involves a thermal pre-treatment, followed by localized exposure to the raster scan of a scanning transmission electron microscopy (STEM) beam. STEM imaging and electron energy-loss spectroscopy show that we achieve atomically sharp interface reconstructions between a 30 nm-thick SrTiO${_3}$ membrane and a niobium-doped SrTiO${_3}$(001)-oriented carrier substrate. These findings indicate new strategies for fabricating synthetic heterostructures with novel structural and electronic properties.

cond-mat.mtrl-sci↗

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

Controlling magnetism with light in a zero orbital angular momentum antiferromagnet

Antiferromagnetic materials feature intrinsic ultrafast spin dynamics, making them ideal candidates for future magnonic devices operating at THz frequencies. A major focus of current research is the investigation of optical methods for the efficient generation of coherent magnons in antiferromagnetic insulators. In magnetic lattices endowed with orbital angular momentum, spin-orbit coupling enables spin dynamics through the resonant excitation of low-energy electric dipoles such as phonons and orbital resonances which interact with spins. However, in magnetic systems with zero orbital angular momentum, microscopic pathways for the resonant and low-energy optical excitation of coherent spin dynamics are lacking. Here, we consider experimentally the relative merits of electronic and vibrational excitations for the optical control of zero orbital angular momentum magnets, focusing on a limit case: the antiferromagnet manganese thiophoshate (MnPS3), constituted by orbital singlet Mn2+ ions. We study the correlation of spins with two types of excitations within its band gap: a bound electron orbital excitation from the singlet orbital ground state of Mn2+ into an orbital triplet state, which causes coherent spin precession, and a vibrational excitation of the crystal field that causes thermal spin disorder. Our findings cast orbital transitions as key targets for magnetic control in insulators constituted by magnetic centers of zero orbital angular momentum.

cond-mat.mtrl-sci↗

arXiv2021

Self-sealing complex oxide resonators

Although 2D materials hold great potential for next-generation pressure sensors, recent studies revealed that gases permeate along the membrane-surface interface that is only weakly bound by van der Waals interactions, necessitating additional sealing procedures. In this work, we demonstrate the use of free-standing complex oxides as self-sealing membranes that allow the reference cavity of pressure sensors to be sealed by a simple anneal. To test the hermeticity, we study the gas permeation time constants in nano-mechanical resonators made from SrRuO3 and SrTiO3 membranes suspended over SiO2/Si cavities which show an improvement up to 4 orders of magnitude in the permeation time constant after annealing the devices for 15 minutes. Similar devices fabricated on Si3N4/Si do not show such improvements, suggesting that the adhesion increase over SiO2 is mediated by oxygen bonds that are formed at the SiO2/complex oxide interface during the self-sealing anneal. We confirm the enhancement of adhesion by picosecond ultrasonics measurements which show an increase in the interfacial stiffness by 70% after annealing. Since it is straigthforward to apply, the presented self-sealing method is thus a promising route toward realizing ultrathin hermetic pressure sensors.

cond-mat.mtrl-sci↗

arXiv2021

Large tunability of strain in WO3 single-crystal microresonators controlled by exposure to H2 gas

Strain engineering is one of the most effective approaches to manipulate the physical state of materials, control their electronic properties, and enable crucial functionalities. Because of their rich phase diagrams arising from competing ground states, quantum materials are an ideal playground for on-demand material control, and can be used to develop emergent technologies, such as adaptive electronics or neuromorphic computing. It was recently suggested that complex oxides could bring unprecedented functionalities to the field of nanomechanics, but the possibility of precisely controlling the stress state of materials is so far lacking. Here we demonstrate the wide and reversible manipulation of the stress state of single-crystal WO3 by strain engineering controlled by catalytic hydrogenation. Progressive incorporation of hydrogen in freestanding ultra-thin structures determines large variations of their mechanical resonance frequencies and induces static deformation. Our results demonstrate hydrogen doping as a new paradigm to reversibly manipulate the mechanical properties of nanodevices based on materials control.

physics.app-ph↗

arXiv2021

Gate-tunable hallmarks of unconventional superconductivity in non-centrosymmetric nanowires

Two dimensional SrTiO3-based interfaces stand out among non-centrosymmetric superconductors due to their intricate interplay of gate tunable Rashba spin-orbit coupling and multi-orbital electronic occupations, whose combination theoretically prefigures various forms of non-standard superconductivity. However, a convincing demonstration by phase sensitive measurements has been elusive so far. Here, by employing superconducting transport measurements in nano-devices we present clear-cut experimental evidences of unconventional superconductivity in the LaAlO3/SrTiO3 interface. The central observations are the substantial anomalous enhancement of the critical current by small magnetic fields applied perpendicularly to the plane of electron motion, and the asymmetric response with respect to the magnetic field direction. These features have a unique trend in intensity and sign upon electrostatic gating that, together with their dependence on temperature and nanowire dimensions, cannot be accommodated within a scenario of canonical spin-singlet superconductivity. We theoretically demonstrate that the hall-marks of the experimental observations unambiguously indicate a coexistence of Josephson channels with sign difference and intrinsic phase shift. The character of these findings establishes the occurrence of independent components of unconventional pairing in the superconducting state due to inversion symmetry breaking. The outcomes open new venues for the investigation of multi-orbital non-centrosymmetric superconductivity and Josephson-based devices for quantum technologies.

cond-mat.supr-con↗

arXiv2021

Non-universal current flow near the metal-insulator transition in an oxide interface

In systems near phase transitions, macroscopic properties often follow algebraic scaling laws, determined by the dimensionality and the underlying symmetries of the system. The emergence of such universal scaling implies that microscopic details are irrelevant. Here, we locally investigate the scaling properties of the metal-insulator transition at the LaAlO3/SrTiO3 interface. We show that, by changing the dimensionality and the symmetries of the electronic system, coupling between structural and electronic properties prevents the universal behavior near the transition. By imaging the current flow in the system, we reveal that structural domain boundaries modify the filamentary flow close to the transition point, preventing a fractal with the expected universal dimension from forming. Our results offer a generic platform to engineer electronic transitions on the nanoscale.

cond-mat.mes-hall↗

arXiv2020

Anisotropic magnetoresistance in spin-orbit semimetal SrIrO3

SrIrO3, the three-dimensional member of the Ruddlesden-Popper iridates, is a paramagnetic semimetal characterised by a the delicate interplay between spin-orbit coupling and Coulomb repulsion. In this work, we study the anisotropic magnetoresistance (AMR) of SrIrO3 thin films, which is closely linked to spin-orbit coupling and probes correlations between electronic transport, magnetic order and orbital states. We show that the low-temperature negative magnetoresistance is anisotropic with respect to the magnetic field orientation, and its angular dependence reveals the appearance of a fourfold symmetric component above a critical magnetic field. We show that this AMR component is of magnetocrystalline origin, and attribute the observed transition to a field-induced magnetic state in SrIrO3.

cond-mat.str-el↗

arXiv2019

Ultrathin complex oxide nanomechanical resonators

Complex oxide thin films and heterostructures exhibit a profusion of exotic phenomena, often resulting from the intricate interplay between film and substrate. Recently it has become possible to isolate epitaxially grown single-crystalline layers of these materials, enabling the study of their properties in the absence of interface effects. In this work, we create ultrathin membranes of strongly correlated materials and demonstrate top-down fabrication of nanomechanical resonators made out of \ce{SrTiO3} and \ce{SrRuO3}. Using laser interferometry, we successfully actuate and measure the motion of the nanodrum resonators. By measuring their temperature-dependent mechanical response, we observe signatures of structural phase transitions in \ce{SrTiO3}, which affect the strain and mechanical dissipation in the resonators. This approach can be extended to investigate phase transitions in a wide range of materials. Our study demonstrates the feasibility of integrating ultrathin complex oxide membranes for realizing nanoelectromechanical systems on arbitrary substrates.

physics.app-ph↗

arXiv2019

Bimodal Phase Diagram of the Superfluid Density in LaAlO3/SrTiO3 Revealed by an Interfacial Waveguide Resonator

We explore the superconducting phase diagram of the two-dimensional electron system at the LaAlO3/SrTiO3 interface by monitoring the frequencies of the cavity modes of a coplanar waveguide resonator fabricated in the interface itself. We determine the phase diagram of the superconducting transition as a function of temperature and electrostatic gating, finding that both the superfluid density and the transition temperature follow a dome shape, but that the two are not monotonically related. The ground state of this 2DES is interpreted as a Josephson junction array, where a transition from long- to short-range order occurs as a function of the electronic doping. The synergy between correlated oxides and superconducting circuits is revealed to be a promising route to investigate these exotic compounds, complementary to standard magneto-transport measurements.

cond-mat.str-el↗

arXiv2018

Balanced electron-hole transport in spin-orbit semimetal SrIrO3 heterostructures

Relating the band structure of correlated semimetals to their transport properties is a complex and often open issue. The partial occupation of numerous electron and hole bands can result in properties that are seemingly in contrast with one another, complicating the extraction of the transport coefficients of different bands. The 5d oxide SrIrO3 hosts parabolic bands of heavy holes and light electrons in gapped Dirac cones due to the interplay between electron-electron interactions and spin-orbit coupling. We present a multifold approach relying on different experimental techniques and theoretical calculations to disentangle its complex electronic properties. By combining magnetotransport and thermoelectric measurements in a field-effect geometry with first-principles calculations, we quantitatively determine the transport coefficients of different conduction channels. Despite their different dispersion relationships, electrons and holes are found to have strikingly similar transport coefficients, yielding a holelike response under field-effect and thermoelectric measurements and a linear, electronlike Hall effect up to 33 T.

cond-mat.str-el↗

arXiv2017

Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3

Tungsten trioxide is a versatile material with widespread applications ranging from electrochromic and optoelectronic devices to water splitting and catalysis of chemical reactions. For technological applications, thin films of WO3 are particularly appealing, taking advantage from high surface-to-volume ratio and tunable physical properties. However, the growth of stoichiometric, crystalline thin films is challenging because the deposition conditions are very sensitive to the formation of oxygen vacancies. In this work, we show how background oxygen pressure during pulsed laser deposition can be used to tune the structural and electronic properties of WO3 thin films. By performing X-ray diffraction and low-temperature transport measurements, we find changes in WO3 lattice volume up to 10%, concomitantly with an insulator-to-metal transition as a function of increased level of electron doping. We use advanced ab initio calculations to describe in detail the properties of the oxygen vacancy defect states, and their evolution in terms of excess charge concentration. Our results depict an intriguing scenario where structural, electronic, optical, and transport properties of WO3 single-crystal thin films can all be purposely tuned by a suited control of oxygen vacancies formation during growth.

cond-mat.mtrl-sci↗