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Rivadulla

Research themes

  • Heat transport at the nanoscale
  • Spin-driven transport in magnetic layers and heterostructures
  • Memristors: material growth, microfabrication and applications

Main researcher(s)

Full Professor
ResearcherID
ORCID
Investigador Ramón y Cajal
ORCID

Group members

Martínez Botana, José Martín

Postdoctoral Researcher
Santos Claro, Marcel

Postdoctoral Researcher
Teixeira Barbosa Costa, José Diogo

Postdoctoral Researcher
Álvarez Martínez, Víctor

PhD Candidate
Corral Sertal, Javier

PhD Candidate
Varela Domínguez, Noa

PhD Candidate

Research

We are a Solid State Chemistry and Physics group with a broad range of research interests, our main research lines at this moment are:

  • Heat transport at the nanoscale
  • Spin-driven transport in magnetic layers and heterostructures
  • Memristors: material growth, microfabrication and applications

 

Heat transport at the nanoscale

The rapid advancement of the electronics industry, together with the continuous miniaturization of devices, has made heat management a critical challenge. In this context, our research focuses on understanding and controlling thermal transport in thin films, from passive thermal conduction to actively tunable systems. We investigate thermal transport in engineered heterostructures, where interfaces play a decisive role. We uncover the microscopic mechanisms that govern heat transport in metal-oxide interfaces, which are ubiquitous in modern electronic devices.

Figure 1. a) Schematic representation of the systems used to study thermal transport across metal-oxide interfaces. b) Experimental thermal boundary conductance (TBC) of all the interfaces studied. Each color represents a metal, regardless of the oxide with which it forms the interface.

We also study oxide superlattices, formed by stacking ultrathin layers with nanometer precision. In these systems, thermal transport is mainly determined by the total thickness and superlattice periodicity. We have demonstrated that an extra degree of control can be achieved in ferroelectric superlattices of PbTiO3/SrTiO3, where the 3D organization of complex polarization patterns suppresses heat conduction. Importantly, these polar textures are sensitive to environmental disruptions such as temperature or electric fields, enabling post-synthesis modulation of thermal transport.

For the experimental measurements we use Frequency Domain Thermoreflectance (FDTR) and the 3-omega method, both available in our laboratory.

Figure 2. a,b) High resolution STEM images of a PbTiO3/SrTiO3 superlattice at increasing magnification. c) Polar displacement map revealing complex polarization patterns in the form of polar vortices. d) Reciprocal space map, showing satellite reflections associated with the vortices (V) and their three-dimensional ordering into a polar supercrystal (SC). (e) Thermal conductivity as a function of temperature, highlighting its dependence on the thermal stability of these ferroelectric textures.

Moreover, we exploit freestanding oxide membranes as a versatile integration platform. By growing high-quality films on optimized substrates and subsequently releasing and transferring them, we overcome conventional substrate constraints while preserving functional properties. This approach enables the integration of oxides onto otherwise incompatible substrates and opens new pathways to tailor thermal transport in complex systems. The stacking of such membranes further expands design possibilities for multifunctional heterostructures, although the increasing density of weakly bonded interfaces dominates thermal transport, making efficient heat dissipation a primary concern.

Figure 3. a) Cross section TEM image of as-grown SrRuO3 on SrCoO2.5 sacrificial layer and SrTiO3 substrate. b) Optical image of a single 5x5 mm free standing SrRuO3 membrane on a polymethyl methacrylate (PMMA). c) Cross section TEM image of the interface between 2 free standing SrRuO3 membranes. d) Equivalent thermal resistance of SrTiO3 and SrRuO3 superlattices and the effect of interface reconstruction on the thermal resistance by an annealing. In the inset an optical image of a SrTiO3 is shown.

In parallel, we are also interested in developing strategies to actively control thermal conductivity in complex oxides by applying an external stimulus. A key mechanism is the manipulation of oxygen vacancies, which act as atomic-scale defects that scatter phonons and hinder heat transport. For example, we have demonstrated that the local accumulation of oxygen vacancies in charge-transfer oxides (such as SrFeO3-x, La0.6Sr0.4CoO3) can be induced by the strong electric field generated with a biased atomic force microscope tip. This process leads to a reduction of thermal conductivity of up to ≈35%, enabling the creation of non-volatile thermal states with sub-micrometric spatial resolution. These states can be reversibly erased by mild thermal annealing in air, providing a pathway to dynamically and locally tune heat transport on demand.

Figure 4. a) Schematic representation of the electric-field modulation of oxygen vacancies: applying a negative bias with an AFM tip drives and accumulates oxygen vacancies (red spheres) in the scanned region, with concentration depending on the applied voltage. b) Optical image of four regions of a SrFeO3-x thin film patterned at different tip biases, showing progressive surface darkening. c) Corresponding thermal conductivity map, revealing a monotonic decrease in thermal conductivity with increasing electric field.

 

Spin-driven transport in magnetic layers and heterostructures

Our research focuses on spin-driven transport phenomena in magnetically ordered systems and related heterostructures. In particular, we explore spin-based thermoelectric conversion through the spin Seebeck and anomalous Nernst effects, as well as the control of thermal transport using external stimuli such as magnetic and electric fields, by exploiting the interplay between spin, charge and lattice degrees of freedom. An emerging direction of interest is the study of altermagnets, a new class of magnetic materials that may enable unconventional spin-transport and spin-caloritronic effects despite their vanishing net magnetization.

Figure 5. Left: geometry of the spin Seebeck effect measurement. Middle and right panels show the spin-based transport and thermoelectric properties of SrRuO3 film: anomalous Hall (middle) and anomalous Nernst effects (right).

 

Memristors: material growth, microfabrication and applications
Figure 6. Fabricated memristor crossbar array (right) and the printed circuit board (PCB) with mounted devices for microelectronic device test.

Finally, we have started a new research line on memristive devices for next-generation computing, covering the entire process from materials growth to functional applications. We explore pulsed laser deposition (PLD) to grow complex-oxide thin films with tailored ionic and electronic properties. These films are subsequently processed through microfabrication to produce memristive devices and arrays, which are electrically characterized to understand and control resistive-switching mechanisms, particularly those driven by oxygen-vacancy migration. In collaboration with CiTIUS, these devices are then leveraged to demonstrate emerging computing concepts, including in-memory and neuromorphic computing, reservoir computing, and unconventional applications that directly harness the intrinsic ionic dynamics of memristors.

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