Transition metal oxides are considered to be the perfect candidate for the development of cheap, compact, green and energy-efficient devices because they are earth-abundant and can host a vast amount of electrical, magnetic, and optical properties. The structural quality of oxide heterostructures now rivals that of the best conventional semiconductors, allowing to envisage an oxide electronics era. However, for implementing such functional material systems in technological applications, it is necessary to understand how to control and engineer their properties at the nanoscale. In MULFOX, we investigate the evolution of these properties when two or more complex oxides are brought together. Various effects can take place including the change of lattice distortions (epitaxial strain), electrostatic coupling when materials with different polarity are involved (polar catastrophe), charge transfer via chemical potential shift, frustration due to sublattice connectivity (oxygen octahedra and tetrahedra), size effects due to reduced dimensionality, structure-periodicity tuning (superlattices) and so on. The idea is to explore the phase diagrams of complex oxide heterostructures to assemble the knowledge required for developing the technologies of tomorrow.

The role of reduced dimensionality and the structure of interfaces, point and planar defects, dislocations, etc, remains obscure in many cases but are central to macroscopic materials properties. Imaging interfaces and defects at sub-Angstrom resolution, and chemical mapping at atomic level are some of the hot points to be addressed in materials science.

We concentrate on establishing relations between the structure, chemistry and physical properties of transition-metal oxide nanostructures by means of scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). The recent successful correction of aberrations in electron optics allows us accessing the structure and chemistry of low dimensional materials due to its unparalleled spatial resolution, and combined with monochromated EELS it has the potential to probe optical excitations—plasmons, photons, excitons— with sub-nanometer resolution. This gives unprecedented power to understand the ultimate origin of the properties of materials at the nanoscale.

Solids may display a variety of order parameters, such as magnetic, polar, charge, orbital, etc. that determine complex phase diagrams where different properties are at display. Exciting prospects emerge towards new understanding that goes deep into the nature of condensed matter and its responsiveness and open perspectives of novel applications. 

Building on a long and wide expertise on transition metal oxides, our current research spans several branches. First, charge dynamics in transition metals oxides as a tool to explore charge-lattice coupling. Next, light-matter interaction in polar materials and heterostructures which offer new opportunities for above-band gap photoresponsive materials and sensing. Last, spin-orbit interactions in solids is emerging as new tool towards energy efficient spintronic devices. Whereas spin-orbit coupling in heavy metals is known and much used, plenty of room is still available for light transition metals, which are cheaper and more abundant, and were spin dynamics may offer new opportunities. 

Our research focuses on the development of superconducting radiation and particle detectors, operating at very low temperatures, for astrophysics, particle physics and quantum technologies. Each application requires development of suitable materials and designs, including absorbers, and the study of the relevant physical phenomena that determine their performances.  

Cryogenic detectors based on superconductors display unprecedented performances. Combining nearly zero dark counts, very low thresholds, excellent sensitivity and high quantum efficiency, they are essential for new instruments in astrophysics and cosmology, and are considered next frontier, strategic instrumentation, with applications in quantum technologies, security, biomedicine, environment and several industries.

Our research concentrates on the so-called Transition-Edge Sensors (TES); making use of a very sharp superconducting transition, they constitute extremely sensitive microcalorimeters and bolometers operating at temperatures far below 1K. We accumulate years of expertise in the development of Mo/Au based TES for X-ray astrophysics. Recently we have extended our interests towards the development of prototypes for (1) detection of lower energy photons, in the NIR-VIS-UV, for applications in photonics and astronomy; and (2) phonon detection for direct search of low-mass dark matter.

The focus is on electronic transport in bulk crystals and low-dimensional systems, and their interaction with light. We study quantum wells formed at the interface between transition metal oxides, with emphasis on spin-orbit physics and superconductivity. We also study the interaction of electromagnetic waves at optical wavelengths with transition metal systems and photonic crystals. 

We investigate electronic transport in oxide quantum wells in transition metal perovskites (involving, e.g., SrTiO3– and KTaO3- interfaces). Our focus is on Rashba spin-orbit fields and unconventional superconductivity for application in spintronics and quantum technologies. In parallel, we investigate light-matter interactions in different systems. In the area of photonic and plasmonic crystals, our interest is in achieving nonreciprocal propagation of confined electromagnetic waves, tunable with external fields, of interest for integrated photonic circuitry. On the other hand, we investigate the possibility of using electromagnetic waves to entangle spin and orbital degrees of freedom in transition metals. The idea behind is to explore theoretical models and find experimental optical signatures of spin-orbital mixing in strongly correlated systems that could serve as platform to achieve entanglement for quantum technologies.