Technological progress made nowadays possible the design and patterning of new quantum materials with remarkable properties, and the investigation of known materials under unusual, yet controlled, conditions. One can gain control of crucial aspects, like the quantum confinement or the crystal strain, or endow a material with new characteristics. Within this context, we will investigate various systems that share some common properties, like being layered or nearly two-dimensional, hosting superconductivity, competing phenomena, the interplay of different bands, and/or disorder at different scales. We will study high-temperature cuprates and pnictide superconductors, oxide interfaces and transition metal dichalcogenides, hosting gate-tunable superconductivity, and disordered superconducting thin films. In these systems, the superconducting transition can be tuned changing the carrier density and/or the microscopic disorder. As a consequence of the competition of ordered phases with superconductivity, the electrons tend to be clumpy in these systems, and the charge density is modulated at the nanoscale. In cuprates, the competing phase is charge-ordered, and the related dynamical charge fluctuations may be responsible for superconducting pairing, and for the anomalies in the metallic phase, like a specific heath that seemingly diverges at low temperature, or a resistivity that is a linear function of the temperature down to very low temperature (the so-called Planckian behavior). We plan to improve our understanding of these intriguing phenomena. Moreover, cuprates, oxide interfaces, transition metal dichalcogenides, and disordered superconducting film, under some specific conditions, host an inhomogeneous, seemingly filamentary, superconducting state, whose equilibrium and non-equilibrium behavior will be thoroughly investigated. Some of these systems exhibit multi-band superconductivity, and the resulting variety of physical behaviors will be likewise investigated.
Our project addresses both fundamental properties and potential applications of quantum materials hosting superconductivity. A wealth of recent results trigger a renewed interest in these systems. Experimental evidence points to the ubiquitous presence of dynamical charge modulations in cuprates, and calls for a deeper understanding of their competition/interplay with superconductivity and their role in the strange metallic behavior observed in these systems. In transition metal dichalcogenides and oxide interfaces, the occurrence of nanoscale inhomogeneity calls for new paradigms, in view of potential device applications. Several open issues have been raised by the progresses in time-resolved spectroscopies, where the combination of intense fields and time resolution allows to follow the relaxation of system back to equilibrium. Our project is at the core of the current research in condensed matter physics, as it focuses on the interplay between superconductivity and dynamical or nearly static charge density modulations, and investigates the nanoscale inhomogeneity as an intrinsic emergent phenomenon in quantum materials. The proposal that electrons can be generically clumpy in low-dimensional superconductors, opens the possibility to design, pattern and manipulate the quantum properties of these materials. The details of tendency to inhomogeneity can be peculiar of the various materials and it is fundamental to identify the common aspects. The relevance and impact of our research is witnessed by the reference list, which includes many recent papers. Although the pivotal role of dynamical charge density modulations in cuprates was proposed by our group long ago [1], it found compelling experimental evidence only recently [2]. The consolidated collaboration with experimental groups active in RXS and transport experiments, allow us to define the details our theory, and gain a deeper understanding of these systems. Experiments on transition metal dichalcogenides and oxide interfaces attracted an increasing attention in the last years. We played a relevant role in this field too, assessing the inhomogeneous character of these systems [14-19,22] and providing possible microscopic explanations. A deeper understanding of the mechanisms at the root of this nanoscale inhomogeneity, will open the way to its patterning and control, in view of practical applications [33-35].