Theoretical Physics Group
Group Leader: Pedro Bicudo
The members of the Theoretical Physics Group are experts in the area of Quantum Matter and Information, in particular in the topics of Condensed Matter Physics and of Hadronic and Nuclear Physics, where CeFEMA is a leading research unit of IST.
Condensed Matter Physics
In the area of Condensed Matter Physics, the group develops several projects with topics ranging from low-dimensional systems, magnetic and superconducting materials and topological matter to quantum chaos and quantum information. Our main topics are described below.
Topology provides a guiding principle for the classification of phases of matter. The recent classification of gapped non- interacting systems – topological insulators and superconductors – relies on the fact that two systems in the same phase share the same momentum space topology. Some gapless materials, such as nodal loop semimetals, also have non-trivial phase space topology. One line of work of our group is to study the robustness of these topological phases to disorder and interactions.
Information-Based Characterization of Phases of Matter
This research line consists of applying information theory methods and concepts to the study and characterization of condensed matter systems and phase transitions. We have explored the use of quantum fidelity to detect phase transitions at zero and, recently, at finite temperature. We have also been interested in understanding how to manipulate Majorana fermions in topological superconductors as a route to implement topological quantum computation.
Non-Equilibrium and Strongly-Correlated Quantum Materials
Non-equilibrium open quantum systems fundamentally differ from their closed equilibrium counterparts as exchanges with the environment induce decoherence, dissipation and finite thermodynamic flows. This opens up a possibility for novel physical phenomena that are hard or even forbidden to realize in equilibrium. We work on several aspects of non-equilibrium systems including: Non-equilibrium ordered phases; Open quantum dynamics; Periodically driven systems; Non-equilibrium critical phenomena.
Historically, the group has been involved in several aspects related to superconducting materials, namely high-temperature superconductors and iron pnictides. While our focus has shifted in the last few years, we continue to be interested in the study of superconductivity in novel materials and to identify and characterize mechanisms to enhance superconducting correlations.
In low dimensions, quantum and thermal fluctuations are particularly important and sometimes preclude the appearance of order. This gives rise to many interesting phenomena including liquid phases that fail to order down to zero temperature and may support fractional excitations. Another interesting aspect of 2D physics is the recent experimental discovery of unexpected transport properties in twisted bilayer graphene. Our work on 2D materials can be divided into two main categories: the study of bilayer graphene structures, including transport and interaction effects, and the use of effective models to explore strongly interacting systems with liquid-like features.
Hadronic and Nuclear Physics
In hadronic and nuclear physics, we have projects on QCD-inspired non-perturbative methods and models applied to the study of QCD vacua, confinement, symmetries, hadrons, exotic hadrons, nuclear physics beyond the drip-lines and the study of exotic nuclei.
Physical concepts and methods are common to the areas of physics of strongly interacting and strongly correlated systems, and fruitful interchanges of ideas and experience will be pursued.
Resonances and Excited Phases of QCD
Recently, exotic hadrons such as tetraquarks or hybrids, finally have been observed experimentally. Recently we confirmed with lattice QCD techniques the udbb tetraquarks. We will develop the theoretical techniques to study quantitatively exotic resonances such as the tantalizing Zb, Zc and Pi1 new resonances.
A unitarised quark model and unitary data-analysis methods, all S-matrix based, will also be used to describe meson resonances like e.g. scalar charmonium states, the a1(1420), and the controversial rho(1250). Also, the tentative E(38) scalar boson at 38 MeV, will be further studied.
We study excited QCD vacua, the replicas. Due to the non-linearity of the Mass gap, or Dyson-Schwinger equations, several solutions for the vacuum stability may occur. This has been demonstrated with entire classes of confining potentials. We will study in more detail the different replicas and their stability.
High Performance Computation in QCD
We apply High Performance Computing and utilize GPUs for massively parallel processes. c++ and CUDA codes for CPU and GPU servers to develop non-perturbative field theory, including Lattice QCD. We had NVIDIA grants supporting our research, and this boosted our research, requiring HPC codes and servers.
Nuclei at the Extremes of Stability
To establish how nucleosynthesis processes evolve with time, is one of the main goals of contemporary Nuclear Physics. This requires the experimental access to new nuclei with exotic configurations at the extremes of spin, and isospin, and to determine their nuclear structure. With our models, we can interpret accurately new features of proton rich nuclei, that can be effectively used to discuss the feasibility of new experiments, providing the theoretical support to guide their search, and interpret the experimental data.