#### Theoretical Physics Group

Group Leader: Pedro Sacramento

The Theoretical Physics Group promotes research in the areas of Physics and Mathematical Physics. The research activity has been centred on the study of non-perturbative phenomena. The main areas are Condensed Matter Physics, Hadronic and Nuclear Physics, Differential Geometry and Relativity.

In the area of condensed matter physics, we have had projects in the areas of low-dimensional systems and materials, spintronics, cold atoms, superconductivity and quantum information. In hadronic and nuclear physics, we have had projects on QCD-inspired non-perturbative methods and models applied to hadrons, nuclear physics beyond the drip-lines and the study of exotic nuclei.

The current work of the group concentrates, on the one hand, on work on theoretical physics to study fundamental properties of quite varied systems, over various energy scales, and on the other hand on possible applications in materials science. Physics thrives on analogies and the varied expertise of the group members will be used to provide a better understanding of unifying properties of different systems, ranging from condensed matter physics to nuclear and hadronic physics. 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. Also, various aspects of physical systems involve geometrical aspects and a growing importance of topology in physical systems establishes a strong link to mathematics such as differential geometry.

An important part of the work will focus on possible technological applications such as in the context of devices relevant to spintronics, fast spin dynamics in various configurations and using various methods to induce changes in spin orientation, and in the search for engineering materials (such as nanograins) with enhanced superconducting transitions of great technological potential. Also, an important goal is to contribute to the wide effort to construct a useful quantum computer based on a technology of condensed matter systems. In particular, we will be involved with possible technological uses of states that emerge in topological systems, such as the Majorana fermions predicted in topological superconductors.

#### Current and future interests

##### Search for new phases of matter

Study of the interplay between electron-electron and electron-lattice interactions in graphene and related systems (bilayer, trilayer). The electron-lattice coupling in graphene is very unusual and, when complemented with electron-electron interactions, is expected to lead to novel phases of matter.

Study of possible intrinsic magnetism, superconductivity and topological phases in novel 2D materials (transition metal dechalcogenides, silicene) including topological superconductors. Hybrid heterostructures of graphene and novel 2D materials are then expected to have new functionalities with technological potential.

In the search for novel phases of matter, the study of bosonic systems in optical lattices allows mappings to spin Heisenberg Hamiltonians or Josephson junction arrays.

##### Dense and condensed systems

Continuation of the study of superconductivity in novel materials, and identification and characterization of theoretical mechanisms that enhance superconductivity. Also, superconductivity in nanostructures, heterostructures and interfaces, exotic/novel forms of superconductivity based on Efimov physics, topological and holographic superconductivity. Holographic methods will be used to study universal properties of strongly correlated systems.

##### Spintronics

Theory of spin dynamics in magnetic materials and nanostructures induced by ultrafast optical injection of charge and magnetic excitations will be developed and subsequent relaxation and long-term dynamics will be studied.

We will be working on a method of characterization of the magnetic tunnel junctions by measuring the shot noise in magnetic structures, and plan to identify important parameters like spin relaxation time and electron correlation energy.

##### Application of information theory

Applications of information theory methods and concepts to the study and characterization of condensed matter systems and phase transitions, namely fidelity.

Manipulation of Majorana fermions in topological superconductors as a possible application to topological quantum computers.

##### Systems far from equilibrium

An important part of the work will be focused on the study of non-equilibrium phase transitions and conditions, and a route to thermalization in strongly interacting systems using conventional methods and holographic techniques. In particular, we will focus on the dynamics of transitions to topological phases.

##### Nuclei far from stability

We plan to achieve a consistent understanding of the structure of exotic odd-even and odd-odd nuclei at the extremes of stability;

To extend the self-consistent relativistic density functional formalism based on realistic interactions and describe exotic decays of deformed nuclei; To study process of nuclear astrophysics, and nuclear reactions where a realistic equation of state derived from many body theory is relevant.

##### Resonances and bound states

Fractionalization and confinement of degrees of freedom in low-dimensional systems will be studied. Conditions for the formation of bound-states will be studied in the context of scattering theories and the Bethe-Salpeter equation.

Further employment of Resonance-Spectrum Expansion, both for scattering and production processes. More empirical analysis of mesonic production data, to be modeled with resonances and threshold effects. Search for additional data supporting light E(38) boson. Model description of oscillations and CP violation in K, D, and B sectors due to W-boson width.

##### Differential geometry and applications to physical systems

Comparison of results on the principal eigenvalue of a drift-gradient Laplace operator on compact domains of manifolds. Minimum principles, Rayleigh-type inequalities, diffusion equation. Isoperimetric inequalities for periodic regions with symmetries with applications in crystallography and materials, least area interfaces separating two liquids.

Geometric phases and their connection to physical problems will be pursued.