Full text
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| Author(s): |
Lucas Madeira
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2015-03-08 |
| Examining board members: |
Silvio Antonio Sachetto Vitiello;
Alex Antonelli;
Arnaldo Gammal
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| Advisor: | Silvio Antonio Sachetto Vitiello |
| Abstract | |
In this dissertation we investigated two many-body systems. For the first part we chose a classical approach to study the adsorption of heavy rare-gases, Ne, Ar, Kr, Xe and Rn, on graphene substrates. We presented evidences of commensurate adlayers, which depend strongly on the symmetry of the substrate, for two structures: Ne adlayers in the sqrt{7} X sqrt{7} superlattice and Kr in the sqrt{3} X sqrt{3} lattice. In order to study the melting of the system we introduced an order parameter, and its susceptibility. The specific heat and susceptibility as a function of the temperature were calculated for the heavy noble gases at various densities. The position and characteristic width of the specific heat and susceptibility peaks of these systems were determined. Finally, we investigated the first neighbor distance and the distance between the adlayer and the substrate, identifying contributions related to specific heat and melting peaks. The second part of the dissertation deals with a vortex line in the unitary Fermi gas. Ultracold Fermi gases are remarkable due to the experimental possibility to tune interparticle interactions through Feshbach resonances, which allows the observation of the BCS-BEC crossover. Right in the middle of the crossover lies a strongly interacting state, the unitary Fermi gas. A vortex line corresponds to an excitation of this system with quantized units of circulation. We developed wavefunctions, inspired by the BCS wavefunction, to describe the ground state and also for a system with a vortex line. Our results for the ground state elucidate aspects of the cylindrical geometry of the problem. The density profile is flat in the center of the cylinder and vanishes smoothly at the wall. We were able to separate from the ground state of the system the wall contribution and we have determined the bulk energy as epsilon_0=(0.42 +- 0.01) E_{FG} per particle. We also calculated the superfluid pairing gap for this geometry, Delta=(0.76 +- 0.01) E_{FG}. For the system with a vortex line we obtained the density profile, which corresponds to a non-zero density at the core, and the excitation energy, epsilon_{ex}=(0.0058 +- 0.0003) E_{FG} per particle. The methods employed in this dissertation, Molecular Dynamics, Variational Monte Carlo and Diffusion Monte Carlo, give us a solid basis for the investigation of related and other many-body systems in the future (AU) | |
| FAPESP's process: | 12/24195-2 - Heavy rare-gas atoms adsorbed on graphene |
| Grantee: | Lucas Madeira |
| Support Opportunities: | Scholarships in Brazil - Master |