Quantum monte carlo study of bosonic quantum solids at zero temperature

• Autores: Claudio Cazorla Silva
• Directores de la Tesis: Jordi Boronat Medico (dir. tes.)
• Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2006
• Idioma: español
• Tribunal Calificador de la Tesis: Manuel Barranco Gómez (presid.), Ana María Serra Tort (secret.), Marco Zoppi (voc.), Antonio Jesús Sarsa Rubio (voc.), Frederic Caupin (voc.)
• Materias:
  • Física
    • Física de fluidos
      • Fluidos cuánticos
    • Física atómica y nuclear
      • Átomo de helio
    • Física del estado sólido
    • Termodinámica
      • Bajas temperaturas
• Texto completo no disponible (Saber más ...)
• Resumen

  • Quantum solids conform an intriguing class of crystals where quantum effects have a leading relevance. Contrarily to their classical counterparts, quantum solids present an unusually large kinetic energy and atomic mean squared displacement of the particles around the equilibrium positions of the crystalline lattice. By large it is understood, a kinetic energy similar in magnitude to short-range interactions and a mean squared displacementcomparable to the distance between nearest positions in the perfect lattice (large Lindemann's ratio). In fact, the constituents of these solids are characterized by small atomic masses, and the interactions acting among them are weakly attractive. From a thermodynamic point of view, quantum solids are described by large compressibilities, low Debye temperatures and speeds of sound, non-ordinary melting properties, anharmonicity, etc. Point and line defects (vacancies, dislocations, etc.) are easily formed on their interior due to the wide excursions of the atoms around the lattice sites. These structural defects are expected to exist in quantum solids even at absolute zero temperature.

    Some illustrative examples of quantum solids are 4He, 3He, H2, D2, LiH and LiD. In the outstanding case of solid helium, the possibility of superfluid-like behaviour has resulted in a long-standing topic of intense speculation.

    Recent experiments carried out by E. Kim and M. H. Chan in solid 4He, seem to allow the existence of a practically suppressed superfluid fraction below 0.2K (~1-2%).

    Early in the 60's, Quantum Monte Carlo (QMC) methods emerged in close relation to quantum many-body problems posed in the field of condensed matter. The QMC approach is a fully quantum one (it does not rely on any basic assumption or approximation), which it is best suited to deal with systems where quantum effects are dominant. The basic strategy underlying QMC methods is stochastic, that is, random number generation and probabilit