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UID:DSC-19780
DTSTART;TZID=Europe/Berlin:20230512T100000
SEQUENCE:1683869860
TRANSP:OPAQUE
DTEND;TZID=Europe/Berlin:20230512T110000
URL:https://dresden-science-calendar.org/calendar/en/detail/19780
LOCATION:IFW\, Helmholtzstraße 2001069 Dresden
SUMMARY:Zaccone: Topological transition due to quantum confinement in thin 
 superconductor films
CLASS:PUBLIC
DESCRIPTION:Speaker: Prof. Dr. Alessio Zaccone\nInstitute of Speaker: Unive
 rsity of Milan\, Department of Physics \nTopics:\n\n Location:\n  Name: IF
 W (A1E.10\, Hörsaal\, IFW Dresden)\n  Street: Helmholtzstraße 20\n  City
 : 01069 Dresden\n  Phone: \n  Fax: \nDescription: The quantum states of pa
 rticles in materials and devices are the solutions of the Schr&amp\;amp\;#
 1255\;dinger equation in a “box” of a certain shape\, in the space dimen
 sionality of interest. There is always the question of what to do with the
  boundary conditions at the walls: These must be irrelevant for a large sy
 stem\, but they may be important for mesoscopic systems at the nano-scale.
  I will start from the basic principle that shrinking a 3D material along 
 one of the three space dimensions puts a restriction on the propagation of
  quantum waves inside the material [1\,2]. This leads to a number of state
 s in momentum space that remain unoccupied. For the simple example of boso
 ns (e.g. phonons) the problem admits an analytical solution valid for thin
  films\, from which we can compute fundamentally new laws\, and surprising
  effects for the phonon density of states of thin films at low energy [3]\
 , the elasticity of thin films [1]\, as well as Bose-Einstein condensation
  in thin films [4]. The same principle can be applied to the distribution 
 of quantum states of electrons in confined metallic systems such as superc
 onducting thin films. In particular\, the Fermi sphere develops two spheri
 cal cavities of unoccupied states that grow upon shrinking the film thickn
 ess. By implementing this model within the BCS theory of superconductivity
 \, the critical superconducting temperature can be calculated as a functio
 n of film thickness in good agreement with experiments on Pb thin films\, 
 with a strong enhancement of the Tc upon decreasing the thickness followed
  by a maximum and a decrease to zero upon approaching the 2D limit (in acc
 ord with the Mermin-Wagner theorem) [5]. Intriguingly\, as the two spheric
 al cavities keep growing\, a new topological transition in the Fermi surfa
 ce of metallic thin films is predicted [5]\, which is different from any p
 reviously known topological transitions of the Fermi surface (e.g. the Lif
 shitz transition). Interestingly\, previous numerical models based on hard
 -wall boundary conditions (e.g. Thompson-Blatt) predict large fluctuations
  of the Tc as a function of film thickness\, which are not visible in the 
 experimental data\, as the latter are instead very well matched by the new
  theory.  [1] A. Zaccone &amp\;amp\; K. Trachenko\, PNAS 117 (33) 19653-19
 655 (2020) [2] A. E. Phillips et al.\, Phys. Rev. Materials 5\, 035602 (20
 21) [3] Y. Yu et al.\, Nature Communications 13\, 3649 (2022) [4] R. Trava
 glino and A. Zaccone\, J. Phys. B: At. Mol. Opt. Phys. 55 055301 (2022) [5
 ] R. Travaglino and A. Zaccone\, J. Appl. Phys. 133\, 033901 (2023)
DTSTAMP:20260408T014922Z
CREATED:20230412T053618Z
LAST-MODIFIED:20230512T053740Z
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