Séminaire DQMP

Carte non disponible

Day / Time
Date(s) - 20/10/2015
1 h 00 min - 2 h 00 min

Category


Mardi 20 octobre 2015 à 13.00 heures

Auditoire Stückelberg

Ecole de physique

 

Professor Leonid S. Levitov

MIT

Department of Physics

 

Atomic Collapse in Graphene

Since the discovery that electrons in graphene behave as massless Dirac
fermions, the single-atom-thick material has become a fertile playground
for testing exotic predictions of quantum electrodynamics, such as Klein
tunneling and the fractional quantum Hall effect. Now add to that list atomic
collapse, the spontaneous formation of electrons and positrons in the
electrostatic field of a superheavy atomic nucleus. The atomic collapse was predicted to
manifest itself in quasistationary states which have complex-valued energies and
which decay rapidly. However, the atoms created artificially in laboratory have
nuclear charge only up to Z = 118, which falls short of the predicted
threshold for collapse. Interest in this problem has been revived with the advent of
graphene, where because of a large fine structure constant the collapse is
expected for Z of order unity. In this talk we will discuss the symmetry
aspects of atomic collapse, in particular the anomalous breaking of scale
invariance. We will also describe recent experiments that use scanning
tunneling microscopy (STM) to probe atomic collapse near STM-controlled
artificial compound nuclei.

Réalisation : Sur Mesure concept