Zero--energy Majorana modes in condensed matter physics

dr inż. Anna Gorczyca-GoraZakład Fizyki Teoretycznej, Instytut Fizyki UŚ,

05.04.2019, 12:00 w sali A/1/04

Quasiparticles induced at the edges of spinless ($p$-wave) 
superconducting sample in one or two dimensions have the exotic 
character of zero-energy bound states. These emergent Majorana-type 
objects have been predicted in various systems, such as topological 
insulators, semiconducting nanowires, ferromagnetic chains coupled to 
$s$-wave superconducting reservoirs. The most convincing experimental 
evidence for the zero-energy Majorana modes has been provided so far by 
the tunneling measurement using the nanoscopic chains proximity coupled 
to the $s$-wave superconducting reservoir.

In my talk I will discuss the properties of the inhomogeneous Rashba 
chain coupled to a superconducting substrate, hosting the Majorana 
quasiparticles near its edges. Despite common belief that the Majorana 
quasiparticles are robust to environmental influence, our results 
indicate that this is not truly the case and reveal that sufficiently 
strong disorder would be detrimental for the Majorana quasiparticles, 
causing a transition from the topologically nontrivial to trivial 
superconducting phases. On the other hand, single quantum impurities 
have also very unusual interplay with the Majorana quasiparticle states. 
Under specific conditions they can effectively induce additional pairs 
of the Majorana states.

Yet, the Rashba chain model has its limitations important for 
experimental realization. That is why we propose another model of 
experimental relevance, namely  a chain of the localized magnetic 
impurities whose moments are coupled to the spins of itinerant 
electrons, deposited on a surface of  $s$--wave bulk superconductor. 
With use of Monte Carlo simulations we have checked thermal stability of 
Majorana modes and estimated $T_c$.This evaluation should also be taken 
into account when considering future applications of the Majorana 
quasiparticles for quantum computing.