Particule de Majorana | EPFL Graph Search

En physique des particules, une particule de Majorana ou fermion de Majorana est un fermion qui est sa propre antiparticule. Ces particules sont nommées en hommage au physicien Ettore Majorana, qui a proposé ce modèle en établissant l'équation qui porte son nom. Ce terme est parfois utilisé en opposition aux particules de Dirac (ou fermions de Dirac) qui ont une antiparticule différente d'elles-mêmes. Historique En 1928, Paul Dirac publie l'article qui contient l'équation de Dirac. Motivé par l'étude des électrons, l'article généralise l'équation aux particules de spin 1/2, mais impose des facteurs imaginaires. En 1937, Majorana revoit l'équation de Dirac et trouve une interprétation avec des facteurs réels. Les travaux de Majorana restèrent sans suite près de 20 ans quand la découverte des neutrinos en 1956 amène à réétudier ses résultats ; depuis, les travaux de Majorana sont régulièrement au cœur de la physique. Études théoriques et détection

Charge transport properties of spin-orbit coupled materials in different correlation regimes

Soudabeh Sheikholharam Mashhadi

From recent advances in solid state physics, a novel material classification scheme has evolved which is based on the concept of topology and provides an understanding of different phenomena ranging from quantum transport to unusual flavors of superconductivity. Spin-orbit coupling is a major term in defining the topology of materials, and its interplay with electron electron correlations yields novel, intriguing phenomena. In the weak to intermediate correlation regime, spin-orbital entanglement leads to the emergence of topological insulators, which constitute Dirac materials with 2D spin-polarized helical edge or surface states and an insulating bulk. In the specific case of topological insulators, theory predicts that their unique band structure leads to a high thermoelectric performance, which is of practical relevance for energy conversion applications.In the strong correlation regime, the spin-orbit coupling removes the orbital degeneracy, thereby enhancing quantum fluctuations of the spin-orbit entangled states. This in turn can lead to the emergence of novel phases such as quantum spin liquids and unconventional superconductivity. The Kitaev quantum spin liquid (QSL) is a topological state of matter that exhibits fractionalized excitations in the form of Majorana fermions. The main aim of this thesis was to study these novel states of matter in the form of two different materials that fall in the weak and strong correlation regime, respectively. On this basis, it should furthermore be explored whether benefit can be taken of their properties by combining them with other quantum materials into heterostructures.In the first part of this thesis, nanoplatelets of bismuth chalcogenide-based 3D topological insulators were grown by chemical vapor deposition, and characterized by magnetotransport experiments. Having established charge transport characteristics of the single components, in the aim to exploit their high thermoelectric efficiency, the lateral heteroctructures of them are fabricated. Their investigation by scanning photocurrent microscopy revealed strong photocurrent generation at the p-n junction. The obtained results demonstrate that such type of hybrid heterostructure is a promising route to enhance the thermoelectric performance in nanostructured devices. In the second part of this thesis, the Kitaev spin liquid candidate, RuCl3 was studied. Raman spectroscopy on exfoliated RuCl3 revealed a broad magnetic continuumat low energies which according to its particular deviation from bosonic character is assigned to the fractionalized excitations. Furthermore, in complementary charge transport experiments, it was found that themagnetic fluctuations and structural changes in thismaterial are highly entangled, and influence the emergence of the fractionalized excitations. Finally, it was investigated whether the magnetic insulator character of ®-RuCl3 can be exploited to alter the graphene band structure through a proximity effect in vertical graphene/ RuCl3 heterostructures. Measurements of their low-temperature, nonlocal resistance confirmed the possibility to induce pure spin currents in this manner. At the same time, the charge transport through the graphene served as a probe of the magnetic ordering in RuCl3, although the complex magnetic behavior in this material necessitates more studies.

EPFL2018

Initial state radiation in Majorana Dark Matter annihilations

Andrea De Simone

The cross section for a Majorana Dark Matter particle annihilating into light fermions is helicity suppressed. We show that, if the Dark Matter is the neutral Majorana component of a multiplet which is charged under the electroweak interactions of the Standard Model, the emission of gauge bosons from the initial state lifts the suppression and allows an s-wave annihilation. The resulting energy spectra of stable Standard Model particles are importantly affected. This has an impact on indirect searches for Dark Matter.

2011

Charge transport properties of spin-orbit coupled materials in different correlation regimes

Soudabeh Sheikholharam Mashhadi

EPFL2018