Семинар международной лаборатории физики конденсированного состояния: D. Ghazaryan, (University of Manchester) "Tunneling spectroscopy in Van der Waals heterostructures"

  В среду 23 мая 2018 в 11:30

состоится научный семинар Международной лаборатории физики конденсированного состояния НИУ ВШЭ

Davit Ghazaryan
(University of Manchester)

Tunneling spectroscopy in Van der Waals heterostructures

 Abstract:

I would report on the study of the tunnel effect in van der Waals heterostructures assembled from two-dimensional crystals of various materials. The talk would be devoted to shed a light on three conceptually different tunnelling structures; (i) graphene-hexagonal boron nitride-graphene tunnel transistors, (ii) graphene-two dimensional ferromagnetic semiconductor-graphene junctions, (iii) graphene-hexagonal boron nitride-two dimensional superconductor junctions.

The field-effect vertical tunnel transistors constructed of atomically thin graphene and hexagonal boron nitride layers are an exceptional platform for the study of various resonant mechanisms due to their outstanding synergetic properties. I will report on the realization of (a) the inelastic phonon-assisted resonant tunnelling process, (b) sequential resonant tunnelling apparatus through the localized electronic states of hexagonal boron nitride, and most important, (c) the twist controlled resonant tunnelling process in vertical tunnelling transistors, which consists of monolayer/bilayer graphene electrodes. The latter is prompted by the precise crystallographic alignment of graphene layers, where the momentum mismatch between the Dirac cones is compensated by the energy obtained from the electrostatic field. Notably, the momentum of tunnelling electrons is conserved within such an event, therefore, owing to a peculiar property of graphene, the momentum-pseudospin coupling, it was possible to both directly visualize and control the chiral quantum state of electrons (holes), which is of a fundamental importance for the graphene physics, and condensed matter physics in general.

Recently, the family of two-dimensional materials has been expanded to include both ferromagnetic semiconductors and unconventional superconductors. I will show that a few layers of exfoliated CrBr₃ are ferromagnetic, by characterizing functional tunnel devices, where a CrBr₃ layer is sandwiched in-between graphene electrodes. Also, I will report on a new type of tunnelling mechanism in van der Waals heterostructures by demonstrating that electrons in such a junction are tunnelling with the help of an emission (and, at high temperature, absorption) of magnons within the CrBr₃ layer. Additionally, I will show that NbSe₂ remains superconducting down to the thicknesses of a monolayer, by electrical measurements of graphene-hexagonal boron nitride-NbSe₂ tunnel junctions, where in particular, a fully developed gap that is rapidly reduced with the layer thickness is demonstrated.

Семинар пройдет в помещении факультета физики и лаборатории по адресу:

ул.Ст. Басманная, 21/4, стр. 5, ауд. Б-312.

При необходимости заказа пропуска в НИУ ВШЭ обращайтесь к Ирине Аванесовой, iavanesova@hse.ru

Начало в 11:30.