Ofertes de Feina i Beques Ofertes de Feina
Select Page
Seminaris
21 de juny 2024
SEMINAR | Correlated electron states in multilayer graphene: from superconductivity to half-integer quantum Hall effects

Hora: Des de 12:00h a 13:00h

Lloc: Seminar Room

SEMINAR | Correlated electron states in multilayer graphene: from superconductivity to half-integer quantum Hall effects

MARC BOCKRATH
The Ohio State University

Thin graphite flakes behave as two-dimensional conductors in sufficiently high magnetic fields, with quantum Hall states extended throughout the bulk of the flake for low doping, and confined to the surfaces for large doping. I will discuss our observation of half-integer fractional quantum Hall states at large total filling factors. These single-component states likely stem from Pfaffian wavefunctions derived from those in graphene bilayers, which are predicted to host nonabelian quasiparticles. The facile integration of graphite with top and back surface gates makes this an excellent system to explore device geometries capable of manipulating such quasiparticles. Moreover, the group velocity $v_F$ of the electrons in a flat band superconductor is extremely slow, resulting in quenched kinetic energy. Superconductivity thus appears impossible, as conventional theory implies a vanishing superfluid stiffness, coherence length, and critical current. Using twisted bilayer graphene (tBLG), we explore the profound effect very small $v_F$ in a superconducting Dirac flat band system. We find an extremely slow $v_F\sim$ 1000 m/s for filling fraction between -1/2 and -3/4 of the moiré superlattice. This velocity yields a new limiting mechanism for the superconducting critical current, with analogies to a relativistic superfluid. We estimate the superfluid stiffness, which determines the electrodynamic response of the superconductor, showing that it is not dominated by the kinetic energy, but by the interaction-driven superconducting gap, consistent with recent theories on quantum geometric contributions.

Hosted by Prof. Dr. Adrian Bachtold
Seminaris
21 de juny 2024
SEMINAR | Correlated electron states in multilayer graphene: from superconductivity to half-integer quantum Hall effects

Hora: Des de 12:00h a 13:00h

Lloc: Seminar Room

SEMINAR | Correlated electron states in multilayer graphene: from superconductivity to half-integer quantum Hall effects

MARC BOCKRATH
The Ohio State University

Thin graphite flakes behave as two-dimensional conductors in sufficiently high magnetic fields, with quantum Hall states extended throughout the bulk of the flake for low doping, and confined to the surfaces for large doping. I will discuss our observation of half-integer fractional quantum Hall states at large total filling factors. These single-component states likely stem from Pfaffian wavefunctions derived from those in graphene bilayers, which are predicted to host nonabelian quasiparticles. The facile integration of graphite with top and back surface gates makes this an excellent system to explore device geometries capable of manipulating such quasiparticles. Moreover, the group velocity $v_F$ of the electrons in a flat band superconductor is extremely slow, resulting in quenched kinetic energy. Superconductivity thus appears impossible, as conventional theory implies a vanishing superfluid stiffness, coherence length, and critical current. Using twisted bilayer graphene (tBLG), we explore the profound effect very small $v_F$ in a superconducting Dirac flat band system. We find an extremely slow $v_F\sim$ 1000 m/s for filling fraction between -1/2 and -3/4 of the moiré superlattice. This velocity yields a new limiting mechanism for the superconducting critical current, with analogies to a relativistic superfluid. We estimate the superfluid stiffness, which determines the electrodynamic response of the superconductor, showing that it is not dominated by the kinetic energy, but by the interaction-driven superconducting gap, consistent with recent theories on quantum geometric contributions.

Hosted by Prof. Dr. Adrian Bachtold
This site is registered on wpml.org as a development site. Switch to a production site key to remove this banner.