Forum DQMP

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Day / Time
Date(s) - 21/02/2017
13 h 00 min - 15 h 00 min

Category


Tuesday, February 21st 2017 – 13h00
Auditoire Stückelberg
Ecole de physique
Coffee and tea will be available from 12h50 at the entrance of the Auditoire

  

Manifestation of ballistic transport in suspended graphene nanostructures
Dong-Keun Ki (group of Prof. Morpurgo)

Here, we report how technical advances in device fabrication can help us to reveal the ballistic transport properties of “defect-free” suspended graphene, and briefly discuss our recent understanding of the microscopic mechanism that governs the process. Due to technical limitations, suspended graphene has been realized mostly in a global-gated, two-terminal geometry, where the ballistic transport effects (which are expected for the devices with such a high quality) cannot be directly measured. To overcome this, we first realized local-gated suspended graphene devices, and found clear conductance oscillations originating from the ballistic Fabry-Perot interference inside the cavity formed between electrical contacts and the p-n junction created by the local gates. Secondly, we realized a multiterminal geometry and used it to observe negative four-terminal resistances, manifested due to the ballistic transport. At last, we briefly discuss our recent finding of the “new” mechanism that limits the ballistic transport in undoped graphene.

Quantum transport in many-body localized systems
Michele Filippone (group of Prof. Giamarchi)

Whether and how electron-electron interactions restore a finite conductivity in disordered systems undergoing Anderson localization is a longstanding problem in theoretical and experimental physics. Recent theoretical works argued that interactions in disordered systems drive a transition from a metallicphase to a completely new phase of matter called Many-Body Localization (MBL). In this phase, the system is supposed to be perfectly insulating for temperatures below a critical temperature Tc, to be unable to thermalize and to reliably store quantum information. In this talk, I will review recent theoretical and experimental progress concerning these systems and focus on their quantum transport properties. In particular, I will discuss the behavior of persistent currents in disordered one-dimensional rings hosting interacting electrons and show how persistent currents, in particular a strongly related quantity: Drude weights, give sensitive information about the MBL transition based on its transport properties.

Forum Committee : C.Lichtensteiger, A.Tamai, N.Ubrig (13.02.2017)

Réalisation : Sur Mesure concept