【Seminars】Special Seminars by Prof. Mauro Ferreira and Prof. Wolfgang Belzig
Information
Date
September 24, 2015 14:00 – 16:00
Venue
TOKYO ELECTRON House of Creativity 3F, Lecture Theater, Katahira Campus, Tohoku University【Access】
Speakers
Mauro Ferreira (Trinity College Dublin, Ireland)
Wolfgang Belzig (University of Konstanz, Germany)
Titles and Abstracts
Prof. Mauro Ferreira, Trinity College Dublin, Ireland
Title:
Friedel oscillations in graphene: from flawed DFT calculations to sublattice segregation of dopants
Abstract:
Friedel oscillations are fluctuations on the local density of states that arise whenever the underlying symmetry of a material is broken. While such oscillations are ubiquitous in many nanoscale structures, they may be hidden in graphene-based materials due to the peculiar symmetry of these systems. We argue that these unusual features may: (i) have an impact in Density Functional Theory (DFT) calculations in graphene and (ii) explain the sublattice asymmetry seen in doped graphene structures.
Prof. Wolfgang Belzig, University of Konstanz, Germany
Title:
Cooling a nanomechanical resonator using spin-dependent and superconducting electron transport
Abstract:
An important challenge in the development of nano-electronic devices is the electric control of nanoelectronic excitations such as photons, phonons or mechanical vibrations. An interesting perspective is the engineering of quantum states for such excitations, for which the ability of cooling a necessary condition, for instance, to prepare a resonator in its quantum ground state.
I will discuss the quantum transport in a quantum dot coupled to a mechanical resonator at low temperature. This can e.g. be realized with a carbon nanotube quantum dot suspended between two electric nanocontacts. Due to the interaction between electrons and flexural mechanical eigenmodes, the electron transport results in inelastic, vibrational-assisted tunneling processes. These give rise to a mechanical damping and, for an applied bias-voltage, a steady non-equilibrium phonon occupation of the resonator. I will discuss these effects for two different coherent transport regimes: (i) spin-polarized current between two ferromagnets and (ii) sub-gap Andreev current between a superconductor and normal metal. I will show that the vibrational energy can be efficiently controlled by varying the transport parameters, e.g. the gate voltage, magnetic field, orientation of the ferromagnetic leads, etc. Active ground state cooling of the resonator can be achieved for realistic parameters of the system. Finally, I will discuss the signatures of the non-equilibrium nanomechanical motion in the current-voltage characteristic.