Ultrafast All Optical Control of the Magnetization
Fig1: Experimental setup (left) and results (right) where single laser shots are used for switching the magnetization of a GdFeCo ferrimagnetic films. The magneto-optical micrographs (right) represent the magnetization of the FeCo lattice of the sample. The optically switched domain (contrasted circular region) has been shown to be strongly dependent on the laser fluence. Figures extracted from Ref.
In 1996 it was discovered that the magnetization of a Ni film could be quenched in less than a picosecond . This triggered the field of ultrafast magnetism, where the main objective is to understand the dynamics of the magnetization in the femtosecond-picosecond scales and ultimately to control it. In 2007 the first all-optically (laser) induced picosecond-switching of the magnetization was achieved in a GdFeCo ferrimagnet , (as shown in Fig.1) and has since been reproduced in different systems. However, a good understanding of the underlaying mechanisms is still lacking.
Following up on these exciting experiments and with the goal of shining some light on such open questions, his research group is studying the ultrafast demagnetization and all-optical switching in different systems by the combination of different magneto-optical techniques (MOKE, MSHG…).
 E. Beaurepaire et al., Phys. Rev. Lett. 1996
 C. Stanciu et al., Phys. Rev. Lett 2007
 K. Vahaplar et al., Phys. Rev. B 2012
Atomically Precise Graphene Nanoribbon Devices
Figure 1. STM of synthesized GNRs
Figure 2. Fabricated GNRFET
Chemically synthesized graphene nanoribbons (GNRs) present an attractive alternative to carbon nanotubes as high performance semiconducting channel material. Because of their deterministic growth process, these GNRs possess identical electronic properties en masse and, unlike other GNRs, lack rough edges that potentially reduce mobility and transport.
Jeffrey Bokor's research group develops the techniques required to integrate these GNRs into electronic devices, enabling us to measure and characterize their electronic response directly through transport and optical spectroscopy. Working directly with chemists and physicists, they are developing new synthesis methods and precursors that improve device performance and yield, while also developing fabrication techniques that enable electrical probing of molecular heterojunctions at the nanometer scale.
In the News
Experiments show magnetic chips could dramatically increase computing’s energy efficiency.
Information theory dictates that a logical operation in a computer must consume a minimum amount of energy. Today’s computers consume a million times more energy per operation than this limit, but magnetic computers with no moving electrons could theoretically operate at the minimum energy, called the Landauer limit, according to UC Berkeley electrical engineers.
In early May, Intel announced a radical new transistor design: a 3D device that will enable the production of integrated-circuit chips that operate faster with less power. The breakthrough has its roots in research begun in 1997 by a team led by Berkeley electrical engineers Chenming Hu, Jeff Bokor and Tsu-Jae King Liu.