Jarillo-Herrero Group

Thiti succesfully defended his Thesis “From Hopping to Ballistic Transport in Graphene-Based Electronic Devices” today! Congratulations to him for being the first Jarillo Lab group member to defend!

Congratulations to Pablo for being awarded an ONR Young Investigator Award for “Quantum Transport and Optoelectronics in Atomically Layered Materials.” The MIT news article can be found here.

Congratulations to graduate student Thiti Taychatanapat for his paper being accepted to Nature Physics! A link to the preprint can be found here:
http://arxiv.org/abs/1301.1969

Electrically tunable transverse magnetic focusing in graphene
Thiti Taychatanapat, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero
Nature Physics (in press) arXiv:1301.1969

Electrons in a periodic lattice can propagate without scattering for macroscopic distances despite the presence of the non-uniform Coulomb potential due to the nuclei. Such ballistic motion of electrons allows the use of a transverse magnetic field to focus electrons. This phenomenon, known as transverse magnetic focusing (TMF), has been used to study the Fermi surface of metals and semiconductor heterostructures, as well as to investigate Andreev reflection, spin-orbit interaction, and to detect composite fermions. Here we report on the experimental observation of transverse magnetic focusing in high mobility mono-, bi-, and tri-layer graphene devices. The ability to tune the graphene carrier density enables us for the first time to investigate TMF continuously from the hole to the electron regime and analyze the resulting focusing fan. Moreover, by applying a transverse electric field to tri-layer graphene, we use TMF as a ballistic electron spectroscopy method to investigate controlled changes in the electronic structure of a material. Finally, we demonstrate that TMF survives in graphene up to 300 K, by far the highest temperature reported for any system, opening the door to novel room temperature applications based on electron-optics.

Congratulations to Postdoc Leonardo Campos for getting a faculty position at Federal University of Minas Gerais (UFMG) in Brazil! After 3 years in the group Leonardo will be moving on to start his own lab back in Brazil. All of us in the group wish him the best of luck in future research endeavors!

Congratulations to Leonardo, Andrea and North for their paper, “Quantum and classical confinement of resonant states in a trilayer graphene Fabry-Pérot interferometer” being published in Nature Communications!

Nature Communications 3, Article number: 1239 doi:10.1038/ncomms2243
Abstract
The advent of few-layer graphene has given rise to a new family of two-dimensional systems with emergent electronic properties governed by relativistic quantum mechanics. The multiple carbon sublattices endow the electronic wavefunctions with pseudospin, a lattice analogue of the relativistic electron spin, whereas the multilayer structure leads to electric-field-effect tunable electronic bands. Here we use these properties to realize giant conductance oscillations in ballistic trilayer graphene Fabry-Pérot interferometers, which result from phase coherent transport through resonant bound states beneath an electrostatic barrier. We confine these states by selectively decoupling them from the leads, resulting in transport via non-resonant states and suppression of the giant oscillations. The confinement is achieved both classically, by manipulating quasiparticle momenta with a magnetic field, and quantum mechanically, by locally varying the pseudospin character of the carrier wavefunctions. Our results illustrate the unique potential of trilayer graphene as a versatile platform for electron optics and pseudospintronics.

Professor Jarillo-Herrero was one of five MIT faculty members named by President Barack Obama today as a recipient of a Presidential Early Career Award for Scientists and Engineers (PECASE), the highest honor bestowed by the U.S. government on science and engineering professionals in the early stages of their independent research careers.

Read more at MIT News: Five MIT researchers win presidential early career honors.

A collaboration work between our group and Michael Strano’s group at MIT has been recently accepted to Nature Chemistry! Preprint is available at arXiv:1207.3369.

Chemical reactivity imprint lithography on graphene: Controlling the substrate influence on electron transfer reactions
Qing Hua Wang, Zhong Jin, Ki Kang Kim, Andrew J. Hilmer, Geraldine L.C. Paulus, Chih-Jen Shih, Moon-Ho Ham, Javier D. Sanchez-Yamagishi, Kenji Watanabe, Takashi Taniguchi, Jing Kong, Pablo Jarillo-Herrero, Michael S. Strano

The chemical functionalization of graphene enables control over electronic properties and sensor recognition sites. However, its study is confounded by an unusually strong influence of the underlying substrate. In this paper, we show a stark difference in the rate of electron transfer chemistry with aryl diazonium salts on monolayer graphene supported on a broad range of substrates. Reactions proceed rapidly when graphene is on SiO_2 and Al_2O_3 (sapphire), but negligibly on alkyl-terminated and hexagonal boron nitride (hBN) surfaces. The effect is contrary to expectations based on doping levels and can instead be described using a reactivity model accounting for substrate-induced electron-hole puddles in graphene. Raman spectroscopic mapping is used to characterize the effect of the substrates on graphene. Reactivity imprint lithography (RIL) is demonstrated as a technique for spatially patterning chemical groups on graphene by patterning the underlying substrate, and is applied to the covalent tethering of proteins on graphene.

Congratulations to 2nd year graduate student Valla Fatemi for receiving a National Defense Science and Engineering Graduate Fellowship!

Undergraduate researcher Nityan Nair is one of two MIT students to be named a Goldwater Scholar this year. Nityan currently works with the graphene optoelectronics team. More details at MIT News

Congratulations to Javier and Thiti for their publication, Quantum Hall Effect, Screening and Layer-Polarized Insulating States in Twisted Bilayer Graphene, being accepted to Physical Review Letters.

The paper is currently available on arxiv:

http://arxiv.org/abs/1110.4628