Cloaking and uncloaking impurities in graphene by populating magnetic quantum states

Eva Y. Andrei, Rutgers University New Brunswick, DMR 0906711

Charged impurities, by deflecting the motion of electrons or even stopping them altogether, can have a dramatic effect on the electronic properties of a material. In this work a single charged impurity was isolated to probe its influence on the electronic spectrum of graphene. Spatially resolved scanning tunneling microscopy and spectroscopy in a magnetic field were employed to follow the evolution of the electronic spectrum with number of mobile charge carriers introduced by a gate voltage. This led to the first direct demonstration that the apparent strength of a charged impurity is controlled by the density of mobile carriers. For a sufficiently high density of carriers we found that the impurity becomes essentially invisible. This cloaking effect diminishes as the number of carriers is decreased by gating the sample towards the edge of the conduction band, seen as a step in the Landau level map (middle panel of the figure). Cloaking is directly seen in the position dependence of the Landau level map (bottom panels) taken across the impurity. Right bottom panel: the sample is gated into the insulating state. In the absence of mobile carriers to screen the impurity it remains exposed and its effect on the spectrum is strongest. In the left panel the sample is gated into the conducting state where a sufficient density of mobile carriers is available to screen the impurity. In this regime the impurity is essentially invisible. 1. A. Luican et al, submited2. A. Luican et al Phys. Rev. Lett. 106, 126802 (2011) 0 40 80

Position (nm)0 40 80

Position (nm)

Broader impactsEducation

Research training of 4 undergraduate and 2 graduate students. Undergraduate honors thesis director

Outreach and public lectures• Tutorial organizer at March meeting of

the American Physical Society, Boston (2012)

• Lecturer at Graphene Teachers' Conference at KITP, Santa Barbara, CA (2012)

• Lecturer at New Jersey Section of the American Association of Physics Teachers (2011)

• Distinguished Women Scientists and Engineers public lecture, University of Minnesota.

• “Kamerling-Onnes” public lecture, Indian Institute of Technology Kanpur, India..

• Round table discussion leader with women students in Physics (U. Minnesota)

• “APS Lunch with experts” leading round table discussions with students at APS March meeting.

Conference Organization and scientific committees

• Graphene week, Delft, Netherlands, (2012)• Gordon conference in condensed matter (2012)• Graphene 2011 Bilbao, Spain,• Winterschool on Electronic Properties of Novel

Materials, Kirchberg Austria (2012, 2013)

Cloaking and uncloaking impurities in graphene by populating magnetic quantum states

Eva Y. Andrei, Rutgers University New Brunswick, DMR 0906711