APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011;
Dallas, Texas
Abstract: P2.00001 : Topological Kondo Ground State in Graphene
8:00 AM–8:36 AM
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Author:
Dirac electrons in graphene comprise two-component wavefunctions and quantum
symmetries intertwining pseudospin, chirality, and Berry's phase, all
ultimately stemming from a node or topological degeneracy in the spectrum
known as the Dirac point. Graphene represents one prototype example of a
larger class of nodal metals in which a relativistic spectrum causes the
density of states to vanish linearly. Based on the unique electronic
structure of such systems, a large body of theoretical work has highlighted
the propensity for Dirac electrons to condense in strongly correlated ground
states when additionally coupled to the real spin degree of freedom. We
report the observation of one of these elusive ground states, realized in
graphene via unconventional Kondo screening of individual atomic spins by
massless Dirac fermions. Low-temperature scanning tunneling microscopy
reveals the emergence of a new energy scale and a striking bimodal Kondo
resonance localized around magnetic atoms placed on a clean graphene
monolayer. Quasiparticle interference maps and concomitant spectroscopy in a
high magnetic field demonstrate the spin origin of the associated ground
states, and their direct link to local conservation or breaking of effective
time-reversal symmetry in the underlying Dirac Hamiltonian. We find these
novel spin states to be topologically controlled by Berry phase
interference; in the most exotic manifestation, we show experimental
evidence for two electron flavors---decoupled in momentum space by a $\pi $
Berry phase shift cancellation---participating in a chiral two-channel Kondo
effect. We link these results to a new platform we have developed for the
study of topological phases, artificial graphene assembled by atomic
manipulation.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.P2.1