Ultrafast and nanoscale plasmonic phenomena in exfoliated graphene revealed by infrared pump-probe nanoscopy.
Pump-probe spectroscopy is central for exploring ultrafast dynamics of fundamental excitations, collective modes, and energy transfer processes. Typically carried out using conventional diffraction-limited optics, pump-probe experiments inherently average over local chemical, compositional, and electronic inhomogeneities. Here, we circumvent this deficiency and introduce pump-probe infrared spectroscopy with ∼ 20 nm spatial resolution, far below the diffraction limit, which is accomplished using a scattering scanning near-field optical microscope (s-SNOM). This technique allows us to investigate exfoliated graphene single-layers on SiO2 at technologically significant mid-infrared (MIR) frequencies where the local optical conductivity becomes experimentally accessible through the excitation of surface plasmons via the s-SNOM tip. Optical pumping at near-infrared (NIR) frequencies prompts distinct changes in the plasmonic behavior on 200 fs time scales. The origin of the pump-induced, enhanced plasmonic response is identified as an increase in the effective electron temperature up to several thousand Kelvin, as deduced directly from the Drude weight associated with the plasmonic resonances.
Department of Physics, University of California , San Diego, La Jolla, California 92093, United States.
Martin
M
Wagner
Zhe
Z
Fei
Alexander S
AS
McLeod
Aleksandr S
AS
Rodin
Wenzhong
W
Bao
Eric G
EG
Iwinski
Zeng
Z
Zhao
Michael
M
Goldflam
Mengkun
M
Liu
Gerardo
G
Dominguez
Mark
M
Thiemens
Michael M
MM
Fogler
Antonio H
AH
Castro Neto
Chun Ning
CN
Lau
Sergiu
S
Amarie
Fritz
F
Keilmann
D N
DN
Basov