Cryo-SNOM studies of 2D electron gas at oxide interfaces
We performed the first cryo-SNOM studies of 2D electron gas between LaAlO3 (LAO) and SrTiO3 (STO) as a function temperature and gate voltage (at 6 K) . We imaged the patterns of conducting 2DEG channels produced by AFM writing and photolitography . We established that the high sensitivity of the s-SNOM signal to the presence of the 2DEG and to its metallic properties, such as carrier and mobility, comes from the formation of coupled electron-phonon surface plasmons.
Currently we are studying the propagation of surface phonon-polartions (PhP) in the Restrahlen band of the STO and LAO/STO systems using the nano-FTIR module of our cryo-SNOM setup. W. Luo, M. Boselli, J.M. Poumirol, I. Ardizzone, J. Teyssier, D. van Der Marel, S. Gariglio, J.M. Triscone, and A.B. Kuzmenko, High sensitivity variable-temperature infrared nanoscopy of conducting oxide interfaces,
Nature Communications, 10, 8 (2019).
 M. Boselli, G. Scheerer, M. Filippone, W. Luo, A. Waelchli, A.B. Kuzmenko, S. Gariglio, T. Giamarchi, and J.-M. Triscone, Electronic transport in sub-micrometric channels at the LaAlO3 /SrTiO3 interface,
arXiv:2009.07867, submitted to Phys. Rev. B (2020).
This work is done in collaboration with the group of Prof. J.-M. Triscone (DQMP). More information is here.
Landau-level infrared absorption and infrared magneto-plasmons in encapsulated graphene
We measured magneto-transmission and Faraday rotation in suspended hBN encapsulated monolayer graphene using a custom-designed set-up for magneto-infrared microspectroscopy . Our results show strongly enhanced magneto-optical activity in the infrared and terahertz ranges, characterized by absorption of light near to the 50% maximum allowed, 100% magnetic circular dichroism and high Faraday rotation. Considering that sizeable effects have been already observed at routinely achievable magnetic fields, our findings demonstrate the potential of magnetic tuning in 2D Dirac materials for long-wavelength optoelectronics and plasmonics.
Based on these results we theoretically predicted the existence of interband plasmon-polaritons in neutral graphene in a magnetic field . They should be tunable by the magnetic field.
We are currently preparing s-SNOM experiments to observe these plasmons in hBN encapsulated graphene. Ievgeniia O Nedoliuk, Sheng Hu, Andre K Geim and Alexey B Kuzmenko, Colossal infrared and terahertz magneto-optical activity in a two-dimensional Dirac material,
Nature Natotechnology, 14, 756 (2019).
 T. M. Slipchenko, J. -M. Poumirol, A. B. Kuzmenko, A. Yu. Nikitin, L. Martin-Moreno, Interband plasmon polaritons in magnetized charge-neutral graphene ,
arXiv:2010.00306, submitted (2020).
This work is done in collaboration with the groups of Prof. A.K. Geim (University of Manchester), Prof. L. Martin-Moreno (University of Zaragoza) and Dr. A. Nikitin (CIC Nanogune, San Sebastian)
Cryo-SNOM study of the metal-insulator transition in the nickelates RNiO3
Metal-insulator transitions (MITs) are among the most spectacular and application-rich phenomena observed in correlated electronic materials. It is of particular importance is to understand the coexistence and separation of the conducting and the insulating phases in the critical region and to control them using external fields such as electric field or local strain. Here we perform extensive research on thin epitaxial NdNiO3 films of different thickness on various substrates and employing cryogenic infrared near-field imaging, in combination with far-field reflectivity and DC resistivity measurements.
This work is done in collaboration with the group of Prof. J.-M. Triscone (DQMP).