Alexey B. Kuzmenko - Optics @ Unige - Université de Genève

Couplings between charge, spin, orbital and lattice degrees of freedom in solids
Superconductivity
Most significant scientific results
Discovery of a giant Faraday rotation (up to 6 degrees) in single atomic graphene layer on SiC and its
explanation as due to the cyclotron resonance [I. Crassee et al. arxiv: 1007:5286, submitted to Nature
Physics].
First observation of a strong doping dependence of the intensity and the Fano asymmetry of the
infrared phonon G-peak in electrostatically gated bilayer graphene. An explanation of this effect
using the theories of Fano and Rice.This can be used for a contact-free characterization of graphene
[A.B.Kuzmenko et al., Phys. Rev. Lett. 103, 116804 (2009); E.Cappelluti et al., Phys. Rev. B 82
041402(R) (2010)].
Optical measurement of the electric-field induced bandgap in gated bilayer graphene [A.B.
Kuzmenko et al., Phys. Rev. B 80 165406 (2009)]. The existence of this gap is extremely important
for applications of graphene in electronics. Our paper appeared simultaneously with two other
independent papers reporting similar results [K.F. Mak et al. Rev. Lett. 102, 256405 (2009) and Y.
Zhang et al.Nature 459, 820 (2009)]. However, in contrast to other papers, we extracted selfconsistently
all tight-binding (SWMcC) parameters from the same set of optical data.
2
Experimental demonstration that the optical conductivity of graphite is equal to e / 4h
[A.B.
Kuzmenko et al., Phys. Rev. Lett. 100, 117401 (2008)], which is the universal value expected for
monolayer graphene. In the same paper we predicted that the optical transmission of monolayer
graphene should be dependent only on the fine-structure constant: T = 1−
πα . This was indeed
experimentally found in the group of A.K. Geim [R.R: Nair et al., Science 320, 1308 (2008)]. This
universal behaviour is of fundamental importance for the optical applications of graphene.
Establishing the two-band nature of the superconductivity in MgB2 using optical measurements [A.B.
Kuzmenko et al., Solid State Commun.121, 479 (2002)] and theoretical input [I.I. Mazin et al., Phys.
Rev. Lett. 89, 107002 (2002)].
Systematic study of the optical sum rules in a high-temperature superconductor Bi2212 as function of
doping [A.B. Kuzmenko et al. Phys. Rev. B. 72, 144503 (2005), F, Carbone et al., Phys. Rev. B. 74,
064510 (2006)]. It was shown that in the optimally and underdoped regime the total Drude weight
increases when entering the superconducting state, which implies a possible lowering of the
electronic kinetic energy below the SC transition, contrary to the predictions of the BCS theory.
However, in the overdoped regime, the BCS-like behaviour is observed. These finding have
important implications for the mechanism of superconductivity in the high-Tc cuprates, which is not
yet understood.
Development of a novel Kramers-Kronig constrained variational method of the analysis of optical
spectra [A.B. Kuzmenko, Rev. Sci. Instrum.76, 083108 (2005)], allowing the analysis of a great
variety of spectroscopic data. This method I implemented in a freely available program RefFIT
[http://optics.unige.ch/alexey/reffit.html], used at present by more the 50 optics groups in the world.
Observation of a strong spin-phonon coupling and an anomalous phonon softening in cupric oxide
CuO [Phys. Rev. B 63, 094303 (2001)], which was found later to be multiferroic. This material is a
parent compound of high-Tc cuprates. It is also widely used in the production of various
nanostructures.
References