Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

Personnel involved:
Organic conductors
Permanents: A. Audouard (CR1), M. Nardone (IR), D. Vignolles (MC)
Collaborations: V.N Laukhin, E. Canadell (ICMAB Barcelona)
R.B. Lyubovskii, R.N. Lyubovskaya, E.B. Yagubskii (IPCP, Chernogolovka)
J.-Y. Fortin (Laboratoire Physique théorique, Strasbourg and Institut Jean Lamour, Nancy)
Due to their rather simple Fermi surface (FS), organic metals provide a powerful playground for the
investigation of quantum oscillation physics. Indeed, in most cases, their FS can be regarded as networks of
orbits coupled by magnetic breakdown (MB) giving rise to quantum oscillations spectra with numerous
frequency combinations that cannot be accounted for by the semiclassical model of Falicov and Stachowiak.
This phenomenon which is attributed to either the formation of Landau bands or (and) the oscillation of the
chemical potential in magnetic field needs to be better understood.
Frequency combinations in linear chains of orbits with high scattering
rate
The FS of (BEDO) 5Ni(CN) 4·3C 2H 4(OH) 2 (see the opposite figure)
corresponds to a linear chain of quasi-two-dimensional orbits coupled by
MB. Remarkably, the scattering rate can be consistently deduced from the
Shubnikov-de Haas oscillations data relevant to both the basica, the second
harmonic 2a and the MB-induced b orbits. Its large value points to a
significant reduction of the chemical potential oscillations. Despite of this
feature, the oscillations spectrum exhibits many frequency combinations [1].
Their effective masses and (or) Dingle temperature are not in agreement
with neither the predictions of the quantum interference model nor the
semiclassical model.
Frequency combinations in networks of compensated orbits
According to calculations [2] chemical potential oscillations are strongly
reduced for 2D metals with compensated orbits. 2D networks of
compensated orbits are achieved in the compound (ET) 8[Hg 4Cl 12(C 6H 5Br) 2]
as displayed in the opposite figure where the two a orbits with different
shapes are compensated while thed and D pieces are forbidden orbits. In
agreement with the above statement, all the frequency combinations
observed in early de Haas-van Alphen (dHvA) oscillations spectra up to 28
T data are consistent with the semiclassical picture [3]. Oppositely, recent
dHvA data obtained from torque measurements up to 55 T exhibit many
frequency combinations, most of them being forbidden within the
semiclassical framework [4]. Otherwise, the pressure dependence of the
effective mass linked to the basic a orbits scales with the coefficient of the T² law of the zero-field resistance
which is in line with a Brinkman-Rice scenario expected for strongly correlated compounds [5].
References
[1] D. Vignolles et al., Eur. Phys. J. B. 55 383 (2007).
[2] J.-Y. Fortin and A. Audouard, Phys. Rev. B 77 134440 (2008).
[3] A. Audouard et al. EPL 71 783 (2005).
[4] D. Vignolles et al., in preparation
[5] D. Vignolles et al., Eur. Phys. J. B. 66 489 (2008).
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