190 research outputs found
de Haas-van Alphen oscillations with non-parabolic dispersions
de Haas-van Alphen oscillation spectrum of two-dimensional systems is studied
for general power law energy dispersion, yielding a Fermi surface area of the
form for a given energy . The case stands
for the parabolic energy dispersion. It is demonstrated that the periodicity of
the magnetic oscillations in inverse field can depend notably on the
temperature. We evaluated analytically the Fourier spectrum of these
oscillations to evidence the frequency shift and smearing of the main peak
structure as the temperature increases.Comment: 14 pages, 2 figures, to appear in Eur. Phys. J.
Effect of electronic band dispersion curvature on de Haas-van Alphen oscillations
The effect of electronic band curvature, i.e. the deviation from parabolicity
of electronic dispersion, on de Haas-van Alphen oscillations spectra is
studied. Although the oscillations amplitude remain unaffected, it is
demonstrated that non-quadratic terms of the Landau bands dispersion, which is
particularly relevant in the case of Dirac fermions, induces a field- and
temperature-dependent Onsager phase. As a result, a temperature-dependent shift
of the de Haas-van Alphen oscillations frequency is predicted.Comment: 16 pages, 2 figure
Grassmann techniques applied to classical spin systems
We review problems involving the use of Grassmann techniques in the field of
classical spin systems in two dimensions. These techniques are useful to
perform exact correspondences between classical spin Hamiltonians and
field-theory fermionic actions. This contributes to a better understanding of
critical behavior of these models in term of non-quadratic effective actions
which can been seen as an extension of the free fermion Ising model. Within
this method, identification of bare masses allows for an accurate estimation of
critical points or lines and which is supported by Monte-Carlo results and
diagrammatic techniques
Random walks and magnetic oscillations in compensated metals
The field- and temperature-dependent de Haas-van Alphen oscillations spectrum
is studied for an ideal two-dimensional compensated metal whose Fermi surface
is made of a linear chain of successive orbits with electron and hole
character, coupled by magnetic breakdown. We show that the first harmonics
amplitude can be accurately evaluated on the basis of the Lifshits-Kosevich
(LK) formula by considering a set of random walks on the orbit network, in
agreement with the numerical resolution of semi-classical equations.
Oppositely, the second harmonics amplitude does not follow the LK behavior and
vanishes at a critical value of the field-to-temperature ratio which depends
explicitly on the relative value between the hole and electron effective
masses.Comment: 9 pages, 10 figures. Submitted to Physical Review
Critical properties of cluster size distribution in an asymmetric diffusion-aggregation model
International audienceWe consider a stochastic dynamics for a system of diffusing hard-core particles on a periodic chain with asymmetric diffusion rules. A given cluster of particles can diffuse to the right as a whole but the particle located on the left boundary of the cluster is allowed to break off from it and diffuse to the left. Clusters of particles can eventually merge with other clusters. These rules allow for the creation of clusters of different sizes. We discuss the size distribution of the clusters in the long time or steady state limit, as a function of the particle concentration c. We consider the general time dependent master equation based on Smoluchowski's theory for local cluster merging or fragmentation and diffusion processes, and study the solutions using the generating function in the large size limit. We found that there exists a critical density c∗ =√2 − 1 for which the cluster distribution decays like a power law with exponent 5/
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