9,338 research outputs found
Parametric resonance and spin-charge separation in 1D fermionic systems
We show that the periodic modulation of the Hamiltonian parameters for 1D
correlated fermionic systems can be used to parametrically amplify their
bosonic collective modes. Treating the problem within the Luttinger liquid
picture, we show how charge and spin density waves with different momenta are
simultaneously amplified. We discuss the implementation of our predictions for
cold atoms in 1D modulated optical lattices, showing that the fermionic
momentum distribution directly provides a clear signature of spin-charge
separation.Comment: 6 pages, 3 figures, published versio
Electronic structure of the substitutional versus interstitial manganese in GaN
Density-functional studies of the electron states in the dilute magnetic
semiconductor GaN:Mn reveal major differences for the case of the Mn impurity
at the substitutional site Mn_Ga versus the interstitial site Mn_I. The
splitting of the two-fold and the three-fold degenerate Mn(d)states in the gap
are reversed between the two cases, which is understood in terms of the
symmetry-controlled hybridization with the neighboring atoms. In contrast to
Mn_Ga, which acts as a deep acceptor, Mn_I acts as a donor, suggesting the
formation of Coulomb-stabilized complexes such as (Mn_Ga Mn_I Mn_Ga), where the
acceptor level of Mn_Ga is passivated by the Mn_I donor. Formation of such
passivated clusters might be the reason for the observed low carrier-doping
efficiency of Mn in GaN. Even though the Mn states are located well inside the
gap,the wave functions are spread far away from the impurity center. This is
caused by the hybridization with the nitrogen atoms, which acquire small
magnetic moments aligned with the Mn moment. Implications of the differences in
the electronic structure for the optical properties are discussed
Strong correlation effects and optical conductivity in electron doped cuprates
We demonstrate that most features ascribed to strong correlation effects in
various spectroscopies of the cuprates are captured by a calculation of the
self-energy incorporating effects of spin and charge fluctuations. The self
energy is calculated over the full doping range of electron-doped cuprates from
half filling to the overdoped system. The spectral function reveals four
subbands, two widely split incoherent bands representing the remnant of the
split Hubbard bands, and two additional coherent, spin- and charge-dressed
in-gap bands split by a spin-density wave, which collapses in the overdoped
regime. The incoherent features persist to high doping, producing a remnant
Mott gap in the optical spectra, while transitions between the in-gap states
lead to pseudogap features in the mid-infrared.Comment: 5 pages, 4 figure
Tunable Coulomb blockade in nanostructured graphene
We report on Coulomb blockade and Coulomb diamond measurements on an etched,
tunable single-layer graphene quantum dot. The device consisting of a graphene
island connected via two narrow graphene constrictions is fully tunable by
three lateral graphene gates. Coulomb blockade resonances are observed and from
Coulomb diamond measurements a charging energy of ~3.5 meV is extracted. For
increasing temperatures we detect a peak broadening and a transmission increase
of the nanostructured graphene barriers
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