888 research outputs found
Magnetic Miniband Structure and Quantum Oscillations in Lateral Semiconductor Superlattices
We present fully quantum-mechanical magnetotransport calculations for
short-period lateral superlattices with one-dimensional electrostatic
modulation. A non-perturbative treatment of both magnetic field and modulation
potential proves to be necessary to reproduce novel quantum oscillations in the
magnetoresistance found in recent experiments in the resistance component
parallel to the modulation potential. In addition, we predict oscillations of
opposite phase in the component perpendicular to the modulation not yet
observed experimentally. We show that the new oscillations originate from the
magnetic miniband structure in the regime of overlapping minibands.Comment: 6 pages with 4 figure
Gating of high-mobility two-dimensional electron gases in GaAs/AlGaAs heterostructures
We investigate high-mobility two-dimensional electron gases in AlGaAs
heterostructures by employing Schottky-gate-dependent measurements of the
samples' electron density and mobility. Surprisingly, we find that two
different sample configurations can be set in situ with mobilities diering by a
factor of more than two in a wide range of densities. This observation is
discussed in view of charge redistributions between the doping layers and is
relevant for the design of future gateable high-mobility electron gases
Vertically Inhomogeneous Models of the Upper Crustal Structure in the West-Bohemian Seismoactive Region Inferred from the Celebration 2000 Refraction Data
Optical creation of vibrational intrinsic localized modes in anharmonic lattices with realistic interatomic potentials
Using an efficient optimal control scheme to determine the exciting fields,
we theoretically demonstrate the optical creation of vibrational intrinsic
localized modes (ILMs) in anharmonic perfect lattices with realistic
interatomic potentials. For systems with finite size, we show that ILMs can be
excited directly by applying a sequence of femtosecond visible laser pulses at
THz repetition rates. For periodic lattices, ILMs can be created indirectly via
decay of an unstable extended lattice mode which is excited optically either by
a sequence of pulses as described above or by a single picosecond far-infrared
laser pulse with linearly chirped frequency. In light of recent advances in
experimental laser pulse shaping capabilities, the approach is experimentally
promising.Comment: 20 pages, 7 eps figures. Accepted, Phys. Rev.
Ferrimagnetism in the Hubbard, dimmer-connector frustrated chain
We study the AB2 "dimmer-connector" chain within a generalized Hubbard model, which contains site-dependent parameters, and different chemical potentials for A and B sites. Considering one electron per atom, we carry out exact calculations for finite clusters, and derive some asymptotic results, valid for macroscopic chains. We take a non-vanishing intra-dimmer electron hopping, thus departing from the condition of a bipartite lattice. In spite of that, the system persists ferrimagnetic in some region of the parameter space, thus generalizing a theorem of Lieb for bipartite lattices. A somewhat surprising result is that the ferrimagnetic phase is possible, even for a very large chemical potential jump between A and B sites. In another respect, we show that a previously reported macroscopic (2N) degenerancy of the AB2 Heisenberg chain ground state (GS) is fully removed on going to the (more fundamental) Hubbard model, yielding a non-magnetic GS
Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by Muon Spin Rotation
We have studied by muon spin resonance ({\mu}SR) the helical ground state and
fluctuating chiral phase recently observed in the MnGe chiral magnet. At low
temperature, the muon polarization shows double period oscillations at short
time scales. Their analysis, akin to that recently developed for MnSi [A. Amato
et al., Phys. Rev. B 89, 184425 (2014)], provides an estimation of the field
distribution induced by the Mn helical order at the muon site. The refined muon
position agrees nicely with ab initio calculations. With increasing
temperature, an inhomogeneous fluctuating chiral phase sets in, characterized
by two well separated frequency ranges which coexist in the sample. Rapid and
slow fluctuations, respectively associated with short range and long range
ordered helices, coexist in a large temperature range below T = 170 K. We
discuss the results with respect to MnSi, taking the short helical period,
metastable quenched state and peculiar band structure of MnGe into account.Comment: 13 pages, 11 figure
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