128 research outputs found
High magnetic field induced charge density waves and sign reversal of the Hall coefficient in graphite
We report on the investigation of magnetic field induced charge density wave
and Hall coefficient sign reversal in a quasi-two dimensional electronic system
of highly oriented pyrolytic graphite under very strong magnetic field. The
change of Hall sign coefficient from negative to positive occurs at low
temperature and high magnetic field just after the charge density wave
transition, suggesting the role of hole-like quasi-particles in this effect.
Angular dependent measurements show that the charge density wave transition and
Hall sign reversal fields follow the magnetic field component along the c-axis
of graphite
Relationship between heating atmosphere and copper foil impurities during graphene growth via low pressure chemical vapor deposition
Low-pressure chemical vapor deposition synthesis of graphene films on two different Cu foils, with different surface oxygen and carbon contents, was performed by controlling H2 and/or Ar flow rates during heating. The influences of heating atmosphere on the final impurity level, quality of the synthesized graphene films and thickness uniformity were investigated depending on Cu foil impurities. Heating of carbon-rich, but oxygen-poor Cu foil in H2 environment resulted in covering the foil surface by residual carbon which then acted as active sites for multilayer graphene growth. Ar-only flow was required during heating to promote high quality graphene growth on this foil. On carbon-poor, but oxygen-rich Cu foil high quality graphene growth was promoted when the heating was carried out under Ar/H2 environment. Almost no carbon residues were observed on this foil even under H2 only flow during heating. The heating atmosphere affected not only graphene growth, but also the type and amount of impurities formed on the surface. H2 and Ar/H2 heating resulted in the formation of spherical nanometer-sized impurities, while irregular-shaped, large (a few mm) SiO2 impurities were observed when Ar alone was used during heating. Quality of the grown films was tested by Quantum Hall Effect measurements
Edge Magneto-Fingerprints in Disordered Graphene Nanoribbons
We report on (magneto)-transport experiments in chemically derived narrow
graphene nanoribbons under high magnetic fields (up to 60 Tesla). Evidences of
field-dependent electronic confinement features are given, and allow estimating
the possible ribbon edge symmetry. Besides, the measured large positive
magnetoconductance indicates a strong suppression of backscattering induced by
the magnetic field. Such scenario is supported by quantum simulations which
consider different types of underlying disorders (smooth edge disorder and long
range Coulomb scatters).Comment: 4 pages, 4 figure
Magneto-transport Subbands Spectroscopy in InAs Nanowires
We report on magneto-transport measurements in InAs nanowires under large
magnetic field (up to 55T), providing a direct spectroscopy of the 1D
electronic band structure. Large modulations of the magneto-conductance
mediated by an accurate control of the Fermi energy reveal the Landau
fragmentation, carrying the fingerprints of the confined InAs material. Our
numerical simulations of the magnetic band structure consistently support the
experimental results and reveal key parameters of the electronic confinement.Comment: 13 Pages, 5 figure
Band bending inversion in BiSe nanostructures
Shubnikov-de-Haas oscillations were studied under high magnetic field in
BiSe nanostructures grown by Chemical Vapor Transport, for different
bulk carrier densities ranging from to
. The contribution of topological surface states
to electrical transport can be identified and separated from bulk carriers and
massive two-dimensional electron gas. Band bending is investigated, and a
crossover from upward to downward band bending is found at low bulk density, as
a result of a competition between bulk and interface doping. These results
highlight the need to control electrical doping both in the bulk and at
interfaces in order to study only topological surface states.Comment: 6 pages, 4 figure
Unveiling the Landau Levels Structure of Graphene Nanoribbons
Magnetotransport measurements are performed in ultraclean (lithographically
patterned) graphene nanoribbons down to 70 nm. At high magnetic fields, a
fragmentation of the electronic spectrum into a Landau levels pattern with
unusual features is unveiled. The singular Landau spectrum reveals large
magneto-oscillations of the Fermi energy and valley degeneracy lifting. Quantum
simulations suggest some disorder threshold at the origin of mixing between
opposite chiral magnetic edge states and disappearance of quantum Hall effect
Unconventional quantum oscillations and evidence of non-trivial electronic states in quasi-two-dimensional electron system at complex oxide interfaces
The simultaneous occurrence of electric-field controlled superconductivity
and spin-orbit interaction makes two-dimensional electron systems (2DES)
constructed from perovskite transition metal oxides promising candidates for
the next generation of spintronics and quantum computing. It is, however,
essential to understand the electronic bands thoroughly and verify the
predicted electronic states experimentally in these 2DES to advance
technological applications. Here, we present novel insights into the electronic
states of the 2DES at oxide interfaces through comprehensive investigations of
Shubnikov-de Haas oscillations in two different systems: EuO/KTaO (EuO/KTO)
and LaAlO/SrTiO (LAO/STO). To accurately resolve these oscillations, we
conducted transport measurements in high magnetic fields up to 60 T and low
temperatures down to 100 mK. For 2D confined electrons at both interfaces, we
observed a progressive increase of oscillations frequency and cyclotron mass
with the magnetic field. We interpret these intriguing findings by considering
the existence of non-trivial electronic bands, for which the dispersion
incorporates both linear and parabolic dispersion relations. In addition to
providing experimental evidence for topological-like electronic states in
KTO-2DES and STO-2DES, the unconventional oscillations presented in this study
establish a new paradigm for quantum oscillations in 2DES based on perovskite
transition metal oxides, where the oscillations frequency exhibits quadratic
dependence on the magnetic field
Anisotropic transport properties of quasiballistic InAs nanowires under high magnetic field
The magnetoconductance of a long channel InAs nanowire based field effect transistor in the quasiballistic regime under large magnetic field is investigated. The quasi-1D nanowire is fully characterized by a bias voltage spectroscopy and measurements under magnetic field up to 50 T applied either perpendicular or parallel to the nanowire axis lifting the spin and orbital degeneracies of the subbands. Under normal magnetic field, the conductance shows quantized steps due to the backscattering reduction and a decrease due to depopulation of the 1D modes. Under axial magnetic field, a quasioscillatory behavior is evidenced due to the coupling of the magnetic field with the angular momentum of the wave function. In addition the formation of cyclotron orbits is highlighted under high magnetic field. The experimental results are compared with theoretical calculation of the 1D band structure and related parameters.High magnetic field measurements were performed at
LNCMI under the EMFL proposal TSC10-213. Parts of the
calculations were run on the CCRT/Curie machine using
allocations from GENCI. This work is supported by the
Grant NEXT N°.ANR-10-LABX-0037 in the framework of
the âProgramme des Investissements dâAvenirâ
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