Jean-Marc Broto

High mobility in LaAlO3/SrTiO3 heterostructures: origin, dimensionality, and perspectives.

We have investigated the dimensionality and origin of the magnetotransport properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001) substrates. High-mobility conduction is observed at low deposition oxygen pressures (P(O2)<10(-5) mbar) and has a three-dimensional character. However, at higher P(O2) the conduction is dramatically suppressed and nonmetallic behavior appears. Experimental data strongly support an interpretation of these properties based on the creation of oxygen vacancies in the SrTiO3 substrates during the growth of the LaAlO3 layer. When grown on SrTiO3 substrates at low P(O2), other oxides generate the same high mobility as LaAlO3 films. This opens interesting prospects for all-oxide electronics.

Electron–hole coexistence in disordered graphene probed by high-field magneto-transport

We report on magneto-transport measurement in disordered graphene under a pulsed magnetic field of up to 57 T. For large electron or hole doping, the system displays the expected anomalous integer quantum Hall effect (IQHE) specific to graphene down to the filling factor ν=2. In the close vicinity of the charge neutrality point, the system breaks up into coexisting puddles of holes and electrons, leading to a vanishing Hall and finite longitudinal resistance with no hint of divergence at very high magnetic field. Large resistance fluctuations are observed near the Dirac point. They are interpreted as the natural consequence of the presence of electron and hole puddles. The magnetic field at which the amplitude of the fluctuations is the largest is directly linked to the mean size of the puddles.

Anharmonic effects in ZnO optical phonons probed by Raman spectroscopy

We report Raman spectroscopy measurements on ZnO crystals grown by the vapor transport method and annealed. Vacuum annealing is found to yield single crystals with ultra low density of defects. We focus on the optical E2 phonon linewidth temperature dependence in the 10–500 K range. The linewidth decrease at low temperature is analyzed and discussed in the light of anharmonic up- and down-conversion processes, unveiling strongly different behaviors for the two E2 phonons.

Evidence of type-I direct recombination in InP/GaP quantum dots via magnetoluminescence

Photoluminescence from InP quantum dots within a GaP matrix is investigated as a function of magnetic field. By fitting the magnetoluminescence data to the energy states of the electrons and holes confined in quantum dots in a perpendicular magnetic field, the electron-hole reduced effective mass is determined to be 0.094m0. The diamagnetic shift in the luminescence peak gives an average exciton radius of about 5 nm, smaller than the dot radius. These results indicate that the recombining electrons are primarily composed of states originating from the InP Γ valley although the conduction band discontinuity between the InP and the GaP barrier is expected to be very small or even negative.

Electronic conductivity in 1D Co spin chain single crystal

We have measured the transport and magnetic properties of the model spin chain single crystal Ca3Co2O6 in high pulsed fields. A crossover between 1D and 3D transport is observed, with the opening of a Coulomb gap below the order temperature of the individual chains. The samples show changes in the variable range hopping transport dimensionality and gap; the magnetic field suppresses the gap, inducing a significant reduction of the resistance, while dimensionality seems governed by temperature. At fields associated with the levels of magnetization of the frustrated triangular lattice formed by the Co lines, and below the critical magnetic temperature, a further increase of the conductivity is observed. This effect is associated with planar magnetic states perpendicular to the lines.

Weak ferrimagnetism and multiple magnetization reversal in α-Cr3(PO4)2

The chromium(II) orthophosphate

New diamond anvil cell for optical and transport measurements under high magnetic fields up to 60 T

\ensuremath{\alpha}

Electronic fluctuations in multi-walled carbon nanotubes

-Cr

Pressure dependence of Raman modes in double wall carbon nanotubes filled with α-Fe

{}_{3}

High Field Level Crossing Studies on Spin Dimers in the Low Dimensional Quantum Spin System Na2T2(C2O4)3(H2O)2 with T = Ni, Co, Fe, Mn

(PO