Grenoble High Magnetic Field Laboratory Research Articles

Excitation Mechanisms of CdTe/ZnTe Quantum Dots under Non-Resonant and Quasi-Resonant Regime

Excitation Mechanisms of CdTe/ZnTe Quantum Dots under Non-Resonant and Quasi-Resonant Regime T. Kazimierczuka,∗, J.A. Gaj , A. Golnik, M. Goryca, M. Nawrocki, M. Koperski, T. Smolenski, J. Suffczynski, P. Wojnar and P. Kossacki Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Hoza 69, 00-681 Warsaw, Poland Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland Grenoble High Magnetic Field Laboratory, CNRS, BP 166, 38042 Grenoble Cedex 9, France We discuss possible mechanisms of quantum dot population control. A set of experiments, including time-resolved photoluminescence, single photon correlations, excitation correlation, and photoluminescence excitation is used to determine the actual mechanism under non-resonant and quasi-resonant regime.

Characterization of industrial NbTi strands at variable field for JT-60SA toroidal field coils

The mission of the JT-60SA Tokamak, to be built in Japan, is to contribute to the early realization of fusion energy by its exploitation in support of the ITER program. JT-60SA project is an important part of the “broader approach” activity as a satellite program for ITER. The toroidal field (TF) coils are a European “in kind” contribution and they will partly be built by France. JT-60SA TF coil uses the Cable In Conduit Conductor (CICC) with NbTi superconductor strands. TF conductors will have to operate at 5.7 T, 5 K and at current density of 450 A/mm 2 with sufficient margins. In the framework of JT-60SA TF coil manufacture, the variable temperature characterization is an important step to select NbTi strand. At an early stage of design, we had to choose the strand with acceptable performances. During the design qualification and validation stage, it is important to qualify strands in conditions close to the operation conditions. The industry has proposed various strands manufactured with different processes. This work and publication examines a strand with an internal CuNi barrier, which is expected to lead to better current distribution between strands, by more precise calibration and control of the inter-strand resistance. The strands were tested at the Grenoble High Magnetic Field Laboratory facility. The domain (B, T, J) explored was in the range of 4.5–11 T for the magnetic field intensity, 4.2–6.5 K for the temperature and between 40 A/mm 2 and 1200 A/mm 2 for the current density. For each strand, “critical current density” and “current sharing temperature” measurements have been carried out, with a temperature precision of few tens of mK. Once the measurements performed, the fitting parameters (of type J C = f(B, T)) of each strand have been found, by performing regression analysis. This work will lead to select the strand with the best characteristics. In this paper, we present the results of this measurement task, the data and regression analysis (fits, T cs, etc.) and the conclusion about the strand choice.

Preliminary Results of Final Test of the GHMFL 40 T Hybrid Magnet

The Grenoble High Magnetic Field Laboratory (GHMFL) has completed the development of a 40-T Hybrid Magnet System to support research in steady, high magnetic fields. Oxford Instruments Superconducting has carried out the design, development and construction of the superconducting outsert system for the hybrid magnet. The superconducting magnet has been successfully tested in steady conditions on its own in a bucket-dewar at 2.8 K and at fields up to 7 T. Subsequently, the magnet has then been assembled in its cryostat in Grenoble in its final position. The magnet has been cooled down to 1.8 K and an additional test is being carried out. The resistive magnet is presently being assembled. A description of the system, its manufacture processes and main test results obtained so far will be presented.

Upper Critical Fields Up to 60 T in Dirty Magnesium Diboride Thin Films

Upper critical fields of several magnesium diboride thin films were measured up to 28 T at the Grenoble High Magnetic Field Laboratory (GHMFL) in Grenoble and up to 60 T at the Laboratoire National des Champs Magnetiques Pulses (LNCMP) in Toulouse. The samples were prepared both by pulsed laser deposition (PLD) and hybrid physical chemical vapour deposition (HPCVD) technique; they have critical temperatures between 29 and 39 K and normal state resistivities between 5 and 250 μohmcm; one of them has been intentionally doped with carbon. The measured critical fields were exceptionally high; we obtained the record value of 52 T at 4.2 K in the parallel orientation. In contrast with the BCS predictions, no saturation in Hc2 at low temperature was observed. Furthermore, films with a wide range of resistivity values showed similar critical fields, suggesting that in a two band system resistivity and Hc2 are not trivially linked. The high Hc2 values seem to be related with the expanded c-axis. The structure of one of the samples was carefully investigated with X-ray diffraction at European Synchrotron Radiation Facility (ESRF) in Grenoble.

The Investigation of Helicon Maser

Radio frequency magnetoplasmic waves know as helicons will propagate in solid – state plasmas of metals and semiconductors when a strong magnetic field is applied. In Helicon Maser the helicons are excited by RFs much higher than the Helicon generation frequency. The bandwidth of HM is much narrower than in case of isolated sample resonator (the same situation as in laser). InSb was used for active material in the experimental device. The constant magnetic field varied within the interval 0 – 20 Tesla. The equivalent circuit of the HM is considered. The experiments were performed at the Grenoble High Magnetic Field Laboratory (France) through the EEC Access to Research Infrastructure action Program. Ill.4. bibl. 3 (English, summaries in Lithuanian, English and Russian).

High-Field NMR Insights into Quantum Spin Systems

Possibilities of NMR technique will be illustrated by a selection of high-field NMR results on antiferromagnetic quantum spin systems, obtained at the Grenoble High Magnetic Field Laboratory. We present results for two well known systems, doped Haldane spin chain Y2BaNi1-xMgxO5 and spin-Peierls compound CuGeO3, as well as two newly studied compounds, the NaCU2O2 chain (or zigzag ladder) and the 2D dimer compound BaCuSi2O6 (Han purple).

Epitaxial MgB2 thin films on ZrB2 buffer layers: structural characterization by synchrotron radiation

Structural and superconducting properties of magnesium diboride thin films grown by pulsedlaser deposition on zirconium diboride buffer layers were studied. We demonstrate that theZrB2 layer is compatiblewith the MgB2 two step deposition process. Synchrotron radiation measurements, inparticular anomalous diffraction measurements, allowed us to separateMgB2 peaksfrom ZrB2 ones and revealed that both layers have a single in plane orientation with a sharp interfacebetween them. Moreover, the buffer layer avoids oxygen contamination from the sapphiresubstrate. The critical temperature of this film is near 37.6 K and the upper critical fieldmeasured at the Grenoble High Magnetic Field Laboratory up to 20.3 T is comparable withthe highest ones reported in literature.

Hybrid and Giga-NMR Projects at the Grenoble High Magnetic Field Laboratory

The Grenoble High Magnetic Field Laboratory, (GHMFL) is a French German Research Institute funded by the CNRS (Centre National de la Recherche Scientifique, France) and the MPG (Max-Planck Gesellschaft, Germany) which provides high magnetic fields and scientific support to the scientific and technologic international community. It is now setting into operation a large superconducting magnet which delivers 8 T in a 800 mm warm bore diameter. This magnet has been constructed and the first tests were performed in August 2002. Two projects are based on the use of this superconducting magnetic field. The first one give researchers' access to 40 T in a 34 mm bore with the help of a resistive magnet that gives 32 T. The second version provides 23.5 T in a 160 mm room temperature bore with a homogeneity of 1 part per million on a sphere of 1 cubic centimeter. These fields should be available at the laboratory during the year 2004. This paper presents key points of the technical development that were achieved at the laboratory in order to fulfill the high level of specifications of these two projects.

The Grenoble High Magnetic Field Laboratory as a user facility

The Grenoble High Magnetic Field Laboratory is one of the leading laboratories pursuing research in the highest static magnetic fields technically feasible. Located in Grenoble, it is a French–German laboratory, jointly funded by the Max Planck Institut für Festkörperforschung, in Stuttgart and the Centre National de la Recherche Scientifique. Five years ago, the laboratory has undertaken the development of 20 MW magnets. Two of them are now in operation and yield steady magnetic fields up to 30 T. The facility delivers around 5000 h of magnet time every year.

Effect of two bands on critical fields inMgB2thin films with various resistivity values

Upper critical fields of four MgB2 thin films were measured up to 28 Tesla at Grenoble High Magnetic Field Laboratory. The films were grown by Pulsed Laser Deposition and showed critical temperatures ranging between 29.5 and 38.8 K and resistivities at 40 K varying from 5 to 50 mWcm. The critical fields in the perpendicular direction turned out to be in the 13-24 T range while they were estimated to be in 42-57 T the range in ab-planes. In contrast to the prediction of the BCS theory, we did not observe any saturation at low temperatures: a linear temperature dependence is exhibited even at lowest temperatures at which we made the measurements. Moreover, the critical field values seemed not to depend on the normal state resistivity value. In this paper, we analyze these data considering the multiband nature of superconductivity in MgB2 We will show how the scattering mechanisms that determine critical fields and resistivity can be different.

A Topological Look at the Quantum Hall Effect

The amazingly precise quantization of Hall conductance in a two-dimensional electron gas can be understood in terms of a topological invariant known as the Chern number.

The Cotton–Mouton effect of furan and its homologues in the gas phase, for the pure liquids and in solution

The tensor components of the electric dipole polarizability at a wavelength of 632.8 nm, those of the magnetizability and the anisotropy of the static hypermagnetizability of furan, thiophene, and selenophene are computed using density functional theory (DFT). The polarizable continuum model (PCM) is employed to describe the system in the condensed phase. We can thus compare the temperature dependence of the Cotton–Mouton constant for the three molecules, both in the gas and in the condensed phase, pure liquids, and solutions, with the results of experiment performed using a 17 T radial access Bitter magnet at the Grenoble High Magnetic Field Laboratory. This allows to analyze, in a direct interaction of theory and experiment, the performance of DFT and PCM in describing high order nonlinear mixed electric and magnetic effects in condensed phase.

Performing experiments at the Grenoble High Magnetic Field Laboratory: application to the study of the Jc( B) dependence of Bi-2223/Ag multi-filamentary superconducting tapes

The Grenoble High Magnetic Field Laboratory was built to meet the requirements of scientists for experiments implying the use of very high magnetic fields. Currently, the facility operates for over 5000 h a year and thanks to its most powerful magnets, it allows the production of steady magnetic fields up to 30 T. Scientists have access to the high magnetic field facility provided they have submitted a proposal for experiments in high magnetic fields and have obtained the Program Committee’s approval to carry out their research project. As illustration of the use of our specific instrumentation, we present a study of the behavior of the critical currents of superconducting tapes, performed in collaboration between CNRS Grenoble, France and NIN Xi’an, China.

Magneto-chiral anisotropy of the free electron on a helix

The free electron on a helix as a simple model of a molecular chiral conductor is considered. In the presence of a static magnetic field parallel to the helix axis, it is found that both ballistic and diffusive electrical transport along the helix show a conductivity that depends linearly on the current and the magnetic field and on the handedness of the helix. These results agree qualitatively with the recently experimentally observed electrical magneto-chiral anisotropy in carbon nanotubes [V. Krstić, S. Roth, M. Burghard, K. Kern, G.L.J.A. Rikken, Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany; Grenoble High Magnetic Field Laboratory, MPI-CNRS, Grenoble, France; Laboratoire National des Champs Magnétiques Pulsés, CNRS/INSA/UPS, UMS 5462, Toulouse, France].

HIGH FIELD NMR IN STRONGLY CORRELATED LOW-DIMENSIONAL FERMIONIC SYSTEMS

We review some recent NMR results obtained in Grenoble High Magnetic Field Laboratory on magnetic field induced phenomena in strongly correlated low-dimensional fermionic systems: i) magnetic field dependence of the soliton lattice in the IC phase of the spin-Peierls system CuGeO3, ii) NMR study of the complete H-T phase diagram of the organo-metallic spin ladder Cu2(C5H12N2)2Cl4, and iii) the first "standard" NMR measurements (i.e., without optical pumping) on 2D electrons in Quantum wells, providing a detailed description of the fractional quantum Hall effect state at ν = 1/2 with the first determination of the corresponding effective polarization mass of composite fermions. Latest study of the ν = 2/3 state revealed, among other features, an unexpected phase transition.

The Grenoble High Magnetic Field Laboratory as a USER FACILITY

The Grenoble High Magnetic Field Laboratory (GHMFL), run jointly by the Centre National de la Recherche Scientifique (C.N.R.S, France) and the Max-Planck Gesellschaft (MPG, Germany) is a leading laboratory pursuing research in the highest static magnetic fields technically feasible. The laboratory maintains strong in-house research activities and partly operates as a user facility for qualified external researchers. It has developed highly sophisticated instrumentation for specific use under high magnetic fields, including transport, magnetization, visible and infrared optical measurements at low temperatures and/or high pressures, EPR and NMR investigations in high magnetic fields. The laboratory delivers around 5000 hours of magnet time per year. Access for users to the high magnetic field facility is supported by the European Union, in the framework of the Human Potential Program: "Transnational Access to Major Research Infrastructures". The authors give an overview of the technical aspects of the facility and of the laboratory activities as a facility over the last years. The general organization of the user community and repartition between countries is also reviewed.

Quasi-stationary magnetic fields of 60 T using inductive energy storage

A pulsed magnet for the generation of fields up to 60 T using inductive energy storage has been built, tested and used for experiments at the Grenoble High Magnetic Field Laboratory (GHMFL). The pulse magnet system consists of a magnetic energy storage coil, made from aluminum of rectangular cross-section with a warm bore diameter of 1.1 m. Inside the warm bore is a smaller high-field magnet made from copper wire with a cold bore diameter of 24 mm. An electrical supply network consisting of a shock alternator, transformer and a rectifier provides the storage coil with a maximum dc current of 120 kA. High-current circuit breakers then direct the stored energy into the high field magnet. For safety and redundancy, two independent monitoring systems control the energy transfers. The design layout of the magnet system and the generation of pulses with fields up to 60.3 T with a pulse duration of 100 ms is described.

Magnet calculations at the Grenoble High Magnetic Field Laboratory

An axisymmetrical constrained semi-analytic optimization process is our basic tool for designing magnets. Developments of 3-D numerical models are undertaken to complement this approach. Such models are needed to investigate the overall behavior of our magnets. They are likely to provide suitable insights to solve the design problems arising from the demand for high magnetic field with both great spatial homogeneity and temporal stability.

The Grenoble High Magnetic Field Laboratory

The Grenoble High Magnetic Field Laboratory (GHMFL) was built to meet the requirements of scientists for experiments implying the use of high magnetic fields. It is established in Grenoble, France. It is a French–German laboratory, jointly operated by the Max Planck Institut für Festkörperforschung, in Stuttgart (MPI-FKF) and the Centre National de la Recherche Scientifique (CNRS). Scientists have access to the magnetic field facility provided they have written a proposal for experiments in high magnetic fields and have obtained the approval of the Program Committee to carry out their research. Since the foundation of the laboratory, the research effort has been mainly devoted to solid state physics (i.e. research on metals, superconductors, semiconductors, magnetism, etc.) which can be performed in a volume as small as a few cm 3. Five years ago the laboratory has undertaken the development of 20 MW magnets. Two of them are now in operation and deliver fields up to 30 T in a 50 mm room temperature bore. A 20 MW magnet is composed of two concentric 10 MW magnets. The outer 10 MW part alone achieves a field up to 10 T in a 376 mm diameter bore. It is obvious that this large diameter is convenient for MHD flow studies under high magnetic fields.

The Grenoble High Magnetic Field Laboratory as a user facility

The Grenoble High Magnetic Field Laboratory (GHMFL), run jointly by the Centre National de la Recherche Scientifique (CNRS, France) and the Max–Planck Gesellschaft (MPG, Germany) is a leading laboratory pursuing research in the highest static magnetic fields technically feasible. The laboratory maintains strong in-house research activities and partly operates as a user facility for qualified external researchers. It has developed highly sophisticated instrumentation for specific use under high magnetic fields, including transport, magnetization, visible and infrared optical measurements at low temperatures and/or high pressures, EPR and NMR investigations in high magnetic fields. The laboratory delivers around 5000 h of magnet time per year. Access for users to the high magnetic field facility is supported by the European Union, in the framework of the Human Potential Program : “Transnational Access to Major Research Infrastructures”.We give an overview of the technical aspects of the facility and of the laboratory activities as a facility over the last few years. The general organization of the user community and repartition between countries will also be reviewed.