Institut Néel Highlights 2006
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Bose-Einstein Condensation in a Solid A superconducting interferometer using carbon nanotubes When silicon turns into a superconductor http://www.neel.cnrs.fr Institut Néel Highlights 2006 Number 0 Director of publication : Alain Fontaine Editor : Laurent Lévy Associate editors : R. Cox, D. Givord, K. Hasselbach, J.-L. Hodeau, T. Klein, J.-P. Poizat, L. Saminadayar Institut Néel - Grenoble, France Date of publication : September 2007 The fi rst highlights... On the occasion of the inauguration of the Néel Institute by Arnold Migus, Director-General of the CNRS, we are pleased to present our fi rst booklet of “Highlights”, which will appear twice a year from now on. This fi rst issue shows our Institute’s three Departments all involved in a scientifi c approach fl avoured “nano” but anchored in their own core disciplines. It shows too how originality and excellence in research rest on visionary scientifi c-instrument building and on the making of the “dream-sample”. • Our physics of the 21st century opens with control of the phase of the electron wavefunction, and of its interferences. The single spin and the single charge make their mark on new phenomena. Photons and schools of electrons unite in the new land of “plasmonics”. In the solid state, the Bose Einstein condensate - mythical object of quantum mechanics - comes in from the cold to 20 degrees K, and generates a fruitful international collaboration. Carbon - in the shape of a conducting nanotube joined onto a superconducting loop - makes an interferometric probe so sensitive it should soon measure a single spin. • A single spin is indeed seen in a CdTe quantum dot - identifi ed by six peaks of light intensity - a magnifi cent fundamental experiment illustrating atomic physics. Carbon again, now unfurls in single sheets felicitously named «graphene», which host a cloud of electrons that are highly mobile in their plane, and move all with one velocity whatever their energy. • Instrumentation at the nano-scale for the world of low temperatures yields nanosquids to map vortices, and attojoule heat sensors to chase them : the magnetic singularities of the superconducting state. At 0.1 degrees above absolute zero, there is still electromagnetic radiation (light) to transport heat between two small islands connected by a superconducting wire. • Our Very Low Temperatures are installed at the heart of Edelweiss (six French labs, two Ger- man labs, one Russian lab), a patient hunt for elusive WIMPs (Weakly Interacting Massive Particles) - which must be there in the 23% Dark Matter of the standard cosmological model. • To attach organic nanocrystals to a protein is to fl ag it with an identity, thanks to the art of the chemist (patent 2007). Magnesium, the photographer’s metal of a hundred years ago, now virtuously stores hydrogen, energy source for thermal motors (two patents and tech-transfer to MCP of Romans on Isère). • Frustration, imposed on an array of spins, prevents them pairing up as each pair alone would wish. Theoreticians and experimentalists meet harmoniously around concepts like this, where creating new materials and new devices guides development of a theme. Alain FONTAINE Director iiI DÉPARTEMENT MCBT MATIÈRE CONDENSÉE ET BASSES TEMPÉRATURES The Department of Condensed Matter and Low Temperatures conducts fundamental studies of new states of matter (magnetism, charge density waves, superconductivity, etc.) and of the physics of helium between 100 µ K and room temperature. The department develops transverse activities in cryogenic electro- technology, fluid mechanics, astronomy, the life sciences and associated applications (cryogenics, aero-space). Edelweiss Cryostat DÉPARTEMENT NANO NANOSCIENCES The Department of Nanosciences is engaged in the study of the physical properties of nanostruc- tures : electronic transport, magnetism, nano- mechanics, spectroscopy... at both experimental and theoretical levels. These nanostructures are prepared from various types of materials cho- sen for their specific properties - novel semi- conductors, superconductors, metals, magnetic materials and molecules... Their fabrication at Surface electronic waves Ondes électroniques de surface the nanometre scale - molecular films, nanowi- res, nanotubes, quantum wells and dots - leads to novel functions resulting from the most fun- damental aspects of quantum physics. DÉPARTEMENT MCMF MATIÈRE CONDENSÉE MATÉRIAUX & FONCTIONS The Department of Condensed Matter, Ma- terials & Functions fosters fundamental re- search of materials and their applications. It has wide range experimental and theoretical expertises in material preparation, crystallo- graphy, electronic structure, magnetism, la- sers, non-linear optics, catalysis and energy. The Department is distinguished by a strong interplay between physics and chemistry. It Image furnace for crystal growth manages national projects at the ESRF and ILL and coordinates two thematic networks of the CNRS. Contents - Magnetic imaging of unconventional superconductors p1 - Thermal nanoworld p2 DÉPARTEMENT - Polarons in organic transistors p3 MCBT - High Curie temperature ferromagnetic oxides without MATIÈRE CONDENSÉE ET BASSES TEMPÉRATURES magnetic atoms p4 - Magnetic competition in a lattice of molecular helices p5 - In search of Dark Matter : the EDELWEISS experiment p6 - Bose-Einstein Condensation in a Solid p7 - A superconducting interferometer using carbon nanotubes : towards detection of a single spin p8 - When silicon becomes a superconductor p9 DÉPARTEMENT - Graphene : a new material for nanoelectronics p10 NANO - Quantum heat conduction p11 NANOSCIENCES - Probing a single spin p12 - Quantum coherence and Kondo effect p13 - Electronic spin fi ltering in nanostructures p14 - Scanning-Probe Imaging of Electron Interference Phenomena in Quantum Rings p15 - Effect of composition and ordering on magnetism of FePt p16 - Frustration in magnetic langasites p17 - Luminescent organic nanocrystals for detection of DÉPARTEMENT biological molecules p18 MCMF - Controlling the localisation of strong electromagnetic fi elds MATIÈRE CONDENSÉE MATÉRIAUX at sub-wavelengh scales P19 & FONCTIONS - Using X-Rays to observe catalysis on gold nanoparticles p20 - Very high pressure valves and gas pressure regulator p21 Magnetic imaging of unconventional Matière CONDENSéE, superconductors BASSES TEMPéRATURES Local imaging of the magnetization can be We have indeed observed vortices in this a very useful tool for understanding the physics of material, for the fi rst time. Individual vortices, each superconductors at the micron scale. A magnetic fi eld can carrying a quantum of fl ux, appear in very weak fi eld penetrate into a superconductor in the form of vortices, (H<10-4 Tesla). At higher fi elds, the vortices merge which are microscopic tubes of magnetic fl ux each together to form magnetic domains. We deduce that carrying one fl ux quantum Φ = h/2e. The vortex core is there is a mechanism in this compound that alters the not superconducting, so vortices constitute defects in the usual repulsion between vortices. superconductor whose behaviour gives information about the material’s superconducting mechanisms. We have developed a unique instrument : a magnetic microscope working at very low temperature (0.1 K< T< 10 K) which can draw a map of magnetic fi eld at the micron scale. The detector is a one micron diameter superconducting loop (a microSQUID) which we move over the sample surface to map the surface magnetic fi eld. Figure 2. Microsquid microscopy image (17 x 31 µm2) of NanoSQUID magnetic fl ux distribution on Sr2Ru04 at T= 0.38 K after “fi eld cooling” in H = 10 Gauss at angles (a) 70°, (b) 60° and (c) 50° to the c axis. Graph (d) shows the fl ux profi le through both a vortex and a “vortex line”, along the black trace shown in (a). Figure 1. (a) Magnetic probe (µSQUID) made in aluminium. (b) The silicon beam used for imaging, with the µSQUID We also observe the anisotropy of this lamellar (magenta colour) near its end. superconductor, which coexists with the fusion of the vortices. The vortex domains are stretched out and We have demonstrated the power of this lengthened when the magnetic fi eld is tilted towards “microSQUID microscopy” technique in studies the crystal planes. of magnetic fl ux structures at the surface of the Our novel µSQUID-based instrument has thus superconductor Sr2Ru04 (Tc ~1.5 K). The monocrystal enabled us to probe the nature of the superconductivity was grown in our institute by a molten zone method of Sr2Ru04 via the behaviour and interactions of vortices in an imaging furnace. Sr2Ru04 is a material with an in the material. This technique could be applicable to “unconventional” superconducting state. We use a many other magnetic materials. µSQUID to probe this material under a magnetic fi eld. We expect to fi nd domains where the Cooper pairs have antiparallel orbital moments (opposite chilarity); the presence of fractional vortices on the domain walls is predicted, and also preferential nucleation of vortices in one of the two kinds of domains. Contact: Klaus Hasselbach Further reading : [email protected] • “Observation of two species of vortices in the anisotropic spin-triplet supercon- Tel: +33 476881154 ductor Sr2RuO4,” ,V. O. Dolocan, P. Lejay, D. Mailly, and K. Hasselbach, Phys. Rev. B 74, 144505 (2006). • “Observation of Vortex Coalescence in the Anisotropic Spin-Triplet Supercon- ductor Sr2RuO4”, V. O. Dolocan, C. Veauvy, F. Servant, P. Lejay, K. Hasselbach, Y. Liu, and D. Mailly, Phys. Rev. Lett. 95, 097004 (2005). -1- matière