Presentation on theme: "Literature Reviews 2005/06 Christoph Bergemann Quantum Matter Group, Cavendish Laboratory Phone: 37389 1.Electronic Structure of Quasicrystals."— Presentation transcript:
Literature Reviews 2005/06 Christoph Bergemann Quantum Matter Group, Cavendish Laboratory Phone: Electronic Structure of Quasicrystals 2.20 Years of High-Tc Superconductivity – Why Isn’t My Power Cord Made of It? 3.The Quest for Metallic (and Superconducting!) Hydrogen 4.Focusing X Rays to Nanometer Dimensions
Quasicrystals Major result in QCMP course (Lent) Ordinary crystals have periodic lattices Solid state physics = quantum mechanics in periodic potential (+ interactions…) Solutions are wave-like – Bloch’s theorem
Quasicrystals Quasicrystals have non-periodic lattices But still perfectly ordered – sharp Bragg peaks in X-ray diffraction! 5-fold and 10-fold symmetry axes forbidden for ordinary crystals – dodecahedral shapes! Quantum mechanics in quasiperiodic potential - solutions are tricky – Bloch’s theorem is violated Laue XRD pattern
Quasicrystals Some more food for thought: Quasicrystals are 3D slices through periodic structures in higher-D “hyperspace” 1D Quasicrystal: Fibonacci stack Substitution rule: A ! AB, B ! A ABAABABA Ã ABAAB Ã ABA Ã AB Ã A 2D Quasicrystal: Penrose tilings
Quasicrystals Some theoretical results: Electrons are (probably) localised Density of states is fractal or even wilder Experimental situation is highly unsatisfactory: Metallic constituents (Al, Ni, Co, Pd, Mn, …) but bad conductivity Some experiments see “proper” bands, even though they shouldn’t This literature review: Survey both theory and experiment as to what’s going on
High-T c Superconductivity BednorzMüller Nobel Prize 1987
High-T c Superconductivity Many scientific issues: Why copper oxides, and why such complicated materials? What is the superconducting mechanism? The “normal” state is actually quite abnormal – why? Can we reach room temperature superconductivity? Crystal Structure of YBa 2 Cu 3 O 7- Not the subject of this review
High-T c Superconductivity Engineering issues: How to form cables from brittle ceramics? How to beat the cooling challenge? How to exploit superconducting phase coherence effects? ! SQUIDs etc. How are high-T c materials used today? – And what are realistic future prospects? This literature review
High-T c Superconductivity Some examples: Maglev trains Power cables Fault current limiters High-T c SQUIDs
Metallic Hydrogen We all know hydrogen as a gas Under high pressures, it becomes a liquid Speculation since 1935 that hydrogen might become metallic! Wigner Is Jupiter a giant blob of superhot liquid metal?
Metallic Hydrogen “Arms race” between theorists and experimentalists re: the pressure needed for metallisation High pressure techniques: need 2 Mbars Clamp cell: 30 kbar Ocean floor: 1 kbar Anvil cell: 150 kbar
Metallic Hydrogen Experiment finally caught up in 1996… Not just experimental tour de force, but also deep theoretical statement – metal-insulator transition is highly non-trivial phenomenon relating to electron correlations
Metallic Hydrogen Latest results: theory, again… At very low temperatures, de Broglie wavelength becomes comparable to inter-atom separation ! Metallic superfluid - or even a superconducting superfluid - at 4 Mbars? Electron vs. proton flow This review: physics background, history, experiment & latest ideas Vortex tornados inside a metallic superfluid – or merely inside the mind of a theorist?
X-Ray Nanofocusing Flux gain X-ray microscopy – with nm resolution? Nanoparticle (and single molecule?) imaging (diffraction/ fluorescence) Nanolithography J. Kirz, Stony Brook Latest Intel chip, launched this month: Pentium 4 “Prescott” 90nm (!) features Roadmap: 13nm EUV
X-Ray Nanofocusing Small absorption Index of refraction near unity… …and actually smaller than 1 Any lensing is a tremendous challenge! Things get tougher for hard X rays ie. short wavelengths
X-Ray Nanofocusing Some approaches: “Swiss cheese” lens Zone plates with ultra- high aspect ratios Orthogonal curved mirrors (Kirkpatrick-Baez)
X-Ray Nanofocusing Fundamental focusing limits? Full wave optics approach is similar to Schrodinger equation – does uncertainty relation apply?