Transcript Metal
20th century physics Relativity Quantum mechanics • Particle physics • Study of fields Brownian motion • 21st century Condensed Matter Physics electronically complex functional materials Soft matter: Amphiphile + [water & oil] (Molecule of both hydrophilic and hydrophobic nature. It has an oily tail chemically bonded to a water soluble head group) The mixture causes frustration and oil & water molecules associated with the amphiphile are near each other Leads to mesoscopic phase separation occurring dynamically with many equilibrium phases due to competition between oil and water for the two parts of the amphiphile Towards the electronic analogue: Metal - Ammonia solutions Temperature (K) • 200 • Regions of high density free e-’s, owing to the Pauli principle, avoid the e- rich ammonia N o n metallic solution However, the ammonia phase attempts to retain the +ve charged metal ions, which can then be solvated. Metallic solution • Phase separation Solid ammonia 100 Solid two-phase mixture 4 8 Metal concentration (mole per cent metal) In the drive to local electrical neutrality, the +ve metal ions act much like amphiphiles in microemulsions: Here the metal ions separate the high and low density e- phases Materials at the border between being Metals – Insulators – SC’s • With the help of little, but inevitable, lattice disorder we have several bona fide phase transitions • • Close to a phase transition, materials exhibit large responses to small external signals driving the system from one phase to the other. This • changes dramatically the We anticipate the electronic degrees of freedom to become preorganised on intermediate length scales and then properties of the material. fluctuate collectively on longer scales, much like Concurrently, activated transitions the systems we encounter in colloids between electronic structures lead to very slow dynamics … Modern complex electronic systems: Spin, charge & Orbital • Intrinsic complexity The many degrees of freedom interact in a nonlinear & synergic manner, and with charge & spin as fundamental order we can imagine equilibrium phase degrees at least as complex as oil-water-amphiphile • Hard & Soft Condensed matter In such systems in addition to periodically ordered phases, we may also have long lived aperiodically inhomogeneous systems, like gel or glass • Electron liquid crystals The resulting electronically complex systems may be intermediate between electron liquid and electron crystal. Materials needed to study e- - complexity: Possessing the widest range of a tuneable ground state at T=0 (quantum comes in) Insulating, Delocalised, Metallic, High-Tc Superconducting 350-400 metallic Nonmetallic Temperature (K) Transition Metal Oxides displaying a zoology of phases with: AF ? properties using charge carrier doping as the Quantum Tuning Parameter 30 -135 K 0 SC Quantum control parameter: Carrier concentration (%) 30 Metal-Ammonia solution Temperature (K) 300 250 metallic Nonmetallic AF Non-metal to metal transition Non metal solvated electrons Metal free electrons 1 SC 0 Carrier concentration (%) Behaviour may generic Phase separation 200 0.1 350-400 Temperature (K) The tendency for electronic phase separation reminds us of amphiphile & (water+oil), or metalammonia solutions or even structural glass among the many SC’s on 10 Moles percent metal J. Thompson Rev. Mod. Phys. 40, 704 (1968) the border of magnetism 30 Could be mistaken for phase separated Amphiphile & (water+oil) 350-400 metallic Temperature (K) J.C. Davis group Cornell University Nonmetallic AF SC 0 Carrier concentration (%) 30 Ordered crystalline, checkerboard and striped electronic glasses emerge as candidate forms of correlated electronic matter