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Published byΊακχος Δημαράς Modified over 6 years ago
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TRADITIONAL SUBJECT-MATTER OF CONDENSED MATTER THEORY: CRYSTALLINE SOLIDS, LIQUIDS ….
On the cosmic scale: Stars density Interstellar Space temperature Liquids and crystalline solids: ~ 1 part in 1011! And yet… 10– – – – – Temp. of Outer Space Room Temp. 9/5/ :54 AM
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WHAT IS (MODERN) CONDENSED MATTER THEORY?
by a liberal definition, the study of any system where we — must deal with a very large number of mutually interacting objects — have incomplete description at the level of single objects — must allow for the effects of a noisy “environment” — can (usually) get little useful information out of an exact “microscopic” description, even were one available — can compare theoretical predictions directly with experiment Some non-traditional areas of applicability of condensed matter theory: polymers nano/mesoscopic systems glasses (amorphous materials) high-temperature (cuprate) superconductors neural networks the human genome the stock market the Internet…
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? Some generic principles we have learned:
— Effects of interactions between ~1023 “objects” (atoms, etc.) may be qualitatively different from those of 2–, 3– … n-body interactions — essential to develop phenomenological, intermediate-level models — models do not need to be derivable from “microscopic” description, but must be consistent with it. ? — quite different types of structure at the “microscopic” level may nevertheless lead to “universal” behavior at the macro-level exx: 2nd order phase transitions ? Glasses ?? 1/f noise — sometimes useful to change the question (ex: Landau theory of Fermi liquid)
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A TYPICAL “INTERMEDIATE-LEVEL” MODEL: THE CONCEPT OF A QUASIPARTICLE
object which may be a very complex combination of “elementary” particles, but nevertheless behaves very much like a “particle” itself. examples: fermionic quasiparticle in Landau Fermi liquid phonon in crystalline solid phonon in superfluid liquid 4He Laughlin quasiparticle in fractional quantum Hall effect (“fractional” charge, statistics) “nonabelian” anyons intrinsically many-body phenomenon! screening cloud compression rarefaction extra charge , ,
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Liquid 4He in Annular Geometry
A Spectacular Example of how “Many-Body” Effects can Produce Qualitatively New Forms of Behavior: Liquid 4He in Annular Geometry R Rotate container at T>T with <½c: liquid rotates with container. Cool below T: liquid comes out of equilibrium with container, to rest in () frame of laboratory. (“Hess-Fairbank” effect/nonclassical rotational inertia) Set liquid into “fast” rotation (»c), then stop container: liquid continues to rotate indefinitely (“persistent currents”) “quantum unit of rotation” Both effects consequences of quantum mechanics: for any individual atom, Bose-Einstein condensation (“BEC”) : (at T=0), all atoms must behave identically (for (6)): (repulsive) inter-atomic interactions BEC amplifies microscopic effects to macroscopic level!
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WHY AN ICMT NOW? — unprecedented awareness, in many areas of science, of crucial significance of collective behavior. — the bread and butter of condensed matter theory! Material Science Traditional Solid-State Physics Theoretical Chemistry Astrophysics Neuroscience Modern Condensed-Matter Theory Medical Physics Geophysics Biology High-Energy Physics Nanoscience Cosmology Quantum Information Quantum information: originally, dealt with well isolated atomic-level systems In 2008: (a) solid-state qubits, even based on collective degrees of freedom (e.g., SQUIDs) (b) topological ideas in quantum computing
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CONDENSED MATTER THEORY: WHAT LIES IN THE FUTURE?
— partnerships beyond traditional boundaries — exploration along “axis” of complexity — more concentration on individual quantum states — technological spinoffs, e.g. ?? RT superconductivity?? — input to fundamental questions of physics: (a) quantum measurement paradox: B C “neither B nor C” “neither dead nor alive”? (b) arrow of time: A K Q J . . . 2 K 8 J A 7 intersection of considerations from thermodynamics, EM theory, cosmology(?), biology, psychology…. and condensed matter theory!
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