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Site Details References on Neutron Scattering History of the High Flux Beam Reactor (pdf format) Related Sites Condensed Matter Physics & Materials Science Center for Functional Nanomaterials National Synchrotron Light Source National Synchrotron Light Source II BNL Basic Energy Sciences Directorate Other Information |
## Quantum Spin ChainsQuantum spin chains have for a number of years been a test bed for understanding fundamental physical properties of many-body quantum systems. Studies of spin chains have provided examples of novel ground states, fractional excitations, quantum disorder and critical behavior. The new knowledge obtained from studying these systems is used to explain, predict and tune phenomena both on the fundamental level and those employed in technological applications such as magnetic recording media, CMR read-heads, magnetic sensors, spin-based electronics, etc. Recent experiments on doped layered curates and nickelates have also indicated close connection between quantum magnetism of doped two-dimensional (2D) Mott insulators, including high-temperature superconductors, and the physics of quantum spin chains and ladders. In fact, one approach to understanding the two-dimensional quantum antiferromagnetics (AFM) realized in Mott insulating state of layered metal oxides is based on studying dimensional cross-over in an array of one-dimensional Mott insulators, or coupled spin chains. This approach takes advantage of significant theoretical breakthroughs that have occurred in this field in the past decade. Two main research directions pursued by our group are ## Covalency, itinerancy, dimensional cross-over and spinons in S=1/2 chainsAmong
the most important recent theoretical developments is that of quantum
field theory methods yielding exact analytical expressions for two- and
four-spinon contributions to the dynamical structure factor of S=1/2
Heisenberg chain. Not only these results can be used for extending
theoretical predictions to 2D via examination of dimensional crossover in
arrays of coupled S=1/2 chains, they can also be accurately matched against
results of neutron scattering experiments probing quantum spin dynamics in
real 1D Mott-insulating materials, such as Sr ## Haldane spin gap in S=1 chains: doping and dimensional cross-over effectsProperties
of 1D quantum antiferromagnet change dramatically when its spin increases
from 1/2 to 1. In fact, as was first established by Haldane, integer
and half-integer spin chains belong to different universality classes, of
which spin-1/2 and spin-1 chains are the ultimate quantum representatives.
Spin-1/2 chains are Luttinger liquids with critical ground state and gapless
continuum spectrum composed of fractional spinon excitations, while AFM S=1
Haldane chains have robust singlet ground state and coherent magnon
excitations separated from it by a finite gap. These magnon quasiparticles
become unstable and yield to a continuum at high energies when their pair
decays become cinematically allowed. When doped, S=1 AFM chain develops
peculiar spin-density polarons, whose structure reflects hidden order
existing in the Haldane state and which can be probed by magnetic neutron
scattering. A finite interchain coupling J' More information on these topics and an overview of our recent results can be obtained by visiting presentations and selected publications pages. Last Modified: Friday, 21-Mar-2008 18:19:00 EDT |