158 research outputs found
Phil Anderson's Magnetic Ideas in Science
In Philip W. Anderson's research, magnetism has always played a special role,
providing a prism through which other more complex forms of collective behavior
and broken symmetry could be examined. I discuss his work on magnetism from the
1950s, where his early work on antiferromagnetism led to the pseudospin
treatment of superconductivity - to the 70s and 80s, highlighting his
contribution to the physics of local magnetic moments. Phil's interest in the
mechanism of moment formation, and screening evolved into the modern theory of
the Kondo effect and heavy fermions.Comment: References fully hypertexed with live links to historic papers.
"PWA90: A Lifetime of Emergence", editors P. Chandra, P. Coleman, G. Kotliar,
P. Ong, D. Stein and C. Yu, pp 187-213, World Scientific (2016
The symplectic-N t-J model and s superconductors
The possible discovery of superconducting gaps in the moderately
correlated iron-based superconductors has raised the question of how to
properly treat gaps in strongly correlated superconductors. Unlike the
d-wave cuprates, the Coulomb repulsion does not vanish by symmetry, and a
careful treatment is essential. Thus far, only the weak correlation approaches
have included this Coulomb pseudopotential, so here we introduce a symplectic N
treatment of the t-J model that incorporates the strong Coulomb repulsion
through the complete elimination of on-site pairing. Through a proper extension
of time-reversal symmetry to the large N limit, symplectic-N is the first
superconducting large N solution of the t-J model. For d-wave superconductors,
the previous uncontrolled mean field solutions are reproduced, while for
superconductors, the SU(2) constraint enforcing single occupancy acts
as a pair chemical potential adjusting the location of the gap nodes. This
adjustment can capture the wide variety of gaps proposed for the iron based
superconductors: line and point nodes, as well as two different, but related
full gaps on different Fermi surfaces.Comment: 8 pages, 3 figure
Spins, electrons and broken symmetries: realizations of two channel Kondo physics
Adding a second Kondo channel to heavy fermion materials reveals new exotic
symmetry breaking phases associated with the development of Kondo coherence. In
this paper, we review two such phases, the "hastatic order" associated with
non-Kramers doublet ground states, where the two-channel nature of the Kondo
coupling is guaranteed by virtual valence fluctuations to an excited Kramers
doublet, and "composite pair superconductivity," where the two channels differ
by charge 2e and can be thought of as virtual valence fluctuations to a
pseudo-isospin doublet. The similarities and differences between these two
orders will be discussed, along with possible realizations in actinide and rare
earth materials like URu2Si2 and NpPd5Al2.Comment: 13 pages, 4 figures. Prepared for Comptes Rendu Physiques, Emergent
phenomena in actinide
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