27,685 research outputs found
Multidimensional Bosonization
Bosonization of degenerate fermions yields insight both into Landau Fermi
liquids, and into non-Fermi liquids. We begin our review with a pedagogical
introduction to bosonization, emphasizing its applicability in spatial
dimensions greater than one. After a brief historical overview, we present the
essentials of the method. Well known results of Landau theory are recovered,
demonstrating that this new tool of many-body theory is robust. Limits of
multidimensional bosonization are tested by considering several examples of
non-Fermi liquids, in particular the composite fermion theory of the
half-filled Landau level. Nested Fermi surfaces present a different challenge,
and these may be relevant in the cuprate superconductors. We conclude by
discussing the future of multidimensional bosonization.Comment: 91 pages, 15 eps figures, LaTeX. Minor changes to match the published
versio
Electronic Structures of Antiperovskite Superconductor MgCNi and Related Compounds
Electronic structure of a newly discovered antiperovskite superconductor
MgCNi is investigated by using the LMTO band method. The main contribution
to the density of states (DOS) at the Fermi energy comes from Ni
3 states which are hybridized with C 2 states. The DOS at is
varied substantially by the hole or electron doping due to the very high and
narrow DOS peak located just below . We have also explored
electronic structures of C-site and Mg-site doped MgCNi systems, and
described the superconductivity in terms of the conventional phonon mechanism.Comment: 3 pages, presented at ORBITAL2001 September 11-14, 2001 (Sendai,
JAPAN
Electronic structures of antiperovskite superconductors: MgXNi (X=B,C,N)
We have investigated electronic structures of a newly discovered
antiperovskite superconductor MgCNi and related compounds MgBNi and
MgNNi. In MgCNi, a peak of very narrow and high density of states is
located just below , which corresponds to the antibonding
state of Ni-3d and C- but with the predominant Ni-3d character. The
prominent nesting feature is observed in the -centered electron Fermi
surface of an octahedron-cage-like shape that originates from the 19th band.
The estimated superconducting parameters based on the simple rigid-ion
approximation are in reasonable agreement with experiment, suggesting that the
superconductivity in MgCNi is described well by the conventional phonon
mechanism.Comment: 5 pages, 5 figure
Electronic structure of metallic antiperovskite compound GaCMn
We have investigated electronic structures of antiperovskite GaCMn and
related Mn compounds SnCMn, ZnCMn, and ZnNMn. In the paramagnetic
state of GaCMn, the Fermi surface nesting feature along the
direction is observed, which induces the antiferromagnetic (AFM) spin ordering
with the nesting vector {\bf Q} . Calculated
susceptibilities confirm the nesting scenario for GaCMn and also explain
various magnetic structures of other antiperovskite compounds. Through the band
folding effect, the AFM phase of GaCMn is stabilized. Nearly equal
densities of states at the Fermi level in the ferromagnetic and AFM phases of
GaCMn indicate that two phases are competing in the ground state.Comment: 4 pages, 5 figure
Electron-boson spectral density of LiFeAs obtained from optical data
We analyze existing optical data in the superconducting state of LiFeAs at 4 K, to recover its electron-boson spectral density. A maximum entropy
technique is employed to extract the spectral density from
the optical scattering rate. Care is taken to properly account for elastic
impurity scattering which can importantly affect the optics in an -wave
superconductor, but does not eliminate the boson structure. We find a robust
peak in centered about 8.0 meV or 5.3 (with 17.6 K). Its position in energy agrees well with a similar
structure seen in scanning tunneling spectroscopy (STS). There is also a peak
in the inelastic neutron scattering (INS) data at this same energy. This peak
is found to persist in the normal state at 23 K. There is evidence that
the superconducting gap is anisotropic as was also found in low temperature
angular resolved photoemission (ARPES) data.Comment: 17 pages, 6 figure
Nonchaotic Nonlinear Motion Visualized in Complex Nanostructures by Stereographic 4D Electron Microscopy
Direct electron imaging with sufficient time resolution is a powerful tool for visualizing the three-dimensional (3D) mechanical motion and resolving the four-dimensional (4D) trajectories of many different components of a nanomachine, e.g., a NEMS device. Here, we report a nanoscale nonchaotic motion of a nano- and microstructured NiTi shape memory alloy in 4D electron microscopy. A huge amplitude oscillatory mechanical motion following laser heating is observed repetitively, likened to a 3D motion of a conductor’s baton. By time-resolved 4D stereographic reconstruction of the motion, prominent vibrational frequencies (3.0, 3.8, 6.8, and 14.5 MHz) are fully characterized, showing evidence of nonlinear behavior. Moreover, it is found that a stress (fluence)−strain (displacement) profile shows nonlinear elasticity. The observed resonances of the nanostructure are reminiscent of classical molecular quasi-periodic behavior, but here both the amplitude and frequency of the motion are visualized using ultrafast electron microscopy
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