792 research outputs found
Luttinger theorem for a spin-density-wave state
We obtained the analog of the Luttinger relation for a commensurate
spin-density-wave state. We show that while the relation between the area of
the occupied states and the density of particles gets modified in a simple and
predictable way when the system becomes ordered, a perturbative consideration
of the Luttinger theorem does not work due to the presence of an anomaly
similar to the chiral anomaly in quantum electrodynamics.Comment: 4 pages, RevTeX, 1 figure embedded in the text, ps-file is also
available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm
Non-fermi liquid behavior in itinerant antiferromagnets
We consider a two dimensional itinerant antiferromagnet near a quantum
critical point. We show that, contrary to conventional wisdom, fermionic
excitations in the ordered state are not the usual Fermi liquid quasiparticles.
Instead, down to very low frequencies, the fermionic self energy varies as
. This non-Fermi liquid behavior originates in the coupling of
fermions to the longitudinal spin susceptibility
in which the order-induced ``gap'' in the spectrum at dissolves into the
Landau damping term at . The transverse spin fluctuations obey
scaling characteristic of spin waves, but remain overdamped in a finite
range near the critical point.Comment: 5p., 3fig
Spin-liquid model of the sharp resistivity drop in
We use the phenomenological model proposed in our previous paper [Phys. Rev.
Lett. {\bf 98}, 237001 (2007)] to analyse the magnetic field dependence of the
onset temperature for two-dimensional fluctuating superconductivity . We demonstrate that the slope of progressively goes down as
increases, such that the upper critical field progressively increases as
decreases. The quantitative agreement with the recent measurements of
in is achieved for the same parameter
value as was derived in our previous publication from the analysis of the
electron self energy.Comment: 4 pages, 2 figure
Dispersion Anomalies in Cuprate Superconductors
We argue that the shape of the dispersion along the nodal and antinodal
directions in the cuprates can be understood as a consequence of the
interaction of the electrons with collective spin excitations. In the normal
state, the dispersion displays a crossover at an energy where the decay into
spin fluctuations becomes relevant. In the superconducting state, the antinodal
dispersion is strongly affected by the spin resonance and displays an S-shape
whose magnitude scales with the resonance intensity. For nodal fermions,
relevant spin excitations do not have resonance behavior, rather they are
better characterized as a gapped continuum. As a consequence, the S-shape
becomes a kink, and superconductivity does not affect the dispersion as
strongly. Finally, we note that optical phonons typically lead to a temperature
independent S-shape, in disagreement with the observed dispersion.Comment: 12 pages, 7 eps figure
Inter-pocket pairing and gap symmetry in Fe-based superconductors with only electron pockets
Pairing symmetry in recently discovered Fe-based metallic superconductors
AFeSe (A = K, Rb, Cs) with high transition temperature K
is currently a subject of intensive debates. These systems contain only
electron pockets, according to photoemission, and differ from the majority of
Fe-based superconductors in which both electron and hole pockets are present.
Both d-wave and s-wave pairing symmetries have been proposed for AFeSe,
but a d-wave gap generally has nodes, while experiments clearly point to
no-nodal behavior, and a conventional s-wave gap is inconsistent with the
observation of the neutron resonance below . We argue that current
theories of pairing in such systems are incomplete and must include not only
intra-pocket pairing condensate but also inter-pocket condensate made of
fermions belonging to different electron pockets. We analyze the interplay
between intra-pocket and inter-pocket pairing depending on the ellipticity of
electron pockets and the strength of their hybridization and show that
hybridization brings the system into a new state, in which the gap
changes sign between hybridized pockets. This state has the full gap and at the
same time supports spin resonance, in agreement with the data. Near the
boundary of state we found a long-thought state which breaks
time-reversal symmetry.Comment: 19 pages, 5 figure
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