188 research outputs found
Competition/Enhancement of Two Probe Order Parameters in the Unbalanced Holographic Superconductor
We introduce and study a simple unbalanced holographic superconductor model
with two scalar order parameters. The attention is focused on the possibility
of coexisting orderings corresponding to the concomitant condensation of two
scalar operators. Through a probe analysis we show that an attractive or
repulsive direct interaction between the two bulk scalars leads respectively to
competition and enhancement of the associated condensates. The system at hand
is a toy model for studying generic multiple ordering in a strongly coupled
context and some comments are given about its applicability to the
ferromagnetic unconventional superconductors.Comment: 17 pages, 8 figure
Minimal Model for an Unbalanced Holographic Superconductor
We describe the simplest holographic model for an s-wave unbalanced
superconductor in 2+1 dimensions. We study its phase diagram and linear
response features with particular attention to the possibility of spatially
modulated phases (LOFF) and mixed spin-electric properties. The normal phase of
the model at hand allows us to analyze a strong-coupling generalization of Mott
two-current model for spintronic systems; the superconducting phase features an
interesting DC spin-superconductivity without spin-symmetry breaking .Comment: 14 pages, 12 figures, Proceedings of the Corfu Summer Institute 2012
"School and Workshops on Elementary Particle Physics and Gravity", September
8-27, 2012, Corfu, Greec
Simplest phonons and pseudo-phonons in field theory
We study the emergence of Nambu-Goldstone modes due to broken translation
symmetry in field theory. Purely spontaneous breaking yields a massless phonon
which develops a mass upon introducing a perturbative explicit breaking. The
pseudo-phonon mass agrees with Gell Mann-Oakes-Renner relations. We analyze the
simplest possible theories featuring gradient Mexican hats and describing
space-dependent order parameters. We comment on homogeneous translation
breaking and the connections with holographic Q-lattices.Comment: 25 pages, 1 figure; (v3 extended analysis, typo fixed
Magneto-transport from momentum dissipating holography
We obtain explicit expressions for the thermoelectric transport coefficients
of a strongly coupled, planar medium in the presence of an orthogonal magnetic
field and momentum-dissipating processes. The computations are performed within
the gauge/gravity framework where the momentum dissipation mechanism is
introduced by including a mass term for the bulk graviton. Relying on the
structure of the computed transport coefficients and promoting the parameters
to become dynamical functions, we propose a holography inspired phenomenology
open to a direct comparison with experimental data from the cuprates.Comment: 23 page
Electromagnetic response of strongly coupled plasmas
We present a thorough analysis of the electromagnetic response of strongly
coupled neutral plasmas described by the gauge/gravity correspondence. The
coupling of the external electromagnetic field with the tower of quasi-normal
modes of the plasmas supports the presence of various electromagnetic modes
with different properties. Among them we underline the existence of negative
refraction with low dissipation for a transverse non-hydrodynamical mode.
Previous hydrodynamical approaches have shown the ubiquitous character of
negative refraction in charged plasmas and the absence thereof in neutral
plasmas. Our results here extend the analysis for neutral plasmas beyond the
hydrodynamical regime. As an application of these new insights we briefly
discuss the case of the quark gluon plasma in the temperature dominated regime.Comment: 29 pages, 15 figure
Chasing the cuprates with dilatonic dyons
Magnetic field and momentum dissipation are key ingredients in describing
condensed matter systems. We include them in gauge/gravity and systematically
explore the bottom-up panorama of holographic IR effective field theories based
on bulk Einstein-Maxwell Lagrangians plus scalars. The class of solutions here
examined appear insufficient to capture the phenomenology of charge transport
in the cuprates. We analyze in particular the temperature scaling of the
resistivity and of the Hall angle. Keeping an open attitude, we illustrate weak
and strong points of the approach.Comment: 30 pages, 2 figures, Version to appear in JHE
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