466 research outputs found
Non-Fermi liquids from holography
We report on a potentially new class of non-Fermi liquids in
(2+1)-dimensions. They are identified via the response functions of composite
fermionic operators in a class of strongly interacting quantum field theories
at finite density, computed using the AdS/CFT correspondence. We find strong
evidence of Fermi surfaces: gapless fermionic excitations at discrete shells in
momentum space. The spectral weight exhibits novel phenomena, including
particle-hole asymmetry, discrete scale invariance, and scaling behavior
consistent with that of a critical Fermi surface postulated by Senthil.Comment: 10 pages, 16 figures. v2: added references, corrected figures, some
minor changes. v3: figure 5 replace
Adventures in Holographic Dimer Models
We abstract the essential features of holographic dimer models, and develop
several new applications of these models. First, semi-holographically coupling
free band fermions to holographic dimers, we uncover novel phase transitions
between conventional Fermi liquids and non-Fermi liquids, accompanied by a
change in the structure of the Fermi surface. Second, we make dimer vibrations
propagate through the whole crystal by way of double trace deformations,
obtaining nontrivial band structure. In a simple toy model, the topology of the
band structure experiences an interesting reorganization as we vary the
strength of the double trace deformations. Finally, we develop tools that would
allow one to build, in a bottom-up fashion, a holographic avatar of the Hubbard
model.Comment: 22 pages, 8 figures; v2: brief description of case of pure D5 lattice
added in sec.3; v3: minor typo fixed; v4: minor change
Holographic Aspects of Fermi Liquids in a Background Magnetic Field
We study the effects of an external magnetic field on the properties of the
quasiparticle spectrum of the class of 2+1 dimensional strongly coupled
theories holographically dual to charged AdS black holes at zero
temperature. We uncover several interesting features. At certain values of the
magnetic field, there are multiple quasiparticle peaks representing a novel
level structure of the associated Fermi surfaces. Furthermore, increasing
magnetic field deforms the dispersion characteristics of the quasiparticle
peaks from non-Landau toward Landau behaviour. At a certain value of the
magnetic field, just at the onset of Landau-like behaviour of the Fermi liquid,
the quasiparticles and Fermi surface disappear.Comment: 18 pages, 10 figures. Revised some of the terminology: changed
non-separable solutions to infinite-sum solution
Label-free detection of anticancer drug paclitaxel in living cells by confocal Raman microscopy
Confocal Raman microscopy, a non-invasive, label-free, and high spatial resolution imaging technique is employed to trace the anticancer drug paclitaxel in living Michigan Cancer Foundation-7 (MCF-7) cells. The Raman images were treated by K-mean cluster analysis to detect the drug in cells. Distribution of paclitaxel in cells is verified by calculating the correlation coefficient between the reference spectrum of the drug and the whole Raman image spectra. A time dependent gradual diffusion of paclitaxel all over the cell is observed suggesting a complementary picture of the pharmaceutical action of this drug based on rapid binding of free tubulin to crystallized paclitaxel. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794871
Chaotic Strings in AdS/CFT.
Holographic theories with classical gravity duals are maximally chaotic; i.e., they saturate the universal bound on the rate of growth of chaos [J. Maldacena, S. H. Shenker, and D. Stanford, J. High Energy Phys. 08 (2016) 106JHEPFG1029-847910.1007/JHEP08(2016)106]. It is interesting to ask whether this property is true only for leading large N correlators or if it can show up elsewhere. In this Letter, we consider the simplest setup to tackle this question: a Brownian particle coupled to a thermal ensemble. We find that the four-point out-of-time-order correlator that diagnoses chaos initially grows at an exponential rate that saturates the chaos bound, i.e., with a Lyapunov exponent λ_{L}=2π/β. However, the scrambling time is parametrically smaller than for plasma excitations, t_{*}∼βlogsqrt[λ] instead of t_{*}∼βlogN^{2}. Our result shows that, at least in certain cases, maximal chaos can be attained in the probe sector without the explicit need of gravitational degrees of freedom.Funded by SCOAP3
Landau Levels, Magnetic Fields and Holographic Fermi Liquids
We further consider a probe fermion in a dyonic black hole background in
anti-de Sitter spacetime, at zero temperature, comparing and contrasting two
distinct classes of solution that have previously appeared in the literature.
Each class has members labeled by an integer n, corresponding to the n-th
Landau level for the fermion. Our interest is the study of the spectral
function of the fermion, interpreting poles in it as indicative of
quasiparticles associated with the edge of a Fermi surface in the
holographically dual strongly coupled theory in a background magnetic field H
at finite chemical potential. Using both analytical and numerical methods, we
explicitly show how one class of solutions naturally leads to an infinite
family of quasiparticle peaks, signaling the presence of a Fermi surface for
each level n. We present some of the properties of these peaks, which fall into
a well behaved pattern at large n, extracting the scaling of Fermi energy with
n and H, as well as the dispersion of the quasiparticles.Comment: 23 pages, 4 figures. Changed some of the terminology: non-separable
-> infinite-sum. Clarified the relationship between our ansatz and the
separable ansat
Deconstructing holographic liquids
We argue that there exist simple effective field theories describing the
long-distance dynamics of holographic liquids. The degrees of freedom
responsible for the transport of charge and energy-momentum are Goldstone
modes. These modes are coupled to a strongly coupled infrared sector through
emergent gauge and gravitational fields. The IR degrees of freedom are
described holographically by the near-horizon part of the metric, while the
Goldstone bosons are described by a field-theoretical Lagrangian. In the cases
where the holographic dual involves a black hole, this picture allows for a
direct connection between the holographic prescription where currents live on
the boundary, and the membrane paradigm where currents live on the horizon. The
zero-temperature sound mode in the D3-D7 system is also re-analyzed and
re-interpreted within this formalism.Comment: 21 pages, 2 figure
Magnetic Field Induced Quantum Criticality via new Asymptotically AdS_5 Solutions
Using analytical methods, we derive and extend previously obtained numerical
results on the low temperature properties of holographic duals to
four-dimensional gauge theories at finite density in a nonzero magnetic field.
We find a new asymptotically AdS_5 solution representing the system at zero
temperature. This solution has vanishing entropy density, and the charge
density in the bulk is carried entirely by fluxes. The dimensionless magnetic
field to charge density ratio for these solutions is bounded from below, with a
quantum critical point appearing at the lower bound. Using matched asymptotic
expansions, we extract the low temperature thermodynamics of the system. Above
the critical magnetic field, the low temperature entropy density takes a simple
form, linear in the temperature, and with a specific heat coefficient diverging
at the critical point. At the critical magnetic field, we derive the scaling
law s ~ T^{1/3} inferred previously from numerical analysis. We also compute
the full scaling function describing the region near the critical point, and
identify the dynamical critical exponent: z=3.
These solutions are expected to holographically represent boundary theories
in which strongly interacting fermions are filling up a Fermi sea. They are
fully top-down constructions in which both the bulk and boundary theories have
well known embeddings in string theory.Comment: 50 page
Non-relativistic metrics from back-reacting fermions
It has recently been pointed out that under certain circumstances the
back-reaction of charged, massive Dirac fermions causes important modifications
to AdS_2 spacetimes arising as the near horizon geometry of extremal black
holes. In a WKB approximation, the modified geometry becomes a non-relativistic
Lifshitz spacetime. In three dimensions, it is known that integrating out
charged, massive fermions gives rise to gravitational and Maxwell Chern-Simons
terms. We show that Schrodinger (warped AdS_3) spacetimes exist as solutions to
a gravitational and Maxwell Chern-Simons theory with a cosmological constant.
Motivated by this, we look for warped AdS_3 or Schrodinger metrics as exact
solutions to a fully back-reacted theory containing Dirac fermions in three and
four dimensions. We work out the dynamical exponent in terms of the fermion
mass and generalize this result to arbitrary dimensions.Comment: 26 pages, v2: typos corrected, references added, minor change
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