1,782 research outputs found
The Sound of Strongly Coupled Field Theories: Quasinormal Modes In AdS
The AdS/CFT correspondence has developed over the last years into a very
useful and powerful tool for studying strongly coupled field theories at finite
temperature and density. Of particular interest is the regime of near
equilibrium real time evolution that can be captured via linear response
theory. The AdS/CFT correspondence allows the calculation of retarded two point
functions of gauge invariant operators by studying fluctuations around
asymptotically AdS black holes. A major role is played by the poles of these
holographic response functions: the quasinormal frequencies. I will review the
applications of these ideas to the hydrodynamics of the strongly coupled quark
gluon plasma and the holographic realization of strongly coupled superfluids.Comment: 16 pages, 8 figures, 1 cow, Contribution to Proceedings of ERE2011,
v2: minor changes, refs adde
Measuring the gap in ARPES experiments
Angle-resolved photoemission spectroscopy (ARPES) is considered as the only
experimental tool from which the momentum distribution of both the
superconducting and pseudo-gap can be quantitatively derived. The binding
energy of the leading edge of the photoemission spectrum, usually called the
leading edge gap (LEG), is the model-independent quantity which can be measured
in the modern ARPES experiments with the very high accuracy--better than 1 meV.
This, however, may be useless as long as the relation between the LEG and the
real gap is unknown. We present a systematic study of the LEG as a function of
a number of physical and experimental parameters. The absolute gap values which
have been derived from the numerical simulation prove, for example that the
nodal direction in the underdoped Bi-2212 in superconducting state is really
the node--the gap is zero. The other consequences of the simulations are
discussed.Comment: revtex4, 9 pages, 6 figure
Longitudinal and Transverse Zeeman Ladders in the Ising-Like Chain Antiferromagnet BaCo2V2O8
We explore the spin dynamics emerging from the N\'eel phase of the chain
compound antiferromagnet BaCo2V2O8. Our inelastic neutron scattering study
reveals unconventional discrete spin excitations, so called Zeeman ladders,
understood in terms of spinon confinement, due to the interchain attractive
linear potential. These excitations consist in two interlaced series of modes,
respectively with transverse and longitudinal polarization. The latter have no
classical counterpart and are related to the zero-point fluctuations that
weaken the ordered moment in weakly coupled quantum chains. Our analysis
reveals that BaCo2V2O8, with moderate Ising anisotropy and sizable interchain
interactions, remarkably fulfills the conditions necessary for the observation
of these longitudinal excitations.Comment: 5 pages, 4 figures, 2 additional pages of supplemental material with
2 figures; Journal ref. added; 1 page erratum added at the end with 1 figur
Topological superconductivity of spin-3/2 carriers in a three-dimensional doped Luttinger semimetal
We investigate topological Cooper pairing, including gapless Weyl and fully
gapped class DIII superconductivity, in a three-dimensional doped Luttinger
semimetal. The latter describes effective spin-3/2 carriers near a quadratic
band touching and captures the normal-state properties of the 227 pyrochlore
iridates and half-Heusler alloys. Electron-electron interactions may favor
non--wave pairing in such systems, including even-parity -wave pairing.
We argue that the lowest energy -wave pairings are always of complex (e.g.,
) type, with nodal Weyl quasiparticles. This implies scaling of the density of states (DoS) at low energies in the clean
limit, or over a wide critical region in the presence of
disorder. The latter is consistent with the -dependence of the penetration
depth in the half-Heusler compound YPtBi. We enumerate routes for experimental
verification, including specific heat, thermal conductivity, NMR relaxation
time, and topological Fermi arcs. Nucleation of any -wave pairing also
causes a small lattice distortion and induces an -wave component; this gives
a route to strain-engineer exotic pairings. We also consider odd-parity,
fully gapped -wave superconductivity. For hole doping, a gapless Majorana
fluid with cubic dispersion appears at the surface. We invent a generalized
surface model with -fold dispersion to simulate a bulk with winding number
. Using exact diagonalization, we show that disorder drives the surface
into a critically delocalized phase, with universal DoS and multifractal
scaling consistent with the conformal field theory (CFT) SO(), where
counts replicas. This is contrary to the naive expectation of
a surface thermal metal, and implies that the topology tunes the surface
renormalization group to the CFT in the presence of disorder.Comment: Published Version in PRB (Editors' Suggestion): 49 Pages, 17 Figures,
3 Table
High mobility in a van der Waals layered antiferromagnetic metal
Magnetic van der Waals (vdW) materials have been heavily pursued for
fundamental physics as well as for device design. Despite the rapid advances,
so far magnetic vdW materials are mainly insulating or semiconducting, and none
of them possesses a high electronic mobility - a property that is rare in
layered vdW materials in general. The realization of a magnetic high-mobility
vdW material would open the possibility for novel magnetic twistronic or
spintronic devices. Here we report very high carrier mobility in the layered
vdW antiferromagnet GdTe3. The electron mobility is beyond 60,000 cm2 V-1 s-1,
which is the highest among all known layered magnetic materials, to the best of
our knowledge. Among all known vdW materials, the mobility of bulk GdTe3 is
comparable to that of black phosphorus, and is only surpassed by graphite. By
mechanical exfoliation, we further demonstrate that GdTe3 can be exfoliated to
ultrathin flakes of three monolayers, and that the magnetic order and
relatively high mobility is retained in approximately 20-nm-thin flakes
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