142 research outputs found
Planckian dissipation, minimal viscosity and the transport in cuprate strange metals
Could it be that the matter from the electrons in high Tc superconductors is
of a radically new kind that may be called "many body entangled compressible
quantum matter"? Much of this text is intended as an easy to read tutorial,
explaining recent theoretical advances that have been unfolding at the cross
roads of condensed matter- and string theory, black hole physics as well as
quantum information theory. These developments suggest that the physics of such
matter may be governed by surprisingly simple principles. My real objective is
to present an experimental strategy to test critically whether these principles
are actually at work, revolving around the famous linear resistivity
characterizing the strange metal phase. The theory suggests a very simple
explanation of this "unreasonably simple" behavior that is actually directly
linked to remarkable results from the study of the quark gluon plasma formed at
the heavy ion colliders: the "fast hydrodynamization" and the "minimal
viscosity". This leads to high quality predictions for experiment: the momentum
relaxation rate governing the resistivity relates directly to the electronic
entropy, while at low temperatures the electron fluid should become unviscous
to a degree that turbulent flows can develop even on the nanometre scale.Comment: 23 pages, no figures. Submission to SciPos
Quantum Thermalization and the Expansion of Atomic Clouds
The ultimate consequence of quantum many-body physics is that even the air we
breathe is governed by strictly unitary time evolution. The reason that we
perceive it nonetheless as a completely classical high temperature gas is due
to the incapacity of our measurement machines to keep track of the dense
many-body entanglement of the gas molecules. The question thus arises whether
there are instances where the quantum time evolution of a macroscopic system is
qualitatively different from the equivalent classical system? Here we study
this question through the expansion of noninteracting atomic clouds. While in
many cases the full quantum dynamics is indeed indistinguishable from classical
ballistic motion, we do find a notable exception. The subtle quantum
correlations in a Bose gas approaching the condensation temperature appear to
affect the expansion of the cloud, as if the system has turned into a diffusive
collision-full classical system.Comment: 6 pages, 4 figures, and a 4-page supplementary informatio
Quasiparticle Density of States, Localization, and Distributed Disorder in the Cuprate Superconductors
We explore the effects of various kinds of random disorder on the
quasiparticle density of states of two-dimensional d-wave superconductors using
an exact real-space method, incorporating realistic details known about the
cuprates. Random on-site energy and pointlike unitary impurity models are found
to give rise to a vanishing DOS at the Fermi energy for narrow distributions
and low concentrations, respectively, and lead to a finite, but suppressed, DOS
at unrealistically large levels of disorder. Smooth disorder arising from
impurities located away from the copper-oxide planes meanwhile gives rise to a
finite DOS at realistic impurity concentrations. For the case of smooth
disorder whose average potential is zero, a resonance is found at zero energy
for the quasiparticle DOS at large impurity concentrations. We discuss the
implications of these results on the computed low-temperature specific heat,
the behavior of which we find is strongly affected by the amount of disorder
present in the system. We also compute the localization length as a function of
disorder strength for various types of disorder and find that intermediate- and
high-energy states are quasi-extended for low disorder, and that states near
the Fermi energy are strongly localized and have a localization length that
exhibits an unusual dependence on the amount of disorder. We comment on the
origin of disorder in the cuprates and provide constraints on these based on
known results from scanning tunneling spectroscopy and specific heat
experiments.Comment: 29 pages, 19 figures, published version, includes minor change
Interplay between electronic topology and crystal symmetry: Dislocation-line modes in topological band-insulators
We elucidate the general rule governing the response of dislocation lines in
three-dimensional topological band insulators. According to this rule, the lattice topology, represented by
dislocation lines oriented in direction with Burgers vector , combines with the electronic-band topology, characterized by the
band-inversion momentum , to produce gapless propagating
modes when the plane orthogonal to the dislocation line features a band
inversion with a nontrivial ensuing flux . Although it has already been discovered by Y. Ran
{\it et al.}, Nature Phys. {\bf 5}, 298 (2009), that dislocation lines host
propagating modes, the exact mechanism of their appearance in conjunction with
the crystal symmetries of a topological state is provided by the rule . Finally, we discuss possible
experimentally consequential examples in which the modes are oblivious for the
direction of propagation, such as the recently proposed
topologically-insulating state in electron-doped BaBiO.Comment: Main text + supplementary material, published versio
Impurity Bound States and Greens Function Zeroes as Local Signatures of Topology
We show that the local in-gap Greens function of a band insulator
, with
the position perpendicular to a codimension-1 or -2
impurity, reveals the topological nature of the phase. For a topological
insulator, the eigenvalues of this Greens function attain zeros in the gap,
whereas for a trivial insulator the eigenvalues remain nonzero. This
topological classification is related to the existence of in-gap bound states
along codimension-1 and -2 impurities. Whereas codimension-1 impurities can be
viewed as 'soft edges', the result for codimension-2 impurities is nontrivial
and allows for a direct experimental measurement of the topological nature of
2d insulators.Comment: 11 pages, 8 figure
Self-organized pseudo-graphene on grain boundaries in topological band insulators
Semi-metals are characterized by nodal band structures that give rise to
exotic electronic properties. The stability of Dirac semi-metals, such as
graphene in two spatial dimensions (2D), requires the presence of lattice
symmetries, while akin to the surface states of topological band insulators,
Weyl semi-metals in three spatial dimensions (3D) are protected by band
topology. Here we show that in the bulk of topological band insulators,
self-organized topologically protected semi-metals can emerge along a grain
boundary, a ubiquitous extended lattice defect in any crystalline material. In
addition to experimentally accessible electronic transport measurements, these
states exhibit valley anomaly in 2D influencing edge spin transport, whereas in
3D they appear as graphene-like states that may exhibit an odd-integer quantum
Hall effect. The general mechanism underlying these novel semi-metals -- the
hybridization of spinon modes bound to the grain boundary -- suggests that
topological semi-metals can emerge in any topological material where lattice
dislocations bind localized topological modes.Comment: 14 pages, 6 figures. Improved discussion compared to the earlier
versio
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