44,577 research outputs found
Screening effects in Coulomb frustrated phase separation
We solve a model of phase separation among two competing phases frustrated by
the long-range Coulomb interaction in two and three dimensions (2D/3D) taking
into account finite compressibility effects. In the limit of strong frustration
in 2D, we recover the results of R. Jamei, S. Kivelson, and B. Spivak, Phys.
Rev. Lett. 94, 056805 (2005) and the system always breaks into domains in a
narrow range of densities, no matter how big is the frustration. For weak
frustration in 2D and for arbitrary frustration in 3D the finite
compressibility of the phases is shown to play a fundamental role. Our results
clarify the different role of screening in 2D and 3D systems. We discuss the
thermodynamic stability of the system near the transition to the phase
separated state and the possibility to observe it in real systems.Comment: 8 pages, 8 figure
Proof of Luck: an Efficient Blockchain Consensus Protocol
In the paper, we present designs for multiple blockchain consensus primitives
and a novel blockchain system, all based on the use of trusted execution
environments (TEEs), such as Intel SGX-enabled CPUs. First, we show how using
TEEs for existing proof of work schemes can make mining equitably distributed
by preventing the use of ASICs. Next, we extend the design with proof of time
and proof of ownership consensus primitives to make mining energy- and
time-efficient. Further improving on these designs, we present a blockchain
using a proof of luck consensus protocol. Our proof of luck blockchain uses a
TEE platform's random number generation to choose a consensus leader, which
offers low-latency transaction validation, deterministic confirmation time,
negligible energy consumption, and equitably distributed mining. Lastly, we
discuss a potential protection against up to a constant number of compromised
TEEs.Comment: SysTEX '16, December 12-16, 2016, Trento, Ital
Electronic polymers and soft-matter-like broken symmetries in underdoped cuprates
Empirical evidence in heavy fermion, pnictide, and other systems suggests
that unconventional superconductivity appears associated to some form of
real-space electronic order. For the cuprates, despite several proposals, the
emergence of order in the phase diagram between the commensurate
antiferromagnetic state and the superconducting state is not well understood.
Here we show that in this regime doped holes assemble in "electronic polymers."
Within a Monte Carlo study we find, that in clean systems by lowering the
temperature the polymer melt condenses first in a smectic state and then in a
Wigner crystal both with the addition of inversion symmetry breaking. Disorder
blurs the positional order leaving a robust inversion symmetry breaking and a
nematic order, accompanied by vector chiral spin order and with the persistence
of a thermodynamic transition. Such electronic phases, whose properties are
reminiscent of soft-matter physics, produce charge and spin responses in good
accord with experiments.Comment: 10 pages, 4 figures plus supplementary informatio
Hidden Ferronematic Order in Underdoped Cuprates
We study a model for low doped cuprates where holes aggregate into oriented
stripe segments which have a vortex and an antivortex fixed to the extremes. We
argue that due to the interaction between segments a state with macroscopic
polarization is stabilized, which we call a ferronematic. This state can be
characterized as a charge nematic which, due to the net polarization, breaks
inversion symmetry and also exhibits an incommensurate spin modulation. Our
calculation can reproduce the doping dependent spin structure factor of
lanthanum cuprates in excellent agreement with experiment and allows to
rationalize experiments in which the incommensurability has an order
parameter-like temperature dependence.Comment: 5 pages, 4 figure
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