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