Imaging twisty magnets Twisting monolayers of graphene with respect to each other has led to a number of unusual correlated states. This approach has inspired researchers to try their hand at twisting two-dimensional (2D) magnets, but such experiments have proven a difficult challenge. Song et al . made structures out of layers of the 2D magnet chromium triiodide with a small twist angle (see the Perspective by Lado). Using nitrogen vacancy centers in diamond as a magnetometer, the authors imaged the magnetic domains in both twisted monolayer and twisted trilayer structures. For twisted trilayers, a periodic pattern of ferromagnetic and antiferromagnetic domains was revealed. —JS

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The emergence of atomically thin van der Waals magnets provides a new platform for the studies of two-dimensional magnetism and its applications. However, the widely used measurement methods in recent studies cannot provide quantitative information of the magnetization nor achieve nanoscale spatial resolution. These capabilities are essential to explore the rich properties of magnetic domains and spin textures. Here, we employ cryogenic scanning magnetometry using a single-electron spin of a nitrogen-vacancy center in a diamond probe to unambiguously prove the existence of magnetic domains and study their dynamics in atomically thin CrBr3. By controlling the magnetic domain evolution as a function of magnetic field, we find that the pinning effect is a dominant coercivity mechanism and determine the magnetization of a CrBr3 bilayer to be about 26 Bohr magnetons per square nanometer. The high spatial resolution of this technique enables imaging of magnetic domains and allows to locate the sites of defects that pin the domain walls and nucleate the reverse domains. Our work highlights scanning nitrogen-vacancy center magnetometry as a quantitative probe to explore nanoscale features in two-dimensional magnets.

This paper presents cooperative prefetching and caching -the use of network-wide global resources (memories, CPUs, and disks) to support prefetching and caching in the presence of hints of future demands. Cooperative prefetching and caching effectively unites disk-latency reduction techniques from three lines of research: prefetching algorithms, cluster-wide memory management, and parallel I/O. When used together, these techniques greatly increase the power of prefetching relative to a conventional (nonglobal-memory) system. We have designed and implemented PGMS, a cooperative prefetching and caching system, under the Digital Unix operating system running on a 1.28 Gb/sec Myrinetconnected cluster of DEC Alpha workstations. Our measurements and analysis show that by using available global resources, cooperative prefetching can obtain significant speedups for I/O-bound programs. For example, for a graphics rendering application, our system achieves a speedup of 4.9 over a non-prefetching version of the same program, and a 3.1 -fold improvement over that program using local-disk prefetching alone.

Spin-photovoltaic effect in 2D magnet CrI 3 exhibits interplay between magneto-excitons, photon energy, and light helicity.

Abstract-Efficient use of network resources has long been an important problem for large-scale network operators. To this end, several recent research efforts have proposed automated methods for optimizing routes based on traffic measurements. However, these efforts have not considered the stability of the dual feedback control mechanisms of adaptive routing and congestion control, when operating together. In this paper, we demonstrate that an important class of adaptive routing algorithms can yield stable optimal routes in the presence of congestion control, provided that either the congestion control mechanism is fair or the network workload behaves under reasonable constraints. We further show that one or the other of these assumptions is necessary for this class of adaptive routing algorithmsotherwise, unstable, sub-optimal routes may result in some pathological cases.

In this paper we examine the application of offline algorithms for determining the optimal sequence of loads and superloads (a load of multiple consecutive cache lines) for direct-mapped caches. We evaluate potential gains in terms of miss rate and bandwidth and find that in many cases optimal superloading can noticeably reduce the miss rate without appreciably increasing bandwidth. Then we examine how this performance potential might be realized. We examine the effectiveness of a dynamic online algorithm and of static analysis (profiling) for superloading and compare these to next-line prefetching. Experimental results show improvements comparable to those of the optimal algorithm in terms of miss rates. §1 IntroductionSince their introduction over thirty years ago, caches have become ubiquitous as components of the memory hierarchy. Caches have been successful because programs exhibit locality: spatial locality, the tendency for neighboring memory locations to be referenced close together in time; and temporal locality, the tendency for referencing in the future those locations that have been referenced in the recent past. However, as the speed of processors increases much faster than the decrease in memory latency, the efficiency of caches has received more scrutiny.Combinations of hardware and software techniques have been proposed and often implemented to improve locality and to reduce or tolerate memory latency. The basic goal is to reduce cache miss rates without unduly increasing the amount of bytes transferred between levels of the memory hierarchy. When couched in terms of improving spatial locality for data caches, the main theme of this paper, the usual policy is to support larger cache lines. Potential detrimental effects of this policy are a possible increase in cache miss rate because of more frequent conflict misses and the lack of reuse of portions of the larger lines, and to lengthen the occupancy of the bus between levels of the memory hierarchy servicing the miss. In order to palliate these effects and to take advantage of large lines, when deemed profitable, we examine the potential benefit of implementing the cache controller so that on a miss, either the missing regular size line is loaded -hereafter called the base case -or the line is superloaded, i.e., the missing line and surrounding lines are brought into the cache. Note that the advantages of superloading depend on the cost model for the level of the memory hierarchy under investigation. Of particular importance are the relative costs of a load and a superload.Although the impact of these techniques has been investigated using heuristics and software or hardware assists, how much can be gained if these techniques were used optimally is not known. In this paper, after briefly introducing an optimal offline algorithm for choosing between loads and superloads, we derive the margin of maximum possible improvement on the integer Spec95 benchmark suite. We then analyze the performances, when compared to the optimal and base cases, ...

The ability to control the underlying lattice geometry of a system may enable transitions between emergent quantum ground states. Here, we report in-situ gate switching between honeycomb and triangular lattice geometries of an electron many-body Hamiltonian in R-stacked MoTe 2 moiré bilayers, resulting in switchable magnetic exchange interactions. At zero electric field, we observe a correlated ferromagnetic insulator near one hole per moiré unit cell with a widely tunable Curie temperature up to 14K. Applying an electric field switches the system into a half-filled triangular lattice with antiferromagnetic interactions; further doping this layer-polarized superlattice tunes the antiferromagnetic exchange interaction back to ferromagnetic. Our work demonstrates R-stacked MoTe 2 moirés to be a laboratory for engineering correlated states with nontrivial topology.