Runaway Merging of Black Holes: Analytical Constraint on the Timescale

Following the discovery of a black hole (BH) with a mass of 10^3-10^6 M(sun) in a starburst galaxy M82, we study formation of such a BH via successive merging of stellar-mass BHs within a star cluster. The merging has a runaway characteristic. This is because massive BHs sink into the cluster core and have a high number density, and because the merging probability is higher for more massive BHs. We use the Smoluchowski equation to study analytically the evolution of the BH mass distribution. Under favorable conditions, which are expected for some star clusters in starburst galaxies, the timescale of the runaway merging is at most of order 10^7 yr. This is short enough to account for the presence of a BH heavier than 10^3 M(sun) in an ongoing starburst region.Comment: 10 pages, no figures, to appear in The Astrophysical Journal (Letters

Evidence for defect-mediated tunneling in hexagonal boron nitride-based junctions

We investigate tunneling in metal-insulator-metal junctions employing few atomic layers of hexagonal boron nitride (hBN) as the insulating barrier. While the low-bias tunnel resistance increases nearly exponentially with barrier thickness, subtle features are seen in the current-voltage curves, indicating marked influence of the intrinsic defects present in the hBN insulator on the tunneling transport. In particular, single electron charging events are observed, which are more evident in thicker-barrier devices where direct tunneling is substantially low. Furthermore, we find that annealing the devices modifies the defect states and hence the tunneling signatures.Comment: 5 pages, 5 figure

Local characterization and engineering of proximitized correlated states in graphene-NbSe2_2 vertical heterostructures

Using a van der Waals vertical heterostructure consisting of monolayer graphene, monolayer hBN and NbSe$_2$, we have performed local characterization of induced correlated states in different configurations. At a temperature of 4.6 K, we have shown that both superconductivity and charge density waves can be induced in graphene from NbSe2 by proximity effects. By applying a vertical magnetic field, we imaged the Abrikosov vortex lattice and extracted the coherence length for the proximitized superconducting graphene. We further show that the induced correlated states can be completely blocked by adding a monolayer hBN between the graphene and the NbSe$_2$, which demonstrates the importance of the tunnel barrier and surface conditions between the normal metal and superconductor for the proximity effect.Comment: 7 pages, 5 figure

Shot noise detection in hBN-based tunnel junctions

High quality Au/hBN/Au tunnel devices are fabricated using transferred atomically thin hexagonal boron nitride as the tunneling barrier. All tunnel junctions show tunneling resistance on the order of several k$\Omega$/$\mu$m$^{2}$. Ohmic I-V curves at small bias with no signs of resonances indicate the sparsity of defects. Tunneling current shot noise is measured in these devices, and the excess shot noise shows consistency with theoretical expectations. These results show that atomically thin hBN is an excellent tunnel barrier, especially for the study of shot noise properties, and this can enable the study of tunneling density of states and shot noise spectroscopy in more complex systems.Comment: 20 pages, 4 figure

Lands, Laws, and Women: Decisions of the General Land Office, 1881~ 1920 A Preliminary Report

S ettlement of the West-by common understanding-has meant the taking up of the public domain, especially homesteads and preemptions, under federal law. Obviously, settlement in this sense has little to do with actual occupation, or the property rights of Native Americans and long-resident Hispanics would not have been so long ignored. The specific process of settling involved three steps: filing a claim, proving up and/or making payment, and obtaining title or ownership. Each of these steps had its pitfalls, which, when they occurred, were usually resolved by the General Land Office (GLO), a division of the Department of the Interior from 1849 to 1946. This body, composed of an advisory board under a presidentally appointed commissioner, reported to the Secretary of the Interior and its decisions could also be appealed to him.1 Selected decisions, usually chosen for their illustration of some new point or clarification of a rule, were then published annually. In addition, regulations promulgated independently of any case, pronouncements of the Land Commissioners and the Secretary of the Interior, and infrequent advisory statements by the Department of Justice and other federal entities dealing with public lands were also published in the series.2 The richness of these volumes for scholars derives not only from their geographical, social, and economic spread, but from the generally short presentation of each of the cases (one to four pages), the anecdotal nature of the illustrative material, and the precise legal wording.

Pressure-induced commensurate stacking of graphene on boron nitride

Combining atomically-thin van der Waals materials into heterostructures provides a powerful path towards the creation of designer electronic devices. The interaction strength between neighboring layers, most easily controlled through their interlayer separation, can have significant influence on the electronic properties of these composite materials. Here, we demonstrate unprecedented control over interlayer interactions by locally modifying the interlayer separation between graphene and boron nitride, which we achieve by applying pressure with a scanning tunneling microscopy tip. For the special case of aligned or nearly-aligned graphene on boron nitride, the graphene lattice can stretch and compress locally to compensate for the slight lattice mismatch between the two materials. We find that modifying the interlayer separation directly tunes the lattice strain and induces commensurate stacking underneath the tip. Our results motivate future studies tailoring the electronic properties of van der Waals heterostructures by controlling the interlayer separation of the entire device using hydrostatic pressure.Comment: 17 pages, 4 figures and supplementary information. Updated to published versio

Lands, Laws, and Women: Decisions of the General Land Office, 1881~ 1920 A Preliminary Report

S ettlement of the West-by common understanding-has meant the taking up of the public domain, especially homesteads and preemptions, under federal law. Obviously, settlement in this sense has little to do with actual occupation, or the property rights of Native Americans and long-resident Hispanics would not have been so long ignored. The specific process of settling involved three steps: filing a claim, proving up and/or making payment, and obtaining title or ownership. Each of these steps had its pitfalls, which, when they occurred, were usually resolved by the General Land Office (GLO), a division of the Department of the Interior from 1849 to 1946. This body, composed of an advisory board under a presidentally appointed commissioner, reported to the Secretary of the Interior and its decisions could also be appealed to him.1 Selected decisions, usually chosen for their illustration of some new point or clarification of a rule, were then published annually. In addition, regulations promulgated independently of any case, pronouncements of the Land Commissioners and the Secretary of the Interior, and infrequent advisory statements by the Department of Justice and other federal entities dealing with public lands were also published in the series.2 The richness of these volumes for scholars derives not only from their geographical, social, and economic spread, but from the generally short presentation of each of the cases (one to four pages), the anecdotal nature of the illustrative material, and the precise legal wording.