Tunneling into the vortex state of NbSe2_2 with van der Waals junctions

We have performed device-based tunnelling spectroscopy of NbSe$_2$ in the vortex state with a magnetic field applied both parallel and perpendicular to the $a-b$ plane. Our devices consist of layered semiconductors placed on top of exfoliated NbSe$_2$ using the van der Waals transfer technique. At zero field, the spectrum exhibits a hard gap, and the quasiparticle peak is split into low and high energy features. The two features, associated with the effective two-band nature of superconductivity in NbSe$_2$, exhibit markedly distinct responses to the application of magnetic field, suggesting an order-of-magnitude difference in the spatial extent of the vortex cores of the two bands. At energies below the superconducting gap, the hard gap gives way to vortex-bound Caroli-de Gennes-Matricon states, allowing the detection of individual vortices as they enter and exit the junction. Analysis of the sub-gap spectra upon application of parallel magnetic field allows us to track the process of vortex surface formation and spatial rearrangement in the bulk

Spectroscopy of bulk and few-layer superconducting NbSe2_2 with van der Waals tunnel junctions

Tunnel junctions, a well-established platform for high-resolution spectroscopy of superconductors, require defect-free insulating barriers with clean engagement to metals on both sides. Extending the range of materials accessible to tunnel junction fabrication, beyond the limited selection which allows high-quality oxide formation, requires the development of alternative fabrication techniques. Here we show that van-der-Waals (vdW) tunnel barriers, fabricated by stacking layered semiconductors on top of the transition metal dichalcogenide (TMD) superconductor NbSe$_2$, sustain a stable, low noise tunneling current, and exhibit strong suppression of sub-gap tunneling. We utilize the technique to measure the spectra of bulk (20 nm) and ultrathin (3- and 4-layer) devices at 70 mK. The spectra exhibit two distinct energy gaps, the larger of which decreases monotonously with thickness and $T_C$, in agreement with BCS theory. The spectra are analyzed using a two-band model modified to account for depairing. We show that in the bulk, the smaller gap exhibits strong depairing in an in-plane magnetic field, consistent with a high Fermi velocity. In the few-layer devices, depairing of the large gap is negligible, consistent with out-of-plane spin-locking due to Ising spin-orbit coupling. Our results demonstrate the utility of vdW tunnel junctions in mapping the intricate spectral evolution of TMD superconductors over a range of magnetic fields.Comment: This submission contains the first part of arxiv:1703.07677 with the addition of spectra taken on this devices. The second part of 1703.07677 will be published separatel

Post-ISCO Ringdown Amplitudes in Extreme Mass Ratio Inspiral

An extreme mass ratio inspiral consists of two parts: adiabatic inspiral and plunge. The plunge trajectory from the innermost stable circular orbit (ISCO) is special (somewhat independent of initial conditions). We write an expression for its solution in closed-form and for the emitted waveform. In particular we extract an expression for the associated black-hole ringdown amplitudes, and evaluate them numerically.Comment: 21 pages, 5 figures. v4: added section with numerical evaluation of the ringdown amplitude

Gender, war and militarism: making and questioning the links

The gender dynamics of militarism have traditionally been seen as straightforward, given the cultural mythologies of warfare and the disciplining of ‘masculinity’ that occurs in the training and use of men's capacity for violence in the armed services. However, women's relation to both war and peace has been varied and complex. It is women who have often been most prominent in working for peace, although there are no necessary links between women and opposition to militarism. In addition, more women than ever are serving in many of today's armies, with feminists rather uncertain on how to relate to this phenomenon. In this article, I explore some of the complexities of applying gender analyses to militarism and peace work in sites of conflict today, looking most closely at the Israeli feminist group, New Profile, and their insistence upon the costs of the militarized nature of Israeli society. They expose the very permeable boundaries between the military and civil society, as violence seeps into the fears and practices of everyday life in Israel. I place their work in the context of broader feminist analysis offered by researchers such as Cynthia Enloe and Cynthia Cockburn, who have for decades been writing about the ‘masculinist’ postures and practices of warfare, as well as the situation of women caught up in them. Finally, I suggest that rethinking the gendered nature of warfare must also encompass the costs of war to men, whose fundamental vulnerability to psychological abuse and physical injury is often downplayed, whether in mainstream accounts of warfare or in more specific gender analysis. Feminists need to pay careful attention to masculinity and its fragmentations in addressing the topic of gender, war and militarism

Inequitable Enforcement: Introducing the Concept of Equity into Constitutional Review of Law Enforcement

This Article addresses a series of situations in which the exercise of police discretion, while passing current constitutional thresholds, seems unfair and unforeseeable. We call this problem inequitable enforcement. Current constitutional review of police action assesses all stops, searches, and arrests-regardless of how minor the offenseby focusing on the officer\u27s level of suspicion and the officer\u27s compliance with equal protection standards. In this Article, we argue that these existing constitutional mechanisms are flawed and fail to provide an appropriate remedy in cases of arbitrary and disproportionate enforcement for minor infractions. We begin by discussing the necessity of police discretion and the factors that guide officers in exercising it. After tracing the recent development of Fourth and Fourteenth Amendment law in the context of police discretion, we explain why these constitutional protections are inadequate for addressing the problem of inequitable enforcement. This inadequacy, we argue, is a result of the narrow and myopic lens through which the Supreme Court assesses reasonableness in its Fourth Amendment analysis, and discrimination in its Equal Protection analysis. We then suggest a set of considerations for assessing inequitability and present some ways in which those considerations can be integrated into constitutional doctrine. We conclude by discussing the promises and pitfalls of addressing inequitable enforcement through constitutional review

Inequitable Enforcement: Introducing the Concept of Equity into Constitutional Review of Law Enforcement

This Article addresses a series of situations in which the exercise of police discretion, while passing current constitutional thresholds, seems unfair and unforeseeable. We call this problem inequitable enforcement. Current constitutional review of police action assesses all stops, searches, and arrests-regardless of how minor the offenseby focusing on the officer\u27s level of suspicion and the officer\u27s compliance with equal protection standards. In this Article, we argue that these existing constitutional mechanisms are flawed and fail to provide an appropriate remedy in cases of arbitrary and disproportionate enforcement for minor infractions. We begin by discussing the necessity of police discretion and the factors that guide officers in exercising it. After tracing the recent development of Fourth and Fourteenth Amendment law in the context of police discretion, we explain why these constitutional protections are inadequate for addressing the problem of inequitable enforcement. This inadequacy, we argue, is a result of the narrow and myopic lens through which the Supreme Court assesses reasonableness in its Fourth Amendment analysis, and discrimination in its Equal Protection analysis. We then suggest a set of considerations for assessing inequitability and present some ways in which those considerations can be integrated into constitutional doctrine. We conclude by discussing the promises and pitfalls of addressing inequitable enforcement through constitutional review