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In The Curse of Cash, Kenneth Rogoff lists reductions in criminal activity and tax evasion among the primary benefits of eliminating cash. We maintain that, to the extent that individuals are interested in purchasing illicit goods and services or evading taxes, eliminating cash will encourage them to switch to close substitutes. Hence, governments intent on realizing the benefits cited by Rogoff would not merely need to eliminate cash. They would also need to ban alternatives. This is especially relevant given the proliferation of cryptocurrencies, which provide a fair degree of anonymity for users.

Two-dimensional chalcogenide semiconductors have recently emerged as a host material for quantum emitters of single photons. While several reports on defect and strain-induced single photon emission from 2D chalcogenides exist, a bottom-up, lithography-free approach to producing a high density of emitters remains elusive. Further, the physical properties of quantum emission in the case of strained 2D semiconductors are far from being understood. Here, we demonstrate a bottom-up, scalable, and lithography-free approach to creating large areas of localized emitters with high density (~150 emitters/um2) in a WSe2 monolayer. We induce strain inside the WSe2 monolayer with high spatial density by conformally placing the WSe2 monolayer over a uniform array of Pt nanoparticles with a size of 10 nm. Cryogenic, time-resolved, and gate-tunable luminescence measurements combined with near-field luminescence spectroscopy suggest the formation of localized states in strained regions that emit single photons with a high spatial density. Our approach of using a metal nanoparticle array to generate a high density of strained quantum emitters opens a new path towards scalable, tunable, and versatile quantum light sources., Comment: 45 pages, 20 figures (5 main figures, 15 supporting figures)

Optical birefringence is a fundamental optical property of crystals widely used for filtering and beam splitting of photons. Birefringent crystals concurrently possess the property of linear dichroism (LD) that allows asymmetric propagation or attenuation of light with two different polarizations. This property of LD has been widely studied from small molecules to polymers and crystals but has rarely been engineered per will. Here, we use the newly discovered spin-charge coupling in van der Waals antiferromagnetic (AFM) insulator FePS3 to induce large in-plane optical anisotropy and consequently LD. We report that the LD in this AFM insulator is tunable both spectrally and magnitude-wise as a function of cavity coupling. We demonstrate near-unity LD in the visible-near infrared range in cavity-coupled FePS3 crystals and derive its dispersion as a function of cavity length and FePS3 thickness. Our results hold wide implications for use of cavity tuned LD as a diagnostic probe for strongly correlated quantum materials as well as opens new opportunities for miniaturized, on-chip beam-splitters and tunable filters., 14 pages, 5 figures

Planar optical device with continuous phase shifting (CPS) has raised widespread interest recently. Formed by subwavelength micro/nano structures, planar optics are able to control wavefront in multi aspects including phase and polarization. Most phase shifters for CPS devices are individual structures such as cylinders or cuboids. In this study, we specifically discuss grating based continuous phase shifting lenses comparing with aforementioned counterparts, in terms of differences of design mechanism and polarization responses. In addition we found that grating based metalens has outstanding potential in generating emerging artificial focus pattern. A grating based CPS lens with ‘U’ shaped focus was fabricated and characterized for prove of concept. Planar optics with artificial focus pattern has great potential for future applications including micro beam shaping and maskless nano lithography.

In this paper, I show the validity of and the relationship between two previously unrelated claims in monetary theory. The first claim, made by Earl Thompson, is that privately-issued bank notes pay a positive rate of return in a competitive equilibrium. The second claim, made by Fischer Black, is that it is possible to have a gold standard in which the gold reserves of the central bank are near zero. I show that both of these claims are correct under the assumption of complete markets and perfect commitment. The link between these claims is the Black-Scholes equation applied to convertible bank notes. In commodity-based monetary systems, bank notes are perpetual American options. I extend the model to consider the implications of a lack of commitment on the part of the bank and incomplete markets. I show that both arguments break down when banks lack commitment to redemption or markets are incomplete. I conclude with implications for macroeconomic theory.

Historically, Medicare has operated under the assumption that providers respond to reductions in reimbursement through increased provision of services in an effort to offset declining practice revenue; however, some recent empirical work examining fee reductions has found evidence of either small offsetting effects or reductions in the quantity supplied. Using a distance matching approach that matches practices to nearby practices that are subject to different reimbursement rates, we find overall evidence in support of Medicare’s offsetting assumption collectively for all services and for evaluation and management services. We also find evidence consistent with a traditional volume response for imaging and testing services.

Using data on office visits for Medicare-treating physicians, this study examines the effects of several policy changes that reduced real reimbursement for some, but not all physicians, from 2012-2017. Using genetic propensity score weighted Difference- in-Differences (DID) models that include individual physician and county fixed-effects, this study finds strong evidence that those who experienced a reimbursement reduction increased their service provision, indicative of a supplier-induced demand response. Our estimates imply that 27-33% of a reimbursement reduction will be offset through changes in provider behavior.

Indium tin oxide (ITO) has become a very useful plasmonic and nonlinear optical material because of its highly tunable electrical and optical properties and strong optical nonlinearity. In this work, the authors conducted detailed fabrication process studies by using high-temperature reactive sputtering to finely tune the optical properties of ITO thin films, particularly the epsilon-near-zero (ENZ) wavelength in the near and mid-IR spectrum. Sputtered ITO thin films are characterized by using spectroscopic ellipsometry, surface profilometry, Hall measurements, and 4-point probe testing. Additionally, the effect of post-deposition annealing of ITO films is also investigated.

In this paper, we explore the effects of primary care physician (PCP) practice competition on five distinct quality metrics directly tied to screening, follow-up care, and prescribing behavior under Medicare Part B and D. Controlling for physician, practice, and area characteristics as well as zip code fixed effects, we find strong evidence that PCP practices in more concentrated areas provide lower quality of care. More specifically, PCPs in more concentrated areas are less likely to perform screening and follow-up care for high blood pressure, unhealthy bodyweight, and tobacco use. They are also less likely to document current medications. Furthermore, PCPs in more concentrated areas have a higher amount of opioid prescriptions as a fraction of total prescriptions.

At the beginning of the 18th century, Sweden was an imperial power that had just sustained a century of modest economic growth. In 1800, Sweden’s empire was gone, after a series of military defeats. Real GDP per capita had fallen to the same level as the early 1600s. In other words, the 18th century witnessed the end of the Swedish Empire and a startling reversal of economic progress. In this paper, I propose a possible explanation for both of these outcomes. First, I argue that Sweden’s limited fiscal capacity played an important role. The creation of the Riksbank should have facilitated government borrowing and military spending as the Bank of England did for the British. However, the Riksbank was not designed or equipped for this role. I document the constraints on financing national defense through the Riksbank and argue that the bank was ill-equipped to finance an adequate national defense. This explains the reversal of the empire. Second, when the Hats took power in the Riksdag in 1739, they used the Riksbank to give loans to firms, which were financed through the issuance of bank notes. The objective was to increase investment and economic activity. I find no evidence that these loans had any effect on real GDP per capita. However, the resulting inflation has a negative and significant effect on output during the period of inconvertible paper money. The combined evidence suggests that Hat policy contributed to the decline in economic activity during the reversal of fortune.

We propose and demonstrate a two-dimensional 4-bit fully optical nonvolatile memory using Ge2Sb2Te5 (GST) phase change materials, with encoding via a 1550 nm laser. Using the telecom-band laser, we...

With the ability to confine light to subwavelength volumes, plasmonic nanostructures and metamaterials have proven to be powerful tools for nanophotonic applications. For nonlinear processes, however, the small dimensions of nanophotonic devices can become problematic, as phase-matching techniques—designed to increase interaction lengths—are no longer applicable. In this work, we utilize the field confining properties of plasmonic nanoparticles in a modified metal-insulator-metal (MIM) patch nanoantenna to efficiently couple to an epsilon near zero (ENZ) mode in a nanolayer film of indium tin oxide (ITO). The modified MIM device differs from traditional MIM structures in that the insulator spacing layer makes use of a low index, 12 nm nanolayer ITO film on top of a higher index SiO2 layer, allowing for highly confined electric fields. Combined with the enhanced nonlinear response at the ENZ point of the ITO film, we are able to achieve second harmonic generation (SHG) enhancements of up to 50,000 relative...

We report an investigation on the photo-response from a GeSn-based photodetector using a tunable laser with a range of incident light power. An exponential increase in photocurrent and an exponential decay of responsivity with increase in incident optical power intensity were observed at higher optical power range. Time-resolved measurement provided evidence that indicated monomolecular and bimolecular recombination mechanisms for the photo-generated carriers for different incident optical power intensities. This investigation establishes the appropriate range of optical power intensity for GeSn-based photodetector operation.

We investigate erbium-doped indium tin oxide and report increases to the resistivity and epsilon-near-zero wavelength with increased erbium concentration. These films are being investigated for plasmonics, second harmonic generation, perfect absorption and photoluminescence.

We experimentally investigate the tunable Doppler shift in an 80 nm thick indium-tin-oxide (ITO) film at its epsilon-near-zero (ENZ) region. Under strong and pulsed excitation, ITO exhibits a time-varying change in the refractive index. A maximum frequency redshift of 1.8 THz is observed in the reflected light when the pump light has a peak intensity of ∼ 140 G W / c m 2 and a pulse duration of ∼ 580 f s , at an incident angle of 40°. The frequency shift increases with the increase in pump intensity and saturates at the intensity of ∼ 140 G W / c m 2 . When the pump pulse duration increases from ∼ 580 f s to ∼ 1380 f s , the maximum attainable frequency shift decreases from 1.8 THz to 0.7 THz. In addition, the pump energy required to saturate the frequency shift decreases with the increase in pump pulse duration for ∼ x < 1 p s and remains unchanged for ∼ x > 1 p s durations. Tunability exists among the pump pulse energy, duration, and incident angle for the Doppler shift of the ITO-ENZ material, which can be employed to design efficient frequency shifters for telecom applications.

In this article, we draw on the literature on political property rights, political accountability, and strategic management and entrepreneurship to propose a cost neutral reform aimed at promoting long‐run economic prosperity. We propose replacing politicians' defined benefit pensions with a financial contract that is tied to economic performance. In particular, we propose a contract that pays out a lump sum to a politician 30 years after their election if real gross domestic product per capita is above some preset benchmark. Furthermore, we show that the contract can be priced such that it is cost neutral in terms of present value with a defined‐benefit pension. We argue that this contract provides a net benefit to society. (JEL D70, D72)

In this work, we investigated the edge doping effect to graphene plasmon resonances in graphene nanoribbons (GNRs), which is known to affect the electronic doping of GNRs but has not been systematically studied. We found the Fermi levels, which reflect that the sheet charge carrier densities, extracted from the graphene plasmon resonance frequencies, vary across GNRs of different widths on the same sample. Using Raman spectroscopy, we confirmed that the variation of the sheet charge carrier density is caused by edge doping, which has a stronger effect on narrower GNRs. To further understand the edge doping effect, electron beam irradiation (EBI) is applied to modify the charge state of the edge. Using EBI, we successfully demonstrated the tuning of the graphene plasmon resonances due to the change of the edge doping states. These findings demonstrated the importance of the edge doping effect in determination of the surface plasmon frequency in GNRs.

We present a paradigm for encoding strain into two-dimensional materials (2DMs) to create and deterministically place single-photon emitters (SPEs) in arbitrary locations with nanometer-scale precision. Our material platform consists of a 2DM placed on top of a deformable polymer film. Upon application of sufficient mechanical stress using an atomic force microscope tip, the 2DM/polymer composite deforms, resulting in formation of highly localized strain fields with excellent control and repeatability. We show that SPEs are created and localized at these nanoindents and exhibit single-photon emission up to 60 K, the highest temperature reported in these materials. This quantum calligraphy allows deterministic placement and real time design of arbitrary patterns of SPEs for facile coupling with photonic waveguides, cavities, and plasmonic structures. In addition to enabling versatile placement of SPEs, these results present a general methodology for imparting strain into 2DM with nanometer-scale precision, providing an invaluable tool for further investigations and future applications of strain engineering of 2DM and 2DM devices.

For active beam manipulation devices, such as those based on liquid crystals, phase-change materials, or electro-optic materials, measuring accumulated phase of the light passing through a layer of the material is imperative to understand the functionality of the overall device. In this work we discuss a way of measuring the phase accumulation through a switched layer of Ge2Sb2Te5, which is seeing rapid use as means to high speed dynamic reconfiguration of free space light. Utilizing an interferometer in the switching setup and modulating the phase of one arm, the intensity of a probe beam can be captured and phase data pulled from it. Simulations were used to discover the connection between the intensity modulations and the phase information. The technique was tested experimentally and it was found that within error, the measurement was robust and repeatable.

A growing body of research highlights the correlation between strong, centralized states and economic growth. Given the important role that national defense has played in the development of the state, it seems as though this would imply some relationship between military expenditures and economic development. However, there is no consensus on the direction of the relationship between military expenditures and economic growth. In this paper, we propose a resolution to this puzzle. We argue that military technology is a limiting factor for wealth (and therefore capital) accumulation. Since wealth must be protected from plunder and/or destruction, the amount of wealth that can be accumulated is constrained by a society’s ability to adequately defend it. We present a theoretical model consistent with this idea and perform a Monte Carlo experiment to determine the implications of this hypothesis for empirical work. We find that the long-run relationship between military expenditures and private production is positive. However, in sample sizes consistent with existing data, the relationship is ambiguous. As a result, we provide support for this idea by relying on historical examples consistent with our hypothesis. Finally, we consider the implications of our hypothesis for the development of state capacity.

Light-matter coupling in excitonic materials has been the subject of intense investigation due to emergence of new excitonic materials. Two-dimensional layered hybrid organic/inorganic perovskites (2D HOIPs) support strongly bound excitons at room-temperatures with some of the highest oscillator strengths and electric loss tangents among the known excitonic materials. Here, we report strong light-matter coupling in Ruddlesden-Popper phase 2D-HOIPs crystals without the necessity of an external cavity. We report concurrent occurrence of multiple-orders of hybrid light-matter states via both reflectance and luminescence spectroscopy in thick (> 100 nm) crystals and near-unity absorption in thin (< 20 nm) crystals. We observe resonances with quality factors > 250 in hybridized exciton-polaritons and identify a linear correlation between exciton-polariton mode splitting and extinction coefficient of the various 2D-HOIPs. Our work opens the door to studying polariton dynamics in self-hybridized and open cavity systems with broad applications in optoelectronics and photochemistry.

We experimentally demonstrate wavelength conversion by four-wave mixing in an epsilon-near-zero based metasurface. We observed conversion efficiency of 0.16% using a 127-nm thick metasurface near the 1550-nm C band with 4-GW/cm2 pump peak intensity.

We demonstrate self-phase-modulation induced spectral manipulations of 700 fs pulses using an epsilon-near-zero based plasmonic metasurface. We observe an 84% spectral broadening and 47% of FWHM wavelength blueshift.

The emergence of bitcoin poses an important question for monetary theorists: can bitcoin compete with or even replace existing fiat monies? To answer this question, one must be able to determine what gives intrinsically useless monies their value, what determines the coexistence of alternative monies, and under what conditions economic agents would prefer to hold one money relative to another. We attempt to answer these questions in light of the emergence of bitcoin. In particular, we outline a theoretical model in which an intrinsically useless money is essential.

The price-specie-flow mechanism (PSFM) is a theory of the adjustment of the balance of trade and gold flows in response to deviations in relative price levels across countries under a gold standard. The PSFM is central to quantity-theoretic discussions of economic fluctuations under a gold standard as well as analysis of whether central banks followed "the rules of the game" of the gold standard. The PSFM is often the standard working assumption when it comes to gold standard adjustment. However, at least since Adam Smith there has been an alternative to the PSFM that has come to be known as the monetary approach to the balance of payments. The distinction between the PSFM and the monetary approach have important implications for both quantity-theoretic explanations of economic fluctuations as well as the interpretation of the so-called "rules of the game." In this paper, we outline and test the empirical predictions of each theory to determine which is more accurate. The evidence is mixed, but largely favors the monetary approach to the balance of payments.

We investigate the thickness-and-loss-dependent nonlinear response of ITO-based epsilon-near-zero (ENZ) thin films under different coupling conditions. We find that the surface plasmon modes of the ENZ film can exhibit a nonlinear response at least two orders of magnitude larger than its bulk nonlinear response.

A synthetic challenge in faceted metal oxide nanocrystals (NCs) is realizing tunable localized surface plasmon resonance (LSPR) near-field response in the infrared (IR). Cube-shaped nanoparticles of noble metals exhibit LSPR spectral tunability limited to visible spectral range. Here, we describe the colloidal synthesis of fluorine, tin codoped indium oxide (F,Sn:In

We present an advancement towards high speed (sub ps) phase change material based spatial light modulators by electrically addressing single pixels with high-speed optical monitoring at 1550nm light.

In the midst of a pandemic, the most pressing issues are those of containment and mitigation—both in terms of the virus itself and the economic costs. However, it is also in the midst of a pandemic that one can learn important lessons about preparedness for possible future pandemics. The difficult thing about pandemics is that they require hospitals to be capable of expanding capacity rapidly and significantly. Ventilators for patients, as well as masks and other protective gear for doctors and nurses, are critical for keeping patients alive and keeping doctors and nurses healthy so that they can care for those patients. Government should subsidize industries so that they produce additional quantities of this kind of equipment during non-crisis times in preparation for a possible pandemic. Given the need to ramp up production, policymakers need to use lessons from this pandemic to prepare for the future.

We created a system for the characterization of Ge2Sb2Te5 starting with a 1550 nm CW laser and utilizing second harmonic generation through a PPLN crystal in order to achieve full pulse control at 775 nm.