Electronic interactions in Dirac fluids visualized by nano-terahertz spacetime mapping

Ultraclean graphene at charge neutrality hosts a quantum critical Dirac fluid of interacting electrons and holes. Interactions profoundly affect the charge dynamics of graphene, which is encoded in the properties of its collective modes: surface plasmon polaritons (SPPs). The group velocity and lifetime of SPPs have a direct correspondence with the reactive and dissipative parts of the tera-Hertz (THz) conductivity of the Dirac fluid. We succeeded in tracking the propagation of SPPs over sub-micron distances at femto-second (fs) time scales. Our experiments uncovered prominent departures from the predictions of the conventional Fermi-liquid theory. The deviations are particularly strong when the densities of electrons and holes are approximately equal. Our imaging methodology can be used to probe the electromagnetics of quantum materials other than graphene in order to provide fs-scale diagnostics under near-equilibrium conditions

Graphene/α\alpha-RuCl3_3: An Emergent 2D Plasmonic Interface

Work function-mediated charge transfer in graphene/$\alpha$-RuCl$_3$ heterostructures has been proposed as a strategy for generating highly-doped 2D interfaces. In this geometry, graphene should become sufficiently doped to host surface and edge plasmon-polaritons (SPPs and EPPs, respectively). Characterization of the SPP and EPP behavior as a function of frequency and temperature can be used to simultaneously probe the magnitude of interlayer charge transfer while extracting the optical response of the interfacial doped $\alpha$-RuCl$_3$. We accomplish this using scanning near-field optical microscopy (SNOM) in conjunction with first-principles DFT calculations. This reveals massive interlayer charge transfer (2.7 $\times$ 10$^{13}$ cm$^{-2}$) and enhanced optical conductivity in $\alpha$-RuCl$_3$ as a result of significant electron doping. Our results provide a general strategy for generating highly-doped plasmonic interfaces in the 2D limit in a scanning probe-accessible geometry without need of an electrostatic gate.Comment: 22 pages, 5 figure

Infrared plasmons propagate through a hyperbolic nodal metal

Metals are canonical plasmonic media at infrared and optical wavelengths, allowing one to guide and manipulate light at the nanoscale. A special form of optical waveguiding is afforded by highly anisotropic crystals revealing the opposite signs of the dielectric functions along orthogonal directions. These media are classified as hyperbolic and include crystalline insulators, semiconductors, and artificial metamaterials. Layered anisotropic metals are also anticipated to support hyperbolic waveguiding. However, this behavior remains elusive, primarily because interband losses arrest the propagation of infrared modes. Here, we report on the observation of propagating hyperbolic waves in a prototypical layered nodal-line semimetal ZrSiSe. The observed waveguiding originates from polaritonic hybridization between near-infrared light and nodal-line plasmons. Unique nodal electronic structures simultaneously suppress interband loss and boost the plasmonic response, ultimately enabling the propagation of infrared modes through the bulk of the crystal

Long-Lived Phonon Polaritons in Hyperbolic Materials

Natural hyperbolic materials with dielectric permittivities of opposite signs along different principal axes can confine long-wavelength electromagnetic waves down to the nanoscale, well below the diffraction limit. Confined electromagnetic waves coupled to phonons in hyperbolic dielectrics including hexagonal boron nitride (hBN) and α-MoO3 are referred to as hyperbolic phonon polaritons (HPPs). HPP dissipation at ambient conditions is substantial, and its fundamental limits remain unexplored. Here, we exploit cryogenic nanoinfrared imaging to investigate propagating HPPs in isotopically pure hBN and naturally abundant α-MoO3 crystals. Close to liquid-nitrogen temperatures, losses for HPPs in isotopic hBN drop significantly, resulting in propagation lengths in excess of 8 μm, with lifetimes exceeding 5 ps, thereby surpassing prior reports on such highly confined polaritonic modes. Our nanoscale, temperature-dependent imaging reveals the relevance of acoustic phonons in HPP damping and will be instrumental in mitigating such losses for miniaturized mid-infrared technologies operating at liquid-nitrogen temperatures.Research at Columbia is supported by Vannevar Bush Faculty Fellowship ONR-VB: N00014-19-1-2630. We thank A. Sternbach and S. Zhang for helpful discussions. Exfoliation and transfer of hBN onto desired substrates and electron beam lithography of gold disks were performed by J.T.M. and supported by the National Science Foundation (DMR1904793). Additional structure fabrication was supported by the Center on Precision-Assembled Quantum Materials, funded through the U.S. National Science Foundation (NSF) Materials Research Science and Engineering Centers (award no. DMR-2011738). Initial simulations and experimental design from Vanderbilt were provided by J.D.C. in collaboration with the Columbia team (D.N.B. and G.N.) and was supported by the Office of Naval Research (N00014-18-1-2107). The hBN phonon band structure calculation was performed by R.C. and L.A. and supported by the Spanish MINECO/FEDER grant (MAT2015-71035- R). Cryogenics nano-optics experiments at Columbia were solely supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0019443. D.N.B is the Gordon and Betty Moore Foundation’s EPiQS Initiative Investigator no. 9455.Peer reviewe

The Demise of Islet Allotransplantation in the US: A Call for an Urgent Regulatory Update The ISLETS FOR US Collaborative

Islet allotransplantation in the United States (US) is facing an imminent demise. Despite nearly three decades of progress in the field, an archaic regulatory framework has stymied US clinical practice. Current regulations do not reflect the state-of-the-art in clinical or technical practices. In the US, islets are considered biologic drugs and more than minimally manipulated human cell and tissue products (HCT/Ps). Across the world, human islets are appropriately defined as minimally manipulated tissue which has led to islet transplantation becoming a standard-of-care procedure for patients with type 1 diabetes mellitus and problematic hypoglycemia. As a result of the outdated US regulations, only eleven patients underwent allo-ITx in the US between 2011-2016 and all in the setting of a clinical trial. Herein, we describe the current regulations pertaining to islet transplantation in the United States. We explore the progress which has been made in the field and demonstrate why the regulatory framework must be updated to both, better reflect our current clinical practice and to deal with upcoming challenges. We propose specific updates to current regulations which are required for the renaissance of ethical, safe, effective, and affordable allo-ITx in the United States

The demise of islet allotransplantation in the United States: A call for an urgent regulatory update

Islet allotransplantation in the United States (US) is facing an imminent demise. Despite nearly three decades of progress in the field, an archaic regulatory framework has stymied US clinical practice. Current regulations do not reflect the state-of-the-art in clinical or technical practices. In the US, islets are considered biologic drugs and “more than minimally manipulated” human cell and tissue products (HCT/Ps). In contrast, across the world, human islets are appropriately defined as “minimally manipulated tissue” and not regulated as a drug, which has led to islet allotransplantation (allo-ITx) becoming a standard-of-care procedure for selected patients with type 1 diabetes mellitus. This regulatory distinction impedes patient access to islets for transplantation in the US. As a result only 11 patients underwent allo-ITx in the US between 2016 and 2019, and all as investigational procedures in the settings of a clinical trials. Herein, we describe the current regulations pertaining to islet transplantation in the United States. We explore the progress which has been made in the field and demonstrate why the regulatory framework must be updated to both better reflect our current clinical practice and to deal with upcoming challenges. We propose specific updates to current regulations which are required for the renaissance of ethical, safe, effective, and affordable allo-ITx in the United States

Concussion Symptom Inventory: An Empirically Derived Scale for Monitoring Resolution of Symptoms Following Sport-Related Concussion

Self-report post-concussion symptom scales have been a key method for monitoring recovery from sport-related concussion, to assist in medical management, and return-to-play decision-making. To date, however, item selection and scaling metrics for these instruments have been based solely upon clinical judgment, and no one scale has been identified as the “gold standard”. We analyzed a large set of data from existing scales obtained from three separate case–control studies in order to derive a sensitive and efficient scale for this application by eliminating items that were found to be insensitive to concussion. Baseline data from symptom checklists including a total of 27 symptom variables were collected from a total of 16,350 high school and college athletes. Follow-up data were obtained from 641 athletes who subsequently incurred a concussion. Symptom checklists were administered at baseline (preseason), immediately post-concussion, post-game, and at 1, 3, and 5 days post-injury. Effect-size analyses resulted in the retention of only 12 of the 27 variables. Receiver-operating characteristic analyses were used to confirm that the reduction in items did not reduce sensitivity or specificity. The newly derived Concussion Symptom Inventory is presented and recommended as a research and clinical tool for monitoring recovery from sport-related concussion

Polaritonic Vortices with a Half-Integer Charge.

Topological spin textures are field arrangements that cannot be continuously deformed to a fully polarized state. In particular, merons are topological textures characterized by half-integer topological charge ±1/2 and vortex-like swirling patterns at large distances. Merons have been studied previously in the context of cosmology, fluid dynamics, condensed matter physics and plasmonics. Here, we visualized optical spin angular momentum of phonon polaritons that resembles nanoscale meron spin textures. Phonon polaritons, hybrids of infrared photons and phonons in hexagonal boron nitride, were excited by circularly polarized light incident on a ring-shaped antenna and imaged using infrared near-field techniques. The polariton field reveals a half-integer topological charge determined by the handedness of the incident beam. Our phonon polaritonic platform opens up new pathways to create, control, and visualize topological textures

Decreased Collagen Production in Chronologically Aged Skin : Roles of Age-Dependent Alteration in Fibroblast Function and Defective Mechanical Stimulation

Reduced synthesis of collagen types I and III is characteristic of chronologically aged skin. The present report provides evidence that both cellular fibroblast aging and defective mechanical stimulation in the aged tissue contribute to reduced collagen synthesis. The reduction in collagen synthesis due to fibroblast aging was demonstrated by a lower in vitro production of type I procollagen by dermal fibroblasts isolated from skin of young (18 to 29 years) versus old (80+ years) individuals (82 ± 16 versus 56 ± 8 ng/ml; P < 0.05). A reduction in mechanical stimulation in chronologically aged skin was inferred from morphological, ultrastructural, and fluorescence microscopic studies. These studies, comparing dermal sections from young and old individuals, demonstrated a greater percentage of the cell surface attached to collagen fibers (78 ± 6 versus 58 ± 8%; P < 0.01) and more extensive cell spreading (1.0 ± 0.3 vs. 0.5 ± 0.3; P < 0.05) in young skin compared with old skin. These features are consistent with a lower level of mechanical stimulation on the cells in old versus young skin. Based on the findings presented here, we conclude that reduced collagen synthesis in chronologically aged skin reflects at least two different underlying mechanisms: cellular fibroblast aging and a lower level of mechanical stimulation

Infrared plasmons propagate through a hyperbolic nodal metal

Metals are canonical plasmonic media at infrared and optical wavelengths, allowing one to guide and manipulate light at the nanoscale. A special form of optical waveguiding is afforded by highly anisotropic crystals revealing the opposite signs of the dielectric functions along orthogonal directions. These media are classified as hyperbolic and include crystalline insulators, semiconductors, and artificial metamaterials. Layered anisotropic metals are also anticipated to support hyperbolic waveguiding. However, this behavior remains elusive, primarily because interband losses arrest the propagation of infrared modes. Here, we report on the observation of propagating hyperbolic waves in a prototypical layered nodal-line semimetal ZrSiSe. The observed waveguiding originates from polaritonic hybridization between near-infrared light and nodal-line plasmons. Unique nodal electronic structures simultaneously suppress interband loss and boost the plasmonic response, ultimately enabling the propagation of infrared modes through the bulk of the crystal