Impact of Rapid Transition to Telemedicine-Based Delivery on Allergy/Immunology Care During COVID-19.

BACKGROUND: Coronavirus disease 2019 (COVID-19) necessitated wide-scale adoption of telemedicine (TM) and restriction of in-person care. The impacts on allergy/immunology (A/I) care delivery are still being studied. OBJECTIVE: To describe the outcomes of rapid transition to TM-based care (video visit followed by in-person visits dedicated to diagnostic and therapeutic procedures when needed) at an academic A/I practice during COVID-19. METHODS: Demographic data were compared for patients originally scheduled for in-person visits between March 10, 2020, and April 30, 2020, who completed a video visit instead between March 10, 2020, and June 30, 2020, and those who did not. Appointment completion, diagnoses, and drug allergy and skin testing completion were compared for visits between March 10, 2020, and June 30, 2020, and 1 year prior (March 10, 2019-June 30, 2019). RESULTS: Sixty-nine percent (265 of 382) of patients originally scheduled between March 10, 2020, and April 30, 2020, were able to complete video visits. Patients who completed video visits were more likely to be white (52% vs 33%; P < .001), English-speaking (96% vs 89%; P = .01), and privately insured (70% vs 54%; P = .004). With TM-based care compared with in-person care, there were significant decreases in environmental and food skin testing completion rates (91% and 92% in 2019 vs 60% and 64% in 2020, respectively, P < .001). Drug allergy testing completed after internal referral remained low but comparable (51% in 2019 vs 52% in 2020). Transitioning nonprocedural visits to video allowed allergen immunotherapy and biologic injection visits to resume at a volume similar to pre-COVID. No COVID-19 infections resulted from in-clinic exposure. CONCLUSIONS: Although transitioning to TM-based care allowed continued A/I care delivery, strategies are needed to achieve higher testing completion rates and ensure video visits do not exacerbate existing health disparities.

Quantum critical scaling and fluctuations in Kondo lattice materials.

We propose a phenomenological framework for three classes of Kondo lattice materials that incorporates the interplay between the fluctuations associated with the antiferromagnetic quantum critical point and those produced by the hybridization quantum critical point that marks the end of local moment behavior. We show that these fluctuations give rise to two distinct regions of quantum critical scaling: Hybridization fluctuations are responsible for the logarithmic scaling in the density of states of the heavy electron Kondo liquid that emerges below the coherence temperature [Formula: see text], whereas the unconventional power law scaling in the resistivity that emerges at lower temperatures below [Formula: see text] may reflect the combined effects of hybridization and antiferromagnetic quantum critical fluctuations. Our framework is supported by experimental measurements on CeCoIn5, CeRhIn5, and other heavy electron materials.

Toward a new microscopic framework for Kondo lattice materials.

Understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials is one of the grand challenges in condensed matter physics. From this perspective we review the progress that has been made during the past decade and suggest some directions for future research. Our focus will be on developing a new microscopic framework that incorporates the basic concepts that emerge from a phenomenological description of the key experimental findings.

Emergent behavior in strongly correlated electron systems.

I describe early work on strongly correlated electron systems (SCES) from the perspective of a theoretical physicist who, while a participant in their reductionist top-down beginnings, is now part of the paradigm change to a bottom-up 'emergent' approach with its focus on using phenomenology to find the organizing principles responsible for their emergent behavior disclosed by experiment-and only then constructing microscopic models that incorporate these. After considering the organizing principles responsible for the emergence of plasmons, quasiparticles, and conventional superconductivity in SCES, I consider their application to three of SCES's sister systems, the helium liquids, nuclei, and the nuclear matter found in neutron stars. I note some recent applications of the random phase approximation and examine briefly the role that paradigm change is playing in two central problems in our field: understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials; and finding the mechanism for the unconventional superconductivity found in heavy electron, organic, cuprate, and iron-based materials.

Emergence of superconductivity in heavy-electron materials.

Although the pairing glue for the attractive quasiparticle interaction responsible for unconventional superconductivity in heavy-electron materials has been identified as the spin fluctuations that arise from their proximity to a magnetic quantum critical point, there has been no model to describe their superconducting transition at temperature Tc that is comparable to that found by Bardeen, Cooper, and Schrieffer (BCS) for conventional superconductors, where phonons provide the pairing glue. Here we propose such a model: a phenomenological BCS-like expression for Tc in heavy-electron materials that is based on a simple model for the effective range and strength of the spin-fluctuation-induced quasiparticle interaction and reflects the unusual properties of the heavy-electron normal state from which superconductivity emerges. We show that it provides a quantitative understanding of the pressure-induced variation of Tc in the "hydrogen atoms" of unconventional superconductivity, CeCoIn5 and CeRhIn5, predicts scaling behavior and a dome-like structure for Tc in all heavy-electron quantum critical superconductors, provides unexpected connections between members of this family, and quantifies their variations in Tc with a single parameter.

Quantum critical behavior in heavy electron materials.

Quantum critical behavior in heavy electron materials is typically brought about by changes in pressure or magnetic field. In this paper, we develop a simple unified model for the combined influence of pressure and magnetic field on the effectiveness of the hybridization that plays a central role in the two-fluid description of heavy electron emergence. We show that it leads to quantum critical and delocalization lines that accord well with those measured for CeCoIn5, yields a quantitative explanation of the field and pressure-induced changes in antiferromagnetic ordering and quantum critical behavior measured for YbRh2Si2, and provides a valuable framework for describing the role of magnetic fields in bringing about quantum critical behavior in other heavy electron materials.

Finding new superconductors: the spin-fluctuation gateway to high Tc and possible room temperature superconductivity.

We propose an experiment-based strategy for finding new high transition temperature superconductors that is based on the well-established spin fluctuation magnetic gateway to superconductivity in which the attractive quasiparticle interaction needed for superconductivity comes from their coupling to dynamical spin fluctuations originating in the proximity of the material to an antiferromagnetic state. We show how lessons learned by combining the results of almost three decades of intensive experimental and theoretical study of the cuprates with those found in the decade-long study of a strikingly similar family of unconventional heavy electron superconductors, the 115 materials, can prove helpful in carrying out that search. We conclude that, since Tc in these materials scales approximately with the strength of the interaction, J, between the nearest neighbor local moments in their parent antiferromagnetic state, there may not be a magnetic ceiling that would prevent one from discovering a room temperature superconductor.

Emergent states in heavy-electron materials.

We obtain the conditions necessary for the emergence of various low-temperature ordered states (local-moment antiferromagnetism, unconventional superconductivity, quantum criticality, and Landau Fermi liquid behavior) in Kondo lattice materials by extending the two-fluid phenomenological theory of heavy-electron behavior to incorporate the concept of hybridization effectiveness. We use this expanded framework to present a new phase diagram and consistent physical explanation and quantitative description of measured emergent behaviors such as the pressure variation of the onset of local-moment antiferromagnetic ordering at T(N), the magnitude of the ordered moment, the growth of superconductivity within that ordered state, the location of a quantum critical point, and of a delocalization line in the pressure/temperature phase diagram at which local moments have disappeared and the heavy-electron Fermi surface has grown to its maximum size. We apply our model to CeRhIn(5) and a number of other heavy-electron materials and find good agreement with experiment.

Magnetic excitations in the kondo liquid: superconductivity and hidden magnetic quantum critical fluctuations.

We report Knight-shift experiments on the superconducting heavy-electron material CeCoIn5 that allow one to track with some precision the behavior of the heavy-electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the 115In nuclear quadrupole resonance spin-lattice relaxation rate T1(-1) measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy-electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point located at slightly negative pressure in CeCoIn5 and provide additional evidence for significant similarities between the heavy-electron materials and the high-T(c) cuprates.

Scaling the Kondo lattice.

The origin of magnetic order in metals has two extremes: an instability in a liquid of local magnetic moments interacting through conduction electrons, and a spin-density wave instability in a Fermi liquid of itinerant electrons. This dichotomy between 'local-moment' magnetism and 'itinerant-electron' magnetism is reminiscent of the valence bond/molecular orbital dichotomy present in studies of chemical bonding. The class of heavy-electron intermetallic compounds of cerium, ytterbium and various 5f elements bridges the extremes, with itinerant-electron magnetic characteristics at low temperatures that grow out of a high-temperature local-moment state. Describing this transition quantitatively has proved difficult, and one of the main unsolved problems is finding what determines the temperature scale for the evolution of this behaviour. Here we present a simple, semi-quantitative solution to this problem that provides a basic framework for interpreting the physics of heavy-electron materials and offers the prospect of a quantitative determination of the physical origin of their magnetic ordering and superconductivity. It also reveals the difference between the temperature scales that distinguish the conduction electrons' response to a single magnetic impurity and their response to a lattice of local moments, and provides an updated version of the well-known Doniach diagram.

Universal behavior in heavy-electron materials.

We present our finding that an especially simple scaling expression describes the formation of a new state of quantum matter, the Kondo Fermi liquid (KL) in heavy-electron materials. Emerging at T* as a result of the collective coherent hybridization of localized f electrons and conduction electrons, the KL possesses a non-Landau density of states varying as (1-T/T*)3/2[1+ln(T*/T)]. We show that four independent experimental probes verify this scaling behavior and that for CeIrIn5 the KL state density is in excellent agreement with the recent microscopic calculations.

Phenomenological model of protected behavior in the pseudogap state of underdoped cuprate superconductors.

By extending previous work on the scaling of low frequency magnetic properties of the 2-1-4 cuprates to the 1-2-3 materials, we arrive at a consistent phenomenological description of protected behavior in the pseudogap state of the magnetically underdoped cuprates. Between zero hole doping and a doping level of approximately 0.22, it reflects the presence of a mixture of an insulating spin liquid that produces the measured magnetic scaling behavior and a Fermi liquid that becomes superconducting for doping levels x>0.06. Our analysis suggests the existence of two quantum critical points, at doping levels x approximately 0.05 and x approximately 0.22, and that d-wave superconductivity in the pseudogap region arises from quasiparticle-spin liquid interaction, i.e., magnetic interactions between quasiparticles in the Fermi liquid induced by their coupling to the spin liquid excitations.

Two fluid description of the Kondo lattice.

We present a two-fluid description of the Kondo lattice that is based on an analysis of CeCoIn5 at various levels of dilution with La. We show that thermal and transport measurements provide evidence for the survival of the Kondo impurity component in the lattice as T-->0 K, and that the evolution of the low temperature properties of the Kondo lattice can be viewed as the partial condensation of the lattice of Kondo centers into a heavy fermion fluid. The resulting two-fluid model is shown to be applicable to the general problem of the ground state of the Kondo lattice.

Effect of dissolved cobalt(II) on the ozonation of oxalic acid.

Cobalt(II) was examined as an ozonation catalyst. Laboratory-scale batch ozonation experiments were run at near-neutral pH and 24 degrees C. A hydroxyl radical probe compound, p-chlorobenzoic acid (pCBA), was also included in the solution matrix. Batch experiments showed that trace amounts of cobalt(II) accelerated the ozonation of oxalate. The rate of oxalate removal increased with decreasing pH from pH 6.7 to pH 5.3. The presence of cobalt(II) also increased the removal rate of pCBA indicating that the generation of hydroxyl radicals are byproducts of cobalt(II)-catalyzed ozonation of oxalate. It is proposed that the first step in the catalytic ozonation reaction pathway is the formation of a cobalt(II)--oxalate complex. Cobalt(II) oxalate is then oxidized by ozone to form cobalt(III) oxalate. The catalytic cycle is completed with decomposition of the cobalt(III) complex to form cobalt(II) and an oxalate radical. Assuming that cobalt, oxalate, and water were in equilibrium, the second-order reaction rate constants at pH 6 for ozonation of the cobalt(II) monooxalate and dioxalate species were 30 +/- 9 and 4000 +/- 500 M-1 s-1, respectively. These are both much greater than the reaction rate constant for the ozonation of free oxalate (kO3 < or = 0.04 M-1 s-1).