Modeling Unconventional Superconductivity at the Crossover between Strong and Weak Electronic Interactions

High-temperature superconductivity emerges in many different quantum materials, often in regions of the phase diagram where the electronic kinetic energy is comparable to the electron-electron repulsion. Describing such intermediate-coupling regimes has proven challenging as standard perturbative approaches are inapplicable. Here, we employ quantum Monte Carlo methods to solve a multiband Hubbard model that does not suffer from the sign problem and in which only repulsive interband interactions are present. In contrast to previous sign-problem-free studies, we treat magnetic, superconducting, and charge degrees of freedom on an equal footing. We find an antiferromagnetic dome accompanied by a metal-to-insulator crossover line in the intermediate-coupling regime, with a smaller superconducting dome appearing in the metallic region. Across the antiferromagnetic dome, the magnetic fluctuations change from overdamped in the metallic region to propagating in the insulating region. Our findings shed new light on the intertwining between superconductivity, magnetism, and charge correlations in quantum materials.

Evidence for a pressure-induced antiferromagnetic quantum critical point in intermediate-valence UTe2

UTe2 is a recently discovered unconventional superconductor that has attracted much interest because of its potentially spin-triplet topological superconductivity. Our ac calorimetry, electrical resistivity, and x-ray absorption study of UTe2 under applied pressure reveals key insights on the superconducting and magnetic states surrounding pressure-induced quantum criticality at P c1 = 1.3 GPa. First, our specific heat data at low pressures, combined with a phenomenological model, show that pressure alters the balance between two closely competing superconducting orders. Second, near 1.5 GPa, we detect two bulk transitions that trigger changes in the resistivity, which are consistent with antiferromagnetic order, rather than ferromagnetism. Third, the emergence of magnetism is accompanied by an increase in valence toward a U4+ (5f 2) state, which indicates that UTe2 exhibits intermediate valence at ambient pressure. Our results suggest that antiferromagnetic fluctuations may play a more substantial role on the superconducting state of UTe2 than previously thought.

Sixfold enhancement of superconductivity in a tunable electronic nematic system

The electronic nematic phase-in which electronic degrees of freedom lower the crystal rotational symmetry-is commonly observed in high-temperature superconductors. However, understanding the role of nematicity and nematic fluctuations in Cooper pairing is often made more complicated by the coexistence of other orders, particularly long-range magnetic order. Here we report the enhancement of superconductivity in a model electronic nematic system that is not magnetic, and show that the enhancement is directly born out of strong nematic fluctuations associated with a quantum phase transition. We present measurements of the resistance as a function of strain in Ba_1-x Sr _x Ni₂As₂ to show that strontium substitution promotes an electronically driven nematic order in this system. In addition, the complete suppression of that order to absolute zero temperature leads to an enhancement of the pairing strength, as evidenced by a sixfold increase in the superconducting transition temperature. The direct relation between enhanced pairing and nematic fluctuations in this model system, as well as the interplay with a unidirectional charge-density-wave order comparable to that found in the cuprates, offers a means to investigate the role of nematicity in strengthening superconductivity.

Emergent Magnetic Degeneracy in Iron Pnictides due to the Interplay between Spin-Orbit Coupling and Quantum Fluctuations

Recent experiments in iron pnictide superconductors reveal that, as the putative magnetic quantum critical point is approached, different types of magnetic order coexist over a narrow region of the phase diagram. Although these magnetic configurations share the same wave vectors, they break distinct symmetries of the lattice. Importantly, the highest superconducting transition temperature takes place close to this proliferation of near-degenerate magnetic states. In this Letter, we employ a renormalization group calculation to show that such a behavior naturally arises due to the effects of spin-orbit coupling on the quantum magnetic fluctuations. Formally, the enhanced magnetic degeneracy near the quantum critical point is manifested as a stable Gaussian fixed point with a large basin of attraction. Implications of our findings to the superconductivity of the iron pnictides are also discussed.

Magnetic Fluctuations in Pair-Density-Wave Superconductors

Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d-wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La_{1.905}Ba_{0.095}CuO_{4} [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)].

Chronic adrenergic stimulation induces brown adipose tissue differentiation in visceral adipose tissue

BACKGROUND

Recruitment of brown adipose tissue is a promising strategy to treat obesity and Type 2 diabetes, but the physiological effects of a large amount of metabolically active brown adipose tissue in humans are unknown.

CASE REPORT

In the present paper, we report a case of massive brown adipose tissue infiltration of the visceral adipose tissue depot in a person with Type 2 diabetes with a catecholamine-secreting paraganglioma. The patient was evaluated with [18F]-fludeoxyglucose positron emission tomography/computed tomography on three occasions: pre-therapy, during α-blockade and postoperatively. During surgery, biopsies of visceral and subcutaneous adipose tissue were obtained and evaluated for brown adipose tissue. At diagnosis, brown adipose tissue glucose uptake, assessed by [18F]-fludeoxyglucose-positron emission tomography, was massively increased. [18F]-fludeoxyglucose uptake was confined to known locations for brown adipose tissue, with additional uptake in the visceral adipose tissue. As a result of increased thermogenesis, resting energy expenditure was doubled. After surgical removal of the tumour, antidiabetic medicine was no longer needed, despite an 8.2-kg weight gain.

CONCLUSION

These results show that human visceral adipose tissue holds an unprecedented potential for brown adipogenic differentiation; however, a detrimental effect on glucose metabolism persisted despite massive brown adipose tissue activity, with a doubling of resting energy expenditure.

γ-Hydroxybutyric acid induces actions via the GABAB receptor in arousal and motor control-related nuclei: implications for therapeutic actions in behavioral state disorders

γ-Hydroxybutyric acid (GHB) is used as an effective therapeutic for reducing the hypersomnolence and cataplexy (loss of motor control) of the sleeping disorder, narcolepsy, with an immediate pharmacologic behavioral action of inducing a natural sleep-like state. Despite its clinical use, few studies have examined the cellular actions of this drug on behavioral state-related neurons. Therefore, we monitored GHB-induced responses using calcium imaging within the laterodorsal tegmentum (LDT) and the dorsal raphe (DR), two pontine nuclei important in state and motor control. In addition, we recorded GHB-induced membrane responses using whole cell, patch clamp electrophysiology of immunohistochemically-identified principal neurons within these nuclei. GHB induced GABAB receptor-mediated rises in calcium in neurons of the LDT and the DR. However, the pattern and amplitude of calcium rises differed greatly between these two nuclei. GHB induced GABAB receptor antagonist-sensitive outward currents/hyperpolarizations in immunohistochemically-identified cholinergic LDT and serotonergic DR neurons. However, GHB had this action in a greater proportion of DR cells than LDT neurons. Further, larger inhibitory currents were induced in DR cells when compared to the amplitude of GHB-induced current in LDT-responding cells. Finally, NCS-382 and HOCPCA, a reported antagonist and agonist specific to activity at the putative GHB receptor, respectively, with no demonstrated binding at the GABAB receptor, failed to block GHB-induced effects or elicit any discernible electrophysiological action when applied alone, indicating a lack of involvement of a GHB receptor in mediating GHB actions. Taken together, our data support the conclusion that GHB may be exerting its actions on state and motor control, in part, via an acutely mediated strong inhibition of serotonergic DR neurons and a more modest inhibitory action on a smaller proportion of LDT cholinergic neurons. Given the roles played by these nuclei, these actions are consistent with acute pharmacologic effects of GHB: hypotonia and promotion of sleep, including presence of REM, a sub-state of sleep. Differences in GHB-mediated calcium suggest differential regulation of calcium-dependent processes, which may also contribute to functioning of the LDT and DR in state and motor control and the therapeutic pharmacologic actions of GHB, which develop following chronic administration. These findings add to knowledge of cellular actions of GHB and it is hoped that, combined with findings from other studies examining GHB neurotransmission, these data can contribute to development of highly targeted therapeutics at the GABAB receptor for management of human disorders presenting with alterations in motor and arousal control.

Meeting folks where they are: collecting data from ethnic groups in the community

Since the Nazi medical experiments in Europe and the Tuskegee Syphilis Study in the United States, members of ethnic groups have been reluctant to participate in research. However, a National Institutes of Health policy mandates that researchers develop and implement strategies to insure the inclusion of women and minorities as subjects in clinical investigations. The purpose of this paper is to discuss methods found to be effective in recruiting and retaining members of ethnic groups as participants in three research projects. The three studies were: (a) Gambling Behaviors in African American Elders and Perceived Effects on Health, (b) Adolescent Risk Behavior, Self Esteem, and Social Influence: Comparison of Dominican Youth in Their Homeland and in the United States, and (c) A Multicultural Study of Support for Alzheimer's Caregivers.

Health care providers' experiences with problem gamblers

The purpose of this study was to document health care providers' awareness of problem gambling and frequency of recognition and treatment. An exploratory survey was designed to collect data on awareness and knowledge of problem gambling. A structured questionnaire was completed anonymously by 180 health care providers (nurses, physicians, social workers, and other allied health professionals). Almost all respondents (96%) reported knowledge of problem gambling, and 30% reported asking clients about gambling problems when they presented with stress related symptoms. A third of the respondents reported identifying and treating clients for a gambling problem. The most frequently reported intervention was referral to counseling and other gambling resources. Respondents were generally interested in learning more about gambling problems, particularly those providers who have had a client discuss gambling related concerns. There were no significant differences in findings between provider groups.

COMPUTER Addiction: When Monitor Becomes Control Center

Computer addiction is a newly recognized problem. While controversy exists about whether computer addiction should be considered a primary psychiatric disorder, clinicians are treating increasing numbers of clients experiencing problems caused by excessive computer use. Case studies are provided that include typical histories and symptoms. Behavioral cognitive therapy is discussed as a treatment approach. The stages of change theory is recommended as a strategy to help clients plan and implement change.

Mother-bingo bonding: screening for gambling addiction in the neonatal intensive care unit

As the prevalence of gambling increases in society, problem or pathologic gambling in new mothers may interfere with the bonding process as well as with infant and child care. Although neonatal nurses routinely screen for maternal addictions to substances such as alcohol, cocaine, and heroin, they are less likely to be alerted to signs of gambling addiction in new parents. This article presents a case study of a mother with a bingo preoccupation, provides neonatal nurses with an overview of problem and pathologic gambling, presents brief interview questions and a standardized screening tool for assessing gambling problems in parents, and suggests areas for intervention.

Tattoos: a photo essay

Images

The President Clinton crisis and the Starr report: children's perceptions and parents' awareness

INTRODUCTION

The media have suggested that the President Clinton crisis, as publicized by the Starr Report, has had detrimental effects on school-age children. Parents, too, have been concerned that their children are confused about the presidential controversies involving dishonesty, mistrust, betrayal, infidelity, and misuse of authority. The purpose of this study was to explore the perceptions and reactions of school-age children to information surrounding the President Clinton situation, as well as parents' perceptions of their children's knowledge and reactions.

METHOD

A descriptive, qualitative design was used in this study. Data collection took place during the 2-week period following publication of the 1998 Starr Report. Fifty-one parents and 67 school-age children were interviewed using semi-structured interview guides with 5 open-ended questions addressing the President Clinton situation.

RESULTS

Major themes that emerged from children's interviews were lying, getting caught, infidelity, and role modeling. Parents' awareness of their children's knowledge regarding the President Clinton situation varied; few were aware of the depth of knowledge their children had, nor had they discussed this situation with their children.

DISCUSSION

Findings have relevance for nurse practitioners as they support parents in listening to and talking with their children about tough issues such as morality and sexuality in the context of real life events.

Characterization of a cellobiose dehydrogenase from Humicola insolens

The major cellobiose dehydrogenase (oxidase) (CBDH) secreted by the soft-rot thermophilic fungus Humicola insolens during growth on cellulose has been isolated and purified. It was shown to be a haemoflavoprotein with a molecular weight of 92 kDa and a pI of 4.0, capable of oxidizing the anomeric carbon of cellobiose, soluble cellooligosaccharides, lactose, xylobiose and maltose. Possible electron acceptors are 2,6-dichlorophenol-indophenol (DCPIP), Methylene Blue, 3,5-di-t-butyl-1,2-benzoquinone, potassium ferricyanide, cytochrome c and molecular oxygen. The oxidation of the prosthetic groups by oxygen was monitored at 449 nm for the flavin group and at 562 nm for the haem group. The curves were very similar to those of the cellobiose dehydrogenase from Phanerochaete chrysosporium, suggesting a similar mechanism. The pH-optima for the oxidation varied remarkably depending on the electron acceptor. For the organic electron acceptors, the pH-optima ranged from pH 4 for Methylene Blue to pH 7 for DCPIP and the benzoquinone. In the case of the FeIII-containing electron acceptors, the enzyme displayed alkaline pH-optima, in contrast to the properties of cellobiose dehydrogenases from Phanerochaete chrysosporium and Myceliophthora (Sporotrichum) thermophila. The enzyme has optimal activity at 65 degrees C.

[Effect of sublingual nitroglycerin on pain following ERCP]

Nitroglycerine, acting a nitric oxide donor, is known to relax visceral smooth muscle. We report a case where pain associated with pancreatitis after ERCP was successfully treated with sublingual nitroglycerine 0.5 mg. The analgesic effect lasted approximately two hours. Further controlled studies should evaluate the effect of nitroglycerine on pain associated with pancreatitis as well as clarify the mechanisms involved.

Effectiveness of a Foot Care Education Program on Attitudes and Behaviors of Staff Nurses

The purpose of this study was to determine differences in nurse attitude and clinical practice following a foot care education program. In a survey completed after the program, 23 nurses reported that they had less difficulty touching a smelly foot (p less than .02), that they would be less bothered by a foot with an odor (p less than .03), that they would have less difficulty touching an unsightly foot depicted in a slide (p less than .03), and that they felt less anger at patients who don't follow recommendations (p less than .03). The nurses also expressed more belief that patients quickly forget important information (p less than .03) and that if patients knew the effects of their poor health habits they would change (p less than .02). Ninety-one percent of the RN sample reported that their foot assessment and care practices had changed as a result of the program.