Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride

Single crystal specimens of the actinide compound uranium ditelluride, UTe2, are of great importance to the study and characterization of its dramatic unconventional superconductivity, believed to entail spin-triplet electron pairing. A variety in the superconducting properties of UTe2 reported in the literature indicates that discrepancies between synthesis methods yield crystals with different superconducting properties, including the absence of superconductivity entirely. This protocol describes a process to synthesize crystals that exhibit superconductivity via chemical vapor transport, which has consistently exhibited a superconducting critical temperature of 1.6 K and a double transition indicative of a multi-component order parameter. This is compared to a second protocol that is used to synthesize crystals via the molten metal flux growth technique, which produces samples that are not bulk superconductors. Differences in the crystal properties are revealed through a comparison of structural, chemical, and electronic property measurements, showing that the most dramatic disparity occurs in the low-temperature electrical resistance of the samples.

Anomalous normal fluid response in a chiral superconductor UTe2

Chiral superconductors have been proposed as one pathway to realize Majorana normal fluid at its boundary. However, the long-sought 2D and 3D chiral superconductors with edge and surface Majorana normal fluid are yet to be conclusively found. Here, we report evidence for a chiral spin-triplet pairing state of UTe2 with surface normal fluid response. The microwave surface impedance of the UTe2 crystal was measured and converted to complex conductivity, which is sensitive to both normal and superfluid responses. The anomalous residual normal fluid conductivity supports the presence of a significant normal fluid response. The superfluid conductivity follows the temperature behavior predicted for an axial spin-triplet state, which is further narrowed down to a chiral spin-triplet state with evidence of broken time-reversal symmetry. Further analysis excludes trivial origins for the observed normal fluid response. Our findings suggest that UTe2 can be a new platform to study exotic topological excitations in higher dimension.

Effect of chemical substitution on the skyrmion phase in Cu2OSeO3

Magnetic skyrmions have been the focus of intense research due to their unique qualities which result from their topological protections. Previous work on Cu2OSeO3, the only known insulating multiferroic skyrmion material, has shown that chemical substitution alters the skyrmion phase. We chemically substitute Zn, Ag, and S into powdered Cu2OSeO3 to study the effect on the magnetic phase diagram. In both the Ag and the S substitutions, we find that the skyrmion phase is stabilized over a larger temperature range, as determined via magnetometry and small-angle neutron scattering (SANS). Meanwhile, while previous magnetometry characterization suggests two high temperature skyrmion phases in the Zn-substituted sample, SANS reveals the high temperature phase to be skyrmionic while we are unable to distinguish the other from helical order. Overall, chemical substitution weakens helical and skyrmion order as inferred from neutron scattering of the q ≈ 0.01 Å - 1 magnetic peak.

Enhancement and reentrance of spin triplet superconductivity in UTe2 under pressure

Spin triplet superconductivity in the Kondo lattice UTe2 appears to be associated with spin fluctuations originating from incipient ferromagnetic order. Here we show clear evidence of twofold enhancement of superconductivity under pressure, which discontinuously transitions to magnetic order, likely of ferromagnetic nature, at higher pressures. The application of a magnetic field tunes the system back across a first-order phase boundary. Straddling this phase boundary, we find another example of reentrant superconductivity in UTe2. As the superconductivity and magnetism exist on two opposite sides of the first-order phase boundary, our results indicate other microscopic mechanisms may be playing a role in stabilizing spin triplet superconductivity in addition to spin fluctuations associated with magnetism.

Plasmacytoid dendritic cells suppress Th2 responses induced by epicutaneous sensitization

Epicutaneous (EC) sensitization with protein allergens is the most important sensitization route for atopic dermatitis. Plasmacytoid dendritic cells (pDCs) are characterized by massive secretion of interferon-α (IFNα). B6 mice are T helper type 1 (Th1)-prone and are representative of non-atopic humans, whereas BALB/c mice are Th2-prone and are representative of atopic humans. Here, we show that naïve BALB/c mice contain a greater number of nonactivated pDCs in peripheral lymph nodes (LNs) than do naïve B6 mice. Naïve BALB/c mice also have more of the CD8α^- subset in LNs than naïve B6 mice. Moreover, in vivo depletion of pDCs during EC sensitization results in enhanced Th2 responses in BALB/c mice, but not in B6 mice. Mechanistically, when BALB/c mice undergo EC sensitization, there is an increase in pDCs entering draining LNs. These cells exhibit modest activation including comparable costimulation expression but increased cytokine expression compared with those of naïve mice. In vivo depletion of pDCs during EC sensitization significantly increases the activation of dermal dendritic cells (dDCs) suggesting a regulatory effect on these cells. To this end, a suppressive effect of pDCs on conventional dendritic cells was also demonstrated in vitro. Further, in vivo blockade of IFNα by an anti-IFNAR antibody (Ab) or in vivo reduction of IFNα production of pDCs by anti-siglec-H Ab both resulted in enhanced activation of dDCs. Collectively, our results demonstrate that pDCs suppress Th2 responses induced by EC sensitization via IFNα-mediated regulation of dDCs.

Point-node gap structure of the spin-triplet superconductor UTe2

Low-temperature electrical and thermal transport, magnetic penetration depth, and heat capacity measurements were performed on single crystals of the actinide superconductor UTe2 to determine the structure of the superconducting energy gap. Heat transport measurements performed with currents directed along both crystallographic a and b axes reveal a vanishingly small residual fermionic component of the thermal conductivity. The magnetic field dependence of the residual term follows a rapid, quasilinear increase consistent with the presence of nodal quasiparticles, rising toward the a-axis upper critical field where the Wiedemann-Franz law is recovered. Together with a quadratic temperature dependence of the magnetic penetration depth up to T/T c = 0.3, these measurements provide evidence for an unconventional spin-triplet superconducting order parameter with point nodes. Millikelvin specific heat measurements performed on the same crystals used for thermal transport reveal an upturn below 300 mK that is well described by a divergent quantum-critical contribution to the density of states (DOS). Modeling this contribution with a T -1/3 power law allows restoration of the full entropy balance in the superconducting state and a resultant cubic power law for the electronic DOS below T c , consistent with the point-node gap structure determined by thermal conductivity and penetration depth measurements.

Nearly ferromagnetic spin-triplet superconductivity

Spin-triplet superconductors potentially host topological excitations that are of interest for quantum information processing. We report the discovery of spin-triplet superconductivity in UTe2, featuring a transition temperature of 1.6 kelvin and a very large and anisotropic upper critical field exceeding 40 teslas. This superconducting phase stability suggests that UTe2 is related to ferromagnetic superconductors such as UGe2, URhGe, and UCoGe. However, the lack of magnetic order and the observation of quantum critical scaling place UTe2 at the paramagnetic end of this ferromagnetic superconductor series. A large intrinsic zero-temperature reservoir of ungapped fermions indicates a highly unconventional type of superconducting pairing.

Extreme magnetic field-boosted superconductivity

Applied magnetic fields underlie exotic quantum states, such as the fractional quantum Hall effect¹ and Bose-Einstein condensation of spin excitations². Superconductivity, however, is inherently antagonistic towards magnetic fields. Only in rare cases^3-5 can these effects be mitigated over limited fields, leading to re-entrant superconductivity. Here, we report the coexistence of multiple high-field re-entrant superconducting phases in the spin-triplet superconductor UTe₂ (ref. ⁶). We observe superconductivity in the highest magnetic field range identified for any re-entrant superconductor, beyond 65 T. Although the stability of superconductivity in these high magnetic fields challenges current theoretical models, these extreme properties seem to reflect a new kind of exotic superconductivity rooted in magnetic fluctuations⁷ and boosted by a quantum dimensional crossover⁸.

Behavior of the breathing pyrochlore lattice Ba3Yb2Zn5O11 in applied magnetic field

The breathing pyrochlore lattice material Ba₃Yb₂Zn₅O₁₁ exists in the nearly decoupled limit, in contrast to most other well-studied breathing pyrochlore compounds. As a result, it constitutes a useful platform to benchmark theoretical calculations of exchange interactions in insulating Yb³⁺ magnets. Here we study Ba₃Yb₂Zn₅O₁₁ at low temperatures in applied magnetic fields as a further probe of the physics of this model system. Experimentally, we consider the behavior of polycrystalline samples of Ba₃Yb₂Zn₅O₁₁ with a combination of inelastic neutron scattering and heat capacity measurements down to 75 mK and up to fields of 10 T. Consistent with previous work, inelastic neutron scattering finds a level crossing near 3 T, but no significant dispersion of the spin excitations is detected up to the highest applied fields. Refinement of the theoretical model previously determined at zero field can reproduce much of the inelastic neutron scattering spectra and specific heat data. A notable exception is a low temperature peak in the specific heat at  ∼0.1 K. This may indicate the scale of interactions between tetrahedra or may reflect undetected disorder in Ba₃Yb₂Zn₅O₁₁.

The risk of autoimmune connective tissue diseases in patients with atopy: A nationwide population-based cohort study

BACKGROUND

The relationship between autoimmune connective tissue disease (ACTD) and atopy is controversial.

OBJECTIVES

To investigate the risks of ACTDs in patients with atopic triad diseases, including atopic dermatitis, allergic rhinitis, and asthma, by using a nationwide data base.

METHODS

A cohort of 155,311 patients newly diagnosed with atopic dermatitis, allergic rhinitis, or asthma in 2002-2011 was obtained from the Taiwan National Health Insurance Research Database. An age- and sex-matched control group was selected from the same data base. The association between atopy and ACTD was investigated by using Cox proportional hazards regression analyses.

RESULTS

Atopic dermatitis, allergic rhinitis, and asthma were present in 12.1, 78.6, and 26.3%, respectively, of the patients with atopy. The presence of atopic diseases increased the overall risk of ACTDs (incidence rate ratio 1.85 [95% confidence interval {CI}, 1.52-2.25]). The hazard ratio (HR) for ACTDs remained higher after adjusting for age, sex, urbanization level, socioeconomic status, and comorbidities. Individual risks of systemic lupus erythematosus (HR 1.58 [95% CI, 1.06-2.37]), rheumatoid arthritis (HR 1.74 [95% CI, 1.31-2.33]), and Sjögren syndrome (HR 2.49 [95% CI, 1.71-3.63]) were also higher. The coexistence of atopic triad diseases increased the risk of ACTDs from 1.80 (95% CI, 1.48-2.21) for one atopic disease to 3.29 (95% CI, 1.22-8.88) for three atopic diseases.

CONCLUSION

The presence of atopic triad diseases is significantly associated with risks of systemic lupus erythematosus, rheumatoid arthritis, and Sjögren syndrome, and their coexistence exacerbates this risk. To our knowledge, this was the first study that reported an increased risk of Sjögren syndrome among patients with atopy.

Evolution of magnetic and crystal structure of FeTe doped with Cr and Ni

Due to inherent phase separation, it has been so far impossible to grow ideally stoichiometric (1:1) tetragonal (P 4/n m m) iron telluride. The excess iron ions are located in the inter-planar positions and usually represented as a fraction x in a general formula Fe1+xTe [1], where x ranges from about 4% to 17%. The additional iron has been found to negatively correlate with the level of anion site doping and subsequently with hindering the superconductivity (SC), for example in the Fe(Te,Se,S) [2] series, where SC can be induced by doping with selenium or small amounts of sulfur. A binary Fe1+xTe orders magnetically into incommensurate magnetic structure with the transition temperature and crystal structure in the magnetic state depending on the excess iron. For x<0.12 a monoclinic (P 21/m) distortion was observed and for x>0.12 an orthorhombic one (P m m n). In our work, we attempted to create and investigate compounds electronically equivalent to variable iron stoichometry by substituting Fe with chromium (3d electron deficient) or nickel (3d electron rich). Single crystal samples several millimeter in size were grown by solidification from melt method in the substitution range 0.025 to 0.1 and only in the case of nickel the incorporation of dopant into host lattice was confirmed. Despite low effective Cr content in the single crystal form [3], neutron powder diffraction (NPD) of polycrystaline specimens revealed systematic decrease of long range magnetic moment and gradual suppression of monoclinic (M) distortion in both series. In the Cr doped series, the structure evolved through a mixed phase region into orthorhombic (O) one (Fig. 1), whereas in the nickel system a complete restoration of tetragonal symmetry was found. The suppression of magnetic ordering and lack of the structural distortion did not result in the SC. This work is supported by the Polish National Science Centre grant No 2011/01/B/ST3/00425

Optimization of three-color laser field for the generation of single ultrashort attosecond pulse

We present an efficient and realizable scheme for the generation of an ultrashort single attosecond (as) pulse. The feasibility of such a scheme is demonstrated by solving accurately the time-dependent Schrödinger equation using the time-dependent generalized pseudospectral (TDGPS) method. This scheme involves the use of the optimization of the three-color laser fields. The optimized laser pulse is synthesized by three one-color laser pulses with proper relative phases. It can provide a longer acceleration time for the tunneling and oscillating electrons, and allows the electrons to gain more kinetic energy. We show that the plateau of high-order harmonic generation is extended dramatically and a broadband supercontinuum spectra is produced. As a result, an isolated 23 as pulse with a bandwidth of 163 eV can be obtained directly by superposing the supercontinuum harmonics near the cutoff region. We will show that such a metrology can be realized experimentally.

Genomic deletion and p53 inactivation in cervical carcinoma

The tumor-suppressor gene p53 acts as "the guardian of the genome", sensing DNA damage and initiating protective responses. To examine the hypothesis that p53 abnormality leads to increased genomic alterations in primary tumor cells, our study utilized 51 primary tumors of cervical carcinoma and 10 microsatellite markers. These markers were mapped to the short arms of chromosomes 3 and 5, covering the regions 3p13-25 and 5p15.1-15.3. Genomic deletion on 3p and 5p was correlated with genetic or epigenetic p53 inactivation pathways, including p53 mutation, genetic deletion of p53 and cervical infection with human papillomavirus. The proportion of abnormal p53 was found to be significantly higher in the cases exhibiting loss of heterozygosity (LOH) on 5p (p < 0.001), supporting the hypothesis of the presence of a p53-dependent pathway to cervical tumorigenesis. In contrast, however, LOH on 3p was found to be independent of p53 inactivation. A common deletion region, 3p22-24, was identified in 44% of informative cases, and genomic loss at this specific region was correlated with early tumorigenic onset and poor grade of tumor differentiation. Diversity within the patterns of genomic alteration in the same form of cancer suggests different sets of risk/tumorigenic profiles, molecular pathogenesis, as well as prognosis and outcome.