Enhanced superconductivity and ferroelectric quantum criticality in plastically deformed strontium titanate.

The properties of quantum materials are commonly tuned using experimental variables such as pressure, magnetic field and doping. Here we explore a different approach using irreversible, plastic deformation of single crystals. We show that compressive plastic deformation induces low-dimensional superconductivity well above the superconducting transition temperature (Tc) of undeformed SrTiO3, with evidence of possible superconducting correlations at temperatures two orders of magnitude above the bulk Tc. The enhanced superconductivity is correlated with the appearance of self-organized dislocation structures, as revealed by diffuse neutron and X-ray scattering. We also observe deformation-induced signatures of quantum-critical ferroelectric fluctuations and inhomogeneous ferroelectric order using Raman scattering. Our results suggest that strain surrounding the self-organized dislocation structures induces local ferroelectricity and quantum-critical dynamics that strongly influence Tc, consistent with a theory of superconductivity enhanced by soft polar fluctuations. Our results demonstrate the potential of plastic deformation and dislocation engineering for the manipulation of electronic properties of quantum materials.

Two-dimensional overdamped fluctuations of the soft perovskite lattice in CsPbBr3.

Lead halide perovskites exhibit structural instabilities and large atomic fluctuations thought to impact their optical and thermal properties, yet detailed structural and temporal correlations of their atomic motions remain poorly understood. Here, these correlations are resolved in CsPbBr3 crystals using momentum-resolved neutron and X-ray scattering measurements as a function of temperature, complemented with first-principles simulations. We uncover a striking network of diffuse scattering rods, arising from the liquid-like damping of low-energy Br-dominated phonons, reproduced in our simulations of the anharmonic phonon self-energy. These overdamped modes cover a continuum of wave vectors along the edges of the cubic Brillouin zone, corresponding to two-dimensional sheets of correlated rotations in real space, and could represent precursors to proposed two-dimensional polarons. Further, these motions directly impact the electronic gap edge states, linking soft anharmonic lattice dynamics and optoelectronic properties. These results provide insights into the highly unusual atomic dynamics of halide perovskites, relevant to further optimization of their optical and thermal properties.

The relation of local order to material properties in relaxor ferroelectrics.

Correlating electromechanical and dielectric properties with nanometre-scale order is the defining challenge for the development of piezoelectric oxides. Current lead (Pb)-based relaxor ferroelectrics can serve as model systems with which to unravel these correlations, but the nature of the local order and its relation to material properties remains controversial. Here we employ recent advances in diffuse scattering instrumentation to investigate crystals that span the phase diagram of PbMg1/3Nb2/3O3-xPbTiO3 (PMN-xPT) and identify four forms of local order. From the compositional dependence, we resolve the coupling of each form to the dielectric and electromechanical properties observed. We show that relaxor behaviour does not correlate simply with ferroic diffuse scattering; instead, it results from a competition between local antiferroelectric correlations, seeded by chemical short-range order, and local ferroic order. The ferroic diffuse scattering is strongest where piezoelectricity is maximal and displays previously unrecognized modulations caused by anion displacements. Our observations provide new guidelines for evaluating displacive models and hence the piezoelectric properties of environmentally friendly next-generation materials.

Unconventional superconductivity in Ba(0.6)K(0.4)Fe2As2 from inelastic neutron scattering.

A new family of superconductors containing layers of iron arsenide has attracted considerable interest because of their high transition temperatures (T(c)), some of which are >50 K, and because of similarities with the high-T(c) copper oxide superconductors. In both the iron arsenides and the copper oxides, superconductivity arises when an antiferromagnetically ordered phase has been suppressed by chemical doping. A universal feature of the copper oxide superconductors is the existence of a resonant magnetic excitation, localized in both energy and wavevector, within the superconducting phase. This resonance, which has also been observed in several heavy-fermion superconductors, is predicted to occur when the sign of the superconducting energy gap takes opposite values on different parts of the Fermi surface, an unusual gap symmetry which implies that the electron pairing interaction is repulsive at short range. Angle-resolved photoelectron spectroscopy shows no evidence of gap anisotropy in the iron arsenides, but such measurements are insensitive to the phase of the gap on separate parts of the Fermi surface. Here we report inelastic neutron scattering observations of a magnetic resonance below T(c) in Ba(0.6)K(0.4)Fe(2)As(2), a phase-sensitive measurement demonstrating that the superconducting energy gap has unconventional symmetry in the iron arsenide superconductors.

Local inversion-symmetry breaking in a bismuthate high-Tc superconductor.

The doped perovskite BaBiO3 exhibits a maximum superconducting transition temperature (Tc) of 34 K and was the first high-Tc oxide to be discovered, yet pivotal questions regarding the nature of both the metallic and superconducting states remain unresolved. Although it is generally thought that superconductivity in the bismuthates is of the conventional s-wave type, the pairing mechanism is still debated, with strong electron-phonon coupling and bismuth valence or bond disproportionation possibly playing a role. Here we use diffuse x-ray scattering and Monte Carlo modeling to study the local structure of Ba1-xKxBiO3 across its insulator-metal boundary. We find no evidence for either long- or short-range disproportionation, which resolves a major conundrum, as disproportionation and the related polaronic effects are likely not relevant for the metallic and superconducting states. Instead, we uncover nanoscale structural correlations that break inversion symmetry, with far-reaching implications for the electronic physics. This unexpected finding furthermore establishes that the bismuthates belong to the broader classes of materials with hidden spin-orbit coupling and a tendency towards inversion-breaking displacements.

Electron-phonon coupling in the conventional superconductor YNi2B2C at high phonon energies studied by time-of-flight neutron spectroscopy.

We report an inelastic neutron scattering investigation of phonons with energies up to 159 meV in the conventional superconductor YNi(2)B(2)C. Using the sweep mode, a newly developed time-of-flight technique involving the continuous rotation of a single crystal specimen, allowed us to measure a four-dimensional volume in (Q, E) space and, thus, determine the dispersion surface and linewidths of the A(1g) (≈102 meV) and A(u) (≈159 meV) type phonon modes over the whole Brillouin zone. Despite of having linewidths of Γ=10 meV, A(1g) modes do not strongly contribute to the total electron-phonon coupling constant λ. However, experimental linewidths show a remarkable agreement with ab initio calculations over the complete phonon energy range, demonstrating the accuracy of such calculations in a rare comparison to a comprehensive experimental data set.

Active and passive defects in tetragonal tungsten bronze relaxor ferroelectrics.

Tetragonal tungsten bronze (TTB) based oxides constitute a large family of dielectric materials which are known to exhibit complex distortions producing incommensurately modulated superstructures as well as significant local deviations from their average symmetry. The local deviations produce diffuse scattering in diffraction experiments. The structure as well as the charge dynamics of these materials are anticipated to be sensitive to defects, such as cation or oxygen vacancies. In this work, in an effort to understand how the structural and charge dynamical properties respond to these two types of vacancy defects, we have performed measurements of dielectric susceptibilities and single crystal diffraction experiments of two types of TTB materials with both 'filled' (Ba2NdFeNb4O15and Ba2PrFeNb4O15) and 'unfilled' (Sr0.5Ba0.5Nb2O6) cation sublattices. We also perform these measurements before and after oxygen annealing, which alters the oxygen vacancy concentrations. Surprisingly, we find that many of the diffuse scattering features that are present in the unfilled structure are also present in the filled structure, suggesting that the random fields and disorder that are characteristic of the unfilled structure are not responsible for many of the local structural features that are reflected in the diffuse scattering. Oxygen annealing clearly affected both color and dielectric properties, consistent with a diminishment of the oxygen vacancy concentration, but had little effect on observed diffuse patterns.

Unconventional short-range structural fluctuations in cuprate superconductors.

The interplay between structural and electronic degrees of freedom in complex materials is the subject of extensive debate in physics and materials science. Particularly interesting questions pertain to the nature and extent of pre-transitional short-range order in diverse systems ranging from shape-memory alloys to unconventional superconductors, and how this microstructure affects macroscopic properties. Here we use neutron and X-ray diffuse scattering to uncover universal structural fluctuations in La2-xSrxCuO4 and Tl2Ba2CuO6+δ, two cuprate superconductors with distinct point disorder effects and with optimal superconducting transition temperatures that differ by more than a factor of two. The fluctuations are present in wide doping and temperature ranges, including compositions that maintain high average structural symmetry, and they exhibit unusual, yet simple scaling behaviour. The scaling regime is robust and universal, similar to the well-known critical fluctuations close to second-order phase transitions, but with a distinctly different physical origin. We relate this behaviour to pre-transitional phenomena in a broad class of systems with structural and magnetic transitions, and propose an explanation based on rare structural fluctuations caused by intrinsic nanoscale inhomogeneity. We also uncover parallels with superconducting fluctuations, which indicates that the underlying inhomogeneity plays an important role in cuprate physics.

Electron-phonon coupling and the soft phonon mode in TiSe2.

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe(2). We observe a complete softening of a transverse optic phonon at the L point, i.e., q=(0.5, 0, 0.5), at T≈T(CDW). Detailed ab initio calculations for the electronic and lattice dynamical properties of TiSe(2) are in quantitative agreement with experimental frequencies for the soft phonon mode. The observed broad range of renormalized phonon frequencies, (0.3, 0, 0.5)≤q≤(0.5, 0, 0.5), is directly related to a broad peak in the electronic susceptibility stabilizing the charge-density-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe(2) although other mechanisms might further boost the transition temperature.

Extended phonon collapse and the origin of the charge-density wave in 2H-NbSe2.

We report inelastic x-ray scattering measurements of the temperature dependence of phonon dispersion in the prototypical charge-density-wave (CDW) compound 2H-NbSe2. Surprisingly, acoustic phonons soften to zero frequency and become overdamped over an extended region around the CDW wave vector. This extended phonon collapse is dramatically different from the sharp cusp in the phonon dispersion expected from Fermi surface nesting. Instead, our experiments, combined with ab initio calculations, show that it is the wave vector dependence of the electron-phonon coupling that drives the CDW formation in 2H-NbSe2 and determines its periodicity. This mechanism explains the so far enigmatic behavior of CDW in 2H-NbSe2 and may provide a new approach to other strongly correlated systems where electron-phonon coupling is important.

Response of acoustic phonons to charge and orbital order in the 50% doped bilayer manganite LaSr2Mn2O7.

We report an inelastic neutron scattering study of acoustic phonons in the charge and orbitally ordered bilayer manganite LaSr(2)Mn(2)O(7). For excitation energies less than 15 meV, we observe an abrupt increase (decrease) of the phonon energies (linewidths) of a transverse acoustic phonon branch at q = (h, h, 0), h ≤ 0.3, upon entering the low temperature charge and orbital ordered state (T(COO) = 225 K). This indicates a reduced electron-phonon coupling due to a decrease of electronic states at the Fermi level leading to a partial removal of the Fermi surface below T(COO) and provides direct experimental evidence for a link between electron-phonon coupling and charge order in manganites.

Effect of Fermi surface nesting on resonant spin excitations in Ba(1-x)K(x)Fe2As2.

We report inelastic neutron scattering measurements of the resonant spin excitations in Ba(1-x)K(x)Fe(2)As(2) over a broad range of electron band filling. The fall in the superconducting transition temperature with hole doping coincides with the magnetic excitations splitting into two incommensurate peaks because of the growing mismatch in the hole and electron Fermi surface volumes, as confirmed by a tight-binding model with s(±)-symmetry pairing. The reduction in Fermi surface nesting is accompanied by a collapse of the resonance binding energy and its spectral weight, caused by the weakening of electron-electron correlations.

Evaluating the Antimicrobial Properties of Commercial Hand Sanitizers.

Hand sanitizers have been developed as a convenient means to decontaminate an individual's hands of bacterial pathogens in situations in which soap and water are not available. Yet to our knowledge, no study has compared the antibacterial efficacy of a large collection of hand sanitizers. Using zone of growth inhibition and kill curve assays, we assessed the performance of 46 commercially available hand sanitizers that were obtained from national chain big-box stores, gasoline stations, pharmacies, and boutiques for antibacterial activity toward prototypical Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial pathogens. Results revealed substantial variability in the efficacy of many sanitizers evaluated. Formulations following World Health Organization-recommended ingredients (80% ethanol or 75% isopropyl alcohol) or those including benzalkonium chloride as the active principal ingredient displayed excellent antibacterial activity, whereas others exhibited modest or poor activity in the assays performed. Results also revealed that E. coli was generally more susceptible to most sanitizers in comparison to S. aureus and that there was significant strain-to-strain variability in hand sanitizer antimicrobial efficacy regardless of the organism evaluated. Further, tests of a subset of hand sanitizers toward severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) revealed no direct correlation between antibacterial and antiviral performance, with all ethyl alcohol formulations performing equally well and displaying improved activity in comparison to benzalkonium chloride-containing sanitizer. Taken together, these results indicate that there is likely to be substantial variability in the antimicrobial performance of commercially available hand sanitizers, particularly toward bacterial pathogens, and a need to evaluate the efficacy of sanitizers under development.IMPORTANCE In response to the coronavirus disease 2019 (COVID-19) pandemic, hand hygiene has taken on a prominent role in efforts to mitigate SARS-CoV-2 transmission and infection, which has led to a radical increase in the number and types of hand sanitizers manufactured to meet public demand. To our knowledge, no studies have evaluated or compared the antimicrobial performance of hand sanitizers that are being produced under COVID-19 emergency authorization. Tests of 46 commercially available hand sanitizers purchased from national chain brick-and-mortar stores revealed considerable variability in their antibacterial performance toward two bacterial pathogens of immediate health care concern, S. aureus and E. coli Expanded testing of a subset of hand sanitizers revealed no direct correlation between antibacterial performance of individual sanitizers and their activity toward SARS-CoV-2. These results indicate that as the pandemic subsides, there will be a need to validate the antimicrobial efficacy of sanitizers being produced.

Transition from heavy-fermion to mixed-valence behavior in Ce(1-x)Y(x)Al3: a quantitative comparison with the anderson impurity model.

We present a neutron scattering investigation of Ce1-xYxAl3 as a function of chemical pressure, which induces a transition from heavy-fermion behavior in CeAl3 (T{K}=5 K) to a mixed-valence state at x=0.5 (T{K}=150 K). The crossover can be modeled accurately on an absolute intensity scale by an increase in the k-f hybridization, V{kf}, within the Anderson impurity model. Surprisingly, the principal effect of the increasing V{kf} is not to broaden the low-energy components of the dynamic magnetic susceptibility but to transfer spectral weight to high energy.

Intertwined density waves in a metallic nickelate.

Nickelates are a rich class of materials, ranging from insulating magnets to superconductors. But for stoichiometric materials, insulating behavior is the norm, as for most late transition metal oxides. Notable exceptions are the 3D perovskite LaNiO3, an unconventional paramagnetic metal, and the layered Ruddlesden-Popper phases R4Ni3O10, (R = La, Pr, Nd). The latter are particularly intriguing because they exhibit an unusual metal-to-metal transition. Here, we demonstrate that this transition results from an incommensurate density wave with both charge and magnetic character that lies closer in its behavior to the metallic density wave seen in chromium metal than the insulating stripes typically found in single-layer nickelates like La2-xSrxNiO4. We identify these intertwined density waves as being Fermi surface-driven, revealing a novel ordering mechanism in this nickelate that reflects a coupling among charge, spin, and lattice degrees of freedom that differs not only from the single-layer materials, but from the 3D perovskites as well.

Transforming c-Ki-ras mutation is a preneoplastic event in mouse mammary carcinogenesis induced in vitro by N-methyl-N-nitrosourea.

Mouse mammary epithelial cells can be transformed in primary cultures to preneoplastic and neoplastic states when treated with N-methyl-N-nitrosourea (MNU). Mammary carcinomas arising from MNU-induced hyperplastic alveolar nodules (a type of mouse mammary preneoplastic lesion) contained transforming c-Ki-ras genes when examined by the NIH 3T3 focus assay. Hybridization of allele-specific oligonucleotides to c-Ki-ras sequences amplified by the polymerase chain reaction demonstrated the presence of a specific G-35----A-35 point mutation in codon 12 in each of the NIH 3T3 foci as well as the mammary carcinomas. This mutation resulted in the substitution of the normal glycine with an aspartic acid. Furthermore, this mutation in the c-Ki-ras proto-oncogenes was also detected in 9 of 10 hyperplastic alveolar nodules. These results demonstrate that the specific c-Ki-ras mutation is a preneoplastic event in MNU-induced mouse mammary carcinogenesis.

Effects of phorbol esters on normal and tumorous mouse mammary epithelial cells embedded in collagen gels.

The effects of phorbol esters on mammary epithelial cells from BALB/cfC3H/Crgl "midpregnant mice" (i.e., mice at the midterm of pregnancy) and from mammary adenocarcinomas (also from BALB/cfC3H/Crgl mice) grown in a collagen gel matrix were studied. 12-O-Tetradecanoylphorbol 13-acetate (TPA), when added to the media, caused an increased proliferation of both normal and cancerous mammary epithelial cells in a dose-dependent manner. The degree of enhancement of proliferation by TPA ranged from no increase in cell number at 3% swine serum (SW) concentration to two to three times the number of cells in the control cultures when 10 or 25% SW was used. Optimal growth was obtained with a TPA concentration of 0.1 or 1.0 microgram/ml. Increasing the SW concentration (3, 5, 10, or 25%) enhanced the proliferative effect of TPA. Cholera toxin (0.01 microgram/ml) enhanced the proliferative effect of TPA on normal cells but had a variable effect on tumor cells. The addition of TPA also resulted in a morphologic change in the epithelial colonies from midpregnant mice and from mammary tumors and caused them to assume a fibroblastic appearance. The addition of 4 alpha-phorbol or 4 alpha-phorbol 12,13-didecanoate to mammary epithelial cultures had no proliferative or morphologic effect. The results demonstrate that TPA has a growth-promoting effect on normal and cancerous mouse mammary epithelial cells.

Effect of hormones and epidermal growth factor on the growth of the hormone-responsive 13762NF rat mammary tumor in collagen gel culture.

The hormone-responsive mammary tumor 13762NF of the F344 rat was cultured in a collagen gel matrix with the use of a serum-free medium supplemented with hormones and epidermal growth factor (EGF). Hydrocortisone (F) had the greatest effect on cell growth. EGF had no growth-promoting activity when used alone, but it had a significant effect when used with F. There was also a population of cells responsive to progesterone (P) and prolactin (PRL). P synergized with EGF as well as with PRL to promote growth. 17 beta-Estradiol alone or in combination with other hormones had no growth-promoting activity. Receptor levels in the tumor were high for glucocorticoids, intermediate for P and EGF, and low for estrogens. Metastasis in the lung and lymph node showed the same basic hormonal responses as the parent tumor. Cultured cells produced tumors with the same histopathology as the parent tumor when transplanted back into female rats; they had the same receptor levels and when placed back in culture showed a growth response to the same set of hormones. The tumor cells formed colonies that were spherical, which was different from the branching structures formed by normal mammary cells in collagen gel.

Cultured mouse mammary epithelial cells: normal phenotype after implantation.

Mammary epithelial cells from normal virgin BALB/c mice were cultivated in vitro by the feeder cell technique developed and reported previously. These cells were cultured up to the 10th passage, equivalent to 60 cell divisions in culture. They were then tested for normality by several criteria, namely, the ability to regrow into normal mammary glands after implantation into cleared mammary fat pads of both syngeneic and nude mice, chromosome numbers, and response to mammogenic hormones. The cultured cells did form normal mammary ducts after implantation. The fraction of fat pads with ductal outgrowths as well as the size of the outgrowths was proportional to the number of cells implanted. When 10(6) cells were implanted into BALB/c mice, 83% of the fat pads contained outgrowths, filling, on the average, approximately 87% of the fat pad. More ductal outgrowths occurred from implanted cells taken from lower tissue culture passages than from high ones, and the number of outgrowths was greater in BALB/c mice than in nude mice. A small fraction of the cells in culture reacted with antibodies to casein, but there was no evidence of alpha-lactalbumin in the cells. However, ductal outgrowths from implanted cells responded to hormone stimulation of an estrogen deoxycorticosteroid pellet by forming well-developed lobulo-alveolar structures characteristic of pregnancy. Of the cells that were studied in passages 3 and 7, 85% were diploid. An abnormally growing culture in passage 10 was composed of cells in the tetraploid range. These tetraploid cells formed normal mammary ducts when implanted into animals.

Recovery of transformed nodule and ductal mammary cells from carcinogen-treated C57BL mice.

Transformed nodule and ductal mammary cells were recovered by cell dissociation and transplantation of mammary cells from C57BL/Crgl mice treated with 7,12-dimethylbenz(a)anthracene. Four-week-old mice were divided into the following groups: Group A, not treated; Group B, 2 pituitary isografts under the kidney capsule; Group C, 1.0 mg 7,12-dimethylbenz(a)anthracene intragastrically at 5 and 6 weeks of age; and Group D, 2 pituitary isografts and 1.0 mg 7,12-dimethylbenz(a)anthracene intragastrically at 5 and 6 weeks of age. At 10, 14, 18, and 22 weeks of age, the mammary glands were enzymatically dissociated, and 10(5) cells were injected into the gland-free mammary fat pads of 3-week-old syngeneic mice. After 10 weeks, the outgrowths were examined and classified as ductal, ductal dysplasia, or hyperplastic alveolar nodule. Ductal dysplasias and hyperplastic alveolar nodule outgrowths were recovered from carcinogen-treated mice. Pituitary isografting enhanced the recovery of ductal dysplasia. Five serially transplanted dysplastic outgrowth lines were established and are their fifty and sixth transplant generations. The data demonstrate that transformed mammary gland cells can be removed from carcinogen-treated mice by means of cell dissociation and transplantation.