Tuning the Multiferroic Properties of BiFeO_{3} under Uniaxial Strain.

More than twenty years ago, multiferroic compounds combining in particular magnetism and ferroelectricity were rediscovered. Since then, BiFeO_{3} has emerged as the most outstanding multiferroic by combining at room temperature almost all the fundamental or applicative properties that may be desired: electroactive spin wave excitations called electromagnons, conductive domain walls, or a low band gap of interest for magnonic devices. All these properties have so far only been discontinuously strain engineered in thin films according to the lattice parameter imposed by the substrate. Here we explore the ferroelectricity and the dynamic magnetic response of BiFeO_{3} bulk under continuously tunable uniaxial strain. Using elasto-Raman spectroscopy, we show that the ferroelectric soft mode is strongly enhanced under tensile strain and driven by the volume preserving deformation at low strain. The magnonic response is entirely modified with low energy magnon modes being suppressed for tensile strain above pointing out a transition from a cycloid to an homogeneous magnetic state. Effective Hamiltonian calculations show that the ferroelectric and the antiferrodistortive modes compete in the tensile regime. In addition, the homogeneous antiferromagnetic state becomes more stable compared to the cycloidal state above a +2% tensile strain close to the experimental value. Finally, we reveal the ferroelectric and magnetic orders of BiFeO_{3} under uniaxial strain and how the tensile strain allows us to unlock and to modify in a differentiated way the polarization and the magnetic structure.

Should we abandon hormonal therapy in endometrial cancer? Outcomes of recurrent and metastatic endometrial cancer treated with systemic progestins.

PURPOSE: The objective of this study is to determine primary survival endpoints in women with recurrent and metastatic endometrial carcinoma (RMEC) treated with progestins. METHODS: A retrospective chart review was conducted at The Ottawa Hospital using electronic medical records. Inclusion criteria were a diagnosis of RMEC between 2000 and 2019, endometrioid histology, and ≥one line of progestin treatment. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method. RESULTS: Of 2342 cases reviewed, 74 met inclusion criteria. Sixty-six (88.0%) patients received megestrol acetate and 9 (12.0%) received a progestin alternative. The distribution of tumors by grade was: 1: 25 (33.3%), 2: 30 (40.0%), and 3: 20 (26.7%). The PFS and OS for the entire study sample was 14.3 months (95% CI 6.2-17.9) and 23.3 months (14.8-36.8), respectively. The PFS for patients with Grade 1-2 RMEC was 15.7 months (8.0, 19.5), compared to 5.0 months (3.0, 23.0) with Grade 3 disease. The OS for patients with Grade 1-2 versus Grade 3, was 25.9 months (15.3, 40.3) versus 12.5 months (5.7, 35.9), respectively. Thirty-four (45.9%) and 40 (54.1%) patients were treated with 0 and ≥1 line of chemotherapy. The PFS for chemotherapy-naïve patients was 17.9 months (14.3, 27.0), versus 6.2 months (3.9, 14.8) following ≥1 line of treatment. The OS was 29.1 months (17.9, 61.1) for chemotherapy-naïve patients versus 23.0 months (10.5, 37.6) for patients previously exposed. CONCLUSIONS: This real-world data on RMEC suggests there is a role for progestins in select subgroups of women. The PFS for chemotherapy-naïve patients was 17.9 months (14.3, 27.0), versus 6.2 months (3.9, 14.8) following ≥1 line of treatment. The OS was 29.1 months (17.9, 61.1) for chemotherapy-OS was 29.1 months (17.9, 61.1) for chemotherapy-naïve patients versus 23.0 months (10.5, 37.6) for patients previously exposed.

Lattice dynamics of BaFe2Se3.

This paper presents a study of the lattice dynamics in BaFe2Se3. We combined first-principle calculations, infrared measurements and a thorough symmetry analysis. Our study confirms thatPnmacannot be the space group of BaFe2Se3, even at room temperature. The phonons assignment requiresPmto be the BaFe2Se3space group, not only in the magnetic phase, but also in the paramagnetic phase at room temperature. This is due to a strong coupling between a short-range spin-order along the ladders, and the lattice degrees of freedom associated with the Fe-Fe bond length. This coupling induces a change in the bond-length pattern from an alternated trapezoidal one (as inPnma) to an alternated small/large rectangular one. Out of the two patterns, only the latter is fully compatible with the observed block-type magnetic structure. Finally, we propose a complete symmetry analysis of the BaFe2Se3phase diagram in the 0-600 K range.

Magnetotransport signatures of antiferromagnetism coexisting with charge order in the trilayer cuprate HgBa2Ca2Cu3O8+δ.

Multilayered cuprates possess not only the highest superconducting temperature transition but also offer a unique platform to study disorder-free CuO2 planes and the interplay between competing orders with superconductivity. Here, we study the underdoped trilayer cuprate HgBa2Ca2Cu3O8+δ and we report quantum oscillation and Hall effect measurements in magnetic field up to 88 T. A careful analysis of the complex spectra of quantum oscillations strongly supports the coexistence of an antiferromagnetic order in the inner plane and a charge order in the outer planes. The presence of an ordered antiferromagnetic metallic state that extends deep in the superconducting phase is a key ingredient that supports magnetically mediated pairing interaction in cuprates.

Nematic fluctuations in the cuprate superconductor Bi2Sr2CaCu2O8+δ.

Establishing the presence and the nature of a quantum critical point in their phase diagram is a central enigma of the high-temperature superconducting cuprates. It could explain their pseudogap and strange metal phases, and ultimately their high superconducting temperatures. Yet, while solid evidences exist in several unconventional superconductors of ubiquitous critical fluctuations associated to a quantum critical point, in the cuprates they remain undetected until now. Here using symmetry-resolved electronic Raman scattering in the cuprate [Formula: see text], we report the observation of enhanced electronic nematic fluctuations near the endpoint of the pseudogap phase. While our data hint at the possible presence of an incipient nematic quantum critical point, the doping dependence of the nematic fluctuations deviates significantly from a canonical quantum critical scenario. The observed nematic instability rather appears to be tied to the presence of a van Hove singularity in the band structure.

Long-Range Order in the Dipolar XY Antiferromagnet Er_{2}Sn_{2}O_{7}.

Er_{2}Sn_{2}O_{7} remains a puzzling case among the extensively studied frustrated compounds of the rare-earth pyrochlore family. Indeed, while a first-order transition towards a long-range antiferromagnetic state with the so-called Palmer-Chalker structure is theoretically predicted, it has not yet been observed, leaving the issue as to whether it is a spin-liquid candidate open. We report on neutron scattering and magnetization measurements which evidence a second-order transition towards this Palmer-Chalker ordered state around 108 mK. Extreme care was taken to ensure a proper thermalization of the sample, which has proved to be crucial to successfully observe the magnetic Bragg peaks. At the transition, a gap opens in the excitations, superimposed on a strong quasielastic signal. The exchange parameters, refined from a spin-wave analysis in applied magnetic field, confirm that Er_{2}Sn_{2}O_{7} is a realization of the dipolar XY pyrochlore antiferromagnet. The proximity of competing phases and the strong XY anisotropy of the Er^{3+} magnetic moment might be at the origin of enhanced fluctuations, leading to the unexpected nature of the transition, the low ordering temperature, and the observed multiscale dynamics.

Correction: Rapid fabrication of functionalised poly(dimethylsiloxane) microwells for cell aggregate formation.

Correction for 'Rapid fabrication of functionalised poly(dimethylsiloxane) microwells for cell aggregate formation' by A. Forget et al., Biomater. Sci., 2017, 5, 828-836.

Rapid fabrication of functionalised poly(dimethylsiloxane) microwells for cell aggregate formation.

Cell aggregates reproduce many features of the natural architecture of functional tissues, and have therefore become an important in vitro model of tissue function. In this study, we present an efficient and rapid method for the fabrication of site specific functionalised poly(dimethylsiloxane) (PDMS) microwell arrays that promote the formation of insulin-producing beta cell (MIN6) aggregates. Microwells were prepared using an ice templating technique whereby aqueous droplets were frozen on a surface and PDMS was cast on top to form a replica. By employing an aqueous alkali hydroxide solution, we demonstrate exclusive etching and functionalisation of the microwell inner surface, thereby allowing the selective absorption of biological factors within the microwells. Additionally, by manipulating surface wettability of the substrate through plasma polymer coating, the shape and profile of the microwells could be tailored. Microwells coated with antifouling Pluronic 123, bovine serum albumin, collagen type IV or insulin growth factor 2 were employed to investigate the formation and stability of MIN6 aggregates in microwells of different shapes. MIN6 aggregates formed with this technique retained insulin expression. These results demonstrate the potential of this platform for the rapid screening of biological factors influencing the formation and response of insulin-producing cell aggregates without the need for expensive micromachining techniques.

IGF-2 coated porous collagen microwells for the culture of pancreatic islets.

Islet transplantation, the only curative therapy for type I diabetes, requires isolation of the graft in highly specialized facilities for its later dispatch to remote transplantation centres. During transport and culture, many valuable cells are lost due to several factors such as mechanical stress, islet aggregation and dissociation. Here, we evaluate a porous microwell array sheet made of natural collagen type I extracellular matrix (ECM) protein as a novel islet culture substrate. This culture platform can be coated with IGF-2, a growth factor favorable for islet survival, and allows segregation of the islets within the porous microwell sheet, preventing aggregation. This design shows promising results for improving human pancreatic islets viability and function during culture and could form a novel paradigm for the transport of islets between isolation and transplantation centres.

Optical Writing of Magnetic Properties by Remanent Photostriction.

We present an optically induced remanent photostriction in BiFeO_{3}, resulting from the photovoltaic effect, which is used to modify the ferromagnetism of Ni film in a hybrid BiFeO_{3}/Ni structure. The 75% change in coercivity in the Ni film is achieved via optical and nonvolatile control. This photoferromagnetic effect can be reversed by static or ac electric depolarization of BiFeO_{3}. Hence, the strain dependent changes in magnetic properties are written optically, and erased electrically. Light-mediated straintronics is therefore a possible approach for low-power multistate control of magnetic elements relevant for memory and spintronic applications.

A novel type of splayed ferromagnetic order observed in Yb2Ti2O7.

The pyrochlore insulator Yb2Ti2O7 has attracted the attention of experimentalists and theoreticians alike for about 15 years. Conflicting neutron diffraction data on the possible existence of magnetic Bragg reflections at low temperature have been published. Here we report the observation of magnetic Bragg reflections by neutron powder diffraction at 60 mK. The magnetic diffraction pattern is analyzed using representation theory. We find Yb2Ti2O7 to be a splayed ferromagnet as reported for Yb2Sn2O7, a sibling compound with also dominating ferromagnetic interactions as inferred from the positive Curie-Weiss temperature. However, the configuration of the magnetic moment components perpendicular to the easy axis is of the all-in-all-out type in Yb2Ti2O7 while it is two-in-two-out in the Yb2Sn2O7. An overall experimental picture of the magnetic properties emerges.

Unconventional High-Energy-State Contribution to the Cooper Pairing in the Underdoped Copper-Oxide Superconductor HgBa_{2}Ca_{2}Cu_{3}O_{8+δ}.

We study the temperature-dependent electronic B_{1g} Raman response of a slightly underdoped single crystal HgBa_{2}Ca_{2}Cu_{3}O_{8+δ} with a superconducting critical temperature T_{c}=122 K. Our main finding is that the superconducting pair-breaking peak is associated with a dip on its higher-energy side, disappearing together at T_{c}. This result reveals a key aspect of the unconventional pairing mechanism: spectral weight lost in the dip is transferred to the pair-breaking peak at lower energies. This conclusion is supported by cellular dynamical mean-field theory on the Hubbard model, which is able to reproduce all the main features of the B_{1g} Raman response and explain the peak-dip behavior in terms of a nontrivial relationship between the superconducting gap and the pseudogap.

Collapse of the normal-state pseudogap at a Lifshitz transition in the Bi(2)Sr(2)CaCu(2)O(8+δ) cuprate superconductor.

We report a fine tuned doping study of strongly overdoped Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} single crystals using electronic Raman scattering. Combined with theoretical calculations, we show that the doping, at which the normal-state pseudogap closes, coincides with a Lifshitz quantum phase transition where the active holelike Fermi surface becomes electronlike. This conclusion suggests that the microscopic cause of the pseudogap is sensitive to the Fermi surface topology. Furthermore, we find that the superconducting transition temperature is unaffected by this transition, demonstrating that their origins are different on the overdoped side.

Tuning the reactivity of nanostructured indium tin oxide electrodes toward chemisorption.

This contribution highlights correlation between the surface concentration of a chemisorbed organophosphorous probe (flavin mononucleotide) and the relative hydroxyl surface coverage of nanostructured ITO electrodes, which can be tuned during post-deposition reductive annealing. The resulting modified electrodes are very stable in aqueous solution, highly hydrophilic and fully-accessible to the bulk solution.

Driving Spin Excitations by Hydrostatic Pressure in BiFeO(3).

Optical spectroscopy has been combined with computational and theoretical techniques to show how the spin dynamics in the model multiferroic BiFeO(3) responds to the application of hydrostatic pressure and its corresponding series of structural phase transitions from R3c to the Pnma phases. As pressure increases, multiple spin excitations associated with noncollinear cycloidal magnetism collapse into two excitations, which show jump discontinuities at some of the ensuing crystal phase transitions. The effective Hamiltonian approach provides information on the electrical polarization and structural changes of the oxygen octahedra through the successive structural phases. The extracted parameters are then used in a Ginzburg-Landau model to reproduce the evolution with pressure of the spin wave excitations observed at low energy, and we demonstrate that the structural phases and the magnetic anisotropy drive and control the spin excitations.

Large temperature dependence of the number of carriers in co-doped BaFe(2)As(2).

Using angle-resolved photoemission spectroscopy, we study the evolution of the number of carriers in Ba(Fe(1-x)Co(x))(2)As(2) as a function of Co content and temperature. We show that there is a k-dependent energy shift compared to density functional calculations, which is large below 100 K at low Co contents and reduces the volume of hole and electron pockets by a factor 2. This k shift becomes negligible at high Co content and could be due to interband charge or spin fluctuations. We further reveal that the bands shift with temperature, changing significantly the number of carriers they contain (up to 50%). We explain this evolution by thermal excitations of carriers among the narrow bands, possibly combined with a temperature evolution of the k-dependent fluctuations.

Observation of incipient charge nematicity in Ba(Fe(1-x)Co(x))2As2.

Using electronic Raman spectroscopy, we report direct measurements of charge nematic fluctuations in the tetragonal phase of strain-free Ba(Fe(1-x)Co(x))2As2 single crystals. The strong enhancement of the Raman response at low temperatures unveils an underlying charge nematic state that extends to superconducting compositions and which has hitherto remained unnoticed. Comparison between the extracted charge nematic susceptibility and the elastic modulus allows us to disentangle the charge contribution to the nematic instability, and to show that charge nematic fluctuations are weakly coupled to the lattice.

Dynamical splayed ferromagnetic ground state in the quantum spin ice Yb(2)Sn(2)O(7).

From magnetic, specific heat, (170)Yb Mössbauer effect, neutron diffraction, and muon spin relaxation measurements on polycrystalline Yb(2)Sn(2)O(7), we show that below the first order transition at 0.15 K all of the Yb(3+) ions are long-range magnetically ordered and each has a moment of 1.1 µ(B) which lies at ≃ 10° to a common fourfold cubic axis. The four sublattice moments have four different directions away from this axis and are therefore noncoplanar. We term this arrangement splayed ferromagnetism. This ground state has a dynamical component with a fluctuation rate in the megahertz range. The net ferromagnetic exchange interaction has an anisotropy that favors the local threefold axis. We discuss our results in terms of the phase diagram proposed by Savary and Balents [Phys. Rev. Lett. 108, 037202 (2012)] for a pyrochlore lattice of Kramers 1/2 effective spins.

Multiorbital effects on the transport and the superconducting fluctuations in LiFeAs.

The resistivity, Hall effect, and transverse magnetoresistance have been measured in low residual resistivity single crystals of LiFeAs. A comparison with angle resolved photoemission spectroscopy and quantum oscillation data implies that four carrier bands unevenly contribute to the transport. However the scattering rates of the carriers all display the T(2) behavior expected for a Fermi liquid. Near T(c) low field deviations of the magnetoresistance with respect to a H(2) variation permit us to extract the superconducting fluctuation contribution to the conductivity. Though below T(c) the anisotropy of superconductivity is rather small, the superconducting fluctuation displays a quasi-ideal two-dimensional behavior which persists up to 1.4 T(c). These results call for a refined theoretical understanding of the multiband behavior of superconductivity in this pnictide.