Vanishing nematic order beyond the pseudogap phase in overdoped cuprate superconductors.

During the last decade, translational and rotational symmetry-breaking phases-density wave order and electronic nematicity-have been established as generic and distinct features of many correlated electron systems, including pnictide and cuprate superconductors. However, in cuprates, the relationship between these electronic symmetry-breaking phases and the enigmatic pseudogap phase remains unclear. Here, we employ resonant X-ray scattering in a cuprate high-temperature superconductor [Formula: see text] (Nd-LSCO) to navigate the cuprate phase diagram, probing the relationship between electronic nematicity of the Cu 3d orbitals, charge order, and the pseudogap phase as a function of doping. We find evidence for a considerable decrease in electronic nematicity beyond the pseudogap phase, either by raising the temperature through the pseudogap onset temperature T* or increasing doping through the pseudogap critical point, p*. These results establish a clear link between electronic nematicity, the pseudogap, and its associated quantum criticality in overdoped cuprates. Our findings anticipate that electronic nematicity may play a larger role in understanding the cuprate phase diagram than previously recognized, possibly having a crucial role in the phenomenology of the pseudogap phase.

Quenching of Long Range Order and the Mn3+ Ordered Moment in the Layered Antiferromagnet, Ba xSr1- xLaMnO4. A Polarized Neutron Scattering Study.

SrLaMnO4 is a layered antiferromagnetic (AF) oxide with the tetragonal ( I4/ mmm) n = 1 Ruddlesden-Popper phase structure (also known as the K2NiF4 structure) with TN = 128 K. Remarkably, substitution of Sr2+ by Ba2+, forming the solid solution Ba1- xSr xLaMnO4, results in the destruction of long-range magnetic order and of the ordered moment on Mn3+ for x > 0.35, although the effective paramagnetic moment remains unchanged, an unprecedented behavior for this class of magnetic materials. Four members, x = 0.0, 0.25, 0.35, and 1.0, have been studied using XYZ neutron polarization analysis which permits isolation of the magnetic, nuclear and nuclear spin components of the scattering and the measurement of the absolute value of the magnetic cross section. Data analysis is done using model independent reverse Monte Carlo methods (SPINVERT). The results for x = 0.0 (SrLaMnO4), T > TN(128 K), show an asymmetric diffuse peak which evolves into resolution limited Bragg peaks below T N and a fully ordered AF ground state with a Mn3+ moment of 3.06 µB. For x = 0.25 the magnetic scattering below T N displays a remarkable phase separation-Bragg reflections coexisting with diffuse scattering. The ordered Mn3+ moment is 1.1 µB, much reduced from that obtained via unpolarized neutrons. There are no Bragg peaks for x = 0.35 at any measured temperature ( T > 3 K) but there is highly structured diffuse scattering indicating strong short-range order reminiscent of x = 0 and 0.25 above their respective transition temperatures. For x = 1.00 (BaLaMnO4) the diffuse scattering roughly follows a paramagnetic form-factor indicating no short or long-range magnetic correlations. It is argued that the observed phenomena are due to a competition between AF and ferromagnetic (F) superexchange interactions for the 180° Mn3+-O-Mn3+ geometry within the ab plane and that the changes in the local geometry of the Mn-O octahedron leads to reduction of the AF interaction with a likely enhancement of the F interaction with increasing Ba content, ultimately giving rise to a glassy ground state. Analysis of the diffuse magnetic components show clear 2D AF spin correlations above TN for x = 0.00, 0.25, and 0.35 with correlation lengths, ξ ∼ 14-7 Å and no spin correlations for x = 1.00.

Origins of the large piezoelectric response of samarium-doped lead magnesium niobate-lead titanate ceramics.

The recent discovery of the large piezoelectric response of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) ceramics induced by samarium doping has provided a substantially improved functionality to the group of lead-based relaxor-ferroelectric materials. Different mechanisms have been so far proposed for the large piezoelectricity; however, the explanations are contradictory and focused on a unified description. Here, we use nonlinear harmonic piezoelectric measurements combined with multiscale structural analysis to clarify the origins of the ultrahigh piezoelectric response of samarium-doped PMN-PT. Our methodological approach allowed us to separate the multiple piezoelectric contributions, revealing their quantitative role in the total response. The results show that the ultrahigh piezoelectricity cannot be attributed to a single mechanism but is rather a complex combination of different contributions originating from the multiple effects of samarium doping on the long- and short-range structure of PMN-PT. The study offers a baseline for future engineering of the key material parameters affecting the large piezoelectric response of relaxor-ferroelectric ceramics.

Crystal structure reinvestigation of silver(I) fluoride, AgF.

A crystal structure reinvestigation of AgF based on a low-temperature high-resolution single-crystal X-ray diffraction data is reported. Silver(I) fluoride crystallizes in the rock salt structure type (Fm m) with a unit-cell parameter of 4.92171 (14) Šat 100 K, resulting in an Ag-F bond length of 2.46085 (7) Å.

Structure and Dynamics of Ferroelectric Domains in Polycrystalline Pb(Fe1/2Nb1/2)O3.

A complex domain structure with variations in the morphology is observed at ambient temperature in monoclinic Pb(Fe1/2Nb1/2)O3. Using electron microscopy and piezoresponse force microscopy, it is possible to reveal micrometre-sized wedge, lamellar-like, and irregularly shaped domains. By increasing the temperature, the domain structure persists up to 80 °C, and then starts to disappear at around 100 °C due to the proximity of the ferroelectric-paraelectric phase transition, in agreement with macroscopic dielectric measurements. In order to understand to what degree domain switching can occur in the ceramic, the mobility of the domain walls was studied at ambient temperature. The in situ poling experiment performed using piezoresponse force microscopy resulted in an almost perfectly poled area, providing evidence that all types of domains can be easily switched. By poling half an area with 20 V and the other half with -20 V, two domains separated by a straight domain wall were created, indicating that Pb(Fe1/2Nb1/2)O3 is a promising material for domain-wall engineering.

Room-Temperature Synthesis and Optical Properties of NdVO4 Nanoneedles.

Tetragonal NdVO4 nanoneedles were prepared via a simple room-temperature precipitation method in the absence of any surfactant or template, starting from simple inorganic salts, NdCl3 and Na3VO4, as raw materials. The nanoneedles were characterized by XRPD, SEM, Raman, PL, and lifetime spectroscopy. The particles have a length of about 100 nm and a diameter of 20 nm and grow along <112> direction. The advantages of this method lie in the high yield, non-toxic solvents, mild reaction conditions, and that it can potentially be employed for the preparation of other 1D lanthanide vanadates.