Topology stabilized fluctuations in a magnetic nodal semimetal.

The interplay between magnetism and electronic band topology enriches topological phases and has promising applications. However, the role of topology in magnetic fluctuations has been elusive. Here, we report evidence for topology stabilized magnetism above the magnetic transition temperature in magnetic Weyl semimetal candidate CeAlGe. Electrical transport, thermal transport, resonant elastic X-ray scattering, and dilatometry consistently indicate the presence of locally correlated magnetism within a narrow temperature window well above the thermodynamic magnetic transition temperature. The wavevector of this short-range order is consistent with the nesting condition of topological Weyl nodes, suggesting that it arises from the interaction between magnetic fluctuations and the emergent Weyl fermions. Effective field theory shows that this topology stabilized order is wavevector dependent and can be stabilized when the interband Weyl fermion scattering is dominant. Our work highlights the role of electronic band topology in stabilizing magnetic order even in the classically disordered regime.

Quantized thermoelectric Hall effect induces giant power factor in a topological semimetal.

Thermoelectrics are promising by directly generating electricity from waste heat. However, (sub-)room-temperature thermoelectrics have been a long-standing challenge due to vanishing electronic entropy at low temperatures. Topological materials offer a new avenue for energy harvesting applications. Recent theories predicted that topological semimetals at the quantum limit can lead to a large, non-saturating thermopower and a quantized thermoelectric Hall conductivity approaching a universal value. Here, we experimentally demonstrate the non-saturating thermopower and quantized thermoelectric Hall effect in the topological Weyl semimetal (WSM) tantalum phosphide (TaP). An ultrahigh longitudinal thermopower [Formula: see text] and giant power factor [Formula: see text] are observed at ~40 K, which is largely attributed to the quantized thermoelectric Hall effect. Our work highlights the unique quantized thermoelectric Hall effect realized in a WSM toward low-temperature energy harvesting applications.

Topological Singularity Induced Chiral Kohn Anomaly in a Weyl Semimetal.

The electron-phonon interaction (EPI) is instrumental in a wide variety of phenomena in solid-state physics, such as electrical resistivity in metals, carrier mobility, optical transition, and polaron effects in semiconductors, lifetime of hot carriers, transition temperature in BCS superconductors, and even spin relaxation in diamond nitrogen-vacancy centers for quantum information processing. However, due to the weak EPI strength, most phenomena have focused on electronic properties rather than on phonon properties. One prominent exception is the Kohn anomaly, where phonon softening can emerge when the phonon wave vector nests the Fermi surface of metals. Here we report a new class of Kohn anomaly in a topological Weyl semimetal (WSM), predicted by field-theoretical calculations, and experimentally observed through inelastic x-ray and neutron scattering on WSM tantalum phosphide. Compared to the conventional Kohn anomaly, the Fermi surface in a WSM exhibits multiple topological singularities of Weyl nodes, leading to a distinct nesting condition with chiral selection, a power-law divergence, and non-negligible dynamical effects. Our work brings the concept of the Kohn anomaly into WSMs and sheds light on elucidating the EPI mechanism in emergent topological materials.

High resolution neutron Larmor diffraction using superconducting magnetic Wollaston prisms.

The neutron Larmor diffraction technique has been implemented using superconducting magnetic Wollaston prisms in both single-arm and double-arm configurations. Successful measurements of the coefficient of thermal expansion of a single-crystal copper sample demonstrates that the method works as expected. The experiment involves a new method of tuning by varying the magnetic field configurations in the device and the tuning results agree well with previous measurements. The difference between single-arm and double-arm configurations has been investigated experimentally. We conclude that this measurement benchmarks the applications of magnetic Wollaston prisms in Larmor diffraction and shows in principle that the setup can be used for inelastic phonon line-width measurements. The achievable resolution for Larmor diffraction is comparable to that using Neutron Resonance Spin Echo (NRSE) coils. The use of superconducting materials in the prisms allows high neutron polarization and transmission efficiency to be achieved.

Nanoscale Atomic Displacements Ordering for Enhanced Piezoelectric Properties in Lead-Free ABO3 Ferroelectrics.

In situ synchrotron X-ray diffuse scattering and inelastic neutron scattering measurements from a prototype ABO3 ferroelectric single-crystal are used to elucidate how electric fields along a nonpolar direction can enhance its piezoelectric properties. The central mechanism is found to be a nanoscale ordering of B atom displacements, which induces increased lattice instability and therefore a greater susceptibility to electric-field-induced mechanical deformation.

Neutron diffraction of ice in hydrogels.

Neutron diffraction patterns for deuterated poly-N,N,-dimethylacrylamide (PDMAA) hydrogels were measured from 10 to 300 K to investigate the structure and properties of water in the gels. Diffraction peaks observed below 250 K indicate the existence of ice in the hydrogels. Some diffraction peaks from the ice are at lower diffraction angles than those in ordinary hexagonal ice (Ih). These shifts in peaks indicate that the lattice constants of the a and c axes in the ice are about 0.29 and 0.3% higher than those in ice Ih, respectively. The results show that bulk low-density ice can exist in PDMAA hydrogels. The distortions in the lattice structure of ice imply significant interactions between water molecules and the surrounding polymer chains, which play an important role in the chemical and mechanical properties of the hydrogel.

Perú: Gestión del riesgo de desastres y adaptación al cambio climático: Marco de la preparación de la estrategia 2012-2016 del BID en Perú / Peru: Disaster Risk Management and Climate Change Adaptation: Framework for the Preparation of the IDB's 2012-2016 Strategy in Peru

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