Resonant Ultrasound Spectroscopy for Irregularly Shaped Samples and Its Application to Uranium Ditelluride.

Resonant ultrasound spectroscopy (RUS) is a powerful technique for measuring the full elastic tensor of a given material in a single experiment. Previously, this technique was practically limited to regularly shaped samples such as rectangular parallelepipeds, spheres, and cylinders [W. M.

SdH Oscillations from the Dirac Surface State in the Fermi-Arc Antiferromagnet NdBi.

The recent progress in CuMnAs and Mn3X (X = Sn, Ge, Pt) shows that antiferromagnets (AFMs) provide a promising platform for advanced spintronics device innovations. Most recently, a switchable Fermi-arc is discovered by the ARPES technique in antiferromagnet NdBi, but the knowledge about electron-transport property and the manipulability of the magnetic structure in NdBi is still vacant to date. In this study, SdH oscillations are successfully verified from the Dirac surface states (SSs) with 2-dimensionality and nonzero Berry phase.

Large anomalous Nernst effect and nodal plane in an iron-based kagome ferromagnet.

Anomalous Nernst effect (ANE), converting a heat flow to transverse electric voltage, originates from the Berry phase of electronic wave function near the Fermi energy . Thus, the ANE provides a sensitive probe to detect a topological state that produces large Berry curvature. In addition, a magnet that exhibits a large ANE using low-cost and safe elements will be useful to develop a novel energy harvesting technology.

Anomalous transport due to Weyl fermions in the chiral antiferromagnets MnX, X = Sn, Ge.

The recent discoveries of strikingly large zero-field Hall and Nernst effects in antiferromagnets MnX (X = Sn, Ge) have brought the study of magnetic topological states to the forefront of condensed matter research and technological innovation. These effects are considered fingerprints of Weyl nodes residing near the Fermi energy, promoting MnX (X = Sn, Ge) as a fascinating platform to explore the elusive magnetic Weyl fermions. In this review, we provide recent updates on the insights drawn from experimental and theoretical studies of MnX (X = Sn, Ge) by combining previous reports with our new, comprehensive set of transport measurements of high-quality MnSn and MnGe single crystals.

Identifying Native Point Defects in the Topological Insulator BiTe.

We successfully identified native point defects that occur in BiTe crystals by combining high-resolution bias-dependent scanning tunneling microscopy and density functional theory based calculations. As-grown BiTe crystals contain vacancies, antisites, and interstitial defects that may result in bulk conductivity and therefore may change the insulating bulk character. Here, we demonstrate the interplay between the growth conditions and the density of different types of native near-surface defects.

Author Correction: Iron-based binary ferromagnets for transverse thermoelectric conversion.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Iron-based binary ferromagnets for transverse thermoelectric conversion.

Thermoelectric generation using the anomalous Nernst effect (ANE) has great potential for application in energy harvesting technology because the transverse geometry of the Nernst effect should enable efficient, large-area and flexible coverage of a heat source. For such applications to be viable, substantial improvements will be necessary not only for their performance but also for the associated material costs, safety and stability. In terms of the electronic structure, the anomalous Nernst effect (ANE) originates from the Berry curvature of the conduction electrons near the Fermi energy.

Scanning probe microscopy induced surface modifications of the topological insulator BiTe in different environments.

We investigated the topological insulator (TI) BiTe in four different environments (ambient, ultra-high vacuum (UHV), nitrogen gas and organic solvent environment) using scanning probe microscopy (SPM) techniques. Upon prolonged exposure to ambient conditions and organic solvent environments the cleaved surface of the pristine BiTe is observed to be strongly modified during SPM measurements, while imaging of freshly cleaved BiTe in UHV and nitrogen gas shows considerably less changes of the BiTe surface. We conclude that the reduced surface stability upon exposure to ambient conditions is triggered by adsorption of molecular species from ambient, including HO, CO, etc which is verified by Auger electron spectroscopy.

Annealing-Induced Bi Bilayer on Bi2Te3 Investigated via Quasi-Particle-Interference Mapping.

Topological insulators (TIs) are renowned for their exotic topological surface states (TSSs) that reside in the top atomic layers, and hence, detailed knowledge of the surface top atomic layers is of utmost importance. Here we present the remarkable morphology changes of Bi2Te3 surfaces, which have been freshly cleaved in air, upon subsequent systematic annealing in ultrahigh vacuum and the resulting effects on the local and area-averaging electronic properties of the surface states, which are investigated by combining scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and Auger electron spectroscopy (AES) experiments with density functional theory (DFT) calculations. Our findings demonstrate that the annealing induces the formation of a Bi bilayer atop the Bi2Te3 surface.

Moiré superlattices at the topological insulator Bi2Te3.

We report on the observation of complex superlattices at the surface of the topological insulator Bi2Te3. Scanning tunneling microscopy reveals the existence of two different periodic structures in addition to the Bi2Te3 atomic lattice, which is found to strongly affect the local electronic structure. These three different periodicities are interpreted to result from a single small in-plane rotation of the topmost quintuple layer only.

Electronic interference transport and its electron-phonon interaction in the Sb-doped Bi2Se3 nanoplates synthesized by a solvothermal method.

Here we synthesized the antimony doped [Formula: see text] nanoplates by the solvothermal method. The angle-dependent magnetoconductance study was carried out and all the [Formula: see text] were found to be normalized to the perpendicular field, indicating a clear 2D electronic state. The features of weak antilocalization and universal conductance fluctuations were clearly identified in the magnetoresistance transport of the 4-probe nanodevices.

High-Mobility Sm-Doped Bi2 Se3 Ferromagnetic Topological Insulators and Robust Exchange Coupling.

High-mobility (Smx Bi1-x )2 Se3 topological insulators (with x = 0.05) show a Curie temperature of about 52 K, and the carrier concentration and Fermi wave vector can be manipulated by intentional Te introduction with no significant influence on the Curie temperature. The origin of the ferromagnetism is attributed to the trivalent Sm dopant, as confirmed by X-ray magnetic circular dichroism and first-principles calculations.

Topological transport and atomic tunnelling-clustering dynamics for aged Cu-doped Bi2Te3 crystals.

Enhancing the transport contribution of surface states in topological insulators is vital if they are to be incorporated into practical devices. Such efforts have been limited by the defect behaviour of Bi2Te3 (Se3) topological materials, where the subtle bulk carrier from intrinsic defects is dominant over the surface electrons. Compensating such defect carriers is unexpectedly achieved in (Cu0.

Two-dimensional universal conductance fluctuations and the electron-phonon interaction of surface states in Bi2Te2Se microflakes.

The universal conductance fluctuations (UCFs), one of the most important manifestations of mesoscopic electronic interference, have not yet been demonstrated for the two-dimensional surface state of topological insulators (TIs). Even if one delicately suppresses the bulk conductance by improving the quality of TI crystals, the fluctuation of the bulk conductance still keeps competitive and difficult to be separated from the desired UCFs of surface carriers. Here we report on the experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se microflakes.

Visualizing topological insulating Bi2Te3 quintuple layers on SiO2-capped Si substrates and its contrast optimization.

Thin Bi2Te3 flakes, with as few as 3 quintuple layers, are optically visualized on the SiO2-capped Si substrates. Their optical contrasts vary with the illumination wavelength, flake thickness and capping layers. The maximum contrast appears at the optimized light with the 570 nm wavelength.