Archive for the ‘Year’ Category

Posted by Kenneth Burch On June - 5 - 2018 0 Comment

News and Views: Electric switching of magnetism in 2D Combined electrostatic gating and magnetic fields switch a 2D atomic crystal from an antiferromagnetic to a ferromagnetic state.

Posted by Kenneth Burch On May - 6 - 2018 Comments Off on Controlling Magnetic and Optical Properties of a van der Waals Crystal

Magnetic van der Waals (vdW) materials are the centerpiece of atomically thin devices with spintronic and optoelectronic functions. Exploring new chemistry paths to tune their magnetic and optical properties enables significant progress in fabricating heterostructures and ultracompact devices by mechanical exfoliation. The key parameter to sustain ferromagnetism in 2D is magnetic anisotropy—a tendency of spins to align in a certain crystallographic direction known as easy‐axis. In layered materials, two limits of easy‐axis are in‐plane (XY) and out‐of‐plane (Ising). Light polarization and the helicity of topological states can couple to magnetic anisotropy with promising photoluminescence or spin‐orbitronic functions. Here, a unique  [ Read More ]

Posted by Kenneth Burch On February - 12 - 2018 Comments Off on Possible structural transformation and enhanced magnetic fluctuations in exfoliated α-RuCl3

We present Raman spectroscopy experiments on exfoliated α-RuCl3, from tens of nm thick down to single layers. Besides unexpectedly finding this material to be air stable, in the thinnest layers we observe the appearance with decreasing temperature of a symmetry-forbidden mode in crossed polarization, along with an anomalous broadening of a mode at 164 cm−1 that is known to couple to a continuum of magnetic excitations. This may be due to an enhancement of magnetic fluctuations and evidence for a distorted honeycomb lattice in single- and bilayer samples. Journal of Physics and Chemistry of Solids 

Posted by Kenneth Burch On May - 6 - 2017 Comments Off on Andreev Reflection without Fermi Surface Alignment

We address the controversy over the proximity effect between topological materials and high-T csuperconductors. Junctions are produced between Bi2Sr2CaCu2O and materials with different Fermi surfaces (Bi2Te3 and graphite). Both cases reveal tunneling spectra that are consistent with Andreev reflection. This is confirmed by a magnetic field that shifts features via the Doppler effect. This is modeled with a single parameter that accounts for tunneling into a screening supercurrent. Thus the tunneling involves Cooper pairs crossing the heterostructure, showing that the Fermi surface mismatch does not hinder the ability to form transparent interfaces, which is accounted for by the extended Brillouin zone and different lattice  [ Read More ]

Posted by Kenneth Burch On March - 13 - 2017 Comments Off on Understanding the evolution of anomalous anharmonicity in Bi2Te3−xSex

The anharmonic effect in thermoelectrics has been a central topic for decades in both condensed matter physics and material science. However, despite the long-believed strong and complex anharmonicity in the Bi2 Te3−x Sex series, experimental verification of anharmonicity and its evolution with doping remains elusive. We fill this important gap with high-resolution, temperature-dependent Raman spectroscopy in high-quality single crystals of Bi2Te3, Bi2Te2Se, and Bi2Se3 over the temperature range from 4 to 293 K. Klemens’s model was employed to explain the renormalization of their phonon linewidths. The phonon energies of Bi2Se3 and Bi2Te3 are analyzed in detail from three aspects: lattice  [ Read More ]