Archive for the ‘Publications’ Category

Posted by Kenneth Burch On November - 2 - 2018 Comments Off on Magnetism in two-dimensional van der Waals materials

The discovery of materials has often introduced new physical paradigms and enabled the development of novel devices. Two-dimensional magnetism, which is associated with strong intrinsic spin fluctuations, has long been the focus of fundamental questions in condensed matter physics regarding our understanding and control of new phases. Here we discuss magnetic van der Waals materials: two-dimensional atomic crystals that contain magnetic elements and thus exhibit intrinsic magnetic properties. These cleavable materials provide the ideal platform for exploring magnetism in the two-dimensional limit, where new physical phenomena are expected, and represent a substantial shift in our ability to control and investigate nanoscale  [ Read More ]

Posted by Kenneth Burch On July - 31 - 2018 Comments Off on Charge transfer in EuS/Bi2Se3 heterostructures as indicated by the absence of Raman scattering

Heterostructures of topological insulators and ferromagnets offer new opportunities in spintronics and a route to novel anomalous Hall states. In one such structure, EuS/Bi2Se3, a dramatic enhancement of the Curie temperature was recently observed. We performed Raman spectroscopy on a similar set of thin films to investigate the magnetic and lattice excitations. Interfacial strain was monitored through its effects on the Bi2Se3 phonon modes while the magnetic system was probed through the EuS Raman mode. Despite its appearance in bare EuS, the heterostructures lack the corresponding EuS Raman signal. Through numerical calculations, we rule out the possibility of Fabry-Perot interference  [ Read More ]

Posted by Kenneth Burch On July - 1 - 2018 Comments Off on Atomic-scale strain manipulation of a charge density wave

A charge density wave (CDW) is one of the fundamental instabilities of the Fermi surface occurring in a wide range of quantum materials. In dimensions higher than one, where Fermi surface nesting can play only a limited role, the selection of the particular wavevector and geometry of an emerging CDW should in principle be susceptible to controllable manipulation. In this work, we implement a simple method for straining materials compatible with low-temperature scanning tunneling microscopy/spectros- copy (STM/S), and use it to strain-engineer CDWs in 2H-NbSe2. Our STM/S measurements, combined with theory, reveal how small strain-induced changes in the electronic band  [ Read More ]

Posted by Kenneth Burch On June - 5 - 2018 Comments Off on Electric switching of magnetism in 2D

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 ]