Rhenium diselenide (ReSe₂) is a layered indirect gap semiconductor for which micromechanical cleavage can produce monolayers consisting of a plane of rhenium atoms with selenium atoms above and below. ReSe₂ is unusual among the transition-metal dichalcogenides in having a low symmetry; it is triclinic, with four formula units per unit cell, and has the bulk space group P1̅. Experimental studies of Raman scattering in monolayer, few-layer, and bulk ReSe₂ show a rich spectrum consisting of up to 16 of the 18 expected lines with good signal strength, pronounced in-plane anisotropy of the intensities, and no evidence of degradation of the sample during typical measurements. No changes in the frequencies of the Raman bands with layer thickness down to one monolayer are observed, but significant changes in relative intensity of the bands allow the determination of crystal orientation and of monolayer regions. Supporting theory includes calculations of the electronic band structure and Brillouin zone center phonon modes of bulk and monolayer ReSe₂ as well as the Raman tensors determining the scattering intensity of each mode. It is found that, as for other transition-metal dichalcogenides, Raman scattering provides a powerful diagnostic tool for studying layer thickness and also layer orientation in few-layer ReSe₂.

We report on the magnetoresistance of a two-dimensional electron gas subjected to an abrupt magnetic field gradient arising from a ferromagnetic stripe fabricated at its surface. A sharp resistance resonance effect is observed at $B_p$ due to the formation of two types of magnetic edge states that drift in opposite directions perpendicular to the magnetic field gradient for $B<\mathrm{}{B}_p$ and $B>\mathrm{}{B}_p$. A semiclassical drift-diffusion model gives a good description of the effects of the magnetic confinement on both the diagonal and off-diagonal components of the resistivity tensor.

Scanning Hall probe microscopy has been used to study vortex structures in very-high-quality single crystals of the unconventional superconductor Sr${}_2$RuO${}_4$ $(T_c\cong 1.5$ K). In none of our samples do we find credible evidence for the existence of the spontaneous fields or chiral domains predicted for the expected time-reversal symmetry-breaking order parameter. Even in our highest-quality samples we observe very strong vortex pinning and anomalous broadening of vortex profiles. The best samples also exhibit a clear field-driven triangular to square vortex lattice transition at low fields, as predicted by extended London theory calculations. In stark contrast, slightly less well-ordered samples exhibit pronounced vortex chaining/banding that we tentatively attribute to an extrinsic source of disorder.

Scanning Hall probe microscopy has been used to search for spontaneous fields at the well-defined edges of large mesoscopic disks, etched into the $ab$ surface of very high quality single crystal ${\mathrm{Sr}}_2\mathrm{Ru}{\mathrm{O}}_4$. Such fields are predicted to exist at locations of broken translational symmetry as a consequence of the proposed two-component spin-triplet chiral order parameter $\widehat{d}={\Delta }_0(k_x\pm i{k}_y)\widehat{z}$. We find no evidence for such fields and impose an upper limit of $\pm$2.5 mG on their magnitude. We do, however, observe an abrupt apparent loss of strong bulk pinning and a change in the screening behavior above $H\sim 25$ Oe. At high fields ($H>25$ Oe) pronounced magnetic screening by the disks is very well described by a model containing only strong edge currents, and bulk critical currents do not appear to play a significant role. Our results are discussed in terms of relevant theoretical predictions.