Exploring two-dimensional semimetals such as WTe₂ with a novel sample rotation scheme

The electronic properties of layered semimetals such as graphene, WTe₂, and ZrTe₅ are highly sensitive to magnetic fields, and the dependence on the direction of the field can be very informative. For example, the conductance of the edge states of monolayer WTe₂, which behaves as a 2D topological insulator, depends on the field orientation relative to the spin axis. Furthermore, when n-doped monolayer WTe₂ becomes superconducting below 1 K, the critical field is expected to be anisotropic in the plane and yield information about the spin-orbit coupling and pairing symmetry. We are therefore developing a novel two-axis sample rotation scheme which uses piezoelectric stepper motors held near room temperature in order to achieve independent, two-axis rotation of a sample held at He³ dilution refrigerator temperatures at the field center of a solenoid. We discuss the merits and challenges of the design, which avoids the unwanted heating, unreliability, and geometric constraints associated with conventional piezoelectric rotator schemes, and report our progress in using it to study magnetic anisotropy in WTe₂ and in other 2D semimetals, including hybrids of monolayer WTe₂ with other materials.