Ballistic PbTe Nanowire Devices.

Disorder is the primary obstacle in the current Majorana nanowire experiments. Reducing disorder or achieving ballistic transport is thus of paramount importance. In clean and ballistic nanowire devices, quantized conductance is expected, with plateau quality serving as a benchmark for disorder assessment. Here, we introduce ballistic PbTe nanowire devices grown by using the selective-area-growth (SAG) technique. Quantized conductance plateaus in units of 2e2/h are observed at zero magnetic field. This observation represents an advancement in diminishing disorder within SAG nanowires as most of the previously studied SAG nanowires (InSb or InAs) have not exhibited zero-field ballistic transport. Notably, the plateau values indicate that the ubiquitous valley degeneracy in PbTe is lifted in nanowire devices. This degeneracy lifting addresses an additional concern in the pursuit of Majorana realization. Moreover, these ballistic PbTe nanowires may enable the search for clean signatures of the spin-orbit helical gap in future devices.

Asymmetric Modulation on Exchange Field in a Graphene/BiFeO3 Heterostructure by External Magnetic Field.

Graphene, having all atoms on its surface, is favorable to extend the functions by introducing the spin-orbit coupling and magnetism through proximity effect. Here, we report the tunable interfacial exchange field produced by proximity coupling in graphene/BiFeO3 heterostructures. The exchange field has a notable dependence with external magnetic field, and it is much larger under negative magnetic field than that under positive magnetic field. For negative external magnetic field, interfacial exchange coupling gives rise to evident spin splitting for N ≠ 0 Landau levels and a quantum Hall metal state for N = 0 Landau level. Our findings suggest graphene/BiFeO3 heterostructures are promising for spintronics.

Lateral graphene p-n junctions formed by the graphene/MoS2 hybrid interface.

Graphene/two-dimensional (2D) semiconductor heterostructures have been demonstrated to possess many advantages for electronic and optoelectronic devices. However, there are few reports about the utilization of a 2D semiconductor monolayer to tune the properties of graphene. Here, we report the fabrication and characterization of graphene p-n junctions based on graphene/MoS2 hybrid interfaces. Monolayered graphene across the monolayered MoS2 boundary is divided into n-type regions on the MoS2 and p-type regions on the SiO2 substrate. Such van der Waals heterostructure based graphene p-n junctions show good photoelectric properties. The photocurrent modulation of such devices by a single back gate is also demonstrated for the first time, which shows that the graphene on and off MoS2 regions have different responses to the gate voltage. Our results suggest that the atomic thin hybrid structure can remarkably extend the device applications.