Inge Leermakers

Extremely high magnetoresistance and conductivity in the type-II Weyl semimetals WP2 and MoP2

The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings can lead to spectacular electronic properties such as large mobilities accompanied by extremely high magnetoresistance. In particular, two closely neighboring Weyl points of the same chirality are protected from annihilation by structural distortions or defects, thereby significantly reducing the scattering probability between them. Here we present the electronic properties of the transition metal diphosphides, WP2 and MoP2, which are type-II Weyl semimetals with robust Weyl points by transport, angle resolved photoemission spectroscopy and first principles calculations. Our single crystals of WP2 display an extremely low residual low-temperature resistivity of 3 nΩ cm accompanied by an enormous and highly anisotropic magnetoresistance above 200 million % at 63 T and 2.5 K. We observe a large suppression of charge carrier backscattering in WP2 from transport measurements. These properties are likely a consequence of the novel Weyl fermions expressed in this compound.Semimetals with the band structure exhibiting Dirac and Weyl crossings can show special electronic and magnetic properties. Here the authors explore the electronic properties of the type-II Weyl semimetals, MoP2 and WP2 with robust Weyl points which display very high magnetoresistance and conductivity.

Observation of pseudo-two-dimensional electron transport in the rock salt-type topological semimetal LaBi

Topological insulators are characterized by an inverted band structure in the bulk and metallic surface states on the surface. In LaBi, a semimetal with a band inversion equivalent to a topological insulator, we observe surface state like behavior in the magnetoresistance. The electrons responsible for this pseudo two dimensional transport, however, originate from the bulk states rather topological surface states, which is witnessed by the angle dependent quantum oscillations of the magnetoresistance and ab initio calculations. As a consequence, the magnetoresistance exhibits strong anisotropy with large amplitude (~ 10^5 %).

Full superconducting dome of strong Ising protection in gated monolayer WS2

Significance Compared with 3D superconductors, atomically thin superconductors are expected to be easier to engineer for electronic applications. Here, we use field effect gating to induce superconductivity in a monolayer semiconducting transition metal dichalcogenide, WS2, grown by chemical vapor deposition. The remarkable doping range allows access to a cascade of electronic phases from a band insulator, a superconductor, to a reentrant insulator at high doping. The large spin-orbit coupling of ∼30 meV makes the Ising paring in WS2 arguably the most strongly protected superconducting state against external magnetic field. The wide tunability revealed by spanning over a complete superconducting dome paves the way for the integration of monolayer superconductors to functional electronic devices exploiting the field effect control of quantum phases. Many recent studies show that superconductivity not only exists in atomically thin monolayers but can exhibit enhanced properties such as a higher transition temperature and a stronger critical field. Nevertheless, besides being unstable in air, the weak tunability in these intrinsically metallic monolayers has limited the exploration of monolayer superconductivity, hindering their potential in electronic applications (e.g., superconductor–semiconductor hybrid devices). Here we show that using field effect gating, we can induce superconductivity in monolayer WS2 grown by chemical vapor deposition, a typical ambient-stable semiconducting transition metal dichalcogenide (TMD), and we are able to access a complete set of competing electronic phases over an unprecedented doping range from band insulator, superconductor, to a reentrant insulator at high doping. Throughout the superconducting dome, the Cooper pair spin is pinned by a strong internal spin–orbit interaction, making this material arguably the most resilient superconductor in the external magnetic field. The reentrant insulating state at positive high gating voltages is attributed to localization induced by the characteristically weak screening of the monolayer, providing insight into many dome-like superconducting phases observed in field-induced quasi-2D superconductors.