A research team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the University of Salerno in Italy has discovered that thin films of elemental bismuth exhibit the so-called nonlinear Hall effect, which can be implemented in technologies for controlled use. terahertz high-frequency signals in electronic microcircuits. As reported by the Nature Electronics teamBismuth combines several advantages not currently available in other systems. The quantum effect is observed especially at room temperature. Thin films can even be applied to plastic surfaces and are therefore suitable for modern high-frequency technologies.

“When we apply current to certain materials, they can produce a voltage perpendicular to it. We physicists call this phenomenon the Hall effect, which is a collective term for effects that essentially have the same effect but differ in the underlying mechanisms at the electron level. As a rule, the recorded Hall voltage depends linearly on the applied current ” says Dr. from the HZDR Institute for Ion Beam Physics and Materials Research. Denys Makarov.

Many of these effects are the result of exposure to magnetic fields or magnetism in the material. However, in 2015, scientists discovered that the Hall effect can occur without the influence of magnetism. “We achieve this with materials whose crystal structure allows us to create Hall voltages that are no longer linearly dependent on the current,” adds Professor Carmine Ortix from the Faculty of Physics at the University of Salerno. This effect is of great interest because it enables new types of components for high-speed electronics.

The two researchers joined forces to find suitable materials and possible practical applications of the nonlinear Hall effect. While Ortix is ​​a theoretical physicist, Makarov brings experimental knowledge and connections to other institutes at HZDR, whose expertise is significantly involved in the work. “We came together with colleagues from the ELBE Center for Strong Radiation Sources, the Strong Magnetic Field Laboratory and the Institute of Source Ecology. The common goal: to identify a suitable material in which this quantum effect can occur in a controlled manner at room temperature, which is also easy to process and non-toxic,” says Makarov. , describes the starting point of the collaboration.

Familiar material, new features

The team found a candidate that exhibited these properties in the base material bismuth. Bismuth is known for the strong classical Hall effect present in most of the material. The researchers found that quantum effects dominate and control current on surfaces even at room temperature.

The main advantage of this approach is that researchers can apply their thin films with quantum properties to a variety of electronic substrates, such as silicon wafers and even plastic. The team manages to gain control over the effect through advanced microfabrication: they can directly influence the currents through the geometry of the channels on the chip.

New quantum materials of technological importance

Other teams have already created a number of materials that exhibit the nonlinear Hall effect, but they do not combine all the desired properties. For example, graphene is environmentally safe and the nonlinear Hall effect can be well controlled, but only at temperatures below -70 degrees Celsius. This means that if researchers want to use this effect, they need to cool it with liquid nitrogen. For other compounds they will have to use even lower temperatures.

Research is now focused on finding the right materials, but scientists are already thinking ahead. “We see the technological potential primarily in converting terahertz electromagnetic waves into direct current using our thin-film materials. This will enable new components for high-frequency communications,” says Ortix. To guarantee significantly higher data rates, future wireless communications systems will need to extend the carrier frequency beyond 100 gigahertz into the terahertz range unachievable with current technologies.