A groundbreaking study by a research team from the University of Science and Technology of China (USTC) has unveiled significant discoveries regarding nonlinear Hall and wireless rectification effects in elemental semiconductor tellurium (Te) at room temperature. This revelation, published in Nature Communications, marks a remarkable step forward in the exploration of nonlinear Hall effects (NLHE), which are critical for the development of advanced electronic devices. Traditionally, NLHE, which involves the generation of second-harmonic signals in response to alternating current (AC) without requiring an external magnetic field, has faced numerous limitations, such as low Hall voltage outputs and temperature constraints.
Previous investigations into the nonlinear Hall effect have predominantly reported findings at low temperatures, with notable examples including Dirac semimetal BaMnSb2 and Weyl semimetal TaIrTe4. While these materials have demonstrated NLHE, their limited voltage outputs and lack of tunability have dampened their practical applicability. These challenges have necessitated a search for alternative materials that can present a more favorable environment for observing NLHE under practical conditions.
The Promise of Tellurium
Motivated by these challenges, the research team directed their focus toward tellurium, a narrow-bandgap semiconductor. The unique structural characteristics of Te, particularly its one-dimensional helical chains, contribute to breaking inversion symmetry, thereby making it an excellent candidate for exhibiting NLHE. The team’s efforts paid off when they discovered substantial NLHE in thin flakes of Te at room temperature. Notably, these flakes displayed tunable Hall voltage outputs that could be modulated using external gate voltages, achieving an impressive maximum second-harmonic output of 2.8 mV at 300 K—an output significantly surpassing previous records in the field.
Mechanisms Behind the Discovery
Further experimental investigations and theoretical analyses indicated that the observed NLHE in tellurium is primarily influenced by extrinsic scattering phenomena. The breaking of surface symmetry intrinsic to the thin flake structure emerged as a pivotal factor in facilitating nonlinear transport. This insight provides a deeper understanding of how surface characteristics and material properties interplay in governing nonlinear effects, paving the way for future explorations into similar materials and effects.
Advancement in Wireless Rectification
In an exciting extension of their findings, the research team experimented by substituting AC currents with radiofrequency (RF) signals, effectively achieving wireless RF rectification in Te thin flakes. This innovative Hall rectifier offers stable rectified voltage outputs across a wide frequency range of 0.3 to 4.5 GHz. This breakthrough distinguishes the Hall rectifier from conventional methods which rely on p-n or metal-semiconductor junctions. The unique attributes of tellurium allow for a broadband response under zero bias, positioning it as a viable candidate for efficient energy harvesting and wireless charging applications.
The insights gleaned from this study not only advance our understanding of nonlinear transport phenomena in solid materials but also herald new opportunities for innovation in electronic device design. By unraveling the mechanisms behind NLHE in tellurium, researchers open the door to a realm of advanced applications, potentially transforming how we approach energy harvesting and electronic component design. Under the adept leadership of Prof. Zeng Changgan and Associate Researcher Li Lin, the implications of this research could be profound, guiding the future landscape of semiconductor research and electronic engineering.
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