Will electric fields lead the way to developing semiconductors with high power efficiency?

In the realm of material science, the phenomena of polarization and polarity have conventionally been associated with insulators. However, envision a scenario where these characteristics could be induced in metals, potentially mitigating power losses attributed to semiconductors and extending the lifespan of batteries integrated into electronic devices. Existing technologies have posed limitations to date despite the intensive research in academia to achieve polarization and polarity in metals.

Recent breakthrough by the collaborative efforts of Professor Daesu Lee from the Department of Physics at Pohang University of Science and Technology (POSTECH), Professor Tae Won Noh and Dr. Wei Peng from the Department of Physics and Astronomy at Seoul National University (SNU), and Professor Se Young Park from the Department of Physics at Soongsil University (SSU), have led to the discovery of a method to induce and control polarization and polarity states within metals. This groundbreaking research was published in the online edition of the international physics journal Nature Physics on January 17, 2024.

Free electrons within metals, given their name, exhibit unrestricted movement, making it difficult to align them in specific directions to induce polarization or polarity states. Additionally, the symmetric structure of metal crystals at both ends has historically posed challenges in inducing these electrical effects.

However, the research team employed flexoelectric fields to implement polarization and polarity states within metals. This type of field arises when the surface of an object undergoes non-uniform deformation, allowing for the manipulation of charge movement and electrical characteristics by subtly altering the lattice structure of metals.

The team applied external pressure to the widely used strontium ruthenate (SrRuO₃) in the field of electronic components and semiconductors, generating a flexoelectric field. This metal oxide, characterized by heteroepitaxy, where crystals of strontium and ruthenium oxide with different shapes grow in the same direction, possesses a centrosymmetric structure.

The flexoelectric field altered the electronic interactions and lattice structure within strontium ruthenate, leading to a successful induction of polarization within the metal, causing a transformation in its electrical and mechanical properties and breaking the previously central symmetric structure. By employing flexoelectric polarizing and control of a ferromagnetic metal, the research team has successfully unraveled the mystery surrounding the implementation of polarization and polarity within metallic substances.

The study's lead researcher, Professor Daesu Lee from POSTECH, stressed, “We are the first researchers to verify the universal implementation of polarity states within metallic substances. I am hopeful that the findings from this study will prove beneficial in crafting highly efficient devices within the semiconductor and electrical fields.”

This work was supported by the Mid-Career Researcher Program of the National Research Foundation of Korea and by the Research Center Program of the Institute for Basic Science in Korea.