An international research team has identified that chiral phonons can generate orbital current without requiring magnetic elements. This is attributed partly to the intrinsic magnetic moments of chiral phonons. The phenomenon can be observed in common crystal materials and holds implications for developing more cost-effective and energy-efficient orbitronic devices.
Orbitronics and Current Generation
Electronic devices utilize the electron's charge, but electrons also possess spin and orbital angular momentum. While spin has been investigated for efficient current generation, orbitronics, which uses an electron's orbital angular momentum, is a more recent area of study.
Historically, generating orbital current has been technically challenging, often requiring the injection of charge current into specific transition metals. Many of these elements are categorized as critical materials. The new research demonstrates that a heat gradient can induce chiral phonons in a quartz (SiO2) substrate, which can then be converted into orbital current. This method offers the advantage of utilizing more affordable and abundant materials.
Chiral Phonons and Their Role
This study expands upon prior research indicating that spin current can be generated and controlled by applying a thermal gradient to non-magnetic hybrid semiconductors containing chiral phonons.
Chiral phonons are defined as atomic groups exhibiting circular motion when excited by an energy source, such as heat. Their movement through a material propagates this circular motion, or angular momentum.
Associate Professor Jun Liu noted that the research demonstrates the conversion of angular momentum from chiral phonons into orbital current. This process is achievable in non-magnetic insulators that contain chiral phonons, due to the magnetic properties generated by the chiral phonon's rotation.
Implications
The researchers anticipate this work could contribute to the development of cost-effective orbitronic applications and address foundational questions regarding the relationship between structural chirality and orbital currents, potentially advancing the field of orbitronics.
The study was published in Nature Physics. Co-corresponding authors include Dali Sun, Jun Liu, and Jun Zhou. Yoji Nabei is listed as the first author. Dali Sun's work received support from the Department of Energy and the Air Force Office of Scientific Research.