Press Release
☷Twisted Science NIST Researchers Find a New Quantum Ruler to Explore Exotic Matter
National Institute of Standards and Technology ( By Press Release office)
Oct 07,2023
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Graphene , a super thin sheet of carbon , has some pretty cool properties on its own . But when you stack multiple sheets together and twist them at certain angles , things get even more interesting . These twisted sheets , known as moiré quantum matter , can do all sorts of crazy things . Depending on the twist angle , they can generate their own magnetic fields , become superconductors , or turn into insulators . A team of researchers , led by Joseph A . Stroscio from the National Institute of Standards and Technology , has developed a "quantum ruler" to measure and explore these strange properties . This could lead to a new standard for electrical resistance and make calibrating electronic devices easier . The team used a scanning tunneling microscope to measure the energy levels of electrons in the twisted graphene layers . By applying a voltage and recording the current , they were able to see how the energy levels changed in the presence of a magnetic field . This could be really useful for designing and manufacturing semiconductor devices . The background of the ladder looks like graph paper and shows the energy level , which can be used as a quantum ruler to figure out the electrical and magnetic properties of the material . In a magnetic field , electrons move in circular paths . Normally , the circular orbits of electrons in solid materials have a special connection with a magnetic field: the area enclosed by each orbit multiplied by the magnetic field can only have specific values because of the quantum nature of electrons . This fixed product is used as a ruler to measure the material ' s electronic and magnetic properties . Any slight deviation from this pattern would represent a new quantum ruler that reflects the magnetic properties of the quantum moiré material being studied . The researchers found evidence of this new quantum ruler when they varied the magnetic field applied to the moiré graphene bilayers . The product of the area enclosed by the circular orbit and the magnetic field no longer equaled a fixed value , but instead shifted depending on the magnetization of the bilayers . This shift resulted in different tick marks for the energy levels of the electrons , revealing new magnetic properties . The researchers hope that by using this new quantum ruler to study how the circular orbits change with magnetic field , they can uncover the magnetic properties of these moiré quantum materials . In moiré quantum materials , electrons have a range of energies determined by the electric field , with the lower energy states concentrated in the valleys . The large spacing between the valleys in the bilayers , which is greater than the atomic spacing in any single layer of graphene , explains some of the unique magnetic properties observed . The research was published in the October 6 issue of Science . Because you can choose the properties of moiré quantum matter by picking a specific twist angle and number of atomically thin layers , these new measurements could help us understand how scientists can customize and improve the magnetic and electronic properties of quantum materials for various uses in microelectronics and related fields . For example , we already know that ultrathin superconductors are extremely sensitive detectors of single photons , and quantum moiré superconductors are among the thinnest . Another interesting application is that moiré quantum matter might offer a new and easier standard for electrical resistance . Right now , the standard is based on the resistance values that a material has when a strong magnetic field is applied to the electrons in a two - dimensional layer . This is called the quantum Hall effect , which comes from the quantized energy levels of the electrons in circular orbits . These resistance values can be used to calibrate electrical devices , but it can only be done at a metrology facility like NIST because it requires a strong magnetic field . However , if we can manipulate quantum moiré matter so that it has a net magnetization even without an external magnetic field , we could potentially create a portable version of the most precise resistance standard , known as the anomalous quantum Hall resistance standard . This would allow calibrations to be done at the manufacturing site , potentially saving a lot of money .
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