High precision determination of the Planck constant by modern photoemission spectroscopy

The Planck constant, with its mathematical symbol h, is a fundamental constant in quantum mechanics that is associated with the quantization of light and matter. It is also of fundamental importance to metrology, such as the definition of ohm and volt and the latest definition of kilogram. One of the first measurements to determine the Planck constant is based on the photoelectric effect; however, the values thus obtained so far have exhibited a large uncertainty. The accepted value of the Planck constant, 6.626 070 15 × 10−34 J s, is obtained from one of the most precise methods, the Kibble balance, which involves the quantum Hall effect, the Josephson effect, and the use of the international prototype of the kilogram or its copies. Here, we present a precise determination of the Planck constant by modern photoemission spectroscopy technique. Through the direct use of Einstein’s photoelectric equation, the Planck constant is determined by accurately measuring the energy position of the gold Fermi level using light sources with various photon wavelengths. The precision of the Planck constant as measured in this work, 6.626 10(13) × 10−34 J s, is improved by four to five orders of magnitude from the previous photoelectric effect measurements. We propose that this direct method of photoemission spectroscopy has potential to further increase its measurement precision of the Planck constant to be comparable to the most accurate methods available at present.