Jones A C L, Rutbeck-Goldman H J, Hisakado T H, Piñeiro A M, Tom H W K, Mills A P, Barbiellini B, Kuriplach J
Department of Physics and Astronomy, University of California Riverside, Riverside, California 92521, USA.
Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
Phys Rev Lett. 2016 Nov 18;117(21):216402. doi: 10.1103/PhysRevLett.117.216402. Epub 2016 Nov 15.
The affinity A_{Ps} of positronium (Ps) atoms for a metal is the negative of the maximum kinetic energy with which Ps is emitted into vacuum when thermalized positrons in a metal encounter the surface. When this quantity is measured by ground state Ps time of flight (TOF), the precision is severely limited by the short triplet state lifetime of 142 ns. By quickly converting the emitted Ps atoms into long-lived Rydberg states, we are able to dramatically increase the TOF to allow precision measurements of A_{Ps}. From our measurements made on a Cu(110) sample at T=128 K, we find A_{Ps}(128 K)=(-2.476±0.010_{stat}±0.013_{syst}) eV, compared with the result A_{Ps}(128 K)=(-2.545±0.010_{num}±0.010_{syst}) eV found using highly accurate generalized gradient approximations for both electrons and positrons within density functional theory. Such precision opens up opportunities in the quest for an improved density functional.
正电子素（Ps）原子对金属的亲和势(A_{Ps})是指当金属中的热化正电子与表面相遇时，发射到真空中的Ps的最大动能的负值。当通过基态Ps飞行时间（TOF）测量这个量时，精度会受到142纳秒的短三重态寿命的严重限制。通过将发射出的Ps原子快速转化为长寿命的里德堡态，我们能够显著增加飞行时间，从而实现对(A_{Ps})的精确测量。根据我们在(T = 128)K下对铜（110）样品的测量，我们发现(A_{Ps}(128)K() = (-2.476 ± 0.010_{统计} ± 0.013_{系统}))电子伏特，而在密度泛函理论中，使用高度精确的广义梯度近似计算电子和正电子得到的结果是(A_{Ps}(128)K() = (-2.545 ± 0.010_{数值} ± 0.010_{系统}))电子伏特。这样的精度为寻求改进的密度泛函提供了机会。
