Borisenko Sergey V, Zabolotnyy Volodymyr B, Kordyuk Alexander A, Evtushinsky Danil V, Kim Timur K, Carleschi Emanuela, Doyle Bryan P, Fittipaldi Rosalba, Cuoco Mario, Vecchione Antonio, Berger Helmut
Institute for Solid State Research, IFW-Dresden.
J Vis Exp. 2012 Oct 9(68):50129. doi: 10.3791/50129.
The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (ω) and momentum (k) and the probability to find them in a particular state with given ω and k is described by the spectral function A(k, ω). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample. In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He(3) cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be determined with an unprecedented clarity.
材料的物理性质由其电子结构决定。固体中的电子具有能量（ω）和动量（k）的特征，在给定的ω和k下处于特定状态的电子出现的概率由谱函数A(k, ω)描述。这个函数可以在基于著名的光电效应的实验中直接测量，阿尔伯特·爱因斯坦正是因其对光电效应的解释在1921年获得了诺贝尔奖。在光电效应中，照射在表面的光会使材料中的电子逸出。根据爱因斯坦的理论，只要已知光子能量和出射光电子的动能，能量守恒就能确定样品内部电子的能量。动量守恒还使得通过测量光电子离开表面的角度来估计与光电子动量相关的k成为可能。这种技术的现代版本称为角分辨光电子能谱（ARPES），它利用这两个守恒定律来确定电子结构，即固体内部电子的能量和动量。为了解析对于理解凝聚态物理热点问题至关重要的细节，需要将三个量最小化：光子能量的不确定性、光电子动能的不确定性以及样品的温度。在我们的方法中，我们结合了同步辐射、表面科学和低温学领域的三项最新成果。我们使用具有可调光子能量的同步辐射，其不确定性约为1毫电子伏特；使用电子能量分析仪，其检测动能的精度约为1毫电子伏特；使用He(3)低温恒温器，它能使我们将样品温度保持在1 K以下。我们讨论了在Sr2RuO4单晶和其他一些材料上获得的示例性结果。这种材料的电子结构能够以前所未有的清晰度被确定。
