Angle-resolved photoemission spectroscopy below 2 K

Angle-resolved photoemission spectroscopy (ARPES) is a technique that measures the energy and momentum of electrons in a material. It is a powerful tool for studying the electronic structure of solids and has been used to study a wide range of materials, from high-T_c superconductors to topological insulators. Particularly, direct measurements of the superconducting gap structure in high-T_c superconductors with ARPES have provided important insights into the nature of superconductivity. However, the base temperature of ARPES measurements is typically limited to around 10 K due to the high thermal load and the need for an ultrahigh vacuum (UHV) environment. This limits the ability to study materials that exhibit interesting properties that often manifest at lower temperatures, such as topological superconductivity.

Here, we present our latest developments on a custom-built ARPES system that allows for measurements at temperatures as low as 1.6 K with a kinetic energy resolution below 0.5 meV. A pulse tube refrigerator and a He-4 sorption cooler are used to cool down the cold head below 1 K. To maintain low thermal mass and high thermal conductivity, a 6-axis sample manipulator with piezoelectric actuators is used to position the sample in the chamber. We demonstrate the performance of the system by measuring the superconducting gap structure of an unconventional superconductor. Our results show that the system can resolve low-energy features of the electronic structure with unprecedented precision. This system opens new possibilities for studying the electronic structure of materials at low temperatures and will enable new insights into the physics of superconductors and other quantum materials.