Infrared spectroscopy simultaneously combined with strong magnetic field, high pressure, and low temperature

Establishing a measurement system for infrared spectroscopy experiments under the three synergetic extreme physical conditions—strong magnetic fields, high pressures, and low temperatures—is quite challenging. Here, we present an experimental setup for performing infrared spectroscopy measurements (in the photon energy range from 100 to 6000 cm−1) simultaneously at strong static magnetic fields (up to 22 T), high hydrostatic pressures (up to ∼20 GPa), and low temperatures (down to 2.0 K). In this setup, a diamond anvil cell (DAC) and a superconducting solenoid magnet are utilized to apply high hydrostatic pressures and strong static magnetic fields on a tiny sample. Moreover, a small-diameter optical parabolic cone compatible with the sample chamber of the superconducting solenoid magnet is employed to condense the infrared light on the tiny sample, which solves the difficulty in making the light flux through the tiny sample inside the restricted sample chamber high enough. In addition, a probe containing the optical parabolic cone, the sample, the DAC, and the bolometer detector is inserted into the liquid helium immersing the superconducting solenoid of the magnet not only to cool the sample by cold helium gas between the DAC and the probe shell but also to place the tiny sample at the magnetic-field center. We demonstrated the application of this setup in the infrared spectroscopy measurements of a topological insulator, ZrTe5, which reveals the pressure-induced redshift of the absorption features arising from the optical transitions of the magnetic-field-caused Landau levels at low temperatures.