THz spectroscopy in high magnetic field at mK temperatures
L. Peedu, J.Viirok, D. Hüvonen, U. Nagel, T. Rõõm
National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
Low temperatures are fascinating in physics because many substances undergo great change in their structural, thermal, electric and magnetic properties. Also the possibility to suppress thermal excitations, therefore simplifying the experimental result, has allured scientists long time. Low temperatures has influenced science greatly by revealing superconductivity, superfluidity, quantum interference and Bose-Einstein condensate.
In recent years the interest in spin correlations that are dominated by disorder near quantum critical points has got lot of attention because they are expected to be qualitatively different from unperturbed materials. Low temperature spectroscopy at THz frequencies in magnetic field gives the possibility to study quantum critical points in great details in ordered and disordered phases.
For investigating low temperature effects we have developed unique far-infrared magneto-optic setup with modified Oxford Instruments TLE200 dilution refrigerator cryostat. In this setup we use Oxford Instruments superconducting magnet and a Martin-Puplett type polarizing interferometer SPS200 from Scientech Inc. THz light is detected with Si bolometer cooled to 0.3 K with its own closed circuit 3He cryostat inside TLE200. The samples are attached to Attocube rotator and it is possible to measure three samples in one measurement. Dilution refrigerator cooling system is connected to the sample compartment by cold finger. The vacuum tight sample compartment with optical windows is filled with 4He gas at room temperature to provide the heat contact between the samples and the walls of the compartment. We can measure in frequency range 2.5 – 100 cm-1, sample temperature down to 120 mK and in magnetic field up to ±12 T.