Suggested New Correlated Phase in Mn-doped NbSe₂

We report on the growth, characterization, and measurements of quasi-2D NbSe₂ when doped with approx. 1% Mn. This relatively low alloying concentration is chosen so that some of the low temperature charge density wave (CDW) and BCS superconductivity properties are not significantly altered, while we examine the influence of the Mn spins on the electronic, optical, magnetic and other properties. XRD measurements show no major modifications to the base NbSe₂ structure. Compared to pure NbSe₂ samples, there are additional peaks in the differential conductance measurements, indicating measureable modification of the density of states due to the presence of the dilute amount of Mn ions. Infrared reflectivity data in the temperature range between superconducting temperature T_BCS (7.2 K or lower) and the Peierls transition of T_CDW (~33 K) show a number of interesting features that appear unique to the Mn-doped samples, in the far infrared range 3.0 to 12.0 meV, as well as some features in mid-infrared range. These peaks are sensitive to moderately high magnetic fields (up to 8 T). The phase diagram with respect to temperature and magnetic field is deduced from raw IR spectra to strongly suggest the presence of a novel correlated phase in the temperature range [10 K, 25 K]. This phase might be either spin density wave (SDW) or a mixed CDW-SDW phase. Our hypothesis is also tested by the X-ray diffraction scans at the DW peak in magnetic field in this temperature range. Lower thickness samples show stronger signal of this kind.