Composition Dependence of the Energy Gap in HgFeSe - Optical Verification

Abstract

Infrared reflectivity was investigated for the mixed Hg 1-xFexSe crystals for x < 0.1. The theoretical analysis of the experimental curves suggests opening of the energy gap for the composition x = 0.087 at the temperature close to 80 K.PACS numbers: 71.25. Tn, 78.30.Fs The purpose of the present work was to study the infrared optical properties of Hg1-xFexSe mixed crystal in order to determine the composition dependence of the energy gap in this material.It is believed that the absolute value of the negative energy gap for Hg1-xFexSe decreases with increasing Fe content and at low temperatures is equal to zero for the mixed crystal composition corresponding to about 15% of Fe. This value was given in some recent papers analysing the results of the optical measurements performed at temperatures above 100 K [1] and the helium temperature quantum oscillations observed for the magnetoplasma waves [2].In this paper we analysed the infrared reflectivity spectra taken with the use of the Buker FTIR 113v spectrometer. The measurements were performed on different Hg1-xFexSe mixed crystals in a wide temperature range (4.5 K ≤ T ≤ 295 K). The crystals were obtained by the Bridgman method in the Institute of Physics, Polish Academy of Sciences in Warsaw, the sample composition (0 ≤ x ≤ 0.1) was determined by the energy dispersive X-ray fluorescence analysis.The Hall measurements at various temperatures have also been performed for the most of crystals .The Fe level energy at 4.2 K increases with the Fe concentration. This effect in the high-doping range (x < 0.01) suggested in [2] is two times stronger than that given in [3]. Morever, according to [2] the important nonlinear effect in such (757)