Detection of highly conductive surface electron states in topological crystalline insulators Pb1−xSnxSe using laser terahertz radiation

We suggest a method for detection of highly conductive surface electron states including topological ones. The method is based on measurements of the photoelectromagnetic effect using terahertz laser pulses. In contrast to conventional transport measurements, the method is not sensitive to the bulk conductivity. The method is demonstrated on an example of topological crystalline insulators Pb1−xSnxSe. It is shown that highly conductive surface electron states are present in Pb1−xSnxSe both in the inverse and direct electron energy spectrum

Observation of local electron states linked to the quasi-Fermi level

We report on the observation of semiconductor local electron states linked to the quasi-Fermi level and, consequently, not characterized by the defined position in the energy spectrum which is familiar for shallow and deep impurities. This type of local electron states have been found in the doped narrow-gap semiconductor Pb1−xSnxTe(In). The binding energy of these states is less than 10 meV providing photoresponse at the wavelengths exceeding 100 μm

Magnetic-field-induced terahertz photogeneration in PbTe(Ga)

It has been shown that a magnetic field in PbTe(Ga) single crystals induces the appearance of a positive photoresponse in the terahertz spectral range. Nonequilibrium charge carriers are generated from states located against the background of the continuum of the conduction band near the quasi-Fermi level. The density of states on the quasi- Fermi level is a critical parameter responsible for the process of generation

Manifestation of topological surface electron states in the photoelectromagnetic effect induced by terahertz laser radiation

We demonstrate that measurements of the photoelectromagnetic effect using terahertz laser radiation may provide a unique opportunity to discriminate between the topological surface states and other highly conductive surface electron states. We performed a case study of mixed (Bi1-xInx)(2)Se-3 crystals undergoing a topological phase transformation due to the transition from the inverse to the direct electron energy spectrum in the crystal bulk at variation of the composition. x. We show that for the topological insulator phase, the photoelectromagnetic effect amplitude is defined by the number of incident radiation quanta, whereas for the trivial insulator phase, it depends on the power in a laser pulse irrespective of its wavelength. We assume that such behavior is attributed to a strong damping of the electron-electron interaction in the topological insulator phase compared to the trivial insulator

Photoconductivity of PbTe:In films with variable microstructure

It is shown that the microstructure and features of formation of surface states in nanocrystalline and polycrystalline PbTe:In films most significantly affect the character of photoconductivity in the spectral range of 1–2.5 THz. We present the results of a study and comparative analysis of the character of conductivity of PbTe:In films in the temperature range from 4.2 to 300 K in a static mode and in variable electric fields with a frequency of up to 1 MHz with illumination with white light and under the effect of high-power terahertz laser pulses with a wavelength of up to 280 μm