Temperature dependence of Raman-active optical phonons in Bi2Se3 and Sb2Te3

Abstract

Inelastic light scattering spectra of Bi2Se3 and Sb2Te3 single crystals have been measured over the temperature range from 5 K to 300 K. The temperature dependence of dominant A 2 1g phonons shows similar behavior in both materials. The temperature dependence of the peak position and linewidth is analyzed considering the anharmonic decay of optical phonons and the material thermal expansion. This work suggests that Raman spectroscopy can be used for thermometry in Bi2Se3-and Sb2Te3-based devices in a wide temperature range.Recently, much attention has been paid to the study of Bi 2 Se 3 , Sb 2 Te 3 and other layered stoichiometric compounds, as a promising playground for the realization of a new class of quantum matter, topological insulators [1]. A topological insulator has a "conventional" energy gap in the bulk and gapless Dirac-like states on the surface, which are protected against any time-invariant perturbations such as crystal imperfections [2][3][4]. These topologically protected surface states hold great promise for a broad range of potential applications, including field effect transistors [5][6][7], infrared-THz detectors [8,9], and magnetic field sensors [10,11]. It is essential to understand the dynamics of phonons in these materials, particularly the phonon-phonon and electron-phonon interactions, in order to achieve the best device performance. While the room-temperature Raman characterizations of optical phonons in Bi 2 Se 3 and Sb 2 Te 3 have been well documented in the literature [12,13], accurate measurements of the temperature dependence are still lacking. In this Letter, we present a Raman spectroscopy study of Bi 2 Se 3 and Sb 2 Te 3 crystals in the temperature range between 5 K and 300 K. We uncover a characteristic temperature dependence of the phonon peak position and linewidth, and interpret it in the context of thermal expansion and three-phonon anharmonic decay. The observed linear dependence in the elevated temperature range (80-300 K) allows for applications using Raman spectroscopy as thermometry in Bi 2 Se 3 -and Sb 2 Te 3 -based devices.The Bi 2 Se 3 and Sb 2 Te 3 single crystals studied in this work were synthesized at the University of California -Riverside, Purdue University, and the Sandia National Laboratories. Electronic transport characterization revealed that the as-grown crystals were naturally doped, with bulk carrier density in the range of 10 18 -10 19 cm −3 . The typical onset magnetic field for observing

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

“…These modes transform as 2 + 2 1 + 2 + 2 1 , where 2 + 2 1 and 2 + 2 1 are, respectively, Raman and infrared-active representations [19]. We note that the bulk optical phonons of Bi2Se3 and Bi2Te3 have been previously measured using Raman [20,26,27,28] and neutron scattering [29], and infrared spectroscopy [19,20,30], Figure 1 shows Raman spectra of Bi2Se3 and Bi2Te3 at various temperatures in the ( ) ̅ ( + ) scattering configuration; note the logarithmic scale. Consistent with previous reports [20,27], the bulk Raman-active modes at 10 K are at 38.5 cm -1 ( 1 ), 75.5 cm -1 ( 1 1 ), 135.8 cm -1…”

Lifetime of the phonons in the PLT ceramic

“…While it provides a fairly accurate description of the phonon temperature dependence in diamond,more general models have been suggested for other materials accounting for anharmonic contributions due to the thermal expansion and/or asymmetric decay into two or more different phonons [16]. We uncover a characteristic temperature dependence of the phonon peak position and linewidth and interpret it in the context of thermal expansion and three-phonon anharmonic decay.…”

Understanding the evolution of anomalous anharmonicity in Bi2Te3−xSex

“…The "coalescence" process where two phonons fuse into a third is neglected, because it requires thermal populations of the second phonon which are very small at low temperatures 24 . As found in many low anharmonicity materials, the model works well for describing the lifetime 15 . In the supplemental material a detailed analysis of the lifetime of all phonons modes is provided, where we generally find an increase in A as the energy of the mode is increased.…”

“…Typically, in a non-magnetic insulating material, the temperature dependence of a phonon energy comes from two primary sources 15 ,…”

“…While there have been some studies of Bi 2 Te 3−x Se x using Raman spectroscopy 14,15 , these either were limited to fewer phonon modes or samples were measured just at room temperature. A high temperature and spectral resolution study across the series is still lacking.…”