Electron Spin resonance of Gd³⁺in three dimensional topological insulator Bi₂Se₃

Abstract

Abstract. Bi2Se3 has been claimed to be a three dimensional topological insulator (TI) with topologically protected metallic surface states with exotic properties. We have performed electron spin resonance (ESR) measurements on Gd 3+ doped (x ≈ 0.01) Bi2Se3 single crystal grown from stoichiometric melt. For the studied crystals, our preliminary results revealed a partly resolved Gd 3+ fine structure spectrum with Dysonian (metallic character) lines. At room temperature, the central line has a g ≈ 1.98, a linewidth ∆H ≈ 95 G and the spectra have a overall splitting of roughly 1300 Oe. As the temperature is decreased, the Gd 3+ ESR ∆H of the central line presents a very small Korringa-like behavior b = ∆H/∆T ≈ 0.013 Oe/K and nearly T -independent g-value. However, for T 40 K, ∆H shows a stronger narrowing effect evolving to Korringa-like behavior (b ≈ 0.15 Oe/K) for T 30 K. Concomitantly with the change in ∆H behavior, the Gd 3+ central line g value starts to decrease reaching a value of 1.976 at T = 4.2 K. The ESR results are discussed in terms of possible effects of protected topological surface states enlightened by complementary data from macroscopic measurements. IntroductionTopological insulators are a type of condensed matter materials where a bulk insulator is coated by topologically protected metallic surface states which are robust to disorder [1]. These surface states have exotic properties which are claimed to be of interest to spintronics development. Usually, surface sensitive spectroscopic techniques such as ARPES (angle resolved photoemission spectroscopy) and STM (scanning tunneling microscopy) are used to probe this type of materials. However, to our knowledge, these materials were not studied by Electron Spin Resonance (ESR), which is a spectroscopic technique that can yield local information about the conduction electrons. Also, it is suggested that a periodic perturbation can affect the band topology [2,3], such as microwave radiation in the ESR experiment. In this work, we have performed ESR measurements on Gd 3+ doped Bi 2 Se 3 single crystals. Our results indicate a non-trivial evolution of Gd 3+ spectra at low-T (below 40 K) that we attempt to correlate to the presence the topological metallic surface states. Furthermore, our Gd 3+ ESR data suggest that the studied samples show coexistence of both insulator and metallic behavior inside the microwave skin depth.

Comprehensive Insight into p-Type Bi2Te3-Based Thermoelectrics near Room Temperature

“…Positron annihilation spectroscopy can provide unique information in the characterization of vacancies and vacancies attached defects ( e . g ., dislocations, misfit defects, and interfaces). , In the case of Bi 2 Te 3 -based alloys doped with transition metals or rare-earth elements, electron spin resonance can explore localized spins and reveal the intensity of electron–phonon coupling, which is important for evaluating TE properties. , The local structure information can be observed via extended X-ray-absorption fine-structure spectra, such as the interatomic distance, the locations of impurity sites, the locational fluctuations around impurity atoms, and the lattice distortions. − In turn, the crystallographic structure in detail can provide basic information for first-principles calculations to quantify research on TE properties.…”

Spin dynamics of 3d and 4d impurities embedded in prototypical topological insulators

“…Moreover, the electron spin resonance of single Gd ions embedded in Bi 2 Se 3 was examined in Ref. 33. The temperature dependence of the g-factor was investigated and the coexistence of a metallic and an insulating phase (dual character) was reported.…”