Investigation of spin fluctuations' evolution in newly available low-Tellurium-doped FeSe single crystals

Recently, we have grown low-tellurium-doped FeSe single crystals with concentration of Tellurium x ~ 0.15 and 0.33 successfully by the chemical vapor transport method. Our previous inelastic neutron scattering measurements have revealed strong spin fluctuations at the stripe and Néel wave vectors in FeSe, both of which are strongly coupled with nematicity. The nematic transition temperature in FeSe decreases with increasing tellurium concentration, and a nematic critical point is further proposed by transport measurements. Tc exhibits a highly unusual non-monotonic behaviour, reaching a local minimum of about 6 K at the critical tellurium concentration ~ 0.3 and displays two domes riding on the minum at x ~ 0.3. To understand these exotic phenomena, studying Fe(Te,Se) from FeSe side, i.e., with low tellurium dopant level is important. In this experiment, we propose to map out the spin fluctuation spectrum and its interplay with nematicity and superconductivity in FeSe0.67Te0.33 and FeSe0.85Te0.15. The success of the proposed experiment, combined with the previous results, will lead to a comprehensive understanding of the magnetic ground state and its relationship with nematicity and superconductivity in Fe(Te, Se) system and offer important indications on the roles of the stripe and the Néel spin fluctuations in iron chalcogenides.