Magnetic-impurity-induced modifications to ultrafast carrier dynamics in the ferromagnetic topological insulators SbVTe

Sumida, Kazuki*; Kakoki, Masaaki*; Reimann, J.*; Nurmamat, M.*; Goto, Shinichi*; Takeda, Yukiharu   ; Saito, Yuji  ; Kokh, K. A.*; Tereshchenko, O. E.*; Gdde, J.*; Hfer, U.*; Kimura, Akio*

We systematically investigate the magnetic, structural and electronic properties and the ultrafast carrier dynamics in a series of V-doped SbTe samples of composition SbVTe with x = 0, 0.015 and 0.03. Element specific X-ray magnetic circular dichroism signifies that the ferromagnetism of V-doped SbTe is governed by the p-d hybridization between the host carrier and the magnetic dopant. Time- and angle-resolved photoemission spectroscopy has revealed that the V impurity induced states underlying the topological surface state (TSS) add scattering channels that significantly shorten the duration of transient surface electrons down to 100 fs scale. This is in a sharp contrast to the prolonged duration reported for pristine samples though the TSS is located inside the bulk energy gap of the host in either magnetic or non-magnetic cases. It implies the presence of a mobility gap in the bulk energy gap region of the host material.