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Codoping of Sb2Te3 thin films with V and Cr

DOI: 10.1103/PhysRevMaterials.1.064409 DOI Help

Authors: L. B. Duffy (Oxford) , A. I. Figueroa (Diamond Light Source) , G. Van Der Laan (Diamond Light Source) , T. Hesjedal (Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review Materials , VOL 1 , PAGES 064409

State: Published (Approved)
Published: November 2017
Diamond Proposal Number(s): 13759 , 15702

Abstract: Magnetically doped topological insulators (TIs) are key to realizing the quantum anomalous Hall (QAH) effect, with the prospect of enabling dissipationless electronic devices in the future. Doping of the well-established three-dimensional TIs of the (Bi,Sb)2(Se,Te)3 family with the transition metals Cr and V is now an established approach for observing the QAH state at very low temperatures. While the magnetic transition temperatures of these materials are on the order of tens of degrees Kelvin, full quantization of the QAH state is achieved below ∼100 mK, governed by the size of the magnetic gap and thus the out-of-plane magnetic moment. In an attempt to raise the size of the magnetic moment and transition temperature, we carried out a structural and magnetic investigation of codoped (V,Cr):Sb2Te3 thin films. Starting from singly doped Cr:Sb2Te3 films, free of secondary phases and with a transition temperature of ∼72 K, we introduced increasing fractions of V and found a doubling of the transition temperature, while the magnetic moment decreases. In order to separate the properties and contributions of the two transition metals in the complex doping scenario independently, we employed spectroscopic x-ray techniques. Surprisingly, already small amounts of V lead to the formation of the secondary phase Cr2Te3. No V was detectable in the Sb2Te3 matrix. Instead, it acts as a surfactant and can be found in the near-surface layers at the end of the growth. Our paper highlights the importance of x-ray-based studies for the doping of van der Waals systems, for which the optimization of magnetic moment or transition temperature alone is not necessarily a good strategy.

Journal Keywords: topological insulators, quantum anomalous Hall effect, XMCD, MBE

Subject Areas: Physics, Materials, Technique Development

Diamond Offline Facilities: Magnetic Spectroscopy Lab
Instruments: B18-Core EXAFS , I10-Beamline for Advanced Dichroism

Other Facilities: No