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0EVOLUTION OF SURFACE CONDUCTIVITY IN SmB6 UNDER NONMAGNETIC (Yb2+) AND MAGNETIC (Eu2+) DOPING
Anisimov M.1' 2, Zhurkin V.1, Voronov V.1, Bogach A.1, Bozhko A.1, Demishev S.1' 2' 3, Shitsevalova N.4, Gabani S.5, Flachbart K.5, Glushkov V.1
1Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia,
E-mail: anisimov.m.a@gmail.com 2Vereshchagin Institute for High Pressure Physics of RAS, Troitsk, Russia 3National Research University 'Higher School of Economics', Moscow, Russia
4Frantsevich Institute for Problems of Materials Science NASU, Kyiv, Ukraine 5Institute of Experimental Physics SAS, Kosice, Slovakia
Among of rare-earth (RE) hexaborides only two compounds SmB6 and YbB6 are discussed in literature to be members of a new class of 3D topological insulators (TI) [1]. However, their ground states originate due to different physical mechanisms, including Kondo 4f-5d hybridization and 5d-2p band inversion, respectively. Current activity in SmB6 physics includes also the study of diluted systems.
Here we report a comparative research of magnetotransport (resistivity and transverse magnetoresistance) measured on high quality single crystals of YbxSm1-xB6 and EuxSm1-xB6 solid solutions (x < 0.05) at temperatures 1.7 - 300 K in magnetic fields up to 82 kOe. The choice of dopant was determined by the fact that the presence of magnetic/nonmagnetic (Eu2+/Yb2+) impurity in parent SmB6 matrix should lift/not lift the topological protection of surface states.
Based on the two-gap paradigm the x-evolution of electron spectra in YbxSm1-xB6 and EuxSm1-xB6 was studied. Our data show that both the 4f lattice coherence (Eg) and the intrinsic gap (Ea) related to many-body states (lower inset in Fig.1a) survive under RE doping at least for x ~ 0.02 - 0.024. We also suggest that the point x(Eu) = 0.05 can be treated as an upper limit of the small gap closing in EuxSm1-xB6 materials. In YbxSm1-xB6 family a negative linear transverse magnetoresistance (TMR) was detected for the first time in the regime of surface conductivity (T < T ~ 5 K). It was found, that the effect of surface treatment survives for diluted compounds regardless of the substitution with magnetic or nonmagnetic divalent impurity (Figs.1a-b). The TMR anomaly at T caused possibly by the topological protection of surface states in SmB6 is found to survive in Eu-doped compounds but disappears almost completely for Yb-doped compositions in the same fixed magnetic fields (upper insets in Figs.1a-b). This paradoxical observation is not consistent with general predictions of the topological Kondo insulator model.
This work was supported by the Russian Science Foundation №22-22-00990.
References
1. Dzero M., Sun K., Galitskii V., Coleman P. // Phys. Rev. Lett. - 2010. - V. 104. - P. 106408.
