Optimizing composition of Pb(B i1-x S bx)2 T e4 topological insulator to achieve a bulk-insulating state

Abstract

A series of Pb(Bi1-xSbx)2Te4 topological-insulator crystals with various Sb molar ratios x was fabricated, and a systematic study of their transport properties was performed, aiming at realizing enhanced bulk insulation in this system. Hall-effect measurements showed that n- to p-type transition in bulk conduction occurred at x≈0.80. Semiconducting behavior with a negative temperature coefficient of resistivity was observed with resistivity values as high as 180 m cm at 2 K around the transition composition. The conduction mechanism in the semiconducting samples is discussed in relation to an impurity band formed within the bandgap.