Investigation of the Gapless State in Bismuth-Antimony Alloys

The results are presented from an experimental study of the gapless state produced in semiconducting alloys Bi1-xSbx by pressure-induced band inversion. The magnetoresistance properties of the alloys have been investigated both in weak magnetic fields (mu H <= 1) and in strong fields (H=75 kOe) at liquidhelium temperatures in the Sb concentration interval 0.06=x=0.15 and pressure interval 1 bar =p<20 kbar. At pressuresp close to the pressurep k at which the gapless state is realized a semiconductor-semimetal-semiconductor transition is detected inBi 1-x Sb x alloys withx=0.070 and 0.071. The rates of change of the gap e gL before and after inversion are determined: -(2.5 0.5) x 10-6 eV/bar and (1.5 0.5) x10-6 eV/bar, respectively. A reduction in the carrier effective mass as e gL -> 0 is observed down to values of 10(-4) m 0. It is shown that as e gL -> 0 the carrier mobilities in the alloys increase abruptly, the effect being a maximum in the purest alloys, where forT=4.2 K the mobility along the binary axis attains the record-high value of 3 x 0(8) cm2/V sec.