Disorder suppression and precise conductance quantization in constrictions of PbTe quantum wells

Abstract

Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,12 nm wide quantum wells deposited between Pb0.92Eu0.08Te barriers. Because the quantum confinement imposed by the barriers is much stronger than the lateral one, the one-dimensional electron energy level structure is very similar to that usually met in constrictions of AlGaAs/GaAs heterostructures. However, in contrast to any other system studied so far, we observe precise conductance quantization in 2e 2 /h units, despite of significant amount of charged defects in the vicinity of the constriction. We show that such extraordinary results is a consequence of the paraelectric properties of PbTe, namely, the suppression of long-range tails of the Coulomb potentials due to the huge dielectric constant.

Ballistic Transport Phenomena in Nanostructures of Paraelectric Lead Telluride

“…All these findings prove the efficiency of the dielectric screening of the Coulomb potentials caused by various defects existing in the vicinity of the conducting channel. This conclusion has been supported by the model calculations [12]. It is also worth noting here that we have not observed the "0.7" feature at the lowest conductance plateau [27], most probably due to the effective screening of the electron-electron interaction in PbTe.…”

“…In fact, detailed studies of the single constriction geometry have shown that the step heights correspond to the quantized values within an accuracy of a few percent. This means that the electron transmission is close to 1, even at zero magnetic field [12]. A further evidence of weak disorder in PbTe constrictions has been found by conductance measurements in a millikelvin temperature range.…”

“…For this reason, observations of the conductance quantization can be used as a tool for detecting potential fluctuations in the host medium. Accordingly, we have demonstrated [9][10][11][12][13][14][15] that in PbTe nanostructures the amplitude of potential fluctuations is strongly suppressed, even in the presence of a significant concentration of charged impurities in the close vicinity of the device. This is concluded from the pronounced 1D quantization in a modulation doped PbTe wires, indicating a rather small backscattering, despite only a few nm separation of the conducting channel from the heavily doped layer.…”

Absence of nonlocal resistance in microstructures of PbTe quantum wells

“…Previously it had been shown [35][36][37] that quantum Hall effect can be observed in such molecular beam epitaxy grown PbEuTe/PbTe/PbEuTe structures, i.e., edge channel transport was demonstrated for applied magnetic fields. Furthermore, in narrow constrictions fabricated from such/PbTequantum wells embedded in PbEuTe barriers our group has reported precise zerofield conductance quantization in units of 2e 2 =h [38,39]. We demonstrate that electron transport measurements on H-shaped microstructures do not show any nonlocal resistance in this case.…”

“…Because of the [111] growth direction, the fourfold L-valley degeneracy of the conduction band in PbTe QW is lifted by the quantum confinement, so that the ground-state two-dimensional (2D) subband is formed of the single valley with its main axis parallel to the growth direction [38]. The lowest states formed by the three remaining valleys obliquely oriented to the growth directions, have a higher energy of 35 meV above the ground state for this QW thickness.…”