We report an experimental study of the scaling of zero-bias conductance peaks compatible with Majorana zero modes as a function of magnetic field, tunnel coupling, and temperature in onedimensional structures fabricated from an epitaxial semiconductor-superconductor heterostructure. Results are consistent with theory, including a peak conductance that is proportional to tunnel coupling, saturates at 2e 2 /h, decreases as expected with field-dependent gap, and collapses onto a simple scaling function in the dimensionless ratio of temperature and tunnel coupling.Recent years have seen rapid progress in the study of Majorana zero modes (MZMs) in condensed matter. Following initial reports of zero-bias peaks (ZBPs) in conductance of nanowire-superconductor hybrids appearing at moderate magnetic fields [1], improvements in materials [2-4] resulted in harder induced gaps and the emergence of zero-bias peaks from coalescing Andreev bound states (ABSs) [5,6], as well as the observation of exponential suppression of Coulomb peak oscillations with nanowire length [7]. Recently, indications of MZMs were also identified in wires lithographically patterned on hybrid two-dimensional heterostructures [8,9]. In many respects, experimentally observed ZBPs are consistent with theoretical expectations for MZMs, but important questions remain, particularly concerning theoretical models that show ZBPs arising from nontopological ABSs in localized states at the wire ends [10,11]. Furthermore, the fact that observed zero-bias peaks [1,5,6,12] were considerably smaller than the theoretically expected value of 2e 2 /h [13-18] has raised concern. Speculations about the origin of this discrepancy included effects of dissipation [19] as well as nontopological ZBPs induced by disorder [20][21][22] or a spin-orbit-induced precursor [10].In this Letter, we investigate ZBPs in lithographically defined wires as a function of temperature, tunnel coupling to a metallic lead (parametrized by the normal state conductance G N ), and magnetic field. For weak coupling to the lead (G N e 2 /h), a small ZBP with strong temperature dependence is observed over an extended range of magnetic fields. For strong coupling (G N ∼ e 2 /h), the dependence of the ZBP on G N and temperature weakens, with a low-temperature saturation at ∼ 2e 2 /h. Experimental results are well described by a theoretical model of resonant transport through a zero-energy state that includes both broadening due to coupling to a normal lead and temperature.Fitting ZBP heights as a function of temperature, T , and G N yields values for the energy broadening, Γ, which we find obey the linear relationship Γ ∝ G N . The fit results for Γ are found to be in excellent agreement with a scaling function that depends only on the dimensionless ratio Γ/k B T . The observed magnetic field dependence of the ZBP is quantitatively consistent with a picture in which field reduces the induced superconducting gap, ∆ * , which in turn reduces the ZBP height through the dependence of Γ on ∆ * .Overall, the...

We report on the temperature dependence of microwave-induced resistance oscillations in high-mobility two-dimensional electron systems. We find that the oscillation amplitude decays exponentially with increasing temperature, as exp(-alphaT;{2}), where alpha scales with the inverse magnetic field. This observation indicates that the temperature dependence originates primarily from the modification of the single particle lifetime, which we attribute to electron-electron interaction effects.

We report on a giant negative magnetoresistance in very high mobility GaAs/AlGaAs heterostructures and quantum wells. The effect is the strongest at B ≃ 1 kG, where the magnetoresistivity develops a minimum emerging at T 2 K. Unlike the zero-field resistivity which saturates at T ≃ 2 K, the resistivity at this minimum continues to drop at an accelerated rate to much lower temperatures and becomes several times smaller than the zero-field resistivity. Unexpectedly, we also find that the effect is destroyed not only by increasing temperature but also by modest in-plane magnetic fields. The analysis shows that giant negative magnetoresistance cannot be explained by existing theories considering interaction-induced or disorder-induced corrections.

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We report the observation of a remarkably strong microwave photoresistivity effect in a high-mobility twodimensional electron system subject to a weak magnetic field and low temperature. The effect manifests itself as a giant microwave-induced resistivity peak which, in contrast to microwave-induced resistance oscillations, appears only near the second harmonic of the cyclotron resonance and only at sufficiently high microwave frequencies. Appearing in the regime linear in microwave intensity, the peak can be more than an order of magnitude stronger than the microwave-induced resistance oscillations and cannot be explained by existing theories.