We analyze the evolution of the normal and superconducting electronic properties in epitaxial TiN films, characterized by high Ioffe-Regel parameter values, as a function of the film thickness. As the film thickness decreases, we observe an increase of the residual resistivity, which becomes dominated by diffusive surface scattering for d ≤ 20 nm. At the same time, a substantial thicknessdependent reduction of the superconducting critical temperature is observed compared to the bulk TiN value. In such a high quality material films, this effect can be explained by a weak magnetic disorder residing in the surface layer with a characteristic magnetic defect density of ∼ 10 12 cm −2 . Our results suggest that surface magnetic disorder is generally present in oxidized TiN films. arXiv:1903.05009v3 [cond-mat.mtrl-sci]

We experimentally investigate electron transport through the interface between a superconductor and the edge of a two-dimensional electron system with band inversion. The interface is realized as a tunnel NbN side contact to a narrow 8 nm HgTe quantum well. It demonstrates a typical Andreev behavior with finite conductance within the superconducting gap. Surprisingly, the conductance is modulated by a number of equally-spaced oscillations. The oscillations are present only within the superconducting gap and at lowest, below 1 K, temperatures. The oscillations disappear completely in magnetic fields, normal to the two-dimensional electron system plane. In contrast, the oscillations' period is only weakly affected by the highest, up to 14 T, in-plane oriented magnetic fields. We interpret this behavior as the interference oscillations in a helical one-dimensional edge channel due to a proximity with a superconductor. PACS numbers: 73.40.Qv 71.30.+h Recently, a strong interest appears to the investigations of electron transport through the interface between a superconductor (S) and a normal (N) semiconductorbased low-dimensional structure. Because of the Majorana problem 1 , this interest is mostly connected with different SNS type structures, where the N region is a one-dimensional quantum wire 2-7 or a topological surface state 8,9 .An attractive example of a one-dimensional topological surface state is a current-carrying helical edge channel, realized in a narrow HgTe quantum well 10 . This channel originates if the well thickness exceeds the critical 6.3 nm due to the inverted band structure in the bulk HgTe two-dimensional system [11][12][13][14] . In contrast to the conventional quantum Hall edge states 15 , this channel is helical, i.e. it consists of two spin-resolved counterpropagating states in zero magnetic field. Despite the initial idea of a topological protection 10,12-14 , backscattering appears at macroscopic distances 16,17 , possibly due to the allowed two-particle process 18 and to the electron puddles 19 . The edge current has been directly demonstrated in a visualization experiment 20 in zero magnetic field. Also, the supercurrents have been investigated for a two-terminal SNS Josephson junction, with a rectangular section of quantum well located between two superconducting leads 9 . So, a narrow HgTe quantum well is a promising candidate 21 for the search for a topological superconductivity 22,23 .On the other hand, even a single SN interface is predicted to demonstrate a number of intriguing effects, e.g. conductance oscillations due to a proximity effect 24,25 , giant spin rotation 26 , and localized edge states 27 . Pronounced Fabry-Perot oscillations have been demonstrated for a three-dimensional Bi 2 Se 3 topological insulator sandwiched between a superconducting and normal leads 28 . In this experiment, a proximity with a superconductor doubled the period of the oscillations, although they were present also for normal leads. Thus, it seems to be reasonable to investigate electron trans...

We consider the carrier transport and plasmonic phenomena in the lateral carbon nanotube (CNT) networks forming the device channel with asymmetric electrodes. One electrode is the Ohmic contact to the CNT network and the another contact is the Schottky contact. These structures can serve as detectors of the terahertz (THz) radiation. We develop the device model for response of the lateral CNT networks which comprise a mixture of randomly oriented semiconductor CNTs (s-CNTs) and quasi-metal CNTs ( m-CNTs). The proposed model includes the concept of the two-dimensional plasmons in relatively dense networks of randomly oriented CNTs (CNT "felt") and predicts the detector responsivity spectral characteristics. The detection mechanism is the rectification of the ac current due the nonlinearity of the Schottky contact current-voltage characteristics under the conditions of a strong enhancement of the potential drop at this contact associated with the plasmon excitation. We demonstrate that the excitation of the two-dimensional plasmons by incoming THz radiation the detector responsivity can induce sharp resonant peaks of the detector responsivity at the signal frequencies corresponding to the plasmonic resonances. The detector responsivity depends on the fractions of the s-and m-CNTs. The burning of the near-contact regions of the m-CNTs or destruction of these CNTs leads to a marked increase in the responsivity in agreement with our experimental data. The resonant THz detectors with sufficiently dense lateral CNT networks can compete and surpass other THz detectors using plasmonic effects at room temperatures.

Nonlocal quasiparticle transport in normal-superconductor-normal (NSN) hybrid structures probes sub-gap states in the proximity region and is especially attractive in the context of Majorana research. Conductance measurement provides only partial information about nonlocal response composed from both electron-like and hole-like quasiparticle excitations. In this work, we show how a nonlocal shot noise measurement delivers a missing puzzle piece in NSN InAs nanowire-based devices. We demonstrate that in a trivial superconducting phase quasiparticle response is practically charge-neutral, dominated by the heat transport component with a thermal conductance being on the order of conductance quantum. This is qualitatively explained by numerous Andreev reflections of a diffusing quasiparticle, that makes its charge completely uncertain. Consistently, strong fluctuations and sign reversal are observed in the sub-gap nonlocal conductance, including occasional Andreev rectification signals. Our results prove conductance and noise as complementary measurements to characterize quasiparticle transport in superconducting proximity devices.