A. P. Orlov

Orbital quantization in a system of edge Dirac fermions in nanoperforated graphene

The dependence of the electric resistance R of nanoperforated graphene samples on the position of the Fermi level EF, which is varied by the gate voltage Vg, has been studied. Nanoperforation has been performed by irradiating graphene samples on a Si/SiO2 substrate by heavy (xenon) or light (helium) ions. A series of regular peaks have been revealed on the R(Vg) dependence at low temperatures in zero magnetic field. These peaks are attributed to the passage of EF through an equidistant set of levels formed by orbitally quantized states of edge Dirac fermions rotating around each nanohole. The results are in agreement with the theory of edge states for massless Dirac fermions.

Energy gap of a charge density wave in NbSe3 induced by a high magnetic field above the Peierls transition temperature

The effect of a magnetic field on the energy gap of the charge density wave (CDW) in NbSe3 near the temperature Tp2 of the lower Peierls transition has been investigated using interlayer tunneling spectroscopy. It has been shown that the magnetic field increases the energy gap and can even induce it at temperatures higher than Tp2 by 15–20 K. As the field strength increases, the peak amplitude of the gap singularity of the tunneling spectrum first increases, reaches its maximum at 20–30 T, and then decreases. The increase in the gap peak amplitude is attributed to the field-induced improvement of the condition of the CDW nesting, while the decrease in the amplitude in high fields, to the breakdown of the ground state caused by its Zeeman splitting.

Interaction of both charge density waves in NbSe3 from interlayer tunneling experiments

An interlayer tunneling technique has been used for spectroscopy of charge density wave (CDW) energy gaps (Δ1,2) in NbSe3 subsequently opened at the Fermi surface on decreasing temperature at Tp1 = 145 K (CDW1) and at Tp2 = 60 K (CDW2). We found that the CDW2 formation is accompanied by an increase of the CDW1 gap below Tp2. The maximum enhancement of Δ1, δΔ1 is about 10%. The effect observed has been predicted theoretically as resulting from the joint phase locking of both CDWs with the underlying crystalline lattice below Tp2.

Field-periodic magnetoresistance oscillations in thin graphite single crystals with columnar defects

The magnetoresistance of thin graphite single crystals with columnar defects has been studied. The field-periodic contribution to the magnetoresistance with a period of 7.5 T has been revealed. The atomic force microscope estimation of the columnar defect diameter shows that the period of the contribution oscillatory as a function of the flux is close to hc/e per defect. The result agrees with the measurements of Aharonov-Bohm magnetoresistance oscillations in graphene mesoscopic rings [S. Russo et al., Phys. Rev. B 77, 085413 (2008)].

Nonlinear interlayer transport in the aligned carbon nanotube films and graphite

Interlayer tunneling spectroscopy on graphite stacked junctions and on aligned carbon nanotube (ACN) films shows universal zero bias anomaly (dip) for both type of objects. For graphite this anomaly disappears above 30K while for aligned nanotube films that persists up to 350K. We consider this anomaly as a pseudogap that appears due to a presence of interlayer correlated state. In a presence of magnetic field of 1-10T oriented across the layers we found characteristic peaks on interlayer tunneling spectra of graphite mesas. Their voltage position and square root dependence on magnetic field let us to identify the origin of those peaks to be related with interlayer tunneling between Landau levels (LLs) in graphite typical for Dirac fermions in graphene.

Interlayer tunnelling spectroscopy of charge density waves

A brief review of recent results on interlayer tunnelling spectroscopy of layered charge density wave (CDW) materials is presented, demonstrating the high capability of this method for studies of this electron condensed state. We discuss some features observed in comparison with high temperature superconductors (HTS).

Charge density wave transport in NbSe3 at low temperatures under high magnetic field

Charge density wave (CDW) depinning and sliding regimes have been studied in NbSe3 at low temperatures down to 1.5 K under magnetic field of 19 T oriented along the c-axis. We found that the threshold field for CDW depinning becomes temperature independent below T0 ≈ 15 K. Also CDW current to frequency ratio characterizing CDW sliding regime increases by factor 1.7 below this temperature. The results are discussed as a crossover from thermal fluctuation to tunneling CDW depinning at T < T0. Besides, we found that CDW sliding strongly suppresses the amplitude of Shubnikov-de Haas oscillations of magnetoresistance.

Gossamer high-temperature bulk superconductivity in FeSe

The cuprates and iron-based high-temperature superconductors share many common features: layered strongly anisotropic crystal structure, strong electronic correlations, interplay between different types of electronic ordering, the intrinsic spatial inhomogeneity due to doping. The understanding of complex interplay between these factors is crucial for a directed search of new high-temperature superconductors. Here we show the appearance of inhomogeneous gossamer superconductivity in bulk FeSe compound at ambient pressure and at temperature 5 times higher than its zero-resistance

Shape memory effect in nanosized Ti2NiCu alloy-based composites

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The smallest and the fastest shape memory alloy actuator for micro- and nanorobotics

. This discovery helps to understand numerous remarkable superconducting properties of FeSe. We also find and prove a general property: if inhomogeneous superconductivity in a anisotropic conductor first appears in the form of isolated superconducting islands, it reduces electric resistivity anisotropically with maximal effect along the least conducting axis. This gives a simple and very general tool to detect inhomogeneous superconductivity in anisotropic compounds, which is critically important to study the onset of high-temperature superconductivity.