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We investigate the properties of quasi-two-dimensional electron gas at the interface between ferroelectric oxide and insulating oxide in Ba0.8Sr0.2TiO3/LaMnO3 heterostructure after applying magneti...

It is demonstrated that the PT-symmetric terahertz photoconductivity observed in heterostructures based on thick Hg1 – xCdxTe films in the topological phase is due to the photoexcitation of charge carriers in the film bulk. At the same time, the place of localization of the effect is the topological film–trivial buffer layer heterointerface. The model describing such a spatial separation of the source of nonequilibrium charge carriers and the effect localization is discussed.

In this paper, we report on photoconductivity induced by high-power laser radiation with a frequency of 2 THz in Hg0.87Cd0.13Te-based epitaxial structures. Experimental results obtained for a set of the samples with variable geometric parameters allow us to determine the photoresponse features of both bulk and nonlocal contributions to the net response. We show that the persistent photoconductivity effect originates from the non-equilibrium processes related to the bulk carrier excitation.

A structural reason for superconductivity in a Cu-, Sr-, or Nb-atom-doped Bi2Se3 topological insulator is still unclear. To understand this reason, a codoping approach has been developed and BaySrxBi2Se3 single crystals with different x and y values have been grown. The composition and structural and transport properties of the grown crystals have been studied. With X-ray diffraction data, it has been shown that barium and strontium intercalate the system, although barium is present in the structure in a very small amount. The addition of barium surprisingly destroys superconductivity, slightly changing the lattice constants, the strontium doping level of the crystal matrix, and the electron density. Thus, a key role of a certain coordination arrangement of positions of strontium atoms between Bi2Se3 quintuples for achieving superconductivity in this material has been demonstrated.

Nematic superconductors are characterized by an apparent crystal symmetry breaking that results in the anisotropy of the in-plane upper critical magnetic field $H_{c2}$. The symmetry breaking is usually attributed to the strain of the crystal lattice. The nature and the value of the strain are debatable. We perform systematic measurements of the $H_{c2}$ anisotropy in the high-quality Sr$_x$Bi$_2$Se$_3$ single crystals in the temperature range 1.8~K$, Comment: 8 pages, 5 figures (including Supplemental Material). Accepted to PRB

We have shown that in heterostructures based on the topological phase Hg 1-x Cd x Te, the properties of two-dimensional topological states formed at the trivial buffer - topological film heterointerface differ from the states at the topological film - vacuum interface, and it is the former that are responsible for the appearance of PT-symmetric photoconductivity. It has been shown that the source of nonequilibrium electrons is the film bulk, while the place of manifestation of the effect is the trivial buffer - topological film heterointerface.

In this paper, we show that electron states formed in topological insulators at the interfaces topological phase–trivial phase and topological phase–vacuum may possess different properties. This is demonstrated on an example of heterostructures based on thick topological Hg1−xCdxTe films, in which the PT-symmetric terahertz photoconductivity is observed. It is shown that the effect originates from features of the interface topological film–trivial buffer/cap layer. The PT-symmetric terahertz photoconductivity is not provided by electron states formed at the interface topological film–vacuum.

We show that the terahertz (THz) photoconductivity in the topological phase of Hg1–xCdxTe-based structures exhibits the apparent PT- (parity-time) symmetry whereas the P-symmetry and the T-symmetry, separately, are not conserved. Moreover, it is demonstrated that the P- and T-symmetry breaking may not be related to any type of the sample anisotropy. This result contradicts the apparent symmetry arguments and means that there exists an external factor that interacts with the sample electronic system and breaks the symmetry. We show that deviations from the ideal experimental geometry may not be such a factor.

We show that the terahertz (THz) photoconductivity in the topological phase of Hg1–xCdxTe-based structures exhibits the apparent PT- (parity-time) symmetry whereas the P-symmetry and the T-symmetry, separately, are not conserved. Moreover, it is demonstrated that the P- and T-symmetry breaking may not be related to any type of the sample anisotropy. This result contradicts the apparent symmetry arguments and means that there exists an external factor that interacts with the sample electronic system and breaks the symmetry. We show that deviations from the ideal experimental geometry may not be such a factor.

We present results on non-local terahertz photoconductivity in Hg 1-x Cd x Te thick epitaxial films with the inverted energy spectrum $(\mathrm{x}\lt \sim 0.16)$. We show that the phototransport features observed in magnetic field indicate realization of the nonlocal electron transport regime, which is inherent to 2D topological insulators. We discuss the results in terms of a qualitative model that takes into account coexistence of the bulk transport and boundary conductive channels.

In this work, we demonstrate that the terahertz photoconductivity in Hg 1-x Cd x Te epitaxial films (x < 0.15) is featured by superimposed positive and negative components. The dramatic drop of the positive photoresponse as the sample thickness decreases indicates that the bulk-related processes crucially contribute to the non-equilibrium transport. At the same time, the features observed in magnetic field provide us with arguments for an edge transport channel formation. We discuss the sign-alternating photoconductivity kinetics in terms of a model that takes into account both the bulk electron excitation and the surface/interface state contribution.

We show that the terahertz photoconductivity in Hg 1-x Cd x Te-based films with the inversed band structure corresponding to the topological phase is asymmetric in magnetic field which may be considered as a T-symmetry breaking. Beside that, the photoconductivity is asymmetric for two mirror-symmetric pairs of potential probes which may be treated as a P- symmetry breaking. At the same time, the photoconductivity remains intact upon simultaneous swapping of both magnetic field and potential probe couple revealing thus the PT-symmetry.