I. V. Makarov

Temperature-dependent magnetospectroscopy of HgTe quantum wells

We report on magnetospectroscopy of HgTe quantum wells in magnetic fields up to 45 T in temperature range from 4.2 K up to 185 K. We observe intra- and inter-band transitions from zero-mode Landau levels, which split from the bottom conduction and upper valence subbands, and merge under the applied magnetic field. To describe experimental results, realistic temperature-dependent calculations of Landau levels have been performed. We show that although our samples are topological insulators at low temperatures only, the signature of such phase persists in optical transitions at high temperatures and high magnetic fields. Our results demonstrate that temperature-dependent magnetospectroscopy is a powerful tool to discriminate trivial and topological insulator phases in HgTe quantum wells.

Investigation of magnetoabsorption at different temperatures in HgTe/CdHgTe quantum-well heterostructures in pulsed magnetic fields

The magnetoabsorption in magnetic fields as high as 40 T is investigated at T > 77 K in HgTe/CdHgTe quantum-well heterostructures (dQW ≈ 8 nm). The spectra reveal two lines associated both with intraband transition from the lower Landau level in the conduction band and with interband transition. It is shown that the band structure in these systems changes from inverted to normal with increasing temperature.

Thermomagnetic instability of metal-insulator phase boundary

We consider diffusion of a magnetic field into a substance, which undergoes a metal-insulator phase transition under Joule heating. A development of a thermomagnetic instability of the interphase boundary is studied analytically and numerically. Solid solution (V/sub 1-x/Cr/sub x/)/sub 2/O/sub 3/ is taken as a model substance. In the non-linear stage the instability development shows a universal behavior that is independent on a shape of the initial disturbance.

A compact research facility for pulsed high magnetic fields of up to 50 T

A facility for generating pulsed magnetic fields with a millisecond duration and maximum peak values of 50 T is presented. The solenoid is produced from a Cu–Nb microcomposite conductor and is reinforced with a bandage made from Armos para-aramid fiber. The capacitor bank is switched to the high magnetic field solenoid by means of a solid-state switch board based on a module of reversely connected dynistors. Since the diameter of the working hole is 19.5 mm, it is possible to place a cryostat in it with operating temperatures as low as the helium temperatures and to measure the magnetization, the complex conductance, and the optical characteristics of substances in the visible and IR ranges. The operation features of the facility are discussed.

Diffusion of high magnetic field in (V1−xCrx)2O3

The penetration of a high magnetic field into a substance that undergoes a metal–insulator phase transition of the first order under Joule heating is discussed. This phenomenon can be used in high-current opening switches. (V1−xCrx)2O3 is taken as a model substance. An analytical treatment of stationary diffusion as well as a numerical analysis are presented. The development of thermomagnetic instabilities of the metal–insulator phase boundary is investigated. It is shown that a switching time of order of few microseconds can be achieved.

Instability development during motion of a metal-insulator phase boundary

Diffusion of a magnetic field into a conductor featuring a metal-insulator phase transition caused by Joule heating is theoretically studied. Development of a thermomagnetic instability at the metal-insulator interphase boundary moving in a fast wave regime is described in the linear stage depending on the wavenumber. Effect of the interphase boundary instability on the operation of a fast-speed electric current breaker based on a (V1−XCrX)2O3 solid solution is assessed.

Electrophysical properties of water and ice under isentropic compression to megabar pressures

The relative permittivity and specific conductivity of water and ice are measured under isentropic compression to pressures above 300 GPa. Compression is initiated by a pulse of an ultrahigh magnetic field generated by an MK-1 magnetocumulative generator. The sample is placed in a coaxial compression chamber with an initial volume of about 40 cm3. The complex relative permittivity was measured by a fast-response reflectometer at a frequency of about 50 MHz. At the compression of water, its relative permittivity increases to ε = 350 at a pressure of 8 GPa, then drops sharply to ε = 140, and further decreases smoothly. It is shown that measurements of the relative permittivity under isentropic compression make it possible to determine interfaces between ordered and disordered phases of water and ice, as well as to reveal features associated with a change in the activation energy of defects.

Solid solution (V/sub 1-x/Cr/sub x/)/sub 2/O/sub 3/ as a material for solid-state opening switches

Different technologies of (V/sub 1-x/Cr/sub x/)/sub 2/O/sub 3/ ceramic sample fabrication are discussed. It is shown that it is possible to make high-quality ceramic breaking elements up to several cm in volume. Temperature dependencies of conductivity and magnetoresistance of the ceramic samples are studied in the vicinity of the phase transition. A technology of contact fabrication on ceramic samples is investigated.

Theoretical and experimental investigation of high-current solid-state opening switch based on solid solution (V/sub 1-x/Cr/sub x/)/sub 2/O/sub 3/

A state of activities on development of a new high-current opening switch with solid solution (V/sub 1-x/Cr/sub x/)/sub 2/O/sub 3/ is reviewed. A non-linear diffusion of a magnetic field into a substance, that undergoes a metal-insulator phase transition, as well as a development of thermomagnetic instability at the interphase boundary are studied analytically and numerically. A design of a high-current opening switch based on this solid solution is presented. Fabrication and fastening of breaking element, made of (V/sub 1-x/Cr/sub x/)/sub 2/O/sub 3/, are discussed. The first experimental results on a full-scale model of high-current solid-state opening switch are presented.

Solid state opening switches of new type

Abstract We discuss two new types of high-current solid-state opening switches based on nonlinear diffusion of a strong magnetic field into a substance. In the first case, a magnetic field penetrates into solid solution (V1−xCrx)2O3, which undergoes a metal–insulator phase transition of the first order under Joule heating. In the second case, a switching of current occurs due to the Hall diffusion of magnetic field into n-InAs. Results of numerical analysis are presented.