O. S. Volkova

New functional materials AC3B4O12 (Review)

The physical properties of perovskites of the type AC3B4O12, whose structure derives from simple perovskites ABO3, are reviewed. The A position is subject to strong structural distortions and splits into two new positions A and C. In the structure of AC3B4O12 vacancies and any cations with a large radius, irrespective of their charge state, can be present in the icosahedral environment of A: Na+, Cd2+, Ca2+, Sr2+, Y3+, Ln3+, and Nd4+. The C position in the square environment of oxygen can be occupied only by the Jahn–Teller cations Cu2+ and Mn3+. Transition and nontransition metal ions—Mn3+, Fe3+, Al3+, Cr3+, Ti4+, Mn4+, Ge4+, Ru4+, Ir4+, Ta5+, Nb5+, Ta5+, Sb5+—can occupy the B position in an octahedral environment. Some members of the family of complex perovskites possess properties which are characteristic for systems with heavy fermions; collinear and noncollinear magnetic structures with high ordering temperatures occur in these materials; tunneling magnetoresistance and high permittivity are observed...

Quasiparticle Dynamics and Phonon Softening in FeSe Superconductors

Quasiparticle dynamics of FeSe single crystals revealed by dual-color transient reflectivity measurements (ΔR/R) provides unprecedented information on Fe-based superconductors. The amplitude of the fast component in ΔR/R clearly gives a competing scenario between spin fluctuations and superconductivity. Together with the transport measurements, the relaxation time analysis further exhibits anomalous changes at 90 and 230 K. The former manifests a structure phase transition as well as the associated phonon softening. The latter suggests a previously overlooked phase transition or crossover in FeSe. The electron-phonon coupling constant λ is found to be 0.16, identical to the value of theoretical calculations. Such a small λ demonstrates an unconventional origin of superconductivity in FeSe.

Superconducting properties of sulfur-doped iron selenide

The recent discovery of high-temperature superconductivity in single-layer iron selenide has generated significant experimental interest for optimizing the superconducting properties of iron-based superconductors through the lattice modification. For simulating the similar effect by changing the chemical composition due to S doping, we investigate the superconducting properties of high-quality single crystals of

Single crystal growth and characterization of tetragonal FeSe1−x superconductors

{\mathrm{FeSe}}_{1\ensuremath{-}x}{\mathrm{S}}_{x}

Multiple Andreev Reflections Spectroscopy of Two-Gap 1111- and 11 Fe-Based Superconductors

(

On the electronic origin of the inverse magnetocaloric effect in Ni?Co?Mn?In Heusler alloys

x=0

Nature of low-temperature phase transitions in CaMn7O12

, 0.04, 0.09, and 0.11) using magnetization, resistivity, the London penetration depth, and low temperature specific heat measurements. We show that the introduction of S to FeSe enhances the superconducting transition temperature

Magnetic and superconducting properties of FeSe1−xTex (x∼0, 0.5, and 1.0)

{T}_{c}

Magnetic properties of superconducting FeSe in the normal state

, anisotropy, upper critical field

On Fermi level pinning in lead telluride based alloys doped with mixed valence impurities

{H}_{c2}