A Room-Temperature Verwey-type Transition in Iron Oxide, Fe O.

Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in next-generation nanoelectronic devices. To date, vanadium dioxide (VO ) is the only known simple transition-metal oxide that demonstrates a near-room-temperature metal-insulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixed-valent iron oxide with an unconventional Fe O stoichiometry.

Pressure-induced Lifshitz and structural transitions in NbAs and TaAs: experiments and theory.

High pressure Raman, resistivity and synchrotron x-ray diffraction studies on Weyl semimetals NbAs and TaAs have been carried out along with density functional theoretical (DFT) analysis to explain pressure induced structural and electronic topological phase transitions. The frequencies of first order Raman modes harden with increasing pressure, exhibiting a slope change at [Formula: see text] GPa for NbAs and [Formula: see text] GPa for TaAs. The resistivities of NbAs and TaAs exhibit a minimum at pressures close to these transition pressures and also a change in the bulk modulus is observed.

Topological Quantum Phase Transition and Superconductivity Induced by Pressure in the Bismuth Tellurohalide BiTeI.

A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor bismuth tellurohalide BiTeI with giant Rashba spin splitting. In this work, evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted topological quantum phase transition in BiTeI.

More Than 50 Years after Its Discovery in SiO Octahedral Coordination Has Also Been Established in SiS at High Pressure.

SiO exhibits a high-pressure-high-temperature polymorphism, leading to an increase in silicon coordination number and density. However, for the related compound SiS such pressure-induced behavior has not been observed with tetrahedral coordination yet. All four crystal structures of SiS known so far contain silicon with tetrahedral coordination.

Superconductivity in Weyl semimetal candidate MoTe2.

Transition metal dichalcogenides have attracted research interest over the last few decades due to their interesting structural chemistry, unusual electronic properties, rich intercalation chemistry and wide spectrum of potential applications. Despite the fact that the majority of related research focuses on semiconducting transition-metal dichalcogenides (for example, MoS2), recently discovered unexpected properties of WTe2 are provoking strong interest in semimetallic transition metal dichalcogenides featuring large magnetoresistance, pressure-driven superconductivity and Weyl semimetal states. We investigate the sister compound of WTe2, MoTe2, predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively.

Ammonia as a case study for the spontaneous ionization of a simple hydrogen-bonded compound.

Modern ab initio calculations predict ionic and superionic states in highly compressed water and ammonia. The prediction apparently contradicts state-of-the-art experimentally established phase diagrams overwhelmingly dominated by molecular phases. Here we present experimental evidence that the threshold pressure of ~120 GPa induces in molecular ammonia the process of autoionization to yet experimentally unknown ionic compound--ammonium amide.

Quantum critical point and spin fluctuations in lower-mantle ferropericlase.

Ferropericlase [(Mg,Fe)O] is one of the most abundant minerals of the earth's lower mantle. The high-spin (HS) to low-spin (LS) transition in the Fe(2+) ions may dramatically alter the physical and chemical properties of (Mg,Fe)O in the deep mantle. To understand the effects of compression on the ground electronic state of iron, electronic and magnetic states of Fe(2+) in (Mg0.