We report the discovery of superconductivity at high pressure in SrFe(2)As(2) and BaFe(2)As(2). The superconducting transition temperatures are up to 27 K in SrFe(2)As(2) and 29 K in BaFe(2)As(2), the highest obtained for materials with pressure-induced superconductivity thus far.

We show that the quasi-skutterudite superconductor Sr(3)Ir(4)Sn(13) undergoes a structural transition from a simple cubic parent structure, the I phase, to a superlattice variant, the I' phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature T(*) can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.

We show that the pressure-temperature phase diagram of the Mott insulator Ca2RuO4 features a metal-insulator transition at 0.5GPa: at 300K from paramagnetic insulator to paramagnetic quasi-two-dimensional metal; at T ≤ 12K from antiferromagnetic insulator to ferromagnetic, highly anisotropic, three-dimensional metal. We compare the metallic state to that of the structurally related p-wave superconductor Sr2RuO4, and discuss the importance of structural distortions, which are expected to couple strongly to pressure. PACS numbers: 71.30+h, 75.30Kz, 74.70Pq, and 74.62Fj

We studied the crystal and magnetic structure of Ca2RuO4 by different diffraction techniques under high pressure. The observed first order phase transition at moderate pressure (0.5 GPa) between the insulating phase and the metallic high pressure phase is characterized by a broad region of phase coexistence. The following structural changes are observed as function of pressure: a) a discontinuous change of both the tilt and rotation angle of the RuO6-Octahedra at this transition, b) a gradual decrease of the tilt angle in the high pressure phase (p>0.5 GPa) and c) the disappearance of the tilt above 5.5GPa leading to a higher symmetry structure. By single crystal neutron diffraction at low temperature, the ferromagnetic component of the high pressure phase and a rearrangement of antiferromagnetic order in the low pressure phase was observed.

We present the observation of an isostructural Mott insulator-metal transition in van-der-Waals honeycomb antiferromagnet V0.9PS3 through high-pressure x-ray diffraction and transport measurements. The MPX3 family of magnetic van-der-Waals materials (M denotes a first row transition metal and X either S or Se) are currently the subject of broad and intense attention, but the vanadium compounds have until this point not been studied beyond their basic properties. We observe insulating variable-range-hopping type resistivity in V0.9PS3, with a gradual increase in effective dimensionality with increasing pressure, followed by a transition to a metallic resistivity temperature dependence between 112 and 124 kbar. The metallic state additionally shows a low-temperature upturn we tentatively attribute to the Kondo Effect. A gradual structural distortion is seen between 26-80 kbar, but no structural change at higher pressures corresponding to the insulator-metal transition. We conclude that the insulator-metal transition occurs in the absence of any distortions to the lattice -an isostructural Mott transition in a new class of two-dimensional material, and in strong contrast to the behavior of the other MPX3 compounds. arXiv:1903.10971v1 [cond-mat.str-el]

Dimensionality is crucial in determining or controlling the magnetic, electronic and structural properties of condensed matter systems. The case of 2D and of graphene is of course a very topical example. The pairing mechanisms of unconventional superconductors such as high-temperature superconductors and FeSe are often seen to be strengthened in 2D. Additionally, new magnetic phases and structures can be found in thin films or layers of otherwise simplistic materials. Crystals with layered structures of atomic planes separated by van-der-Waals gaps form an ideal case for studying a wide

While the highest pressures can be achieved with diamond anvil cells, limited sample size and anvil geometry have hampered their application in nuclear magnetic resonance (NMR) experiments due to weak signal-to-noise. Here we report a new probe design that is based on having the resonant radio frequency coil that encloses the sample within the anvil cell inside the gasket hole. This increases the filling factor tremendously and results in greatly enhanced NMR sensitivity. The setup is described together with room temperature Na and Al NMR experiments.

We present here a microcoil setup for susceptibility measurements in anvil cells. In contrast to previous designs, we have placed the secondary coil inside the high pressure volume. This dramatically boosts the signal and eliminates the need for complex background subtraction. For samples of lead, tin, and the metal–insulator oxide calcium ruthenate (Ca2RuO4), our procedure has produced very clear signals for both superconducting transitions and ferromagnetic ordering with a weak magnetic moment (0.2 μB/Ru), up to 75 kbar, with a signal-to-noise ratio of ∼80.