Patricia Alireza

From Mott insulator to ferromagnetic metal: A pressure study of Ca2RuO4

We show that the pressure-temperature phase diagram of the Mott insulator Ca2RuO4 features a metal-insulator transition at 0.5 GPa: at 300 K from paramagnetic insulator to paramagnetic quasi-two-dimensional metal, and at Tless than or equal to12 K 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.

Susceptibility measurements at high pressures using a microcoil system in an anvil cell

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.

High-pressure diffraction studies on Ca2RuO4

We studied the crystal and magnetic structure of Ca{sub 2}RuO{sub 4} as function of pressure with different diffraction techniques. The first-order phase transition observed at a moderate pressure of P=0.5 GPa between the insulating 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 rotational angle of the RuO{sub 6}-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 5.5 GPa leading to a higher symmetry structure. The magnetism was studied by single-crystal neutron diffraction: The ferromagnetic component of the high-pressure phase and a rearrangement of antiferromagnetic order in the low-pressure phase have been observed.

Miniature anvil cell for high-pressure measurements in a commercial superconducting quantum interference device magnetometer

We describe a miniature diamond anvil cell that can be used in a commercial superconducting quantum interference device (SQUID) magnetometer to detect magnetic and superconducting transitions at applied pressures above 100 kbar. The cell is of simple design but constructed out of ultralow susceptibility materials that allow us to detect changes in the magnetic moment of the specimen at the full sensitivity of the SQUID magnetometer (typically 10(-7) emu). We present examples of the use of the cell to detect ferromagnetic, antiferromagnetic, and superconducting transitions at pressures and temperatures in the range of 0<or=P<or=100 kbar, 1.8 K<or=T<or=290 K, respectively.

Evidence of superconductivity on the border of quasi-2D ferromagnetism in Ca2RuO4 at high pressure

The layered perovskite Ca(2)RuO(4) is a spin-one Mott insulator at ambient pressure and exhibits metallic ferromagnetism at least up to ∼ 80 kbar with a maximum Curie temperature of 28 K. Above ∼ 90 and up to 140 kbar, the highest pressure reached, the resistivity and ac susceptibility show pronounced downturns below ∼ 0.4 K in applied magnetic fields of up to ∼ 10 mT. This indicates that our specimens of Ca(2)RuO(4) are weakly superconducting on the border of a quasi-2D ferromagnetic state.

Unconventional resistivity at the border of metallic antiferromagnetism in Ni S 2

We report low-temperature and high-pressure measurements of the electrical resistivity �(T ) of the antiferromagnetic compound NiS2 in its high-pressure metallic state. The form of �(T ) suggests that metallic antiferromagnetism in NiS2 is quenched at a critical pressure pc = 76 ± 5 kbar. Near pc the temperature variation of �(T ) is similar to that observed in NiS2 xSex near the critical com

Accessing the entire overdoped regime in pristine YBa2Cu3O6+x by application of pressure

We attain the previously unaccessed full superconducting dome in a pristine high temperature cuprate superconductor by applying pressures up to 280 kbar to samples of near stoichiometric YBa2Cu3O7. The obtained superconducting phase boundary as a function of hole doping closely follows the superconducting dome in La2-xSrxCuO4. Measurements are now enabled to trace the evolution of various entangled phases and the Fermi surface from the underdoped to overdoped regime in a single high purity cuprate superconducting family of materials.

Pressure-induced ferromagnetic metal for a Mott insulator Ca2RuO4

Abstract We show that application of very modest pressures to pure Ca 2 RuO 4 transforms it form an antiferromagnetic Mott insulator to a quasi-2D metal with a ferromagnetic ground state. The smallness of the moment compared with the saturated moment of the localized Ru 4+ ion reflects the itinerant character of the magnetism.

Nearly isotropic superconductivity in the layered Weyl semimetal WTe2 at 98.5 kbar

Layered transition metal dichalcogenide WTe

Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2.

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