arXiv subjects

Yogesh K. Vohra

Publications and source records attributed to Yogesh K. Vohra.

23 records · Page 2Linked to original sources

arXiv2012

High pressure transport studies of the LiFeAs analogues CuFeTe2 and Fe2As

We have synthesized two iron-pnictide/chalcogenide materials, CuFeTe2 and Fe2As, which share crystallographic features with known iron-based superconductors, and carried out high-pressure electrical resistivity measurements on these materials to pressures in excess of 30 GPa. Both compounds crystallize in the Cu2Sb-type crystal structure that is characteristic of LiFeAs (with CuFeTe2 exhibiting a disordered variant). At ambient pressure, CuFeTe2 is a semiconductor and has been suggested to exhibit a spin-density-wave transition, while Fe2As is a metallic antiferromagnet. The electrical resistivity of CuFeTe2, measured at 4 K, decreases by almost two orders of magnitude between ambient pressure and 2.4 GPa. At 34 GPa, the electrical resistivity decreases upon cooling the sample below 150 K, suggesting the proximity of the compound to a metal-insulator transition. Neither CuFeTe2 nor Fe2As superconduct above 1.1 K throughout the measured pressure range.

cond-mat.supr-con↗

arXiv2011

Structural Phase Transformations in Iron-Chalcogen under High Pressures

We report high pressure structural phase transformation sequence in a layered Iron-based superconducting compound FeSe0.3Te0.7 to 31 GPa at room temperature. The ambient pressure PbO type tetragonal phase (Space Group - P4/nmm) transforms to a monoclinic phase (Space group - P21/m) at a pressure of 7.3 \pm 0.9 GPa. This monoclinic phase is similar to the one observed below 100 K at ambient pressure. On further increase of pressure above 12 GPa, a transformation to an amorphous phase is observed that is completed by 20 GPa. The amorphous phase is found to be stable to the highest pressure of 31 GPa. This structural sequence of tetragonal \to monoclinic \to amorphous phase transformation appears to be a common feature of iron-based layered superconductors under compression. The pressure induced structural phase transformations are likely to play a key role in the superconductivity in these materials at high pressures.

cond-mat.mtrl-sci↗

arXiv2011

Structural and Magnetic Phase Transitions in NdCoAsO under High Pressures

We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare earth transition metal arsenide oxide NdCoAsO compound that is isostructural to high temperature superconductor NdFeAsO. Four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and anti-ferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained anti-ferromagnetic and non-superconducting to temperatures down to 10 K and to the highest pressure achieved in this experiment of 53 GPa. A P-T phase diagram for NdCoAsO is presented to a pressure of 53 GPa and low temperatures of 10 K.

cond-mat.supr-con↗

arXiv2011

Formation of Collapsed Tetragonal Phase in EuCo2As2 under High Pressure

The structural properties of EuCo2As2 have been studied up to 35 GPa, through the use of x-ray diffraction in a diamond anvil cell at a synchrotron source. At ambient conditions, EuCo2As2 (I4/mmm) has a tetragonal lattice structure with a bulk modulus of 48 +/-4 GPa. With the application of pressure, the a-axis exhibits negative compressibility with a concurrent sharp decrease in c-axis length. The anomalous compressibility of the a-axis continues until 4.7 GPa, at which point the structure undergoes a second-order phase transition to a collapsed tetragonal (CT) state with a bulk modulus of 111 +/- 2 GPa. We found a strong correlation between the ambient pressure volume of 122 parents of superconductors and the corresponding tetragonal to collapsed tetragonal phase transition pressures

cond-mat.mtrl-sci↗

arXiv2011

Search for pressure induced superconductivity in CeFeAsO and CeFePO iron pnictides

The CeFeAsO and CeFePO iron pnictide compounds were studied via electrical transport measurements under high-pressure. In CeFeAsO polycrystals, the magnetic phases involving the Fe and Ce ions coexist up to 15 GPa, with no signs of pressure-induced superconductivity up to 50 GPa. For the CeFePO single crystals, pressure stabilizes the Kondo screening of the Ce 4f-electron magnetic moments.

cond-mat.str-el↗