Nicolò Barbero

Pressure and magnetic field effects on a quasi-two-dimensional spin- 1 2 Heisenberg antiferromagnet

Cu(pz)2(ClO4)2 (with pz denoting pyrazine, C4H4N2) is among the best realizations of a two-dimensional spin-1/2 square-lattice antiferromagnet. Below T_N = 4.21 K, its weak interlayer couplings induce a 3D magnetic order, strongly influenced by external magnetic fields and/or hydrostatic pressure. Previous work, focusing on the [H, T] phase diagram, identified a spin-flop transition, resulting in a field-tunable bicritical point. However, the influence of external pressure has not been investigated yet. Here we explore the extended [p, H, T] phase diagram of Cu(pz)2(ClO4)2 under pressures up to 12 kbar and magnetic fields up to 7.1 T, via magnetometry and 35Cl nuclear magnetic resonance (NMR) measurements. The application of magnetic fields enhances T_XY , the crossover temperature from the Heisenberg to the XY model, thus pointing to an enhancement of the effective anisotropy. The applied pressure has an opposite effect [dT_N/dp = 0.050(8) K/kbar], as it modifies marginally the interlayer couplings, but likely changes more significantly the orbital reorientation and the square-lattice deformation. This results in a remodeling of the effective Hamiltonian, whereby the field and pressure effects compensate each other. Finally, by comparing the experimental data with numerical simulations we estimate T_BKT, the temperature of the Berezinskii-Kosterlitz-Thouless topological transition and argue why it is inaccessible in our case.

Nodal-to-nodeless superconducting order parameter in LaFeAs 1−x P x O synthesized under high pressure

Similar to chemical doping, pressure produces and stabilizes new phases of known materials, whose properties may differ greatly from those of their standard counterparts. Here, by considering a series of LaFeAs1−xPxO iron-pnictides synthesized under high-pressure high-temperature conditions, we investigate the simultaneous effects of pressure and isoelectronic doping in the 1111 family. Results of numerous macroscopic and microscopic technique measurements unambiguously show a radically different phase diagram for the pressure-grown materials, characterized by the lack of magnetic order and the persistence of superconductivity across the whole 0.3 ≤ x ≤ 0.7 doping range. This unexpected scenario is accompanied by a branching in the electronic properties across x = 0.5, involving both the normal and superconducting phases. Most notably, the superconducting order parameter evolves from nodal (for x < 0.5) to nodeless (for x ≥ 0.5), in clear contrast to other 1111 and 122 iron-based materials grown under ambient-pressure conditions.Superconductivity: Putting the pressure on iron-based superconductorsExperiments show how iron-based superconductors synthesized under high pressure differ from those grown under ambient conditions. Iron-based superconductors are an exciting family of materials that exhibit unconventional superconductivity as well as a range of other exotic phases due to a complex interplay between magnetism and superconductivity. Oxypnictides are particularly puzzling members of this family as seemingly similar compounds can exhibit strikingly different electronic properties. By growing and measuring a range of oxypnictide compounds grown under different high-pressure, high-temperature conditions a team of researchers from Switzerland, led by Toni Shiroka from ETH Zürich, show that a close interplay between the magnetism and superconductivity is meditated by spin fluctuations. Furthermore, they show that the superconducting order parameter evolves in a way that is completely opposite to ambient-grown samples.

Microscopic investigation of the weakly correlated noncentrosymmetric superconductor SrAuSi3

SrAuSi

Doping-induced superconductivity of ZrB2 and HfB2

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Pressure and magnetic field effects on a quasi-two-dimensional spin-12Heisenberg antiferromagnet

is a noncentrosymmetric superconductor (NCS) with

Pressure and magnetic field effects on a quasi-2D spin-1/2 Heisenberg antiferromagnet

T_c

Anti-vibration Mounting System

= 1.54 K, which to date has been studied only via macroscopic techniques. By combining nuclear magnetic resonance (NMR) and muon-spin rotation (

Propagation of Thermal Energy

\mu

Fundamentals of X-Ray Diffraction and X-Ray Interferometry

SR) measurements we investigate both the normal and the superconducting phase of SrAuSi

Data Analysis and Interpolation with B-Splines

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