arXiv subjects

Giulio I. Lampronti

Publications and source records attributed to Giulio I. Lampronti.

4 recordsLinked to original sources

arXiv2026

Emergent Polar Metal Phase in a Van der Waals Mott Magnet

We report the emergence of a two-dimensional (2D) polar metal phase in van der Waals compound FePSe$_3$ under moderate pressures. This layered material is a Mott insulator with antiferromagnetic order under ambient conditions. We show that FePSe$_3$ uniquely allows tuning a 2D correlated insulator into an exotic metal state where a loss of inversion symmetry leads to periodic polar displacements of ions, within a conducting phase - a polar metal. Our combined synchrotron and neutron diffraction data allow us to present a long-sought, unambiguous high-pressure structural model and show the polar displacements of this new phase. We also observe the suppression of magnetic ordering at the insulator-to-metal transition correspondent with this structural change. Our work outlines a comprehensive temperature-pressure phase diagram of FePSe$_3$, combining detailed structural, magnetic and transport data. The high-pressure phase exhibits activated semiconductor behavior at high temperatures, a $T^2$-dependence in its resistivity at lower temperatures - despite the conditions required for a `good metal' Fermi-Liquid description not being met in this case - and a low-temperature resistivity upturn which is suppressed as the system is tuned away from the concomitant transitions. The realisation of a tunable 2D polar metal state in FePSe$_3$ due to the loss of its inversion symmetry combined with pressure-induced metallicity offers a promising new platform to investigate this exotic phase at accessible pressures.

cond-mat.str-el↗

arXiv2026

Competing magnetic states in a non-coplanar Kagome magnet

Non-collinear Kagome antiferromagnets (AFMs) Mn3X (X = Sn, Ga, Ge, Ir, Pt) can generate an anomalous Hall effect (AHE) despite vanishing net magnetization, enabled by broken time-reversal and inversion symmetries. However, strong in-plane anisotropy has limited studies of the AFM-AHE and electronic applications to coplanar spin configurations. Non-coplanar spin textures in these systems have been realized only in low temperature spin-glass states or at interfaces with heavy metals. Here, we report an intrinsic non-coplanar spin configuration persisting up to 400 K in cubic-phase Mn3Ge, originating from coexisting symmetric and antisymmetric exchange interactions. Competing magnetic states associated with this non-coplanar spin configuration give rise to an unconventional AHE with a magnetic-field-induced sign reversal and a hump-like feature. Our findings establish a platform for non-coplanar magnetism in AFM spintronics.

cond-mat.mtrl-sci↗

arXiv2022

Comparative structural evolution under pressure of powder and single crystals of the layered antiferromagnet FePS$_3$

The layered antiferromagnet FePS$_3$ has been shown to undergo a structural transition under pressure linked to an insulator-metal transition, with two incompatible models previously proposed for the highest-pressure structure. We present a study of the high-pressure crystal structures of FePS$_3$ using both single-crystal and powder x-ray diffraction. We show that the highest pressure transition involves a collapse of the inter-planar spacing of this material, along with an increase in symmetry from a monoclinic to a trigonal structure, to the exclusion of other models. The extent of this volume collapse is shown to be sensitive to the presence of a helium pressure medium in the sample environment, indicating that consideration of such experimental factors is important for understanding high-pressure behaviours in this material.

cond-mat.str-el↗

arXiv2015

Unconventional superconductivity in the layered iron germanide YFe$_2$Ge$_2$

Since the discovery of superconductivity in LaFePO in 2006, numerous iron-based superconductors have been identified within diverse structure families, all of which combine iron with a group-V (pnictogen) or group-VI (chalco- gen) element. Unconventional superconductivity is extremely rare among transition metal compounds outside these layered iron systems and the cuprates, and it is almost universally associated with highly anisotropic electronic properties and nearly 2D Fermi surface geometries. The iron-based intermetallic YFe$_2$Ge$_2$ features a 3D Fermi surface and a strongly enhanced low temperature heat capacity, which signals strong electronic correlations. We present data from a new generation of high quality samples of YFe$_2$Ge$_2$, which show superconducting transition anomalies below 1.8 K in thermodynamic as well as transport measurements, establishing that superconductivity is intrinsic in this layered iron compound outside the known superconducting iron pnictide or chalcogenide families. The Fermi surface geometry of YFe$_2$Ge$_2$ resembles that of KFe$_2$As$_2$ in the high pressure collapsed tetragonal phase, in which superconductivity at temperatures as high as 10 K has recently been reported, suggesting an underlying connection between the two systems.

cond-mat.str-el↗