NUM division - Publication Highlights

The origin of the metal-to-insulator transition (MIT) in RNiO₃ perovskites with R = trivalent 4f ion has challenged the condensed matter research community for almost three decades. A drawback for progress in this direction has been the lack of studies combining physical properties and accurate structural data covering the full nickelate phase diagram. Here we focus on a small region close to the itinerant limit (R = Pr, 1.5K < T < 300K), where we investigate the gap opening and the simultaneous emergence of charge order in PrNiO₃.

Artificial spin ices consist of nanomagnets arranged on the sites of various periodic and aperiodic lattices. They have enabled the experimental investigation of a variety of fascinating phenomena such as frustration, emergent magnetic monopoles and phase transitions that have previously been the domain of bulk spin crystals and theory, as we discuss in this Review.

Strongly correlated kagome magnets are promising candidates for achieving controllable topological devices owing to the rich interplay between inherent Dirac fermions and correlation-driven magnetism. Here we report tunable local magnetism and its intriguing control of topological electronic response near room temperature in the kagome magnet Fe₃Sn₂ using small angle neutron scattering, muon spin rotation, and magnetoresistivity measurement techniques.

Shape-morphing systems, which can perform complex tasks through morphological transformations, are of great interest for future applications in minimally invasive medicine, soft robotics, active metamaterials and smart surfaces. With current fabrication methods, shape-morphing configurations have been embedded into structural design by, for example, spatial distribution of heterogeneous materials, which cannot be altered once fabricated. 

In addition to the Kitaev (K) interaction, candidate Kitaev materials also possess Heisenberg (J) and off- diagonal symmetric (Γ) couplings. We investigate the quantum (S=1/2) K-J-Γ model on the honeycomb lattice by a variational Monte Carlo method. In addition to the “generic” Kitaev spin liquid (KSL), we find that there is just one proximate KSL (PKSL) phase, while the rest of the phase diagram contains different magnetically ordered states.

We report muon spin rotation and magnetization measurements under pressure on Fe_1+δSe_1−xS_x with x ≈ 0.11. Above p ≈ 0.6 GPa we find a microscopic coexistence of superconductivity with an extended dome of long range magnetic order that spans a pressure range between previously reported separated magnetic phases. 

Phonon engineering of solids enables the creation of materials with tailored heat-transfer properties, controlled elastic and acoustic vibration propagation, and custom phonon-electron and phonon-photon interactions. These can be leveraged for energy transport, harvesting, or isolation applications and in the creation of novel phonon-based devices, including photoacoustic systems and phonon-communication networks.

Recently, the transition metal dichalcogenide (TMD) system 2M-WS₂ has been identified as a Dirac semimetal exhibiting both superconductivity with the highest T_c ~ 8.5 K among all the TMD materials and topological surface states. Here we report on muon spin rotation (μSR) and density functional theory studies of microscopic SC properties and the electronic structure in 2M-WS₂ at ambient and under hydrostatic pressures (p_max = 1.9 GPa).

Quantum materials that feature magnetic long-range order often reveal complex phase diagrams when localized electrons become mobile. In many materials magnetism is rapidly suppressed as electronic charges dissolve into the conduction band. In materials where magnetism persists, it is unclear how the magnetic properties are affected.