We have used the spin-echo capabilities of TRISP at FRM-II to determine the linewidth of critical antiferromagnetic fluctuations in Ca2RuO4 (CRO) above the Néel temperature. CRO hosts a complex interplay between magnetic and electronic correlations, and exhibits a novel type of soft magnetism with strong single-ion anisotropy and ‘Higgs’ amplitude fluctuations in the spin-wave spectrum, as...
Understanding interface phenomena is one of the greatest challenges in both fundamental and applied physics. In particular, interfaces made of strongly correlated oxides have shown unexpected physical properties, such as the exchange bias, proximity effects, charge transfer, exchange springs and orbital reconstruction [1-3]. Given the complexity of its structural and magnetic phase diagram,...
Hidden-order phases that occur in a number of correlated $f$-electron systems are among the most elusive states of electronic matter. Their investigations are hindered by the insensitivity of standard physical probes, such as neutron diffraction, to the order parameter that is usually associated with higher-order multipoles of the $f$-orbitals. The most well-studied member of this family of...
SrRuO$_3$ is one of the very few perovskite metallic ferromagnets; it exhibits anomalous transport, an invar effect, non-Fermi liquid behavior, a magnetic shape-memory effect and it is an important substrate for various oxide heterostructures. Strong spin-orbit coupling (SOC) is visible in the invar effect and the large magnetic anisotropy. Recently, we could grow large single crystals of...
Magnetic nanoparticles reveal unique magnetic properties which make them relevant for data storage, electronic and mechanical engineering, and biomedical applications. Whereas the implementation of nanomagnetic properties into technological applications is progressing rapidly, understanding the microscopic origin of phenomena such as size-dependent magnetization and magnetic anisotropy is...
In ferromagnetic quantum critical systems it is possible to suppress the Curie temperature to 0 K by changing an external control parameter such as a magnetic field or hydrostatic pressure. Recent theories suggest a generic phase diagram for clean quantum critical ferromagnets featuring a tricritical point where the order of the phase transition changes from 2nd to 1st. This behavior has...
Superconductivity in iron-based superconductors emerges from long-range ordered antiferromagnetic phase with nematic order that breaks four-fold rotational symmetry of the underlying lattice. In spite of considerable work over the past decade, much is unclear concerning the microscopic origin of superconductivity and its relationship with magnetism, nematicity, and orbital order. In this...
The study of topological quantum materials is among the most active and fruitful fields in condensed matter physics, largely owing to the topologically protected exotic states and emergent phenomena discovered for instance in topological insulators, Dirac and Weyl fermion semimetals. Recent experimental realizations of large anomalous Hall effect (AHE) at room temperature [1] and possible...
Magnetic flux lines in type-II superconductors as well as skyrmions, are topologically stabilized objects exhibiting strong particle-like behavior. In both cases, the interplay of (i) vortex-vortex interactions, (ii) interactions with the underlying electronic structure and (iii) interactions with impurities results in complex phase diagrams and metastable states. Since the vortices tend to...
I present an overview of recent research into topological magnons in frustrated quantum magnets. By way of illustration, I discuss the case of triplon excitations in the Shastry-Sutherland magnet SrCu2(BO3)2. We provide a detailed inelastic neutron scattering data showing the bulk triplon spectrum and its evolution in small magnetic fields. A theoretical analysis of these data based on an...
Modern condensed matter physics theories are using several assumptions, allowing to solve quantum mechanical problems otherwise hardly solvable. One of them is Born-Oppenheimer approximation: “we can separate motion of nuclei and motion of electrons” [1]. It is known for decades that there exist materials with strong magnetoelastic (ME) coupling, where approximation is no longer valid....
