Category: Achievements

Competing interactions are a prerequisite for geometrical frustration. One well-known example of frustration are Ising spins on triangular corner-sharing plaquettes as for example on the Kagome lattice in 2 dimensions, leading to an extensive ground state degeneracy.  But what happens when different disordered phases co-exist and compete between each other?  By using the same triangular building blocks as for Kagome, we consider the so-called Shuriken lattice (also known as Square-Kagome lattice), which shows, contrary to Kagome, inequivalent sites belonging to loops of different sizes, namely 4 and 8. The presence of these two types of loops together with a large unit-cell offers a natural setting to tune the anisotropy in Continue Reading →

The discovery of Graphene, has sparked a renaissance in the study of two-dimensional materials and their potential technological applications. Graphene quantum dots (GQD’s) bring another new opportunity with potential applications in fields ranging from quantum computation to solar energy. However, in order to tailor the properties of a GQD to a specific purpose it is vital to understand the relationship between the size and shape of the dot and its physical properties. On this work we explore the role that size, shape, edge-type and atomic vacancies play in the optical response of GQD’s. Using group theory, we reveal optical selection rules which follow from the symmetry of a regular shaped Continue Reading →

Understanding what happens in regimes where quantum mechanics and general relativity interface is of fundamental interest.  That said, it is not an easy thing to find systems in which the effects of both are simultaneously measurable and relevant. Parallels in condensed matter systems can provide experimentally accessible alternatives for a the exploration of a wide array of high-energy and gravitational phenomena beyond experimental control, and additionally bring them into a regime where quantum mechanics also plays a relevant role. In this work, we show that spin nematics offer a condensed matter avenue to reproduce gravitational waves. In particular, we show that the massless, spin-2 Goldstone Bosons of ferroquadrupolar nematics are Continue Reading →

Spin-1 magnets allow for dipolar and quadrupolar moments on a single site, leading to rich physical properties as seen in spin nematic phases, Fe-based superconductors and cold atom systems. However, experimental probing of these unconventional phases remains challenging, and therefore requires new theoretical tools to describe and interpret their ground state and excitation properties. In this work, we introduce a new Monte Carlo and Molecular Dynamics method designed to study thermodynamic and dynamic properties of spin-1 magnets. We benchmark our numerical implementation by on the ferroquadrupolar phase of the spin-1 bilinear-biquadratic (BBQ) Hamiltonian on the triangular lattice, and show excellent agreement with analytical flavour-wave theory and low-temperature expansion results. These Continue Reading →

Magnetic frustration leads to the emergence of diverse exotic behaviors, and the study of their theories and phenomenology is crucial. For example, sophisticated understanding has been established for models with underlying U(1) symmetry and the associated pinch-point features in their spin-spin correlations. However, this turned out to be only half the story. Attached to the pinch points, there exists another highly universal feature in the shape of two “half moons” in a wide range of frustrated magnetic models and recent experiments on Nd2Zr2O7. In this work we establish its theoretical interpretation, which turned out to be a hidden side of the pinch-points. It is a result of decomposition and decoupling Continue Reading →