Author: Rico
Eight-color chiral spin liquid in the S=1 bilinear-biquadratic model with Kitaev interactions
Ground state phase diagrams of the S=1 Kitaev model with bilinear-biquadratic interactions, shown for different degrees of freedom in spin space: CP2, CP1, and a discrete eight-color model.
Reentrance of disorder in the anisotropic shuriken Ising model
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 →
Theory of Ca10Cr7O28 as a bilayer breathing-kagome magnet: Classical thermodynamics and semi-classical dynamics
Quantum spin liquids form an exotic class of quantum phases of matter, accompanied by emergent gauge fields, topological order and fractionalized excitations, with strong interaction effects and long-range entanglement. The recently discovered material Ca10Cr7O28 shows strong indications of hosting such a novel phase of matter, but with properties that sets it apart from any previously studied quantum spin liquid. In this work, we make a crucial step towards understanding the nature and origin of the spin liquid behaviour in Ca10Cr7O28. Using a combination of Monte Carlo and molecular dynamics simulation, and spin-wave calculations, we carry out a comprehensive study of a bilayer breathing kagome model derived from experiment. We Continue Reading →
Symmetry and optical selection rules in graphene quantum dots
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 →
Gravitational wave analogs in spin nematics and cold atoms
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 →
Curie-law crossover in spin liquids
The Curie-Weiss law is widely used to estimate the strength of frustration in spin liquid materials. However, the Curie-Weiss law was originally derived as an estimate of magnetic correlations close to a mean-field phase transition, which – by definition – is absent in spin liquids. Consequently, certain materials were reported to exhibit deviations from the Curie-Weiss law, making a conclusive determination of their Curie-Weiss temperature challenging, especially when the high-temperature regime becomes inaccessible in experiments. In this work, we show that the concept of a ”Curie-law crossover” (see Fig.1) provides an accurate description of the thermodynamic properties in spin liquids. We study the generic aspect of the Curie-law crossover Continue Reading →
Spin Nematics Meet Spin Liquids
New discoveries are often made on the border between different disciplines. One major discipline in solid state physics is dedicated to quantum spin liquids, an unconventional state of matter accompanied by emergent gauge fields, topological order, and fractionalized excitations. Another concept is that of spin nematics, a magnetically ordered state dominated by quadrupole moments, which breaks spin-rotation symmetry by selecting an axis, while not choosing a particular direction. Usually seen as two separate areas of study, we are interested in combining those two disciplines, by asking the question: “What happens, when a spin nematic and a spin liquid meet?” To answer this question, we showed that the S=1 Kitaev model Continue Reading →