Messaggio
- Errore
Newsfeeds
Journal of Physics: Condensed Matter - latest papers
Latest articles for Journal of Physics: Condensed Matter
-
Novel inverse oxide/metal catalysts for methanol synthesis: impact of oxide–metal interactions and reversible morphological changes
Inverse oxide/metal catalysts have proved to be excellent systems for the generation of methanol by CO2 hydrogenation or the partial oxidation of methane. These systems can exhibit unique structural and chemical properties due to the nano size of the oxide component and strong oxide–metal interactions. Recent studies for ZnO/Cu, CeO2/Cu, TiO2/Cu, MgO/Cu, In2O3/Cu, and In2O3/Au catalysts have shown large variations in the composition and morphology of the oxide overlayer as a function of temperature and chemical environment. These oxide–metal interfaces are able to react with CO2 and CH4 at room temperature, and both reactants have a strong influence on the physical and chemical properties of the catalysts. Under reaction conditions, switches between oxide–metal and metal–metal interfaces can take in the catalyst surface. A dynamic behavior that can be linked to a high selectivity for methanol production over systems such as ZnO/Cu, CeO2/Cu and In2O3/Au. This type of correlation deserves additional systematic studies since it could be a powerful tool for designing highly efficient catalysts for methanol synthesis.
-
Order-by-disorder in magnets with frustrated spin interactions—classical and large-S limits via the spin functional integral
We investigate spin systems with extensive degeneracies in the classical ground states due to anisotropic frustrated spin interactions, where the degeneracy is not protected by symmetry. Using spin functional integration, we study the lifting of the degeneracies by fluctuations called order-by-disorder (ObD), and the associated gap in the spin-wave spectrum. It is shown that ObD corresponds to gradient-dependent anisotropic interactions of the pseudo-Goldstone modes, which vanish for a classical uniform spin configuration. Fluctuations generate a gradient-independent effective potential which determines the ground state and the pseudo-Goldstone gap. Furthermore, we recover previous predictions for the pseudo-Goldstone gap in type-I and II ObD with two-spin interactions in the large spin-S limit or the classical small temperature limit, by computing the gap explicitly for the type-II cubic compass model and the type-I square compass model. We show that these two limits correspond to the one-loop approximation for the effective potential. We also discuss other types of order by disorder due to m-spin interactions where m > 2.
-
Unveiling the chiral states in multi-Weyl semimetals via theoretical investigation of magneto-optical spectroscopy
The multiple zeroth Landau levels (LLs) in multi-Weyl semimetals (mWSMs), also called chiral states, are fundamental to their distinctive transport and optical properties. This study investigates the transport parameters of mWSMs, with a focus on their magneto-optical response and the critical influence of such multiple zeroth states. Our theoretical analysis highlights the tilting parameters as key determinants in higher-order Weyl nodes, significantly modulating the magneto-optical behavior. A generic LL expression for mWSMs is derived, offering a solid theoretical framework for understanding their quantum transport properties. Comprehensive expressions for the conductivity tensor components are presented, revealing distinctive low-frequency peaks originating from the optical transitions between chiral states as well as that between the bulk and the chiral states. These features are strongly influenced by the tilting parameters, which consequently dictate the low-frequency optical response. These features extend to the Faraday and Kerr rotation spectra, prominently signaling chiral states at frequencies near the tilted Dirac cone. These findings underscore the fundamental role of robust chiral states in the magneto-optical behavior of mWSMs, advancing our understanding of their topological phenomena.
-
Probing electron topology with Raman scattering
Nodal electron spectrum is a characteristic feature of many topological quantum materials, still difficult to experimentally determine and probe. When topology protects the nodes, the low-energy nodal spectrum is distinguished from conventional spectra by its relativistic density of states. Here we review the recent progress in observing and measuring the properties of Weyl electrons with Raman scattering, and argue that, despite being a zero-momentum probe, Raman scattering is a sensitive detector of Weyl electrons capable of extracting the Fermi energy, Fermi momentum and even estimating the Weyl electron lifetime shaped by interactions and disorder. The utility of Raman scattering for the detection of quadratic band touching is also discussed.
-
Topical review: the nature of the ground state and possibility of a quantum spin liquid in 1T metal dichalcogenides
The compounds 1T-TaX2 (X = S, Se) and 1T-NbSe2 have been considered as potential hosts of a quantum spin liquid (QSL) phase. This is based on the widely held view that the Mott–Hubbard mechanism drives the insulating behavior of its charge density wave ground state, resulting in localized spins, interacting antiferromagnetically, on a geometrically frustrated lattice. However this assumes layer-wise independent behavior. A growing body of evidence shows not only that inter-layer interactions are very significant in 1T-TaS2, but also that they mediate some of its most interesting functional properties. Here we offer a perspective from the point of view of scanning tunneling microscopy that helps to visualize the microscopic degrees of freedom of inter-layer interactions in bulk 1T-TaS2, and the associated impact on the local density-of-states, including the occurrence of multiple distinct insulating phases. We consider to what extent the bulk of 1T-TaS2, and its surface terminations can be considered as Mott insulating and whether, or where, QSL behavior might persist. To better understand the bulk behavior we also draw insights from measurements on isolated monolayers of 1T-TaX2 and 1T-NbSe2, where the confounding complications of inter-layer interactions are absent. We highlight some outstanding questions raised by a comprehensive evaluation of the experimental results, and finally suggest future experiments that could address them.