B. Normand

Interlayer electronic hybridization leads to exceptional thickness-dependent vibrational properties in few-layer black phosphorus

Stacking two-dimensional (2D) materials into multi-layers or heterostructures, known as van der Waals (vdW) epitaxy, is an essential degree of freedom for tuning their properties on demand. Few-layer black phosphorus (FLBP), a material with high potential for nano- and optoelectronics applications, appears to have interlayer couplings much stronger than graphene and other 2D systems. Indeed, these couplings call into question whether the stacking of FLBP can be governed only by vdW interactions, which is of crucial importance for epitaxy and property refinement. Here, we perform a theoretical investigation of the vibrational properties of FLBP, which reflect directly its interlayer coupling, by discussing six Raman-observable phonons, including three optical, one breathing and two shear modes. With increasing sample thickness, we find anomalous redshifts of the frequencies for each optical mode but a blueshift for the armchair shear mode. Our calculations also show splitting of the phonon branches, due to anomalous surface phenomena, and strong phonon-phonon coupling. By computing uniaxial stress effects, inter-atomic force constants and electron densities, we provide a compelling demonstration that these properties are the consequence of strong and highly directional interlayer interactions arising from the electronic hybridization of the lone electron-pairs of FLBP, rather than from vdW interactions. This exceptional interlayer coupling mechanism controls the stacking stability of BP layers and thus opens a new avenue beyond vdW epitaxy for understanding the design of 2D heterostructures.

Complete bond-operator theory of the two-chain spin ladder

The discovery of the almost ideal, two-chain spin-ladder material (C

High-dimensional fractionalization and spinon deconfinement in pyrochlore antiferromagnets

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Effect of iron content and potassium substitution in A(0.8)Fe(1.6)Se(2) (A=K, Rb, Tl) superconductors: A Raman scattering investigation

H

Phase Transitions of Ferromagnetic Potts Models on the Simple Cubic Lattice

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Partial order and finite-temperature phase transitions in Potts models on irregular lattices.

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Thermodynamic properties of highly frustrated quantum spin ladders: Influence of many-particle bound states

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Multi-triplet bound states and finite-temperature dynamics in highly frustrated quantum spin ladders

CuBr

Partial Order in Potts Models on the Generalized Decorated Square Lattice

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Multicolored quantum dimer models, resonating valence-bond states, color visons, and the triangular-lattice t 2 g spin-orbital system

has once again focused attention on this most fundamental problem in low-dimensional quantum magnetism. With experimental data now available at all temperatures and magnetic fields, a correspondingly systematic theoretical description is required. This is obtained for the gapped regime within the bond-operator framework, by implementing three qualitative advances that account for triplet correlation effects, their evolution in a field, and the magnetization induced when both field and temperature are finite. Quantitative and parameter-free results are presented as experimental comparisons with the measured specific heat and as predictions for thermal renormalization of the triplet magnon excitations.