Physical Review B

The ternary compounds $\mathrm{CsPb}{X}_{3}$ ($X=\mathrm{Br}$ or Cl) have perovskite structures that are being considered for optical and electronic applications such as lasing and gamma-ray detection. An above-band-gap excitonic photoluminescence (PL) band is seen in both $\mathrm{CsPb}{X}_{3}$ compounds. An excitonic emission peak centered at 2.98 eV, $\ensuremath{\sim}0.1$ eV above the room-te…

We show that any heat definition expressed as an energy change in the reservoir energy plus any fraction of the system-reservoir interaction is not an exact differential when evaluated along reversible isothermal transformations, except when that fraction is zero. Even in that latter case the reversible heat divided by temperature, namely entropy, does not satisfy the third law of thermodynamics …

Exactly solvable models often provide valuable insights in theoretical studies of topological phases. Here the authors introduce exactly solvable models of interacting Majorana fermions each with extensive topological ground-state degeneracy and a hierarchy of pointlike, topological excitations that are only free to move within submanifolds of the full lattice. These very different models make up…

van der Waals heterostructures, created by stacking two-dimensional materials, represent a novel and largely unexplored class of materials with very interesting optoelectronic properties. Excitons, strongly bound electron-hole pairs, play a crucial role in determining these properties, especially in 2D materials where the electron-hole binding is strong. However, a complete understanding of excit…

A Weyl semimetallic state with pairs of nondegenerate Dirac cones in three dimensions was recently predicted to occur in the antiferromagnetic state of the pyrochlore iridates. Here, we show that the THz optical conductivity and temperature dependence of the free carrier response in pyrochlore ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ match the predictions for a Weyl semimetal and sugg…

The spin diffusion length for thermally excited magnon spins is measured by utilizing a nonlocal spin-Seebeck effect measurement. In a bulk single crystal of yttrium iron garnet (YIG) a focused laser thermally excites magnon spins. The spins diffuse laterally and are sampled using a Pt inverse spin Hall effect detector. Thermal transport modeling and temperature dependent measurements demonstrate…

The layered honeycomb magnet $\ensuremath{\alpha}\ensuremath{-}{\mathrm{RuCl}}_{3}$ has been proposed as a candidate to realize a Kitaev spin model with strongly frustrated, bond-dependent, anisotropic interactions between spin-orbit entangled ${j}_{\mathrm{eff}}=\frac{1}{2}\phantom{\rule{4.pt}{0ex}}{\mathrm{Ru}}^{3+}$ magnetic moments. Here, we report a detailed study of the three-dimensional cr…

By using first-principles calculations, we propose that ZrSiO can be looked at as a three-dimensional (3D) oxide weak topological insulator (TI) and its single layer is a long-sought-after 2D oxide TI with a band gap up to 30 meV. Calculated phonon spectrum of the single layer ZrSiO indicates it is dynamically stable and the experimental achievements in growing oxides with atomic precision ensure…

We measured the absolute lengths of three single-crystal silicon samples by means of an imaging Twyman-Green interferometer in the temperature range from 7 K to 293 K with uncertainties of about 1 nm. From these measurements we extracted the coefficient of thermal expansion with uncertainties on the order of $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}/\mathrm{K}$. To access the fun…

Excitons, trions, biexcitons, and exciton-trion complexes in two-dimensional transition metal dichalcogenide sheets of ${\mathrm{MoS}}_{2}, {\mathrm{MoSe}}_{2}, {\mathrm{MoTe}}_{2}, {\mathrm{WS}}_{2}$, and ${\mathrm{WSe}}_{2}$ are studied by means of density functional theory and path-integral Monte Carlo method in order to accurately account for the particle-particle correlations. In addition, t…

Due to the absence of a strong electron-acoustic phonon interaction, a system made up of graphene sheets encapsulated between thin hexagonal boron nitride slabs is ideal for investigating the hydrodynamic behavior of an electron liquid. Using a fully analytical theoretical approach, the authors demonstrate that nonlocal dc transport measurements can be used to extract the hydrodynamic shear visco…

Exploiting the analogy between Pfaffian and anti-Pfaffian states the authors construct a particle-hole conjugate of the composite Fermi liquid state. They suggest that a transition between composite Fermi liquid and anti-composite Fermi liquid states may occur at half-filling and discuss the relevance of such transition to recent magnetoresistance oscillation experiments.

The hybrid halide perovskite ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$ exhibits a complex structural behavior, with successive transitions between orthorhombic, tetragonal, and cubic polymorphs around 165 and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$. The equilibrium structures …

We investigate the orthorhombic phase $({T}_{d})$ of the layered transition-metal dichalcogenide ${\mathrm{MoTe}}_{2}$ as a Weyl semimetal candidate. ${\mathrm{MoTe}}_{2}$ exhibits four pairs of Weyl points lying slightly above $(\ensuremath{\sim}6\phantom{\rule{0.16em}{0ex}}\mathrm{meV})$ the Fermi energy in the bulk band structure. Different from its cousin ${\mathrm{WTe}}_{2}$, which was recen…

The effect of the number of stacking layers and the type of stacking on the electronic and optical properties of bilayer and trilayer black phosphorus are investigated by using first-principles calculations within the framework of density functional theory. We find that inclusion of many-body effects (i.e., electron-electron and electron-hole interactions) modifies strongly both the electronic an…

We investigate spin-orbit torques of metallic CuAu-I-type antiferromagnets using spin-torque ferromagnetic resonance tuned by a dc-bias current. The observed spin torques predominantly arise from diffusive transport of spin current generated by the spin Hall effect. We find a growth-orientation dependence of the spin torques by studying epitaxial samples, which may be correlated to the anisotropy…

We study the spontaneous entanglement generation between two qubits chirally coupled to a waveguide. The maximum achievable concurrence is demonstrated to increase by a factor of $4/e\ensuremath{\sim}1.5$ as compared to the non-chiral coupling situation. The proposed entanglement scheme is shown to be robust against variation of the qubit properties such as detuning and separation, which are crit…

We describe a fluctuating volume-current formulation of electromagnetic fluctuations that extends our recent work on heat exchange and Casimir interactions between arbitrarily shaped homogeneous bodies [A. W. Rodriguez, M. T. H. Reid, and S. G. Johnson, Phys. Rev. B 88, 054305 (2013)] to situations involving incandescence and luminescence problems, including thermal radiation, heat transfer, Casi…

We study the spin-$\frac{1}{2}$ Heisenberg model on the triangular lattice with antiferromagnetic first- $({J}_{1})$ and second- $({J}_{2})$ nearest-neighbor interactions using density matrix renormalization group. By studying the spin correlation function, we find a ${120}^{\ensuremath{\circ}}$ magnetic order phase for ${J}_{2}\ensuremath{\lesssim}0.07{J}_{1}$ and a stripe antiferromagnetic phas…

Here, we formally develop theoretical methods to topologically classify a wide class of bianisotropic continuous media. It is shown that for continuous media, the underlying wave vector space may be regarded as the Riemann sphere. We derive sufficient conditions that ensure that the pseudo-Hamiltonian that describes the electrodynamics of the continuous material is well behaved so that the Chern …