Maxim A. Gorlach

Topological edge states of bound photon pairs

We predict the existence of interaction-driven edge states of bound two-photon quasiparticles in a dimer periodic array of nonlinear optical cavities. Energy spectrum of photon pairs is dramatically richer than in the noninteracting case or in a simple lattice, featuring collapse and revival of multiple edge and bulk modes as well as edge states in continuum. Despite the unexpected breakdown of the Zak phase technique and the edge mixing of internal and center-of-mass motion we link the edge state existence to the two-photon quantum walk graph connectivity, thus uncovering the topological nature of the many-body problem in complex lattices.

Nonlocality in uniaxially polarizable media

We reveal extraordinary electromagnetic properties for a general class of uniaxially polarizable media. Depending on parameters, such metamaterials may have wide range of nontrivial shapes of isofrequency contours including lemniscate, diamond and multiply connected curves with connectivity number reaching five. The possibility of the dispersion engineering paves a way to more flexible manipulation of electromagnetic waves. Employing first-principle considerations we prove that uniaxially polarizable media should be described in terms of the nonlocal permittivity tensor which by no means can be reduced to local permittivity and permeability even in the long-wavelength limit. We introduce an alternative set of local material parameters including quadrupole susceptibility capable to capture all of the second-order spatial dispersion effects.

Interaction-induced two-photon edge states in an extended Hubbard model realized in a cavity array

We study theoretically two-photon states in a periodic array of coupled cavities with both on-site and nonlocal Kerr-type nonlinearities. In the absence of nonlinearity the structure is topologically trivial and possesses no edge states. The interplay of two nonlinear interaction mechanisms described by the extended Hubbard model facilitates formation of edge states of bound photon pairs. Numerical and exact analytical results for the two-photon wave functions are presented. Our findings thus shed light onto the edge states of composite particles and their localization properties.

Topological transition in coated wire medium

Employing nonlocal homogenization approach, we investigate the properties of a metamaterial consisting of parallel metallic wires with dielectric coating. We demonstrate that manipulation of dielectric contrast between wire dielectric shell and host material at fixed frequency results in dynamic switching of metamaterial dispersion regime from elliptic to the hyperbolic one, i.e. the topological transition takes place. It is proved that such transition can be induced by the variation of the metamaterial temperature. Our findings thus pave a way to the implementation of a tunable ‘elliptic-hyperbolic’ metamaterial.

Far-field probing of leaky topological states in all-dielectric metasurfaces

Topological phase transitions in condensed matter systems give rise to exotic states of matter such as topological insulators, superconductors, and superfluids. Photonic topological systems open a whole new realm of research and technological opportunities, exhibiting a number of important distinctions from their condensed matter counterparts. Photonic modes can leak into free space, which makes it possible to probe topological photonic phases by spectroscopic means via Fano resonances. Based on this idea, we develop a technique to retrieve the topological properties of all-dielectric metasurfaces from the measured far-field scattering characteristics. Collected angle-resolved spectra provide the momentum-dependent frequencies and lifetimes of the photonic modes that enable the retrieval of the effective Hamiltonian and extraction of the topological invariant. Our results demonstrate how the topological states of open non-Hermitian systems can be explored via far-field measurements, thus paving a way to the design of metasurfaces with unique scattering characteristics controlled via topological effects.Topological modes in photonics systems are not completely confined to the structure but can leak into free space. Here, Gorlach et al. exploit these leaky modes to probe the topological properties of a dielectric metasurface from far-field scattering measurements.

Scaling laws, pressure anisotropy, and thermodynamic effects for blackbody radiation in a finite cavity

As it is known, the phenomenon of blackbody radiation plays an important role in physics. In 1884 L. Boltzmann derived that internal energy of radiation in a cavity is proportional to the fourth power of the temperature; this statement is known as StefanBoltzmann law ([1]). In 1900, basing of quantum hypothesis, M. Planck obtained a formula describing blackbody radiation spectrum ([2]); this formula was thought to be correct for arbitrary temperatures and cavity volumes for a long period of time. But it turns out that Planck’s formula, Stefan-Boltzmann law, Wien’s displacement law are not accurate in the case of sufficiently small cavities and low temperatures. This remark was apparently first done by Bijl ([3]). He also found a criterion of the Planck’s formula validity:

Topological interface states due to spontaneous symmetry breaking in a chain of anharmonic oscillators

In this work, we propose a one-dimensional system of coupled anharmonic oscillators with nonlinear coupling and study a spontaneous formation of interface excitations in the linearized spectrum of such periodic array. We show that during its evolution such system can undergo a topological transition from the disordered and topologically trivial phase into the nontrivial one. The topological transition is accompanied by the formation of the interface state in the spectrum of linearized excitations of the equilibrium state. Employing the technique based on the calculation of mean chiral displacement we demonstrate that the in-gap interface state exhibits a topological nature and is analogous to that in the well-known Su-Schrieffer-Heeger model. Our results demonstrate the formation of topological interface state induced by spontaneous symmetry breaking mechanism and open novel possibilities for designing various nonlinear electronic, photonic and polaritonic systems with disorder-robust control of information flows.

Spectroscopy of topological photonic states in dielectric metasurfaces

We investigate photonic topological states supported by the metasurface based on the triangular lattice of hexamers. It is demonstrated that the transmittance and reflectance spectra recorded for such structure allow one to extract the information about the topological properties of the metasurface photonic modes and the topological invariant in particular. Our method thus provides a technique complementary to the analysis of edge states.

Resonant optical properties of crystalline silicon nanoparticles fabricated by laser ablation-based methods

In this work we demonstrate resonant Raman scattering from crystalline silicon nanoparticles, fabriacted using a single-stage fabrication process based on femtosecond laser ablation. Experimental and analtyical modelling shows 140-times enhancement of Raman scattering from Resonant nanoparticles, relative to their nonresonant counterparts.In this work we demonstrate resonant Raman scattering from crystalline silicon nanoparticles, fabriacted using a single-stage fabrication process based on femtosecond laser ablation. Experimental and analtyical modelling shows 140-times enhancement of Raman scattering from Resonant nanoparticles, relative to their nonresonant counterparts.

Spatial dispersion in metamaterials based on three-dimensional arrays of spheres and disks

We consider the effect of spatial-dispersion-induced birefringence in metamaterial composed of isotropic spheres located in the sites of a cubic lattice. Strong anisotropy of such metamaterial due to nonlocality is demonstrated both numerically and analytically. For metamaterial composed of dielectric disks, we explore electromagnetic modes that are not captured by the local effective medium model, namely, the longitudinal magnetic mode.