Condensed Matter

Based on symmetry consideration, quasi-one-dimensional (1D) objects, relevant to numerous observables or phenomena, can be classified into eight different types. We provide various examples of each 1D type, and discuss their Symmetry Operational Similarity (SOS) relationships, which are often permutable. A number of recent experimental observations, including current-induced magnetization in polar or chiral conductors, non-linear Hall effect in polar conductors, spin-polarization of tunneling current to chiral conductors, and ferro-rotational domain imaging with linear gyration are discussed in terms of (permutable) SOS. In addition, based on (permutable) SOS, we predict a large number of new phenomena in low symmetry materials that can be experimentally verified in the future.

Intense light-matter interactions and unique structural and electrical properties make Van der Waals heterostructures composed by Graphene (Gr) and monolayer transition metal dichalcogenides (TMD) promising building blocks for tunnelling transistors, flexible electronics, as well as optoelectronic devices, including photodetectors, photovoltaics and QLEDs, bright and narrow-line emitters using minimal amounts of active absorber material. The performance of such devices is critically ruled by interlayer interactions which are still poorly understood in many respects. Specifically, two classes of coupling mechanisms have been proposed: charge transfer (CT) and energy transfer (ET), but their relative efficiency and the underlying physics is an open question. Here, building on a time resolved Raman scattering experiment, we determine the electronic temperature profile of Gr in response to TMD photo-excitation, tracking the picosecond dynamics of the G and 2D bands. Compelling evidence for a dominant role ET process accomplished within a characteristic time of ~ 3 ps is provided. Our results suggest the existence of an intermediate process between the observed picosecond ET and the generation of a net charge underlying the slower electric signals detected in optoelectronic applications.

The planar Hall effect (PHE), wherein a rotating magnetic field in the plane of a sample induces oscillating transverse voltage, has recently garnered attention in a wide range of topological metals and insulators. The observed twofold oscillations in ? yx as the magnetic field completes one rotation are the result of chiral, orbital and/or spin effects. The antiperovskites A 3 B O ( A = Ca, Sr, Ba; B = Sn, Pb) are topological crystalline insulators whose low-energy excitations are described by a generalized Dirac equation for fermions with total angular momentum J=3/2 . We report unusual sixfold oscillations in the PHE of Sr 3 SnO, which persisted nearly up to room temperature. Multiple harmonics (twofold, fourfold and sixfold), which exhibited distinct field and temperature dependencies, were detected in ? xx and ? yx . These observations are more diverse than those in other Dirac and Weyl semimetals and point to a richer interplay of microscopic processes underlying the PHE in the antiperovskites.

Coulomb interactions play an essential role in atomically-thin materials. On one hand, they are strong and long-ranged in layered systems due to the lack of environmental screening. On the other hand, they can be efficiently tuned by means of surrounding dielectric materials. Thus all physical properties which decisively depend on the exact structure of the electronic interactions can be in principle efficiently controlled and manipulated from the outside via Coulomb engineering. Here, we show how this concept can be used to create fundamentally new plasmonic waveguides in metallic layered materials. We discuss in detail how dielectrically structured environments can be utilized to non-invasively confine plasmonic excitations in an otherwise homogeneous metallic 2D system by modification of its many-body interactions. We define optimal energy ranges for this mechanism and demonstrate plasmonic confinement within several nanometers. In contrast to conventional functionalization mechanisms, this scheme relies on a purely many-body concept and does not involve any direct modifications to the active material itself.

Plasmons in two-dimensional (2D) materials beyond graphene have recently gained much attention. However, the experimental investigation is limited due to the lack of suitable materials. Here, we experimentally demonstrate localized plasmons in a correlated 2D charge-density-wave (CDW) material: 2H-TaSe2. The plasmon resonance can cover a broad spectral range from the terahertz (40 {\mu}m) to the telecom (1.55 {\mu}m) region, which is further tunable by changing thickness and dielectric environments. The plasmon dispersion flattens at large wave vectors, resulted from the universal screening effect of interband transitions. More interestingly, anomalous temperature dependence of plasmon resonances associated with CDW excitations is observed. In the CDW phase, the plasmon peak close to the CDW excitation frequency becomes wider and asymmetric, mimicking two coupled oscillators. Our study not only reveals the universal role of the intrinsic screening on 2D plasmons, but also opens an avenue for tunable plasmons in 2D correlated materials.

Multi-level exciton-polariton systems offer an attractive platform for studies of non-linear optical phenomena. However, studies of such consequential non-linear phenomena as polariton condensation and lasing in planar microcavities have so far been limited to two-level systems, where the condensation takes place in the lowest attainable state. Here, we report non-equilibrium Bose-Einstein condensation of exciton-polaritons and low threshold, dual-wavelength polariton lasing in vertically coupled, double planar microcavities. Moreover, we find that the presence of the non-resonantly driven condensate triggers interbranch exciton-polariton transfer in the form of energy-degenerate parametric scattering. Such an effect has so far been observed only under excitation that is strictly resonant in terms of the energy and incidence angle. We describe theoretically our time-integrated and time-resolved photoluminescence investigations by a set of rate equations involving an open-dissipative Gross-Pitaevskii equation. Our platform's inherent tunability is promising for construction of planar lattices, enabling three-dimensional polariton hopping and realization of photonic devices, such as two-qubit polariton-based logic gates.

Resonant interaction between excitonic transitions of molecules and localized electromagnetic field allows the formation of hybrid light-matter polaritonic states. This hybridization of the light and the matter states has been shown to be able to significantly alter the intrinsic properties of molecular ensembles placed inside the optical cavity. Here, we have achieved strong coupling between the excitonic transition in typical oligonucleotide-based molecular beacons labelled with a pair of organic dye molecules, demonstrating an efficient donor to acceptor resonance energy transfer, and the tuneable open-access cavity mode. The photoluminescence of this hybrid system under non-resonant laser excitation and the dependence of the relative population of light-matter hybrid states on cavity detuning have been characterized. Furthermore, by analysing the dependence of the relaxation pathways between energy states in this system, we have demonstrated that predominant strong coupling of the cavity photon to the exciton transition in the donor dye molecule can lead to such a large an energy shift that the energy transfer from the acceptor exciton reservoir to the mainly donor lower polaritonic state can be achieved, thus yielding the chromophores donor-acceptor role reversal or carnival effect. Our experimental data confirm the theoretically predicted possibility for confined electromagnetic fields to control and mediate polariton-assisted remote energy transfer thus paving the way to new approaches to remote-controlled chemistry, energy harvesting, energy transfer and sensing.

Sub-wavelength electromagnetic field localization has been central in photonic research in the last decade, allowing to enhance sensing capabilities as well as increasing the coupling between photons and material excitations. The ultrastrong light-matter coupling regime in the THz range with split-ring resonators coupled to magnetoplasmons has been widely investigated, achieving successive world-records for the largest light-matter coupling ever achieved. Ever shrinking resonators have allowed to approach the regime of few electrons strong coupling, in which single-dipole properties can be modified by the vacuum field. Here we demonstrate, theoretically and experimentally, the existence of a limit to the possibility of arbitrarily increasing electromagnetic confinement in polaritonic systems. Strongly sub-wavelength fields can excite a continuum of high-momenta propagative magnetoplasmons. This leads to peculiar nonlocal polaritonic effects, as certain polaritonic features disappear and the system enters in the regime of bound-to-continuum strong coupling. Emerging nonlinearities due to the local breaking of Kohn's theorem are also reported.

We propose and numerically simulate an optoelectronic compact circular polarimeter. It allows to electrically measure the degree of circular polarization and light intensity at room temperature for a wide range of incidence angles in a single shot. The device, being based on GaAsN, is easy to integrate into standard electronics and does not require bulky movable parts nor extra detectors. Its operation hinges mainly on two phenomena: the spin dependent capture of electrons and the hyperfine interaction between bound electrons and nuclei on Ga 2+ paramagnetic centers in GaAsN. The first phenomenon confers the device with sensitivity to the degree of circular polarization and the latter allows to discriminate the handedness of the incident light.

We investigated the dimensionality transition behavior of graphene localized plasmon resonances in confinement-controlled graphene devices. We first demonstrated a possibility of dimensionality transition, based on the devices carrier-density dependence, from a two-dimensional plasmon resonance to a one-dimensional plasmon one. We fabricated optical transparent devices and electrical transport devices on the same optical transparent wafer. These devices allow detailed control and analysis between carrier density and plasmon resonance peak positions. The carrier density from square root n (two-dimensional) to constant (one-dimensional) is consistent with the theoretical predictions based on the Dirac Fermion carriers in linear-band structure materials.