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Register a new userOptical absorption spectroscopy in hybrid systems of plasmons and excitons
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Understanding the physics of light emitter in quantum nanostructure regarding scalability, geometry, structure of the system and coupling between different degrees of freedom is important as one can improve the design and further provide controls of quantum devices rigorously. The couplings between these degrees of freedom, in general, depends on the external field, the geometry of nano particles, and the experimental design. An effective model is proposed to describe the plasmon-exciton hybrid systems and its optical absorption spectrums are studied in details by exact diagonalization. Two different designs are discussed: nano particle planet surrounded by quantum dot satellites and quantum dot planet surrounded by nano particle satellites. In both setups, details of many quantum dots and nano particles are studied, and the spectrums are discussed in details regarding the energy of transition peaks and the weight distribution of allowed transition peaks. Also, different polarization of external fields are considered which results in anisotropic couplings, and the absorption spectrums clearly reveal the difference qualitatively. Finally, the system will undergo a phase transition in the presence of attractive interaction between excitons. Our work sheds the light on the design of nano scale quantum systems to achieve photon emitter/resonator theory in the plasmon-exciton hybrid systems.
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Ultrafast pump-probe technique is a powerful tool to understand and manipulate properties of materials for designing novel quantum devices. An intense, single cycle terahertz pulse can change the intrinsic properties of semiconductor quantum dots to have different luminescence. In a hybrid system of plasmon and exciton, the coherence and coupling between these two degrees of freedom play an important role on their optical properties. Therefore, we consider a terahertz pump optical probe experiment in the hybrid systems where the terahertz pump pulse couples to the exciton degrees of freedom on the quantum dot. The time resolved photoluminescence of the hybrid system shows that the response of the characteristic frequency shifts according to the overlap between the pump and probe pulses. Furthermore, the resonance between the exciton and plasmons can be induced by the terahertz pump pulse in some parameter regimes. Our results show the terahertz driven hybrid system can be a versatile tool for manipulating the material properties and open a new route to design modern optical devices.
We show that the exciton optical selection rule in gapped chiral fermion systems is governed by their winding number $w$, a topological quantity of the Bloch bands. Specifically, in a $C_N$-invariant chiral fermion system, the angular momentum of bright exciton states is given by $w pm 1 + nN$ with $n$ being an integer. We demonstrate our theory by proposing two chiral fermion systems capable of hosting dark $s$-like excitons: gapped surface states of a topological crystalline insulator with $C_4$ rotational symmetry and biased $3R$-stacked MoS$_2$ bilayers. In the latter case, we show that gating can be used to tune the $s$-like excitons from bright to dark by changing the winding number. Our theory thus provides a pathway to electrical control of optical transitions in two-dimensional material.
We report on the resonant coupling between localized surface plasmon resonances (LSPRs) in nanostructured Ag films, and an adsorbed monolayer of Rhodamine 6G dye. Hybridization of the plasmons and molecular excitons creates new coupled polaritonic modes, which have been tuned by varying the LSPR wavelength. The resulting polariton dispersion curve shows an anticrossing behavior which is very well fit by a simple coupled-oscillator Hamiltonian, giving a giant Rabi-splitting energy of ~400 meV. The strength of this coupling is shown to be proportional to the square root of the molecular density. The Raman spectra of R6G on these films show an enhancement of many orders of magnitude due to surface enhanced scattering mechanisms; we find a maximum signal when a polariton mode lies in the middle of the Stokes shifted emission band.
We study the nonlocal spin and charge current generation in a finite metallic element on the surface of magnetic insulators such as tcb{yttrium iron garnet} due to the absorption of the magnetic surface plasmon (MSP). Whereas a surface plasmon is completely reflected by a metal, tcb{an} MSP tcb{can be} absorbed tcb{due to the absence of backward states}. The tcb{injection of} MSP generates a voltage in the longitudinal direction parallel to the wave vector, tcb{with the voltage} proportional to input power. If the metal is a ferromagnet, a spin current can also be tcb{induced} in the longitudinal direction. Our tcb{results provide a way to improve upon} integrated circuits of spintronics and spin wave logic devices.
We calculate linear and nonlinear optical susceptibilities arising from the excitonic states of mono- layer MoS2 for in-plane light polarizations, using second-quantized bound and unbound exciton operators. Optical selection rules are critical for obtaining the susceptibilities. We derive the valley-chirality rule for the second harmonic generation in monolayer MoS2, and find that the third- harmonic process is efficient only for linearly polarized input light while the third-order two photon process (optical Kerr effect) is efficient for circularly polarized light using a higher order exciton state. The absence of linear absorption due to the band gap and the unusually strong two-photon third-order nonlinearity make the monolayer MoS2 excitonic structure a promising resource for coherent nonlinear photonics.
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