Evidence for Confined Tamm Plasmon Modes under Metallic Microdisks and Application to the Control of Spontaneous Optical Emission

We demonstrate strong confinement of the optical field by depositing a micron sized metallic disk on a planar distributed Bragg reflector. Confined Tamm plasmon modes are evidenced both experimentally and theoretically, with a lateral confinement limited to the disk area and strong coupling to TE polarized fields. Single quantum dots controllably coupled to these modes are shown to experience acceleration of their spontaneous emission when spectrally resonant with the mode. For quantum dots spectrally detuned from the confined Tamm plasmon mode, an inhibition of spontaneous emission by a factor $40\pm 4$ is observed, a record value in the optical domain.

Figure 1

(a): Schematic of the structure. The $z$ scale is 1.5 the scale in other $xy$ directions. (b),(c): 2D Tamm plasmon states (b): calculated spectra of a 40 pair $\mathrm{GaAs}/\mathrm{AlAs}$ DBR without (dashed black line) or with (solid red line) a 50 nm thick gold layer. (c): Top: real part of the refractive index along $z$. Center and Bottom: Spatial distribution of the field intensity along the growth axis for the structure without gold (bottom, dashed black line), with 50 nm of gold (center, red) or 5 nm of gold (bottom, blue). The mode profile is calculated at $E=1.359\mathrm{eV}$. (d): FDTD simulations: norm of the electric field $|E_r|$ at the energy of the CTP fundamental mode for a structure with 30 pairs in the DBR and a $2.5\mu \mathrm{m}$ diameter 50 nm thick gold disk.

Figure 2

(a): Measured emission intensity as a function of energy and in-plane wave vector for various disk diameters. The 2D TP dispersion is measured for a disk size of $20\mu \mathrm{m}$. (b): Measured angularly integrated photoluminescence (PL) spectra (solid black lines). Dashed Red lines are Lorentzian fits to the modes. (c): Experimental (symbols) and theoretical (solid lines) energies of the CTP modes as a function of the disk diameter. (d): Quality factor of the fundamental CTP mode.

Figure 3

(a): Structure of the device: A 50 nm thick gold disk with a diameter of $2.5\mu \mathrm{m}$ is deposited on top of two QDs (QD1 and QD2). The disk is surrounded by a 5 nm thick gold layer. (b): Blue line: PL spectrum recorded from the device. Black line: PL spectrum recorded on a disk with diameter $2.6\mu \mathrm{m}$ containing a high QD density. The dashed green lines are Lorentzian fit to the CTP modes. (c): Decay of the PL recorded at 40 K for the $X_{\mathrm{QD}1}$ line (squares), at 13 K, for a QD exciton in bulk sample (open triangles), for a QD exciton coupled to a 2D TP mode ($X_{2\mathrm{D}\mathrm{TP}}$) (solid triangles) and for the $X_{\mathrm{QD}2}$ line (circles). (d): line: Expected Purcell factor deduced from the $Q$ factor measured in Fig. 2d. Symbol: measured Purcell factor for the $X_{\mathrm{QD}1}$ line. (e): Decay time of the emission of the $X_{\mathrm{QD}2}$ line as a function of temperature.