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Observation of Hybrid States of Tamm and Surface Plasmon-Polaritons in Photonic Crystals
B.I. A finog enov , V.O. Bessonov, I.V. Sobolev a, and A.A. Fedyanin
Lom onosov M oscow St at e Universit y, 1 L eni nski e gory, 119991 Moscow, Russi a afi nogenov@nanolab.phys.m su.ru

Abstra ct: Exp erimental ob servation of Tamm plasmon-p olariton and surface p lasmon-polar iton hybrid mode is reported. Such mode is excited in one-dimensional p hotonic cr ystal ter minated b y semitr ansparent metal film under conditions of total internal reflection for TM-polar ized light.
OCIS codes: ( 350.4238) Nanophotonics and phot oni c cr yst als; (240.6680) S ur face pl asmons

1 . Introduction Tamm p lasmon-polar itons (TPP) in photonic crystals (PC) are op tical analogues of electronic densit y localization at the boundar y of p eriodic atomic potential [1] and ap pear as electromagnetic field localization at the boundar y of p hotonic cr ystal and metal [2]. Unlike sur face electromagnetic waves and sur face plasmon-p olaritons (SPP) Tamm p lasmon-p olaritons do not have p hase-matching conditions for in-plane wave vector, thus TPP can b e excited for any angle of incidence [3]. However b oundar y conditions for out-of-p lane wave vector are critical for TPP. Experimentall y these states manifest themselves as narr ow absorp tion resonances in reflectance sp ectra of Me/PC systems [4 ]. The TPP coup led with other excitations such as excitons or micr ocavit y modes have b een intensively studied last years [5,6] due to prosp ectives of the TPP app lication in new compact lasers and sensors [7 ]. Such states are called "h yb rid" ones and can be detected as a ser ies of several non- overlapp ing resonances in reflectance spectr a. In a photonic cr ystal terminated b y semitr ansparent metal film SPP can emer ge at the metal sur face under total internal reflection, w hile conditions of TPP at the metal/PC inter face excitation would be satisfied automatically b ecause TPP can be excited for any angle of light incidence. Therefor e one can exp ect app earance of SPP-TPP h yb rid state. 2 . Samples and setup The studied samples consisted of 6 p airs of ZrO2/SiO2 quarter-wavelength-thick layers dep osited on quartz sub strate using thermal evaporation. The layer thicknesses ob tained from the scanning electron microscop y image of the samp le cleavage ar e 110 nm (ZrO 2) and 1 45 nm (SiO2), that corresponds to the Bragg wavelength of B = 850 nm. Accor ding to the calculations optimal thickness of the top most layer was estimated as 225 nm, therefore additional 80 nm layer of SiO2 was deposited on the PC sample. The resultant str ucture was covered b y a 30 -nm-thick gold film allowing both good field localization in the TPP mode and p ossib ilit y of the SPP excitation. Reflection spectra wer e measur ed with the 1-nm resolution using polarized collimated beams. For measurement of angular dependences the -2 goniometer was used providing 0.005° accuracy. 3 . Experimenta l results Figur e 1 shows image plots of reflection coefficient sp ectra as a function of the angle of incidence for the TM p olarization of incoming light, measured (Fig.1 a) and calculated (Fig.1b). TPP dip inside p hotonic b and-gap is observed for incident angles less than the angle of total internal r eflection ( ab out 41° for used p rism). B oth PBG and TPP resonances are blue-shifted with the incident angle increase as perp endicular comp onent of the wave vector decreases. TPP resonance ap pears again at = 43 ° and = 620 nm. For the angles exceeding the angle of total internal reflection phase matching conditions for SPP excitation are satisfied. The SPP dip starts fr om = 42 ° and = 1000 nm and rapidl y b lue-shifts with increasing the angle of incidence. However, dispersion cur ve of SPP in Au/PC sample is considerab ly red-shifted comparing to the disp ersion cur ve of SPP in gold film. Inset in Figure1b shows reflection coefficient sp ectrum as a function of angle of incidence for a refer ence samp le -- 30 -nm-thick gold film. Dip corresponding to SPP excitation app ears at 42 °. Sp ectral p osition of SPP in the r eference sample at 50° is approximately 520 nm while spectral position of SPP in the Au/PC samp le at 50° is about 610 nm due to the coupling w ith TPP which leads to repulsion of TPP and SPP resonances.


For TE polarization of incoming light SPP propagation is forbidden. Thus TPP is excited solel y. Sp ectral p osition of the TPP resonance shifts to shorter wavelengths app roaching PBG edge. This is in an agreement w ith numerical calculations. N umerical calculations were also per formed to stud y how coupling of TPP and SPP depends on the thickness of the gold la yer. Image p lots of reflection coefficient spectra as a function of the angle of incidence for the TM p olarization of incoming light for different thicknesses of the Au la yer ar e shown in Fig. 2 . Parameters of the model PC structur e were the same as in exp eriment. With increasing thickness of gold la yer splitting of TPP and SPP comp onents of hybrid state decreases since normalized overlap integr al of exponential tails of SPP and TPP in metal diminishes. For the films thicker than 6 0 nm TPP and SPP do not sense each other and repulsion of their dispersion cur ves b ecomes negligible.

Fi g.1 (Col or onli ne) ( a) I ma ge pl ot of experi mental refl ectivit y (R) spect r um of Au/PC sample for TM polar ization. Arrows i ndi cat e di sper si on cur ves of Tamm pl asmon-polarit on and sur face pl asmon-polarit on. Dashed cur ves i ndi cat e photoni c band-gap. ( b) I mage plot of cal cul at ed r eflect i vit y spectr um for TM pol arization. Inset shows i mage pl ot of experiment al r efl ecti vit y spectr um of a reference gol d fil m for TM polarization. Y ell ow stri pe cor responds to t he SP P di sper si on cur ve.

Fi g. 2 (Col or online) I ma ge plot s of reflectivi t y spectr a for TM polar ization calcul at ed for t hi cknesse s of gold l ayer of 20 nm (a), 40 nm (b) , 50 nm (c), 60 nm ( d), 70 nm (e). D ashed cir cl es empha si ze spect ral -angul ar r egion of TPP and S PP di sper si on cur ves repul sion.

4 . Conclusions In conclusion, we have h yb rid mode in A u/1D opp osite sur faces of m overlapp ing resonances. which can be used for cr 5 . References
[ [ [ [ [ [ [ 1] 2] 3] 4] 5] 6] 7] I .E. Tamm, J ETP 3, 34 (1933). A. V. Kavoki n, I . A. S hel ykh and G. M al puech, Phys. Rev. B 72, 233102 ( 2005). A. Kavoki n, I . S hel ykh and G . Malpuech, App. P hys. Lett. 87, 261105 ( 2005). M. E. S asi n, R.P . Seisyan, M. A. Kalit eevski et al., App. P hys. Lett . 92, 251112 ( 2008) . C. S ymonds, A. Lemaitre, E. Home yer et al., App. P hys. Let t. 95, 151114 ( 2009). R. Bruckner, M. Sudzi us, S. Hi nt schich et al., Phys. Rev. B 83, 033405 (2011). R. Bruckner, A.A. Zakhidov, R. Schol z et al., Nature P hotoni cs 6, 322 ( 2012).

obtained exp erimental evidence of excitation of Tamm and PC structure. For TM polarized incoming light these two s etal film. Tamm and p lasmon components of hyb rid mode Their coup ling leads to r ep ulsion of dispersion curves (75 nm eating tunab le plasmonic filters or sensors.

surface p lasmon-polaritons ur face modes exist on the are revealed as tw o nonfor 30-nm-thick gold film),