Observation of Intersubband Polaritons in a Single Nanoantenna Using Nano-FTIR Spectroscopy.

Strong coupling of an intersubband (ISB) electron transition in quantum wells to a subwavelength plasmonic nanoantenna can give rise to intriguing quantum phenomena, such as ISB polariton condensation, and enable practical devices including low threshold lasers. However, experimental observation of ISB polaritons in an isolated subwavelength system has not yet been reported. Here, we use scanning probe near-field microscopy and Fourier-transform infrared (FTIR) spectroscopy to detect formation of ISB polariton states in a single nanoantenna. We excite the nanoantenna by a broadband IR pulse and spectrally analyze evanescent fields on the nanoantenna surface. We observe the distinctive splitting of the nanoantenna resonance peak into two polariton modes and two π-phase steps corresponding to each of the modes. We map ISB polariton dispersion using a set of nanoantennae of different sizes. This nano-FTIR spectroscopy approach opens doors for investigations of ISB polariton physics in the single subwavelength nanoantenna regime.

[1]  Javier Aizpurua,et al.  Mapping the near fields of plasmonic nanoantennas by scattering‐type scanning near‐field optical microscopy , 2015 .

[2]  N. Mortensen,et al.  Direct Characterization of Near-Field Coupling in Gap Plasmon-Based Metasurfaces. , 2018, Nano letters.

[3]  M. Beck,et al.  Room temperature terahertz polariton emitter , 2012, 1201.2094.

[4]  Mattias Beck,et al.  Room-temperature nine-µm-wavelength photodetectors and GHz-frequency heterodyne receivers , 2018, Nature.

[5]  Franco Nori,et al.  Ultrastrong coupling between light and matter , 2018, Nature Reviews Physics.

[6]  J. Faist,et al.  Quantum Cascade Laser , 1994, Science.

[7]  I. Sagnes,et al.  Towards strong light-matter coupling at the single-resonator level with sub-wavelength mid-infrared antennas , 2016, 2016 Conference on Lasers and Electro-Optics (CLEO).

[8]  B. F. Levine,et al.  Quantum‐well infrared photodetectors , 1993 .

[9]  L. C. West,et al.  First observation of an extremely large‐dipole infrared transition within the conduction band of a GaAs quantum well , 1985 .

[10]  H. Bechtel,et al.  Nanoimaging and Control of Molecular Vibrations through Electromagnetically Induced Scattering Reaching the Strong Coupling Regime , 2018, ACS photonics.

[11]  Federico Capasso,et al.  Near-Field Imaging of Phased Array Metasurfaces. , 2015, Nano letters.

[12]  M. Beck,et al.  Few-Electron Ultrastrong Light-Matter Coupling at 300 GHz with Nanogap Hybrid LC Microcavities. , 2017, Nano letters.

[13]  R. Hillenbrand,et al.  Nanoimaging of resonating hyperbolic polaritons in linear boron nitride antennas , 2017, Nature Communications.

[14]  Oliver G Schmidt,et al.  Intersublevel spectroscopy on single InAs-quantum dots by terahertz near-field microscopy. , 2012, Nano letters.

[15]  C. Sirtori,et al.  Transition from strong to ultrastrong coupling regime in mid-infrared metal-dielectric-metal cavities , 2011, 1212.4439.

[16]  G. Mussler,et al.  Nanoscale Near-Field Tomography of Surface States on (Bi0.5Sb0.5)2Te3. , 2018, Nano letters.

[17]  Jonathan J. Wierer,et al.  Optical Strong Coupling between near-Infrared Metamaterials and Intersubband Transitions in III-Nitride Heterostructures , 2014 .

[18]  F. Capolino,et al.  Strong coupling in the sub-wavelength limit using metamaterial nanocavities , 2013, Nature Communications.

[19]  Y. N. Chen,et al.  Antenna-coupled microcavities for enhanced infrared photo-detection , 2014 .

[20]  Terefe G. Habteyes,et al.  Direct Near-Field Observation of Orientation-Dependent Optical Response of Gold Nanorods , 2014 .

[21]  Andrea Alù,et al.  Giant nonlinear response from plasmonic metasurfaces coupled to intersubband transitions , 2014, Nature.

[22]  T. Taubner,et al.  Phonon-Polaritonic Bowtie Nanoantennas: Controlling Infrared Thermal Radiation at the Nanoscale , 2017 .

[23]  Claire F. Gmachl,et al.  Mid-infrared quantum cascade lasers , 2012, Nature Photonics.

[24]  Rainer Hillenbrand,et al.  Pseudoheterodyne detection for background-free near-field spectroscopy , 2006 .

[25]  Daniele Sanvitto,et al.  The road towards polaritonic devices. , 2016, Nature materials.

[26]  Andrea Alù,et al.  Ultrafast Electrically Tunable Polaritonic Metasurfaces , 2014 .

[27]  B. Williams Terahertz quantum cascade lasers , 2007, 2008 Asia Optical Fiber Communication & Optoelectronic Exposition & Conference.

[28]  K. Thygesen,et al.  Nano-imaging of intersubband transitions in van der Waals quantum wells , 2018, Nature Nanotechnology.

[29]  J. Kono,et al.  Intersubband plasmons in the quantum limit in gated and aligned carbon nanotubes , 2018, Nature Communications.