Conductivity in organic semiconductors hybridized with the vacuum field

Abstract

Organic semiconductors have generated considerable interest for their potential for creating inexpensive and flexible devices easily processed on a large scale [1][2][3][4][5][6][7][8][9][10][11]. However technological applications are currently limited by the low mobility of the charge carriers associated with the disorder in these materials [5][6][7][8]. Much effort over the past decades has therefore been focused on optimizing the organisation of the material or the devices to improve carrier mobility. Here we take a radically different path to solving this problem, namely by injecting carriers into states that are hybridized to the vacuum electromagnetic field. These are coherent states that can extend over as many as 10 5 molecules and should thereby favour conductivity in such materials. To test this idea, organic semiconductors were strongly coupled to the vacuum electromagnetic field on plasmonic structures to form polaritonic states with large Rabi splittings ∼ 0.7 eV. Conductivity experiments show that indeed the current does increase by an order of magnitude at resonance in the coupled state, reflecting mostly a change in field-effect mobility as revealed when the structure is gated in a transistor configuration. A theoretical quantum model is presented that confirms the delocalization of the wave-functions of the hybridized states and the consequences on the conductivity. While this is a proof-of-principle study, in practice conductivity mediated by light-matter hybridized states is easy to implement and we therefore expect that it will be used to improve organic devices. More broadly our findings illustrate the potential of engineering the vacuum electromagnetic environment to modify and to improve properties of materials.Light and matter can enter into the strong coupling regime by exchanging photons faster than any competing dissipation processes. This is normally achieved by placing the material in a confined electromagnetic environment, such as a Fabry-Perot (FP) cavity composed of two parallel mirrors that is resonant with an electronic transition in the material. Alternatively, one can use surface plasmon resonances as in this study. Strong coupling leads to the formation of two hybridized light-matter polaritonic states, P+ and P-, separated by the so-called Rabi splitting, as illustrated in Figure 1a. According to quantum electrodynamics, in the absence of dissipation, the Rabi splitting for a single molecule is given bywhere ω is the cavity resonance or transition energy ( the reduced Planck constant), 0 the vacuum permittivity, v the mode volume, d the transition dipole moment of the material and n ph the number of photons present in the system. The last term implies that, even in the dark, the Rabi splitting has a finite value which is due to the interaction with the vacuum electromagnetic field. This vacuum Rabi splitting can be further increased by coupling a large number N of oscillators to the electromagnetic mode since Ω N R ∝ √ N [12]. In this ensemble coupling, in addition to P+ an...

Ground‐State Chemical Reactivity under Vibrational Coupling to the Vacuum Electromagnetic Field

“…The coupling of molecular electronic transitions to the vacuum field has been more extensively studied13, 14, 15, 16, 17, 18 than VSC and has already shown many exciting results, such as enhanced conductivity19 and non‐radiative energy transfer,20 lasing,21 and condensation 22. Together with VSC, it clearly opens many new possibilities for molecular and materials science that should be fully explored.…”

Perspectives for gapped bilayer graphene polaritonics

“…If such a dimensionless parameter becomes non-negligeable, a regime referred to as ultrastrong coupling regime [43,44], many novel physical phenomena due to higher order processes become observable, ranging from quantum vacuum radiation [45] and quantum phase transitions [46,47], to the modification of energy transport [48,49] and light emission [50][51][52] properties, to the appearance of cavity assisted chemical and thermodynamical effects [53][54][55][56]. Notice that the transition between strong and ultrastrong coupling regimes is a smooth crossover, determined more by experimental sensitivity to those novel phenomena that by any intrinsic qualitative change in the underlying physics.…”

Energy Transfer between Spatially Separated Entangled Molecules

“…Such findings add to ar ich variety of quantum phenomena that can be observed by using hybrid light-matter states such as coherent emission [9,10] and room temperature polariton condensation [11,12] in addition to modifications of chemical and material properties in strongly coupled organic materials. [13][14][15][16][17][18][19][20][21][22] Fort he purpose of this study,w eu sed the same Jaggregates of two cyanine dyes,T DBC as D, and BRK as A (see General method in the Supporting Information, SI) as we did in our previous work [7] because they have all the required spectroscopic features.T obuild the hybrid light-matter states with TDBC and BRK as illustrated in Figure 2a,a no ptical cavity mode is first chosen to be resonant with the D absorption maximum at 590 nm (2.1 eV). Thea bsorption spectrum of the system (donor plus resonant cavity) is then modified by strong coupling leading to the formation of two new hybrid light-matter eigen states (P + and P À ).…”

“…[26] Clearly the energy transfer process described here belongs neither to the Fçrster (short-range dipole-dipole interaction) or the Dexter (electronic wave-function overlap) type mechanisms.I th as become independent of distance due to the entangled and delocalized nature of the hybrid polaritonic states.T his is in line with theoretical studies on exciton transport in polaritonic systems, [14,15,26] and the observation of enhanced electronic transport in organic semiconductors under strong coupling. [13] Interestingly,there is also evidence that quantum coherence plays ar ole in photosynthetic light harvesting systems,thus modifying the traditional incoherent picture of energy transfer. [27,28] Thep resent demonstration of efficient energy transfer between entangled spatially separated D-A systems shows that strong coupling provides ar elatively simple platform to investigate chemical and molecular phenomena under quantum entanglement.…”