Magneto-transport controlled by Landau polariton states

Abstract

Hybrid excitations, called polaritons, emerge in systems with strong light-matter coupling. Usually, they dominate the linear and nonlinear optical properties with applications in quantum optics. Here, we show the crucial role of the electronic component of polaritons in the magnetotransport of a cavity-embedded 2D electron gas in the ultrastrong coupling regime. We show that the linear dc resistivity is significantly modified by the coupling to the cavity even without external irradiation. Our observations confirm recent predictions of vacuum-induced modification of the resistivity. Furthermore, photo-assisted transport in presence of a weak irradiation field at sub-THz frequencies highlights the different roles of localized and delocalized states.The strong light-matter coupling regime [1, 2] is realized when the coupling Ω between photons and a material's excitation of frequency ω exceeds the losses γ tot of both components. An especially interesting situation is attained when quantum fluctuations of the electromagnetic field ground state give rise to the so-called vacuum Rabi splitting of the cavity polaritons. Solid-state systems [3][4][5] have recently proven to be instrumental in achieving the ultimate limit of this kind of coupling. The ultrastrong coupling regime [6-20], realized in the limit of Ω/ω 0.1, exploits the collective nature of the matter excitations [6,21,22] to achieve a peculiar situation where the ground state of the system is constituted by non-trivial quantum vacua [6].The (ultra-)strong coupling regime has so far mostly been investigated by interrogating the photonic component of the polariton quasi-particle weakly probing the coupled system with low photon fluxes [1-5, 7, 9, 10, 13-17, 19, 23-25]. Notable exceptions have been the measurements of the matter part of an exciton polariton condensate with an excitonic 1s-2p transition[26] and a transport experiment in molecules coupled to a plasmonic resonance [18].Recently we pioneered a new experimental platform, the Landau polaritons, to study ultrastrong light matter interactions [15,27] allowing to reach record-high nor-malized light-matter coupling ratios Ω/ω cav > 1 [28]. The inter-Landau level (cyclotron) transition ω c = eB m * (m * : effective electron mass) of a two-dimensional electron gas (2DEG) under strong magnetic field is coupled to a complementary electronic LC resonator [29] at frequencies of 100's of GHz, which plays effectively the role of the optical cavity. This system is especially well suited to study the matter part of ultrastrongly coupled polaritons using low temperature magneto-transport.It was recently proposed theoretically [30] that such transport is actually driven by the bright polariton operator, i.e. the same operator driving the optical response.Here we find experimental evidence consistent with this picture, in which most tellingly the longitudinal resistivity ρ xx bears the signatures of the polariton branches.Further confirmation for polaritonic effects acting on magneto-transport is obtained by observ...

Mott polaritons in cavity-coupled quantum materials

“…where -H D P is defined in equation (19). Combining equations (B1)-(B3) shows that the expression forˆ(…”

“…The resonant electron-photon coupling described by -H D P in equation (19) results in the formation of doublon-photon polaritons. All eigenstates of -H D P with non-zero eigenvalues can be constructed from the eigenstates ofĤ S with non-zero eigenvalues (see appendix C).…”

“…Here we investigate the spectrum of the Hamiltonian -H D P in equation (19). To this end we consider matrix elements of -H D P between states in the  1 manifold.…”

“…equations(19) and (C1), we find of j and k. Second, we consider the eigenstates ñ |g l 0 ofĤ S with eigenvalue zero. The states y ñ = ñ Ä ñ It follows that all matrix elements of -H D P involving y ñ| proof of the spectrum of -H D P .…”

Dark vertical conductance of cavity-embedded semiconductor heterostructures

“…Recent transport experiments in cavity-embedded organic semiconductors [10,11] and in-plane magnetotransport measurements in cavity-embedded high-mobility two-dimensional electron systems [12] have shown that the linear-regime electronic conductance of a material can be significantly affected by a cavity electromagnetic resonator even in the absence of illumination. Early theoretical works exploring the role of a cavity on transport have focused on cavity-modified excitonic linear transport [13,14] and charge nonlinear conduction [15] for chains of two-level systems in the nonlinear regime where electrons are injected in the excited levels.…”