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David Snoke

Publications and source records attributed to David Snoke.

12 recordsLinked to original sources
arXiv2023

Bose condensation of upper-branch exciton-polaritons in a transferrable microcavity

Exciton-polaritons are composite bosonic quasiparticles arising from the strong coupling of excitonic transitions and optical modes. Exciton-polaritons have triggered wide exploration in the past decades not only due to their rich quantum phenomena such as superfluidity, superconductivity and quantized vortices but also due to their potential applications for unconventional coherent light sources and all-optical control elements. Here, we report the observation of Bose-Einstein condensation of the upper polariton branch in a transferrable WS$_2$ monolayer microcavity. Near the condensation threshold, we observe a nonlinear increase in upper polariton intensity. This sharp increase in intensity is accompanied by a decrease of the linewidth and an increase of the upper polariton temporal coherence, all of which are hallmarks of Bose-Einstein condensation. By simulating the quantum Boltzmann equation, we show that the upper polariton condensation only occurs for a particular range of particle density. We can attribute the creation of Bose condensation of the upper polariton to the following requirements: 1) the upper polariton is more excitonic than the lower one; 2) there is relatively more pumping in the upper branch; and 3) the conversion time from the upper to the lower polariton branch is long compared to the lifetime of the upper polaritons.

cond-mat.quant-gas↗
arXiv2022

Ballistic transport of a polariton ring condensate with spin precession

It is now routine to make Bose-Einstein condensates of polaritons with long enough lifetime and low enough disorder to travel ballistically for hundreds of microns in quasi-one-dimensional (1D) wires. We present observations of a polariton condensate injected at one point in a quasi-1D ring, with a well-defined initial velocity and direction. A clear precession of the circular polarization is seen, which arises from an effective spin-orbit coupling term in the Hamiltonian. Our theoretical model accurately predicts the experimentally observed behavior, and shows that "zitterbewegung" behavior plays a role in the motion of the polaritons.

cond-mat.quant-gas↗
arXiv2020

Photoluminescence switching in a two-dimensional atomic crystal

Two-dimensional materials are an emerging class of new materials with a wide range of electrical and optical properties and potential applications. Single-layer structures of semiconducting transition metal dichalcogenides are gaining increasing attention for use in field-effect transistors. Here, we report a photoluminescence switching effect based on single-layer WSe2 transistors. Dual gates are used to tune the photoluminescence intensity. In particular, a side-gate is utilized to control the location of ions within a solid polymer electrolyte to form an electric double layer at the interface of electrolyte and WSe2 and induce a vertical electric field. Additionally, a back-gate is used to apply a 2nd vertical electric field. An on-off ratio of the light emission up to 90 was observed under constant pump light intensity. In addition, a blue shift of the photoluminescence line up to 36 meV was observed. We attribute this blue shift to the decrease of exciton binding energy due to the change of nonlinear in-plane dielectric constant and use it to determine the 3rd order off-diagonal susceptibility \c{hi}^((3) )=3.50*10^(-19)m2/V2.

cond-mat.mtrl-sci↗
arXiv2020

Observation of the Interlayer Exciton Gases in WSe$_2$ -p: WSe$_2$ Heterostructures

Interlayer excitons (IXs) possess a much longer lifetime than intralayer excitons due to the spatial separation of the electrons and holes; hence, they have been pursued to create exciton condensates for decades. The recent emergence of two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs), and of their van der Waals heterostructures (HSs), in which two different 2D materials are layered together, has created new opportunities to study IXs. Here we present the observation of IX gases within two stacked structures consisting of hBN/WSe$_2$/hBN/p: WSe$_2$/hBN. The IX energy of the two different structures differed by 82 meV due to the different thickness of the hBN spacer layer between the TMD layers. We demonstrate that the lifetime of the IXs is shortened when the temperature and the pump power increase. We attribute this nonlinear behavior to an Auger process.

cond-mat.mtrl-sci↗
arXiv2017

Polariton Supercurrent Generation in Unipolar Electro-optic Devices

We describe a mechanism by which an electrical bias voltage applied across a unipolar semiconductor quantum well can drive an exciton or polariton supercurrent. The mechanism depends on the properties of electronic quasiparticles in quantum wells or two-dimensional materials that are dressed by interactions with the coherent exciton field of an exciton condensate or the coherent exciton and photon fields of a polariton condensate, and on approximate conservation laws. We propose experiments that can be performed to realize this new light-matter coupling effect, and discuss possible applications.

cond-mat.mes-hall↗
arXiv2016

Time-resolved two-photon excitation of long-lifetime polaritons

Recent studies of two-photon excitation of exciton-polaritons in microcavities have considered the possibility of an allowed absorption process into the $2p$-state of the excitons which participate in the polariton effect. Here we report time-resolved measurements of two-photon excitation directly into the lower polariton states invoking the $1s$ state of the excitons. Although this process is forbidden by symmetry for light at normal incidence, it is allowed at non-zero angle of incidence due to state mixing.

physics.optics↗
arXiv2015

The Connection of Polaritons and Vacuum Rabi Splitting

Polaritons, in particular microcavity exciton-polaritons, have attracted much attention in recent years, as the phenomena of Bose-Einstein condensation and superfluidity have been observed for these quasiparticles. While the basic physics of these systems is well understood, there has been confusion over the connection of these systems to other phenomena, namely the Jaynes-Cummings Hamiltonian, Rabi flopping, and the vacuum Rabi splitting of atoms in a cavity. This paper reviews the basic theory of polaritons and shows these connections explicitly.

cond-mat.quant-gas↗
arXiv2012

Bose-Einstein Condensation of Excitons in Cu$_2$O: Progress Over Thirty Years

Experiments on Bose-Einstein condensation (BEC) of excitons in the semiconductor Cu$_2$O started over thirty years ago, as one of the first serious attempts at exciton BEC. Early claims were based on spectroscopic signatures and transport data which have since been reinterpreted, in large part because the Auger recombination process for excitons was not well understood. Understanding of the Auger process has also advanced, and recent experiments have made significant progress toward exciton BEC. We review the history of experiments on exciton BEC in Cu$_2$O, the Auger recombination process, and the prospects for observing exciton BEC in this system in the near future.

cond-mat.quant-gas↗
arXiv2012

Polariton Condensation and Lasing

The similarities and differences between polariton condensation in microcavities and standard lasing in a semiconductor cavity structure are reviewed. The recent experiments on "photon condensation" are also reviewed.

cond-mat.quant-gas↗
arXiv2005

Temperature dependence of exciton Auger decay process in Cuprous Oxide

We report theoretical and experimental study on Auger decay of excitons in Cuprous Oxide in a wide range of temperatures, from 2 Kelvin to 325 Kelvin, in single-photon surface excitation. We find that the Auger constant linearly increases with temperature above 100 Kelvin. This constant is important for experiments on Bose condensation of excitons.

cond-mat.other↗
arXiv2004

Resonant two-photon excitation of 1s paraexcitons in Cuprous Oxide

We have created paraexcitons in Cuprous Oxide via resonant two-photon generation, and examined their population dynamics by means of time-correlated single photon detection. Confining the excitons to a constant volume in a harmonic potential trap made with inhomogeneous applied stress along the [001] axis, we find that paraexcitons are created directly, and orthoexcitons appear primarily through the well-known excitonic Auger process. Hot excitons are also created via a three-photon process when the IR laser is non-resonant. Also we generate excitons with two colliding pulses, and the luminescence is weaker than that from one beam excitation with same total laser power. These results show that resonant one-beam two-photon generation of paraexcitons is a promising way to pursue Bose-Einstein condensation of paraexcitons.

cond-mat.other↗