Abstract
Monolayers of transition metal dichalcogenides display a strong excitonic optical response. Additionally encapsulating the monolayer with hexagonal boron nitride allows to reach the limit of a purely homogeneously broadened exciton system. On such a MoSe2‐based system, ultrafast six‐wave mixing spectroscopy is performed and a novel destructive photon echo effect is found. This process manifests as a characteristic depression of the nonlinear signal dynamics when scanning the delay between the applied laser pulses. By theoretically describing the process within a local field model, an excellent agreement with the experiment is reached. An effective Bloch vector representation is developed and thereby it is demonstrated that the destructive photon echo stems from a destructive interference of successive repetitions of the heterodyning experiment.
Highlights
The spin echo [1] is an essential effect in nuclear magnetic resonance spectroscopy and the basis for all sorts of complex radio pulse sequences [2] that are routinely applied in medicine [3], chemistry [4], or physics [5, 6, 7]
We use the same sample as investigated in Ref. [35] where the echo formation in two-pulse four-wave mixing (FWM) signals with φFWM = 2φ2 − φ1 was used to study the inhomogeneity of the structure
The rephasing takes the same time as the dephasing and the FWM signal is significantly enhanced due to constructive interferences at the time precisely given by the delay time t = τ between the two pulses
Summary
The spin echo [1] is an essential effect in nuclear magnetic resonance spectroscopy and the basis for all sorts of complex radio pulse sequences [2] that are routinely applied in medicine [3], chemistry [4], or physics [5, 6, 7]. While spin resonances are driven by radio frequencies, optical frequencies are required to resonantly excite typical charge transitions; in this regime the analogous phenomenon is called photon echo [8]. In single low-dimensional systems like quantum dots it requires large effort to detect such nonlinear optical signals [29, 30]. Due to their strong excitonic optical response, monolayers of transition metal dichalcogenides (TMDCs) show a remarkable signal strength in FWM spectroscopy [31, 32, 33, 34]. The direct correspondence between inhomogeneous spectral broadening and photon echo duration has been used to map the inhomogeneity of TMDC monolayers [31, 32, 34, 35]
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