Time, momentum, and energy resolved pump-probe tunneling spectroscopy of two-dimensional electron systems

Abstract

Real-time probing of electrons can uncover intricate relaxation mechanisms and many-body interactions in strongly correlated materials. Here, we introduce time, momentum, and energy resolved pump-probe tunneling spectroscopy (Tr-MERTS). The method allows the injection of electrons at a particular energy and observation of their subsequent decay in energy-momentum space. Using Tr-MERTS, we visualize electronic decay processes, with lifetimes from tens of nanoseconds to tens of microseconds, in Landau levels formed in a GaAs quantum well. Although most observed features agree with simple energy-relaxation, we discovered a splitting in the nonequilibrium energy spectrum in the vicinity of a ferromagnetic state. An exact diagonalization study suggests that the splitting arises from a maximally spin-polarized state with higher energy than a conventional equilibrium skyrmion. Furthermore, we observe time-dependent relaxation of the splitting, which we attribute to single-flipped spins forming skyrmions. These results establish Tr-MERTS as a powerful tool for studying the properties of a 2DES beyond equilibrium.

Superconducting Cavity-Based Sensing of Band Gaps in 2D Materials

“…The choice of GHz frequency range allows scopes for fast dynamical measurements in a cavity-coupled system 10,13,40 and can be extended to 2D material platforms as well. 41 A theoretical study has recently been conducted on quantum geometry-originated capacitance in insulators; 42 measuring the capacitance of flat-band moirésystems could provide insights into the quantum geometry. In addition, the moiréplatform has been proposed as a route toward the quantum simulation of correlated electronic states.…”

“…Most of the existing techniques to measure the capacitance of low-dimensional materials rely on lumped element circuits operating within a few hundred kHz range. , Whereas, our SCPW cavity operates at a few GHz frequency. The choice of GHz frequency range allows scopes for fast dynamical measurements in a cavity-coupled system ,, and can be extended to 2D material platforms as well . A theoretical study has recently been conducted on quantum geometry-originated capacitance in insulators; measuring the capacitance of flat-band moiré systems could provide insights into the quantum geometry.…”