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1. Ultrafast state-selective tunneling in two-dimensional semiconductors with a phase- and amplitude-controlled THz-scanning tunneling microscope

   https://doi.org/10.1063/5.0200845  

   Bobzien, L.; Allerbeck, J.; Ammerman, S_E; Torsi, R.; Robinson, J_A; Schuler, B. (May 2024, APL Materials)

   THz-pulse driven scanning tunneling microscopy (THz-STM) enables access to the ultrafast quantum dynamics of low-dimensional material systems at simultaneous ultrafast temporal and atomic spatial resolution. State-selective tunneling requires precise amplitude and phase control of the THz pulses combined with quantitative near-field waveform characterization. Here, we employ our state-of-the-art THz-STM with multi-MHz repetition rates, efficient THz generation, and precisely tunable THz waveforms to investigate a single sulfur vacancy in monolayer MoS2. We demonstrate that 2D transition metal dichalcogenides (TMDs) are an ideal platform for near-field waveform sampling by THz cross-correlation. Furthermore, we determine the THz voltage via QEV scans, which measure the THz rectified charge Q as a function of THz field amplitude E and dc bias Vdc. Mapping the complex energy landscape of localized states with a resolution down to 0.01 electrons per pulse facilitates state-selective tunneling to the HOMO and LUMO orbitals of a charged sulfur vacancy. 

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2. Edge-State Wave Functions from Momentum-Conserving Tunneling Spectroscopy

   https://doi.org/10.1103/PhysRevLett.125.087701  

   Patlatiuk, T.; Scheller, C. P.; Hill, D.; Tserkovnyak, Y.; Egues, J. C.; Barak, G.; Yacoby, A.; Pfeiffer, L. N.; West, K. W.; Zumbühl, D. M. (August 2020, Physical Review Letters)

   null (Ed.)
3. Chaos in a tunneling universe

   https://doi.org/10.1088/1475-7516/2023/11/052  

   Bojowald, Martin; Gluckman, Ari (November 2023, Journal of Cosmology and Astroparticle Physics)

   A recent quasiclassical description of a tunneling universe model is shown to exhibit chaotic dynamics by an analysis of fractal dimensions in the plane of initial values. This result relies on non-adiabatic features of the quantum dynamics, captured by new quasiclassical methods. Chaotic dynamics in the early universe, described by such models, implies that a larger set of initial values of an expanding branch can be probed. 

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4. Are Mobiles Ready for BBR?

   https://doi.org/10.1145/3517745.3561438  

   Vargas, Santiago; Gunapati, Gautham; Gandhi, Anshul; Balasubramanian, Aruna (January 2022, Proceedings of the ACM SIGCOMM Internet Measurement Conference)
5. A Room‐Temperature Ferroelectric Resonant Tunneling Diode

   https://doi.org/10.1002/adma.202205359  

   Ma, Zhijun; Zhang, Qi; Tao, Lingling; Wang, Yihao; Sando, Daniel; Zhou, Jinling; Guo, Yizhong; Lord, Michael; Zhou, Peng; Ruan, Yongqi; et al (August 2022, Advanced Materials)

   Abstract Resonant tunneling is a quantum‐mechanical effect in which electron transport is controlled by the discrete energy levels within a quantum‐well (QW) structure. A ferroelectric resonant tunneling diode (RTD) exploits the switchable electric polarization state of the QW barrier to tune the device resistance. Here, the discovery of robust room‐temperature ferroelectric‐modulated resonant tunneling and negative differential resistance (NDR) behaviors in all‐perovskite‐oxide BaTiO₃/SrRuO₃/BaTiO₃QW structures is reported. The resonant current amplitude and voltage are tunable by the switchable polarization of the BaTiO₃ferroelectric with the NDR ratio modulated by ≈3 orders of magnitude and an OFF/ON resistance ratio exceeding a factor of 2 × 10⁴. The observed NDR effect is explained an energy bandgap between Ru‐t_2gand Ru‐e_gorbitals driven by electron–electron correlations, as follows from density functional theory calculations. This study paves the way for ferroelectric‐based quantum‐tunneling devices in future oxide electronics. 

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