Tunneling conductance between parallel two-dimensional electron systems

Quantum Lifetime Spectroscopy and Magnetotunneling in Double Bilayer Graphene Heterostructures

We describe a tunneling spectroscopy technique in a double bilayer graphene heterostructure where momentum-conserving tunneling between different energy bands serves as an energy filter for the tunneling carriers, and allows a measurement of the quasiparticle state broadening at well-defined energies. The broadening increases linearly with the excited state energy with respect to the Fermi level and is weakly dependent on temperature. In-plane magnetotunneling reveals a high degree of rotational alignment between the graphene bilayers, and an absence of momentum randomizing processes.

Spin-Conserving Resonant Tunneling in Twist-Controlled WSe2-hBN-WSe2 Heterostructures

We investigate interlayer tunneling in heterostructures consisting of two tungsten diselenide (WSe₂) monolayers with controlled rotational alignment, and separated by hexagonal boron nitride. In samples where the two WSe₂ monolayers are rotationally aligned we observe resonant tunneling, manifested by a large conductance and negative differential resistance in the vicinity of zero interlayer bias, which stem from energy- and momentum-conserving tunneling. Because the spin-orbit coupling leads to coupled spin-valley degrees of freedom, the twist between the two WSe₂ monolayers allows us to probe the conservation of spin-valley degree of freedom in tunneling. In heterostructures where the two WSe₂ monolayers have a 180° relative twist, such that the Brillouin zone of one layer is aligned with the time-reversed Brillouin zone of the opposite layer, the resonant tunneling between the layers is suppressed. These findings provide evidence that, in addition to momentum, the spin-valley degree of freedom is also conserved in vertical transport.

Coherent Interlayer Tunneling and Negative Differential Resistance with High Current Density in Double Bilayer Graphene-WSe2 Heterostructures

We demonstrate gate-tunable resonant tunneling and negative differential resistance between two rotationally aligned bilayer graphene sheets separated by bilayer WSe₂. We observe large interlayer current densities of 2 and 2.5 μA/μm² and peak-to-valley ratios approaching 4 and 6 at room temperature and 1.5 K, respectively, values that are comparable to epitaxially grown resonant tunneling heterostructures. An excellent agreement between theoretical calculations using a Lorentzian spectral function for the two-dimensional (2D) quasiparticle states, and the experimental data indicates that the interlayer current stems primarily from energy and in-plane momentum conserving 2D-2D tunneling, with minimal contributions from inelastic or non-momentum-conserving tunneling. We demonstrate narrow tunneling resonances with intrinsic half-widths of 4 and 6 meV at 1.5 and 300 K, respectively.

Ultra-compact injection terahertz laser using the resonant inter-layer radiative transitions in multi-graphene-layer structure

The optimization of laser resonators represents a crucial issue for the design of tera-hertz semiconductor lasers with high gain and low absorption loss. In this paper, we put forward and optimize the surface plasmonic metal waveguide geometry for the recently proposed tera-hertz injection laser based on resonant radiative transitions between tunnel-coupled graphene layers. We find an optimal number of active graphene layer pairs corresponding to the maximum net modal gain. The maximum gain increases with frequency and can be as large as ∼ 500 cm^-1 at 8 THz, while the threshold length of laser resonator can be as small as ∼ 50 μm. Our findings substantiate the possibility of ultra-compact voltage-tunable graphene-based lasers operating at room temperature.

Tunneling spectroscopy of a two-dimensionally periodic electron system

The tunneling current between an electron gas with a periodic potential in two dimensions and a plain two-dimensional electron system (2DES) has been studied. The strength of the periodic potential, the subband energy of the plain 2DES, and an applied in-plane magnetic field were varied, mapping the Fourier transform of the periodic wave function. Periodic peaks were observed and explained by translations in the reciprocal lattice. When the potential was strongly modulated to form an array of antidots, commensurability peaks were seen in lateral transport, but, as expected, not in tunneling.