Electromagnetic fields bound tightly to charge carriers in a two-dimensional sheet, namely surface plasmons, are shielded by metallic plates that are a part of a device. It is shown that for epitaxial graphenes, the propagation velocity of surface pl
asmons is suppressed significantly through a partial screening of the electron charge by the interface states. On the basis of analytical calculations of the electron lifetime determined by the screened Coulomb interaction, we show that the screening effect gives results in agreement with those of a recent experiment.
The model of interacting fermion systems in one dimension known as Tomonaga-Luttinger liquid (TLL) provides a simple and exactly solvable theoretical framework, predicting various intriguing physical properties. Evidence of TLL has been observed as p
ower-law behavior in the electronic transport and momentum-resolved spectroscopy on various types of one-dimensional (1D) conductors. However, these measurements, which rely on dc transport involving tunneling processes, cannot identify the eigenmodes of the TLL, i.e., collective excitations characterized by non-trivial effective charge e* and charge velocity v*. The elementary process of charge fractionalization, a phenomenon predicted to occur at the junction of a TLL and non-interacting leads, has not been observed. Here we report time-resolved transport measurements on an artificial TLL comprised of coupled integer quantum Hall edge channels, successfully identifying single charge fractionalization processes. An electron wave packet with charge e incident from a non-interacting region breaks up into several fractionalized charge wave packets at the edges of the artificial TLL region, from which e* and v* can be directly evaluated. These results are informative for elucidating the nature of TLLs and low-energy excitations in the edge channels.
We report experimental and theoretical studies of edge magnetoplasmon (EMP) transport in quantum Hall (QH) devices. We develop a model that allows us to calculate the transport coefficients of EMPs in QH devices with various geometries. In our model,
a QH system is described as a chiral distributed-element (CDE) circuit, where the effects of Coulomb interaction are represented by an electrochemical capacitance distributed along unidirectional transmission lines. We measure the EMP transport coefficients through single- and coupled-edge channels, a quantum point contact, and single- and double-cavity structures. These measured transmission spectra can be reproduced well by simulations using the corresponding CDE circuits. By fitting the experimental results with the simulations, we deduce the circuit parameters that characterize the electrostatic environment around the edge channels in a realistic QH system. The observed gate-voltage dependences of the EMP transport properties in gate-defined structures are explained in terms of the gate tuning of the circuit parameters in CDE circuits.
The fractional quantum Hall (FQH) effect at filling factor v = 5/2 has recently come under close scrutiny, as it may possess quasi-particle excitations obeying nonabelian statistics, a property sought for topologically protected quantum operations. Y
et, its microscopic origin remains unidentified, and candidate model wave functions include those with undesirable abelian statistics. Here we report direct measurements of the electron spin polarization of the v = 5/2 FQH state using resistively detected nuclear magnetic resonance (NMR). We find the system to be fully polarized, which unambiguously rules out the most-likely abelian contender and thus lends strong support for the v = 5/2 state being nonabelian. Our measurements reveal an intrinsically different nature of interaction in the first-excited Landau level underlying the physics at v = 5/2.
We investigate quasiparticles in bilayer quantum Hall systems around total filling factor nu =1 by current-pumped and resistively detected NMR. The measured Knight shift reveals that the spin component in the quasiparticle increases continuously with
$Delta_{SAS}$. Combined with results for the pseudospin component obtained by activation gap measurements, this demonstrates that both spin and pseudospin are contained in a quasiparticle at intermediate $Delta_{SAS}$, providing evidence for the existence of the spin-pseudospin intermixed SU(4) skyrmion. Nuclear spin relaxation measurements show that the collective behavior of the SU(4) skyrmion system qualitatively changes with $Delta_{SAS}$.
