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Register a new userTunneling spectroscopy as a probe of fractionalization in 2D magnetic heterostructures
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Added by
Alessandro Principi
Publication date
2020
fields
Physics
and research's language is
English
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In this paper we develop the theory for 2D-to-2D tunneling spectroscopy aided by magnetic or quantum-order excitations, and apply it to the description of van-der-Waals heterostructures of graphene/ultrathin $alpha-{rm RuCl}_3$. We study the behavior of both the differential conductance and the inelastic electron tunneling spectrum (IETS) of these heterostructures. The IETS in particular exhibits features, such as the gap of continuum spinon excitations and Majorana bound states, whose energies scale {it cubicly} with the applied magnetic field. Such scaling, which exists for a relatively wide range of fields, is at odds with the linear one exhibited by conventional magnons and can be used to prove the existence of Kitaev quantum spin liquids.
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The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density-waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept by computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors -- one single-Q and two double-Q phases. Our results open a promising avenue to investigate complex magnetic configurations in itinerant systems via standard scanning tunneling spectroscopy, without requiring spin-resolved capability.
We consider the effect of electron correlations on tunneling from a 2D electron layer in a magnetic field parallel to the layer. A tunneling electron can exchange its momentum with other electrons, which leads to an exponential increase of the tunneling rate compared to the single-electron approximation. Explicit results are obtained for a Wigner crystal. They provide a qualitative and quantitative explanation of the data on electrons on helium. We also discuss tunneling in semiconductor heterostructures.
We demonstrate gate-tunable resonant tunneling and negative differential resistance in the interlayer current-voltage characteristics of rotationally aligned double bilayer graphene heterostructures separated by hexagonal boron-nitride (hBN) dielectric. An analysis of the heterostructure band alignment using individual layer densities, along with experimentally determined layer chemical potentials indicates that the resonance occurs when the energy bands of the two bilayer graphene are aligned. We discuss the tunneling resistance dependence on the interlayer hBN thickness, as well as the resonance width dependence on mobility and rotational alignment.
The electron tunneling is experimentally studied between two-dimensional electron gases (2DEGs) formed in a single-doped-barrier heterostructure in the magnetic fields directed perpendicular to the 2DEGs planes. It is well known that the quantizing magnetic field induces the Coulomb pseudogap suppressing the electron tunneling at Fermi level. In this paper we firstly present the experimental results revealing the pseudogap in the electron tunneling assisted by elastic electron scattering on disorder.
Scanning tunneling spectroscopy was performed on (110)-oriented thin films of Ca-overdoped Y$_{0.95}$Ca$_{0.05}$Ba$_2$Cu$_3$O$_{7-delta}$ at 4.2K, to probe the local evolution of Andreev$-$Saint-James surface states in a c-axis magnetic field. In zero field, we observed conductance spectra with spontaneously-split peaks and spectra with unsplit zero-bias peaks. The former showed enhanced splitting with field, and the latter showed threshold splitting above finite fields. Although both field evolutions can be described in terms of screening and orbital supercurrents, within the framework of $dpm ialpha$ pairing ($d$=$d_{x^2-y^2}$; $alpha$=$d_{xy}$,$s$), the enhanced splitting is consistent with only the $d$ + $ialpha$ state. Our results have direct implications on the stability of broken time-reversal symmetry in cuprate superconductors.
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