Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userArtificial quantum confinement in LAO3/STO heterostructure
59
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Heterostructures of transition metal oxides (TMO) perovskites represent an ideal platform to explore exotic phenomena involving the complex interplay between the spin, charge, orbital and lattice degrees of freedom available in these compounds. At the interface between such materials, this interplay can lead to phenomena that are present in none of the original constituents such as the formation of the interfacial 2D electron system (2DES) discovered at the LAO3/STO3 (LAO/STO) interface. In samples prepared by growing a LAO layer onto a STO substrate, the 2DES is confined in a band bending potential well, whose width is set by the interface charge density and the STO dielectric properties, and determines the electronic band structure. Growing LAO (2 nm) /STO (x nm)/LAO (2 nm) heterostructures on STO substrates allows us to control the extension of the confining potential of the top 2DES via the thickness of the STO layer. In such samples, we explore the dependence of the electronic structure on the width of the confining potential using soft X-ray ARPES combined with ab-initio calculations. The results indicate that varying the thickness of the STO film modifies the quantization of the 3d t2g bands and, interestingly, redistributes the charge between the dxy and dxz/dyz bands.
rate research
Read More
The unusual electronic properties of graphene, which are a direct consequence of its two-dimensional (2D) honeycomb lattice, have attracted a great deal of attention in recent years. Creation of artificial lattices that recreate graphenes honeycomb topology, known as artificial graphene, can facilitate the investigation of graphene-like phenomena, such as the existence of massless Dirac fermions, in a tunable system. In this work, we present the fabrication of artificial graphene in an ultra-high quality GaAs/AlGaAs quantum well, with lattice period as small as 50 nm, the smallest reported so far for this type of system. Electron-beam lithography is used to define an etch mask with honeycomb geometry on the surface of the sample, and different methodologies are compared and discussed. An optimized anisotropic reactive ion etching process is developed to transfer the pattern into the AlGaAs layer and create the artificial graphene. The achievement of such high-resolution artificial graphene should allow the observation for the first time of massless Dirac fermions in an engineered semiconductor.
The quasi two-dimensional Mott insulator $alpha$-RuCl$_3$ is proximate to the sought-after Kitaev quantum spin liquid (QSL). In a layer of $alpha$-RuCl$_3$ on graphene the dominant Kitaev exchange is further enhanced by strain. Recently, quantum oscillation (QO) measurements of such $alpha$-RuCl$_3$ / graphene heterostructures showed an anomalous temperature dependence beyond the standard Lifshitz-Kosevich (LK) description. Here, we develop a theory of anomalous QO in an effective Kitaev-Kondo lattice model in which the itinerant electrons of the graphene layer interact with the correlated magnetic layer via spin interactions. At low temperatures a heavy Fermi liquid emerges such that the neutral Majorana fermion excitations of the Kitaev QSL acquire charge by hybridising with the graphene Dirac band. Using ab-initio calculations to determine the parameters of our low energy model we provide a microscopic theory of anomalous QOs with a non-LK temperature dependence consistent with our measurements. We show how remnants of fractionalized spin excitations can give rise to characteristic signatures in QO experiments.
Heavy fermion systems represent one of the paradigmatic strongly correlated states of matter. They have been used as a platform for investigating exotic behavior ranging from quantum criticality and non-Fermi liquid behavior to unconventional topological superconductivity. Heavy fermions arise from the exchange interaction between localized magnetic moments and conduction electrons that leads to the well-known Kondo effect. In a Kondo lattice, the interaction between the localized moments gives rise to a band with heavy effective mass. This intriguing phenomenology has so far only been realized in compounds containing rare-earth elements with 4f or 5f electrons. Here, we realize a designer van der Waals heterostructure where artificial heavy fermions emerge from the Kondo coupling between a lattice of localized magnetic moments and itinerant electrons in a 1T/1H-TaS$_2$ heterostructure. We study the heterostructure using scanning tunneling microscopy (STM) and spectroscopy (STS) and show that depending on the stacking order of the monolayers, we can either reveal the localized magnetic moments and the associated Kondo effect, or the conduction electrons with a heavy-fermion hybridization gap. Our experiments realize an ultimately tuneable platform for future experiments probing enhanced many-body correlations, dimensional tuning of quantum criticality, and unconventional superconductivity in two-dimensional artificial heavy-fermion systems.
Magnetic monopoles are hypothesised elementary particles connected by Dirac strings that behave like infinitely thin solenoids. Despite decades of searches, free magnetic monopoles and their Dirac strings have eluded experimental detection, although there is substantial evidence for deconfined magnetic monopole quasiparticles in spin ice materials. Here we report the detection of a hierarchy of unequally-spaced magnetic excitations emph{via} high resolution inelastic neutron spectroscopic measurements on the quantum spin ice candidate Pr$_{2}$Sn$_{2}$O$_{7}$. These excitations are well-described by a simple model of monopole pairs bound by a linear potential with an effective tension of 0.642(8) K~$cdot$AA$^{-1}$ at 1.65~K. The success of the linear potential model suggests that these low energy magnetic excitations are direct spectroscopic evidence for the confinement of magnetic monopole quasiparticles in the quantum spin ice candidate Pr$_{2}$Sn$_{2}$O$_{7}$.
As a foundation of condensed matter physics, the normal states of most metals are successfully described by Landau Fermi liquid theory with quasi-particles and their Fermi surfaces (FSs). The FSs sometimes become deformed or gapped at low temperatures owing to quasi-particle interactions, known as FS instabilities. A notable example of a FS deformation that breaks only the rotation symmetry, namely Pomeranchuk instability, is the d-wave FS distortion, which is also proposed as one possible origin of electron nematicity in iron-based superconductors. However, no clear evidence has been made for its existence, mostly owing to the mixture of multiple orders. Here we report an unequivocally observation of the Pomeranchuk nematic order in floating monolayer (ML) FeSe on 1 ML-FeSe/SrTiO3 substrate. By using angle-resolve photoemission spectroscopy, we find remarkably that the dxz and dyz bands are degenerate at the Brillouin zone center (Gamma point), while their splitting is even larger at zone corner (M point), in stark contrast to that in bulk FeSe. Our detailed analysis show that the momentum-dependent nematic order in floating monolayer FeSe is coming from the d-wave Pomeranchuk instability at M point, shedding light on the origin of the ubiquitous nematicity in iron-based superconductors. Our results establish the single-layer high-Tc superconductors as an excellent material platform for investigating emergent quantum physics under complex intertwinement.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
