Mansour Shayegan

Bio: Mansour Shayegan is an academic researcher from Princeton University. The author has contributed to research in topics: Quantum Hall effect & Landau quantization. The author has an hindex of 51, co-authored 458 publications receiving 9171 citations. Previous affiliations of Mansour Shayegan include Ludwig Maximilian University of Munich & University of Maryland, College Park.

Counterflow measurements in strongly correlated GaAs hole bilayers: Evidence for electron-hole pairing

Abstract: We study interacting GaAs bilayer hole systems, with very small interlayer tunneling, in a counterflow geometry where equal currents are passed in opposite directions in the two, independently contacted layers. At low temperatures, both the longitudinal and Hall counterflow resistances tend to vanish in the quantum Hall state at total bilayer filling nu=1, demonstrating the pairing of oppositely charged carriers in opposite layers. The counterflow Hall resistance decreases much more strongly than the longitudinal resistances as the temperature is reduced.

Observation of a nu =1/2 fractional quantum Hall state in a double-layer electron system.

Abstract: We report the observation, for the first time, of a fractional quantum Hall state at \ensuremath{ u}=1/2 Landau-level filling in a low disorder, double-layer electron system realized in a 680-\AA{}-wide GaAs/AlGaAs single quantum well. A nearly vanishing diagonal resistance and a Hall resistance quantized at 2h/${\mathit{e}}^{2}$ to within 0.3% are observed at \ensuremath{\simeq}15 T and \ensuremath{\simeq}26 mK. The activated temperature dependence of the diagonal resistance minimum yields a quasiparticle excitation energy gap of 230 mK.

Evidence for two-dimentional quantum Wigner crystal.

Abstract: We report observations of an electric-field threshold conduction and of related ac voltage (broad-band noise) generation in low-disorder two-dimensioanl electron systems in the extreme magnetic quantum limit. We interpret these phenomena as definitive evidence for formation of a pinned quantum Wigner crystal and determine its melting phase diagram from the disappearance of threshold and noise behavior at higher temperatures.

Valley susceptibility of an interacting two-dimensional electron system.

Abstract: We report direct measurements of the valley susceptibility, the change of valley population in response to an applied symmetry-breaking strain, in an AlAs two-dimensional electron system As the two-dimensional density is reduced, the valley susceptibility dramatically increases relative to its band value, reflecting the system's strong electron-electron interaction The increase has a remarkable resemblance to the enhancement of the spin susceptibility and establishes the analogy between the spin and valley degrees of freedom

Structural characterization of ion-implanted graphite

Abstract: Ion implantation of graphite is characterized with respect to lattice damage and the distribution of implanted ions. Both the depth profile of the damage and of the implanted ions are shown to follow the models previously developed for ion-implanted semiconductors. Raman spectroscopy is used in a variety of ways to monitor different aspects of the lattice damage while Auger spectroscopy is used to monitor the implantation profile. Both first- and second-order Raman spectra are reported as a function of ionic mass and ion energy. The surface damage is examined by scanning electron microscopy while the microcrystalline regions in an amorphous background are observed by scanning transmission electron microscopy.

Diamond-like amorphous carbon

Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

Abstract: Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...

Control of valley polarization in monolayer MoS2 by optical helicity

Abstract: Circularly polarized light has been used to confine charge carriers in single-layer molybdenum disulphide entirely to a single energy-band valley, representing full valley polarization.

Berry phase effects on electronic properties

Abstract: Ever since its discovery, the Berry phase has permeated through all branches of physics. Over the last three decades, it was gradually realized that the Berry phase of the electronic wave function can have a profound effect on material properties and is responsible for a spectrum of phenomena, such as ferroelectricity, orbital magnetism, various (quantum/anomalous/spin) Hall effects, and quantum charge pumping. This progress is summarized in a pedagogical manner in this review. We start with a brief summary of necessary background, followed by a detailed discussion of the Berry phase effect in a variety of solid state applications. A common thread of the review is the semiclassical formulation of electron dynamics, which is a versatile tool in the study of electron dynamics in the presence of electromagnetic fields and more general perturbations. Finally, we demonstrate a re-quantization method that converts a semiclassical theory to an effective quantum theory. It is clear that the Berry phase should be added as a basic ingredient to our understanding of basic material properties.