Kostya S. Novoselov

Bio: Kostya S. Novoselov is an academic researcher from National University of Singapore. The author has contributed to research in topics: Graphene & Bilayer graphene. The author has an hindex of 115, co-authored 392 publications receiving 207392 citations. Previous affiliations of Kostya S. Novoselov include University of Manchester & Russian Academy of Sciences.

Stronger Interlayer Interactions Contribute to Faster Hot Carrier Cooling of Bilayer Graphene under Pressure

Abstract: We perform femtosecond pump-probe spectroscopy to in situ investigate the ultrafast photocarrier dynamics in bilayer graphene and observe an acceleration of energy relaxation under pressure. In combination with in situ Raman spectroscopy and ab initio molecular dynamics simulations, we reveal that interlayer shear and breathing modes have significant contributions to the faster hot-carrier relaxations by coupling with the in-plane vibration modes under pressure. Our work suggests that further understanding the effect of interlayer interaction on the behaviors of electrons and phonons would be critical to tailor the photocarrier dynamic properties of bilayer graphene.

Domain wall dynamics in two-dimensional van der Waals ferromagnets

Abstract: Domain wall motion is in the core of many information technologies ranging from storage [Beach et al., J. Magn. Magn. Mater. 320, 1272–1281 (2008)], processing [Tatara et al., Phys. Rep. 468, 213–301 (2008)], and sensing [Ralph and Stiles, J. Magn. Magn. Mater. 320, 1190–1216 (2008)] up to novel racetrack memory architectures [Parkin et al., Science 320, 190–194 (2008)]. The finding of magnetism in two-dimensional (2D) van der Waals (vdW) materials [Huang et al., Nature 546, 270 (2017); Gong et al., Nature 546, 265–269 (2017); Guguchia et al., Sci. Adv. 4, eaat3672 (2018); Klein et al., Science 360, 1218–1222 (2018)] has offered a new frontier for the exploration and understanding of domain walls at the limit of few atom-thick layers. However, to use 2D vdW magnets for building spintronics nanodevices such as domain-wall based logic [Allwood et al., Science 309, 1688–1692 (2005); Luo et al., Nature 579, 214–218 (2020); Xu et al., Nat. Nanotechnol. 3, 97–100 (2008)], it is required to gain control of their domain wall dynamics by external driving forces such as spin-polarized currents or magnetic fields, which have so far been elusive. Here, we show that electric currents as well as magnetic fields can efficiently move domain walls in the recently discovered 2D vdW magnets CrI3 and CrBr3 at low temperatures and robust down to monolayer. We realize field- and current-driven domain wall motion with velocities up to 1020 m s−1, which are comparable to the state-of-the-art materials for domain-wall based applications [Yang et al., Nat. Nanotechnol. 10, 221–226 (2015); Woo et al., Nat. Mater. 15, 501–506 (2016); Velez et al., Nat. Commun. 10, 4750 (2019); Siddiqui et al., Phys. Rev. Lett. 121, 057701 (2018); Ryu et al., Nat. Nanotechnol. 8, 527–533 (2013)]. Domain walls keep their coherence driven by the spin-transfer torque induced by the current and magnetic fields up to large values of about 12×109 A cm−2 and 5 T, respectively. For larger magnitudes of current or field, a transition to a hydrodynamic spin-liquid regime is observed with the emission of a periodic train of spin-wave solitons with modulational instability [Rabinovich and Trubetskov, Oscillations and Waves: In Linear and Nonlinear Systems, Mathematics and its Applications (Springer Netherlands, 2011)]. The emitted waveform achieves terahertz (THz) frequency in a wide range of fields and current densities, which opens up perspectives for reconfigurable magnonic devices. Moreover, we found that these spin-waves can transport spin angular momentum through the layers over distances as long as 10 μm without losses for the transport of spin information. Our results push the boundary of what is currently known about the dynamics of domain walls in 2D vdW ferromagnets and unveil strategies to design ultrathin, high-speed, and high-frequency spintronic devices.

Relativistic domain-wall dynamics in van der Waals antiferromagnet MnPS3

Abstract: Abstract The discovery of two-dimensional (2D) magnetic van der Waals (vdW) materials has flourished an endeavor for fundamental problems as well as potential applications in computing, sensing and storage technologies. Of particular interest are antiferromagnets, which due to their intrinsic exchange coupling show several advantages in relation to ferromagnets such as robustness against external magnetic perturbations. Here we show that, despite of this cornerstone, the magnetic domains of recently discovered 2D vdW MnPS 3 antiferromagnet can be controlled via magnetic fields and electric currents. We achieve ultrafast domain-wall dynamics with velocities up to ~3000 m s −1 within a relativistic kinematic. Lorentz contraction and emission of spin-waves in the terahertz gap are observed with dependence on the edge termination of the layers. Our results indicate that the implementation of 2D antiferromagnets in real applications can be further controlled through edge engineering which sets functional characteristics for ultrathin device platforms with relativistic features.

Doping Mechanisms in Graphene-MoS2 Hybrids

Abstract: We present a joint theoretical and experimental investigation of charge doping and electronic potential landscapes in hybrid structures composed of graphene and semiconducting single layer MoS2. From first-principles simulations we find electron doping of graphene due to the presence of rhenium impurities in MoS2. Furthermore, we show that MoS2 edges give rise to charge reordering and a potential shift in graphene, which can be controlled through external gate voltages. The interplay of edge and impurity effects allows the use of the graphene-MoS2 hybrid as a photodetector. Spatially resolved photocurrent signals can be used to resolve potential gradients and local doping levels in the sample.

High-Q dark hyperbolic phonon-polaritons in hexagonal boron nitride nanostructures

Abstract: The anisotropy of hexagonal boron nitride (hBN) gives rise to hyperbolic phonon-polaritons (HPhPs), notable for their volumetric frequency-dependent propagation and strong confinement. For frustum (truncated nanocone) structures, theory predicts five, high-order HPhPs, sets, but only one set was observed previously with far-field reflectance and scattering-type scanning near-field optical microscopy. In contrast, the photothermal induced resonance (PTIR) technique has recently permitted sampling of the full HPhP dispersion and observing such elusive predicted modes; however, the mechanism underlying PTIR sensitivity to these weakly-scattering modes, while critical to their understanding, has not yet been clarified. Here, by comparing conventional contact- and newly developed tapping-mode PTIR, we show that the PTIR sensitivity to those weakly-scattering, high-Q (up to ≈280) modes is, contrary to a previous hypothesis, unrelated to the probe operation (contact or tapping) and is instead linked to PTIR ability to detect tip-launched dark, volumetrically-confined polaritons, rather than nanostructure-launched HPhPs modes observed by other techniques. Furthermore, we show that in contrast with plasmons and surface phonon-polaritons, whose Q-factors and optical cross-sections are typically degraded by the proximity of other nanostructures, the high-Q HPhP resonances are preserved even in high-density hBN frustum arrays, which is useful in sensing and quantum emission applications.

The rise of graphene

Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The electronic properties of graphene

Abstract: This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.

Two-dimensional gas of massless Dirac fermions in graphene

Abstract: Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrodinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.