Sonny Rhim

Author(s): Avik Ghosh

A semimetal nanowire with topological properties carries spin-polarized electron currents that can be switched with a voltage.

[Physics 13, 38] Published Mon Mar 16, 2020

In the fundamental laws of physics, gauge fields mediate the interaction between charged particles. An example is the quantum theory of electrons interacting with the electromagnetic field, based on U(1) gauge symmetry. Solving such gauge theories is in general a hard problem for classical computational techniques. Although quantum computers suggest a way forward, large-scale digital quantum devices for complex simulations are difficult to build. We propose a scalable analog quantum simulator of a U(1) gauge theory in one spatial dimension. Using interspecies spin-changing collisions in an atomic mixture, we achieve gauge-invariant interactions between matter and gauge fields with spin- and species-independent trapping potentials. We experimentally realize the elementary building block as a key step toward a platform for quantum simulations of continuous gauge theories.

The coupling between spin and charge degrees of freedom in a crystal imparts strong optical signatures on scattered electromagnetic waves. This has led to magneto-optical effects with a host of applications, from the sensitive detection of local magnetic order to optical modulation and data storage technologies. Here, we demonstrate a new magneto-optical effect, namely, the tuning of inelastically scattered light through symmetry control in atomically thin chromium triiodide (CrI$_3$). In monolayers, we found an extraordinarily large magneto-optical Raman effect from an A$_{1g}$ phonon mode due to the emergence of ferromagnetic order. The linearly polarized, inelastically scattered light rotates by ~40$^o$, more than two orders of magnitude larger than the rotation from MOKE under the same experimental conditions. In CrI$_3$ bilayers, we show that the same A$_{1g}$ phonon mode becomes Davydov-split into two modes of opposite parity, exhibiting divergent selection rules that depend on inversion symmetry and the underlying magnetic order. By switching between the antiferromagnetic states and the fully spin-polarized states with applied magnetic and electric fields, we demonstrate the magnetoelectrical control over their selection rules. Our work underscores the unique opportunities provided by 2D magnets for controlling the combined time-reversal and inversion symmetries to manipulate Raman optical selection rules and for exploring emergent magneto-optical effects and spin-phonon coupled physics.

Author(s): Igor S. Burmistrov, Moshe Goldstein, Mordecai Kot, Vladislav D. Kurilovich, and Pavel D. Kurilovich

Hydrodynamic charge transport is at the center of recent research efforts. Of particular interest is the nondissipative Hall viscosity, which conveys topological information in clean gapped systems. The prevalence of disorder in the real world calls for a study of its effect on viscosity. Here we ad...

[Phys. Rev. Lett. 123, 026804] Published Tue Jul 09, 2019

Author(s): Martin Hennecke, Ilie Radu, Radu Abrudan, Torsten Kachel, Karsten Holldack, Rolf Mitzner, Arata Tsukamoto, and Stefan Eisebitt

One of the key processes setting the speed of the ultrafast magnetization phenomena is the angular momentum transfer from and into the spin system. However, the way the angular momentum flows during ultrafast demagnetization and magnetization switching phenomena remains elusive so far. We report on ...

[Phys. Rev. Lett. 122, 157202] Published Fri Apr 19, 2019

Author(s): Seulong Kim and Kihong Kim

We study Anderson localization of massless two-dimensional Dirac electrons in random one-dimensional scalar and vector potentials theoretically for two different cases, in which the scalar and vector potentials are either uncorrelated or correlated. From the Dirac equation, we deduce the effective w...

[Phys. Rev. B 99, 014205] Published Thu Jan 17, 2019

Author(s): Hikaru Watanabe and Youichi Yanase

The multipole moment is an established concept of electrons in solids. Entanglement of spin, orbital, and sublattice degrees of freedom is described by the multipole moment, and spontaneous multipole order is a ubiquitous phenomenon in strongly correlated electron systems. In this paper, we present ...

[Phys. Rev. B 98, 245129] Published Wed Dec 19, 2018

Charge trapping and super-Poissonian noise centres in a cuprate superconductor

Charge trapping and super-Poissonian noise centres in a cuprate superconductor, Published online: 08 October 2018; doi:10.1038/s41567-018-0300-z

A new noise spectroscopy technique shows that charges localized as polarons trapped at impurity sites mediate perpendicular ‘c-axis’ electronic transport in cuprate superconductors.

Author(s): A. J. Grutter, S. M. Disseler, E. J. Moon, D. A. Gilbert, E. Arenholz, A. Suter, T. Prokscha, Z. Salman, B. J. Kirby, and S. J. May

We demonstrate emergent antiferromagnetic interactions in strained thin films of the mixed valence manganite (Eu,Sr)MnO3. Although the composition studied, Eu0.7Sr0.3MnO3, will nominally yield a ferromagnetic phase in the bulk, we observe significant suppression of the saturation magnetization in fi...

[Phys. Rev. Materials 2, 094402] Published Tue Sep 04, 2018

Author(s): Marco Perini, Sebastian Meyer, Bertrand Dupé, Stephan von Malottki, André Kubetzka, Kirsten von Bergmann, Roland Wiesendanger, and Stefan Heinze

We use spin-polarized scanning tunneling microscopy and density functional theory (DFT) to study domain walls (DWs) and the Dzyaloshinskii-Moriya interaction (DMI) in epitaxial films of Co/Ir(111) and Pt/Co/Ir(111). Our measurements reveal DWs with fixed rotational sense for one monolayer of Co on I...

[Phys. Rev. B 97, 184425] Published Thu May 24, 2018

We perform charge density functional theory plus $U$ calculation of LaMnO$_3$. While all the previous calculations were based on spin density functionals, our result and analysis show that the use of spin-unpolarized charge-only density is crucial to correctly describe the phase diagram, electronic structure and magnetic property. Using magnetic force linear response calculation, a long-standing issue is clarified regarding the second neighbor out-of-plane interaction strength. We also estimate the orbital-resolved magnetic couplings. Remarkably, the inter-orbital $e_g$-$t_{2g}$ interaction is quite significant due to the Jahn-Teller distortion and orbital ordering.

Amorphous martensite in β-Ti alloys

Amorphous martensite in β-Ti alloys, Published online: 06 February 2018; doi:10.1038/s41467-018-02961-2

Displacive martensitic transformations through lattice distortion usually involve a change from one crystal structure to another. Here however, the authors “melt” metastable Ti alloys during cooling and show that a martensitic transformation can lead to the formation of an intragranular amorphous phase.

Author(s): M. Matsuo, Y. Ohnuma, T. Kato, and S. Maekawa

We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck effect and spin pumping in a normal-metal–(NM-)ferromagnet(FM) bilayer system. Starting with a simple ferromagnet-insulator–(FI-)NM interface model with both spin-conserving and non-spin-conserving proces...

[Phys. Rev. Lett. 120, 037201] Published Thu Jan 18, 2018

Author(s): Peayush Choubey, Andreas Kreisel, T. Berlijn, Brian M. Andersen, and P. J. Hirschfeld

We consider the problem of local tunneling into cuprate superconductors, combining model-based calculations for the superconducting order parameter with wave function information obtained from first-principles electronic structure. For some time it has been proposed that scanning tunneling microscop...

[Phys. Rev. B 96, 174523] Published Tue Nov 28, 2017

The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings can lead to spectacular electronic properties such as large mobilities accompanied by extremely high magnetoresistance. In particular, two closely neighbouring Weyl points of the same chirality are protected from annihilation by structural distortions or defects, thereby significantly reducing the scattering probability between them. Here we present the electronic properties of the transition metal diphosphides, WP2 and MoP2, that are type-II Weyl semimetals with robust Weyl points. We present transport and angle resolved photoemission spectroscopy measurements, and first principles calculations. Our single crystals of WP2 display an extremely low residual low-temperature resistivity of 3 nohm-cm accompanied by an enormous and highly anisotropic magnetoresistance above 200 million % at 63 T and 2.5 K. These properties are likely a consequence of the novel Weyl fermions expressed in this compound. We observe a large suppression of charge carrier backscattering in WP2 from transport measurements.

Author(s): Xianqing Lin and Jun Ni

First-principles calculations have been performed to study the evolution of the inverted bands and the topological phase diagrams of monoclinic transition-metal dichalcogenide monolayers (1T′−MX2 with M=Mo, W and X=S, Se, Te) under strain. We find that the band topology undergoes a nontrivial to tri...

[Phys. Rev. B 95, 245436] Published Fri Jun 30, 2017

Author(s): M. Miniaci, A. S. Gliozzi, B. Morvan, A. Krushynska, F. Bosia, M. Scalerandi, and N. M. Pugno

The appearance of nonlinear effects in elastic wave propagation is one of the most reliable and sensitive indicators of the onset of material damage. However, these effects are usually very small and can be detected only using cumbersome digital signal processing techniques. Here, we propose and exp…

[Phys. Rev. Lett. 118, 214301] Published Fri May 26, 2017

Author(s): Jamileh Beik Mohammadi, Joshua Michael Jones, Soumalya Paul, Behrouz Khodadadi, Claudia K. A. Mewes, Tim Mewes, and Christian Kaiser

The magnetization dynamics of exchange-biased IrMn/CoFe bilayers have been investigated using broadband and in-plane angle-dependent ferromagnetic resonance spectroscopy. The interface energy of the exchange bias effect in these bilayers exceeds values previously reported for metallic antiferromagne…

[Phys. Rev. B 95, 064414] Published Wed Feb 15, 2017

A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other. Electrostatic stabilization of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solvents with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute–solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute–solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.

Nature 542 328 doi: 10.1038/nature21041

Nature 519 421 doi: 10.1038/519421a