Table of contents


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Editorial

Indian promise p105

doi:10.1038/nphys4038

History and cultural depth are assets that benefit Indian science. But do they also hinder it?


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Thesis

The thermodynamics of Earth p106

Mark Buchanan

doi:10.1038/nphys4031


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Commentary

Animal magic pp107 - 108

Matin Durrani

doi:10.1038/nphys4032

Physics teaching in schools could be transformed by highlighting its role in the animal kingdom.


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News and Views

Quantum optics: Photons taught new tricks pp110 - 111

Ady Stern

doi:10.1038/nphys3948

Experiments of the Aharonov–Bohm type typically involve particles that are charged and interact with a magnetic flux. Photons aren't the former and don't do the latter. Yet, an Aharonov–Bohm ring for photons has just been realized experimentally.

See also: Article by Roushan et al.


Superconductivity: Picky about orientation pp111 - 112

Kamran Behnia

doi:10.1038/nphys3932

Not in all superconductors do Cooper pairs respect the lattice symmetry of the crystal in which they move. Now, work finds such 'picky' Cooper pairs in the presence of strong electron–spin interaction — and gives rise to an entire host of new questions.

See also: Letter by Yonezawa et al.


Spin–orbitronics: Skyrmion Hall effect pp112 - 113

Gong Chen

doi:10.1038/nphys4030

Two independent teams have demonstrated that the current-driven motion of a topological charge experiences a transverse deflection analogous to charged particles in the classical Hall effect.

See also: Article by Jiang et al. | Article by Litzius et al.


Organic semiconductors: Dynamic duos pp114 - 115

Michael R. Wasielewski

doi:10.1038/nphys3943

The discovery of intermediate high-spin multiexciton states with surprisingly long lifetimes provides new opportunities for engineering singlet fission, which may also provide an intriguing route to quantum information and spintronic applications.

See also: Article by Weiss et al. | Article by Tayebjee et al.


Multiferroics: Making a point of control pp115 - 116

Sergei V. Kalinin

doi:10.1038/nphys4033

The coexistence of spin order and disorder at a critical point in the phase diagram of multiferroic materials may be exploited to locally control magnetoelectric coupling — as is now shown for doped BiFeO3 by means of scanning probe microscopy.

See also: Article by Jang et al.


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Letters

Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO4 pp117 - 122

Joseph A. M. Paddison, Marcus Daum, Zhiling Dun, Georg Ehlers, Yaohua Liu, Matthew B. Stone, Haidong Zhou & Martin Mourigal

doi:10.1038/nphys3971

A detailed and systematic neutron-scattering study uncovers a continuum of magnetic excitations down to 0.06K in the triangular quantum magnet YbMgGaO4 — an observation consistent with quantum spin liquid behaviour.


Thermodynamic evidence for nematic superconductivity in CuxBi2Se3 pp123 - 126

Shingo Yonezawa, Kengo Tajiri, Suguru Nakata, Yuki Nagai, Zhiwei Wang, Kouji Segawa, Yoichi Ando & Yoshiteru Maeno

doi:10.1038/nphys3907

In a nematic liquid crystal, electron orbitals align themselves along one axis, as rods. Thermodynamic observations of such rod-like alignments in CuxBi2Se3 provide evidence for a nematic superconductor.

See also: News and Views by Behnia


Interlayer electron–phonon coupling in WSe2/hBN heterostructures pp127 - 131

Chenhao Jin, Jonghwan Kim, Joonki Suh, Zhiwen Shi, Bin Chen, Xi Fan, Matthew Kam, Kenji Watanabe, Takashi Taniguchi, Sefaattin Tongay, Alex Zettl, Junqiao Wu & Feng Wang

doi:10.1038/nphys3928

The emergence of optically silent phonons show that strong interlayer electron–phonon coupling can arise in van der Waals heterostructures, with the vibrational modes in one layer coupling to the electronic states in a neighbouring layer.


An effective magnetic field from optically driven phonons pp132 - 136

T. F. Nova, A. Cartella, A. Cantaluppi, M. Först, D. Bossini, R. V. Mikhaylovskiy, A. V. Kimel, R. Merlin & A. Cavalleri

doi:10.1038/nphys3925

Light can be used to directly excite phonon modes in condensed matter. Simultaneously exciting several modes in an antiferromagnetic rare-earth orthoferrite drives behaviour that mimics the application of a magnetic field.


Nonergodic diffusion of single atoms in a periodic potential pp137 - 141

Farina Kindermann, Andreas Dechant, Michael Hohmann, Tobias Lausch, Daniel Mayer, Felix Schmidt, Eric Lutz & Artur Widera

doi:10.1038/nphys3911

Drawing microscopic information out of the diffusive dynamics of complex processes often requires an assumption of ergodicity. Precision experiments on a single atom in a periodic potential suggest that this may be too simplistic in many cases.


Critical slowing down in purely elastic ‘snap-through’ instabilities pp142 - 145

Michael Gomez, Derek E. Moulton & Dominic Vella

doi:10.1038/nphys3915

Critical phenomena are well understood in a wide range of physical systems. The dynamics of snap-through instabilities, a widespread phenomenon in their own right, are now shown to display critical scaling properties.


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Articles

Chiral ground-state currents of interacting photons in a synthetic magnetic field pp146 - 151

P. Roushan, C. Neill, A. Megrant, Y. Chen, R. Babbush, R. Barends, B. Campbell, Z. Chen, B. Chiaro, A. Dunsworth, A. Fowler, E. Jeffrey, J. Kelly, E. Lucero, J. Mutus, P. J. J. OMalley, M. Neeley, C. Quintana, D. Sank, A. Vainsencher, J. Wenner, T. White, E. Kapit, H. Neven & J. Martinis

doi:10.1038/nphys3930

Superconducting circuits, coupled to form a ring in which a photonic excitation can circulate between sites, are established as a versatile platform for studying the interplay of strong particle interactions and external fields.

See also: News and Views by Stern


A proton density bubble in the doubly magic 34Si nucleus pp152 - 156

A. Mutschler, A. Lemasson, O. Sorlin, D. Bazin, C. Borcea, R. Borcea, Z. Dombrádi, J.-P. Ebran, A. Gade, H. Iwasaki, E. Khan, A. Lepailleur, F. Recchia, T. Roger, F. Rotaru, D. Sohler, M. Stanoiu, S. R. Stroberg, J. A. Tostevin, M. Vandebrouck, D. Weisshaar & K. Wimmer

doi:10.1038/nphys3916

The central densities of protons and neutrons in stable atomic nuclei are saturated. More exotic nuclei — with imbalanced proton and neutron numbers — may have depleted central densities. Experiments now suggest such depletion for the 34Si nucleus.


Spiral spin-liquid and the emergence of a vortex-like state in MnSc2S4 pp157 - 161

Shang Gao, Oksana Zaharko, Vladimir Tsurkan, Yixi Su, Jonathan S. White, Gregory S. Tucker, Bertrand Roessli, Frederic Bourdarot, Romain Sibille, Dmitry Chernyshov, Tom Fennell, Alois Loidl & Christian Rüegg

doi:10.1038/nphys3914

A detailed and systematic neutron scattering study uncovers a spiral spin-liquid state in the quantum magnet MnSc2S4.


Direct observation of the skyrmion Hall effect pp162 - 169

Wanjun Jiang, Xichao Zhang, Guoqiang Yu, Wei Zhang, Xiao Wang, M. Benjamin Jungfleisch, John E. Pearson, Xuemei Cheng, Olle Heinonen, Kang L. Wang, Yan Zhou, Axel Hoffmann & Suzanne G. E. te Velthuis

doi:10.1038/nphys3883

Experiments show that when driven by electric currents, magnetic skyrmions experience transverse motion due to their topological charge — similar to the conventional Hall effect experienced by charged particles in a perpendicular magnetic field.

See also: News and Views by Chen


Skyrmion Hall effect revealed by direct time-resolved X-ray microscopy pp170 - 175

Kai Litzius, Ivan Lemesh, Benjamin Krüger, Pedram Bassirian, Lucas Caretta, Kornel Richter, Felix Büttner, Koji Sato, Oleg A. Tretiakov, Johannes Förster, Robert M. Reeve, Markus Weigand, Iuliia Bykova, Hermann Stoll, Gisela Schütz, Geoffrey S. D. Beach & Mathias Kläui

doi:10.1038/nphys4000

Experiments show that when driven by electric currents, magnetic skyrmions experience transverse motion due to their topological charge — similar to the conventional Hall effect experienced by charged particles in a perpendicular magnetic field.

See also: News and Views by Chen


Strongly exchange-coupled triplet pairs in an organic semiconductor pp176 - 181

Leah R. Weiss, Sam L. Bayliss, Felix Kraffert, Karl J. Thorley, John E. Anthony, Robert Bittl, Richard H. Friend, Akshay Rao, Neil C. Greenham & Jan Behrends

doi:10.1038/nphys3908

Experiments show how molecular structure affects the interaction and dynamics of the triplet exciton pairs produced when an excited singlet exciton decays via singlet fission — a process that could be harnessed for optoelectronic applications.

See also: News and Views by Wasielewski


Quintet multiexciton dynamics in singlet fission pp182 - 188

Murad J. Y. Tayebjee, Samuel N. Sanders, Elango Kumarasamy, Luis M. Campos, Matthew Y. Sfeir & Dane R. McCamey

doi:10.1038/nphys3909

Experiments show how molecular structure affects the interaction and dynamics of the triplet exciton pairs produced when an excited singlet exciton decays via singlet fission — a process that could be harnessed for optoelectronic applications.

See also: News and Views by Wasielewski


Electric-field-induced spin disorder-to-order transition near a multiferroic triple phase point pp189 - 196

Byung-Kweon Jang, Jin Hong Lee, Kanghyun Chu, Pankaj Sharma, Gi-Yeop Kim, Kyung-Tae Ko, Kwang-Eun Kim, Yong-Jin Kim, Kyungrok Kang, Han-Byul Jang, Hoyoung Jang, Min Hwa Jung, Kyung Song, Tae Yeong Koo, Si-Young Choi, Jan Seidel, Yoon Hee Jeong, Hendrik Ohldag, Jun-Sik Lee & Chan-Ho Yang

doi:10.1038/nphys3902

The triple point is a well-known feature on pressure–temperature phase diagrams. A multiferroic triple point is now reported for La-doped BiFeO3; La concentration and temperature are the phase variables and the phases display different spin (dis)order.

See also: News and Views by Kalinin


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Measure for Measure

Metrology in 2019 p198

Klaus von Klitzing

doi:10.1038/nphys4029

Klaus von Klitzing tells the story of the quantum Hall effect's impact on metrology.


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