research highlights

TOPOLOGICAL INSULATORS the symmetries related to the spectral TOPOLOGICAL SUPERCONDUCTIVITY Lindblad’s tenfold way features of the Hamiltonian to those of Majorana transparency Phys. Rev. Lett. (in the press); preprint at https:// the superoperator in a Lindblad equation. Science 367, 64–67 (2020) arxiv.org/abs/1908.08834 Topological states can then be classified into ten non-Hermitian symmetry classes In 2017, experimental evidence for one- Number of distinct knots labelled by these symmetries — in analogy dimensional chiral Majorana fermions was 1 234567 with the isolated system. YL shown in a topological insulator device, but 0 has been difficult to replicate. Now, Morteza https://doi.org/10.1038/s41567-020-0805-0 1 Kayyalha and co-workers have completed a 2 comprehensive study to ascertain why. 3 ORGANIC POLARITONS It turns out that the interface between Step into the blue the topological insulator and the 4 Commun. Phys. 3, 18 (2020) superconducting layer is crucial. The authors measured devices where the transport 5 High conductivity, mechanical flexibility signatures and interface characteristics

Number of crossings and bandgaps in the visible frequency could be extracted at the same time. The 6 range make organic semiconductors transport signatures previously associated choice materials for optoelectronic devices. with the chiral Majorana states existed 7 But their charge carrier behaviour is whenever there was a transparent interface surprisingly different from that of their between the topological insulator and the inorganic counterparts; many observations superconductor. This strong coupling at the Credit: Universal Images Group North America interface allows the superconductor to act as LLC / Alamy Stock Photo remain unexplained. For example, when exciton polaritons in organic microcavities a short, modifying the transport properties form a Bose–Einstein condensate — a state from the theoretical predictions. In an isolated system, symmetries are fully related to polariton lasing — a step-like This doesn’t rule out the possibility characterized by the system’s Hamiltonian, blueshift occurs at the threshold. Through that the old experiments observed chiral and play an important role in determining a series of experiments Timur Yagafarov Majorana modes, but it certainly shows that the topology of its quantum states. and colleagues have now pin pointed the more evidence is needed. DA Specifically, three non-spatial symmetries of origin of this blueshift. https://doi.org/10.1038/s41567-020-0801-4 the Hamiltonian — time reversal, particle– Having established a set of possible hole and chiral symmetry — sort topological causes, the team systematically ruled out insulators into ten discrete symmetry classes contributions from the Kerr effect and ECONOMIC COMPLEXITY with distinct spectral properties. Now, frequency pulling and ultimately identified Concentrated cities Simon Lieu and co-workers have asked if a an interplay of saturation effects and Nat. Hum. Behav. https://doi.org/djtz (2020) similar classification can be applied to open intermolecular energy migration as the quantum systems. origin of the blueshift. They further derived A graduate with a specific expertise, such as Unlike isolated systems, the quantum an analytical expression to evaluate the flow cytometry, could move to a city, where state of an open system is described by a relative contributions of all the effects that they will likely find more job opportunities density matrix whose evolution is governed play into the blueshift, which could help in, say, biotechnology labs. While this choice by the Lindblad equation. Therefore, the us understand non-linear light emission in might appear obvious, the reasons for the topological signatures of these states are organic cavities. NM disproportionate concentration of economic given by the Lindblad spectrum. Lieu and activity in urban centres are less clear. Pierre- co-workers found a unique way to extend https://doi.org/10.1038/s41567-020-0803-2 Alexandre Balland and colleagues have now found that such spatial concentration increases with the complexity of activities. NUCELAR PHYSICS An activity is considered complex when it requires a large team of highly-skilled experts Phys. Rev. C 101, 011301(R) (2020) An isomeric isotope with complementary expertise. The authors analysed data on patents, occupations and Previous studies of nobelium-250 observed two different fission decay times. Based on industries in the United States; they used the relative decay cross sections, the longer lifetime was assigned to an isomeric state proxies for knowledge complexity — such and the shorter to the ground state. But whether the longer lifetime is a result of direct as the size of a team responsible for a patent fission of the isomeric state or of a chain of electromagnetic transitions to the ground — and found that spatial concentration state was an open question. increased with the number of inventors. Jinesh Kallunkathariyil and colleagues performed decay spectroscopy of the 250 The connection between economic activity isomeric state in No, revealing that its decay to the ground state proceeds via complexity and urban concentration could electromagnetic transitions. To distinguish between the two decay scenarios, the team explain the spatial inequality between small conducted a pulse-shape analysis to search for low-energy electrons and gamma-ray and large cities. ED signals, which accompany electromagnetic transitions. This work will inform nuclear structure models, and our understanding of the borders of the island of stability of https://doi.org/10.1038/s41567-020-0802-3 superheavy elements. SR David Abergel, Elizaveta Dubrovina, Yun Li, https://doi.org/10.1038/s41567-020-0804-1 Nina Meinzer and Stefanie Reichert

Nature Physics | VOL 16 | February 2020 | 123 | www.nature.com/naturephysics 123