Volume 556 Issue 7699



News Features

News & Views

Forests in flux as climate varies p.35

How do changes in climate affect forest ecosystems? A study of temperate forests in the United States has assessed alterations in biomass and tree-species composition across a 20-year period of climate variability.

doi: 10.1038/d41586-018-02858-6

Novel electronic states seen in graphene p.37

A simple system made from two sheets of graphene has been converted from an insulator to a superconductor. The finding holds promise for opening up studies of an unconventional form of superconductivity.

doi: 10.1038/d41586-018-02660-4

Two-pore channels open up p.38

Two-pore channels span the membranes of acidic organelles inside cells. A structural and functional analysis reveals secrets about how these channels open to allow ions to pass across the membrane.

doi: 10.1038/d41586-018-02783-8

Bacterial persister cells tackled p.40

Chronic infections can be hard to treat because slow-growing bacteria known as persister cells are usually unharmed by antibiotics. The identification of molecules that target such cells might provide a solution.

doi: 10.1038/d41586-018-03440-w



Room-temperature nine-µm-wavelength photodetectors and GHz-frequency heterodyne receivers p.85

Room-temperature operation is essential for any optoelectronics technology that aims to provide low-cost, compact systems for widespread applications. A recent technological advance in this direction is bolometric detection for thermal imaging, which has achieved relatively high sensitivity and video rates (about 60 hertz) at room temperature. However, owing to thermally induced dark current, room-temperature operation is still a great challenge for semiconductor photodetectors targeting the wavelength band between 8 and 12 micrometres, and all relevant applications, such as imaging, environmental remote sensing and laser-based free-space communication, have been realized at low temperatures. For these devices, high sensitivity and high speed have never been compatible with high-temperature operation. Here we show that a long-wavelength (nine micrometres) infrared quantum-well photodetector fabricated from a metamaterial made of sub-wavelength metallic resonators exhibits strongly enhanced performance with respect to the state of the art up to room temperature. This occurs because the photonic collection area of each resonator is much larger than its electrical area, thus substantially reducing the dark current of the device. Furthermore, we show that our photonic architecture overcomes intrinsic limitations of the material, such as the drop of the electronic drift velocity with temperature, which constrains conventional geometries at cryogenic operation. Finally, the reduced physical area of the device and its increased responsivity allow us to take advantage of the intrinsic high-frequency response of the quantum detector at room temperature. By mixing the frequencies of two quantum-cascade lasers on the detector, which acts as a heterodyne receiver, we have measured a high-frequency signal, above four gigahertz (GHz). Therefore, these wide-band uncooled detectors could benefit technologies such as high-speed (gigabits per second) multichannel coherent data transfer and high-precision molecular spectroscopy.

doi: 10.1038/nature25790