Nature (published 20211104) A week-long thesis guide

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nature, 4 november 2021, volume 599 issue 7883

Nature November 4, 2021, Vol. 599, No. 7883

Materials Science material science

reconstruction of bloch wavefunctions of holes in a semiconductor

Reconstruction of the Bloch wave function in semiconductor holes

▲ 作者：j. b. costello, s. d. o’hara, q. wu, d. c. valovcin, l. n. pfeiffer, k. w. west & m. s. sherwin

▲ Link:

https://www.nature.com/articles/s41586-021-03940-2

▲ Abstract

In higher-order sideband generation, electrons and holes generated by nir-infrared lasers in semiconductors are accelerated to high kinetic energy by strong terahertz fields and recoiled before scattering to emit near-infrared sidebands.

Here, we measure sideband polarization experimentally and introduce a theory that relates these polarizations to quantum interference between different recall paths, reconstructing the Bloch wave function of two types of holes in gallium arsenide at wavelengths longer than the atomic spacing. These Bloch wave functions are closely visible on the surface of the sphere. In principle, any direct-gap semiconductor or insulator can observe the generation of high-order sidebands.

Therefore, we expect that the methods presented here can be used to reconstruct the low-energy Bloch wave function in these materials, thus gaining important insights into the origin and engineering of the electronic and optical properties of condensed matter.

▲ abstract

in high-order sideband generation, electrons and holes generated in semiconductors by a near-infrared laser are accelerated to a high kinetic energy by a strong terahertz field, and recollide to emit near-infrared sidebands before they are scattered. here we reconstruct the bloch wavefunctions of two types of hole in gallium arsenide at wavelengths much longer than the spacing between atoms by experimentally measuring sideband polarizations and introducing an elegant theory that ties those polarizations to quantum interference between different recollision pathways. these bloch wavefunctions are compactly visualized on the surface of a sphere. high-order sideband generation can, in principle, be observed from any direct-gap semiconductor or insulator. we thus expect that the method introduced here can be used to reconstruct low-energy bloch wavefunctions in many of these materials, enabling important insights into the origin and engineering of the electronic and optical properties of condensed matter.

percolation transitions in compressed sio2 glasses

Osmotic transformation in compressed silica glass

▲ 作者:a. hasmy, s. ispas & b. hehlen

https://www.nature.com/articles/s41586-021-03918-0

Here, we report de novo calculations of compressed silica glass, indicating a series of osmotic transitions in structural changes from low to high density amorphous structures.

When the pressure increases to 82 gpa, at critical pressure, a series of long-range ("infinite") seepage clusters consisting of tetrahedrons, pentahedra, and final octahedrons shared by angles or edges emerge, replacing the previous "phases" of low-fold coordination polyhedra and low connectivity. This mechanism provides a natural explanation for well-known mechanical anomalies of around 3 gpa and structural irreversibility in excess of 10 gpa.

Some of the amorphous structures that have been found are similar to the recently reported corticolithic iv and v crystals, highlighting the main role of the si5 pentahedra-based polycrystalline in the process of glassy silica densification. Our findings suggest that seepage theory provides a solid framework for understanding the properties and pathways of amorphous-amorphous phase transitions and opens up new avenues for predicting unraveled amorphous solids and associated liquid phases.

here we report ab initio-based calculations of compressed silica (sio2) glasses, showing that the structural changes from low- to high-density amorphous structures occur through a sequence of percolation transitions. when the pressure is increased to 82 gpa, a series of long-range (‘infinite’) percolating clusters composed of corner- or edge-shared tetrahedra, pentahedra and eventually octahedra emerge at critical pressures and replace the previous ‘phase’ of lower-fold coordinated polyhedra and lower connectivity. this mechanism provides a natural explanation for the well-known mechanical anomaly around 3 gpa, as well as the structural irreversibility beyond 10 gpa, among other features. some of the amorphous structures that have been discovered mimic those of coesite iv and v crystals reported recently, highlighting the major role of sio5 pentahedron-based polyamorphs in the densification process of vitreous silica. our results demonstrate that percolation theory provides a robust framework to understand the nature and pathway of amorphous–amorphous transformations and open a new avenue to predict unravelled amorphous solid states and related liquid phases.

transition metal-catalysed molecular n-doping of organic semiconductors

Transition metal catalyzed n-type doping of organic semiconductor molecules

▲ 作者:han guo, chi-yuan yang, xianhe zhang, alessandro motta, kui feng, yu xia, yongqiang shi, ziang wu, kun yang, jianhua chen, qiaogan liao, yumin tang, huiliang sun, han young woo, simone fabiano, antonio facchetti & xugang guo

https://www.nature.com/articles/s41586-021-03942-0

Here, we demonstrate the general concept of catalyzing n-type doping using an organic semiconductor that uses air-stabilized precursor molecule doping.

By evaluating experimental and theoretical evidence, the incorporation of transition metals (e.g., pt, au, pd) as vapor-deposited nanoparticles or solution-treatable organometal complexes (e.g., pd2(dba)3) was significantly improved in a short doping time, with significantly higher η values and high conductivity (greater than 100 s cm−1; ref）。

This method has technical significance for achieving improved semiconductor devices, and provides a broad exploration space for catalysts, molecular dopants and semiconductor ternary systems, thus opening up new opportunities for the research and application of n-type doping.

here we show a general concept of catalysed n-doping of organic semiconductors using air-stable precursor-type molecular dopants. incorporation of a transition metal (for example, pt, au, pd) as vapour-deposited nanoparticles or solution-processable organometallic complexes (for example, pd2(dba)3) catalyses the reaction, as assessed by experimental and theoretical evidence, enabling greatly increased η in a much shorter doping time and high electrical conductivities (above 100 s cm−1; ref.). this methodology has technological implications for realizing improved semiconductor devices and offers a broad exploration space of ternary systems comprising catalysts, molecular dopants and semiconductors, thus opening new opportunities in n-doping research and applications.

Information technology information technology

experimental relativistic zero-knowledge proofs

Experimental relativity zero-knowledge proof

▲ 作者:pouriya alikhani, nicolas brunner, claude crépeau, sébastien designolle, raphaël houlmann, weixu shi, nan yang & hugo zbinden

https://www.nature.com/articles/s41586-021-03998-y

In today's information age, confidentiality is a major challenge. The development of computer science offers an elegant solution through the concept of zero-knowledge proofs: the prover can convince the verifier of the validity of a statement without the need to elaborate on the proof at all.

In this study, we report an experimental implementation of this zero-knowledge protocol involving two separate validator-validator pairs. Security is implemented through the physical principles of special relativity and does not require computational assumptions (such as the existence of one-way functions).

Our implementation relies entirely on off-the-shelf equipment, with both long (≥400 meters) and short (60 meters) distances taking effect in less than 1 second. This proves the real potential of multi-verifier zero-knowledge protocols, promising for identity tasks and blockchain applications such as cryptocurrencies or smart contracts.

protecting secrets is a key challenge in our contemporary information-based era. developments in computer science provide an elegant solution via the concept of zero-knowledge proofs: a prover can convince a verifier of the validity of a certain statement without facilitating the elaboration of a proof at all. in this work, we report the experimental realization of such a zero-knowledge protocol involving two separated verifier–prover pairs. security is enforced via the physical principle of special relativity, and no computational assumption (such as the existence of one-way functions) is required. our implementation exclusively relies on off-the-shelf equipment and works at both short (60 m) and long distances (≥400 m) in about one second. this demonstrates the practical potential of multi-prover zero-knowledge protocols, promising for identification tasks and blockchain applications such as cryptocurrencies or smart contracts.

Geoscience for earth sciences

episodic deluges in simulated hothouse climates

Simulate occasional flooding in greenhouse climates

▲ 作者：jacob t. seeley & robin d. wordsworth

https://www.nature.com/articles/s41586-021-03919-z

Previous work has shown that this can lead to significant changes in temperature inversion and cloud cover, but previous greenhouse regime models have not directly addressed turbulent air motion and cloud cover at the convective scale, thus leaving many greenhouse radiation heating questions unanswered.

Here, our simulations definitively address the convection problem and find that low tropospheric radiative heating in greenhouse climates causes the hydrological cycle to change from a quasi-stable state to a "flaccid oscillation" state – a state in which short, intense precipitation occurs, with multiple days of dry spells.

The transition to an oscillating state is accompanied by a strong increase in local precipitation fluxes, a substantial increase in cloud cover, and a transient positive (unstable) climate feedback parameter. Our findings suggest that greenhouse climates may have a new form of "temporary" convective self-organization and have implications for both cloud cover and erosion processes.

previous work has suggested that this could lead to temperature inversions and substantial changes in cloud cover, but no previous modelling of the hothouse regime has resolved convective-scale turbulent air motions and cloud cover directly, thus leaving many questions about hothouse radiative heating unanswered. here we conduct simulations that explicitly resolve convection and find that lower-tropospheric radiative heating in hothouse climates causes the hydrologic cycle to shift from a quasi-steady regime to a ‘relaxation oscillator’ regime, in which precipitation occurs in short and intense outbursts separated by multi-day dry spells. the transition to the oscillatory regime is accompanied by strongly enhanced local precipitation fluxes, a substantial increase in cloud cover, and a transiently positive (unstable) climate feedback parameter. our results indicate that hothouse climates may feature a novel form of ‘temporal’ convective self-organization, with implications for both cloud coverage and erosion processes.

Economics economics

carbon implications of marginal oils from market-derived demand shocks

Marginal oil impact on carbon from market demand shocks

▲ 作者：mohammad s. masnadi, giacomo benini, hassan m. el-houjeiri, alice milivinti, james e. anderson, timothy j. wallington, robert de kleine, valerio dotti, patrick jochem & adam r. brandt

https://www.nature.com/articles/s41586-021-03932-2

We explore the life-cycle greenhouse gas emissions impacts of marginal crude oil sources, identifying the upstream carbon intensity (CI) of producers most sensitive to declining oil demand (e.g., due to the shift to alternative vehicles).

We linked the production profitability measurement model for 1933 fields (about 90% of global supply in 2015) to their production CI. Then, we look at the reactions to the decline in demand under the three oil market structures.

According to our estimates, small demand shocks have different upstream CI effects than large shocks. Regardless of the market structure, small shocks (demand −2.5%) were replaced primarily by heavy crude oil, which was 25-54% higher than the global average.

However, as the shock becomes larger, this imbalance weakens if producers with market forces coordinate their response to a decline in demand. The carbon efficiency of reducing oil demand is systematically determined by the magnitude of the decline in demand and the structure of the global oil market.

we explore the life-cycle greenhouse gas emissions impacts of marginal crude sources, identifying the upstream carbon intensity (ci) of the producers most sensitive to an oil demand decline (for example, due to a shift to alternative vehicles). we link econometric models of production profitability of 1,933 oilfields (~90% of the 2015 world supply) with their production ci. then, we examine their response to a decline in demand under three oil market structures. according to our estimates, small demand shocks have different upstream ci implications than large shocks. irrespective of the market structure, small shocks (−2.5% demand) displace mostly heavy crudes with ~25–54% higher ci than that of the global average. however, this imbalance diminishes as the shocks become bigger and if producers with market power coordinate their response to a demand decline. the carbon emissions benefits of reduction in oil demand are systematically dependent on the magnitude of demand drop and the global oil market structure.