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Machine learning: New tool in the box

A recent burst of activity in applying machine learning to tackle fundamental questions in physics suggests that associated techniques may soon become as common in physics as numerical simulations or calculus. Nature Physics | doi:10.1038/nphys4053

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New tools to tackle questions in physics.
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Z2Pack released - a tool for computing topological invariants - General announcements - Psi-k

Z2Pack released - a tool for computing topological invariants - General announcements - Psi-k | Physics | Scoop.it
Dear members of the Psi-k community,it is our pleasure to announce the release of Z2Pack - a tool to calculate topological invariants for real materials. The code can identify topological phases from k.p or tight-binding models, or directly from some first principles codes. The method is based on tr
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Numerical Implementation of Hybrid Wannier Centers for Identifying Topological Materials

Search and classify topological materials with this tool. Can be used as a post-processing tool with ab initio calculations or standalone with k.p or tight-binding Hamiltonians.

Link: http://psi-k.net/general-announcements/z2pack-released-a-tool-for-computing-topological/

Link to arXiv paper: https://arxiv.org/abs/1610.08983

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Fundamental Fission Modeling Finds a Foothold

Fundamental Fission Modeling Finds a Foothold | Physics | Scoop.it

Time-dependent superfluid local density approximation model captures detailed dynamics of splitting plutonium-240 nucleus.


Via Theo J. Mertzimekis
Mikko Hakala's insight:
DFT for superfluid fermionic systems to model real-time nuclear dynamics. Heavy supercomputing (GPUs) needed to solve the 56000 partial differential equations.
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Manufacturing thin film tandem solar cells using thin perovskite layer for low cost roll-to-roll production

Manufacturing thin film tandem solar cells using thin perovskite layer for low cost roll-to-roll production | Physics | Scoop.it
Latest breakthroughs in sustainable technology, business and market analysis
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* New procedure for a tandem cell with future potential for low-cost roll-to-roll production. (Low cost due to processing at low temperature.)

* Upper layer: semi-transparent methylammonium lead iodide solar cell module (grown as perovskite crystals)

* Interlayer: phenyl-C61-butyric acid methyl ester

* Lower layer: copper indium gallium diselenide (CIGS) second solar cell module.

 

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This Condensed Life | A Blog About Condensed Matter Physics that Trespasses on Topical Tangents

This Condensed Life | A Blog About Condensed Matter Physics that Trespasses on Topical Tangents | Physics | Scoop.it
A Blog About Condensed Matter Physics that Trespasses on Topical Tangents
Mikko Hakala's insight:

Check out this interesting condensed mattery physics blog with five contributing authors. 

 

The following are some of the most popular tags in the posts: BCS theory, charge density wave, superconductivity, experiment, perspective, philosophy, review.

 

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Ask Ethan #93: Newton’s Random Apple

Ask Ethan #93: Newton's Random Apple - Starts With A Bang! - Medium
If all the random motions of the molecules inside aligned, how far and fast would it go?
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The question is if thermal energy can be converted to the motion of the apple as a whole - Story of basic physical phenomena why this cannot happen.

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Holey Rubber Slab Has Controllable Stiffness

Holey Rubber Slab Has Controllable Stiffness | Physics | Scoop.it
Squeezing a holey rubber slab changes its stiffness over a wide range in the direction perpendicular to the squeeze.
Mikko Hakala's insight:

 

Good materials physics article. Here's my quick summary:

 

* For metamaterials the properties (strength, reflectivity etc.) follow from macroscopic structure, not elemental composition.

* The developed silicone rubber slab has perforated alternative holes, leading to interesting non-linear stress-strain behavior.

* The material could absorb and dissipate energy (transferred to it for ex. by impacts or shocks), rather than only storing it as energy in the spring.

* In other words, the material is not 'bumpy' but 'dissipative'. Applications can be found in robotics etc. and everyday objects which require control of damping.

* The advantage of this material is that it's pure mechanical and doesn't require external energy to operate. 

 

Pin it for later: http://www.pinterest.com/pin/318981586081801924/

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Fundamentals of physics confirmed: Experiments testing Einstein's time dilation and quantum electrodynamics

Fundamentals of physics confirmed: Experiments testing Einstein's time dilation and quantum electrodynamics | Physics | Scoop.it
The special theory of relativity of Albert Einstein and quantum electrodynamics, which was formulated by, among others, Richard Feynman, are two important fundaments of modern physics. In cooperation with colleagues from several international universities and institutes, the research group of Professor ...
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Detecting fluorescence radiation from relativistically moving ions is here used to test two fundamental physics theories: special relativity and QED.  - Better precision obtained in the experiments, no violations found.

 

http://phys.org/news/2014-10-fundamentals-physics-einstein-dilation-quantum.html

 

Direct links to the studies:

 

Special relativity

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.120405

http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.113.120405 ;

 

Hyperfine splitting (predicted by quantum electrodynamics)

http://journals.aps.org/pra/abstract/10.1103/PhysRevA.90.030501

 

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Perovskite Solar Cell Technology of Oxford PV, The Potential Game-Changer | Sun Is The Future

Perovskite Solar Cell Technology of Oxford PV, The Potential Game-Changer | Sun Is The Future | Physics | Scoop.it
Dear Friends, Visitors/Viewers/Readers, (Please click on red links and note magenta) At InterSolar North America 2014 in San Francisco, CA, I came across
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Solar cell technology based on perovskites

 

Useful info in the post and interview on Oxford PV activities in this field. In the video Dr. Christopher Case describes the material and its applications in various ways in solar cell technologies. Here's my quick summary of the video's content:

 

0:45 Fastest increasing photovoltaic efficiency 

1:15 Thin film material

1:35 Applications, initial view of the company was to develop semi-transparent coatings

2:10 Can be made in almost any color

3:00 New application of perovskites: tandem solar cells (perovskite coating on conventional Si)

4:10 What are perovskites

4:45 How to tailor the properties

5:10 Material itself studied already for decades

5:50 Finding the planar form by Prof. Snaith was a breakthrough

6:40 More and more papers coming out on this material

6:55 Perovskite on Si solar cells boosts efficiency, easier to make this product than a fully integrated PV

7:40 Perovskites fundamentally and perspectives for efficiency

8:15 Potential to replace Si?

8:40 About processing: it's solution processed from inexpensive materials

9:30 Future steps. Towards full perovskite-on-perovskite tandem cells

9:50 How to get in contact, what their company's website contains

 

 

 

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Team first to detect exciton in metal

Team first to detect exciton in metal | Physics | Scoop.it
University of Pittsburgh researchers have become the first to detect a fundamental particle of light-matter interaction in metals, the exciton. The team will publish its work online June 1 in Nature Physics.
Mikko Hakala's insight:

Observation of excitons in metals is difficult due to their short lifetimes. This research reports detection on metal surfaces via multiphoton photoemission.

 

Quick info on excitons: http://en.wikipedia.org/wiki/Exciton

 

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Solution to two long-standing mysteries of cuprate superconductivity found

Solution to two long-standing mysteries of cuprate superconductivity found | Physics | Scoop.it
Scientists seeking to understand the intricacies of high-temperature superconductivity—the ability of certain materials to carry electrical current with no energy loss—have been particularly puzzled by a mysterious phase that emerges as charge carriers are added that appears to compete with superconductivity. ...
Mikko Hakala's insight:

More on the superconductivity of cuprates (see http://sco.lt/5pcQjZ).

 

At low hole doping, i.e. at the pseudogap phase, the static electron arrangement (charge density wave or "frozen" stripe patterns) and the associated nanoscale fluctuations prevent the free flow of electrons. At higher hole doping the density wave disappears and unrestricted superconductivity appears.

 

Measurements by spectroscopic imaging scanning tunneling microscope.

 

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Physicists discover how to change the crystal structure of graphene

Physicists discover how to change the crystal structure of graphene | Physics | Scoop.it
A University of Arizona-led team of physicists has discovered how to change the crystal structure of graphene, more commonly known as pencil lead, with an electric field, an important step toward the possible use of graphene in microprocessors that would be smaller and faster than current, silicon-based ...
Mikko Hakala's insight:

The paper shows that the stacking of graphene layers (in a 3-layer case) can be controlled with an external voltage. This way one obtains either metallic or semiconducting behavior. According to the article, for the first time such on-off switch is demonstrated in graphene.

 

This is in early stages but could become very important if the tuning of graphene's electrical properties can be realized at larger scale. The ultimate aim is a graphene-based transistor, with huge advantages compared to silicon-based ones.

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Solar-cell materials and efficiencies

Solar-cell materials and efficiencies | Physics | Scoop.it

What are the types and efficiencies of current phovoltaic materials? This Wikimedia Commons graph is a great, constantly updated reference to various photovoltaic technologies under research. The classification is to following types of cells:

 

1) multijunction

2) single-junction GaAs

3) crystalline Si

4) thin-film (CIGS, CdTe, amorphous and other forms of Si )

5) emerging (perovskite, quantum dot, organic, inorganic, dye-sensitized)

Follow it to stay updated on recent achievements.

 

More information:

 

* Nature Photonics has a focus issue on a set of cutting-edge solar cell technologies. It covers quantum dot, polymer, dye-sensitized and intermediate-band solar cells: http://www.nature.com/nphoton/focus/photovoltaics/index.html

The editorial 'A sunny outlook': http://www.nature.com/nphoton/journal/v6/n3/full/nphoton.2012.38.html

 * Brief info on CdTe: http://spectrum.ieee.org/nanoclast/green-tech/solar/what-makes-for-better-cdte-solar-cells  Figure: By NREL (US Department of Energy) [Public domain], via Wikimedia Commons

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[1702.01361] Deep learning and the Schrödinger equation

We have trained a deep (convolutional) neural network to predict the ground-state energy of an electron in four classes of confining two-dimensional electrostatic potentials. On randomly generated potentials, for which there is no analytic form for either the potential or the ground-state energy, the neural network model was able to predict the ground-state energy to within chemical accuracy, with a median absolute error of 1.49 mHa. We also investigate the performance of the model in predicting other quantities such as the kinetic energy and the first excited-state energy of random potentials. While we demonstrated this approach on a simple, tractable problem, the transferability and excellent performance of the resulting model suggests further applications of deep neural networks to problems of electronic structure.
Mikko Hakala's insight:
Convolutional neural network predicts the energy of one electron in a random 2d electrostatic potential to within chemical accuracy. To be demonstrated for bigger multielectron systems. If successful, would lead to important saving in computational time.
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Machine learning enables predictive modeling of 2-D materials

Machine learning enables predictive modeling of 2-D materials | Physics | Scoop.it
Machine learning, a field focused on training computers to recognize patterns in data and make new predictions, is helping doctors more accurately diagnose diseases and stock analysts forecast the rise and fall of financia
Mikko Hakala's insight:

Modeling of stanene nanostructures with atomic potential based on machine learning

Original paper: http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.6b01562

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Surface Defects on Natural MoS2 - ACS Applied Materials & Interfaces (ACS Publications)

Surface Defects on Natural MoS2 - ACS Applied Materials & Interfaces (ACS Publications) | Physics | Scoop.it

* MoS2, and other TMDs, are promising new materials for devices such as beyond-CMOS transitors, LEDs, sensor and solar cells

* Changes in electrical properties (e.g. p/n type behavior) are likely related to local stoichiometry,, metal-like and structural defects and impurities on the surface

* The work studies intrinsic defects detected by STM, STS, XPS and ICPMS,, finds significantly high concentrations

* Before industrial scale can be reached, the structural factors affecting electronic and optical properties need to be understood and controlled 

[Image: 3113Ian - Made with vesta, CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=42615855]
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A new way to make X-rays

A new way to make X-rays | Physics | Scoop.it
MIT researchers have found a phenomenon that might lead to more compact, tunable X-ray devices made of graphene.

Via Theo J. Mertzimekis
Mikko Hakala's insight:

 

This theoretical research predics a new X-ray generation method based on confined plasmons in graphene. The concept is unique and it would be a highly advantageous method, since low-energy electrons can be used to produce tunable X-rays. In all the current approaches high-energy charged particles are needed (synchrotrons, free-electron lasers), which requires large device sizes and intensities.

 

Press release: http://news.mit.edu/2015/new-way-make-x-rays

Article: http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2015.223.html

 

X-rays are used for research and diagnostics purposes in materials and natural sciences, in engineering, and for biomedical and life sciences.

 

Note the upcoming X-ray workshop in Helsinki 3.-4.12.2015:  http://www.fsruo.fi/index.php/en/workshops-and-schools-2/fsruo2015 (public lectures)

 

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Perovskite quantum dots emit single photons - nanotechweb.org

Perovskite quantum dots emit single photons - nanotechweb.org | Physics | Scoop.it
The nanocrystals might find use in light-emitting diodes, with practical applications in displays.
Mikko Hakala's insight:

 

Early stages in developing organometal trihalide perovskite semiconductors as quantum dots. Advantages could be easy tunability of emission wavelength but challenges remain due to tendency of the material to degrade.

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Electronic structure and phase stability of oxide semiconductors: Performance of dielectric-dependent hybrid functional DFT, benchmarked against GW band structure calculations and experiments

Electronic structure and phase stability of oxide semiconductors: Performance of dielectric-dependent hybrid functional DFT, benchmarked against GW band structure calculations and experiments | Physics | Scoop.it

- Mikko's summary -

 

* New hybrid functional benchmarked, aims to reproduce both ground- and excited state properties within a fully ab initio framework.

 

* A well-written introductory part, with review of the standard LDA/GGA gap problem, how the fraction 'alpha' in the hybrid calculation scheme relates to macroscopic dielectric constant, and what approaches have been used for alpha.

 

* Detailed, useful computational methodology part with discussions on codes and chosen parameters.

 

* The new approach is tested on wide-gap oxide semiconductors that have current or future technological impact (e.g. in photovoltaics and catalysis): ZnO, TiO2, ZrO2 and WO2.

 

* The paper essentially addresses the question of how to tune hybrid functional scheme to be a more applicable tool that can handle in a reliable way both energetics and electronic (ground and excited state) properties.

 

Read the paper:

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.155201

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Any similar recent papers on hybrid functionals? Add your comment.

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Team reveals molecular structure of water at gold electrodes

Team reveals molecular structure of water at gold electrodes | Physics | Scoop.it
When a solid material is immersed in a liquid, the liquid immediately next to its surface differs from that of the bulk liquid at the molecular level. This interfacial layer is critical to our understanding of a diverse set of phenomena from biology to materials science. When the solid surface is charged, ...
Mikko Hakala's insight:

State of the art in the experimental research on structure of water. X-ray absorption spectroscopy reveals the structure of interfacial water (on the gold surface) with sub-nanometer sensitivity.

 

http://phys.org/news/2014-10-team-reveals-molecular-gold-electrodes.html

 

http://www.sciencemag.org/content/early/2014/10/22/science.1259437

 

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The Nobel Prize in Physics 2014

The Nobel Prize in Physics 2014 | Physics | Scoop.it

The Nobel Prize in Physics 2014 was awarded jointly to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura "for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources".

Mikko Hakala's insight:

The Nobel prize website offers both the popular and the more detailed scientific background of blue LEDs.

 

Quoting from the latter: "GaN-based LEDs result from a long series of breakthroughs in basic materials physics and crystal growth, in device physics with advanced heterostructure design, and in optical physics for the optimization of the light out-coupling."

 

The effort was worth it. The luminosity [measured in lumens] / power [measured in watts] increases roughly as follows (from the popular article):

   Light bulb, 1x 

   Fluorescent lamp, 4x 

   LED lamp, 19x

So roughly 20 times less energy consumed compared to light bulbs.

 

More detailed scientific background for blue LEDs:

http://www.nobelprize.org/nobel_prizes/physics/laureates/2014/advanced-physicsprize2014.pdf

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Free Educational Physics Lecture Videos with Lecture Notes

Free Educational Physics Lecture Videos with Lecture Notes | Physics | Scoop.it
After teaching physics in a high school classroom for 13 years, I stepped out of the classroom to start Flipping Physics, a business dedicated to creating free, clear, concise and comedic physics educational videos.
Mikko Hakala's insight:

A nice and fun set of physics lecture videos. Many topics are covered, for example mechanics, electromagnetism, electrical circuits, refraction, interference. Some lectures also on modern physics.

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Scientists discover new magnetic phase in iron-based superconductors

Scientists discover new magnetic phase in iron-based superconductors | Physics | Scoop.it
(Phys.org) —Scientists at the U.S. Department of Energy's Argonne National Laboratory have discovered a previously unknown phase in a class of superconductors called iron arsenides. This sheds light on a debate over the interactions between atoms and electrons that are responsible for their unusual ...
Mikko Hakala's insight:

More research on iron-based superconductors (http://sco.lt/7CfptR), here on doped barium iron arsenide. The electron pairing mechanism is not understood in these unconventional superconductors. To elucidate the mechanism, one issue is to map out the precise phase diagrams.


Here neutron diffraction showed that on lowering the temperature, close to the onset of superconductivity, the structure restores 4-fold symmetry. At higher temperatures the structure has nematic ("thread-like") order with 2-fold symmetry, whereas at room temperature the symmetry is again 4-fold.


The finding appears to support the model that the nematic phase is driven by magnetic interactions and not by iron 3d orbital ordering. And this hints, according to the phys.org article, that it could be magnetism that could be the key to electron pairing. 


Pin it for later:

http://www.pinterest.com/pin/318981586080372229/


The Nature Communications article:

http://www.nature.com/ncomms/2014/140522/ncomms4845/full/ncomms4845.html


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Breakthrough in Study of High-Temperature Superconductivity | Simons Foundation

Breakthrough in Study of High-Temperature Superconductivity | Simons Foundation | Physics | Scoop.it
Experimentalists have pinpointed the microscopic structure of waves inside high-temperature superconductors, which could be the key to understanding the complex materials.
Mikko Hakala's insight:

An interesting, broad and detailed article about the current advancements in understanding the microscopic origin of superconductivity in cuprates. 

 

The article discusses recent findings by various groups. In particlar, it addresses the details of the d-wave charge density order, and how antiferromagnetism is the parent state both to superconductivity and to charge density waves.

 

Challenges remain, for example "[a recently proposed theoretical framework] is not yet refined enough to predict how the balance of charge density waves and superconductivity vary with temperature, magnetic field or type of cuprate."

 

In short, this is a clarifying expert article on a specific condensed matter topic, the origin of d-wave superconductivity and the nature of charge density waves in cuprates.

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Phase transiting to a new quantum universe

Phase transiting to a new quantum universe | Physics | Scoop.it
(Phys.org) —Recent insight and discovery of a new class of quantum transition opens the way for a whole new subfield of materials physics and quantum technologies.
Mikko Hakala's insight:

This phys.org article gives a flavor of the intriguing condensed matter physics related to ferroelectric materials and their quantum phase transitions (QPT) to paraelectric ones. In QPTs, the order-disorder transition takes place at absolute zero temperature, and is achieved by chemical or isotope substitution, or by doping.

 

In this work it was found that for ferroelectrics the physics describing the phase transition is very different from the better know ferromagnetic counterparts. In fact, "the fluctuation spectrum found in quantum critical ferroelectrics is the same as that in elementary particle physics—propagating modes in three spatial dimensions plus one time dimension."

 

Wikipedia article on quantum phase transitions:

http://en.wikipedia.org/wiki/Quantum_phase_transition

 

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