Liquid crystal molecules form nano rings

Quantised self-assembly enables design of materials with novel properties

At DESY’s X-ray source PETRA III, scientists have investigated an intriguing form of self-assembly in liquid crystals: When the liquid crystals are filled into cylindrical nanopores and heated, their molecules form ordered rings as they cool – a condition that otherwise does not naturally occur in the material. This behavior allows nanomaterials with new optical and electrical properties, as the team led by Patrick Huber from Hamburg University of Technology (TUHH) reports in the journal Physical Review Letters.

The scientists had studied a special form of liquid crystals that are composed of disc-shaped molecules called discotic liquid crystals. In these materials, the disk molecules can form high, electrically conductive pillars by themselves, stacking up like coins. The researchers filled discotic liquid crystals in nanopores in a silicate glass. The cylindrical pores had a diameter of only 17 nanometers (millionths of a millimeter) and a depth of 0.36 millimeters.

There, the liquid crystals were heated to around 100 degrees Celsius and then cooled slowly. The initially disorganised disk molecules formed concentric rings arranged like round curved columns. Starting from the edge of the pore, one ring after the other gradually formed with decreasing temperature until at about 70 degrees Celsius the entire cross section of the pore was filled with concentric rings. Upon reheating, the rings gradually disappeared again.

>Read more on the PETRA III at Desy website

Image: Stepwise self-organisation of the cooling liquid crystals. (Extract, see the entire image here)
Credit: A. Zantop/M. Mazza/K. Sentker/P. Huber, Max-Planck Institut für Dynamik und Selbstorganisation/Technische Universität Hamburg; Quantized Self-Assembly of Discotic Rings in a Liquid Crystal Confined in Nanopores, Physical Review Letters, 2018; CC BY 4.

 

40-year controversy in solid-state physics resolved

An international team at BESSY II headed by Prof. Oliver Rader has shown that the puzzling properties of samarium hexaboride do not stem from the material being a topological insulator, as it had been proposed to be.

Theoretical and initial experimental work had previously indicated that this material, which becomes a Kondo insulator at very low temperatures, also possessed the properties of a topological insulator. The team has now published a compelling alternative explanation in Nature Communications, however.

Samarium hexaboride is a dark solid with metallic properties at room temperature. It hosts Samarium, an element having several electrons confined to localized f orbitals in which they interact strongly with one another. The lower the temperature, the more apparent these interactions become. SmB6 becomes what is known as a Kondo insulator, named after Jun Kondo who was first able to explain this quantum effect.

In spite of Kondo-Effect: some conductivity remains

About forty years ago, physicists observed that SmB6 still retained remnant conductivity at temperatures below 4 kelvin, the cause of which had remained unclear until today. After the discovery of the topological-insulator class of materials around 12 years ago, hypotheses grew insistent that SmB6 could be a topological insulator as well as being Kondo insulator, which might explain the conductivity anomaly at a very fundamental level, since this causes particular conductive states at the surface. Initial experiments actually pointed toward this.

>Read more on the Bessy II website

Image: Electrons with differing energies are emitted along various crystal axes in the interior of the sample as well as from the surface. These can be measured with the angular-resolved photoemission station (ARPES) at BESSY II. Left image shows the sample temperature at 25 K, right at only 1 K. The energy distribution of the conducting and valence band electrons can be derived from these data. The surface remains conductive at very low temperature (1 K).
Credit: Helmholtz Zentrum Berlin

Kilian Peter Heeg wins ESRF Young Scientist award

Kilian Peter Heeg has been awarded the title of Young Scientist 2018 by the ESRF User Organisation in recognition of his pioneering work on light-matter interactions enabling resonant brilliance enhancement of X-ray pulses. This award is presented every year at the ESRF annual User Meeting to a scientist aged 37 or younger for outstanding work conducted at the ESRF.

Kilian Heeg is a physicist and postdoctoral researcher at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Aged just 31, Kilian has already significantly shaped the field of X-ray quantum optics.

Kilian says: “I wanted to be a mathematician when I was a child and I was always fascinated by natural sciences. However in my final years in school I fell in love with physics and very quickly became fascinated with quantum mechanics and especially quantum optics. I feel very honoured and pleased to have been chosen as the winner of this year’s ESRF Young Scientist Award.”

>Read more on the ESRF website

Image: Kilian on ESRF’s ID18 beamline
Credit: ESRF/C. Argoud

Magnetic trick triples the power of SLAC’s X-ray laser

The new technique will allow researchers to observe ultrafast chemical processes previously undetectable at the atomic scale.

Scientists at the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to triple the amount of power generated by the world’s most powerful X-ray laser. The new technique, developed at SLAC’s Linac Coherent Light Source (LCLS), will enable researchers to observe the atomic structure of molecules and ultrafast chemical processes that were previously undetectable at the atomic scale.

The results, published in a Jan. 3 study in Physical Review Letters (PRL), will help address long-standing mysteries about photosynthesis and other fundamental chemical processes in biology, medicine and materials science, according to the researchers.

“LCLS produces the world’s most powerful X-ray pulses, which scientists use to create movies of atoms and molecules in action,” said Marc Guetg, a research associate at SLAC and lead author of the PRL study. “Our new technique triples the power of these short pulses, enabling higher contrast.”

>Read more on the LCSL website

Picture: The research team, from left: back row, Yuantao Ding, Matt Gibbs, Nora Norvell, Alex Saad, Uwe Bergmann, Zhirong Huang; front row, Marc Guetg and Timothy Maxwell.
Credit: Dawn Harmer/SLAC

 

Questioning the universality of the charge density wave nature…

… in electron-doped cuprates

The first superconductor materials discovered offer no electrical resistance to a current only at extremely low temperatures (less than 30 K or −243.2°C). The discovery of materials that show superconductivity at much higher temperatures (up to 138 K or −135°C) are called high-temperature superconductors (HTSC). For the last 30 years, scientists have researched cuprate materials, which contain copper-oxide planes in their structures, for their high-temperature superconducting abilities. To understand the superconducting behavior in the cuprates, researchers have looked to correlations with the charge density wave (CDW), caused by the ordered quantum field of electrons in the material. It has been assumed that the CDW in a normal (non-superconducting) state is indicative of the electron behavior at the lower temperature superconducting state. A team of scientists from SLAC, Japan, and Michigan compared the traits of superconducting and non-superconducting cuprate materials in the normal state to test if the CDW is correlated to superconductivity.

>Read more on the SSRL website

Picture: explanation in detail to read in the full scientific highlight (SSRL website)

 

 

 

Scientists discover material ideal for smart photovoltaic windows

Berkeley Lab researchers make thermochromic windows with perovskite solar cell

Smart windows that are transparent when it’s dark or cool but automatically darken when the sun is too bright are increasingly popular energy-saving devices. But imagine that when the window is darkened, it simultaneously produces electricity. Such a material – a photovoltaic glass that is also reversibly thermochromic – is a green technology researchers have long worked toward, and now, scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) have demonstrated a way to make it work.

Researchers at Berkeley Lab, a Department of Energy (DOE) national lab, discovered that a form of perovskite, one of the hottest materials in solar research currently due to its high conversion efficiency, works surprisingly well as a stable and photoactive semiconductor material that can be reversibly switched between a transparent state and a non-transparent state, without degrading its electronic properties.

>Read more on the Advanced Light Source website

Image Credit: iStock

 

G. Ghiringhelli and L. Braicovich win 2018 Europhysics Prize of Condensed Matter

>Read more on the ESRF website

 

X-ray detector for studying characteristics of materials

Sol M. Gruner’s group, Physics, has been a leader in the development of x-ray detectors for scientific synchrotron applications, and the team’s technology is used around the world. Their detectors utilize pixelated integrated circuit silicon layers to absorb x-rays to produce electrical signals. The wide dynamic range, high sensitivity, and rapid image frame rate of the detectors enable many time-resolved x-ray experiments that have been difficult to perform until now.

The detectors are limited by the silicon layer. Low atomic number materials such as silicon become increasingly transparent to x-rays as the energy of the x-rays rises. Gruner’s group is now developing a variant of their detector that will use semiconductors comprised of high atomic weight elements to absorb the x-rays and produce the resultant electrical signals. The Detector Group, led by Antonio Miceli, at the United States Department of Energy’s Advanced Photon Source (APS) will simultaneously develop the ancillary electronics and interfacing required to produce fully functional prototypes suitable for high x-ray energy experiments at the APS and CHESS.

 

>Read more on the CHESS website

Image: Sol M. Gruner, Physics, College of Arts and Sciences
Credit: Jesse Winter

 

Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how important bioinorganic electron transfer systems operate. Using a combination of very different, time-resolved measurement methods at DESY’s X-ray source PETRA III and other facilities, the scientists were able to show that so-called pre-distorted states can speed up photochemical reactions or make them possible in the first place. The group headed by Sonja Herres-Pawlis from the RWTH Aachen University  Michael Rübhausen from the University of Hamburg and Wolfgang Zinth from Munich’s Ludwig Maximilian University, is presenting its findings in the journal Nature Chemistry.

The scientists had studied the pre-distorted, “entatic” state using a model system. An entatic state is the term used by chemists to refer to the configuration of a molecule in which the normal arrangement of the atoms is modified by external binding partners such that the energy threshold for the desired reaction is lowered, resulting in a higher speed of reaction. One example of this is the metalloprotein plastocyanin, which has a copper atom at its centre and is responsible for important steps in the transfer of electrons during photosynthesis. Depending on its oxidation state, the copper atom either prefers a planar configuration, in which all the surrounding atoms are arranged in the same plane (planar geometry), or a tetrahedral arrangement of the neighbouring ligands. However the binding partner in the protein forces the copper atom to adopt a sort of intermediate arrangement. This highly distorted tetrahedron allows a very rapid shift between the two oxidation states of the copper atom.

>Read more on the PETRA III website

Image Caption: Entatic state model complexes optimize the energies of starting and final configuration to enable fast reaction rates (illustrated by the hilly ground). The work demonstrates that the entatic state principle can be used to tune the photochemistry of copper complexes.
Credit: RWTH Aachen, Sonja Herres-Pawlis

Ruling out Weyl points in MoTe2

Sometimes the hunt for new kinds of fundamental particles takes place in the low-energy degrees of freedom of exotic quantum materials

Over the past decade, such strange entities as magnetic monopoles, Majorana fermions, and even Higgs modes have been predicted and identified inside materials at low temperatures.  The goal of learning to manipulate these new quanta for technological purposes is a grand challenge for science, predicted to spark a “second quantum revolution”.  Among the intriguing zoo of new particles which exploit the topological properties of electronic wavefunctions, the Weyl fermions (which are charged, massless, and chiral) were originally postulated in the 1920s but have never been observed in high-energy physics experiments.  However, compelling evidence for Weyl physics inside certain classes of semi-metals has accumulated over the past three years.  The material TaAs, for example, has been shown to host special electronic band crossings (“nodes”) where the quasiparticles act like Weyl fermions.  Subsequently, a second type of Weyl semimetal (called “type-II”) was theoretically predicted to exist in the material MoTe2.  Weyl semi-metals are predicted to host Fermi surface lines with non-trivial topological properties at the material surface. Initial support for the type-II Weyl picture of MoTe2 has been published in the form of ARPES experiments, but the full, bulk electronic structure was until recently unknown.

>Read more on the CHESS website

Synchrotron “X-ray Micromechanics” course now online

An online course for novice X-ray users with backgrounds in engineering

As part of the mission of InSitμ@CHESS, the ONR-funded center focused on developing new High Energy X-ray Diffraction (HEXD) users and methods, the staff has developed and made available an online course for novice X-ray users with backgrounds in engineering.

>Read more on the CHESS website

Ferromagnetism Emerges to Alleviate Polar Mismatch

Alchemists dreamed of turning boring, base metals into exotic, noble metals. Although such dreams were never realized, scientists today can induce unexpected properties at the interface between two materials—including properties not present in either parent material. For example, researchers have discovered that if they combine SrTiO3 (a dielectric and paramagnetic material) together with LaMnO3 (an insulating and antiferromagnetic material) in just the right way, they can induce an insulating ferromagnetic state at the interface.

Read more on the ALS website.

Illustration of the LaMnO3/SrTiO3 heterostructure, showing an LaMnO3 thickness of three unit cells (UC). Source: ALS website

NSRRC User, Jennifer Kung elected as a MSA Fellow

First female scientist ever awarded MSA fellowship in Asia.

NSRRC user, Jennifer Kung is among the 11 new elected fellows for 2018, announced by the Mineralogical Society of America (MSA) Council at its Fall Council Meeting in Seattle, WA, USA. She is the only recipient from Taiwan, as well as the first female scientist ever awarded MSA fellowship in Asia.

Prof. Kung is an Associate Professor in Earth Science at National Cheng-Kung University. She runs “Mineral and Rock Physics Lab” to investigate the behaviors of earth materials under high pressure and high temperature using the knowledge of crystal chemistry, mineral physics to understand the interior of the Earth. The major research methods she employs include X-ray diffraction, vibrational spectroscopy and ultrasonic measurements in conjunction with high pressure facilities, like large volume high pressure apparatus or diamond anvil.

 

2017 ANSTO, Australian Synchrotron Stephen Wilkins Medal awarded

Leonie van ‘t Hag has been awarded the Australian Synchrotron S. Wilkins Medal for her PhD thesis

The award recognises her research to improve the method to crystallise proteins and peptides in order to study their structure, using a technique called crystallography. “Leonie’s insights into crystallisation processes could significantly help the development of treatments for a variety of illnesses,” said Australian Synchrotron Director, Professor Andrew Peele.

Most solid material in the world is made of crystalline structures. Crystals are made up of rows and rows of atoms or molecules stacked up like boxes in a warehouse, in different arrangements.

The science of determining these atomic or molecular structures from crystalline materials is called crystallography.

Scientists Named 2017 American Physical Society Fellows

Five Brookhaven Lab Scientists recognized for their outstanding contributions

The American Physical Society (APS), the world’s largest physics organization, has elected five scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory as 2017 APS fellows. With more than 53,000 members from academia, government, and industry, APS seeks to advance and share physics knowledge through research journals, scientific meetings, and activities in education, outreach, and advocacy. Each year, a very small percentage of APS members are elevated to the status of fellow through a peer nomination process. Fellows are recognized for their exceptional contributions to physics, including in research, applications, leadership and service, and education.

The 2017 APS fellows representing Brookhaven Lab are Anatoly Frenkel, Morgan May, Rachid Nouicer, Eric Stach, and Peter Steinberg.

Anatoly Frenkel, APS Division of Materials Physics

“For seminal contributions to in situ X-ray absorption spectroscopy, transformative development of structural characterization methods for nanoparticles, and their pioneering applications to a broad range of functional nanomaterials in materials physics and catalysis science.”

Anatoly Frenkel holds a joint appointment as a senior chemist in Brookhaven Lab’s Chemistry Division—where he serves as principal investigator of the Structure and Dynamics of Applied Nanomaterials Group—and tenured professor in Stony Brook University’s Materials Science and Chemical Engineering Department. Frenkel’s research focuses on the application of synchrotron-based x-ray methods to characterize materials and study how their structures and properties relate.

 

>Read more on the NSLS II website

Image: Anatoly Frenkel

 

Quantum spectroscopy, for the measurements of dynamical current current thermalization

Nearly all spectroscopic measurements deals with the measurements of the average properties of the material. As an example, the reflectivity of a material is simply defined by the ratio between the number of photons which are reflected by the sample divided by the number of those arriving on it. The interest in measuring mostly average properties is the main drive of the standard scientific practice of repeating the measurements a lot of times so that the error made in one single measurements is averaged out by the repetition of the measurements. In this context the noise which determines fluctuation of the repeated measurements have always been considered as an impediment to a good quality measurements which needs to be mitigated by careful experimentalists.
The approach of repeated measurements is employed conspicuously in pump-probe experiments which are the prime way to study condensed matter out of its equilibrium state. In standards optical pump-probe experiments, ultrashort pulses are always used in pairs. The pump triggers the dynamical response and the probe is used to detect changes in the optical properties of the sample.

Read more on the Elettra website.

Image: Schematic view of the pump-probe set-up used for the experiments. The intensity of every single probe pulse was separately acquired with low-electronic-noise detectors for every pump-probe delay.