Argonne National Laboratory

Science Highlights

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Alexander Zholents is director of Argonne’s Accelerator Systems Division (ASD).  A Senior Scientist of the Russian Academy of Sciences and Fellow of the American Physical Society, Zholents was chosen as one of Argonne’s Distinguished Fellows because of his “outstanding technical leadership of major, complex, high-priority projects.”
(Image by Argonne National Laboratory.)
Argonne appoints Distinguished Fellows for 2017

The U.S. Department of Energy’s (DOE) Argonne National Laboratory has chosen scientists Alexander Zholents, David Tiede, Wai-Kwong Kwok and Tijana Rajh as Distinguished Fellows, the laboratory’s highest scientific and engineering rank.

May 25, 2017
Fig. 1. (a) A boule (9 mm diameter and 85 mm length) of CsPbBr3 grown by Bridgman method. The pulse height energy spectra of CsPbBr3 crystal under (b) unfiltered Ag X-ray and (c) 57Co -ray irradiation.
Perovskite Semiconductor CsPbBr₃ for High Energy Radiation Detector Applications

Semiconducting perovskite metal halides exhibit excellent performance in optics and photonics with high carrier mobility, long carrier lifetime, defect tolerance, strong optical absorption, and high photoluminescence quantum efficiencies. As a promising candidate in the area of hard radiation detection, the orange colored compound CsPbBr3 possessing high density (4.85 g/cm3) and direct band gap (2.25 eV) has attenuation coefficient comparable to Cd1-xZnxTe (CZT) which is a leading semiconductor in radiation detection. Additionally, previous reports on CsPbBr3 show high resistivity (r) ~109 W∙cm, high mobility (m) and lifetime (t) in the range of 1,000 - 4,500 cm2/Vs and 2.5 - 9.2 μs, respectively, depending on bulk form or nanocrystals, by which CsPbBr3 well meets the requirements for good X- and g-ray detector candidate materials.

April 20, 2017
Fig. 1. (a) Tetragonal crystal structure of Sm2Ru3Ge5 as viewed along the c axis.  (b) diffraction pattern above and below TCDW showing the CDW peaks. (c) resistivity, (d) heat capacity, (e) Hall coefficient (RH), and (f) electron concentration of Sm2Ru3Ge5.
Exploring Charge Density Waves To Approach Superconductivity

CDWs and SDWs have received significant attention from the condensed matter physics and chemistry communities as these broken symmetry ground states are often observed in close proximity to superconductivity. We have focused on exploring materials with charge (CDW) or spin (SDW) density wave to approach superconductivity and uncovered a new polymorph 3D structural family of RE2Ru3Ge5 (RE = Pr, Sm, Dy) and a new 2D phase Pb3SbS4Te2-d that show unique types of CDW.

April 20, 2017
ARPES spectrum and fermi surface of semimetallic YSb showing two hole-like bands, a and b, centered at G and one electron-like band, g, centered at X. The electron/hole ratio determined from this measurement deviates markedly from perfect compensation.
Extreme Magnetoresistance in YbSb

Topological features of electronic band structure are key focus of quantum materials, leading to novel protected surface states and the potential for low power circuitry platforms.
An extreme magnetoresistance (XMR) has recently been observed in several non- magnetic semimetals. Increasing experimental and theoretical evidence indicates that the XMR can be driven by either topological protection or electron-hole compensation. Here, by investigating the electronic structure of a XMR material, YSb, we present spectroscopic evidence for a special case which lacks topological protection and perfect electron-hole compensation. Further investigations reveal that a cooperative action of a substantial difference between electron and hole mobility and a moderate carrier compensation might contribute to the XMR in YSb.

April 19, 2017
Redetermined phase diagram of PMN-xPT through neutron diffraction, emphasizing differences between single- and powder samples traced to skin effect.
Relaxors are More Than Skin Deep

We explored the putative role of polar nanoregions (PNR) in the physics of relaxor ferroelectrics in the canonical PMN-xPT system using neutron diffraction on single- and polycrystalline specimens. Our key result was the formation of ferroelectricity (i.e. monoclinic symmetry) in the latter but not the former. We hypothesize that this reflects the importance of near-surface ‘skin effect’ more easily seen in the powders. Importantly, our work implies that in bulk materials there exists a coupling between relaxational properties and suppressed long-range order, a necessary condition for the PNR model.

April 19, 2017
Synchrotron x-ray diffraction measurements on single crystal La<sub>4</sub>
Ni<sub>3</sub>O<sub>8</sub> reveal a charge stripe superlattice with a tripled unit cell.  Detailed profile studies of the superlattice peaks reveal a stacking of the stripes within the trilayer, opposite to what would be expected from a simple Coulomb repulsion model.
Charge Stripe Stacking in Nickel Oxides

A unique, paradoxical ground state of the layered nickelate La4Ni3O8 is associated with charge stripe ordering. Using single crystal synchrotron x-ray diffraction, we find that the stripes are stacked directly on top of one another within nickel oxide trilayers, yet staggered between successive trilayers results in which the electrostatic building principle is respected at long range but violated at short distances. Notably, the charge stripe superlattice propagation vector, q=(⅔, 0, 1), corresponds with that found in the related ⅓-hole doped single layer nickelate, La5/3Sr1/3NiO4 (formal charge state, Ni2.33+) with orientation at 45° to the Ni-O bonds, indicating that the 1/3 fractional charge in both of these compounds controls the charge condensation behavior.

April 19, 2017
Single crystals of LaNiO3 were grown for the first time under a ~40 bar oxygen atmosphere.  The figure shows the gradual transformation from poly- to single crystal in the boule.  Above is electrical resistivity showing metallic behavior.
LaNiO₃ Single Crystals Grown at High pO₂

Rare-earth perovskites RNiO3 (R = rare earth) exhibit metal-insulator transitions and magnetic ordering temperatures that are controlled by ionic size. Single crystals have been elusive, with only small samples prepared under extremely high (6 GPa) pressures. We have successfully grown LaNiO3 single crystals using a high-P zone furnace under conditions of 30-50 bar oxygen and report physical properties of this metallic nickelate perovskite. A small concentration of oxygen vacancies (~0.5%) was found and may contribute to the magnetic susceptibility.

April 19, 2017
A diagram showing the “spiral” of noncollinear magnetic orientations (in pink) of a nickelate material next to a manganite material (Image by Anand Bhattacharya/Argonne National Laboratory.)
Scientists discover magnetic “persuasion” in neighboring metals

Certain materials can be swayed by their neighbors to become magnetic, according to a new Argonne study.

March 1, 2017
Fig. 1. Phase diagram of Sr1-xNaxFe2As2 indicating the tetragonal C4 region. Mössbauer spectra shows coexistence of magnetic and non-magnetic phase in Sr0.63Na0.37Fe2As2 sample at 30 K.
Nematicity and coexistence of magnetic and non-magnetic order

For the 122 iron arsenide superconducting systems, we have refined the synthesis procedures and successfully generated high quality samples with precise compositions in both polycrystalline and single crystal across the entire phase diagram of alkaline earth (AE) alkali metal (A) iron arsenide (AE1-xAxFe2As2) including Ba1-xNaxFe2As2, Sr1-xNaxFe2As2, Ca1-xNaxFe2As2, BaFe2(As1-xPx)2 as well as other combinations that we published in the past years. The recent discovery of coexistence of the C4 symmetry phase in the superconducting region in the Sr1-xNaxFe2As2 phase diagram led to the double Q model which involves the coexistence of magnetic and non-magnetic Fe sites observed by Mössbauer spectroscopy (Fig. 1).

December 20, 2016
Dynamic Compression Sector (DCS) engineers prepare a two-stage launcher for an experiment. The DCS was dedicated at a ceremony today at Argonne National Laboratory’s Advance Photon Source. Argonne partnered with the National Nuclear Security Administration and Washington State University to develop DCS. Photo courtesy Washington State University. Click to view larger.
Extreme behavior: New national security facility will open its doors to study materials at extreme conditions

Washington State University and Argonne National Laboratory will host a dedication ceremony for a first-of-a-kind (worldwide) research facility that has been built to unravel the mysteries of material behavior at extreme conditions and short time scales.

August 4, 2016