Emerging Materials Recent Highlights

Overview:

This program emphasizes materials synthesis and processing, advanced characterizations and studies of materials properties, all aimed at a fundamental understanding of materials that have potential for applications. Currently the program concentrates on complex oxides with two connected goals:

• Understanding the complex interrelationship between charge and spin degrees of freedom and with crystal structure
• Understanding the proximity interactions which occur when an oxide shares a common boundary with a metal or other oxides.

Recent highlights:

Quantum Spins Mimic Refrigerator Magnets

October 11, 2012 The behavior of magnetic moments in metal oxides such as iridates is dominated by strong spin-orbit coupling effects. In layered compounds such as Sr3Ir2O7, the direction of these moments is controlled at the quantum level by dipolar interactions that are akin to those of classical bar magnets. From a functional standpoint, our findings suggest novel routes toward engineered structures that allow manipulation of moments without magnetic fields, a general strategy for future low-power electronics platforms. Read the highlight

Phase Diagram of Ba_1-xK_xFe₂As₂

May 7, 2012 A key goal of this work has been controlling the homogeneity of highly volatile K dopants within strict limits(Δx <0.01) that would allow us to identify structural, magnetic, and superconducting phase boundaries reliably. With highly homogeneous samples in hand, a high-precision phase diagram could be determined by systematically combining neutron and x-ray diffraction with precision magnetic data.  The result is a clearer picture of the competing order parameters in this pnictide superconductor system. Read the highlight

Molten Structure in Polysulfides, from Batteries to Directed Synthesis

May 14, 2012 A tandem approch of in situ, high-temperature vibrational spectroscopy and x-ray total scattering provides a view of molten salts that challenges the established wisdom about species present in the melt. The polysulfide chain length is strongly controlled by the sulfur content, which helps explain how ions react in sulfur-based batteries and during flux growth of complex materials. Read the highlight

Magnetic Modes in Sr₂IrO₄ Revealed by Resonant Inelastic X-ray Scattering

April 23, 2012 Using resonant inelastic x-ray scattering (RIXS), we reveal the nature of magnetic interactions in a 5d transition-metal oxide, Sr2IrO4, where strong spin-orbit coupling induces a complex spin-orbital wave function labeled by the effective total angular momentum. The results bear compelling similarities to high Tc cuprates. Read the highlight

Unconventional Superconductivity in Iron Pnictides: Ba_1-xK_xFe₂As₂

October 18, 2011 A focus on growing highly homogeneous single crystals of the 122 pnictide superconductor has allowed a redrawing of the phase diagram as well as identification of a resonant spin excitation in the superconducting phase. Read the highlight

Electronic Valves in Layered Oxides

June 29, 2011 Two distinct types of electrons are found to coexist in a layered manganese oxide – those moving freely and those frozen into stripes that can act like electronic ‘valves,’ turning off and on the flow of electrons. Read the highlight

Breaking up is Easy to Do: Local Structure of Dimer Pairs in CuIr₂S₄

January 24, 2011 Ir4+—Ir4+ dimer pairs found in an insulating phase of the mixed valence sulfide spinel, CuIr2S4,vanish completely on all length scales during heating through an insulator-metal transition but persist locally during an x-ray induced transition. Read the highlight

Exploring Complexity in Electronic Materials: CaFe₄As₃

August 11, 2010 Discovery synthesis and characterization of a novel tunnel structure, CaFe4As3, is part of an ongoing effort in Emerging Materials to develop a materials database of superconductors and related materials. Read the highlight

Heating Effects in intrinsic Josephson Junction Mesas of Bi₂Sr₂CaCu₂O₈

June 22, 2010 We show that anomalously high and sharp peaks in the conductance of intrinsic Josephson junctions in Bi2Sr2CaCu2O8+d (Bi2212) single crystal mesas result from strong self-heating rather than superconducting energy gaps. Read the highlight

Multifunctional Materials By Design

July 24, 2009 “Materials by Design” takes a step forward with the design, synthesis, and experimental validation of coexisting ferromagnetism and ferroelectricity—multiferroicity—in a high pressure form of iron titanate, FeTiO3. Read the highlight

Narrow Phase Fields for Layered Manganites

October 3, 2008 In the bilayer manganite, La2-2xSr1+2xMn2O7, near x=0.5 and x=0.6, we have established that the phase fields for charge and orbital order (COO) are needle-like with a width of a few per cent at most. Studying such narrow phase fields requires extreme care and validation of dopant concentration gradients during crystal growth. Read the highlight