Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P22: Condensed Matter Research at Global Muon FacilitiesInvited
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Sponsoring Units: FIP Chair: Jason Gardner, National Synchrotron Radiation Research Center, Taiwan Room: New Orleans Theater A |
Wednesday, March 15, 2017 2:30PM - 3:06PM |
P22.00001: Muon Spin Relaxation/Rotation Studies of Novel Magnetic Systems Invited Speaker: Graeme Luke Muon spin relaxation/rotation is a powerful technique for probing magnetism in materials. As a real space probe, the muon complements neutron scattering's reciprocal space sensitivity. Muons probe magnetic fluctuations in a frequency window between inelastic neutron scattering and nuclear magnetic resonance. In this presentation I will describe our recent work on geometrically frustrated materials including the pyrochlore lattice compounds Yb$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$, Gd$_{\mathrm{2}}$Pt$_{\mathrm{2}}$O$_{\mathrm{7}}$, NaCaNi$_{\mathrm{2}}$F$_{\mathrm{7}}$ and others. I will also discuss $\mu$ SR's volume fraction sensitivity as applied to the transition from hidden order to antiferromagnetism in heavy fermion U(Ru$_{\mathrm{1-x}}$Fe$_{\mathrm{x}})_{\mathrm{2}}$Si$_{\mathrm{2}}$ and U(Ru$_{\mathrm{1-x}}$Os$_{\mathrm{x}})_{\mathrm{2}}$Si$_{\mathrm{2}}$. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:42PM |
P22.00002: Nanoscale investigations of thin films, heterostructures and interfaces with low energy polarized muons. Invited Speaker: Elvezio Morenzoni Positive polarized muons act as a non-destructive, non-invasive, and microscopic probe of matter (Muon Spin Rotation/Relaxation, muSR). Over the years they have provided unique information about magnetic, superconducting and other electronic properties of bulk matter. An extension of the muSR technique is given by the availability of muons with 100 {\%} spin polarization and whose energy can be continuously varied in the sub-keV keV range. This allows novel depth dependent muSR-studies on nm scale providing unique information in cases where the order parameters or the electronic properties are not homogeneous such as in heterostructures, thin films, buried layers or near the surface of a crystal. After a brief introduction of the low energy muSR technique at PSI, I will overview some experiments including investigations of unconventional high-Tc superconductors, low dimensional magnetic systems and of compounds and heterostructures, which may be relevant for future spintronics applications. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 4:18PM |
P22.00003: Muon spin rotation and relaxation study for energy materials Invited Speaker: Jun Sugiyama A muon spin rotation and relaxation ($\mu^{+}$SR) technique is very popular for studying microscopic internal magnetic fields in condensed matters. Recently, $\mu^+$SR measurements are also used to investigate the intrinsic nature of battery materials and hydrogen storage materials. Here, I wish to review the recent progress of the $\mu^+$SR research on such materials. In 2009, it was found that Li$^+$-ion diffusion in solids is detectable with $\mu^+$SR even in the materials containing magnetic ions [JS ${\it et~al.}$, PRL ${\bf103}$, 147601], while NMR is unable to do so due to the effect of localized magnetic moments on a spin-lattice relaxation rate. Such finding looks to open the door for the $\mu^+$SR research on energy materials. Since then, many battery materials have been investigated with $\mu^+$SR in order to determine their intrinsic diffusion coefficient ($D$) of Li$^+$ and Na$^+$ ions [M. Mansson $\&$ JS, Phys. Scr. ${\bf88}$, 068509]. Furthermore, using such intrinsic $D$, the other important parameters are successfully derived, such as, the reactive surface area [JS ${\it et~al.}$, Phys. Chem. Chem. Phys. B ${\bf15}$, 10402], diffusion pathway [JS ${\it et~al.}$, PRB ${\bf87}$, 024409], and density of mobile ions [H. Nozaki ${\it et~al.}$, Solid State Ionics ${\bf262}$, 585]. In 2008, the internal magnetic field in a complex hydrogen storage material, NaAlH$_4$, was studied with $\mu^+$SR [R. Kadono ${\it et~al.}$, PRL ${\bf100}$, 026401]. Despite the absence of magnetic ions, $\mu^+$SR spectrum exhibited a clear oscillation, indicating the formation of a H-$\mu^+$-H system in NaAlH$_4$. Moreover, it was proposed that the yield of the H-$\mu^+$-H system depends on the hydrogen desorption temperature ($T_{\rm d}$) through the diffusion of H in NaAlH$_4$. More systematic $\mu^+$SR work on $M$BH$_4 (M=$Li, Na, K, Mg, Ca, Sc) provided a clear relationship between the yield of the H-$\mu^+$-H system and $T_{\rm d}$ [JS ${\it et~al.}$, PRB ${\bf81}$, 092103]. In addition, very recent {\it in-situ} $\mu^+$SR measurements on MgH$_2$ during hydrogen desorption reaction revealed the importance of H-diffusion in solids for determining $T_{\rm d}$ [JS, J. Phys. Soc. Jpn, ${\bf85}$, 091012]. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:54PM |
P22.00004: Role of the Muon in Semiconductor Research Invited Speaker: Rick (P.W.) Mengyan Muons are used in semiconductor research as an experimentally accessible analog to the isolated Hydrogen (H) impurity -- a complex that is very difficult (or impossible) to study by other means. Hydrogen impurities of any concentration can modify the electrical, optical or magnetic properties of the host. For instance, H can be incorporated to remove electrically active levels from the energy gap (i.e. passivation) while some can form isolated centers that tend to be responsible for the trap and release of charge carriers and participate in site and charge-state dynamics which certainly affect the electrical properties of the host. Therefore, it can be quite useful to characterize these impurities in semiconducting materials that are of interest for use in devices. A muon has the same charge and spin as a proton but a mass that is nine times lighter. When implanted in a target material, a positively charged muon can behave as a light proton or bind with an electron to form a complex known as Muonium (Mu) with properties that are very similar to that of ionic or neutral H, respectively. A result of these similarities and direct non-destructive implantation is that Mu provides a direct measure of local electronic structure, thermal stability and charge-state transitions of these impurity centers. Since any material can be subjected to muon implantation and it is the muons themselves that mimic the H impurity centers, these measurements do not depend (at all) on the host's solubility of hydrogen nor do they require some minimum concentration; unlike many other techniques, such as EPR, ENDOR, NMR, or IR vibrational spectroscopy. Here we summarize major contributions muons have made to the field of semiconductor research followed by a few case studies to demonstrate the technique and detailed knowledge of the physical and electronic structures as well as dynamics (e.g.: charge-state and site transitions; local motion; long-range diffusion) of Mu/H that can be obtained. [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:30PM |
P22.00005: Is magnetism relevant to cuprate superconductivity: lanthanides versus charge compensated 123? Invited Speaker: Amit Keren Many theories suggest that the mechanism for cuprate superconductivity is based on super-exchange interaction between electrons. The most obvious test of these theories is a measurement of the correlation between $T_{c}$ and the super-exchange parameter $J$. Alteration of $J$ is achieved by chemical modifications or external pressure. Measurements of $J$ are done with: Neutron scattering, muon spin rotation (muSR), two magnon Raman scattering or resonant inelastic x-ray scattering. However, the experimental data is confusing. A recent Raman study showed an anticorrelation between $T_{c}$ and $J$ in the set of LnBa2Cu3Oy compounds with Ln$=$(La,..Lu,Y) [B.P.P. Mallet \textit{et al.}, Phys. Rev. Lett. 111, 237001 (2013)]. On the other hand, experimental measurements on the charge compensated 123 material (Ca$_{\mathrm{x}}$La$_{\mathrm{1-x}})$(Ba$_{\mathrm{1.75-x}}$La$_{\mathrm{0.25+x}})$Cu3O$_{\mathrm{y}}$ (CLBLCO) inferred an overall positive correlation between $T_{c}$ and $J$ [D.S. Ellis \textit{et al.}, Phys. Rev. B 92, 104507 (2015)]. Thus, the effect of $J$ on $T_{c}$ is not established experimentally. In this talk I will review the experimental situation, mainly from the muSR viewpoint, and shed light on this controversy. [Preview Abstract] |
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