robert h heffner · muon science is applicable . from quanta to the continuum - opportunities for...
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Robert H Heffner
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Brief overview of µSR in the USA. Making the science case. What might a µSR facility at FNAL look like?
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Beginning of SR
+ e + e a=1/3
a=1+
dN(t)/dt exp(-t/) (1 + a G(t) cos )
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LBL – Yamazaki and Crowe groups (1970’s)
Spawned future efforts at meson factories ▪ J. Brewer – TRIUMF, A. Schenck – SIN (now PSI)
Surface muon beam developed (Bowen et al., 1985) SREL – J. Kossler, K. Stronach et al.
Very low intensity; samples inches in diameter LAMPF (Los Alamos) ~1978 – “Practical Applications Group”
Continued until about mid 1990’s when DOE shut down medium energy physics program at LAMPF
Included groups from U. Tokyo, Sandia, Texas Tech, UC Riverside, Wm & Mary, UC Berkeley, San Jose, Vir. State, ….
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Inquiries to SNS planning groups for a µSR facility at ORNL (2000) – draft proposal
BNL/AGS (~2005) – J. Kossler et al. Presentation to SSSC (M. Kastner, chair; Pat
Dehmer /BES/facilities) by D. MacLaughlin (R. Heffner, Y.J. Uemura) 2006
NSF proposal - K. Nagamine (UC Riverside,2010) for design of new facility in meson hall at Los Alamos.
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Main cause: lack of a suitable machine matching (the available) physics techniques (see below)
Secondary causes: ‘nuclear/particle physics’ approach, rather than
‘condensed matter’ approach: Culture
Opposition from other communities, mostly neutron scattering (should be a natural ally).
These issues could greatly impact an effort at FNAL.
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PSIISISTRIUMF
KEKJ-PARC
TRIUMF ISIS PSI
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PSI, TRIUMF
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No muon
detector
Muon pulse
105 muons
e+ detector is
segmented to
handle high
instantaneous
burst rate.
All muons
assumed to
arrive
‘simultaneously.’
Intrinsic time-
spread exists
t ≤ 40 - 100 ns
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Beam Power
(MW)
Rep rate
(Hz)
Pulse width
Separation
(ns)
TRIUMF 0.15 CW -
PSI 1.0 CW -
ISIS
0.16 50 80
340
J-PARC
(2012)
0.21.0 (?) 25 140
600-700 LAMPF
(Los Alamos)
0.8 120 7.5x105
8.3x106
No muon beams
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Ideal: Time structure
▪ Either CW, or ▪ Pulsed at 10-50 kHz, width ≤ 30 ns
(FFAGs are nice!)
Power ≥ 1 MW
LAMPF 5-9% DF: 10-20 x slower data
acquisition rates than CW machines.
Pulse width 750 µs Worst of both worlds! User community migrated to
other meson factories
With permission from J. Brewer, UBC
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In USA (and Canada) µSR facilities developed by nuclear physicists: Culture
▪ Build an experiment, install it, do it, tear it down. ▪ Requires a sizeable team.
Materials science user facilities
Culture ▪ Bring your ‘sample,’ put it in automated spectrometer, go home with data. ▪ Small team (2-3 people)
LAMPF never did -and TRIUMF took a while to almost-adopt a
materials-science culture.
PSI and ISIS more rapidly adopted a materials-science culture. J-PARC (MUSE) will likely do this, too.
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Questions to be answered • How do muon beams contribute to DOE priorities in Materials Science? • Are muons competitive with neutron or light scattering? • Is the planned facility competitive with other muon facilities? • Is there a demand, a user community? • Why Materials Science at Fermilab? • Will FNAL provide a dedicated or parasitic facility? • Cost/benefit – How much $ for how many users?
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Transition from Observational Science to Control Science
• Control of materials’ processes at electronic (quantum) level. • Design new forms of matter with tailored properties. • Understand and control emergent, collective phenomena. • Master energy/information on nanoscale* to rival living systems. • Characterize and control matter very far from equilibrium.
* nanoscale: 0.1 – 0.5 nm
Muon science is applicable
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From quanta to the continuum - Opportunities for mesoscale* science BESAC subcommittee on Mesoscale Science – G. Crabtree (ANL) and J. Sarrao (LANL) Co-chairs
• Master defect mesostructure and its evolution. • Optimize transport and response properties by design/control of mesoscale structure. • Elucidate non-equilibrium and many-body physics of electrons. • Harness fluctuations and degradation for control of metastable mesoscale systems . • Directing assembly of hierarchical functional materials.
* mesoscale 5 – 100 nm Muon science is applicable
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Study materials across a wider range of • Spatial and temporal scales
• 1 – 100 nm, excitations 10-9 to 10 eV
• Under increasingly extreme conditions of
• Temperature, and
• Applied pressure, magnetic and electric fields • Make simultaneous measurements
Probes: neutrons, light , STM, …., muons
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With permission from J. Brewer, UBC
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Excitations involve both energy () and momentum (q) transfer.
Generalized susceptibilities ”(q, ) and ’(0,0)
• µSR: = µB, and for a local probe we have q
• So µSR doesn’t provide full q and information.
• However, it does readily provide measurements of: • Magnetic/non-magnetic volume fractions
• Tiny magnetic fields (< 1 G), fluctuation times 10-4 to 10-12 s
• High statistical precision and small samples compared to neutron scattering
• Nano- to meso- scale depth profiling (LEM) • Muon scattering and radiography provide additional profiling probes
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• µSR dictates spatially inhomogeneous relaxation because see two-exponential relaxation • Fast spins correspond to more metallic regions • Inhomogeneity persists for t > µs • Can track volume fraction of these regions vs. T.
Heffner, Sonier et al., 2001-2004
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22
1
Decay µ+ at PSI
Heffner, Goko, Andreica et al. 2010
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0 10 20 30 40 500.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
25 days old
400 days old
(s
-1)
T(K)
PuCoGa5
Tc
H = 600 Oe
• Normal-state linewidths (n) unchanged
by aging (mesoscale defects)
• TC reduced by predicted amounts
• Quasi-linear T dependence at low T
• Line of nodes
• Linewidth is drastically
reduced by aging
• Breakdown of Abrikosov-Gor’kov
pair-breaking mechanism
H || c-axis
Ohishi , Heffner, Morris et al. 2007
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0.0 0.5 1.0 1.5 2.0 2.5 3.00.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
T(K)
Lin
ew
idth
Sr2RuO
4
The increase in zero-field linewidth indicates the presence
of spin or orbital moments associated with
superconducting state
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0.24
0.25
0.26
0.27
0.28
0.29
0.30
0.31
T(K)
U0.965
Th0.035
Be13
0 1 2 3 4 5 6
0.14
0.16
0.18
T(K)
PrOs4Sb
12
Aoki et al. 2003 Heffner et al., 1990 Luke et al. 1998
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Bator et al. (2012) PSI Monte Carlo simulation Prokscha et al. (2012) PSI
Photo production of charge carriers in Si(100) Mean depth 160 nm Range of surface muon (4 MeV)
in Fe 2x105 nm
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SR rate is reduced as film thickness is reduced
50 nm: = bulk value.
Smaller more rapid fluctuations less freezing.
Morenzoni et al., PRL (2008)
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Yes, in a wide variety of ways!
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Multi-use facility: most optimistic view
J-PARC Materials and Life Science Facility/MUSE
LEM
Surface/Decay
Surface lines
High energy µ/e-
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Low Energy Muons – Method may depend on proton beam structure
Surface muon beam (s) Decay beam (s) Penetrating for high pressure cells
Accelerated beam (s) Radiography and muon scattering
Technology development – synergy with FNAL Improve pressure and field capabilities Higher counting rates
▪ Segmented target – track both µ and e
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Now entire beam rate into sample is limited by pile-up for time-differential measurements: few times 104 s-1
If one segments the sample by tracking incoming µ and outgoing e, the overall rate increases by number of segments and background is reduced to near zero.
May be able to reach sub-mm level (?) and study micro samples.
104 s-1 x 25 !
µ
e
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1 Sr solid angle
Spot size 100 m E/E = 0.2 % 8000/s LEM Nanophysics Spot size few mm E/E = 0.1 % Energy can be increased Radiography Pressure cells
• LANSCE: 800 MeV, > 700 A, 70 Hz rep rate • Microstructure: 200 MHz inside bunch 625 s long is well suited to rf for bunching or acceleration
K. Nagamine A. Jason
Example of new muon beams for materials science/chemistry
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K. Nagamine, A. Jason
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Tomographic imaging technique – energy loss and multiple scattering
Compared to photons (x- or -rays), muons ▪ Pose limited health risks from radiation
▪ Can resolve 3D structures with only one radiation
▪ Can penetrate heavy objects
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X-ray range only several cm of Fe
Muon range in Fe Introductory Muon Science, Kanetada Nagamine, Cambridge University Press (2003)
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Low Energy Muons – Method may depend on proton beam structure
Surface muon beam (s)
Decay beam (s)
Penetrating for high pressure cells
Accelerated beam (s) Radiography and muon scattering
Technology development:
Pressure and field capabilities Higher counting rates
▪ Segmented target – track both µ and e
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Tests of fundamental physics (symmetries) Probe of nuclear matter - capture-(muonic atom → x-rays)
Muon catalyzed fusion (- capture on d or t atom) (dt) molecule → n + (fusion) + -
Radiography (measuring density profiles) Muon as a light isotope of hydrogen Reaction rates, impurities in semiconductors,
free radicals in chemistry Probe of internal magnetic fields in materials
SR
physics chemistry biology
Can the scope of investigation be broadened?
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• Do muon beams contribute to DOE priorities in Materials Science? • Yes, in many cases.
• Are muons competitive with neutron or light scattering? • Yes, in selected cases, but other communities in US not supportive yet.
• Is the planned facility competitive with other muon facilities? • Potentially better, especially for LEM and muon radiography in N America.
• Is there a demand, a user community? • Maybe, needs assessment. Could be seeded by TRIUMF users if compelling.
• Why Materials Science at Fermilab? • Synergy of µSR technique with extraordinary expertise in particle detection and
analysis. Diversification: CW and Pulsed beams available.
• Will FNAL provide a dedicated or parasitic facility? • Fully adopt materials science culture.
• Cost – How much $? • ???
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