Robert H Heffner

Brief overview of µSR in the USA. Making the science case. What might a µSR facility at FNAL look like?

Beginning of SR

+ e + e a=1/3

a=1+

dN(t)/dt exp(-t/) (1 + a G(t) cos )

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, ….

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.

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.

PSIISISTRIUMF

KEKJ-PARC

TRIUMF ISIS PSI

PSI, TRIUMF

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

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

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

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.

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?

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

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

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

With permission from J. Brewer, UBC

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

• 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

22

1

Decay µ+ at PSI

Heffner, Goko, Andreica et al. 2010

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

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

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

SR rate is reduced as film thickness is reduced

50 nm: = bulk value.

Smaller more rapid fluctuations less freezing.

Morenzoni et al., PRL (2008)

Yes, in a wide variety of ways!

Multi-use facility: most optimistic view

J-PARC Materials and Life Science Facility/MUSE

LEM

Surface/Decay

Surface lines

High energy µ/e-

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

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

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

K. Nagamine, A. Jason

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

X-ray range only several cm of Fe

Muon range in Fe Introductory Muon Science, Kanetada Nagamine, Cambridge University Press (2003)

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

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?

• 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 $? • ???