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Ultrafast Materials Program
Ultrafast X-ray Studies of Correlated Materials: Science Challenges and Opportunities
Robert Schoenlein
Materials Sciences Division - Ultrafast Materials Program Chemical Sciences Division – Ultrafast X-ray Sciences Laboratory
Next Generation Light Source
LCLS-II New Instruments Workshops March 19-22, 2012
Lawrence Berkeley National Laboratory
Ultrafast Materials Program
Understand the Interplay between Atomic and Electronic Structure
- Valence electronic structure – energy levels, charge distribution, bonding, spin
- Atomic structure – coordination, atomic arrangements, bond distances
Tlifetime (E-EF)-1/2
- beyond single-electron band structure models, Bloch, Fermi Liquid Theory
complex materials exhibiting strong correlation among charges,
and between charge, spin, orbit, and lattice
Ultrafast Dynamics in Complex Materials - Beyond Bloch
Oxides of Transition Metals
(Cu, Mn, Ni, V…)
How do the properties of matter emerge from the: correlated motion of electrons, and coupled atomic and electronic structure?
Ultrafast Materials Program
atomic vibrational period: Tvib = 2p(k/m)-1/2 ~ 100 fs
k~eV/a2 m~10-25 Kg
Atomic Structural Dynamics
ultrafast chemical reactions
ultrafast phase transitions
ultrafast biological processes
N
N
Fe
O
Fundamental Time Scales in Condensed Matter
electron-phonon interaction ~ 1 ps
e-e scattering ~10 fs
e- correlation time ~100 attoseconds (a/VFermi)
Electronic Structural Dynamics
charge transfer
- correlated electron systems
electronic phase transitions
bond dynamics, valence charge flow
Ultrafast Measurements: - separate correlated phenomena in the time domain - direct observations of the underlying correlations as they develop
Ultrafast Materials Program
• Ultrafast x-rays will probe correlations among charges and between electronic and atomic structure
• On fundamental (meV) energy scales of low-energy excitations, with full momentum resolution
• With sensitivity to spin and magnetic order
• Using tailored excitations to separate correlated phenomena in the time domain
Ultrafast X-rays –
Powerful tool for understanding correlated materials
Ultrafast Materials Program
Crystal structure of Manganites leads to complex phase diagram, and exotic electronic properties
Pr1-xCaxMnO3
AFI
CAFI
FI CI
COI
PI
Pr1-xCaxMnO3
TN
TC
TCO
TN
Tem
per
ature
[K
]
x
400
350
300
250
200
150
100
50
0
0 0.1 0.2 0.3 0.4 0.5
Colossal Magneto- Resistance (CMR)
resistivity ~1/BN
Insulator-Metal Phase transitions driven by applied magnetic field (CMR), and by ultrafast optical excitation (photo-doping): Fth~4 mJ/cm2
Spin-ordered (SO) phases
Ultrafast Materials Program
Mn-O stretch Mn-O
bend
Scientific Questions and Challenges Electronic Structure:
Dynamics of charge localization/delocalization? ultrafast XAS – Mn-3d/O-2p hybridization
Dynamics of charge/orbital/spin ordering? ultrafast resonant x-ray diffraction
Magnetic nature of the metallic phase – ferromagnetic? ultrafast x-ray dichroism, magnetic scattering
Pr1-xCaxMnO3
mid-IR 10-24 mm 1mJ, 200 fs
• THz vibrational control of correlated-electron phases targeting specific vibrational modes - Mn-O stretch
• Ultrafast I-M phase transition - electronic ground state x104 resistivity change
OMn
O
d
d
2
Pr
Tolerance Factor Mn-Mn hopping rate charge de-localization
Mn3+ Mn4+
O
Vibrationally Driven I-M Transition in a Manganite
Ultrafast X-ray techniques relevant for a broad range of complex materials
(organics, multiferroics, novel superconductors…..)
M. Rini, et al., Nature, 2007
Ultrafast Materials Program
Tokura et al., PRB, 1996
AFI
CAFI
FI CI
COI
PI
Pr1-xCaxMnO3
TN
TC
TCO
TN
Tem
per
atu
re [
K]
x
400
350
300
250
200
150
100
50
0 0 0.1 0.2 0.3 0.4 0.5
Charge/Orbital Ordering in Manganites Time-resolved resonant x-ray diffraction
65 K
spin down spin up
Mn3+ Mn4+
Order dynamics (formation/melting) Underpins the insulator to metal transition
CO/OO/SO – charge localization FM – charge delocalization
Pr0.5Ca0.5MnO3
Mn L-edge (¼ ¼ 0)
Ultrafast Materials Program
Charge/Orbit/Spin Ordering in Manganites Resonant X-ray Diffraction – Pr0.7Ca0.3MnO3
Mn L-edge (¼ ¼ 0)
Pr0.5Ca0.5MnO3
spin
ord
erin
g
• Scattering spectra differ dramatically from XAS • Different azimuthal angular dependence • Strong spin ordering component (compared with 50% doping)
S. Zhou et al. Phys. Rev. Lett., 106, 186404 (2011) ALS Beamline 8.0
Ultrafast Materials Program
Pr0.5Ca0.5MnO3
Charge/Orbital Ordering in Manganites
AFI
CAFI
FI CI
COI
PI
Pr1-xCaxMnO3
TN
TC
TCO
TN
Tem
per
atu
re [
K]
x
400
350
300
250
200
150
100
50
0
0 0.1 0.2 0.3 0.4 0.5
Ultrafast Materials Program
SO
OO
•SO stabilized only below TCA
•OO is weak –
disrupted by charge
disproportionation
TCO/OO TN TCA
Pr0.7Ca0.3MnO3
Charge/Orbital Ordering in Manganites
Ultrafast Materials Program
Resonant X-ray scattering selectively probes the spin-ordered (SO) phase
X-ray pulses follow the dynamics of the spin-ordered phase: melting and recovery
PCMO
500 ps delay
Pr0.7Ca0.3MnO3
f=90°
Ultrafast Materials Program
A new microscopic picture of SO and its relation to the insulator/metal phase transition emerges
Insulator: charge dynamics are along 1D spin-ordered chains
FM
FM FM
FM
F < 4 mJ/cm2 F > 4 mJ/cm2
Metal: charge dynamics are 3D, i.e. between chains, due to metallic domains
S.Y. Zhou et al., in review
X = 0.25, Stripe
Non-thermal dynamics of stripe nickelates
• RSXS directly measures the order parameters of both CO and SO.
• Both CO and SO are suppressed by pump laser excitations
• Rich information is contained in the recovery behavior.
W. S. Lee, Y. D. Chuang et al., Nature Comm. (in press)
La2-xSrxNiO4
LCLS - SXR
Number of surprises…
RSXS on CO Optical Reflectivity
SO –CO comparison
No change of diffraction peak position and peak width.
Dynamics of order parameters’ amplitude and phase can be disentangled.
Initial recovery time scale of CO and SO are comparable, despite of distinct microscopic interactions for the spin and charge.
CO and SO’s period and correlation unchanged. -> No topological defects are created.
Order parameter’s phase fluctuation is the bottleneck of the recovery.
Cooperative dynamics of CO and SO due to their strong coupling effect.
CO
W. S. Lee, Y. D. Chuang et al., Nature Comm. (in press)
PSI / ETHZ / LCLS / Stanford / LBNL / Oxford
What is the ultimate speed of magnetic phase transitions?
CuO: antiferromagnetic phase transition
- Time-resolved resonant x-ray diffraction measures time tp for start of transition
- Minimum lag-time of 400 fs: limited by spin dynamics
S. Johnson, de Souza, Staub et al., PRL 108, 037203 (2012)
Johnson (ETH Zurich), Staub, Beaud, Ingold (PSI) LCLS - SXR
Collinear-to-Spiral Anti-Ferromagnetic Phase Transition in CuO
Current and near-future projects
Multiferroics: dynamics of domain switching
• How fast can electric field control of magnetism
occur in an induced multiferroic?
Kimura, Ann. Rev. Mater. Res. 37, 387
Interaction of lattice, orbital,
charge & spin orders
• Can we control electronic
properties of correlated
systems by dynamically
manipulating structure?
Johnson (ETH Zurich), Staub, Beaud, Ingold (PSI)
LCLS - SXR
Ultrafast Materials Program
• La0.5Sr1.5MnO4 mid-IR lattice excitation
• Prompt shift in magnetic- and orbital-order parameters
• Control of magnetism through ultrafast lattice excitation
Importantly, a CCD only measures a slice in reciprocal space
Extended vol. in reciprocal correlations lengths in k-space.
• no measurable change in in-plane correlations (along a- and b- axis)
• Sizeable change in scattering wavevector and line shape along the c-axis
Detector -
• 360o rotation in the horizontal scattering plane (2q)
• 90o rotation in the vertical scattering plane (g)
• 2 APDs + 1 thermopile (IR) (configurable)
• CCD can access back scattering angle ~155o
• Motorized six strut system for alignment
Sample -
• 360o azimuth rotation (f)
• 360o rotation in the horizontal scattering plane (q)
• 100o flip rotation (virtual axis, c)
• 15K (2Hr) up to 450K (limited by diode)
• Transferrable sample holder
(max ~17mm OD mounting area)
RSXS Endstation Overview
Y.-D. Chuang et al.
Advanced Light Source
Incident photon beam Rotary seal
Manipulator and cryostat
CCD
Race-track type bellows
Kaydon bearing
• Kaydon bearing rotates chamber + spectrometer by >30 deg
• Race-track bellows enables the rotation
• Multiple emission port covers scattering angles from ~0 to 150 deg.
Y.-D. Chuang, Z. Hussain et al.
Advanced Light Source
Z.X. Shen et al.
Stanford/SLAC
From TR RSXS to Time- & q-Resolved RIXS
Ultrafast Materials Program
S. Zhou
Y. Zhu
M. Langner
M. Rini
LBNL - Materials Sciences
Acknowledgements
Y.-D. Chuang
Z. Hussain
E. Glover
M. Hertlein
LBNL- Advanced Light Source
Y. Tomioka
JRCAT Tsukuba
Y. Tokura
U. Tokyo
Robert Kaindl
Joseph Robinson
Giacomo Coslovich
LBNL – Materials Sciences
Wei-Sheng Lee
Donghui Lu
Rob Moore
Mariano Trigo
David Reis
Joshua Turner
William Schlotter
Oleg Krupin
Z.X. Shen
Stanford/SLAC
Ultrafast Materials Program
• RSXS scattering chamber with control of sample orientation, software etc.
• High-speed, low-noise X-ray area detectors
• Capability for applied magnetic field >1 Tesla
• Time- and q-resolved RIXS (multiple q, <100 meV resolution)
• Soft X-rays (spanning transition-metal L-edges)
• Full X-ray polarization control (differential signal sensitivity <1%)
• <100 fs (10 fs ) temporal resolution
• <100 meV soft X-ray spectral resolution
• Hard X-rays (~1 Å resolution) q charge order
• Tailored laser excitation (UV-visible-THz), ~10 mJ/cm2, BW/pulse duration
Future directions:
• Coherent stimulated Raman (stimulated scattering)
• XPCS – spontaneous dynamics
Instrumentation Needs