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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


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?


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 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


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


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


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)


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


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


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


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°


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


• 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


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


• 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

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