TNéel

TMIT

Abhijit Biswas, et al. 4

The unintended height of a

crystal placed in a powder x-

ray diffractometer shifts

the Bragg peak locations3:

2 c sin Θ −H

RcosΘ = L λ

x = 0x = 0.34

…where H is the height offset and R is the diffractometer radius.

Two samples’

peaks differing at

the (00L)-type

peak 0010

Motivation

Magnetic and Electronic Transitions in a Highly-Doped Mott InsulatorMichael Aling, Dr. Julian Schmehr, Prof. Stephen D. Wilson

UCSB Department of Materials

It is hoped that this study will reveal new

phases in an electronically-useful material.

Cousins of this Ruddlesden-Popper ruthenium-

doped strontium iridate become superconducting at

low temperatures, while also exhibiting other rich

physical phenomena: fermi liquid ground states,

metamagnetism, colossal magnetoresistance, and

multiple electronic transitions. Sr3Ir2O7’s relation to

cuprate high-temperature superconductors is

further motivation for study.1

The Parent Compounds Previous Work1

Continuing and Future Work

Doping Sr3(Ir1-xRux)2O7

References

Identifying Electronic & Magnetic Phases

Unusual percolative phase transitions in

Sr3(Ir1-xRux)2O7 impact properties:

300

10000

Tem

pera

ture

(K

)

Ru level (%)

*

Interaction strengthens AF order

when it would otherwise die off (*)

Cro

ss sectio

n sch

em

atic

(a single

crystal)

Adapting x-ray diffraction to save time and preserve samples

Paramagnetism

(PM)

Antiferromagnetism

(AF)

Resistivity Analysis Reveals TransitionsStudying little-known region: 40% to 60% Ru

(Will add error bars)(Should also add powder points)

Sr3Ir2O7 (“327”), a Mott insulator, has a smaller

bandgap than its “214” cousin, making it an ideal

candidate to be doped in order to probe the

combination of crystal field splitting, spin-orbit

coupling, and small Coulomb interaction which

together make it insulating.1, 2 Sr3Ru2O7 is a metal

with paramagnetic disorder (contrasting the iridate’s

low-temperature antiferromagnetism) near a

magnetic instability.1

No transitions observed

at x=0.62

Progress on Phase

Diagram

When this material

becomes metallic,

it is only because a

network of

metallic pockets

begins to join

(percolative

threshold.) In

both the insulating

and metallic

regimes, regions of

both phases

coexist on a

nanometer scale.

Utilizing Lattice Parameter Contraction

Dopant Distribution in Growths(Each point represents one crystal)

About 5 samples found in desired range, across 3 growths

Dopant level varies greatly in flux

growths. X-ray diffraction (XRD)

is faster and less costly than

EDX (energy-dispersive x-ray

spectroscopy). While EDX

directly analyzes concentrations,

this technique offers an indirect

method.

Nonlinearity caused by

pull of competing

nanometer-scale

regions

A MATLAB program translates

information about peak location into

the lattice parameter c by solving

the system numerically.

The results from this single-crystal

method are as accurate as powder

results from the previous study.

Lattice Parameter by Dopant Level(Each point represents one sample)

Tem

pera

ture

(K

)M

etal

-in

sula

tor

Mag

net

ic

Lattice Parameter Solver

The MATLAB program will be

expanded into a full Rietveld

refinement capable of overcoming

the primary challenge associated

with a single-crystal technique:

resolving peak splitting due to

uneven crystal surfaces. Human

error will also be reduced by the

further automation of the process.

After first completing the survey of

the x=0.4 to 0.6 region by gathering

heat capacity, magnetization, and

sub-Kelvin resistivity (temperatures

at which cousin compounds become

superconducting), further growths

focused around x=0.75 will push

forward into a regime even less-

studied.

People

Michael Aling

Sophomore

Mechanical Engineering

Julian Schmehr

Postdoctoral Scholar

Materials Science

Stephen D. Wilson

Principal Investigator

Materials Science

1. Dhital, C. et al. Carrier localization and electronic phase separation in a

doped spin-orbit-driven Mott phase in Sr3(Ir1-xRux)2O7. Nat. Commun.

(2014).

2. Dhital, C. et al. Spin ordering and electronic texture in the bilayer iridate

Sr3(Ir1-xRux)2O7. Physical Review B 86, 100401(R) (2012).

3. Jesche, A. et al. X-Ray diffraction on large single crystals using a powder

diffractometer. Philosophical Magazine (2016).

4. Abhijit Biswas, Ki-Seok Kim and Yoon Hee Jeong (2016). Metal–Insulator

Transitions and Non-Fermi Liquid Behaviors in 5d Perovskite Iridates,

Perovskite Materials - Synthesis, Characterisation, Properties, and

Applications, Dr. Likun Pan (Ed.), InTech, DOI: 10.5772/61285.

Both adapted from 1

Supported by NSF CAREER-Award DMR-1056625