Atomic structure at the nanoscale a 21st century materials challenge

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Slide 19

Thiospinel CuIr2S4

HIGHLIGHT

Slide 20

Thiospinel CuIr2S4 properties: structural transition

- in-situ TEM micrographs

W. Sun et al., J. Phys.l Soc. Jpn., 70, 2817 (2001).

- Electron diffraction

- TS226K

Tetragonal

I41/amd

Cubic

Fd-3m

HIGHLIGHT

Slide 21

Thiospinel CuIr2S4 properties

- Metallic at high T

Insulating at low T

TMI226K

PES, NMR, LDA:

Cu1+ Ir3.5+ (half-integer!)

PES of the insulating phase:

~0.1 eV gap near EF

Ir 5d DOS strongly distorted

T. Furubayashi et al., Solid State Comm. 126, 617 (2003).

S. Nagata et al., Physica B. 194, 1077 (1994).

J. Matsuno et al., Phys. Rev. B. 55, R15979 (1997).

HIGHLIGHT

Slide 22

Thiospinel CuIr2S4 properties

- High T: Pauli paramagnetic

Low T: nonmagnetic

(NMR, Mössbauer, magnetic susceptibility)

T. Furuyabashi et al., J. Phys. Soc. Japan. 63, 3333 (1994).

HIGHLIGHT

Slide 23

CuIr2S4: background information

D.I. Khomskii and T. Mizokawa,

PRL 94, 156402 (2005).

Low-T structure

Red octahedra Ir3+

Blue octahedra Ir4+

P.G. Radaelli et al.,

Nature 416, 155 (2002).

- Metal at high temperature (Ir is nominally 3.5+)

- Insulator at low temperature (Ir’s are 3+ AND 4+)

- T-induced Metal-Insulator transition at ~226K

- Charge ordering and spin dimerization at low-T

- Long range charge ordered patterns of isomorphic octamers

- Associated structural change (Peierls distortion)

- Ir4+: short Ir-Ir distances appear (~3.0Å) - DIMER

- Ir3+: no short Ir-Ir distances (~3.5Å)

HIGHLIGHT

Slide 24

Reduced dimensionality due to specifics of xy-orbitals

CuIr2S4

D.I. Khomskii, Physica Scripta 72, CC8-14 (2005)

HIGHLIGHT

Slide 25

CuIr2S4: effect of x-ray irradiation

V. Kiryukhin et al.,

PRL 97, 225503 (2006).

Cubic

Fd-3m

Triclinic

P-1

Tetragonal

I41/amd

Long range

ordered dimers

IC

C

Insulator

Metal

Tetragonal

I41/amd

- Incommensurate (IC) short range

state below ~40K

- Commensurate (C) short range

state 40K<T<~100K

Melting of LRO dimers at low T!

HIGHLIGHT

Slide 26