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Cu(Ir₁ - xCrx)₂S₄: a model system for studying nanoscale phase coexistence at the metal-insulator transition.

Božin ES, Knox KR, Juhás P, Hor YS, Mitchell JF, Billinge SJ - Sci Rep (2014)

Bottom Line: Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood.We demonstrate a hitherto unobserved coexistence of an Ir(4+) charge-localized dimer phase and Cr-ferromagnetism.The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates.

View Article: PubMed Central - PubMed

Affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973.

ABSTRACT
Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood. Despite their ubiquity, they are hard to study because they produce weak diffuse signals in most measurements. Here we propose Cu(Ir₁ - xCrx)₂S₄ as a model system, where robust local structural signals lead to key new insights. We demonstrate a hitherto unobserved coexistence of an Ir(4+) charge-localized dimer phase and Cr-ferromagnetism. The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates. We suggest that the presence of quenched strain from dopant ions acts as an arbiter deciding between the competing ground states.

No MeSH data available.


Related in: MedlinePlus

Dimer signal in the PDF and estimate of the fraction of dimerized Ir4+.(a) Comparison of experimental PDFs at 300 K (red) and 10 K (blue) over a narrow r-range for CuIr2S4, with the difference curve (green) offset for clarity. Shaded features in the difference curve (color coded by green for dimer and red for loss peaks) are used in the dimer fraction evaluation. (b) Evolution of the dimer fraction with Cr-doping: the color code corresponds to that used for marking the features in the difference curve in (a), that were considered in the numeric integration analysis described in the Supplementary Material. Solid black symbols represent an arithmetic average of green and red values, while the dashed line is a guide to the eye.
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f3: Dimer signal in the PDF and estimate of the fraction of dimerized Ir4+.(a) Comparison of experimental PDFs at 300 K (red) and 10 K (blue) over a narrow r-range for CuIr2S4, with the difference curve (green) offset for clarity. Shaded features in the difference curve (color coded by green for dimer and red for loss peaks) are used in the dimer fraction evaluation. (b) Evolution of the dimer fraction with Cr-doping: the color code corresponds to that used for marking the features in the difference curve in (a), that were considered in the numeric integration analysis described in the Supplementary Material. Solid black symbols represent an arithmetic average of green and red values, while the dashed line is a guide to the eye.

Mentions: In the low temperature insulating phase of CuIr2S4 pairs of Ir4+ dimerize by moving closer together by a large 0.5 Å32 distance, resulting in the appearance of a distinct peak in the PDF at 3.0 Å40. This is shown in Fig. 3(a). The low temperature PDF clearly displays an additional peak at around 3.0 Å and this feature disappears in the high temperature data. A signature M-shape in the difference curve can also be observed, originating from the redistribution of PDF intensity from the position of the undistorted bonds before dimerization into short (dimerized) and long (non-dimerized) bonds, in accord with the dimerization invoked bond-length redistribution sketched in Fig. 1(c).


Cu(Ir₁ - xCrx)₂S₄: a model system for studying nanoscale phase coexistence at the metal-insulator transition.

Božin ES, Knox KR, Juhás P, Hor YS, Mitchell JF, Billinge SJ - Sci Rep (2014)

Dimer signal in the PDF and estimate of the fraction of dimerized Ir4+.(a) Comparison of experimental PDFs at 300 K (red) and 10 K (blue) over a narrow r-range for CuIr2S4, with the difference curve (green) offset for clarity. Shaded features in the difference curve (color coded by green for dimer and red for loss peaks) are used in the dimer fraction evaluation. (b) Evolution of the dimer fraction with Cr-doping: the color code corresponds to that used for marking the features in the difference curve in (a), that were considered in the numeric integration analysis described in the Supplementary Material. Solid black symbols represent an arithmetic average of green and red values, while the dashed line is a guide to the eye.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3921632&req=5

f3: Dimer signal in the PDF and estimate of the fraction of dimerized Ir4+.(a) Comparison of experimental PDFs at 300 K (red) and 10 K (blue) over a narrow r-range for CuIr2S4, with the difference curve (green) offset for clarity. Shaded features in the difference curve (color coded by green for dimer and red for loss peaks) are used in the dimer fraction evaluation. (b) Evolution of the dimer fraction with Cr-doping: the color code corresponds to that used for marking the features in the difference curve in (a), that were considered in the numeric integration analysis described in the Supplementary Material. Solid black symbols represent an arithmetic average of green and red values, while the dashed line is a guide to the eye.
Mentions: In the low temperature insulating phase of CuIr2S4 pairs of Ir4+ dimerize by moving closer together by a large 0.5 Å32 distance, resulting in the appearance of a distinct peak in the PDF at 3.0 Å40. This is shown in Fig. 3(a). The low temperature PDF clearly displays an additional peak at around 3.0 Å and this feature disappears in the high temperature data. A signature M-shape in the difference curve can also be observed, originating from the redistribution of PDF intensity from the position of the undistorted bonds before dimerization into short (dimerized) and long (non-dimerized) bonds, in accord with the dimerization invoked bond-length redistribution sketched in Fig. 1(c).

Bottom Line: Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood.We demonstrate a hitherto unobserved coexistence of an Ir(4+) charge-localized dimer phase and Cr-ferromagnetism.The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates.

View Article: PubMed Central - PubMed

Affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973.

ABSTRACT
Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood. Despite their ubiquity, they are hard to study because they produce weak diffuse signals in most measurements. Here we propose Cu(Ir₁ - xCrx)₂S₄ as a model system, where robust local structural signals lead to key new insights. We demonstrate a hitherto unobserved coexistence of an Ir(4+) charge-localized dimer phase and Cr-ferromagnetism. The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates. We suggest that the presence of quenched strain from dopant ions acts as an arbiter deciding between the competing ground states.

No MeSH data available.


Related in: MedlinePlus