Scanning tunneling microscopy was used to analyze a cuprate high-temperature superconductor modified into an insulating state by a team of researchers from Boston College and Brookhaven National Laboratory. (Credit:听Ilija Zeljkovic)
Boston College physicist Ilija Zeljkovic and a team of researchers have succeeded in modifying a cuprate high-temperature superconductor material into an insulating state, where they found an exotic liquid crystal phase.
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The observation of a so-called 鈥渃harge-stripe鈥� crystal phase was the first of its kind in the cuprate, part of a class of materials referred to as Mott insulators, the team reported recently in the journal Nature Materials.
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The absence of free charge carriers denotes the material as 鈥渦ndoped.鈥� The process of doping introduces charge carriers and theorists have held that when doped, a cuprate would see the charge carriers order and form liquid crystal phases marked by periodic 鈥渃harge-stripe鈥� patterns. Such patterns have thus far only been experimentally observed in the superconducting state.
Scanning tunneling microscopy was used to analyze a cuperate high-temperature superconductor modified into an insulating state by a team of researchers from Boston College and Brookhaven National Laboratory. (Credit: Nature Materials)
Zeljkovic and the team, which included members of his lab, Boston College Professor of Physics Ziqiang Wang, and researchers from Brookhaven National Laboratory in New York, used a new methodology to induce the charge ordering in the insulating state, they report in the article, titled 鈥淐harge-Stripe Crystal Phase in an Insulating Cuprate.鈥�
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The team applied a method of surface annealing, a head treatment used to alter the physical and chemical properties of metals, Zeljkovic said. The process allowed the team to extend the accessible doping range in the cuprate, composed of bismuth, strontium, calcium, copper, and oxygen.
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Accessing new regions of the material, the team achieved a 鈥渓ightly doped, charge-transfer insulator state,鈥� Zeljkovic said.
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The team analyzed the insulating state at the atomic level using scanning tunneling microscopy and spectroscopy at liquid helium temperatures.
Ilija Zeljkovic
鈥淥ur measurements reveal the emergence of a unidirectional charge-stripe order with a wave-length of exactly 4 atomic lattice constants,鈥� Zeljkovic said. 鈥淥ur data also proves that lightly-doped cuprates have a tendency to form stripes over the bidirectional 鈥榗heckerboard鈥� order, thus resolving the long-standing controversy in the field that could not be settled using the existing data on higher-doped samples.鈥�
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Zeljkovic said he and his colleagues would like to next explore the relationship of the observed charge ordered phase and the charge ordered phases observed in the superconducting state.
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The discovery raises the question of whether the 鈥渟pin鈥� of charge carriers also orders into periodic patterns, forming so-called spin-density waves, Zeljkovic said.
Zeljkovic鈥檚 research is supported by DARPA, the Army Research Office, and the National Science Foundation. In addition to Zeljkovic and Wang, co-authors of the paper include 情色空间 researchers He Zhao, Zheng Ren, and Bryan Rachmilowitz, and John Schneeloch, Ruidan Zhong, and Genda Gu from Brookhaven National Laboratory.
Ed Hayward / University Communications