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【求助】关于pseudogap的问题
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我是化学出身的,想请教物理方面的高手,pseudogap是什么意思哦?最好能用比较通俗的语言解释一下,我更容易理解,呵呵 [ Last edited by ddx-k on 2008-12-14 at 20:00 ] |
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gaoky2008
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Pseudogap From Wikipedia, the free encyclopedia A pseudogap is a term from the field of high-temperature superconductivity which describes an energy (normally near the Fermi energy) which has very few states associated with it. This is very similar to a 'gap', which is an energy that has no allowed states. Such gaps open up, for example, when electrons interact with the lattice. Interestingly only certain electrons `see' this gap. The gap, which should be associated with an insulating state, only exists for electrons travelling parallel to the copper-oxygen bonds. Electrons travelling at 45 degrees to this bond can move freely throughout the crystal. The Fermi surface therefore consists of Fermi Arcs forming pockets centred on the corner of the Brillouin zone. In the pseudogap phase these arcs gradually disappear as the temperature is lowered until only four points on the diagonals of the Brillouin zone remain ungapped. On one hand, this could indicate a completely new electronic phase which consumes available states, leaving only a few to pair up and superconduct. On the other hand, the similarity between this partial gap and that in the superconducting state could indicate that the pseudogap results from preformed cooper pairs. Mechanism The origin of the pseudogap is controversial and still subject to debate in the condensed matter community. Two main interpretations are emerging: 1. The scenario of preformed pairs In this scenario, electrons form pairs at a temperature T* that can be much larger than the critical temperature Tc where superconductivity appears. T* of the order of 300K have been measured in underdoped cuprates where Tc is about 80k. The superconductivity does not appear at T* because large phase fluctuations of the pairing field cannot order at this temperature. The pseudogap is then produced by non coherent fluctuations of the pairing field. 2. The scenario of a non superconducting related pseudogap In this class of scenarios, many different origins have been put forward: like the formation of electronic stripes, antiferromagnetic ordering, exotic order parameter competing with superconductivity. A pseudogap can be seen with several different experimental methods. One of the first observations was in specific heat measurements of YBa2Cu3O6+x by Loram et al.[1] The pseudogap is also apparent in ARPES (Angle Resolved Photoemission Spectroscopy) data, which can measure the density of states of the electrons in a material. References ^J. W. Loram, K. A. Mirza, J. R. Cooper, and W. Y. Liang (1993). "Electronic specific heat of YBa2Cu3O6+x'' from 1.8 to 300 K".Physical Review Letters71 (11): 1740-1743. doi:10.1103/PhysRevLett.71.1740. Emery et al. Physical Review B, Vol 56, Page 6120 (1997) Kyle McElroy, Nature Physics, Vol 2, Page 441 (2006) External links pseudogap in non-superconducting materials:http://www.physorg.com/news10505.html |
2楼2008-03-26 16:59:01
3楼2008-03-26 20:32:12
supersolid226
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4楼2008-03-27 16:54:33
gaoky2008
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赝隙又称正常态能隙。一般在铜氧化合物高温超导体的弱掺杂区中，正常态（非超导态）T*温度以下就形成了电子配对，但未发展成长程序相干的cooper对系统，只在温度低至Tc时这些cooper电子对间才有位相相干，发生超导凝聚，进入超导态。因此，常温下只显现出赝带隙。高温超导体不同于BCS超导体，对的形成和对间位相相干时的超导凝聚是分两步不同时在不同温度下产生的。也有人称正常态电子间的这种配对为“预配对”。 你说的elecreons from pairs at a temperature T*指正常温度下未发生位相相干的电子对中的电子，配对的电子未被打开。 至于electronic stripes的问题，我跟你一样不是很懂。不过我记得好像是电荷有序里面的问题，那种条纹是否指在晶格尺度的电荷和自旋等周期分布，类似反铁磁系统之类的？ 高温超导里面的问题很多，我不是做这方面的，说得不一定对，多包涵。赝隙的详细介绍你可以看看李正中的《固体理论》第七章最后一节，或者楼上提到的韩汝珊《高温超导物理》；electronic stripes方面的你找几篇电荷有序的paper看看，里面可能会提到，你可以由此挖出原始文献。 [ Last edited by gaoky2008 on 2008-3-28 at 19:59 ] |
5楼2008-03-28 19:57:37
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楼上说的很好，不过关于赝能隙的机理目前还没有一个统一的认识，预配对只是大家普遍接受的一个主流观点，这个还有争议，可以看一下这篇综述文章 Physics Reports 431 (2006) 231 – 259 至于electronic stripes的问题，其实在很多强关联体系里面都发现了类似的electronic phase separation问题，这个是电荷（自旋）在实空间的周期性排列，公度调制的情况下，结构比较稳定。这个可以用衍射技术测量到的，有人认为条纹相结构是高温超导的基态之一，另一个比较稳定的相是最佳掺杂的超导组分。但是对于动态的条纹相目前认识的还不够清楚，如果感兴趣的话可以参考这篇文献 REVIEWS OF MODERN PHYSICS, VOLUME 75 （2003） 1201 |
6楼2008-03-29 11:41:04
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