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4He超流体在一定温度下可用二流体模型描述,包括常规流体和超流体两种成分.用这种二流体模型来描述二分量玻色爱因斯坦凝聚时叫做二超流体模型,是从耦合Gross-Pitaevskii方程出发推导得到的.二超流体模型与4He超流体中的二流体模型非常相近.在特定条件下,二超流体中的两个波模行为非常接近4He超流体中二流体模型中...  相似文献   
2.
路洪艳  王强华 《中国物理快报》2008,25(10):3746-3749
Linear dispersion near the Dirac points in the band structure of graphenes can give rise to novel physical properties. We calculate the electronic contribution to the Raman spectra in graphenes, which also shows novel features. In the clean limit, the Raman spectrum in the undoped graphene is linear (with a universal slope against impurity scattering) at low energy due to the linear dispersion near the Dirae points, and it peaks at a position corresponding to the van Hove singularity in the band structure. In a doped graphene, the electronic Raman absorption is forbidden up to a vertical inter-band particle-hole gap. Beyond the gap the spectrum follows the undoped case. In the presence of impurities, absorption within the gap (in the otherwise clean case) is induced, which is identified as the intra-band contribution. The Drude-like intra-band contribution is seen to be comparable to the higher energy inter-band Raman peak. The results are discussed in connection to experiments.  相似文献   
3.
本文利用基于密度泛函理论(DFT)的第一性原理计算研究了它们的电子结构和光学性质.光学性质的计算结果和实验相一致.结果表明,Fe或Ag掺杂后,K2Ti6O13的带隙中出现了杂质带且其带隙值变小,因而使掺杂后的K2Ti6O13的吸收边发生红移并实现了其对可见光吸收.其中杂质带主要由Fe 3d态或Ag 4d态与Ti 3d态和O 2p态杂化而成.对于Fe掺杂的K2Ti6O13,杂质带位于带隙中间,因此可以作为电子从价带跃迁到导带的桥梁.对于Ag掺杂的K2Ti6O13,杂质带位于价带顶附近为受主能级,可以降低光生载流子的复合概率.实验和计算研究表明,通过Fe或Ag的掺杂可以实现了K2Ti6O13对可见光的吸收,这对进一步研究K2Ti6O13的光学性质具有重要意义.  相似文献   
4.
We study the electronic Raman scattering in the cuprates to distinguish the two possible scenarios of the pseudogap normal state. In one scenario, the pseudogap is assumed to be caused by phase fluctuations of the preformed Cooper pairs. We find that pair-breaking peaks appear in both the B1g and B2g Raman channels, and they axe smeared and tend to shift to the same energy with the increasing strength of phase fluctuations. Thus both channels reflect the same pairing energy scale, irrespectively of the doping level. In another scenario, the pseudogap is assumed to be caused by a hidden order that competes with the superconducting order. As an example, we assume that the hidden order is the d-density-wave (DDW) order. We find analytically and numerically that in the DDW normal state there is no Raman peak in the B2g channel in a tight-binding model up to the second nearest-neighbor hopping, while the Raman peak in the Big channel reflects the energy gap caused by the DDW order. This behavior is in agreement with experiments in the pseudogap normal state. To gain further insights, we also calculate the Raman spectra in the DDW+SC state. We study the doping and temperature dependence of the peak energy in both channels and find a two-gap behavior, which is in agreement with recent Raman experiments. Therefore, our results shed light on the hidden order scenario for the pseudogap.  相似文献   
5.
研究了Anderson掺杂极限Δs/Δd《1的情况下,d+s波对称下的超导态。此模型包括哈密顿量中类似BSC项和自恰平均场似下的Anderson掺杂。随着掺杂中心数的增加或比率Δs/Δd的减小,可推出从低能下在费米能级附近具有双峰的态到N(0)≈(Δs/Δd)2态的转变。如果掺杂共振的能量为最小能量标度,则转变不连续。  相似文献   
6.
戚玉敏  陈恒利  金朋  路洪艳  崔春翔 《物理学报》2018,67(6):67101-067101
六钛酸钾(K_2Ti_6O_(13))是宽带隙半导体光催化材料,只能响应波长较短的紫外光.为了使K_2Ti_6O_(13)对可见光响应,本文采用第一性原理方法,研究过渡金属Mn和Cu掺杂改性后K_2Ti_6O_(13)的电子结构和光学性质.计算结果表明:Mn,Cu掺杂后K_2Ti_6O_(13)禁带中出现了杂质能级,这些杂质能级由O 2p和Ti 3d与Mn 3d或Cu 3d态杂化而成.对于Mn掺杂的K_2Ti_6O_(13),其带隙值变小,位于能带中间的杂质能级可作为电子跃迁的桥梁,从而实现了对可见光的吸收.对于Cu掺杂的K_2Ti_6O_(13),其带隙值虽略有增大,但是若考虑将与价带相连的杂质能级,带隙值将大大减小,且此杂质能级可抑制光生载流子的复合,使得掺杂后K_2Ti_6O_(13)吸收带边红移至可见光区并在可见光范围内吸收强度明显增强.总的而言,Mn,Cu的掺杂实现了钛酸钾对可见光的吸收,同时Cu掺杂的效果要优于Mn掺杂的效果.研究结果对K_2Ti_6O_(13)在光催化领域上的应用具有重要的意义.  相似文献   
7.
在光学实验平台上组建激光干涉仪,给出了测量微小楔角的原理和测量方法,导出了测量公式并进行了实际测量.  相似文献   
8.
文中工作采用t-t′-t″-J模型研究了电子型掺杂铜氧化物超导体在超导序和反铁磁序共存情况下的准粒子激发谱,分别计算了在欠掺杂区、最佳掺杂区和过掺杂区的谱权重,计算结果与角分辨光电子谱实验结果符合较好.  相似文献   
9.
路洪艳  陈三  刘保通 《物理学报》2011,60(3):37402-037402
电子拉曼实验表明在空穴型掺杂的铜氧化物超导体中存在两能隙行为,即在欠掺杂区,随着掺杂浓度的降低,一个能隙逐渐增大而且在超导转变温度以上仍然存在,而另一个能隙逐渐减小且在DDW态依然存在.解释两能隙行为非常重要因为它与赝能隙的机理密切相关.本文计算了超导序和d-density-wave(DDW)序竞争机理下相图上不同区域的电子拉曼谱,发现欠掺杂区能隙表现出两能隙行为,与实验一致.特别地,本文发现B1g峰对应能量由超导和DDW序共同决定,且随着掺杂浓度的降低而增大,在D 关键词: 两能隙 电子拉曼散射 竞争序  相似文献   
10.
Using first-principles calculations, we predict a new type of two-dimensional(2D) boride MB3(M = Be,Ca, Sr), constituted by boron kagome monolayer and the metal atoms adsorbed above the center of the boron hexagons. The band structures show that the three MB3 compounds are metallic, thus the possible phononmediated superconductivity is explored. Based on the Eliashberg equation, for BeB3, CaB3, and SrB3, the calculated electron–phonon coupli...  相似文献   
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