Ferroelectric Mott-Hubbard phase in organic conductors

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CoFeB_Ta_CoFeB中的自旋轨道转矩效应

摘要实现高速，高密度，低功耗的非易失性磁存储是自旋电子学的重点研究方向。

近年来，利用自旋轨道转矩翻转具有垂直易磁化的磁性超薄膜实现信息写入的研究引起了广泛的关注。

目前利用自旋轨道转矩翻转单层铁磁薄膜，由于铁磁材料固有的杂散场，并且翻转需要的临界电流密度在106A/cm2及以上，不利于实现高密度低功耗存储。

人工反铁磁兼具铁磁材料易操控以及反铁磁材料零的杂散场，高的热稳定性，快的磁化动力学等特点，用其替代铁磁材料，有望推动高速，高密度，低功耗磁存储的发展。

本文基于CoFeB/Ta/CoFeB垂直易磁化体系，研究了自旋轨道转矩翻转人工反铁磁，并研究了Ta的厚度变化对于体系翻转所需要的临界电流密度的影响。

实验中制备了同时具有垂直易磁化和层间反铁磁耦合的CoFeB/Ta/CoFeB人工反铁磁结构。

利用重金属Ta自旋霍尔效应产生的自旋流注入到相邻的两层CoFeB中，对CoFeB磁矩产生自旋轨道转矩效应，实现在两层CoFeB磁矩在两个反平行态之间的翻转，翻转临界电流密度为 2.44×107A/cm2。

通过求解Stoner-Wohlfarth模型和Landau-Lifshitz-Gilbert方程，解释了观察到的两层CoFeB磁矩在两个反平行态之间翻转的现象。

实验中制备了上层CoFeB具有强的垂直易磁化和下层CoFeB具有较弱的垂直易磁化的CoFeB的CoFeB/Ta/CoFeB体系，通过调整Ta层的厚度，我们观察到了Ta厚度为3nm时2.1×105A/cm2的临界翻转电流密度。

通过输运测试和磁性表征，揭示了低的临界翻转电流密度的原因是Ta为3nm的样品具有低的矫顽力和磁各向异性。

自旋轨道力矩翻转人工反铁磁为高密度磁存储提供了一个可能的途径。

105A/cm2的临界翻转电流密度进一步降低了自旋轨道转矩的功耗，有望推动磁存储在低功耗方面的发展。

关键词：自旋轨道转矩；人工反铁磁；垂直易磁化；临界翻转电流密度AbstractInvestigating non-volatile magnetic storage with high speed, high density and low power consumption is one of the most important research areas of spintronics. Recently, utilizing spin-orbit torque (SOT) to switch perpendicularly magnetized single layer and realize writing information has drawn extensive attention. However, the stray field of ferromagnetic materials and the critical current density, which is at least 106 A/cm2, for SOT induced magnetization switching impede the implement of high density and low power consumption magnetic storage. Synthetic antiferromagnets (SAF) are easily to be manipulated like ferromagnets and have zero stray field, high thermal stability and fast magnetic dynamics like antiferromagnets. Replacing ferromagnetic materials by SAF is expected to promote the development of high speed, high density and low power consumption magnetic storage. Based on CoFeB/Ta/CoFeB systems with perpendicular magnetic anisotropy (PMA), we study the spin-orbit torque switching SAF and the Ta thickness dependence of the critical current density for SOT switching.We deposited SAF CoFeB/Ta/CoFeB heterostructure with PMA and interlayer antiferromagnetic coupling. The spin current generated by the spin Hall effect of tantalum would diffuse up and down into adjacent CoFeB layers and exert SOT on the magnetic moment of CoFeB. Consequently, the magnetization could be switched between two antiparallel states with a critical current density of 2.44×107A/cm2 and these phenomenon can be well replicated by solving Stoner-Wohlfarth model and Landau-Lifshitz-Gilbert equation.We deposited CoFeB/Ta/CoFeB systems with strong PMA of upper CoFeB layer and relatively weak PMA of lower CoFeB layer. By varying the Ta thickness, we found the critical current density for SOT switching could be reduced to 2.1×105A/cm2for samples with Ta thickness of 3nm. Through transportation measurements and magnetization characterization, we found that the reason for this low critical current density is that samples with Ta thickness of 3nm have relative low coercivity and anisotropy.SOT switching SAFs might advance the high density magnetic memories. Critical current density of 105A/cm2 for SOT switching would promote magnetic storage with lower consumption.Key words:spin-orbit torque; synthetic antiferromagnet; perpendicular magnetization; critical current density目录第1章引言 (1)1.1 自旋电子学简介 (2)1.1.1 自旋电子学的形成与发展 (2)1.1.2 垂直磁化体系与反常霍尔效应 (3)1.2 自旋轨道转矩 (5)1.2.1 自旋转移力矩与自旋轨道转矩 (5)1.2.2 Stoner-Wohlfarth模型和Landau-Lifshitz-Gilbert方程 (8)1.3 人工反铁磁 (8)1.4 研究思路及内容 (10)第2章实验方法 (11)2.1 薄膜样品制备 (11)2.1.1 磁控溅射 (11)2.1.2 电子束蒸镀 (12)2.2 霍尔器件加工 (12)2.2.1 紫外曝光 (13)2.2.2 氩离子刻蚀 (14)2.3 性能测试 (16)2.3.1 超导量子干涉仪 (16)2.3.2 电输运性能测试 (16)第3章自旋轨道转矩翻转CoFeB/Ta/CoFeB人工反铁磁 (18)3.1 CoFeB/Ta/CoFeB人工反铁磁结构的制备和磁性表征 (18)3.2 自旋轨道转矩翻转CoFeB/Ta/CoFeB人工反铁磁 (20)3.3 Stoner-Wohlfarth模型模拟 (22)3.4 Landau-Lifshitz-Gilbert方程模拟 (25)3.5 本章小结 (30)第4章 105A/cm2量级临界翻转电流密度的自旋轨道转矩翻转 (31)4.1 MgO/CoFeB/Ta/CoFeB/MgO器件的制备以及SOT翻转 (31)4.2 矫顽力和各向异性场对临界翻转电流密度的影响 (36)4.5 本章小结 (38)第5章结论 (39)参考文献 (40)致谢 (46)声明 (47)个人简历、在学期间发表的学术论文与研究成果 (48)第1章引言信息时代每天会产生大量的信息，如何实现高速度，低功耗，高密度的信息存储是科学家们长期追求的目标。

第三讲自旋电子学课件

N.H.Mott,Proc.Roy.Soc. A153,699(1936)
近似：电子与（热激发）自旋波散射可以忽略，（低于居里点）只考虑电子与磁性离子自旋间的散射。（s－d散射）
约定：与磁矩同方向的电子处于主要子带（majority）
相反方向自旋电子处于次要子带（minority）
两流体模型（2）
自旋相关散射(磁电阻效应)
FM(Ni-Fe)
S1
S2
(Al-O)
NM(Cu(001))
FM(Co(001))
上下自旋平行时电子容易通过--低电阻态上下自旋反平行时电子被散射—高电阻态
Capping layer
Free layer
Tunnel barrier Reference layer Spacer layer Pinned layer Pinning layer
当然 D d 2 0 不等式成立
Julliere公式（3）
TMR 比率（放大的）
定义 TMR I I I
分子＝ D1 D1 D2 D2
分母＝ D1 D2 D1 D2
Julliere公式（4）
TMR的公式（用自旋极化率表示）
第一个电极 p1 D1 D1 D1 D1 第二个电极 p2 D2 D2 D2 D2
TMR实验结果
韩秀峰等（2000）
隧道磁电阻
隧道磁电阻效应的物理机制
Julliere公式（1）
隧穿电流（近似!）I ∝ 指数衰减部分×状态密度部分
上左图 FM电极的磁矩彼此“平行”
I exp A U0 D1 D2 D1 D2
（注意：数值大小是 D D d d ）
上右图 FM电极的磁矩彼此“反平行”

SrVO3 Hubbard band 和氧空位

PHYSICAL REVIEW B94,241110(R)(2016)Hubbard band versus oxygen vacancy states in the correlated electron metal SrVO3S.Backes,1T.C.R¨o del,2,3F.Fortuna,2E.Frantzeskakis,2P.Le F`e vre,3F.Bertran,3M.Kobayashi,4R.Yukawa,4 T.Mitsuhashi,4M.Kitamura,4K.Horiba,4H.Kumigashira,4R.Saint-Martin,5A.Fouchet,6B.Berini,6Y.Dumont,6A.J.Kim,1F.Lechermann,7,8H.O.Jeschke,1M.J.Rozenberg,9R.Valent´ı,1,*and A.F.Santander-Syro2,†1Institut f¨u r Theoretische Physik,Goethe-Universit¨a t Frankfurt,Max-von-Laue-Strasse1,60438Frankfurt am Main,Germany 2CSNSM,Univ.Paris-Sud,CNRS/IN2P3,Universit´e Paris-Saclay,91405Orsay Cedex,France3Synchrotron SOLEIL,L’Orme des Merisiers,Saint-Aubin-BP48,91192Gif-sur-Yvette,France 4Photon Factory,Institute of Materials Structure Science,High Energy Accelerator Research Organization(KEK),1-1Oho,Tsukuba305-0801,Japan5SP2M-ICMMO-UMR-CNRS8182Universit´e Paris-Sud,Universit´e Paris-Saclay,91405Orsay Cedex,France 6GEMaC,Universit´e de Versailles St.Quentin en Y.-CNRS,Universit´e Paris-Saclay,Versailles,France7Institut f¨u r Theoretische Physik,Universit¨a t Hamburg,Jungiusstrasse9,20355Hamburg,Germany8Institut f¨u r Keramische Hochleistungswerkstoffe,TU Hamburg-Harburg,D-21073Hamburg,Germany 9Laboratoire de Physique des Solides,CNRS,Univ.Paris-Sud,Universit´e Paris-Saclay,91405Orsay Cedex,France(Received22February2016;published19December2016)We study the effect of oxygen vacancies on the electronic structure of the model strongly correlatedmetal SrVO3.By means of angle-resolved photoemission spectroscopy(ARPES)synchrotron experiments,we investigate the systematic effect of the UV dose on the measured spectra.We observe the onset of a spuriousdose-dependent prominent peak at an energy range where the lower Hubbard band has been previously reportedin this compound,raising questions on its previous interpretation.By a careful analysis of the dose-dependenteffects we succeed in disentangling the contributions coming from the oxygen vacancy states and from the lowerHubbard band.We obtain the ARPES spectrum in the limit of a negligible concentration of vacancies,wherea clear signal of a lower Hubbard band remains.We support our study by means of state-of-the-art ab initiocalculations that include correlation effects and the presence of oxygen vacancies.Our results underscore therelevance of potential spurious states affecting ARPES experiments in correlated metals,which are associatedwith the ubiquitous oxygen vacancies as extensively reported in the context of a two-dimensional electron gas atthe surface of insulating d0transition metal oxides.DOI:10.1103/PhysRevB.94.241110Introduction.A major challenge of modern physics is to understand the fascinating phenomena in strongly correlated transition metal oxides(TMOs),which emerge in the neighbor-hood of the Mott insulator state.Some preeminent examples that have gathered interest for almost30years are high temperature superconductivity,colossal magnetoresistance, heavy fermion physics,and,of course,the Mott metal-insulator transition itself[1].Signiﬁcant theoretical progress was made with the introduction of dynamical meanﬁeld theory (DMFT)and its combination with ab initio density functional methods[local density approximation(LDA)+DMFT],which allows treatment of the interactions promoting itinerancy and localization of electrons on equal footing[2–4].Among the most emblematic achievements of DMFT is the prediction of a Hubbard satellite,which separates from the conduction band of a metal.This satellite results from the partial localization of conduction electrons due to their mutual Coulomb repulsion. Early DMFT studies also showed that it is the precursor of the localized electronic states of a Mott insulator[5].Since then,these predictions promoted a large number of studies using photoemission spectroscopy,which is a technique to directly probe the presence of Hubbard bands.In this context, the TMO system SrVO3has emerged as the drosophila model system to test the predictions of strongly correlated electron *valenti@itp.uni-frankfurt.de†andres.santander@csnsm.in2p3.fr theories.In fact,SrVO3is arguably the simplest correlated metal.It is a simple cubic perovskite,with nominally one electron per V site,which occupies a threefold degenerate t2g conduction band.While the presence of a satellite in the photoemission spectra of Ni metal was already well known,in the context of correlated TMOs,the Hubbard band was originally reported in a systematic investigation of Ca1−x Sr x VO3[6],which was followed by many subsequent studies,including angle-resolved photoemission spectroscopy (ARPES)[7–9]and comparisons with theoretical predictions (see,for instance,Refs.[10–20],among others).One of the most salient features in SrVO3is the observation of a broad peak at an energy of about−1.5eV in angle integrated photoemission spectra(upper black curve in Fig.1), which is interpreted as a Hubbard satellite linked to the V t2g electrons.This feature is also seen in a large range of 3d1materials[21,22].The ratio of spectral strength between the quasiparticle(QP)state and the incoherent satellite in SrVO3is an important indicator of the magnitude of electron correlations[1,2].However,photoemission experiments using different photon energies or light brilliance have reported very dissimilar values for such a ratio[11],making the quantitative benchmarking of realistic ab initio theories for correlated electron systems difﬁcult[6,11,18,23,24].Moreover,as shown in Fig.1,a broad peak at about the same energy is also observed in several d0TMO cubic perovskites,such as SrTiO3, KTaO3,or anatase TiO2.Nevertheless,in all these cases the feature has been clearly linked to the presence of oxygenS.BACKES et al.PHYSICAL REVIEW B94,241110(R)(2016)FIG.1.Integrated UV photoemission spectra for various per-ovskite oxides,showing a quasiparticle peak at E F and an in-gap state at energies between1and1.5eV.For SrVO3(upper black curve),a correlated-electron metal,the QP peak corresponds to the bulk conduction band,and as will be shown further,the in-gap state is a superposition of the lower Hubbard band and localized electronic states associated with oxygen vacancies.For the other d0 oxides,such as KTaO3(blue curve),anatase TiO2(green curve), or SrTiO3(red curve),the QP peak and in-gap state correspond respectively to a conﬁned quasi-2D electron gas at the sample surface and to localized states,all formed by oxygen vacancies.The crystal orientation(normal to the samples’surface)is indicated in all cases. defects[25–32].Interestingly,recent ab initio calculations show that the spectral weight at−1.3eV in SrTiO3most likely is not of Ti t2g orbital character,but should be understood as an in-gap defect state with Ti e g character[33–36].Thus,we are confronted with the fact that at about1.5eV below the Fermi level(E F),weﬁnd the lower Hubbard bands of d1systems as well as the in-gap states of oxygen-deﬁcient d0systems.In view of these observations one may unavoidably wonder(and worry),despite the great success of DMFT methods,whether the putative Hubbard satellite of SrVO3might also originate from oxygen vacancy states.Moreover,one should also worry about the possibility of these extrinsic states affecting the features of the conduction band dispersion.In the present Rapid Communication we resolve these issues in a thorough manner.We present a systematic photoemission study of SrVO3,to demonstrate dramatic consequences in the spectra due to the creation of oxygen ing ARPES,we directly show that the UV or x-rays used for measurements can produce a large enhancement, of almost an order of magnitude,of the peak at−1.5eV, similar to the effect observed in d0oxide insulators[25–28,37].Despite these signiﬁcant effects on the energy states around the Mott-Hubbard band,we are able to determine the bulk SrVO3photoemission spectrum in the limit of a negligible concentration of vacancies,where a clear signal of the dispersive correlated Hubbard band remains.We support the interpretation of the experimental data by means of state-of-the-art LDA+DMFT calculations on SrVO3with oxygen vacancies.Consistent with our experimental data,the calculations show that oxygen vacancies produce states(of e g symmetry)at energies near the Hubbard satellite.While our study provides deﬁnite evidence of a correlated Hubbard band in SrVO3as predicted by DMFT,it also underlines the signiﬁcant effects due to oxygen vacancies,which may also affect photoemission data in other TMOs.Methods.The bulk-like relaxed,crystalline(001)oriented SrVO3thinﬁlms were grown by pulsed laser deposition (PLD)either at the GEMaC laboratory,then measured at the CASSIOPEE beamline of Synchrotron SOLEIL,or in a PLD chamber directly connected to the ARPES setup at beamline2A of KEK-Photon Factory(KEK-PF)[9,38,39]. To clean the surfaces in UHV prior to ARPES experiments at SOLEIL,the SrVO3thinﬁlms were annealed at550◦C for t=5–20min at pressures lower than2×10−8Torr.At KEK-PF,the PLD growth was performed under a pressure below10−7Torr,to obtain UHV-clean surfaces,using a Sr2V2O7target,which has excess oxygen with respect to SrVO3,thus minimizing the formation of vacancies during the growth.In all cases,the surface quality was conﬁrmed right before ARPES measurements by low-energy electron diffraction(LEED).The thinﬁlms measured at KEK-PF showed a c(4×4)surface reconstruction,which does not affect the analysis and conclusions of this work.For the ARPES measurements we used linearly polarized photons in the energy range30–110eV and hemispherical electron analyzers with vertical slits at SOLEIL and horizontal slits at KEK-PF.The angular and energy resolutions were0.25◦and 15meV.The mean diameter of the incident photon beam was smaller than100μm.The UV light brilliance,measured using calibrated photodiodes,was≈5×109photons s−1μm−2at SOLEIL,and about100times smaller at KEK-PF.The samples were cooled down to T=20K before measuring.Unless speciﬁed otherwise,all data were taken at that temperature. The results were reproduced on more thanﬁve samples.All through this Rapid Communication,directions and planes are deﬁned in the cubic unit cell of SrVO3.We denote [hkl]the crystallographic directions in real space, hkl the corresponding directions in reciprocal space,and(hkl)the planes orthogonal to those directions.The indices h,k,and l of hkl correspond to the reciprocal lattice vectors of the cubic unit cell of SrVO3.The Supplemental Material[40]presents further details about the sample growth and measurements.Experimental results.Figure2(a)shows the integrated photoemission spectra of SrVO3as a function of the UV dose, measured at CASSIOPEE SOLEIL under the same conditions of light brilliance of any standard ARPES experiment at a third-generation synchrotron.The measurements were done by continuously irradiating the sample with hν=33eV photons while recording the spectra as a function of irradiation time, with an accumulation time of about2min per spectrum.The blue and black curves show spectra for the lowest and highest measured doses,obtained respectively after∼2min and∼2h of irradiation.These data clearly demonstrate that the very UV or x-rays used for photoemission experiments can produce radical changes in the measured spectra of SrVO3.Note in fact that a similar effect has been observed for VO2[41].In particular,from Fig.2(a)we observe that the amplitude ofHUBBARD BAND VERSUS OXYGEN V ACANCY STATES IN THE...PHYSICAL REVIEW B94,241110(R)(2016)FIG.2.(a)Photoemission spectra of SrVO3as a function of UV dose,measured at Synchrotron SOLEIL(hν=33eV).The energy distribution curves(EDCs)were extracted from raw ARPES data around the 002point integrated along the k= 010 direction.(b)Corresponding momentum distribution curves(MDCs)integrated over50meV below E F.Peaks in the MDCs indicate the Fermi momenta.(c),(d)Same as(a),(b)for SrTiO3(hν=47eV).Theﬁlling of a2DEG upon UV irradiation is evidenced by the formation of QP peaks in the EDCs and MDCs at E F[inset of(c)and(d),respectively].All data were taken at20K.the in-gap state at−1.5eV,and,more signiﬁcantly,the ratio of in-gap to quasiparticle(QP)amplitudes,strongly increase with increasing UV dose,going from about1:3in a pristine sample to more than2:1in a heavily irradiated sample. Importantly,note that the QP peak position remains basically dose independent,implying that the carriers created by the UV or x irradiation do not signiﬁcantly dope the conduction band,and form dominantly localized states.This is conﬁrmed in Fig.2(b),which shows that the Fermi momenta of the QP band,given by the peak positions in the momentum distribution curves(MDCs)at E F,are also dose independent. Additional data presented in the Supplemental Material further demonstrate that our measurements yield the expected3D bulk Fermi surface of SrVO3.Thus,the observed increase in intensity of the in-gap state upon UV irradiation cannot be ascribed to a change inﬁlling of the conduction band,which could have affected the electron correlations.Instead,this unambiguously shows the light-assisted formation of localized defect states at essentially the same energy as that of the expected intrinsic lower Hubbard band—which should then resemble the in-gap peak observed at the lowest UV doses.In fact,as mentioned previously,it is well established that strong doses of UV or x-rays create a large concentration of oxygen vacancies in several d0perovskites[25–32,42]. As illustrated in Figs.2(c)and2(d)for the case of SrTiO3, the progressive doping of the surface region with oxygen vacancies,due to synchrotron UV irradiation,has two effects: the formation of a very intense in-gap state at about−1.3eV, and,in contrast to SrVO3,the simultaneous creation of a sharp QP peak at E F corresponding to a conﬁned quasi-2D electron gas(2DEG)at the samples’surface.The effective mass of such2DEG,precisely determined by ARPES,matches the mass expected from density functional theory calcula-tions[25,26,43,44].Thus,as in SrVO3,the increase in intensityof the in-gap state observed in SrTiO3upon UV or x irradiationcannot be due to an onset or increase of electron correlations,and should be ascribed to an extrinsic effect.We therefore conclude that,in SrVO3,exposure to syn-chrotron UV or x-rays creates oxygen vacancies,which are inturn responsible for the extrinsic increase in intensity of thein-gap state evidenced by our measurements.This effect canseriously obscure the determination of the spectral function ofthis model system,thus hampering the advancement of validtheories for correlated electron systems.Theﬁndings described above imply that the correct ex-perimental determination of the vacancy-free photoemissionspectrum of SrVO3should(i)use samples that from thebeginning have the lowest possible concentration of oxygenvacancies,and(ii)use doses of UV or x-ray light low enoughto avoid light-induced changes in the measured spectra.Tothis end,we measured SrVO3thinﬁlms grown directly insitu at beamline2A of KEK-PF.As mentioned before,the growth protocol of such thinﬁlms minimizes the formationof vacancies,while the UV light brilliance at KEK-PF is ∼100times smaller than the one in Figs.2(a)and2(b)from measurements at SOLEIL.We checked(see the SupplementalMaterial)that under these conditions the spectra did notchange with time,even after several hours of measurements.The resulting energy-momentum ARPES map,and its secondderivative,are presented in Figs.3(a)and3(b).One clearlyobserves the dispersing QP band along with an also dispersivein-gap state of weaker intensity,corresponding to the intrinsiclower Hubbard band,as reported in previous works[7].Theintrinsic spectral function of SrVO3will then be given by such aphotoemission spectrum,which approaches the vacancy-freelimit,modulo dipole-transition matrix elements,inherent toS.BACKES et al.PHYSICAL REVIEW B94,241110(R)(2016)FIG.3.(a)Energy-momentum ARPES intensity map measured at KEK-PF with a low UV dose on a SrVO3sample prepared in situ,using a well-established protocol to minimize the formation of oxygen vacancies(see the main text and Supplemental Material).Note that due to the choice of light polarization,the heavy bands along(100)are not observed and only the contribution of the light d xy band is detected.The data were acquired at hν=88eV around ¯103.(b)Second derivative(negative values)of the map in(a).The use of second derivatives allows a better visualization of the dispersion of both the quasiparticle and Mott-Hubbard bands on the same color plot.The dispersionless feature at E F is a spurious effect of such a second derivative on the Fermi-Dirac cutoff.(c),(d)Same as(a),(b)after a strong UV irradiation dose,measured at SOLEIL(hν=33eV),typical of modern third-generation synchrotrons.The measurements were done at hν=33eV close to 002.All data were taken at20K.Note that at constant photon energy,ARPES maps out the electronic structure at a spherical surface of three-dimensional (3D)k space,which can be locally approximated to a plane for all our measurements(details in the Supplemental Material).The different choice of photon energies and k-space positions for measurements at KEK-PF[(a)and(b)]and SOLEIL[(c)and(d)]was dictated by the different geometrical conﬁgurations and constraints of the beamlines in both synchrotrons.the photoemission process,which can still modulate the intensity of the QP peak relative to the Hubbard peak.A calculation of such matrix elements requires a full one-step calculation of the photoemission process,which is beyond the scope of this work.By contrast,Figs.3(c)and3(d) show the momentum-resolved electronic structure of a sample, measured at SOLEIL,that was intensively irradiated.There, the peak at−1.5eV becomes broader,more intense,and nondispersive—all characteristic signatures of a high random concentration of oxygen vacancies.Numerical calculations.To rationalize from a microscopic point of view the inﬂuence of oxygen vacancies on the electronic structure of SrVO3,we performed charge self-consistent LDA+DMFT calculations for bulk SrVO3and var-ious relaxed oxygen-deﬁcient SrVO3supercells.The latter are computationally demanding calculations.We shall focus here on the case of a2×2×3supercell with two oxygen vacancies located at opposite apical sites of one vanadium atom,as shown in the inset of Fig.4(b).We use such a vacancy arrangement as it is the prototypical one for d0compounds[43].For our LDA+DMFT calculations we chose values of U= 2.5eV and J=0.6eV for vanadium and included the effects of bandwidth renormalization due to dynamically screened Coulomb interactions by following the prescription suggested in Ref.[45](the LDA+DMFT unrenormalized data are shown in the Supplemental Material).In Figs.4(a)and4(c)we show, respectively,the results of the k-integrated and k-resolved spectral functions for bulk SrVO3without oxygen vacancies. Weﬁnd the expected features of a t2g quasiparticle peak at the Fermi level and a lower Hubbard band at negative energies of the same t2g nature,in agreement with the photoemission spectra in Fig.2(a)and Figs.3(a)and3(b).The light band at E F along k 100 [Fig.4(c)]consists of two degenerate bands of d xy and d xz characters,while the heavy band along the same direction has d yz character.While comparing with the measured k-resolved spectral function[Figs.3(a)and3(b)],HUBBARD BAND VERSUS OXYGEN V ACANCY STATES IN THE...PHYSICAL REVIEW B94,241110(R)(2016)FIG.4.LDA+DMFT results for SrVO3including bandwidth renormalization effects[45].(a)k-integrated spectral function for bulk SrVO3.The V t2g orbitals show a quasiparticle peak at E F and a lower Hubbard band at−1.6eV.(b)Spectral function for the2×2×3supercell of SrVO3with two oxygen vacancies.An additional nondispersive V e g vacancy state originating from the V atom neighboring the oxygen vacancies leads to a sharp peak below the Fermi level at∼−1.0eV.The V t2g orbitals show a quasiparticle peak at E F and a lower Hubbard band at−1.8eV.(c)and(d)show the corresponding spectral functions(multiplied by a Fermi-Dirac function at20K)along the X- -X path.one should bear in mind that along -X(or -Y)the heavy d yz(or d xz)bands are silenced by dipole-transition selection rules in the experiment[25].Inclusion of bandwidth renormalization[45]renders the lower Hubbard band at an energy(−1.6eV)in reasonable agreement with experiment (−1.5eV).We adopted typical values for U and J from the literature.We did not attempt to further optimize the values to get a better quantitative agreement with the experimental data, for two reasons:First is the heavy numerical cost,and second, as we show next in the calculations with oxygen vacancies, the adopted values facilitate the distinct visualization of the contributions from the Hubbard and localized states to the incoherent peak at∼−1.5eV.The removal of oxygen atoms in the system leads to the donation of two electrons per oxygen to its surrounding. Already at the level of density functional theory(DFT)in the local density approximation(LDA)(see the Supplemental Material),weﬁnd that most of the charge coming from the additional electrons is transferred to the3d z2orbitals of the neighboring V atom,developing into a sharp peak of e g symmetry located around−1.0eV,i.e.,at an energy close to the position of the experimentally observed oxygen vacancy states.In analogy to the experimental average over many lattice sites,note that averaging among various supercells with differentoxygen vacancy locations and concentrations(which is beyondthe scope of the present work)would result in a wider in-gape g band,as demonstrated for the case of SrTiO3(see Fig.3ofRef.[34])and for some cases in SrVO3(see the SupplementalMaterial,Fig.S7).By including electronic correlations within(bandwidth renormalized)LDA+DMFT we then see that allthe experimental observations qualitatively emerge.In fact,the conducting t2g orbitals develop a lower Hubbard bandpeaked at energies about−1.8eV[Figs.4(b)and4(d)],similarto the bulk case without oxygen vacancies.Most notably,this lower Hubbard satellite does not increase in amplitudewith the introduction of vacancies,but rather broadens.Inaddition,the oxygen vacancy defect states situated at about −1eV remain qualitatively unchanged by the correlation effects,but experience a broadening with respect to the pureLDA case.This is in agreement with the photoemission data,evidencing that the increase in intensity of the in-gap statein the oxygen-deﬁcient SrVO3is not to be attributed to anincrease in population of the lower Hubbard satellite,butinstead to the manifestation of vacancy states of e g character.Conclusions.In summary,we performed a detailed study of the effects of oxygen vacancies in the spectroscopy of the archetypal strongly correlated electron system SrVO3.We found that oxygen vacancy states,which are created by UV or x-ray irradiation,occur at energies close to the Hubbard satellite.This dramatically affects the measured line shape of the Mott-Hubbard band and the ratio of intensities between the quasiparticle and the Mott-Hubbard peaks.By means of a systematic study under a controlled irradiation dose, using samples directly grown in situ,we were able to obtain the photoemission spectrum of the bulk SrVO3system in the limit of a negligible concentration of oxygen vacancies. Our experimental interpretation is supported by LDA+DMFT calculations,which provided further insight into the likely nature of the oxygen vacancy states.Acknowledgments.We thank Silke Biermann,Ralph Claessen,Marc Gabay,and Michael Sing for discussions. This work was supported by public grants from the French National Research Agency(ANR),project LACUNES No. ANR-13-BS04-0006-01,and the“Laboratoire d’Excellence Physique Atomes Lumi`e re Mati`e re”(LabEx PALM project ELECTROX)overseen by the ANR as part of the“Investisse-ments d’Avenir”program(reference:ANR-10-LABX-0039). S.B.,A.J.K.,F.L.,H.O.J.,and R.V.gratefully acknowledge the Deutsche Forschungsgemeinschaft forﬁnancial support through Grant FOR1346.T.C.R.acknowledges funding from the RTRA–Triangle de la Physique(project PEGASOS).A.F.S.-S.is thankful for support from the Institut Universitairede France.S.B.and T.C.R.contributed equally to this work.[1]M.Imada,A.Fujimori,and Y.Tokura,Metal-insulator transi-tions,Rev.Mod.Phys.70,1039(1998).[2]A.Georges,G.Kotliar,W.Krauth,and M.J.Rozenberg,Dynamical meanﬁeld theory of strongly correlated electronsS.BACKES et al.PHYSICAL REVIEW B94,241110(R)(2016)and the limit of inﬁnite dimensions,Rev.Mod.Phys.68,13 (1996).[3]G.Kotliar and D.V ollhardt,Strongly correlated materials:Insights from dynamical mean-ﬁeld theory,Phys.Today57(3), 53(2004).[4]G.Kotliar,S.Y.Savrasov,K.Haule,V.S.Oudovenko,O.Parcollet,and C.A.Marianetti,Electronic structure calculations with dynamical mean-ﬁeld theory,Rev.Mod.Phys.78,865 (2006).[5]X.Y.Zhang,M.J.Rozenberg,and G.Kotliar,Mott Transitionin the d=∞Hubbard Model at Zero Temperature,Phys.Rev.Lett.70,1666(1993).[6]I.H.Inoue,I.Hase,Y.Aiura,A.Fujimori,Y.Haruyama,T.Maruyama,and Y.Nishihara,Systematic Development of the Spectral Function in the3d1Mott-Hubbard System Ca1−x Sr x VO3,Phys.Rev.Lett.74,2539(1995).[7]M.Takizawa,M.Minohara,H.Kumigashira,D.Toyota,M.Oshima,H.Wadati,T.Yoshida,A.Fujimori,M.Lippmaa,M.Kawasaki,H.Koinuma,G.Sordi,and M.Rozenberg,Coherent and incoherent d band dispersions in SrVO3,Phys.Rev.B80, 235104(2009).[8]T.Yoshida,M.Hashimoto,T.Takizawa,A.Fujimori,M.Kubota,K.Ono,and H.Eisaki,Mass renormalization in the bandwidth-controlled Mott-Hubbard systems SrVO3and CaVO3studied by angle-resolved photoemission spectroscopy,Phys.Rev.B 82,085119(2010).[9]S.Aizaki,T.Yoshida,K.Yoshimatsu,M.Takizawa,M.Minohara,S.Ideta,A.Fujimori,K.Gupta,P.Mahadevan,K.Horiba,H.Kumigashira,and M.Oshima,Self-Energy on the Low-to High-Energy Electronic Structure of Correlated Metal SrVO3,Phys.Rev.Lett.109,056401(2012).[10]M.J.Rozenberg,I.Inoue,H.Makino,F.Iga,and Y.Nishihara,Low Frequency Spectroscopy of the Correlated Metallic System Ca1−x Sr x VO3,Phys.Rev.Lett.76,4781(1996).[11]A.Sekiyama,H.Fujiwara,S.Imada,S.Suga,H.Eisaki,S.I.Uchida,K.Takegahara,H.Harima,Y.Saitoh,I. A.Nekrasov,G.Keller,D.E.Kondakov,A.V.Kozhevnikov,Th.Pruschke,K.Held,D.V ollhardt,and V.I.Anisimov,Mutual Experimental and Theoretical Validation of Bulk Photoemis-sion Spectra of Sr1−x Ca x VO3,Phys.Rev.Lett.93,156402 (2004).[12]E.Pavarini,S.Biermann,A.Poteryaev,A.I.Lichtenstein,A.Georges,and O.K.Andersen,Mott Transition and Suppression of Orbital Fluctuations in Orthorhombic3d1Perovskites,Phys.Rev.Lett.92,176403(2004).[13]B.Amadon,F.Lechermann,A.Georges,F.Jollet,T.O.Wehling,and A.I.Lichtenstein,Plane-wave based electronic structure calculations for correlated materials using dynamical mean-ﬁeld theory and projected local orbitals,Phys.Rev.B77,205112 (2008).[14]M.Aichhorn,L.Pourovskii,V.Vildosola,M.Ferrero,O.Parcollet,T.Miyake,A.Georges,and S.Biermann,Dynamical mean-ﬁeld theory within an augmented plane-wave framework: Assessing electronic correlations in the iron pnictide LaFeAsO, Phys.Rev.B80,085101(2009).[15]M.Karolak,T.O.Wehling, F.Lechermann,and A.I.Lichtenstein,General DFT++method implemented with pro-jector augmented waves:Electronic structure of SrVO3and the Mott transition in Ca2−x Sr x RuO4,J.Phys.:Condens.Matter23, 085601(2011).[16]H.Lee,K.Foyevtsova,J.Ferber,M.Aichhorn,H.O.Jeschke,and R.Valent´ı,Dynamical cluster approximation within an aug-mented plane wave framework:Spectral properties of SrVO3, Phys.Rev.B85,165103(2012).[17]J.M.Tomczak,M.Casula,T.Miyake, F.Aryasetiawan,and S.Biermann,Combined GW and dynamical mean-ﬁeld theory:Dynamical screening effects in transition metal oxides, Europhys.Lett.100,67001(2012).[18]C.Taranto,M.Kaltak,N.Parragh,G.Sangiovanni,G.Kresse,A.Toschi,and K.Held,Comparing quasiparticle GW+DMFTand LDA+DMFT for the test bed material SrVO3,Phys.Rev.B 88,165119(2013).[19]J.M.Tomczak,M.Casula,T.Miyake,and S.Biermann,Asymmetry in band widening and quasiparticle lifetimes in SrVO3:Competition between screened exchange and local correlations from combined GW and dynamical mean-ﬁeld theory GW+DMFT,Phys.Rev.B90,165138(2014).[20]A.van Roekeghem and S.Biermann,Screened exchangedynamical meanﬁeld theory and its relation to density functional theory:SrVO3and SrTiO3,Europhys.Lett.108,57003(2014).[21]A.Fujimori,I.Hase,H.Namatame,Y.Fujishima,Y.Tokura,H.Eisaki,S.Uchida,K.Takegahara,and F.M.F.de Groot,Evolution of the Spectral Function in Mott-Hubbard Systems with d1Conﬁguration,Phys.Rev.Lett.69,1796(1992). [22]K.Morikawa,T.Mizokawa,A.Fujimori,Y.Taguchi,andY.Tokura,Photoemission spectral weight distribution in Y1−x Ca x TiO3,Phys.Rev.B54,8446(1996).[23]I.A.Nekrasov,G.Keller,D.E.Kondakov,A.V.Kozhevnikov,Th.Pruschke,K.Held, D.V ollhardt,and V.I.Anisimov, Comparative study of correlation effects in CaVO3and SrVO3, Phys.Rev.B72,155106(2005).[24]R.Eguchi,T.Kiss,S.Tsuda,T.Shimojima,T.Mizokami,T.Yokoya,A.Chainani,S.Shin,I.H.Inoue,T.Togashi,S.Watanabe,C.Q.Zhang,C.T.Chen,M.Arita,K.Shimada,H.Namatame,and M.Taniguchi,Bulk-and Surface-SensitiveHigh-Resolution Photoemission Study of Two Mott-Hubbard Systems:SrVO3and CaVO3,Phys.Rev.Lett.96,076402 (2006).[25]A.F.Santander-Syro,O.Copie,T.Kondo,F.Fortuna,S.Pailh`e s,R.Weht,X.G.Qiu,F.Bertran,A.Nicolaou,A.Taleb-Ibrahimi, P.Le F`e vre,G.Herranz,M.Bibes,N.Reyren,Y.Apertet,P.Lecoeur,A.Barth´e l´e my,and M.J.Rozenberg,Two-dimensional electron gas with universal subbands at the surface of SrTiO3, Nature(London)469,189(2011).[26]W.Meevasana,P.D.C.King,R.H.He,S.-K.Mo,M.Hashimoto,A.Tamai,P.Songsiriritthigul,F.Baumberger,and Z.-X.Shen,Creation and control of a two-dimensional electron liquid at the bare SrTiO3surface,Nat.Mater.10,114(2011).[27]P.D.C.King,R.H.He,T.Eknapakul,P.Buaphet,S.-K.Mo,Y.Kaneko,S.Harashima,Y.Hikita,M.S.Bahramy,C.Bell,Z.Hussain,Y.Tokura,Z.-X.Shen,H.Y.Hwang,F.Baumberger, and W.Meevasana,Subband Structure of a Two-Dimensional Electron Gas Formed at the Polar Surface of the Strong Spin-Orbit Perovskite KTaO3,Phys.Rev.Lett.108,117602 (2012).[28]T.C.R¨o del,F.Fortuna,F.Bertran,M.Gabay,M.J.Rozenberg,A.F.Santander-Syro,and P.Le F`e vre,Engineering of two-dimensional electron gases at the(001)and(101)surfaces of TiO2anatase using light,Phys.Rev.B92,041106(R) (2015).。

铁基超导

铁基超导超导是物理世界中最奇妙的现象之一。

正常情况下，电子在金属中运动时，会因为金属晶格的不完整性（如缺陷或杂质等）而发生弹跳损耗能量，即有电阻。

而超导状态下，电子能毫无羁绊地前行。

这是因为当低于某个特定温度时，电子即成对，这时金属要想阻碍电子运动，就需要先拆散电子对，而低于某个温度时，能量就会不足以拆散电子对，因此电子对就能流畅运动。

传统的解释常规超导体的超导电性的微观理论预言，超导体的最高温度不会超过麦克米兰极限的39K。

在以往的研究中，只有1987年发现的铜氧化合物超导体打破了这一极限，被称为高温超导体。

最近，在铁基磷族化合物中发现的超导电性其超导临界温度可达55K，同样突破了传统理论预言的麦克米兰极限。

这是第一个非铜基的高温超导体，掀起了高温超导研究的又一次热潮。

铁基超导的研究进入了一个空前发展的阶段，各国都在进行这一新材料的研究，铁基超导体薄膜研究进展与铁基超导体大同位素效应就是其中的热点。

从2008年新的铁基高温超导体发现以来，铁基超导薄膜的研究进展相对缓慢。

这是因为较难精确控制人们所需要的亚稳相中的多元素配比、以及多种热力学相之间的互相竞争。

由于元素配比和不同热力学相竞争所导致的较少量的杂质，在块状材料的合成中有时可以接受，但对低维的薄膜材料却不能允许。

迄今已发现四种主要晶体结构的铁基超导体，包括含砷或磷（chalcogens）的1111相、122相、111相，以及含氧硫族元素（pnictogens）的11相。

它们都具有超导的Fe-X （X为As、P、Se、S或Te等）层，且前三类超导体中这些层由La-O等隔离层隔开，而超导的11相FeSe、Fe(Se,Te)只有Fe-X层，晶体结构最简单。

目前人们只得到了11相的单相、外延、超导薄膜。

而对含砷的铁基超导体而言，经过近两年的探索，仍未能得到单相的超导薄膜。

中国科学院物理研究所/北京凝聚态物理国家实验室(筹)超导实验室的曹立新副研究员带领博士生韩烨、李位勇，与相关科研人员合作，在国际上率先制备出单相的外延FeSe超导薄膜（第十届全国超导薄膜和超导电子器件学术研讨会，大连，2008年10月11日-15日），率先发表文章（Journal of Physics: Condensed Matter 21, 235702, 2009），并申请了国家专利。

有机场效应晶体管-2014

Current (I)voltage (V) characteristics, at VG
测定迁移率的公式： ID=(W/L) Ci µ (VG﹣VT)VD (linear) ID=(W/2L) Ci µ (VG﹣VT)2 (saturation)
载流子迁移率的测试方法：飞行时间法（TOF）
d
t
寡聚噻吩、硒吩衍生物
噻吩芳环寡聚衍生物
有机场效应晶体管：p型小分子材料
硫族杂稠环衍生物
有机场效应晶体管：p型小分子材料
四硫富瓦烯衍生物含氮杂稠环衍生物
有机场效应晶体管：p型小分子材料
酞菁卟啉衍生物其它p型小分子材料
有机场效应晶体管：n型小分子材料
含氟n型小分子材料酸酐酰亚胺n型小分子材料
有机场效应晶体管
苏仕健 mssjsu@
华南理工大学高分子光电材料与器件研究所
世界第一台计算机
生日：1946年2月14日姓名：电子数值积分和计算机（Electronic Numerical Integrator And Computer，ENIAC）父母：美国陆军军械部、美国宾夕法尼亚大学莫尔学院组成：17468个电子管、6万个电阻器、1万个电容器和6千个开关，重30吨，占地160 平方米，耗电174千瓦，耗资45万美元。运算能力：5千次加法或400次乘法运算/秒
-5
-30 V
-5
-80 V
-5
-20 V
-5
-5
-60 V
-5
-6
-10 V 0V
0.0 0 -20 -40 -60 -80
-40 V -20 V 0V
0.0 0 -10 -20 -30 Drain voltage (V) -40

Gd3+掺杂调控BiFeO3-BaTiO3高温无铅压电陶瓷的结构与性能

第 4 期第 43-53 页材料工程Vol.52Apr. 2024Journal of Materials EngineeringNo.4pp.43-53第 52 卷2024 年 4 月Gd 3+掺杂调控BiFeO 3-BaTiO 3高温无铅压电陶瓷的结构与性能Structures and properties of Gd 3+ doped modified BiFeO 3-BaTiO 3 high -temperature lead -free piezoelectric ceramics唐蓝馨1，王芳1，周治1，李双池1，左鑫1，李凌峰1，杨柳1，谭启2，陈渝1*（1 成都大学机械工程学院，成都 610106；2 广东以色列理工学院材料科学与工程系，广东汕头 515063）TANG Lanxin 1，WANG Fang 1，ZHOU Zhi 1，LI Shuangchi 1，ZUO Xin 1，LI Lingfeng 1，YANG Liu 1，TAN Daniel Q 2，CHEN Yu 1*（1 School of Mechanical Engineering ，Chengdu University ，Chengdu 610106，China ；2 Department of Materials Science and Engineering ，Guangdong Technion -Israel Institute of Technology ，Shantou 515063，Guangdong ，China ）摘要：用于监测航空发动机、重型燃气轮机等重大技术装备高温部件振动状态的压电加速度传感器，需要一种高居里温度压电陶瓷作为敏感元件，而电子元器件的无铅化是环境保护的迫切要求。

采用传统的固相反应法制备一种Gd/Mn 共掺杂的BF -BT （（0.67BiFeO 3-0.33Ba 1-x Gd x TiO 3）+0.5%（质量分数）MnO 2，x =0~0.02）高温无铅压电陶瓷，并研究Gd 3+掺杂浓度（x ）对BF -BT 陶瓷的相组成、微观结构、压电性能、介电弛豫行为及交流阻抗特征的影响。

其实早在反铁磁性发现之前,人们就注意到一些离子化合物

同时都在向着这一氧离子伸出杂拼轨道，就会各自和氧离子的一对2p电子轨道形成两个半共价键。所以无论阳离子 d电子数目多少，这一结合都要求两个阳离子磁矩反平行。如果氧离子两旁的两个阳离子只有一个向氧离子伸出杂拼轨道，就只形成一个共价键的情况下，是另一旁的作用Jpd 决定着两个阳离子的磁矩取向，或平行或反平行。
A site B site
如下图所示，在尖晶石结构中，A-B近邻的距离较短、夹角最接近180度，所以间接交换作用最强。B-B交换作用次之， A-A交换作用最弱。
q 2.1
p a 1.9 1010 m 4
Zn原子的加入，大大降低了A-B之间的交换作用，使居里温度迅速下降。
3.8 RKKY交换作用模型
随着O,S,Se,Te电负性的减弱，它们与Mn的化合物反铁磁居里点增高。
1949年中子衍射证实：氧离子的前后、左右、上下的两个Mn 离子磁矩反平行，而Mn-O-Mn 之间夹角为90度的两个 Mn原子磁矩有平行的也有反平行的。
超交换作用模型可以正确地解释MnO的磁结构，和氧原子成 180°相邻的Mn离子磁距交换作用强，都是反平行排列，成 90°相邻的交换作用弱，离子磁距有平行的，也有反平行的。
1950年Jonker等人发现La1-XCaXMnO3在含有一定Ca量的成分段内具有相当强的铁磁性。
更重要的是，在掺杂锰氧化物体系中，随着温度降低，顺磁－铁磁转变和绝缘－金属转变是关联的。
From Schiffer et al. (1995)
为此，Zener在1951年提出了双交换作用模型：电子在三个离子之间的连续换位的可能条件是两个Mn离子的磁距平行排列。
其实，这一局域电子之间通过传导电子作媒介而产生交换作用的机制很适合于解释稀土金属的自发磁化，其思路是：

主要英文期刊简称、全称对应表

主要英文期刊简称、全称对应表（部分）简称全称MMagn. Reson. Mater. Phys., Biol.Magnetic Resonance Materials in Physics, Biology and Medicine MedMagy. Kem. Foly Magyar Kemiai FolyoiratMain Group Chem Main Group ChemistryManuf. Chem Manufacturing ChemistMar. Biol Marine BiologyMar. Biotechnol Marine BiotechnologyMar. Chem Marine ChemistryMar. Environ. Res Marine Environment ResearchMar. Pollut. Bull.Marine Pollutution BulletinMass Spectrom. Rev Mass Spectrometry ReviewsMater. Charact Materials CharacterizationMater. Chem. Phys Materials Chemistry and PhysicsMater. Corros Materials and CorrosionMater. Des Materials and DesignMater Materials uationMater. Forum Materials ForumMater. High Temp Materials at High TemperaturesMater. Lett Materials LettersMater. Manuf. Processes Materials and Manufacturing ProcessesMater. Org Materials and OrganismsMater. Performance Materials PerformanceMater. Res. Bull Materials Research BulletinMater. Res. Innovations Materials Research InnovationsMater. Sci Materials ScienceMater. 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安德烈夫反射

夫反射/9816333?fr=aladdin
超导体
超导体（superconductor），指可以在在特定温度以下，呈现电阻为零的导体。零电阻和完全抗磁性是超导体的两个重要特性。超导体电阻转变为零的温度，称为超导临界温度，据此超导材料可以分为低温超导体和高温超导体。这里的“高温”是相对于绝对零度而言的，其实远低于冰点摄氏0。科学家一直在寻求提高超导材料的临界温度，高温超导体的最高温度记录是马克普朗克研究所的203K（-70°C）。因为零电阻特性，超导材料在生成强磁场方面有许多应用，如MRI核磁共振成像等。 [1]
请您及时更换请请请您正在使用的模版将于2周后被下线请您及时更换
安德烈夫反射
安德烈夫反射
本词条由“科普中国”科学百科词条编写与应用工作项目审核。
安德烈夫反射(Andreev reflection)是描述一个电子入射超导体(S)和正常金属(N)之现象，是由俄国物理学家亚历山大·F·安德烈夫首度发现。当电子过入射超导体和正常金属之间时，在正常金属这边会形成一个与之前入射电子自旋相反的电洞（又称空穴，空穴并不是真实存在的,只是对大量电子运动的一种等效,空穴的流动其实就是大量电子运动的等效的反运动,这从空穴的定义和特性就可以知道。），而在超导体的另一边会形成一个库柏对(两个自旋不同电子纠缠在一起状态) 所谓正常金属, 这里指在费米面附近, 相反自旋态密度相同的金属。
首先对基本粒子提出自转与相应角动量概念的是1925年由拉尔夫·克罗尼希、乔治·乌伦贝克与山缪·古德斯密特三人所开创。他们在处理电子的磁场理论时，把电子想象为一个带电的球体，自转因而产生磁场。后来在量子力学中，透过理论以及实验验证发现基本粒子可视为是不可分割的点粒子，所以物体自转无法直接套用到自旋角动量上来，因此仅能将自旋视为一种内禀性质，为粒子与生俱来带有的一种角动量，并且其量值是量子化的，无法被改变（但自旋角动量的指向可以透过操作来改变）。

有机超导体

Little 激子模型
. . . . .
A
e
B
A 是导电高分子材料（如聚乙炔）作为导电的主链， B是电子极化率大的侧链, (如：花青系色素分子)。当电子沿着主链运动到A位时，引起B处侧基的极化，
+
-
正电荷诱导电荷分离：靠近主链处感生正电荷，这个正电荷随着传导电流的通过而变得极大，使随之而来的第二个电子被吸引到端部的正电荷附近，形成相互维系着的激子，结果促进了两个传导电子间的相互吸引。这个引力如果克服了传导电子间的库仑斥力，那么两个电子仿佛相互成对，这有利于超导电状态的形成。显然，这个模型类似与BCS理论的以“声子”为媒介的模型。应用激子模型对BCS理论的公式Tc做适当修改后， Little 预言有机超导体的转变温度可提高到2000K.
C60有机超导体的超导转变记录不断更新：
1991.4.
A.F.Hebard, A.R.Kortan K3-C60 Tc=18K; 1991.5. Rb-C60 Tc=28K; Cs-Rb-C60 Tc=33K; 1992.9. I2-C60 Tc=57K 科学家预言：当富勒烯的碳原子数增加8倍，将会实现室温超导，由此对未来世界的各个领域产生不可估量的影响。
高分子科学领域中下一个诺贝尔奖会是谁呢？
谢谢大家！
超导态概述
1911年，荷兰物理学家昂尼(H.Kammerlingh-Onnes) 发现在4.2K附近，汞的电阻突然降为零，昂尼斯猜测超导材料处于一种新的状态，他把这种状态叫超导态，具有超导电性的材料叫超导体。超导体电阻降为零的温度称为转变温度或临界温度Tc

昂尼斯因这一现象的发现于1913年,获诺贝尔物理学奖 o

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arXiv:cond-mat/0304483v2 [cond-mat.str-el] 23 Apr 2003FerroelectricMott-Hubbardphaseinorganicconductors.S.BrazovskiiLPTMS-CNRS,Orsay,FranceandLandauInstitute,Moscow,Russia

P.MonceauCRTBT-CNRS,GrenobleandLLBCEA-CNRS,Saclay,France

F.NadInstituteofRadioelectronics,RussianAc.Sci.,Moscow,Russia(ProceedingsofICSM2002[1].WritteninOctober2002for[2])AbstractWepresentkeyissuesofrelatedphenomenonsoftheFerroelectricityandtheChargeDispro-portionationinorganicmetals.In(TMTTF)2Xthedielectricsusceptibilityεdemonstratesclearcasesoftheferroelectricandanti-ferroelectricphasetransitions.Bothεandσproveindepen-denceandoccasionalcoexistenceof‘structurless’ferroelectrictransitionsandusual‘anionic’ones.Theirsequencegivesaccesstophysicsofthreetypesofsolitonsemerginguponcoolingviaseveralstepsofsymmetrybreaking.ThetheoryinvokesaconceptoftheCombinedMott-HubbardStatewhichfocusesuponweakprocessesofelectronicUmklappscatteringcomingfromboththebuild-innonequivalenceofbondsandthespontaneousoneofsites.WeproposethatthechargeorderinginitsformoftheferroelectricityexistshiddenlyevenintheSesubfamily(TMTSF)2X,givingrisetotheunexplainedyetlowfrequencyopticalpeakandtheenhancedpseudogap.

Keywords:Organicconductors,ferroelectricity,Mott-Hubbardstate,chargedisproportionation,solitons.

1I.FERROELECTRICITYINORGANICCONDUCTORS.Thefamilyofquasione-dimensionalorganicsuperconductors(theBechgard-Fabresalts(TMTSF)2X,(TMTTF)2X)demonstrates,atlowtemperaturesT,transitionstoalmostallknownelectronicphases,see[3].AthigherT=Tao,usuallythereisalsoasetofweakstructuraltransitionsofthe‘anionorderings’(AOs)whichareslightarrangementsofchainsofcounterionsX[4].AtevenhigherT≈T0,alsoother‘structurless’transitions[5]wereobservedsometimesintheTMTTFsubfamilybuttheywerenotexplainedandleftunattended.Recentlytheirmysteriousnaturehasbeenelucidatedbydiscoveriesofthehugeanomalyinthedielectricsusceptibilityε[6,8](seeFig.1)andofthechargedisproportionation(CD)seenbytheNMR[9].Thenewdisplaciveinstabilityandtheusual‘orientational’AOsseemtobeindependent,asprovedbyﬁndingtheirsequencein(TMTTF)2ReO4[8].Thephasetransitionwasinterpreted[6]astheleastexpectedone:totheFerroelectric(FE)state,whichwasprovedbytheclear-cutﬁttingoftheanomalyinε(T)totheCurielaw(seetheﬁgurein[6]).TheFEtransitionisfollowedbyafastformation,orthesteepincrease,oftheconductivitygap∆(seetheFig.2)withnosignsofaspingapformation.HencewedealwithasurprisingFEversionoftheMott-Hubbardstatewhichusuallywasassociatedratherwithmagneticorderings.TheFEtransitionin(TMTTF)2Xisaveryparticular,brightmanifestationofamoregeneralphenomenonoftheCD,whichalreadyhasbeenpredictedin[10]andnowbecomesrecognizedasacommonfeatureoforganicandsomeotherconductors[11].Theanomalousdivergingpolarizabilityiscomingfromtheelectronicsystem,evenifionsareveryimportanttochooseandstabilizethelongrange3Dorder.Thusthetheory[6]suggeststhatthecollectivesingularcontributionε∼(ωp/∆)2/|T/T0−1|(ωpisthemetallicplasmafrequency)developsuponthealreadybigintergapcontribution∼(ωp/∆)2∼103

whichisalsoseenasthebackgroundattheFig.1.TypicalplotsattheFig.1demonstrateverysharp(eveninthelogscale!)FEpeaks,whiletheanti-FEcaseofX=SCNshowsasmoothermaximum.AtthesubsequentIstorderAOtransitioninthecaseofX=ReO4,εdropsdownwhichmightbecausedbytheincreaseof∆seenattheconductivityplotattheFig.2.FinallytheIIndorderspin-PeierlstransitioninthecaseofX=PF6showsuponlyasashoulder.Allthatseemstocollaboratetowardsaconsistentpicture.

2050100150200250300103104105106 ε'

Temperature(K)FIG.1:logεvsTforFEcasesX=PF6(♦),AsF6(△),SbF6(•),ReO4(󰀃)andfortheanti-FEX=SCN(⊙).

AlreadywithinthenonperturbedcrystalstructureatT>T0,thetinydimerizationofbondsbyanionsXprovokesthedielectrization[12],seemorereferencesin[13].Thecountingofthemeanelectronicoccupationchangesfrom1/2permoleculeto1pertheirdimerwhichopens(accordingtoDzyaloshinskii&Larkin,Luther&Emery)theroutetotheMott-Hubbardinsulator.AtTnowbyjointeﬀectsofalternationsofbondsandsites.TheconductivityGplotsattheFig.2showthischangebykinksatT=T0turningdowntomuchhigheractivationenergiesatlowT.ThesteepnessofGjustbelowT0reﬂectsthegrowthoftheCDcontributiontothegap√