• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Controlling Thermodynamic Properties of Ferromagnetic Group-IV Graphene-Like Nanosheets by Dilute Charged Impurity

    2018-01-24 06:23:14MohsenYarmohammadiandKavoosMirabbaszadeh
    Communications in Theoretical Physics 2017年5期

    Mohsen Yarmohammadiand Kavoos Mirabbaszadeh

    Department of Energy Engineering and Physics,Amirkabir University of Technology,Tehran,Iran

    1 Introduction

    The properties of graphene,the one-atom-thick sheet of carbon atoms with thesp2hybridization,were first discussed in the literature more than sixty years ago.[1]Since then,graphene has been intensively investigated with focus on its physical and chemical properties.[2]Because of its unique symmetry,electron and hole bands of graphene show linear band crossing at the Fermi level,[3]resulting in a massless Dirac fermion like behavior of charge carriers.It has found several two-dimensional(2D)materials like group-IV graphene-like structures,hexagonal boron-nitride(h-BN)and MoS2,which present null gaps in both flat or buckled con figurations.Although these materials have a honeycomb lattice,but their properties are different.[4?8]The band gap is a measurement of the threshold voltage and on-off ratio of the field effect transistors.[9?10]In recent years,elemental sheets of silicon and germanium(silicene and germanene respectively)have been emerging as strong contenders in the realm of 2D materials.[11?12]There have been several theoretical studies assessing their fundamental properties while experimental analyses are just in their infancy,as practical synthesis methods are being explored to establish well defined fabrication techniques and parameters.Studies predict that such elemental sheets may also possess Dirac fermions similar to graphene and much simpler techniques may become available for their band gap engineering.Although semi-metallic,the main hurdle experienced in realizing silicene and germanene is that unlike graphene,they do not form a van der Waals layered structures in their bulk phase.Hence,they do not exist as freestanding sheets but synthesized as adlayer structures on ordered substrates.[13]Despite this fact,the exceptional findings through theoretical and preliminary experimental analyses,along with its compatibility to the current silicon based electronics,continues to inspire the exploration of 2D silicene and other group-IV elemental materials(germanene,stanene).However,a lot remains to be explored before these materials can be established as viable alternatives for the next generation of electronic applications.[14?15]

    Successful realization of single crystal silicon monolayer structures[16?17]through chemical exfoliation shows that 2D silicon monolayers with their low resistivity and extremely thin structures can be quite promising for nanoelectronics. Unlike graphene,silicene has a hexagonal atomic arrangement with a buckled con figuration because of its large ionic radius of silicon atoms,[18?21]as presented in Fig.1.From this point,its sublattices(AandB)sit in two parallel planes with a vertical distance of 0.46 ?A.[22?23]The low-energy dynamics of fermions in pristine graphene describes by Dirac Hamiltonian but in silicene,germanene and stanene due to the strong spinorbit coupling(SOC),carriers are massive with an energy gap.[24?25]This gap can be modulated via an applied perpendicular EF to its layer,which leads to the many attractive properties.[26?33]Unlike electronic properties,thermal properties of group-IV are still not well studied.Many works show that the thermal conductivity of silicene is predicted around(20–65)W/mK.[34?38]Electronic heat capacity(EHC)of a semiconductor system is defined as the ratio of the heat used by the carriers(here,Diracfermions)to the rise in temperature of the system.[39]On the other hand,magnetic susceptibility(MS)is the degree of magnetization of a material in response to an external applied magnetic field.Furthermore,our system is considered as a ferromagnetic with an exchange field.Electrons in a system scatter from dilute charged impurities with a scattering rate.This induces a characteristic energy scale at Dirac points.For this reason,impurities have a strong effect on physical properties of materials such as electronic and thermal properties for their applications in electronic devices.Motivated by the recent experimental developments and theoretical investigations on 2D monolayer honeycomb structures,in this paper we carry out a systematic study of three similar structures of group-IV elements based on the Green’s function method.

    In this work,we have investigated the temperature dependence of EHC and MS in ferromagnetic silicene,germanene and stanene in the presence of dilute charged impurity at Dirac points.Also,at a given impurity concentration(IC)and impurity scattering strength(ISS),EHC and MS have been studied with EF.Green’s function approach is carried out with the Kane-Mele Hamiltonian to study the dynamics of carriers in the system.In this work,impurities are randomly doped on sheets.The organization of this paper is as follows:In Sec.2,the methods together with parameters used in our calculations are outlined.The thermodynamic properties of these structures are investigated in Sec.3.In Sec.4,we present our results regarding the calculations.In Sec.5,our conclusions are presented.

    2 Methods

    Here is considered a monolayer system on thexy-plane,exposed to the perpendicular EFEz,as illustrated in Fig.1.The system is described by following model in order to study the dynamics of carriers[25,40]

    in which the first term denotes the nearest-neighbor hopping with energy oft0and the sum runs over all neighboring pairscreates(annihilates)an electron with spinσ=↑,↓ at sitei.The first two terms illustrate the Kane–Mele Hamiltonian describing the SOC with ΔSO,being→σ=(σx,σy,σz)the Pauli matrices.Also is defined

    with→diand→djbeing the two typical vectors,which connect the next nearest neighbors,and sum over all such pairs indicated by 〈i,j〉.[41?42]The third term is the staggered sublattice potential term as mentioned before in Sec.1 with?i=+1(?1)forA(B)sites.The final term is related to the induced exchange magnetic field by the magnetic insulator substrate.The low-energy limit of the above Hamiltonian in a ferromagnetic system in presence of a perpendicular uniform EF is described as:[25,43]

    whereinvFis the Fermi velocity of carriers for the inplane momentum k=(kx,ky)of the first Brillouin zone.ais the equilibrium lattice constant of structures andτi(i=x,y,z)are the Pauli matrices in the sublattice space.The first term in Eq.(1)is the pristine graphene Hamiltonian(Dirac Hamiltonian)at Dirac cone approximation forK(K′)points indexed byη=+1(?1).This term refers to the intra-layer hopping fromAatoms toBatoms and vice versa.The second term is the Kane–Mele Hamiltonian for the intrinsic SOC.[44]If systems rest onto the surface of a magnetic insulator substrate,an exchange magnetization can be induced asM= ΔSO/2.[45?46]σ=+1(?1)are used for spin-up and spin-down subbands.The Green’s function matrix of the unperturbed system can be readily obtained by following equation

    Having substituted Eq.(2)into Eq.(3),the explicit form of the Green’s function matrix is found but has not been written here because it is quite lengthy.The lattice constantsa,SOC and Fermi velocity at the Dirac pointKare given as((3.86,4.02 and 4.70)?A),((5.42,5.24 and 4.70)×105m/s)and((1.55,23.9 and 73.5)meV)for(silicene,germanene and stanene),respectively.[25]According to the Born approximation in the scattering theory[47]and usingTmatrix,[47]the electronic self-energy matrix of disordered system in the presence of finite but small density of impurity atoms,ni=Ni/N,could be obtained as

    whereNis the number of unit cell atoms andνidenotes the electronic on-site energy,which shows the strength of scattering potential.The local propagator of unperturbed system is given by

    In order to include some contributions from multiple site scattering,we replace the local bare Green’s functionby local full one,in the expression of the self-energy matrix in Eq.(4),leading to full self-consistent Born approximation.Under neglecting interstice correlations,the self-consistent problem requires the solution of equation

    The electronic self-energy should be found from a selfconsistent solution of Eq.(6).The pertubative expansion for the Green’s function of disordered system is obtained via the Dyson equation[47]as

    In the next section,EHC and MS are calculated.

    Fig.1 The(a)side view and(b)top view schematic illustration of group-IV graphene-like nanosheets.The A and B sites separated by a distance 2d within the electric field(EF)Ez.The black dashed lines illustrate the Bravais unit cell including two atoms.→diand→djare two typical vectors connecting the next nearest neighbors.

    3 Electronic Heat Capacity and Magnetic Susceptibility

    Density of states(DOS)can be calculated by trace of the imaginary part of the Green’s function matrix,D(ε)= ?? TrG(ε)/π.[48]Taking trace over the quantum numbers,which label the Hamiltonian,engaging Eqs.(1)and(3)along with setting iωn→ε+i0+as an analytical continuation(being 0+a very small real number),the total DOS would be eventuated

    whereμdescribes a sub-site andNcis the number of unit cells.The EHC could be introduced by following expression[39]

    in whichD(ε)calculated by Eq.(8)andf(ε) =1/[eε/kBT+1](kBis the Boltzmann constant)represents the Fermi–Dirac distribution function.By using Eqs.(8)and(9),the EHC would be obtained as

    and MS could be introduced by following expression[39]

    in whichf(E)=1/[eε/kBT+1](beingkBthe Boltzmann constant)stands for the Fermi–Dirac distribution function.Calling Eqs.(8)and(11),the MS would be obtained by

    4 Numerical Results

    In this section,taking into account Eqs.(2),(7),(10),and(12),we obtain the entire low-energy EHC and MS curves around the DiracKpoint and spin-up because of the much number of results besides theK′point and spindown.Because of the unique structure of aforementioned nanosheets and also a symmetry behavior between DiracK(K′)point with spin-up(down)andK′(K)point with spin-down(up),as verified in Refs.[26–27,30,32],we have focused on theKpoint and spin-up cases for reduction of the same results and curves.Also,we have completed our numerical calculations based on the reported parameters in Ref.[25].

    It is well-known that EHC of semiconductors at low temperatures is given byC(T)∝ e?Δ/kBT.[39,49]We see that all curves for EHC exhibit the same behavior with respect to the temperature.Remarkable in every curve is an anomalous peak,so-called the Schottky anomaly,which appears over a small range of temperatures when thermal energy reaches to the energy gap between the subbands.[50?51]The Schottky anomaly as an interesting effect can be explained in terms of the changing in the entropy of the system.As we know,at zero temperature only the lowest energy level is occupied and the entropy is equal to zero.In this regard,there is a very little probability of transition to a higher energy level.As soon as the temperature increases,the entropy increases too monotonausly and therefore the probability of the transition goes up.As soon as the temperature closes to the difference between the energy levels in the system,a broad peak appears,which is corresponding to a large change in the entropy for a small change in temperature.At high temperatures,all of levels are occupied,so there is again a little change in the entropy for small changes in temperature and thus a lower heat capacity.[52?53]Here Δ is the combined EF and impurity scattering potentials.Interaction between conducting electrons and dilute charged impurities affects the scattering rate of electrons.

    Fig.2 Electronic heat capacity in terms of temperature at different electric field strengths for(a)silicene,(b)germanene,(c)stanene and(d)all structures at Δz= ΔSO.

    Fig.3 As Fig.2 but for magnetic susceptibility.

    Fig.4 Temperature-dependent electronic heat capacity for various impurity concentrations for(a)silicene,(b)germanene,(c)stanene and(d)all structures at Δz= ΔSO,νi=0.4ΔSOand ni=0.1.

    Fig.5 Similar to Fig.4 but for magnetic susceptibility.

    Fig.6 Temperature behavior of electronic heat capacity for various impurity scattering strengths for(a)silicene,(b)germanene,(c)stanene and(d)all structures at Δz=(3/2)ΔSO,νi=0.4ΔSOand ni=0.1.

    Fig.7 Like Fig.6 but for magnetic susceptibility.

    The evaluation of EHC with EF has been presented in Fig.2.For silicene,spin-up band gap decreases at Δz≤ ΔSOwhile increases at Δz>ΔSO,which is in agreement with derived findings in Ref.[32].It means that the Schottky anomaly appears atkBT<ΔSO(kBT>ΔSO)for Δz<ΔSO(Δz>ΔSO).For germanene and stanene structures,the spin-up band gaps remain constant because of their large SOC,which does not allow the quantum states to change with EF.In fact,change of Δzin comparison with these large SOCs is negligible.For these nanosheets,there is a critical EF,Δz=(1/2)ΔSO,where EHC is maximum.At low EF strengths,scattering rate is normal and systems see EF as a perturbation that affects their electron transports,but at Δz= ΔSO,systems back to their initial states because of the uniform EF with a smaller transport.For Δz>ΔSO,systems encounter with a unusual scattering rate and EHC increases.These are invalid for germanene and stanene because of their large SOC.For Δz>ΔSO,we have minimum EHC for germanene and stanene structures.In Fig.2(d),silicene(stanene)has the maximum(minimum)EHC at Δz=ΔSO.

    Figure 3 show the temperature-dependent magnetic susceptibility like Fig.2.Each curve bears a crossover,which originates from degenerated energy levels in the electronic minibands and parts the susceptibility into two temperature regions with a sharp positive slope before the apex and a relatively less negative slope after that.[52]According to the concept of magnetic susceptibility,which is a famous topic in every magnetic books and literatures,we have three magnetic orders based on the MS curves for spins including antiferromagnetic,ferromagnetic and paramagnetic.Susceptibility appears as response of the system to the interaction between magnetic field and spin of carriers,which changes the net magnetization of the system.To investigate the temperature behavior of susceptibility,the competition between thermal energy and mentioned interaction plays a key role in the system,leading to the change of magnetization.It is shown that at low temperatures,spin ordering of antiferromagntic systems changes interestingly with magnetic field and MS increases with temperature(albeit in small ranges).When thermal energy reaches to the band gap size of the system,MSmaxoccurs and after that MS decreases,i.e.,system does not answer to magnetic field at high temperatures.Generally,at low temperatures,magnetic field is dominant and MS increases while at high temperatures,temperature is dominant and MS decreases but with a critical temperature,known as Neel temperature.In fact,magnetic field at low temperatures flips the spins and the number of spins with the same directions increases,which leads to the increase of MS but at high temperatures,magnetic field cannot flip the spins and MS decreases because of the high scattering rate of carriers at high temperatures,as shown in the following figure.In ferromagnetic state,all spins have the same directions and at low temperatures,MS decreases with a severe slope up to the Curie temperature.Finally,paramagnetic materials have the random spin directions and MS decreases slightly with temperature because of the weak coupling between spins and external magnetic field.At first,spin-up have the ferromagnetic con figuration while for Δz<ΔSOand Δz>ΔSO,silicene show antiferromagnetic phase and transitions to paramagnetic at Δz= ΔSO.These changes are not valid for germanene and stanene structures and only at Δz<ΔSO,systems show the antiferromagnetic phase.

    Presented in Fig.4 are temperature-dependent EHC for various ICs at Δz= ΔSOandνi/ΔSO=0.4.One can see that EHC increases withniand the band gap size does not change for silicene.Interestingly,EHC decreases withnifor germanene and stanene,which it can be understood by their large intrinsic SOC.Also,it is necessary to say that these changes are at 1<kBT/ΔSO<2 and 1<kBT/ΔSO<3/2 for germanene and stanene,respectively.Figure 4(d)presents silicene(stanene)has the EHCmax(EHCmin).Figure 5 shows that impurity transited the magnetic order of the spins-up from paramagnetic to ferromagnetic phase by flipping.Germanene and stanene do not have phase transition withni.Silicene(stanene)responses to the external magnetic field as maximum(minimum)behavior as shown in Fig.5(d).

    Finally,we have investigated the temperature behavior of EHC and MS of these systems for various ICCs in Figs.6 and 7.Generally,EHC decreases withνi/ΔSOin silicene.Also,the band gap decreases withνi/ΔSObecause the crossover moves towards the lower temperatures.In germanene and stanene,EHC decreases slightly withνi/ΔSOup toνi<ΔSOwhile increases forνi>ΔSO.For MS results,according to the previous descriptions on magnetic order,silicene’s phase is antiferromagnetic while germanene and stanene are at ferromagnetic phase and all structures have MSmaxatνi>ΔSO.

    5 Summary

    In summary,based on symmetry aspects and the massive Dirac theory combined with the Green’s function method,we derived the temperature behavior electronic heat capacity and magnetic susceptibility of silicene,germanene and stanene with electric field,impurity concentration and impurity scattering strength.Spin-up band gap changes with the mentioned above quantities because of the change of the scattering rate of carriers.We have found that the impurity-dependent magnetic susceptibility curves lead to a phase transition from ferromagnetic to paramagnetic and antiferromagnetic phases.

    [1]A.H.Castro Neto,F.Guinea,N.M.R.Peres,K.S.Novoselov,and A.K.Geim,Rev.Mod.Phys.81(2009)109.

    [2]A.K.Geim,Science 324(2009)1530.

    [3]P.R.Wallace,Phys.Rev.71(1947)622.

    [4]K.F.Mak,C.Lee,J.Hone,J.Shan,and T.F.Heinz,Phys.Rev.Lett.105(2010)136805.

    [5]A.H.Castro Neto,F.Guinea,N.M.R.Peres,K.S.Novoselov,and A.K.Geim,Rev.Mod.Phys.81(2009)109.

    [6]N.M.R.Peres,Rev.Mod.Phys.82(2010)2673.

    [7]D.Pacile,J.C.Meyer,C.O.Girit,and A.Zettl,Appl.Phys.Lett.92(2008)133107.

    [8]K.S.Novoselov,D.Jiang,F.Schedin,T.J.Booth,V.V.Khotkevich,S.V.Morozov,and A.K.Geim,Proc.Natl.Acad.Sci.USA 102(2005)10451.

    [9]Y.Lin,K.A.Jenkins,A.Valdes-Garcia,J.P.Small,D.B.Farmer,and P.Avouris,Nano Lett.9(2009)422.

    [10]J.Kedzierski,P.Hsu,P.Healey,P.W.Wyatt,C.L.Keast,M.Sprinkle,C.Berger,and W.A.de Heer,IEEE Trans.Electron Devices.55(2008)2078.

    [11]Q.Tang and Z.Zhou,Prog.Mater.Sci.58(2013)1244.

    [12]L.C.L.Yan Voon and G.G.Guzmn-Verri,MRS Bull.39(2014)366.

    [13]P.Vogt,P.De Padova,C.Quaresima,J.Avila,E.Frantzeskakis,M.C.Asensio,A.Resta,B.Ealet,and G.Le Lay,Phys.Rev.Lett.108(2012)155501.

    [14]L.Li,Y.Yu,G.J.Ye,Q.Ge,X.Ou,H.Wu,D.Feng,X.H.Chen,and Y.Zhang,Nat.Nanotechnol.9(2014)372.

    [15]H.Liu,A.T.Neal,Z.Zhu,Z.Luo,X.Xu,D.Tomnek,and P.D.Ye,ACS Nano 8(2014)4033.

    [16]H.Nakano,T.Mitsuoka,M.Harada,K.Horibuchi,H.Nozaki,N.Takahashi,T.Nonaka,Y.Seno,and H.Nakamura,Angew Chem.118(2006)6451.

    [17]R.Krishnan,Q.Xie,J.Kulik,X.D.Wang,S.Lu,M.Molinari,Y.Gao,T.D.Krauss,and P.M.Fauchet,J.Appl.Phys.96(2004)1.

    [18]B.Lalmi,H.Oughaddou,H.Enriquez,A.Kara,S.Vizzini,B.Ealet,and B.Aufray,Appl.Phys.Lett.97(2010)223109.

    [19]P.E.Padova,C.Quaresima,C.Ottaviani,et al.,Appl.Phys.Lett.96(2010)261905.

    [20]B.Aufray,A.Vizzini,H.Oughaddou,C.Lndri,B.Ealet,and G.L.Lay,Appl.Phys.Lett.96(2010)183102.

    [21]P.Vogt,P.De Padova,C.Quaresima,et al.,

    [22]Z.Ni,Q.Liu,K.Tang,et al.,Nano Lett.12(2012)113.

    [23]N.D.Drummond,V.Z’olyomi,and V.I.Fal’ko,Phys.Rev.B 85(2012)075423.

    [24]C.C.Liu,W.Feng,and Y.Yao,Phys.Rev.Lett.107(2011)076802.

    [25]C.C.Liu,H.Jiang,and Y.Yao,Phys.Rev.B 84(2011)195430.

    [26]M.Ezawa,New J.Phys.14(2012)033003.

    [27]M.Ezawa,Phys.Rev.Lett.109(2012)055502.

    [28]X.T.An,Y.Y.Zhang,J.J.Liu,and S.S.Li,New J.Phys.14(2012)083039.

    [29]M.Tahir and U.Schwingenschlogl,Sci.Rep.3(2013)1075.

    [30]M.Ezawa,Phys.Rev.Lett.110(2013)026603.

    [31]W.F.Tsai,C.Y.Huang,T.R.Chang,H.Lin,H.T.Jeng,and A.Bansil,Nat.Commun.4(2013)1500.

    [32]C.J.Tabert and E.J.Nicol,Phys.Rev.Lett.110(2013)197402.

    [33]H.Pan,Z.Li,C.C.Liu,G.Zhu,Z.Qiao,and Y.Yao,Phys.Rev.Lett.112(2014)106802.

    [34]E.Scalise,M.Houssa,G.Pourtois,B.Broek,V.Afanasev,and A.Stesmans,Nano Res.6(2013)19.

    [35]H.P.Li and R.Q.Zhang,Eur.Phys.Lett.99(2012)36001.

    [36]M.Hu,X.Zhang,and D.Poulikakos,Phys.Rev.B 87(2013)195417.

    [37]Q.X.Pei,Y.W.Zhang,Z.D.Sha,and V.B.Shenoy,J.Appl.Phys.114(2013)033526.

    [38]T.Y.Ng,J.Yeo,and Z.Liu,Int.J.Mech.Mater.Des.9(2013)105.

    [39]C.Kittle,Introduction to Solid State Physicseighth ed.Wiley,New York(2004).

    [40]B.Aufray,A.Vizzini,H.Oughaddou,C.Lndri,B.Ealet,and G.L.Lay,Appl.Phys.Lett.96(2010)183102.

    [41]C.L.Kane and E.J.Mele,Phys.Rev.Lett.95(2005)146802.

    [42]C.L.Kane and E.J.Mele,Phys.Rev.Lett.95(2005)226801.

    [43]T.Yokoyama,Phys.Rev.B 87(2013)241409(R).

    [44]L.Chen,B.J.Feng,and K.H.Wu,Appl.Phys.Lett.102(2013)081602.

    [45]H.Haugen,D.Huertas-Hernando,and A.Brataas,Phys.Rev.B 77(2008)115406.

    [46]Z.Qiao,S.A.Yang,W.Feng,et al.,Phys.Rev.B 82(2010)161414.

    [47]W.Nolthing and A.Ramakanth,Quantum Theory of Magnetism,Springer,New York(2009).

    [48]E.N.Economou,Green’s Functions in Quantum Physics,3rd ed.Springer-Verlag,Berlin,Heidelberg(2006).

    [49]R.K.Pathria,Statistical Mechanics,Oxford Press,London(1997).

    [50]B.Velicky,Phys.Rev.184(1969)614.

    [51]M.Yarmohammadi,Solid State Commun.250(2017)84.

    [52]A.Tari,The Specific Heat of Matter at Low Temperatures,Imperial College Press,London(2003)p.250.

    [53]X.Xu,J.Chen,and B.Li,J.Phys.Condens.Matter.28(2016)483001.

    一个人看视频在线观看www免费| 免费观看无遮挡的男女| 国产熟女欧美一区二区| 18禁动态无遮挡网站| 国产免费一区二区三区四区乱码| 亚洲精品乱久久久久久| av播播在线观看一区| av网站免费在线观看视频| 97超碰精品成人国产| 麻豆乱淫一区二区| 欧美激情在线99| 菩萨蛮人人尽说江南好唐韦庄| 男女无遮挡免费网站观看| 男人狂女人下面高潮的视频| 春色校园在线视频观看| 日韩av免费高清视频| 久久99热这里只有精品18| 国产熟女欧美一区二区| 免费av观看视频| 精品久久久久久久人妻蜜臀av| 免费黄频网站在线观看国产| www.色视频.com| 人体艺术视频欧美日本| 国产成人a区在线观看| 欧美成人一区二区免费高清观看| 国产免费福利视频在线观看| 亚洲经典国产精华液单| 欧美97在线视频| 亚洲人成网站高清观看| 国产69精品久久久久777片| 少妇熟女欧美另类| 欧美日韩国产mv在线观看视频 | 最近最新中文字幕免费大全7| 九九久久精品国产亚洲av麻豆| 欧美另类一区| 亚洲av男天堂| 国产精品av视频在线免费观看| 亚洲精品,欧美精品| 国产av码专区亚洲av| 国产精品国产av在线观看| 亚洲av中文字字幕乱码综合| 白带黄色成豆腐渣| 亚洲色图av天堂| 久久久久久久久久人人人人人人| 国产有黄有色有爽视频| 三级男女做爰猛烈吃奶摸视频| 日韩,欧美,国产一区二区三区| 国产伦理片在线播放av一区| 国产伦在线观看视频一区| 国产成人午夜福利电影在线观看| 久久精品国产亚洲av天美| 国产精品一区www在线观看| 天美传媒精品一区二区| 成人特级av手机在线观看| 日韩成人av中文字幕在线观看| 插阴视频在线观看视频| 18禁裸乳无遮挡免费网站照片| 日本爱情动作片www.在线观看| 一区二区三区免费毛片| 97在线视频观看| 国产av不卡久久| www.色视频.com| 国产成人精品婷婷| 大码成人一级视频| 又粗又硬又长又爽又黄的视频| 精品久久久久久久久亚洲| 久久热精品热| 全区人妻精品视频| 夜夜看夜夜爽夜夜摸| 国产女主播在线喷水免费视频网站| 黄色配什么色好看| 欧美老熟妇乱子伦牲交| 人妻制服诱惑在线中文字幕| 你懂的网址亚洲精品在线观看| 久久久亚洲精品成人影院| 在线观看一区二区三区| 亚洲国产欧美人成| 久久99热这里只频精品6学生| 色婷婷久久久亚洲欧美| 国产精品国产三级国产专区5o| 国产亚洲av片在线观看秒播厂| 欧美高清成人免费视频www| 国产黄片美女视频| freevideosex欧美| 国产欧美另类精品又又久久亚洲欧美| 国产免费视频播放在线视频| 久久久久九九精品影院| 久久精品国产亚洲av天美| 国产色婷婷99| 我的老师免费观看完整版| 蜜臀久久99精品久久宅男| 亚洲欧美成人综合另类久久久| 色视频在线一区二区三区| av国产久精品久网站免费入址| 亚洲精品一区蜜桃| 欧美三级亚洲精品| 搡老乐熟女国产| 热re99久久精品国产66热6| 国产伦理片在线播放av一区| 免费播放大片免费观看视频在线观看| 亚洲婷婷狠狠爱综合网| 联通29元200g的流量卡| 街头女战士在线观看网站| 国产高清有码在线观看视频| 老师上课跳d突然被开到最大视频| 夜夜看夜夜爽夜夜摸| 国产国拍精品亚洲av在线观看| 简卡轻食公司| 亚洲在久久综合| 亚洲欧洲国产日韩| av女优亚洲男人天堂| 国产午夜精品一二区理论片| 免费播放大片免费观看视频在线观看| 在线 av 中文字幕| 欧美+日韩+精品| 久久精品国产自在天天线| 欧美xxxx黑人xx丫x性爽| 丝袜喷水一区| 国产午夜精品久久久久久一区二区三区| 色视频在线一区二区三区| 成年av动漫网址| 夜夜看夜夜爽夜夜摸| 一边亲一边摸免费视频| 美女视频免费永久观看网站| 在线a可以看的网站| 国产精品国产三级国产av玫瑰| 五月天丁香电影| 国产欧美日韩精品一区二区| 日本色播在线视频| 精品久久久久久电影网| 久久久久精品久久久久真实原创| 一区二区三区乱码不卡18| 天堂网av新在线| 身体一侧抽搐| 国产av国产精品国产| 高清在线视频一区二区三区| 男的添女的下面高潮视频| 青春草亚洲视频在线观看| 色视频www国产| 少妇高潮的动态图| 国产成人精品婷婷| 干丝袜人妻中文字幕| 99久久九九国产精品国产免费| 久久久久久久久大av| 2021少妇久久久久久久久久久| 成人一区二区视频在线观看| 蜜臀久久99精品久久宅男| 日日摸夜夜添夜夜爱| 免费黄频网站在线观看国产| 街头女战士在线观看网站| 亚洲精品影视一区二区三区av| 久久久a久久爽久久v久久| av网站免费在线观看视频| 嫩草影院精品99| 女的被弄到高潮叫床怎么办| 1000部很黄的大片| av在线播放精品| 亚洲精品乱码久久久v下载方式| 亚洲国产高清在线一区二区三| 精品午夜福利在线看| 狂野欧美白嫩少妇大欣赏| 不卡视频在线观看欧美| 国产亚洲91精品色在线| 国产欧美日韩一区二区三区在线 | 日本欧美国产在线视频| 国产伦理片在线播放av一区| 精品午夜福利在线看| 免费在线观看成人毛片| 精品国产一区二区三区久久久樱花 | 人人妻人人看人人澡| 亚洲熟女精品中文字幕| 丝袜脚勾引网站| 特级一级黄色大片| 自拍欧美九色日韩亚洲蝌蚪91 | 中文乱码字字幕精品一区二区三区| 久久久欧美国产精品| 亚洲精品成人久久久久久| 一区二区三区乱码不卡18| 小蜜桃在线观看免费完整版高清| www.色视频.com| 狂野欧美白嫩少妇大欣赏| 岛国毛片在线播放| 97在线视频观看| 欧美极品一区二区三区四区| 中文字幕av成人在线电影| 一级毛片电影观看| 免费黄网站久久成人精品| 寂寞人妻少妇视频99o| 亚洲av电影在线观看一区二区三区 | 成年女人看的毛片在线观看| 91在线精品国自产拍蜜月| 乱码一卡2卡4卡精品| 在线看a的网站| 激情五月婷婷亚洲| 丝瓜视频免费看黄片| av.在线天堂| 搡老乐熟女国产| 国产乱人偷精品视频| 全区人妻精品视频| 亚洲最大成人av| 国产精品蜜桃在线观看| 中文天堂在线官网| 男男h啪啪无遮挡| 小蜜桃在线观看免费完整版高清| 亚洲一级一片aⅴ在线观看| 99热这里只有是精品在线观看| 色网站视频免费| 中国国产av一级| 老师上课跳d突然被开到最大视频| 国产精品国产三级专区第一集| 毛片一级片免费看久久久久| 中文资源天堂在线| 久久久国产一区二区| 国产精品蜜桃在线观看| 亚洲精品日韩在线中文字幕| 午夜福利视频1000在线观看| 三级经典国产精品| av一本久久久久| 亚洲精品一区蜜桃| 自拍偷自拍亚洲精品老妇| 最后的刺客免费高清国语| 人人妻人人看人人澡| 少妇人妻久久综合中文| 美女视频免费永久观看网站| 国产黄色免费在线视频| 高清欧美精品videossex| 久久久久久久久久成人| 亚洲国产欧美人成| 精品久久久噜噜| 亚洲成人中文字幕在线播放| 少妇人妻精品综合一区二区| 全区人妻精品视频| 一二三四中文在线观看免费高清| 国产免费又黄又爽又色| 亚洲欧美成人综合另类久久久| 简卡轻食公司| 国产精品一区二区在线观看99| 久久久精品94久久精品| 免费黄频网站在线观看国产| 99热国产这里只有精品6| 久久久久精品性色| 精品国产露脸久久av麻豆| 亚洲av一区综合| 日本一本二区三区精品| 亚洲欧美成人综合另类久久久| 秋霞在线观看毛片| 国产高潮美女av| 亚洲高清免费不卡视频| 91狼人影院| 国产精品人妻久久久影院| 91精品国产九色| 国产女主播在线喷水免费视频网站| 色播亚洲综合网| 国产精品国产av在线观看| av免费在线看不卡| 九九爱精品视频在线观看| 亚洲一区二区三区欧美精品 | 男女啪啪激烈高潮av片| 一区二区三区乱码不卡18| 特级一级黄色大片| 成人漫画全彩无遮挡| 天堂网av新在线| 亚洲欧美成人综合另类久久久| 久久久久性生活片| 麻豆久久精品国产亚洲av| 一二三四中文在线观看免费高清| 免费看不卡的av| 国产成人91sexporn| 久久人人爽人人片av| 在线天堂最新版资源| 欧美一区二区亚洲| 精品视频人人做人人爽| 亚洲一级一片aⅴ在线观看| 国产精品蜜桃在线观看| 欧美日韩视频精品一区| 成年免费大片在线观看| 亚洲第一区二区三区不卡| 久久97久久精品| 赤兔流量卡办理| 日本wwww免费看| 亚洲精品中文字幕在线视频 | 另类亚洲欧美激情| 黑人高潮一二区| 午夜精品国产一区二区电影 | 黄色视频在线播放观看不卡| 在线看a的网站| 一区二区三区免费毛片| 国产黄片美女视频| 久久久久久久精品精品| 小蜜桃在线观看免费完整版高清| 国产亚洲午夜精品一区二区久久 | 成人特级av手机在线观看| 亚洲人成网站高清观看| 国产精品av视频在线免费观看| 干丝袜人妻中文字幕| 日韩av不卡免费在线播放| 一本久久精品| 全区人妻精品视频| 男插女下体视频免费在线播放| 国产成人精品福利久久| 欧美zozozo另类| 欧美老熟妇乱子伦牲交| 久久久精品欧美日韩精品| 亚洲三级黄色毛片| 自拍欧美九色日韩亚洲蝌蚪91 | 狠狠精品人妻久久久久久综合| 免费看a级黄色片| 亚洲欧美中文字幕日韩二区| 国产精品一区二区性色av| 最后的刺客免费高清国语| 国产精品一区二区三区四区免费观看| 一区二区三区四区激情视频| 日日摸夜夜添夜夜添av毛片| 国产精品精品国产色婷婷| 可以在线观看毛片的网站| 国产精品国产三级国产av玫瑰| 国产久久久一区二区三区| 97人妻精品一区二区三区麻豆| 麻豆乱淫一区二区| av在线观看视频网站免费| 简卡轻食公司| 天天躁夜夜躁狠狠久久av| 亚洲欧美清纯卡通| 在线a可以看的网站| 国产免费视频播放在线视频| 成年版毛片免费区| 卡戴珊不雅视频在线播放| 亚洲无线观看免费| 深爱激情五月婷婷| 亚洲无线观看免费| 少妇裸体淫交视频免费看高清| 精品久久久久久久人妻蜜臀av| 一级片'在线观看视频| 真实男女啪啪啪动态图| 免费不卡的大黄色大毛片视频在线观看| 国产在线一区二区三区精| 久久久久精品久久久久真实原创| 欧美成人午夜免费资源| 亚洲欧洲国产日韩| 亚洲国产精品国产精品| 99久久中文字幕三级久久日本| 蜜桃久久精品国产亚洲av| 成人黄色视频免费在线看| 日韩一区二区三区影片| 国产黄频视频在线观看| 国产精品久久久久久精品古装| 2022亚洲国产成人精品| 久久精品久久久久久久性| 免费高清在线观看视频在线观看| 国产亚洲一区二区精品| 亚洲熟女精品中文字幕| 在线亚洲精品国产二区图片欧美 | 中文字幕久久专区| 色哟哟·www| 国产成人精品一,二区| 高清日韩中文字幕在线| 亚洲人成网站高清观看| 一级片'在线观看视频| 欧美97在线视频| 中文精品一卡2卡3卡4更新| 老女人水多毛片| 少妇人妻久久综合中文| 国产色爽女视频免费观看| 亚洲av男天堂| 成人美女网站在线观看视频| 在线观看三级黄色| 精品视频人人做人人爽| 91久久精品国产一区二区三区| 国产欧美日韩精品一区二区| 亚洲精品国产色婷婷电影| 国产伦精品一区二区三区四那| 日韩av免费高清视频| 成人一区二区视频在线观看| 亚洲精品国产色婷婷电影| 欧美高清成人免费视频www| 日韩强制内射视频| 在线精品无人区一区二区三 | 亚洲国产成人一精品久久久| 一区二区av电影网| 极品少妇高潮喷水抽搐| 亚洲国产欧美在线一区| 久热这里只有精品99| 久久久精品94久久精品| 国产成人一区二区在线| 女人十人毛片免费观看3o分钟| 国产毛片a区久久久久| 在线观看免费高清a一片| 亚洲经典国产精华液单| 禁无遮挡网站| 两个人的视频大全免费| 99热6这里只有精品| 蜜臀久久99精品久久宅男| 国产视频内射| 少妇人妻一区二区三区视频| 中文字幕制服av| 亚洲av成人精品一二三区| 亚洲精品乱码久久久v下载方式| 菩萨蛮人人尽说江南好唐韦庄| av黄色大香蕉| 亚洲国产欧美在线一区| 另类亚洲欧美激情| 日本av手机在线免费观看| 国产探花极品一区二区| 色播亚洲综合网| 国产高清不卡午夜福利| 久久久色成人| freevideosex欧美| 晚上一个人看的免费电影| 久久精品久久久久久噜噜老黄| 亚洲人成网站在线播| 久久久久精品久久久久真实原创| videos熟女内射| 777米奇影视久久| 国产淫语在线视频| 青春草亚洲视频在线观看| 欧美人与善性xxx| 欧美zozozo另类| 久久久久久久久久人人人人人人| 好男人在线观看高清免费视频| 我的老师免费观看完整版| 国产成人aa在线观看| 亚洲精品亚洲一区二区| 美女视频免费永久观看网站| 菩萨蛮人人尽说江南好唐韦庄| 丝袜喷水一区| 久久久精品94久久精品| 日本熟妇午夜| 成人无遮挡网站| 成年女人看的毛片在线观看| 少妇人妻精品综合一区二区| 亚洲精品成人久久久久久| 丝瓜视频免费看黄片| 亚洲一级一片aⅴ在线观看| 亚洲av成人精品一二三区| 欧美成人精品欧美一级黄| 成人国产麻豆网| 中文在线观看免费www的网站| 精品午夜福利在线看| 80岁老熟妇乱子伦牲交| 综合色丁香网| 色网站视频免费| 亚洲精品日本国产第一区| 午夜日本视频在线| 晚上一个人看的免费电影| 又大又黄又爽视频免费| 真实男女啪啪啪动态图| 丰满乱子伦码专区| 国产一区二区三区综合在线观看 | 国产欧美日韩一区二区三区在线 | 日韩成人伦理影院| 亚洲aⅴ乱码一区二区在线播放| 老司机影院毛片| 色婷婷久久久亚洲欧美| 免费看a级黄色片| 久久久久久久国产电影| 97超视频在线观看视频| 禁无遮挡网站| 亚洲精品aⅴ在线观看| 日韩 亚洲 欧美在线| 免费高清在线观看视频在线观看| 国产精品蜜桃在线观看| 亚洲av免费在线观看| 亚洲人成网站在线观看播放| 校园人妻丝袜中文字幕| 高清午夜精品一区二区三区| 午夜爱爱视频在线播放| 成人黄色视频免费在线看| 国产精品一二三区在线看| 婷婷色综合大香蕉| 国产色爽女视频免费观看| 欧美少妇被猛烈插入视频| 午夜免费男女啪啪视频观看| 亚洲aⅴ乱码一区二区在线播放| 日本免费在线观看一区| 国产 精品1| 国产午夜精品久久久久久一区二区三区| 九九爱精品视频在线观看| 大码成人一级视频| 人人妻人人爽人人添夜夜欢视频 | 又粗又硬又长又爽又黄的视频| 97超碰精品成人国产| 国精品久久久久久国模美| 精品国产露脸久久av麻豆| 最近2019中文字幕mv第一页| 黄片wwwwww| 国产成人a区在线观看| 国产黄a三级三级三级人| 国产又色又爽无遮挡免| 亚洲四区av| 男女啪啪激烈高潮av片| 在线观看免费高清a一片| 欧美人与善性xxx| 午夜激情久久久久久久| 99久久精品一区二区三区| 蜜臀久久99精品久久宅男| 人妻少妇偷人精品九色| 交换朋友夫妻互换小说| 插阴视频在线观看视频| 亚洲av欧美aⅴ国产| 99热6这里只有精品| 久久精品人妻少妇| 中文字幕亚洲精品专区| 高清日韩中文字幕在线| 亚洲人成网站在线观看播放| 狂野欧美激情性xxxx在线观看| 久久精品国产亚洲av涩爱| 欧美成人一区二区免费高清观看| 伦理电影大哥的女人| 2021少妇久久久久久久久久久| 亚洲精品视频女| 亚洲精品456在线播放app| 精品人妻视频免费看| 新久久久久国产一级毛片| 午夜激情久久久久久久| 亚洲欧美日韩东京热| 日韩免费高清中文字幕av| 男女边摸边吃奶| 美女视频免费永久观看网站| 中国三级夫妇交换| 亚洲丝袜综合中文字幕| 国产高清有码在线观看视频| 九九在线视频观看精品| 亚洲精品成人av观看孕妇| 97人妻精品一区二区三区麻豆| 国产色爽女视频免费观看| 综合色av麻豆| 亚洲av二区三区四区| 80岁老熟妇乱子伦牲交| 校园人妻丝袜中文字幕| av.在线天堂| 国产乱来视频区| 亚洲av成人精品一二三区| 国产探花在线观看一区二区| 天美传媒精品一区二区| 肉色欧美久久久久久久蜜桃 | 日本wwww免费看| 日韩电影二区| 一区二区三区四区激情视频| 寂寞人妻少妇视频99o| 欧美丝袜亚洲另类| 亚洲欧美精品专区久久| 中文字幕人妻熟人妻熟丝袜美| 丰满乱子伦码专区| 成人亚洲精品一区在线观看 | 91精品国产九色| 国产精品国产三级国产av玫瑰| 亚洲精品一二三| videossex国产| 久久热精品热| 国产欧美日韩一区二区三区在线 | 国产精品99久久久久久久久| 亚洲欧美清纯卡通| 欧美亚洲 丝袜 人妻 在线| 亚洲av在线观看美女高潮| 欧美国产精品一级二级三级 | 在线精品无人区一区二区三 | 欧美97在线视频| 日本爱情动作片www.在线观看| 精品熟女少妇av免费看| 如何舔出高潮| 国产av不卡久久| 久久久久国产网址| 国产精品久久久久久精品电影小说 | 亚洲丝袜综合中文字幕| 国产精品久久久久久av不卡| 2022亚洲国产成人精品| 乱码一卡2卡4卡精品| 中国国产av一级| 99视频精品全部免费 在线| 青春草国产在线视频| 亚洲av.av天堂| 国产伦理片在线播放av一区| 亚洲欧美清纯卡通| 亚洲精品成人久久久久久| 精品一区二区三卡| 免费观看无遮挡的男女| 午夜福利高清视频| 欧美成人午夜免费资源| 亚洲精品色激情综合| 久久久久国产网址| 97精品久久久久久久久久精品| 九九久久精品国产亚洲av麻豆| 人人妻人人看人人澡| 一级毛片我不卡| 街头女战士在线观看网站| 亚洲人成网站高清观看| 亚洲精品久久午夜乱码| 边亲边吃奶的免费视频| 九九爱精品视频在线观看| 亚洲内射少妇av| 国产毛片a区久久久久| 乱系列少妇在线播放| 亚洲怡红院男人天堂| 国产成人一区二区在线| 在线 av 中文字幕| 亚洲欧洲国产日韩| 97超碰精品成人国产| 一本久久精品| 亚洲成人中文字幕在线播放| 亚洲丝袜综合中文字幕| 欧美日韩国产mv在线观看视频 | 日本av手机在线免费观看| 国产免费一级a男人的天堂| 精品99又大又爽又粗少妇毛片| 久久久久久久午夜电影| 国产老妇女一区| 国产成人精品福利久久| 乱系列少妇在线播放| 一级毛片 在线播放| 日韩,欧美,国产一区二区三区| 下体分泌物呈黄色| 九九久久精品国产亚洲av麻豆| 特级一级黄色大片| 亚洲欧美中文字幕日韩二区| 日韩制服骚丝袜av|