• <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 ?

    Revealing the A1g-type strain effect on superconductivity and nematicity in FeSe thin flake?

    2021-09-28 02:18:44ZhaohuiCheng程朝暉BinLei雷彬XigangLuo羅習(xí)剛JianjunYing應(yīng)劍俊ZhenyuWang王震宇TaoWu吳濤andXianhuiChen陳仙輝
    Chinese Physics B 2021年9期
    關(guān)鍵詞:吳濤朝暉

    Zhaohui Cheng(程朝暉),Bin Lei(雷彬),Xigang Luo(羅習(xí)剛),2,Jianjun Ying(應(yīng)劍俊),3,Zhenyu Wang(王震宇),3,Tao Wu(吳濤),2,3,5,?,and Xianhui Chen(陳仙輝),2,3,4,5

    1CAS Key Laboratory of Strongly-coupled Quantum Matter Physics,Department of Physics,University of Science and Technology of China,Hefei 230026,China

    2Hefei National Laboratory for Physical Sciences at the Microscale,University of Science and Technology of China,Hefei 230026,China

    3CAS Center for Excellence in Superconducting Electronics(CENSE),Shanghai 200050,China

    4CAS Center for Excellence in Quantum Information and Quantum Physics,Hefei 230026,China

    5Collaborative Innovation Center of Advanced Microstructures,Nanjing University,Nanjing 210093,China

    Keywords:iron-based superconductors,superconductivity,electronic nematicity,strain effect

    Electronic nematic phase,in which the rotational symmetry is broken,exhibits a twist with superconductivity in the electronic phase diagram of iron-based superconductors(IBSCs).[1]Many experiments have already shown conclusive evidences for the electronic nematicity in IBSCs,including anisotropic transport,angle resolved photoemission spectroscopy(ARPES),scanning tunneling microscopy(STM),neutron scattering and so on.[2]So far,although the existence of electronic nematicity in IBSCs is well-established,[3–5]the underlying mechanism and its exact role on the superconducting pairing are still mystery and under hot debate.[1,6,7]Most of the existing experimental results support a direct competition between nematic order and superconductivity in the electronic phase diagram.[8,9]Since the nematic order is tightly twisted with a stripe-type antiferromagnetic order in the iron-pnictide family,[10–12]the competition between the nematic order and the superconductivity is widely believed to stem from the competition between antiferromagnetic order and superconductivity.[8,9]In this case,the nematic order is even considered to be driven by stripe-type spin fluctuations.[1,5,13–16]However,in iron-selenides family such as FeSe1?xSxsystems,there is no direct evidence for the competition between nematic order and superconductivity.[17,18]Interestingly,the stripe-type antiferromagnetic order is also decoupled with nematic order in the electronic phase diagram,which leads to an alternative scenario for electronic nematicity due to orbital order,[19,20]e.g.,the ferro-orbital order.Moreover,orbital fluctuations are also considered to mediate an s++superconducting pairing.[21]So far,the origin of the electronic nematicity and its role on superconductivity are still highly controversial in iron-selenides family.[1,6,7,21,22]

    As a conjugate field for electronic nematicity,strain can be used to manipulate the electronic nematicity,[3–5,24,25]which is helpful to elucidate the relationship between electronic nematicity and superconductivity.[26,27]Recently,a dominant B1g-type strain effect on superconductivity has been revealed in the underdoped Ba(Fe1?xCox)2As2.[24,25]With further electron doping,an A1g-type instead of B1g-type strain effect appears and becomes dominant in the overdoped Ba(Fe1?xCox)2As2.[28,29]These results strongly support a significant role of electronic nematicity on superconductivity.Then,a natural question is whether a similar B1g-type strain effect could be also observed in iron-selenides family or not,which would be helpful to further understand the role of electronic nematicity on the superconducting pairing in IBSCs.

    Previous study on FeSe thin films,utilizing pulsed laser deposition on different substrates,already indicates that the superconducting transition temperature(Tc)in FeSe thin films is highly tunable from 0 K to 12 K by changing the lattice parameters.[30]However,the previous study of the strain effect on Tcin bulk FeSe is not very successful due to the possible damage of FeSe single crystals by large uniaxial strain.[2]Only a small range of uniaxial strain could be applied to FeSe single crystal through a“horseshoe device”or pasting on a piezo-ceramic stack to achieve the measurements of nematic susceptibility.[31,32]In this work,in order to increase the tuning range of uniaxial strain in the bulk FeSe,we adopt a mechanical cleavage method to first cleave FeSe single crystal into thin flakes with the thickness of~25 nm,and then transfer these FeSe thin flakes on a flexible substrate.The uniaxial strain is applied to these thin flakes by bending the flexible substrate.The similar method has been successfully used for the strain tuning of MoS2and black phosphorus thin flakes.[33,34]By utilizing this method for applying uniaxial strain,Tcand Tsof FeSe thin flakes can be largely varied exceeding all previous studies on the strain effect in bulk FeSe.The maximum Tcof FeSe can be increased by 30%through applying a compressive strain up to 12 K,while the nematic transition temperature shows an anti-correlation with Tc.Detailed measuring procedures and data analysis are presented in the following part.We note that,during preparing this manuscript,a couple of similar researches on the strain-tuning effects of bulk FeSe have been published.[35–37]The strain-tuning methods in these researches are different from ours,while the main results are consistent with our experiments.

    In order to achieve continuous change of the uniaxial strain,we use flexible polyethylene terephthalate(PET)films as the substrate to stick FeSe thin flakes and then bend the substrate to produce strain.Bending the flexible substrate downward/upward could induce a tensile/compressive strain on the FeSe thin flakes(Fig.1(b)).The nominal magnitude of the strain is defined asε=ΔL/L0,whereΔL=L?L0,and L0and L are the sample length without and with strain,respectively(see supplementary materials for the details of calculation).

    Fig.1.Crystal structure,device configuration and strain-dependent Raman spectra of FeSe.(a)The crystal structure of the pristine FeSe.(b)Schematic structure of a FeSe thin flake on the flexible polyethylene terephthalate(PET)substrate.Variable compressive/tensile strains are induced on FeSe thin flakes by bending the substrate downward/upward.(c)An optical image of a FeSe thin flake supported on flexible PET substrate.(d),(e)AFM image of the dashed square in(c).The thickness of FeSe thin flake is about 25 nm along the red dashed line.(f)In-situ Raman spectroscopy of the FeSe thin flakes under different tensile and compressive strains with the strain along(110).The peaks of A1g and B1g modes move to the lower wave number with increasing the tensile strain and shift to the higher wave number with increasing the compressive strain.(g)The peak positions of A1g and B1g modes as a function of the strain.The frequencies of the A1g and B1g modes monotonously decrease with increasing the strain from negative to positive.

    As shown in Fig.1(a),due to the van der Waals interaction between different FeSe layers,the FeSe thin flakes can be easily obtained by the mechanical exfoliation with scotch tape method.FeSe thin flakes are first mechanically exfoliated from bulk crystals onto polydimethylsiloxane(PDMS)substrates,and then transferred to PET substrates by the so-called dry-transfer method.[38](see supplementary materials for the details of devices fabrication).Figure 1(b)is the schematic structure of the final strain device.In practical,proper thin flakes with good flatness and regular shape are chosen by using an optical microscopy.Then,the thickness is characterized by an atomic force microscopy(AFM).The typical thickness of the FeSe thin flakes used for the transport measurement is about 25 nm as evidenced by the AFM image as shown in Figs.1(d)and 1(e).Finally,four electrodes(Cr/Au with thicknesses of 5 and 50 nm,respectively)for transport measurements are coated on the surface of the FeSe thin flakes by using mask technique.The coated four electrodes also serve as the clamping points to prevent the sample from slippage during the bending of the substrate.Figure 1(c)displays an optical image of the actual device.It should be noted that the inplane crystal orientation of FeSe single crystal is determined by Laue diffraction measurement.The applied strain by bending the PET substrate is always along the[110]or[100]direction.The direction of the current can be changed by varying the direction of the electrodes.

    The strain induced by bending the PET substrate can be estimated by a continuum-mechanics model for an elastic beam(see supplementary material S2),in which the radius of curvature(R)from the bending of the PET substrate is assumed to be much larger than the thickness(h)of the PET substrate.Then,the magnitude of the applied strain can be calculated byε=h/2R[39](see details in Fig.S1 of the supplementary materials).A positive/negativeεdenotes a tensile/compressive strain,respectively.In this work,the thickness of the PET substrate is about 100μm,and we could extract the value of R from the profile of the bended PET substrate.In order to continuously change the strain in the FeSe thin flakes,the prepared device is fixed in the middle of two parallel plates and the distance between these two plates is continuously changed to bend the PET substrate.If no slippage happens between the FeSe thin flake and PET substrate,then the strainεin the FeSe thin flake can be directly calculated by the above formula.Here,the sample should be mounted in the middle position of the substrate.

    Fig.2.The longitudinal resistance and the temperature derivatives of the resistance at differentεalong(110).(a),(d),(g)and(j)Temperature dependence of resistance for FeSe thin flakes under different strains and different current directions.The inset is a schematic of the strain and the direction of the measured current.(b),(e),(h)and(k)The resistance at low temperatures corresponding to(a),(d),(g)and(j).(c),(f),(i)and(l)Temperature dependence of the temperature derivative of resistance for the samples corresponding to(a),(d),(g)and(j).

    Usually,x-ray diffraction(XRD)experiment is needed to verify the change of lattice parameters due to uniaxial strain.However,due to limited sample’s volume,it is very difficult to perform an in-situ XRD measurement on the FeSe thin flakes as that in large single crystal.[40]Instead,we have performed in-situ Raman measurements,which is sensitive to uniaxial strains on the FeSe thin-flake samples.As shown in Fig.1(f),we successfully obtain in-situ Raman spectra for the FeSe thin flakes under various strains along[110]direction.The A1gand B1gmodes come from the vibrations of Se atoms along the c axis and the vibrations of Fe atoms along the c axis,respectively.[41–43]By increasing the strain from tensile to compressive strain,both A1gand B1gmodes continuously shift to a higher wavenumber.The systematic evolution of A1gand B1gmodes with the uniaxial strain is shown in Fig.1(g).Qualitatively,although the absolute magnitude of the uniaxial strain on the FeSe thin flakes can not be determined precisely,the in-situ Raman result indicates that the uniaxial strain by bending the PET substrate is effectively transferred to the FeSe thin flakes.Similar in-situ Raman results are also obtained in the FeSe thin flakes under various strains along[100]direction(see supplementary materials Fig.S3).Therefore,we assume that the calculated value of strain by the above mentioned method well represents the actual strain in the FeSe thin flakes.Next,we would investigate the strain effects on both superconducting and nematic transitions in the FeSe thin flakes by electronic transport measurements.

    As shown in Fig.2,the temperature dependence of resistance for the FeSe thin flakes are systematically measured under different strains along the[110](Fe–Se–Fe)direction.In order to measure both tensile/compressive strain effects with the electric current parallel or perpendicular to the bending direction,we have prepared four similar strain devices to measure the temperature-dependent resistance.Figures 2(a)and 2(d)show the temperature dependences of resistances under tensile strain,with the electric current parallel and perpendicular to the direction of the uniaxial strain,respectively.The overall temperature dependence of resistance is very similar to the previous report on the bulk FeSe,[18]excepting a higher superconducting temperature and a lower nematic transition temperature.Such difference in superconducting and nematic temperatures between bulk FeSe and FeSe thin flake has already been reported in previous study.[44]Moreover,with increasing the tensile strain,the temperature-dependent resistances show a clear difference below the nematic transition temperature with current parallel and perpendicular to[110]direction,which suggests that the FeSe thin flake on the PET substrate is detwinned with the applied tensile substrate.The superconducting temperature(defined as the middle point of the resistive transition Tmidc)drops from the initial 9 K to 7.8 K with a tensile strain up to 0.47%in the device,when the electric current flows perpendicular to the direction of uniaxial strain.In the device with the electric current parallel to the direction of uniaxial strain,Tmidc drops from the initial 9.6 K to 6.9 K with a tensile strain up to 0.61%.In spite of slightly difference between different devices,it is clear that the superconducting temperature is almost linearly suppressed by increasing the tensile strain along the[110]direction.On the other hand,the nematic transition temperature(Ts)is determined from the derivative of the temperature-dependent resistance.As shown in Figs.2(c)and 2(f),there is a clear sharp jump due to the nematic transition in the differential curves.Tsis determined by the minimum of the jump.In the device with current parallel to the direction of uniaxial strain,Tsgradually increases from initial 71.2 K to 91.2 K with a tensile strain up to 0.61%.In the device with current perpendicular to the direction of uniaxial strain,Tsgradually increases from initial 70.4 K to 83 K with a tensile strain up to 0.47%.Therefore,in contrast to the superconducting temperature,the nematic transition temperature is clearly increased as the tensile strain increases.

    Fig.3.(a)Tc and Ts as a function of the strainεwhen the strain is applied along the[110]direction.With increasing the tensile strain,Tc gradually decreases and Ts gradually increases.With increasing the compressive strain,Tc gradually increases and Ts gradually decreases.There is a negative correlation between Tc and Ts.(b)and(c)Schematics of different strain types.εA1g is symmetry-preserving strain andεB1g is the strain component which breaks the four-fold rotational symmetry.

    In general,a uniaxial stress applied along one in-plane direction(a or b axis)will induce strains along all three principal axes.[28]Then we haveεjj=?vijεii,where vijis the intrinsic Poisson ratio for materials.This gives

    whereεA1g1andεA1g2are the non-symmetry-breaking strain such as volume expansion and change of tetragonality;and εB1gis the strain component which breaks the four-fold rotational symmetry.Based on symmetry considerations,Tcshould depend quadratically onεB2gbut linearly onεA1g.Accordingly,we have[28]

    whereαandβare the dimensionless coefficients of the dependence of TconεA1gandεB1g,respectively.In the previous study on the underdoped Ba(Fe1?xCox)2As2,the straindependent Tcis found to be dominant by aεB1gcomponent and shows a quadratical dependence.In that case,the coefficient of the quadratic termαis believed to be related to the longrange antiferromagnetic order existing in Ba(Fe1?xCox)2As2andεB1gwould enhance spin fluctuations while suppress nematic fluctuations.[45]With increasing the amount of Co doping to the overdoped region,the antiferromagnetic order in Ba(Fe1?xCox)2As2is gradually suppressed and thenεA1gbecomes dominant on the strain dependence of Tc.Following this explanation on strain-dependent Tc,the absence of longrange antiferromagnetic order in bulk FeSe would lead to a negligible value ofαand then only a linear term would be left.This is definitely confirmed by the observation in the present study.Therefore,our results indirectly support a role of stripe-type spin fluctuations on superconductivity.In addition,as reported in previous literatures,Tcis found to be very sensitive to the change of the c-axis lattice constant in FeSe thin films,[27]which might be responsible for the observed predominant A1g-type strain effect.In fact,the A1gtype strain effect could be also compared with the pressure effect in FeSe,in which the superconducting transition temperature would be enhanced by low pressure below 1 GPa while the nematic transition temperature is suppressed.However,with further increasing pressure,a long-range antiferromagnetic order would appear and then Tcwould be slightly suppressed by the development of antiferromagnetic order.[46]Here,whether a long-range antiferromagnetic order would appear or not with further increasing strain is still elusive.It may deserve further study to clarify the underlying physics for the A1g-type strain effect.On the other hand,a similar B1g-type strain effect on the nematic transition temperature was also revealed in the underdoped Ba(Fe1?xCox)2As2.[28]However,our results clearly demonstrate that such a B1g-type strain effect on Tsis absent in FeSe.If assuming a key role of spin degree of freedom on the electronic nematicity in iron-pnictides,the absence of B1g-type strain effect on Tssuggests that the orbital degree of freedom might play a key role instead of the spin degree of freedom to drive the electronic nematicity.Since the orbital order is sensitive to the change of lattice parameter,[47–49]the dominant A1g-type strain effect on Tscould be also related to the change of lattice parameter induce by uniaxial strain as that for Tc.Therefore,combining the strain effect in both FeSe and Ba(Fe1?xCox)2As,the stripe-type spin fluctuations,which would lead to a B1g-type strain effect on both Tcand Ts,play a more important role than orbital fluctuations on the superconductivity in IBSCs.In fact,this is also supported by a slight change of Tcacross the nematic quantum critical point in FeSe1?xSxsystem.[25]Recently,several experiments on the strain-tuning effects of bulk FeSe have been conducted by different groups.[35–37]Owing to different measuring methods and sample dimensions,there is a few slight differences in the detailed behavior of Ts(ε)and Tc(ε)among different experiments.[35–37]Nevertheless,consistent conclusions are obtained,which suggest intrinsic strain-tuning effects revealed in this study.

    In summary,by utilizing PET substrate,we successfully obtain a wide-range strain tuning for FeSe thin flake with both tensile and compressive strain up to about 0.7%.Our results reveal a predominant A1g-type strain effect on Tc,which is different from that of B1g-type in underdoped Ba(Fe1?xCox)2As2.Meanwhile,Tsexhibits a monotonic anticorrelation with Tcand the maximum Tcreaches to 12 K when Tsis strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe1?xCox)2As2,the absence of B1g-type strain effect in FeSe further supports a role of stripe-type spin fluctuations on superconductivity.Our findings provide new insights for clarifying the underlying mechanism of nematic order and its twist with superconductivity in iron-based superconductors.

    猜你喜歡
    吳濤朝暉
    紅燈亮了
    好詩(shī)與好人
    芙蓉國(guó)里盡朝暉
    Recent advances in quasi-2D superconductors via organic molecule intercalation
    CENTRAL LIMIT THEOREM AND CONVERGENCE RATES FOR A SUPERCRITICAL BRANCHING PROCESS WITH IMMIGRATION IN A RANDOM ENVIRONMENT*
    觀巖畫(huà)
    三只蚊子
    Module 10 Units 3-4單元點(diǎn)撥
    Module 10 Units 1—2 單元點(diǎn)撥
    唆拜(外一首)
    文藝論壇(2015年23期)2015-03-04 07:57:15
    草草在线视频免费看| 一级二级三级毛片免费看| 久久精品综合一区二区三区| 99久国产av精品国产电影| 亚洲不卡免费看| 中文资源天堂在线| 男人舔奶头视频| 国产男人的电影天堂91| 精品欧美国产一区二区三| 中文字幕免费在线视频6| 国产伦理片在线播放av一区 | 久久这里只有精品中国| 夜夜爽天天搞| 亚洲国产精品国产精品| 欧美日韩综合久久久久久| av国产免费在线观看| 我要看日韩黄色一级片| 日本黄色片子视频| 欧美高清成人免费视频www| 欧美三级亚洲精品| 亚洲国产欧洲综合997久久,| 国产亚洲av嫩草精品影院| 亚洲图色成人| 99久久九九国产精品国产免费| 日韩欧美精品v在线| 国产一区二区三区在线臀色熟女| 麻豆av噜噜一区二区三区| 小蜜桃在线观看免费完整版高清| 国产三级中文精品| 国产精品爽爽va在线观看网站| 日韩高清综合在线| 日韩欧美国产在线观看| 精品熟女少妇av免费看| 精品午夜福利在线看| 一本久久精品| 尤物成人国产欧美一区二区三区| 国产老妇女一区| 婷婷六月久久综合丁香| 99riav亚洲国产免费| 国内久久婷婷六月综合欲色啪| 欧美激情久久久久久爽电影| 久久精品国产亚洲av香蕉五月| 夜夜爽天天搞| 亚洲天堂国产精品一区在线| 人妻夜夜爽99麻豆av| 亚洲18禁久久av| 免费观看的影片在线观看| 最近最新中文字幕大全电影3| av天堂中文字幕网| 亚洲精品色激情综合| 日本一二三区视频观看| 国内精品久久久久精免费| 在线天堂最新版资源| 最新中文字幕久久久久| 男人的好看免费观看在线视频| 尤物成人国产欧美一区二区三区| 精品一区二区三区人妻视频| 高清日韩中文字幕在线| 色综合站精品国产| 午夜福利在线观看吧| 能在线免费看毛片的网站| 成年版毛片免费区| 久久精品91蜜桃| 自拍偷自拍亚洲精品老妇| 国产精品,欧美在线| 一夜夜www| 亚洲人与动物交配视频| 在线播放国产精品三级| 欧美日本视频| 少妇熟女aⅴ在线视频| 插逼视频在线观看| 国产成人一区二区在线| 国产高清不卡午夜福利| 又粗又爽又猛毛片免费看| 一区福利在线观看| 国产精品日韩av在线免费观看| 色播亚洲综合网| 麻豆成人午夜福利视频| 极品教师在线视频| 波多野结衣巨乳人妻| 不卡视频在线观看欧美| 亚洲色图av天堂| 天堂中文最新版在线下载 | 欧美3d第一页| 在线观看一区二区三区| www.色视频.com| 免费电影在线观看免费观看| 99热网站在线观看| 精品久久国产蜜桃| 毛片一级片免费看久久久久| 国产成人aa在线观看| 国产精品永久免费网站| 国产精品人妻久久久久久| av天堂中文字幕网| 只有这里有精品99| 免费不卡的大黄色大毛片视频在线观看 | 欧美xxxx黑人xx丫x性爽| 最近的中文字幕免费完整| av黄色大香蕉| 黄色一级大片看看| 久久精品国产亚洲av香蕉五月| 亚洲精品国产av成人精品| 国产成人a区在线观看| 亚洲成人久久性| 亚洲国产欧美人成| 99久国产av精品| 一个人看的www免费观看视频| 99热网站在线观看| 亚洲国产精品成人久久小说 | 校园人妻丝袜中文字幕| 女的被弄到高潮叫床怎么办| 日本-黄色视频高清免费观看| 少妇的逼好多水| 久久人人爽人人片av| 欧美日韩国产亚洲二区| 久久久久久久久大av| 男人的好看免费观看在线视频| 欧美最黄视频在线播放免费| 亚洲精品成人久久久久久| 少妇猛男粗大的猛烈进出视频 | 色哟哟·www| 一级黄片播放器| 久久久久久久久久成人| 日韩欧美一区二区三区在线观看| 亚洲精品国产av成人精品| 成人一区二区视频在线观看| 久久精品久久久久久噜噜老黄 | 精品久久久久久久久久免费视频| 日韩欧美 国产精品| 成人特级av手机在线观看| 国产中年淑女户外野战色| 国产精品99久久久久久久久| 黑人高潮一二区| 最近2019中文字幕mv第一页| 黄色日韩在线| 亚洲精品国产成人久久av| 国产v大片淫在线免费观看| 欧美日韩综合久久久久久| АⅤ资源中文在线天堂| 99热这里只有是精品在线观看| 国产毛片a区久久久久| 91麻豆精品激情在线观看国产| 在线免费十八禁| 日韩在线高清观看一区二区三区| 美女大奶头视频| 久久午夜福利片| 99精品在免费线老司机午夜| 中文欧美无线码| 69av精品久久久久久| 观看免费一级毛片| 神马国产精品三级电影在线观看| 成人无遮挡网站| 啦啦啦韩国在线观看视频| 日日啪夜夜撸| 精品久久久久久久末码| 午夜免费男女啪啪视频观看| 精品一区二区免费观看| 精品无人区乱码1区二区| 日韩,欧美,国产一区二区三区 | 美女cb高潮喷水在线观看| 久久这里有精品视频免费| 欧美日韩在线观看h| av卡一久久| 成人美女网站在线观看视频| 哪个播放器可以免费观看大片| 亚洲精品影视一区二区三区av| 日本一本二区三区精品| 日韩中字成人| 国产人妻一区二区三区在| 国产伦一二天堂av在线观看| 亚洲国产欧洲综合997久久,| 精品久久久久久成人av| 又粗又爽又猛毛片免费看| 欧美激情在线99| 真实男女啪啪啪动态图| 美女大奶头视频| 春色校园在线视频观看| 国内精品一区二区在线观看| 国产一区二区激情短视频| 一级av片app| 全区人妻精品视频| 搡老妇女老女人老熟妇| 看片在线看免费视频| 亚洲成人中文字幕在线播放| 麻豆国产av国片精品| 久久精品国产亚洲av涩爱 | 亚洲人成网站在线观看播放| 亚洲综合色惰| 免费看av在线观看网站| 国产精品一区二区性色av| 超碰av人人做人人爽久久| 一本精品99久久精品77| 91av网一区二区| 久久久久九九精品影院| 国产精品人妻久久久久久| 毛片女人毛片| 免费av观看视频| 成人国产麻豆网| 亚洲国产精品成人久久小说 | 国产亚洲精品久久久com| 亚洲国产日韩欧美精品在线观看| 搡女人真爽免费视频火全软件| 国产精品久久久久久精品电影小说 | 亚洲av二区三区四区| 精品久久国产蜜桃| 丝袜喷水一区| 少妇被粗大猛烈的视频| 国产真实乱freesex| 成人综合一区亚洲| 搞女人的毛片| 久久99热6这里只有精品| 内地一区二区视频在线| 亚洲三级黄色毛片| 亚洲电影在线观看av| 国内揄拍国产精品人妻在线| 午夜亚洲福利在线播放| 久久久国产成人精品二区| 亚洲av中文字字幕乱码综合| 亚洲精品亚洲一区二区| 成人漫画全彩无遮挡| 99热全是精品| 日韩欧美在线乱码| 亚洲精品自拍成人| 日韩强制内射视频| 人妻系列 视频| 18+在线观看网站| 波多野结衣高清无吗| 亚洲最大成人av| 婷婷色av中文字幕| 国产免费一级a男人的天堂| 国产黄片视频在线免费观看| 看片在线看免费视频| 久久久成人免费电影| 51国产日韩欧美| 在线观看66精品国产| 国产一区二区三区在线臀色熟女| 国产探花在线观看一区二区| 国产成人91sexporn| 麻豆乱淫一区二区| 一区二区三区高清视频在线| 18禁在线无遮挡免费观看视频| 亚洲欧美成人精品一区二区| 99热只有精品国产| 色尼玛亚洲综合影院| 国产极品天堂在线| 99久久精品国产国产毛片| 一个人看视频在线观看www免费| 国产av不卡久久| 中文字幕免费在线视频6| 亚洲精品乱码久久久久久按摩| 国产精品久久视频播放| 伦精品一区二区三区| 国产精品一区二区三区四区久久| 国产乱人偷精品视频| 亚洲乱码一区二区免费版| 国产亚洲av嫩草精品影院| 少妇熟女aⅴ在线视频| 久久久久久久午夜电影| 免费人成在线观看视频色| 国产伦精品一区二区三区视频9| 99热这里只有是精品在线观看| 国产一级毛片七仙女欲春2| 亚洲七黄色美女视频| 99精品在免费线老司机午夜| 亚洲自偷自拍三级| 中文在线观看免费www的网站| 少妇人妻一区二区三区视频| 久久99热6这里只有精品| 成人毛片60女人毛片免费| 性插视频无遮挡在线免费观看| 亚洲精华国产精华液的使用体验 | 欧洲精品卡2卡3卡4卡5卡区| eeuss影院久久| 久久精品夜色国产| 午夜福利高清视频| 最近手机中文字幕大全| 精品不卡国产一区二区三区| 亚洲国产精品成人综合色| 久久亚洲国产成人精品v| 国产精品人妻久久久影院| 亚洲精品乱码久久久v下载方式| 欧美日本亚洲视频在线播放| 久久久国产成人免费| 三级男女做爰猛烈吃奶摸视频| 国产黄色小视频在线观看| 午夜视频国产福利| 国产一区二区激情短视频| 最近最新中文字幕大全电影3| 欧美日韩精品成人综合77777| 99热全是精品| 神马国产精品三级电影在线观看| 久久精品夜色国产| 身体一侧抽搐| 久久久色成人| 婷婷亚洲欧美| 我的女老师完整版在线观看| 久久午夜福利片| 国产精品人妻久久久久久| 日韩三级伦理在线观看| 又黄又爽又刺激的免费视频.| 久久精品夜夜夜夜夜久久蜜豆| 日韩欧美精品免费久久| 久久精品国产99精品国产亚洲性色| 在线观看美女被高潮喷水网站| 欧美3d第一页| 免费无遮挡裸体视频| 91麻豆精品激情在线观看国产| 99riav亚洲国产免费| 亚洲图色成人| 国产一级毛片七仙女欲春2| a级毛片免费高清观看在线播放| 免费看av在线观看网站| 在线观看66精品国产| 国产国拍精品亚洲av在线观看| 麻豆精品久久久久久蜜桃| 大香蕉久久网| 久久久久久久久久黄片| 51国产日韩欧美| 大香蕉久久网| 五月玫瑰六月丁香| 国产日本99.免费观看| 免费看光身美女| 美女黄网站色视频| 麻豆精品久久久久久蜜桃| 一级黄色大片毛片| 久久精品综合一区二区三区| 麻豆一二三区av精品| 天堂√8在线中文| 久久人妻av系列| 亚洲美女视频黄频| 日本三级黄在线观看| 亚洲成人中文字幕在线播放| 成熟少妇高潮喷水视频| 午夜a级毛片| 中出人妻视频一区二区| av国产免费在线观看| 成人二区视频| 3wmmmm亚洲av在线观看| 亚洲久久久久久中文字幕| 亚洲国产精品sss在线观看| 麻豆精品久久久久久蜜桃| 亚洲精品亚洲一区二区| 国产日本99.免费观看| 男人舔奶头视频| 国产美女午夜福利| 神马国产精品三级电影在线观看| 欧美色欧美亚洲另类二区| 国产精品久久久久久亚洲av鲁大| 欧美色欧美亚洲另类二区| 久久欧美精品欧美久久欧美| 日本撒尿小便嘘嘘汇集6| 神马国产精品三级电影在线观看| 99热这里只有是精品在线观看| 中文字幕人妻熟人妻熟丝袜美| 26uuu在线亚洲综合色| 女人被狂操c到高潮| 只有这里有精品99| 青春草国产在线视频 | 一级毛片久久久久久久久女| 亚洲,欧美,日韩| 在线观看美女被高潮喷水网站| 国产成人一区二区在线| av在线播放精品| 黄色配什么色好看| 美女内射精品一级片tv| 成人特级黄色片久久久久久久| 最近手机中文字幕大全| 亚洲一区二区三区色噜噜| 久久久色成人| 中文字幕av成人在线电影| 国产麻豆成人av免费视频| 在线观看av片永久免费下载| 午夜激情福利司机影院| 日本五十路高清| 成年免费大片在线观看| www日本黄色视频网| 国产精品伦人一区二区| 久久亚洲精品不卡| 国产 一区 欧美 日韩| 亚洲av.av天堂| 国产又黄又爽又无遮挡在线| 国产精品人妻久久久影院| 国产日韩欧美在线精品| 成年女人永久免费观看视频| 久久久欧美国产精品| 我要看日韩黄色一级片| 日韩,欧美,国产一区二区三区 | 欧洲精品卡2卡3卡4卡5卡区| 国产精品一及| 十八禁国产超污无遮挡网站| 欧美精品国产亚洲| 少妇的逼水好多| 我要看日韩黄色一级片| 成人高潮视频无遮挡免费网站| 欧美一区二区亚洲| 99久久九九国产精品国产免费| 毛片一级片免费看久久久久| 国产精品久久久久久久电影| 亚洲欧美日韩高清专用| 天天躁夜夜躁狠狠久久av| av女优亚洲男人天堂| 一区二区三区高清视频在线| 美女 人体艺术 gogo| 久久99精品国语久久久| 老司机福利观看| 最新中文字幕久久久久| 观看免费一级毛片| 男女边吃奶边做爰视频| 亚洲,欧美,日韩| 欧美zozozo另类| 黄色日韩在线| 国产精品嫩草影院av在线观看| 成人毛片a级毛片在线播放| 亚洲成人久久爱视频| 国产极品天堂在线| 成熟少妇高潮喷水视频| 免费电影在线观看免费观看| 成人一区二区视频在线观看| 国产精品三级大全| 最近最新中文字幕大全电影3| 久久精品久久久久久噜噜老黄 | 波野结衣二区三区在线| 黑人高潮一二区| 欧洲精品卡2卡3卡4卡5卡区| 26uuu在线亚洲综合色| 国产一级毛片在线| 免费看a级黄色片| 日本撒尿小便嘘嘘汇集6| 大型黄色视频在线免费观看| 亚洲婷婷狠狠爱综合网| 中文资源天堂在线| 亚洲一级一片aⅴ在线观看| 嘟嘟电影网在线观看| 亚洲一区二区三区色噜噜| 美女内射精品一级片tv| 亚洲,欧美,日韩| 九九热线精品视视频播放| 国产高清三级在线| 国产精品无大码| 少妇人妻精品综合一区二区 | 国产黄a三级三级三级人| 乱码一卡2卡4卡精品| 欧美日韩精品成人综合77777| 国产日本99.免费观看| 两个人的视频大全免费| 春色校园在线视频观看| 免费无遮挡裸体视频| 日韩成人av中文字幕在线观看| a级一级毛片免费在线观看| 嫩草影院精品99| 国产毛片a区久久久久| 中国国产av一级| 成人一区二区视频在线观看| 国产精品女同一区二区软件| 波野结衣二区三区在线| 国产真实乱freesex| 最好的美女福利视频网| 直男gayav资源| 黑人高潮一二区| 日韩欧美在线乱码| 少妇猛男粗大的猛烈进出视频 | 久久99热6这里只有精品| 久久精品久久久久久噜噜老黄 | 身体一侧抽搐| 啦啦啦啦在线视频资源| 久久99热这里只有精品18| 亚洲在线自拍视频| 国产一区二区三区在线臀色熟女| 久久久久久久久久久免费av| 麻豆成人午夜福利视频| 日本色播在线视频| 乱码一卡2卡4卡精品| 97在线视频观看| 成人高潮视频无遮挡免费网站| 性色avwww在线观看| 成人毛片60女人毛片免费| 成年免费大片在线观看| 亚洲综合色惰| 小蜜桃在线观看免费完整版高清| 69av精品久久久久久| 天堂中文最新版在线下载 | 午夜福利高清视频| 特大巨黑吊av在线直播| 丰满人妻一区二区三区视频av| av专区在线播放| 日本爱情动作片www.在线观看| 99视频精品全部免费 在线| 国产人妻一区二区三区在| 亚洲国产精品sss在线观看| av黄色大香蕉| 噜噜噜噜噜久久久久久91| 欧美不卡视频在线免费观看| 国产片特级美女逼逼视频| 99国产极品粉嫩在线观看| 欧洲精品卡2卡3卡4卡5卡区| 国产黄a三级三级三级人| 国产探花极品一区二区| 给我免费播放毛片高清在线观看| 久久99蜜桃精品久久| 高清在线视频一区二区三区 | 夜夜爽天天搞| 日本免费一区二区三区高清不卡| 欧美3d第一页| 免费不卡的大黄色大毛片视频在线观看 | 精品一区二区三区视频在线| 亚洲精品日韩av片在线观看| 国产成人a区在线观看| 深爱激情五月婷婷| 国产精品久久久久久久电影| 国产淫片久久久久久久久| 日本与韩国留学比较| 又爽又黄a免费视频| 综合色av麻豆| 在线a可以看的网站| 乱系列少妇在线播放| 国产 一区精品| 老师上课跳d突然被开到最大视频| a级毛片a级免费在线| 人人妻人人澡人人爽人人夜夜 | 黄片wwwwww| 亚洲av成人精品一区久久| 一级毛片久久久久久久久女| 日本-黄色视频高清免费观看| 桃色一区二区三区在线观看| 99热网站在线观看| 久久久久免费精品人妻一区二区| 午夜免费激情av| 久久人人精品亚洲av| 日韩欧美国产在线观看| 成人漫画全彩无遮挡| 亚洲人成网站在线播放欧美日韩| 国产精品一二三区在线看| 国产私拍福利视频在线观看| 亚洲性久久影院| 免费观看的影片在线观看| 亚洲欧美精品专区久久| 最近最新中文字幕大全电影3| 一级二级三级毛片免费看| 亚洲中文字幕日韩| 99热全是精品| 国产精品,欧美在线| 国产午夜精品论理片| 高清毛片免费观看视频网站| 中文欧美无线码| 成人美女网站在线观看视频| 狠狠狠狠99中文字幕| 12—13女人毛片做爰片一| 成人亚洲精品av一区二区| 国产精品三级大全| .国产精品久久| 日韩一区二区三区影片| 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 91av网一区二区| 日韩大尺度精品在线看网址| 丝袜美腿在线中文| 人妻夜夜爽99麻豆av| 一卡2卡三卡四卡精品乱码亚洲| 国产国拍精品亚洲av在线观看| 岛国毛片在线播放| 狂野欧美白嫩少妇大欣赏| 久久精品国产亚洲av香蕉五月| kizo精华| 国产亚洲精品久久久com| 免费观看a级毛片全部| 国产精品电影一区二区三区| 搡老妇女老女人老熟妇| 欧美一区二区精品小视频在线| 精品99又大又爽又粗少妇毛片| 国产一区二区激情短视频| av天堂中文字幕网| 欧美丝袜亚洲另类| 亚洲av.av天堂| 欧美激情国产日韩精品一区| av女优亚洲男人天堂| 草草在线视频免费看| 欧美日本视频| 男人和女人高潮做爰伦理| 精华霜和精华液先用哪个| 久久这里有精品视频免费| 一区二区三区免费毛片| 黄片无遮挡物在线观看| 黄色欧美视频在线观看| 夜夜爽天天搞| 久久99蜜桃精品久久| 大又大粗又爽又黄少妇毛片口| 女人十人毛片免费观看3o分钟| 国产乱人视频| 国产 一区 欧美 日韩| 国产av不卡久久| 波多野结衣巨乳人妻| 日本爱情动作片www.在线观看| 国产大屁股一区二区在线视频| 天堂中文最新版在线下载 | 国产精品女同一区二区软件| 岛国毛片在线播放| 高清毛片免费观看视频网站| 欧美一区二区精品小视频在线| 欧美丝袜亚洲另类| 五月伊人婷婷丁香| 亚洲天堂国产精品一区在线| 亚洲精品粉嫩美女一区| 国产免费男女视频| 成人无遮挡网站| 久久久久久九九精品二区国产| 久久久国产成人精品二区| 丰满的人妻完整版| 成人欧美大片| 91在线精品国自产拍蜜月| 九九在线视频观看精品| 欧美色视频一区免费| 自拍偷自拍亚洲精品老妇| 国产久久久一区二区三区| 国产成年人精品一区二区| 人人妻人人看人人澡| 免费人成视频x8x8入口观看|