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liuyanping105銀蟲 (小有名氣)
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graphene 研究的一個(gè)問題（請(qǐng)教前輩） 已有1人參與
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graphene 研究的一個(gè)問題（請(qǐng)教前輩）： graphene 在電場的gate的作用下，可以打開bandgap,i.e bilayer----- tunnable bandgap, trilayer -----overlap band gap. 1.那么在perpendicular magnetic field 的作用下，graphene 的情況如何呢？bandgap 能打開？ 還是打開excitonic condensation gap? 2. four-terminal graphene device 在perpendicular magnetic field 的作用下，發(fā)現(xiàn)測量的電阻（不是hall effect 磁阻）線性或者非線性的隨著磁場增加而增加，也就是： R vs B， 這個(gè)如何解釋？ 希望前輩指教！ |
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leongoall: 金幣+2, 鼓勵(lì)認(rèn)真回帖應(yīng)助！ 2012-12-09 17:45:03
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1。垂直磁場，是可以直接改變gap的大小的。在一些比較簡化的理論中，這些是可以直接算出來的。 而且對(duì)于單層和多層，會(huì)有不同的規(guī)律。但是基本的結(jié)論，是隨著磁場增強(qiáng)而增大的。磁場較強(qiáng)時(shí)，gap大小跟磁場有的是一次關(guān)系，有的是二次。 2。電阻也是應(yīng)該在2x2矩陣?yán)锩娴陌�。你這里說的，是對(duì)角的電阻嗎？ 無論是電阻矩陣?yán)锏哪膫�(gè)元素，應(yīng)該都與gap，繼而與磁場有關(guān)。 可參考文獻(xiàn)：http://arxiv.org/abs/1108.0650，以及其中的一些實(shí)驗(yàn)結(jié)果。 |
2樓2012-12-09 16:50:06
liuyanping105
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Thanks for your good explains and good comments. 1。垂直磁場，是可以直接改變gap的大小的。在一些比較簡化的理論中，這些是可以直接算出來的。 而且對(duì)于單層和多層，會(huì)有不同的規(guī)律。但是基本的結(jié)論，是隨著磁場增強(qiáng)而增大的。磁場較強(qiáng)時(shí)，gap大小跟磁場有的是一次關(guān)系，有的是二次。 請(qǐng)問這個(gè)GAP 是band gap 還是excitonic gap. delta gap 大小 ~ square root B FOR MONOLAYER Graphene delta gap 大小~ B FOR bilayer, trilayer Graphene 所以 Rxx~ exp(delta gap/kT) 這樣解釋對(duì)嗎？ 有人認(rèn)為：強(qiáng)磁場下當(dāng)然是形成朗道能級(jí)啦，不過graphene有零能的LL，弱場下應(yīng)該沒有g(shù)ap The effect of the applied perpendicular magnetic can induce the splitting of Landau Level and the zero-energy Level is characteristic of half filling.So the bandstucture show discrete dispersion (splitting of Landau Level). i want to know that the gap is band gap or excitonic gap when the application of the magnetic field on the graphene. My understanding is that band gap corresponds to the effect of the electric field and the excitonic gap corresponds to the effect of the magnetic field . 2。電阻也是應(yīng)該在2x2矩陣?yán)锩娴陌伞Ｄ氵@里說的，是對(duì)角的電阻嗎？ 無論是電阻矩陣?yán)锏哪膫�(gè)元素，應(yīng)該都與gap，繼而與磁場有關(guān)。 可參考文獻(xiàn)：http://arxiv.org/abs/1108.0650，以及其中的一些實(shí)驗(yàn)結(jié)果。 我這電阻，就是4電極電阻測量法（不同于HALL Effect, Rxy, Rxx)， 也就是4個(gè)電極穿過graphene,所以這個(gè)電阻可以看做Rxx嗎？ The magnetic field range of 0-12T. The negative resistance at low field and low temperature (weak localization effect) originates from the interval scattering but the i want to know the origins of the non-linear magneto resistance increase with the increasing magnetic field ( i think it is originated from the electron-hole puddles). |
3樓2012-12-12 00:48:40
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小木蟲: 金幣+0.5, 給個(gè)紅包，謝謝回帖
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Liu, About the "excitonic gap" and band gap, I believe Delta should be refered as the gap between the conductance and valance band. So it is the gap the enters the expression for conductivity/resistance. About what your resistence really is, I am not sure how 4 gates only measures 1 resistence. You need to describe your set-up in more details, or can you refer paper for me in order to tell more about this? |
4樓2012-12-12 01:24:32
liuyanping105
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What is the effect of the applied perpendicular magnetic for graphene? As we known, graphene is subjected to an electric field with the gate control, resulting in the opening bandgap. For example, the bilayer shows a tunable bandgap and the trilayer displays an overlapping bandgap (energy gap). So, I want to know the effect of the perpendicular magnetic field. Does it have a similar effect to open the bandgap energy gap)? Or others, i.e. the opening excitonic condensation gap? 1.jpg 3.jpg The effect of the applied perpendicular magnetic can induce the splitting of Landau Level and the zero-energy Level is characteristic of half filling. So the bandstucture show discrete dispersion (splitting of Landau Level, as shown in Figure 2.2). i want to know that the gap is band gap (energy gap) or excitonic gap when the application of the magnetic field on the graphene. My understanding is that band gap corresponds to the effect of the electric field and the excitonic gap corresponds to the effect of the magnetic field, is correct??? Additionally, I put the four-terminal graphene device on the perpendicular magnetic field (as shown in the Figure 2); the observed resistance (not Hall Effect resistance Rxx and Rxy) shows a nonlinear increase with the increasing magnetic field. What is the origin of the nonlinear magneto resistance? The magnetic field range of 0-12T. The negative resistance at low field and low temperature (weak localization effect) originates from the intervalley scattering( you told me ) but the i want to know the origins of the non-linear magneto resistance increase with the increasing magnetic field ( i think it is originated from the electron-hole puddles). 2.jpg Figure 2.(LEFT)schematic drawing of the four-terminal device and Resistance.(Right) experimental results indicate that non-linear magneto resistance increase with the increasing magnetic field. [ Last edited by liuyanping105 on 2012-12-12 at 22:22 ] |
5樓2012-12-12 22:00:55
6樓2012-12-12 22:25:34
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