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liuyanping105銀蟲 (小有名氣)
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graphene 研究的一個問題（請教前輩） 已有1人參與
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graphene 研究的一個問題（請教前輩）： 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， 這個如何解釋？ 希望前輩指教！ |
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liuyanping105
銀蟲 (小有名氣)
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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
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小木蟲: 金幣+0.5, 給個紅包，謝謝回帖
leongoall: 金幣+2, 鼓勵認真回帖應助！ 2012-12-09 17:45:03
小木蟲: 金幣+0.5, 給個紅包，謝謝回帖
leongoall: 金幣+2, 鼓勵認真回帖應助！ 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。 而且對于單層和多層，會有不同的規(guī)律。但是基本的結(jié)論，是隨著磁場增強而增大的。磁場較強時，gap大小跟磁場有的是一次關系，有的是二次。 2。電阻也是應該在2x2矩陣里面的吧。你這里說的，是對角的電阻嗎？ 無論是電阻矩陣里的哪個元素，應該都與gap，繼而與磁場有關。 可參考文獻：http://arxiv.org/abs/1108.0650，以及其中的一些實驗結(jié)果。 |
2樓2012-12-09 16:50:06
liuyanping105
銀蟲 (小有名氣)
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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。 而且對于單層和多層，會有不同的規(guī)律。但是基本的結(jié)論，是隨著磁場增強而增大的。磁場較強時，gap大小跟磁場有的是一次關系，有的是二次。 請問這個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) 這樣解釋對嗎？ 有人認為：強磁場下當然是形成朗道能級啦，不過graphene有零能的LL，弱場下應該沒有gap 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。電阻也是應該在2x2矩陣里面的吧。你這里說的，是對角的電阻嗎？ 無論是電阻矩陣里的哪個元素，應該都與gap，繼而與磁場有關。 可參考文獻：http://arxiv.org/abs/1108.0650，以及其中的一些實驗結(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個電極穿過graphene,所以這個電阻可以看做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
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