Flat-band physics of moirésuperlattices,originally discovered in the celebrated twisted bilayer graphene,have recently been intensively explored in multilayer graphene systems that can be further controlled by el...Flat-band physics of moirésuperlattices,originally discovered in the celebrated twisted bilayer graphene,have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field.In this work,we experimentally find the evidence of correlated insulators at half filling of the electron moiréband of twisted monolayer–trilayer graphene with a twist angle around 1.2°.Van Hove singularity(VHS),manifested as enhanced resistance and zero Hall voltage,is observed to be distinct in conduction and valence flat bands.It also depends on the direction and magnitude of the displacement fields,consistent with the asymmetric crystal structure.While the resistance ridges at VHS can be enhanced by magnetic fields,when they cross commensurate fillings of the moirésuperlattice in the conduction band,the enhancement is so strong that signatures of correlated insulator appear,which may further develop into an energy gap depending on the correlation strength.At last,Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields.It is found that electronic correlation has a negative dependence on the Fermi velocity,which in turn could be used to quantify the correlation strength.展开更多
Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and no...Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and nontrivial topological properties. To gain a deep understanding of such exotic properties, it is essential to clarify the broken symmetry between spin and valley flavors which universally exists in these ground states. Here in a rhombohedral trilayer graphene crystallographically aligned with a hexagonal boron nitride, we report various kinds of symmetry-breaking transition tuned by displacement fields(D) and magnetic fields:(ⅰ) While it is well known that a finite D can enhance correlation to result in correlated insulators at fractional fillings of a flat band, we find the correlation gap emerges before the flavor is fully filled at a positive D, but the sequence is reversed at a negative D.(ⅱ) Around zero D, electronic correlation can be invoked by narrow Landau levels, leading to quantum Hall ferromagnetism that lifts all the degeneracies including not only spin and valley but also orbital degrees of freedom. Our result unveils the complication of transitions between symmetry-breaking phases, shedding light on the mechanisms of various exotic phenomena in strongly correlated systems.展开更多
Highly controlled electronic correlation in twisted graphene heterostructures has gained enormous research interests recently,encouraging exploration in a wide range of moirésuperlattices beyond the celebrated tw...Highly controlled electronic correlation in twisted graphene heterostructures has gained enormous research interests recently,encouraging exploration in a wide range of moirésuperlattices beyond the celebrated twisted bilayer graphene.Here we characterize correlated states in an alternating twisted Bernal bilayer–monolayer–monolayer graphene of~1.74°,and find that both van Hove singularities and multiple correlated states are asymmetrically tuned by displacement fields.In particular,when one electron per moiréunit cell is occupied in the electron-side flat band,or the hole-side flat band(i.e.,three holes per moiréunit cell),the correlated peaks are found to counterintuitively grow with heating and maximize around 20 K–a signature of Pomeranchuk effect.Our multilayer heterostructure opens more opportunities to engineer complicated systems for investigating correlated phenomena.展开更多
目的探讨苯磺酸左旋氨氯地平对腹主动脉部分缩窄大鼠心肌能量代谢的影响及其机制。方法将18只Wistar大鼠随机分为3组:假手术组(Sham组)、手术组(AAC组)和手术+苯磺酸左旋氨氯地平治疗组(AAC+LA组),采用腹主动脉部分缩窄法建立压力超负...目的探讨苯磺酸左旋氨氯地平对腹主动脉部分缩窄大鼠心肌能量代谢的影响及其机制。方法将18只Wistar大鼠随机分为3组:假手术组(Sham组)、手术组(AAC组)和手术+苯磺酸左旋氨氯地平治疗组(AAC+LA组),采用腹主动脉部分缩窄法建立压力超负荷致心肌肥厚的动物模型,AAC+LA组每天给予苯磺酸左旋氨氯地平2.5 mg·kg^(-1)(溶于2 m L的生理盐水中),Sham组及AAC组给予等体积的生理盐水;8周后,测量全心/体质量的比值;颈总动脉插管检测血压;小动物超声测量心脏功能;采用荧光定量(QT-PCR)法检测心肌组织GLUT4 m RNA表达,试剂盒测定心肌组织ADP/ATP比值。结果 8周后与Sham组比较,AAC组血压、全心/体质量比值、左室壁厚度、ADP/ATP比值增加,心脏功能、GLUT4表达下降;AAC+LA组血压、全心/体质量比值、左室壁厚度、ADP/ATP比值下降,心脏功能改善,GLUT4表达上升。结论苯磺酸左旋氨氯地平具有改善压力负荷大鼠心肌收缩、舒张功能的作用,其机制可能与其降低血压的同时增加肥厚心肌GLUT4的表达、改善心肌的能量代谢有关。展开更多
基金support from the National Natural Science Foundation of China(Grant No.11974027)the National Key R&D Program of China(Grant Nos.2019YFA0307800 and 2021YFA1400100)+2 种基金Beijing Natural Science Foundation(Grant No.Z190011)Beijing Natural Science Foundation(Grant No.4222084)support from the National Natural Science Foundation of China(Grant No.62275265)。
文摘Flat-band physics of moirésuperlattices,originally discovered in the celebrated twisted bilayer graphene,have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field.In this work,we experimentally find the evidence of correlated insulators at half filling of the electron moiréband of twisted monolayer–trilayer graphene with a twist angle around 1.2°.Van Hove singularity(VHS),manifested as enhanced resistance and zero Hall voltage,is observed to be distinct in conduction and valence flat bands.It also depends on the direction and magnitude of the displacement fields,consistent with the asymmetric crystal structure.While the resistance ridges at VHS can be enhanced by magnetic fields,when they cross commensurate fillings of the moirésuperlattice in the conduction band,the enhancement is so strong that signatures of correlated insulator appear,which may further develop into an energy gap depending on the correlation strength.At last,Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields.It is found that electronic correlation has a negative dependence on the Fermi velocity,which in turn could be used to quantify the correlation strength.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11974027 and 62275265)the National Key Research and Development Program of China (Grant Nos. 2019YFA0307800 and 2021YFA1400100)Beijing Natural Science Foundation (Grant Nos. Z190011 and 4222084)。
文摘Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and nontrivial topological properties. To gain a deep understanding of such exotic properties, it is essential to clarify the broken symmetry between spin and valley flavors which universally exists in these ground states. Here in a rhombohedral trilayer graphene crystallographically aligned with a hexagonal boron nitride, we report various kinds of symmetry-breaking transition tuned by displacement fields(D) and magnetic fields:(ⅰ) While it is well known that a finite D can enhance correlation to result in correlated insulators at fractional fillings of a flat band, we find the correlation gap emerges before the flavor is fully filled at a positive D, but the sequence is reversed at a negative D.(ⅱ) Around zero D, electronic correlation can be invoked by narrow Landau levels, leading to quantum Hall ferromagnetism that lifts all the degeneracies including not only spin and valley but also orbital degrees of freedom. Our result unveils the complication of transitions between symmetry-breaking phases, shedding light on the mechanisms of various exotic phenomena in strongly correlated systems.
基金support from the National Key R&D Program of China (Grant Nos.2021YFA1400100 and 2019YFA0307800)the National Natural Science Foundation of China (Grant No.11974027)+2 种基金support from the National Natural Science Foundation of China (Grant No.62275265)Beijing Natural Science Foundation (Grant No.Z190011)Beijing Natural Science Foundation (Grant No.4222084)。
文摘Highly controlled electronic correlation in twisted graphene heterostructures has gained enormous research interests recently,encouraging exploration in a wide range of moirésuperlattices beyond the celebrated twisted bilayer graphene.Here we characterize correlated states in an alternating twisted Bernal bilayer–monolayer–monolayer graphene of~1.74°,and find that both van Hove singularities and multiple correlated states are asymmetrically tuned by displacement fields.In particular,when one electron per moiréunit cell is occupied in the electron-side flat band,or the hole-side flat band(i.e.,three holes per moiréunit cell),the correlated peaks are found to counterintuitively grow with heating and maximize around 20 K–a signature of Pomeranchuk effect.Our multilayer heterostructure opens more opportunities to engineer complicated systems for investigating correlated phenomena.
文摘目的探讨苯磺酸左旋氨氯地平对腹主动脉部分缩窄大鼠心肌能量代谢的影响及其机制。方法将18只Wistar大鼠随机分为3组:假手术组(Sham组)、手术组(AAC组)和手术+苯磺酸左旋氨氯地平治疗组(AAC+LA组),采用腹主动脉部分缩窄法建立压力超负荷致心肌肥厚的动物模型,AAC+LA组每天给予苯磺酸左旋氨氯地平2.5 mg·kg^(-1)(溶于2 m L的生理盐水中),Sham组及AAC组给予等体积的生理盐水;8周后,测量全心/体质量的比值;颈总动脉插管检测血压;小动物超声测量心脏功能;采用荧光定量(QT-PCR)法检测心肌组织GLUT4 m RNA表达,试剂盒测定心肌组织ADP/ATP比值。结果 8周后与Sham组比较,AAC组血压、全心/体质量比值、左室壁厚度、ADP/ATP比值增加,心脏功能、GLUT4表达下降;AAC+LA组血压、全心/体质量比值、左室壁厚度、ADP/ATP比值下降,心脏功能改善,GLUT4表达上升。结论苯磺酸左旋氨氯地平具有改善压力负荷大鼠心肌收缩、舒张功能的作用,其机制可能与其降低血压的同时增加肥厚心肌GLUT4的表达、改善心肌的能量代谢有关。
