@inproceedings{10692,
  abstract     = {We experimentally investigate narrow and topologically nontrivial moiré minibands hosted by van der Waals heterostructures consisting of a graphene monolayer rotationally faulted with respect to a Bernal-stacked bilayer. At fillings ν= 1 and 3 electrons per moiré unit cell within these bands, we observe quantized anomalous Hall effects with Rxy≈h/2e2, indicative of spontaneous polarization of the system into a single valley-projected band with Chern number C= 2. Remarkably, we also observe the evidence of symmetry broken Chern insulator states at ν= 1.5 and 3.5. At ν= 3 we find that the sign of the quantum anomalous Hall effect can be reversed via field-effect control of the chemical potential. This curious effect arises from the magnetization contribution due to topological edge states, which drive a reversal of the total magnetization and thus a switch of the favored magnetic state. Remarkably, we find that this switch is hysteretic, which we use to demonstrate non-volatile electric-field-induced reversal of the magnetic state. Voltage control of magnetic states can be used to electrically pattern nonvolatile magnetic domain structures hosting chiral edge states, with applications ranging from reconfigurable microwave circuit elements to ultra-low-power magnetic memory.},
  author       = {Polshyn, Hryhoriy and Zhu, Jihang and Kumar, Manish and Zhang, Yuxuan and Yang, Fangyuan and Tschirhart, Charles and Serlin, Marec and Watanabe, Kenji and Tanaguchi, Takashi and MacDonald, Allan and Young, Andrea},
  booktitle    = {APS March Meeting 2021},
  issn         = {0003-0503},
  location     = {Virtual},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Orbital Chern insulator states in twisted monolayer-bilayer graphene and electrical switching of topological and magnetic order}},
  volume       = {66},
  year         = {2021},
}

@article{10616,
  abstract     = {Electrons in moiré flat band systems can spontaneously break time-reversal symmetry, giving rise to a quantized anomalous Hall effect. In this study, we use a superconducting quantum interference device to image stray magnetic fields in twisted bilayer graphene aligned to hexagonal boron nitride. We find a magnetization of several Bohr magnetons per charge carrier, demonstrating that the magnetism is primarily orbital in nature. Our measurements reveal a large change in the magnetization as the chemical potential is swept across the quantum anomalous Hall gap, consistent with the expected contribution of chiral edge states to the magnetization of an orbital Chern insulator. Mapping the spatial evolution of field-driven magnetic reversal, we find a series of reproducible micrometer-scale domains pinned to structural disorder.},
  author       = {Tschirhart, C. L. and Serlin, M. and Polshyn, Hryhoriy and Shragai, A. and Xia, Z. and Zhu, J. and Zhang, Y. and Watanabe, K. and Taniguchi, T. and Huber, M. E. and Young, A. F.},
  issn         = {1095-9203},
  journal      = {Science},
  keywords     = {multidisciplinary},
  number       = {6548},
  pages        = {1323--1327},
  publisher    = {American Association for the Advancement of Science},
  title        = {{Imaging orbital ferromagnetism in a moiré Chern insulator}},
  doi          = {10.1126/science.abd3190},
  volume       = {372},
  year         = {2021},
}

@article{10617,
  abstract     = {When a flat band is partially filled with electrons, strong Coulomb interactions between them may lead to the emergence of topological gapped states with quantized Hall conductivity. Such emergent topological states have been found in partially filled Landau levels1 and Hofstadter bands2,3; however, in both cases, a large magnetic field is required to produce the underlying flat band. The recent observation of quantum anomalous Hall effects in narrow-band moiré materials4,5,6,7 has led to the theoretical prediction that such phases could be realized at zero magnetic field8,9,10,11,12. Here we report the observation of insulators with Chern number C = 1 in the zero-magnetic-field limit at half-integer filling of the moiré superlattice unit cell in twisted monolayer–bilayer graphene7,13,14,15. Chern insulators in a half-filled band suggest the spontaneous doubling of the superlattice unit cell2,3,16, and our calculations find a ground state of the topological charge density wave at half-filling of the underlying band. The discovery of these topological phases at fractional superlattice filling enables the further pursuit of zero-magnetic-field phases that have fractional statistics that exist either as elementary excitations or bound to lattice dislocations.},
  author       = {Polshyn, Hryhoriy and Zhang, Y. and Kumar, M. A. and Soejima, T. and Ledwith, P. and Watanabe, K. and Taniguchi, T. and Vishwanath, A. and Zaletel, M. P. and Young, A. F.},
  issn         = {1745-2481},
  journal      = {Nature Physics},
  keywords     = {general physics, astronomy},
  publisher    = {Springer Nature},
  title        = {{Topological charge density waves at half-integer filling of a moiré superlattice}},
  doi          = {10.1038/s41567-021-01418-6},
  year         = {2021},
}

@article{10649,
  abstract     = {Harnessing the properties of vortices in superconductors is crucial for fundamental science and technological applications; thus, it has been an ongoing goal to locally probe and control vortices. Here, we use a scanning probe technique that enables studies of vortex dynamics in superconducting systems by leveraging the resonant behavior of a raster-scanned, magnetic-tipped cantilever. This experimental setup allows us to image and control vortices, as well as extract key energy scales of the vortex interactions. Applying this technique to lattices of superconductor island arrays on a metal, we obtain a variety of striking spatial patterns that encode information about the energy landscape for vortices in the system. We interpret these patterns in terms of local vortex dynamics and extract the relative strengths of the characteristic energy scales in the system, such as the vortex-magnetic field and vortex-vortex interaction strengths, as well as the vortex chemical potential. We also demonstrate that the relative strengths of the interactions can be tuned and show how these interactions shift with an applied bias. The high degree of tunability and local nature of such vortex imaging and control not only enable new understanding of vortex interactions, but also have potential applications in more complex systems such as those relevant to quantum computing.},
  author       = {Naibert, Tyler R. and Polshyn, Hryhoriy and Garrido-Menacho, Rita and Durkin, Malcolm and Wolin, Brian and Chua, Victor and Mondragon-Shem, Ian and Hughes, Taylor and Mason, Nadya and Budakian, Raffi},
  issn         = {2469-9969},
  journal      = {Physical Review B},
  number       = {22},
  publisher    = {American Physical Society},
  title        = {{Imaging and controlling vortex dynamics in mesoscopic superconductor-normal-metal-superconductor arrays}},
  doi          = {10.1103/physrevb.103.224526},
  volume       = {103},
  year         = {2021},
}

@inproceedings{10651,
  abstract     = {Electrons in the moiré flat bands of magic angle twisted bilayer graphene aligned to hexagonal boron nitride can break time reversal symmetry and open an interaction-driven, topological gap. The resulting magnetic order and associated quantized anomalous Hall effect have properties that diverge substantially from quantized anomalous Hall effects observed in other systems. I will present transport data and scanning probe magnetometry data acquired using a nanoSQUID-on-tip microscope. A quantitative analysis of the magnitude of the magnetization of the Chern magnet shows that the magnetic moment per moiré unit cell substantially exceeds 1 μB and grows rapidly in the topological gap, consistent with an orbital origin for the magnetic order. We find that the Barkhausen jumps observed in transport measurements can be mapped directly to microscopic motion of ferromagnetic domain walls. These domain walls are strongly pinned to disorder in the device and are reproducible across thermal cycles, suggesting coupling between the magnetic degrees of freedom and structural inhomogeneity.},
  author       = {Tschirhart, Charles and Serlin, Marec and Polshyn, Hryhoriy and Shragai, Avi G. and Xia, Zhengchao and Zhu, Jiacheng and Zhang, Yuxuan and Watanabe, Kenji and Taniguchi, Takashi and Huber, Martin E. and Young, Andrea},
  booktitle    = {APS March Meeting 2021},
  issn         = {0003-0503},
  location     = {Virtual, United States},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Probing orbital Chern ferromagnet phase in twisted bilayer graphene}},
  volume       = {66},
  year         = {2021},
}

@inproceedings{10693,
  abstract     = {High quality graphene heterostructures host an array of fractional quantum Hall isospin ferromagnets with diverse spin and valley orders. While a variety of phase transitions have been observed, disentangling the isospin phase diagram of these states is hampered by the absence of direct probes of spin and valley order. I will describe nonlocal transport measurements based on launching spin waves from a gate defined lateral heterojunction, performed in ultra-clean Corbino geometry graphene devices. At high magnetic fields, we find that the spin-wave transport signal is detected in all FQH states between ν = 0 and 1; however, between ν = 1 and 2 only odd numerator FQH states show finite nonlocal transport, despite the identical ground state spin polarizations in odd- and even numerator states. The results reveal that the neutral spin-waves are both spin and sublattice polarized making them a sensitive probe of ground state sublattice structure. Armed with this understanding, we use nonlocal transport signal to a magnetic field tuned isospin phase transition, showing that the emergent even denominator state at ν = 1/2 in monolayer graphene is indeed a multicomponent state featuring equal populations on each sublattice.},
  author       = {Zhou, Haoxin and Polshyn, Hryhoriy and Tanaguchi, Takashi and Watanabe, Kenji and Young, Andrea},
  booktitle    = {APS March Meeting 2020},
  issn         = {0003-0503},
  location     = {Denver, CO, United States},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Sublattice resolved spin wave transport through graphene fractional quantum Hall states as a probe of isospin order}},
  volume       = {65},
  year         = {2020},
}

@inproceedings{10696,
  abstract     = {We experimentally investigate twisted van der Waals heterostructures of monolayer graphene rotated with respect to a bernal stacked graphene bilayer. We report transport measurements for devices with twist angles between 0.9 and 1.4°. The electric field allows efficient tuning of the width, isolation and the topology of the moiré bands in this system. By comparing magnetoresistance measurements to numerical simulations, we develop an understanding of the band structure. Finally, we observe correlated states at half- and quarter-fillings, which arise when narrow moire sublattice band is isolated by energy gaps from dispersive bands. We investigate the effects of in-plane and out-of-plane magnetic field on these states and discuss the implication for their spin- and valley- polarization.},
  author       = {Polshyn, Hryhoriy and Zhu, Jihang and Kumar, Manish and Taniguchi, Takashi and Watanabe, Kenji and MacDonald, Allan and Young, Andrea},
  booktitle    = {APS March Meeting 2020},
  issn         = {0003-0503},
  location     = {Denver, CO, United States},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Correlated states and tunable topological bands in twisted monolayer-bilayer graphene heterostructures}},
  volume       = {65},
  year         = {2020},
}

@inproceedings{10697,
  abstract     = {We report the observation of a quantized anomalous Hall effect in a moiré heterostructure consisting of twisted bilayer graphene aligned to an encapsulating hBN substrate. The effect occurs at a density of 3 electrons per superlattice unit cell, where we observe magnetic hysteresis and a Hall resistance quantized to within 0.1% of the resistance quantum at temperatures as high as 3K. In this first of 3 talks, I will describe the fabrication procedure for our device as well as basic transport characterization measurements. I will introduce the phenomenology of twisted bilayer graphene and present evidence for hBN alignment as manifested in the hierarchy of symmetry-breaking gaps and anomalous magnetoresistance.},
  author       = {Zhang, Yuxuan and Serlin, Marec and Tschirhart, Charles and Polshyn, Hryhoriy and Zhu, Jiacheng and Balents, Leon and Huber, Martin E. and Taniguchi, Takashi and Watanabe, Kenji and Young, Andrea},
  booktitle    = {APS March Meeting 2020},
  location     = {Denver, CO, United States},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Intrinsic quantized anomalous Hall effect in a moiré heterostructure, part I: Device fabrication and transport}},
  volume       = {65},
  year         = {2020},
}

@inproceedings{10698,
  abstract     = {This is the second of three talks describing the observation and characterization of a ferromagnetic moiré heterostructure based on twisted bilayer graphene aligned to hexagonal boron nitride. I will compare the qualitative and quantitative features of this observed quantum anomalous Hall state to traditional systems engineered from thin film (Bi,Sb)2Te3 topological insulators. In particular, we find that the measured electronic energy gap of ~30K is several times higher than the Curie temperature, consistent with a lack of disorder associated with magnetic dopants. In this system, the quantization arises from spontaneous ferromagnetic polarization into a single spin and valley moiré subband, which is topological despite the lack of spin orbit coupling. I will also discuss the observation of current induced switching, which allows the magnetic state of the heterostructure to be controllably reversed with currents as small as a few nanoamperes.},
  author       = {Serlin, Marec and Tschirhart, Charles and Polshyn, Hryhoriy and Zhang, Yuxuan and Zhu, Jiacheng and Huber, Martin E. and Balents, Leon and Watanabe, Kenji and Tanaguchi, Takashi and Young, Andrea},
  booktitle    = {APS March Meeting 2020},
  location     = {Denver, CO, United States},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Intrinsic quantized anomalous Hall effect in a moiré heterostructure, part II: Temperature dependence and current switching}},
  volume       = {65},
  year         = {2020},
}

@inproceedings{10699,
  abstract     = {This is the third of three talks describing the observation and characterization of a ferromagnetic moiré heterostructure based on twisted bilayer graphene aligned to hexagonal boron nitride. In this segment I will present scanning probe magnetometry data acquired using a nanoSQUID-on-tip microscope, which provides ~150 nm spatial resolution and a field sensitivity of ~10 nT/rtHz. We study the distribution of magnetic domains within the device as a function of density, magnetic field training, and DC current. Our data allow us to constrain the magnitude of the orbital magnetic moment of the electrons in the QAH state. Comparison with simultaneously acquired transport data allows us to precisely correlate single domain dynamics with discrete jumps in the observed anomalous Hall signal.},
  author       = {Tschirhart, Charles and Serlin, Marec and Polshyn, Hryhoriy and Zhang, Yuxuan and Zhu, Jiacheng and Balents, Leon and Huber, Martin E. and Watanabe, Kenji and Tanaguchi, Takashi and Young, Andrea},
  booktitle    = {APS March Meeting 2020},
  issn         = {0003-0503},
  location     = {Denver, CO, United States},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Intrinsic quantized anomalous Hall effect in a moiré heterostructure, part III: Scanning probe magnetometry}},
  volume       = {65},
  year         = {2020},
}

@article{10701,
  abstract     = {Partially filled Landau levels host competing electronic orders. For example, electron solids may prevail close to integer filling of the Landau levels before giving way to fractional quantum Hall liquids at higher carrier density1,2. Here, we report the observation of an electron solid with non-collinear spin texture in monolayer graphene, consistent with solidification of skyrmions3—topological spin textures characterized by quantized electrical charge4,5. We probe the spin texture of the solids using a modified Corbino geometry that allows ferromagnetic magnons to be launched and detected6,7. We find that magnon transport is highly efficient when one Landau level is filled (ν=1), consistent with quantum Hall ferromagnetic spin polarization. However, even minimal doping immediately quenches the magnon signal while leaving the vanishing low-temperature charge conductivity unchanged. Our results can be understood by the formation of a solid of charged skyrmions near ν=1, whose non-collinear spin texture leads to rapid magnon decay. Data near fractional fillings show evidence of several fractional skyrmion solids, suggesting that graphene hosts a highly tunable landscape of coupled spin and charge orders.},
  author       = {Zhou, Haoxin and Polshyn, Hryhoriy and Taniguchi, Takashi and Watanabe, Kenji and Young, Andrea F.},
  issn         = {1745-2481},
  journal      = {Nature Physics},
  number       = {2},
  pages        = {154--158},
  publisher    = {Springer Nature},
  title        = {{Skyrmion solids in monolayer graphene}},
  doi          = {10.1038/s41567-019-0729-8},
  volume       = {16},
  year         = {2020},
}

@article{10618,
  abstract     = {Magnetism typically arises from the joint effect of Fermi statistics and repulsive Coulomb interactions, which favours ground states with non-zero electron spin. As a result, controlling spin magnetism with electric fields—a longstanding technological goal in spintronics and multiferroics1,2—can be achieved only indirectly. Here we experimentally demonstrate direct electric-field control of magnetic states in an orbital Chern insulator3,4,5,6, a magnetic system in which non-trivial band topology favours long-range order of orbital angular momentum but the spins are thought to remain disordered7,8,9,10,11,12,13,14. We use van der Waals heterostructures consisting of a graphene monolayer rotationally faulted with respect to a Bernal-stacked bilayer to realize narrow and topologically non-trivial valley-projected moiré minibands15,16,17. At fillings of one and three electrons per moiré unit cell within these bands, we observe quantized anomalous Hall effects18 with transverse resistance approximately equal to h/2e2 (where h is Planck’s constant and e is the charge on the electron), which is indicative of spontaneous polarization of the system into a single-valley-projected band with a Chern number equal to two. At a filling of three electrons per moiré unit cell, we find that the sign of the quantum anomalous Hall effect can be reversed via field-effect control of the chemical potential; moreover, this transition is hysteretic, which we use to demonstrate non-volatile electric-field-induced reversal of the magnetic state. A theoretical analysis19 indicates that the effect arises from the topological edge states, which drive a change in sign of the magnetization and thus a reversal in the favoured magnetic state. Voltage control of magnetic states can be used to electrically pattern non-volatile magnetic-domain structures hosting chiral edge states, with applications ranging from reconfigurable microwave circuit elements to ultralow-power magnetic memories.},
  author       = {Polshyn, Hryhoriy and Zhu, J. and Kumar, M. A. and Zhang, Y. and Yang, F. and Tschirhart, C. L. and Serlin, M. and Watanabe, K. and Taniguchi, T. and MacDonald, A. H. and Young, A. F.},
  issn         = {1476-4687},
  journal      = {Nature},
  keywords     = {multidisciplinary},
  number       = {7836},
  pages        = {66--70},
  publisher    = {Springer Nature},
  title        = {{Electrical switching of magnetic order in an orbital Chern insulator}},
  doi          = {10.1038/s41586-020-2963-8},
  volume       = {588},
  year         = {2020},
}

@unpublished{10650,
  abstract     = {The understanding of material systems with strong electron-electron interactions is the central problem in modern condensed matter physics. Despite this, the essential physics of many of these materials is still not understood and we have no overall perspective on their properties. Moreover, we have very little ability to make predictions in this class of systems. In this manuscript we share our personal views of what the major open problems are in correlated electron systems and we discuss some possible routes to make progress in this rich and fascinating field. This manuscript is the result of the vigorous discussions and deliberations that took place at Johns Hopkins University during a three-day workshop January 27, 28, and 29, 2020 that brought together six senior scientists and 46 more junior scientists. Our hope, is that the topics we have presented will provide inspiration for others working in this field and motivation for the idea that significant progress can be made on very hard problems if we focus our collective energies.},
  author       = {Alexandradinata, A and Armitage, N.P. and Baydin, Andrey and Bi, Wenli and Cao, Yue and Changlani, Hitesh J. and Chertkov, Eli and da Silva Neto, Eduardo H. and Delacretaz, Luca and El Baggari, Ismail and Ferguson, G.M. and Gannon, William J. and Ghorashi, Sayed Ali Akbar and Goodge, Berit H. and Goulko, Olga and Grissonnache, G. and Hallas, Alannah and Hayes, Ian M. and He, Yu and Huang, Edwin W. and Kogar, Anshu and Kumah, Divine and Lee, Jong Yeon and Legros, A. and Mahmood, Fahad and Maximenko, Yulia and Pellatz, Nick and Polshyn, Hryhoriy and Sarkar, Tarapada and Scheie, Allen and Seyler, Kyle L. and Shi, Zhenzhong and Skinner, Brian and Steinke, Lucia and Thirunavukkuarasu, K. and Trevisan, Thaís Victa and Vogl, Michael and Volkov, Pavel A. and Wang, Yao and Wang, Yishu and Wei, Di and Wei, Kaya and Yang, Shuolong and Zhang, Xian and Zhang, Ya-Hui and Zhao, Liuyan and Zong, Alfred},
  booktitle    = {arXiv},
  pages        = {55},
  title        = {{The future of the correlated electron problem}},
  year         = {2020},
}

@article{10664,
  abstract     = {Since the discovery of correlated insulators and superconductivity in magic-angle twisted bilayer graphene (tBLG) ([1, 2], JCCM April 2018), theorists have been excitedly pursuing the alluring mix of band topology, symmetry breaking, Mott insulators and superconductivity at play, as well as the potential relation (if any) to high-Tc physics. Now a new stream
of experimental work is arriving which further enriches the story. To briefly recap Episodes 1 and 2 (JCCM April and November 2018), when two graphene layers are stacked with a small rotational mismatch θ, the resulting long-wavelength moire pattern leads to a superlattice potential which reconstructs the low energy band structure. When θ approaches the “magic-angle” θM ∼ 1 ◦, the band structure features eight nearly-flat bands which fill when the electron number per moire unit cell, n/n0, lies between −4 < n/n0 < 4. The bands can be counted as 8 = 2 × 2 × 2: for each spin (2×) and valley (2×) characteristic of monolayergraphene, tBLG has has 2× flat bands which cross at mini-Dirac points.},
  author       = {Yankowitz, Mathew and Chen, Shaowen and Polshyn, Hryhoriy and Watanabe, K. and Taniguchi, T. and Graf, David and Young, Andrea F. and Dean, Cory R. and Sharpe, Aaron L. and Fox, E.J. and Barnard, A.W. and Finney, Joe},
  journal      = {Journal Club for Condensed Matter Physics},
  publisher    = {Simons Foundation ; University of California, Riverside},
  title        = {{New correlated phenomena in magic-angle twisted bilayer graphene/s}},
  doi          = {10.36471/jccm_february_2019_03},
  volume       = {03},
  year         = {2019},
}

@inproceedings{10722,
  abstract     = {Bilayer graphene, rotationally faulted to ~1.1 degree misalignment, has recently been shown to host superconducting and resistive states associated with the formation of a flat electronic band. While numerous theories exist for the origins of both states, direct validation of these theories remains an outstanding experimental problem. Here, we focus on the resistive states occurring at commensurate filling (1/2, 1/4, and 3/4) of the two lowest superlattice bands. We test theoretical proposals that these states arise due to broken spin—and/or valley—symmetry by performing direct magnetic imaging with nanoscale SQUID-on-tip microscopy. This technique provides single-spin resolved magnetometry on sub-100nm length scales. I will present imaging data from our 4.2K nSOT microscope on graphite-gated twisted bilayers near the flat band condition and discuss the implications for the physics of the commensurate resistive states.},
  author       = {Serlin, Marec and Tschirhart, Charles and Polshyn, Hryhoriy and Zhu, Jiacheng and Huber, Martin E. and Young, Andrea},
  booktitle    = {APS March Meeting 2019},
  issn         = {0003-0503},
  location     = {Boston, MA, United States},
  number       = {2},
  publisher    = {American Physical Society},
  title        = {{Direct Imaging of magnetic structure in twisted bilayer graphene with scanning nanoSQUID-On-Tip microscopy}},
  volume       = {64},
  year         = {2019},
}

@inproceedings{10723,
  abstract     = {In monolayer graphene, the interplay of electronic correlations with the internal spin- and valley- degrees of freedom leads to a complex phase diagram of isospin symmetry breaking at high magnetic fields. Recently, Wei et al. (Science (2018)) demonstrated that spin waves can be electrically generated and detected in graphene heterojunctions, allowing direct experiment access to the spin degree of freedom. Here, we apply this technique to high quality graphite-gated graphene devices showing robust fractional quantum Hall phases and isospin phase transitions. We use an edgeless Corbino geometry to eliminate the contributions of edge states to the spin-wave mediated nonlocal voltage, allowing unambiguous identification of spin wave transport signatures. Our data reveal two phases within the ν = 1 plateau. For exactly ν=1, charge is localized but spin waves propagate freely while small carrier doping completely quenches the low-energy spin-wave transport, even as those charges remain localized. We identify this new phase as a spin textured electron solid. We also find that spin-wave transport is modulated by phase transitions in the valley order that preserve spin polarization, suggesting that this technique is sensitive to both spin and valley order.},
  author       = {Zhou, Haoxin and Polshyn, Hryhoriy and Tanaguchi, Takashi and Watanabe, Kenji and Young, Andrea},
  booktitle    = {APS March Meeting 2019},
  issn         = {0003-0503},
  location     = {Boston, MA, United States},
  number       = {2},
  publisher    = {American Physical Society},
  title        = {{Spin wave transport through electron solids and fractional quantum Hall liquids in graphene}},
  volume       = {64},
  year         = {2019},
}

@inproceedings{10724,
  abstract     = {Twisted bilayer graphene (tBLG) near the flat band condition is a versatile new platform for the study of correlated physics in 2D. Resistive states have been observed at several commensurate fillings of the flat miniband, along with superconducting states near half filling. To better understand the electronic structure of this system, we study electronic transport of graphite gated superconducting tBLG devices in the normal regime. At high magnetic fields, we observe full lifting of the spin and valley degeneracy. The transitions in the splitting of this four-fold degeneracy as a function of carrier density indicate Landau level (LL) crossings, which tilted field measurements show occur between LLs with different valley polarization. Similar LL structure measured in two devices, one with twist angle θ=1.08° at ambient pressure and one at θ=1.27° and 1.33GPa, suggests that the dimensionless combination of twist angle and interlayer coupling controls the relevant details of the band structure. In addition, we find that the temperature dependence of the resistance at B=0 shows linear growth at several hundred Ohm/K in a broad range of temperatures. We discuss the implications for modeling the scattering processes in this system.},
  author       = {Polshyn, Hryhoriy and Zhang, Yuxuan and Yankowitz, Matthew and Chen, Shaowen and Taniguchi, Takashi and Watanabe, Kenji and Graf, David E. and Dean, Cory R. and Young, Andrea},
  booktitle    = {APS March Meeting 2019},
  issn         = {0003-0503},
  location     = {Boston, MA, United States},
  number       = {2},
  publisher    = {American Physical Society},
  title        = {{Normal state transport in superconducting twisted bilayer graphene}},
  volume       = {64},
  year         = {2019},
}

@inproceedings{10725,
  abstract     = {Bilayer graphene with ~ 1.1 degrees twist mismatch between the layers hosts a low energy flat band in which the Coulomb interaction is large relative to the bandwidth, promoting correlated insulating states at half band filling, and superconducting (SC) phases with dome-like structure neighboring correlated insulating states. Here we show measurements of a dual-graphite-gated twisted bilayer graphene device, which minimizes charge inhomogeneity. We observe new correlated phases, including for the first time a SC pocket near half-filling of the electron-doped band and resistive states at quarter-filling of both bands that emerge in a magnetic field. Changing the layer polarization with vertical electric field reveals an unexpected competition between SC and correlated insulator phases, which we interpret to result from differences in disorder of each graphene layer and underscores the spatial inhomogeneity like twist angle as a significant source of disorder in these devices [1].},
  author       = {Chen, Shaowen and Yankowitz, Matthew and Polshyn, Hryhoriy and Watanabe, Kenji and Taniguchi, Takashi and Graf, David E. and Young, Andrea and Dean, Cory R.},
  booktitle    = {APS March Meeting 2019},
  issn         = {0003-0503},
  location     = {Boston, MA, United States},
  number       = {2},
  publisher    = {American Physical Society},
  title        = {{Correlated insulating and superconducting phases in twisted bilayer graphene}},
  volume       = {64},
  year         = {2019},
}

@article{10619,
  abstract     = {The quantum anomalous Hall (QAH) effect combines topology and magnetism to produce precisely quantized Hall resistance at zero magnetic field. We report the observation of a QAH effect in twisted bilayer graphene aligned to hexagonal boron nitride. The effect is driven by intrinsic strong interactions, which polarize the electrons into a single spin- and valley-resolved moiré miniband with Chern number C = 1. In contrast to magnetically doped systems, the measured transport energy gap is larger than the Curie temperature for magnetic ordering, and quantization to within 0.1% of the von Klitzing constant persists to temperatures of several kelvin at zero magnetic field. Electrical currents as small as 1 nanoampere controllably switch the magnetic order between states of opposite polarization, forming an electrically rewritable magnetic memory.},
  author       = {Serlin, M. and Tschirhart, C. L. and Polshyn, Hryhoriy and Zhang, Y. and Zhu, J. and Watanabe, K. and Taniguchi, T. and Balents, L. and Young, A. F.},
  issn         = {1095-9203},
  journal      = {Science},
  keywords     = {multidisciplinary},
  number       = {6480},
  pages        = {900--903},
  publisher    = {American Association for the Advancement of Science},
  title        = {{Intrinsic quantized anomalous Hall effect in a moiré heterostructure}},
  doi          = {10.1126/science.aay5533},
  volume       = {367},
  year         = {2019},
}

@article{10620,
  abstract     = {Partially filled Landau levels host competing electronic orders. For example, electron solids may prevail close to integer filling of the Landau levels before giving way to fractional quantum Hall liquids at higher carrier density1,2. Here, we report the observation of an electron solid with non-collinear spin texture in monolayer graphene, consistent with solidification of skyrmions3—topological spin textures characterized by quantized electrical charge4,5. We probe the spin texture of the solids using a modified Corbino geometry that allows ferromagnetic magnons to be launched and detected6,7. We find that magnon transport is highly efficient when one Landau level is filled (ν=1), consistent with quantum Hall ferromagnetic spin polarization. However, even minimal doping immediately quenches the magnon signal while leaving the vanishing low-temperature charge conductivity unchanged. Our results can be understood by the formation of a solid of charged skyrmions near ν=1, whose non-collinear spin texture leads to rapid magnon decay. Data near fractional fillings show evidence of several fractional skyrmion solids, suggesting that graphene hosts a highly tunable landscape of coupled spin and charge orders.},
  author       = {Zhou, H. and Polshyn, Hryhoriy and Taniguchi, T. and Watanabe, K. and Young, A. F.},
  issn         = {1745-2481},
  journal      = {Nature Physics},
  keywords     = {General Physics and Astronomy},
  number       = {2},
  pages        = {154--158},
  publisher    = {Springer Nature},
  title        = {{Solids of quantum Hall skyrmions in graphene}},
  doi          = {10.1038/s41567-019-0729-8},
  volume       = {16},
  year         = {2019},
}