Nuckolls, K. P., et al.Strongly correlated Chern insulators in magic-angle twisted bilayer graphene”. Nature (2020). Web. Fee linkAbstract
Interactions among electrons and the topology of their energy bands can create novel quantum phases of matter. Most topological electronic phases appear in systems with weak electron-electron interactions. The instances where topological phases emerge only as a result of strong interactions are rare, and mostly limited to those realized in the presence of intense magnetic fields. The discovery of flat electronic bands with topological character in magic-angle twisted bilayer graphene (MATBG) has created a unique opportunity to search for new strongly correlated topological phases. Here we introduce a novel local spectroscopic technique using a scanning tunneling microscope (STM) to detect a sequence of topological insulators in MATBG with Chern numbers C = ± 1, ± 2, ± 3, which form near ν = ± 3, ± 2, ± 1 electrons per moiré unit cell respectively, and are stabilized by the application of modest magnetic fields. One of the phases detected here (C = +1) has been previously observed when the sublattice symmetry of MATBG was intentionally broken by hexagonal boron nitride (hBN) substrates, with interactions playing a secondary role. We demonstrate that strong electron-electron interactions alone can produce not only the previously observed phase, but also new and unexpected Chern insulating phases in MATBG. The full sequence of phases we observed can be understood by postulating that strong correlations favor breaking time-reversal symmetry to form Chern insulators that are stabilized by weak magnetic fields. Our findings illustrate that many-body correlations can create topological phases in moiré systems beyond those anticipated from weakly interacting models
Jäck, B.Observation of backscattering induced by magnetism in a topological edge state”. Proceedings of the National Academy of Sciences , 202005071 (2020). Web.Abstract
The boundary modes of topological insulators are protected by the symmetries of the nontrivial bulk electronic states. Unless these symmetries are broken, they can give rise to novel phenomena, such as the quantum spin Hall effect in one-dimensional (1D) topological edge states, where quasiparticle backscattering is suppressed by time-reversal symmetry (TRS). Here, we investigate the properties of the 1D topological edge state of bismuth in the absence of TRS, where backscattering is predicted to occur. Using spectroscopic imaging and spin-polarized measurements with a scanning tunneling microscope, we compared quasiparticle interference (QPI) occurring in the edge state of a pristine bismuth bilayer with that occurring in the edge state of a bilayer, which is terminated by ferromagnetic iron clusters that break TRS. Our experiments on the decorated bilayer edge reveal an additional QPI branch, which can be associated with spin-flip scattering across the Brioullin zone center between time-reversal band partners. The observed QPI characteristics exactly match with theoretical expectations for a topological edge state, having one Kramer’s pair of bands. Together, our results provide further evidence for the nontrivial nature of bismuth and in particular, demonstrate backscattering inside a helical topological edge state induced by broken TRS through local magnetism.
Wong, D., et al.A modular ultra-high vacuum millikelvin scanning tunneling microscope”. Review of Scientific Instruments 91, 023703, 2020. Print.Abstract
We describe the design, construction, and performance of an ultra-high vacuum (UHV) scanning tunneling microscope (STM) capable of imaging at dilution-refrigerator temperatures and equipped with a vector magnet. The primary objective of our design is to achieve a high level of modularity by partitioning the STM system into a set of easily separable, interchangeable components. This naturally segregates the UHV needs of STM instrumentation from the typically non-UHV construction of a dilution refrigerator, facilitating the usage of non-UHV materials while maintaining a fully bakeable UHV chamber that houses the STM. The modular design also permits speedy removal of the microscope head from the rest of the system, allowing for repairs, modifications, and even replacement of the entire microscope head to be made at any time without warming the cryostat or compromising the vacuum. Without using cryogenic filters, we measured an electron temperature of 184 mK on a superconducting Al(100) single crystal.
Wong, D., et al.Cascade of electronic transitions in magic-angle twisted bilayer graphene”. Nature 2020, 582, 198-202. Web. Free LinkAbstract
Magic-angle twisted bilayer graphene (MATBG) exhibits a rich variety of electronic states, including correlated insulators, superconductors, and topological phases. Understanding the microscopic mechanisms responsible for these phases requires determining the interplay between electron-electron interactions and quantum degeneracy due to spin and valley degrees of freedom. Signatures of strong electron-electron correlations have been observed at partial fillings of the flat electronic bands in recent spectroscopic measurements. Transport experiments have shown changes in the Landau level degeneracy at fillings corresponding to an integer number of electrons per moiré unit cell. However, the interplay between interaction effects and the degeneracy of the system is currently unclear. Using high-resolution scanning tunneling microscopy (STM), we observed a cascade of transitions in the spectroscopic properties of MATBG as a function of electron filling. We find distinct changes in the chemical potential and a rearrangement of the low-energy excitations at each integer filling of the moiré flat bands. These spectroscopic features are a direct consequence of Coulomb interactions, which split the degenerate flat bands into Hubbard sub-bands. We find these interactions, the strength of which we can extract experimentally, to be surprisingly sensitive to the presence of a perpendicular magnetic field, which strongly modifies the spectroscopic transitions. The cascade of transitions we report here characterizes the correlated high-temperature parent phase from which various insulating and superconducting ground-state phases emerge at low temperatures in MATBG.
Agarwal, K., et al.Topology- and symmetry-protected domain wall conduction in quantum Hall nematics”. Physical Review B 100, 16, 165103, 2019. Print.Abstract
We consider domain walls in nematic quantum Hall ferromagnets predicted to form in multivalley semiconductors, recently probed by scanning tunneling microscopy experiments on Bi(111) surfaces. We show that the domain wall properties depend sensitively on the filling factor ν of the underlying (integer) quantum Hall states. For ν=1 and in the absence of impurity scattering we argue that the wall hosts a single-channel Luttinger liquid whose gaplessness is a consequence of valley and charge conservation. For ν=2, it supports a two-channel Luttinger liquid, which for sufficiently strong interactions enters a symmetry-preserving thermal metal phase with a charge gap coexisting with gapless neutral intervalley modes. The domain wall physics in this state is identical to that of a bosonic topological insulator protected by U(1)×U(1) symmetry, and we provide a formal mapping between these problems. We discuss other unusual properties and experimental signatures of these anomalous one-dimensional systems.
Bernevig, B. A., and A. Yazdani. “New Research Reveals how Electrons Interact in Twisted Graphene”. Scientific American 2019. Print.Abstract
With our study, we may have gotten closer to solving the problem of high-temperature superconductivity
Yazdani, Ali. “Conjuring Majorana with synthetic magnetism”. Nature Materials 18, 1036-1037, 2019. Web.Abstract
Majorana zero modes — useful for quantum computing — are revealed in carbon nanotubes by utilizing a synthetic spin–orbit interaction.
Xie, Y., et al.Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene”. Nature 572, 101-105, (2019). Print.Abstract
The discovery of superconducting and insulating states in magic-angle twisted bilayer graphene (MATBG) has ignited considerable interest in understanding the nature of electronic interactions in this chemically pristine material. The transport properties of MATBG as a function of doping are similar to those of high-transition-temperature copper oxides and other unconventional superconductors, which suggests that MATBG may be a highly interacting system. However, to our knowledge, there is no direct experimental evidence of strong many-body correlations in MATBG. Here we present high-resolution spectroscopic measurements, obtained using a scanning tunnelling microscope, that provide such evidence as a function of carrier density. MATBG displays unusual spectroscopic characteristics that can be attributed to electron–electron interactions over a wide range of doping levels, including those at which superconductivity emerges in this system. We show that our measurements cannot be explained with a mean-field approach for modelling electron–electron interactions in MATBG. The breakdown of a mean-field approach when applied to other correlated superconductors, such as copper oxides, has long inspired the study of the highly correlated Hubbard model. We show that a phenomenological extended-Hubbard-model cluster calculation, which is motivated by the nearly localized nature of the relevant electronic states of MATBG, produces spectroscopic features that are similar to those that we observed experimentally. Our findings demonstrate the critical role of many-body correlations in understanding the properties of MATBG.
Jack, B., et al.Observation of a Majorana zero mode in a topologically protected edge channel”. Science 364, 1255-1259 (2019). Print.Abstract
Superconducting proximity pairing in helical edge modes, such as those of topological insulators, is predicted to provide a unique platform for realizing Majorana zero modes (MZMs).We used scanning tunneling microscopy measurements to probe the influence of proximity-induced superconductivity and magnetism on the helical hinge states of bismuth(111) films grown on a superconducting niobium substrate and decorated with magnetic iron clusters. Consistent with model calculations, our measurements revealed the emergence of a localized MZM at the interface between the superconducting helical edge channel and the iron clusters, with a strong magnetization component along the edge. Our experiments also resolve the MZM’s spin signature, which distinguishes it from trivial in-gap states that may accidentally occur at zero energy in a superconductor. 
Mishmash, R. V., A. Yazdani, and M. P. Zaletel. “Majorana lattices from the quantized Hall limit of a proximitized spin-orbit coupled electron gas”. Physical Review B 99, 11, 115427, (2019). Web.Abstract
Motivated by recent experiments demonstrating intricate quantum Hall physics on the surface of elemental bismuth, we consider proximity coupling an s-wave superconductor to a two-dimensional electron gas with strong Rashba spin-orbit interactions in the presence of a strong perpendicular magnetic field. We focus on the high-field limit so that the superconductivity can be treated as a perturbation to the low-lying Landau levels. In the clean case, wherein the superconducting order parameter takes the form of an Abrikosov vortex lattice, we show that a lattice of hybridized Majorana modes emerges near the plateau transition of the lowest Landau level. However, unless magnetic-symmetry-violating perturbations are present, the system always has an even number of chiral Majorana edge modes and thus is strictly speaking Abelian in nature, in agreement with previous work on related setups. Interestingly, however, a weak topological superconducting phase can very naturally be stabilized near the plateau transition for the square vortex lattice. The relevance of our findings to potential near-term experiments on proximitized materials such as bismuth will be discussed.
Randeria, M. T., et al.Interacting multi-channel topological boundary modes in a quantum Hall valley system”. Nature 566, 363-367, (2019). Print.Abstract

Symmetry and topology are central to understanding quantum Hall ferromagnets (QHFMs), two-dimensional electronic phases with spontaneously broken spin or pseudospin symmetry whose wavefunctions also have topological properties1,2. Domain walls between distinct broken-symmetry QHFM phases are predicted to host gapless one-dimensional modes—that is, quantum channels that emerge because of a topological change in the underlying electronic wavefunctions at such interfaces. Although various QHFMs have been identified in different materials3,4,5,6,7,8, interacting electronic modes at these domain walls have not been probed. Here we use a scanning tunnelling microscope to directly visualize the spontaneous formation of boundary modes at domain walls between QHFM phases with different valley polarization (that is, the occupation of equal-energy but quantum mechanically distinct valleys in the electronic structure) on the surface of bismuth. Spectroscopy shows that these modes occur within a topological energy gap, which closes and reopens as the valley polarization switches across the domain wall. By changing the valley flavour and the number of modes at the domain wall, we can realize different regimes in which the valley-polarized channels are either metallic or develop a spectroscopic gap. This behaviour is a consequence of Coulomb interactions constrained by the valley flavour, which determines whether electrons in the topological modes can backscatter, making these channels a unique class of interacting one-dimensional quantum wires. QHFM domain walls can be realized in different classes of two-dimensional materials, providing the opportunity to explore a rich phase space of interactions in these quantum wires.

Recommended for Journal Club for Condensed Matter Physics with a commentary by Liang Fu.

Schindler, F., et al.Higher-order topology in bismuth”. Nature Physics 14, 918-924, (2018). Print.Abstract
The mathematical field of topology has become a framework in which to describe the low-energy electronic structure of crystalline solids. Typical of a bulk insulating three-dimensional topological crystal are conducting two-dimensional surface states. This constitutes the topological bulk–boundary correspondence. Here, we establish that the electronic structure of bismuth, an element consistently described as bulk topologically trivial, is in fact topological and follows a generalized bulk–boundary correspondence of higher-order: not the surfaces of the crystal, but its hinges host topologically protected conducting modes. These hinge modes are protected against localization by time-reversal symmetry locally, and globally by the three-fold rotational symmetry and inversion symmetry of the bismuth crystal. We support our claim theoretically and experimentally. Our theoretical analysis is based on symmetry arguments, topological indices, first-principles calculations, and the recently introduced framework of topological quantum chemistry. We provide supporting evidence from two complementary experimental techniques. With scanning-tunnelling spectroscopy, we probe the signatures of the rotational symmetry of the one-dimensional states located at the step edges of the crystal surface. With Josephson interferometry, we demonstrate their universal topological contribution to the electronic transport. Our work establishes bismuth as a higher-order topological insulator.
Li, Jian, et al.Majorana spin in magnetic atomic chain systems”. Physical Review B 97, 125119, 12 (2018). Print.Abstract
In this paper, we establish that Majorana zero modes emerging from a topological band structure of a chain of magnetic atoms embedded in a superconductor can be distinguished from trivial localized zero energy states that may accidentally form in this system using spin-resolved measurements. To demonstrate this key Majorana diagnostics, we study the spin composition of magnetic impurity induced in-gap Shiba states in a superconductor using a hybrid model. By examining the spin and spectral densities in the context of the Bogoliubov-de Gennes (BdG) particle-hole symmetry, we derive a sum rule that relates the spin densities of localized Shiba states with those in the normal state without superconductivity. Extending our investigations to a ferromagnetic chain of magnetic impurities, we identify key features of the spin properties of the extended Shiba state bands, as well as those associated with a localized Majorana end mode when the effect of spin-orbit interaction is included. We then formulate a phenomenological theory for the measurement of the local spin densities with spin-polarized scanning tunneling microscopy (STM) techniques. By combining the calculated spin densities and the measurement theory, we show that spin-polarized STM measurements can reveal a sharp contrast in spin polarization between an accidental-zero-energy trivial Shiba state and a Majorana zero mode in a topological superconducting phase in atomic chains. We further confirm our results with numerical simulations that address generic parameter settings.
Randeria, Mallika T., et al.Ferroelectric quantum Hall phase revealed by visualizing Landau level wavefunction interference”. Nature Physics 14, 796-800, (2018). Web. Publisher's VersionAbstract
States with spontaneously broken symmetry can form due to Coulomb interactions in electronic systems with multiple internal degrees of freedom. Materials with several degenerate regions in the Brillouin zone—called valleys—offer a rich setting for the emergence of such states, which have potential electronic and optical applications1,2,3,4. To date, identification of these broken-symmetry phases has mostly relied on macroscopic transport or optical properties. Here we demonstrate a direct approach by visualizing the wavefunctions of bismuth surface states with a scanning tunnelling microscope. Strong spin–orbit coupling on the surface of bismuth leads to six degenerate, teardrop-shaped, hole valleys5. Our spectroscopic measurements reveal that exchange interactions fully lift this degeneracy at high magnetic field, and we are able to determine the nature of the valley ordering by imaging the broken-symmetry Landau level wavefunctions. The spatial features of singly degenerate Landau level wavefunctions near isolated defects contain unique signatures of interference between spin-textured valleys, which identify the electronic ground state as a quantum Hall ferroelectric. Our observations confirm the recent prediction6 that interactions in strongly anisotropic valley systems favour the occupation of a single valley, giving rise to emergent ferroelectricity in the surface state of bismuth.
Gyenis, A., et al.Visualizing heavy fermion confinement and Pauli-limited superconductivity in layered CeCoIn5”. Nature Communications 9 .549 (2018). Print.Abstract
Layered material structures play a key role in enhancing electron–electron interactions to create correlated metallic phases that can transform into unconventional superconducting states. The quasi-two-dimensional electronic properties of such compounds are often inferred indirectly through examination of bulk properties. Here we use scanning tunneling microscopy to directly probe in cross-section the quasi-two-dimensional electronic states of the heavy fermion superconductor CeCoIn5. Our measurements reveal the strong confined nature of quasiparticles, anisotropy of tunneling characteristics, and layer-by-layer modulated behavior of the precursor pseudogap gap phase. In the interlayer coupled superconducting state, the orientation of line defects relative to the d-wave order parameter determines whether in-gap states form due to scattering. Spectroscopic imaging of the anisotropic magnetic vortex cores directly characterizes the short interlayer superconducting coherence length and shows an electronic phase separation near the upper critical in-plane magnetic field, consistent with a Pauli-limited first-order phase transition into a pseudogap phase.
Papić, Z., et al.Imaging Anyons with Scanning Tunneling Microscopy”. Physical Review X 8011037 (2018). Print.Abstract
Anyons are exotic quasiparticles with fractional charge that can emerge as fundamental excitations of strongly interacting topological quantum phases of matter. Unlike ordinary fermions and bosons, they may obey non-Abelian statistics—a property that would help realize fault-tolerant quantum computation. Non-Abelian anyons have long been predicted to occur in the fractional quantum Hall (FQH) phases that form in two-dimensional electron gases in the presence of a large magnetic field, such as the ν=5/2 FQH state. However, direct experimental evidence of anyons and tests that can distinguish between Abelian and non-Abelian quantum ground states with such excitations have remained elusive. Here, we propose a new experimental approach to directly visualize the structure of interacting electronic states of FQH states with the STM. Our theoretical calculations show how spectroscopy mapping with the STM near individual impurity defects can be used to image fractional statistics in FQH states, identifying unique signatures in such measurements that can distinguish different proposed ground states. The presence of locally trapped anyons should leave distinct signatures in STM spectroscopic maps, and enables a new approach to directly detect—and perhaps ultimately manipulate—these exotic quasiparticles.
Jeon, S., et al.Distinguishing a Majorana zero mode using spin resolved measurements”. Science 358, 772, (2017). Print.Abstract

One-dimensional topological superconductors host Majorana zero modes (MZMs), the non-local property of which could be exploited for quantum computing applications. We use spin-polarized scanning tunneling microscopy to show that MZMs realized in self-assembled Fe chains on the surface of Pb have a spin polarization that exceeds that stemming from the magnetism of these chains. This feature, captured by our model calculations, is a direct consequence of the nonlocality of the Hilbert space of MZMs emerging from a topological band structure. Our study establishes spin polarization measurements as a diagnostic tool to distinguish topological MZMs from trivial in-gap states of a superconductor.

Feldman, B. E., et al.High-resolution studies of the Majorana atomic chain platform”. Nature Physics 13, 286, (2016). Print.
Gyenis, A., et al.Imaging electronic states on topological semimetals using scanning tunneling microscopy”. New Journal of Physics 18, 105003 18.105003 (2016). Print.
Liu, M., et al.Large discrete jumps observed in the transition between Chern states in a ferromagnetic topological insulator”. Science Advances 29, No. 7, e1600167, 2016. Print.
Feldman, B. E., et al.Observation of a nematic quantum Hall liquid on the surface of bismuth”. Science, vol. 354, issue 6310, pp. 316-321, 2016. Print.

Princeton University press release: "Unusual quantum liquid on crystal surface could inspire future electronics"

Gyenis, A., et al.Quasiparticle interference of heavy fermions in resonant x-ray scattering”. Science Advances 2, No. 10, e1601086, 2016. Print.
Inoue, H., et al.Quasiparticle interference of the Fermi arcs and surface-bulk connectivity of Weyl semimetals”. Science 351, 6278, pp. 1184-1187, 2016. Print.

Princeton University press release: "Down the rabbit hole: how electrons travel through exotic new material (Science)"

Randeria, M. T., et al.Scanning Josephson spectroscopy on the atomic scale”. Physical Review B Rapid Communications 93, 161115R, 2016: , 16115R, (selected as Editor's choice). Print.
Kushwaha, S. K., et al.Sn-doped Bi1.1 Sb 0.9Te2S, a bulk topological insulator with ideal properties”. Nature Communication 7, 2016. Print.
Li, J., et al.Two-dimensional chiral topological superconductivity in Shiba lattices”. Nature Communication 7, 12297, 2016. Print.
Das, P. K., et al.Layer-Dependent Quantum Cooperation of Electron and Hole States In the Anomalous Semimetal WTe2”. Nature Communication 7, 10847 2016. Print.
Li, J., et al.Manipulating Majorana Zero Modes on Atomic Rings With External Magnetic Field”. Nature Communication 7, 10395, 2016. Print.
Neupert, T., A. Yazdani, and B. A. Bernevig. “Shiba Chains of Scalar Impurities on Unconventional Superconductors”. Physical Review B 2016. Print.
Yazdani, A., E.H. Silva da Neto, and P. Aynajian. “Spectroscopic Imaging of Strongly Correlated Electronic States”. Annual Review of Condensed Matter Physics 7, 11, 2016. Print.
Kourtic, S., et al.Universal Signatures of Fermi Arcs in Quasiparticle Interference on the Surface of Weyi Semimetals”. Physical Review B Rapid Communication 2016. Print.
Kushwaha, S. K., et al.Bulk Crystal Growth and Electronic Characterization of the 3D Dirac Semimetal Na3Bi”. Applied Physics Letters Materials 3, 041504, 2015. Print.
Luo, H., et al.Polytypism, Polymorphism, and Superconductivity in TaSe2-x Tex”. Proceeding of National Academy of Sciences 112, no. 11, 2015. Print.
Yazdani, A.Visualizing Majorana Fermions in a Chain of Magnetic Atoms on a Superconductor”. Physical Scripta 2015. Print.

Proceedings of Nobel Symposium on Topological Phases of Matter

Kushwaha, S. K., et al.Bulk crystal growth and electronic characterization of the 3D Dirac semimetal Na3Bi”. Applied Physics Letters Materials 2015. Print.
Ali, M. N., et al.The Crystal and Electronic Structures of Cd3As2, the Three-Dimensional Electronic Analogue of Graphene”. Inorganic Chemistry 53, 4062-4067, 2014. Print.
Drozdov, I. K., et al.One-Dimensional Topological Edge States of Bismuth Bilayers”. Nature Physics 10, 663-669, 2014. Print.

Recommended for Journal Club for Condensed Matter Physics with a commentary by Leonid Glazman

da Neto, E.H. Silva, et al.Ubiquitous Interplay Between Charge Ordering and High-Temperature Superconductivity in Cuprates”. Science 343, 6169, pp. 393-396 2014. Print.
Aynajian, P., et al.Visualizing Heavy Fermion Formation and Their Unconventional Superconductivity in F-Electron Materials”. Journal of the Physical Society of Japan 2014. Print.
Jeon, S., et al.Landau Quantization and Quasiparticle Interference in the Three Dimensional Dirac Semimetal Cd3As2”. Nature Materials 13, 851-856, 2014. Print.
Nadj-Perge, S., et al.Observation of Majorana Fermions in Ferromagnetic Atomic Chains on a Superconductor”. Science 2014. Print.

Princeton University press release
YouTube movie showing how the experiment is performed
Also see perspective by Patrick Lee

Li, J., et al.Topological Superconductivity Induced by Ferromagnetic Metal Chains”. Physical Review B 90, 235433, 2014. Print.
Nadj-Perge, S., et al.Observation of Majorana fermions in ferromagnetic atomic chains on a superconductor”. Science 346, 6209, pp. 602-607, 2014. Print.
Misra, S., et al.Design and Performance of an Ultra-High Vacuum Scanning Tunneling Microscope Operating at Dilution Refrigerator Temperatures and High Magnetic Fields”. Review of Scientific Instruments 84, 103903 2013. Print.
da Neto, E.H. Silva, et al.Detection of Electronic Nematicity Using Scanning Tunneling Microscope”. Physical Review B 2013. Print.
Misra, S., et al.Measurements of the Magnetic-Field-Tuned Conductivity of Disordered Two-Dimensional Mo43Ge577 and InOx Superconducting Films: Evidence for a Universal Minimum Superfluid Response”. Physical Review Letters 110, 037002, 2013. Print.
Nadj-Perge, S., et al.Proposal for Realizing Majorana Fermions in Chains of Magnetic Atoms on a Superconductor”. Rapid Communications in Physical Review B 2013. Print.
Gyenis, A., et al.Quasiparticle Interference on the Surface of the Topological Crystalline Insulator Pb1-xSnxSe”. Physical Rewiew B 2013. Print.
Gibson, Q. D., et al.Termination-Dependent Topological Surface states of the Natural Superlattice Phase Bi4Se3”. Physical Review B 2013. Print.
Klinovaja, J., et al.Toplological Superconductivity and Majorana Fermions in RKKY Systems”. Physical Review Letters 111, 186805, 2013. Print.
Zhou, B. B., et al.Visualizing Nodal Heavy Fermion Superconductivity in CeCoIn5”. Nature Physics 9, 474-479, 2013. Print.

Also see News and Views by Louis Taillefer.
Work featured as the cover image of Nature Physics.
Also see 2Physics coverage.

Beidenkopf, H., P. Roushan, and A. Yazdani. “Visualizing Topological Surface States and Their Novel Properties Using Scanning Tunneling Microscopy and Spetroscopy”. Topological Insulators. Unknown: Elsevier, 2013. Print.
Yazdani, A.Visualizing Critical Correlations Near the Metal-Insulator Transition in Ga1-xMnxAs”. Conductor-Insulator Quantum Phase Transitions. Oxford University Press, 2012. 244-255. Print.
Jia, S., et al.Defects and High Bulk Resistivities in the Bi-Rich Tetradymite Topological Insulator Bi2+xTe2-xSe”. Physical Review B 2012. Print.
da Neto, E.H. Silva, et al.Detecting Incipient Stripe Order in the High-Temperature Superconductor Bi2SrsCaCu2O8+d”. Physica C 2012: , 481, 153. Print.
Zhang, D., et al.Interplay Between Ferromagnetism, Surface States, and Quantum Corrections in a Magnetically Doped Topological Insulator”. Physics Review B 2012. Print.
da Neto, E.H. Silva, et al.Scattering from Incipient Stripe Order in the High-Temperature Superconductor Bi2SrsCaCu2O8+d”. Physical Review B 2012. Print.
Yazdani, A.Topological Surface States: Science and Potential Applications”. SPIE 2012. Print.Abstract
Topological surface states are a new class of electronic states with novel properties. In this talk, I will review the properties of these novel quantum states and highlight some of their key properties that may be harnessed for potential applications. In particular, I will describe efforts in which combination of voltage controlled magnetism and topological surface states may be used to realize a novel low voltage transistor.
Aynajian, P., et al.Visualizing Heavy Fermions Emerging in a Quantum Critical Kondo Lattice”. Nature 486, 201, 2012. Print.
Beidenkopf, H., et al.Spatial Fluctuations of Helical Dirac Fermions on the Surface of Topological Insulators”. Nature Physics 2011: , 7, 939. Print.
Hor, Y. S., et al.Development of Ferromagnetism in the Doped Topological Insulator Bi2-xMnxTe3”. Physical Review B 2010. Print.
Parker, C. V., et al.Nanoscale Proximity Effect in the High Temperature Superconductor Bi2Sr2CaCu2O8+3”. Physical Review Letters 2010. Print.
Hor, Y. S., et al.Superconductivity in CuxBi2Se3 and Its Implications for Pairing in the Undoped Topological Insulator”. Physical Review Letters 2010. Print.
Richardella, A., et al.Visualizing critical correlations near the metal-insulator transition Ga1-xMnxAs”. Science 2010: , 327, 665. Print.
Aynajian, P., et al.Visualizing the Formation of the Kondo Lattice and the Hidden Order in URu2Si2”. PNAS 107, 10383-10388, 2010. Print.
Parker, C. V., et al.Fluctuating Stripes at the Onset of the Pseudogap in the High-Tc Supercondutor Bi2Sr2CaCu2O8+x”. Nature 468, 677, 2010. Print.
Seo, J., et al.Transimission of Topological Surface States Through Surface Barriers”. Nature 466, 343, 2010. Print.
Pushp, A., et al.Extending Universal Nodal Excitations Optimizes Superconductivity in Bi2Sr2CaCu2O8+3”. Science 2009: , 324, 1689. Print.
Richardella, A., D. Kitchen, and A. Yazdani. “Mapping the Wave Function of Transition Metal Acceptor States in the GaAs Surface”. Physical Review B 2009. Print.
Hor, Y. S., et al.p-Type Bi2Se3 for Topological Insulator and Low-Temperature Thermoelectric Applications”. Physical Review B 2009. Print.
Roushan, P., et al.Topological Surface States Protected From Backscattering by Chiral Spin Texture”. Nature 2009: , 460, 1106. Print.
Yazdani, A.Visualizing Pair Formation on the Atomic Scale and Search for the Mechanism Superconductivity in High-Tc Cuprates”. Journal of Physics: Condensed Matter 2009. Print.
Pasupathy, A. N., et al.Electronic Origin of the Inhomogeneous Pairing Interaction in the High-Tc Superconductor Bi2Sr2CaCu2O8+3”. Science 2008: , 320, 196. Print.
Hsieh, D., et al.Experimental Determination of the Microscopic Origin of Magnetism in Parent Iron Pnictides”. arXiv:0812.2289 [cond-mat.supr-con] 2008. Print.
Gomes, K. K., et al.Mapping of the Formation of the Pairing Gap in Bi2Sr2CaCu2O8+3”. Journal of Physics and Chemistry of Solids 2008: , 69, 3034-3038. Print.
Wray, L., et al.Momentum-Dependence of Superconducting Gap, Strong-Coupling Dispersion Kink, and Tightly Bound Cooper Pairs in the High-Tc (Sr,Ba)1-x(K-,Na)xFe2As2 Superconductors”. Physical Review B 2008. Print.
Gomes, K., et al.Gap Distributions and Spatial Variation of Electronic States in Superconducting and Pseudogap States of Bi2Sr2Ca2CuO8+3”. Physica C 2007: , 212, 460-462. Print.
Kitchen, D., et al.Hole-Mediated Interactions of Mn Acceptors on GaAs (110)”. Journal of Applied Physics 2007. Print.
Quay, C. H. L., et al.Transport Properties of Carbon Nanotube C60 Peapods”. Physical Review B 2007. Print.
Jura, M. P., et al.Unexpected Features of Branched Flow Through High Mobility Two-Dimensional Electron Gases”. Nature Physics 2007: , 3, 841. Print.
Gomes, K., et al.Visualizing Pair Formation on the Atomic Scale in the High-Tc Superconductor Bi2Sr2CaCu2O8+3”. Nature 2007: , 447, 569. Print.
Kitchen, D., et al.Atom-by-Atom Substitution of Mn in GaAs and Visualization of Their Hole-Mediated Interactions”. Nature 2006. Print.

Cover Story

Yazdani, A.Lean and Mean Superconductivity”. Nature Physics 2006: , 2, 151-152. Print.
Kitchen, D., A. Richardella, and A. Yazdani. “Spatial Structure of a Single Mn Impurity State on GaAs (110) Surface”. Journal of Superconductivity: Incorporating Novel Magnetism 2005: , 18, 23. Print.
Vershinin, M., et al.Electron Standing Waves on the Surface of Bi2Sr2Ca2CuO8+3”. Physica C 2004: , 408-410, 764-767. Print.
Misra, S., et al.Failure of Scattering Interference in the Pseudogap State of Cuprate Superconductors”. Physical Review B 2004. Print.
Vershinin, M., et al.Local Ordering in the Pseudogap State of the High-Tc Superconductor Bi2Sr2Ca2CuO8+3”. Science 2004: , 303, 1995. Print.
Chen, H.-D., et al.Pair Density Wave in the Pseudogap State of High Temperature Superconductors”. Physical Review Letters 2004. Print.
Yazdani, A., and E. J. Mele. “Probing Electronic Structure of Nanotube Peapods with the STM”. Applied Physics 2003: , 76, 469-474. Print.
Yazdani, A.Atomic scale imaging & spectroscopy of Fullerene peapods," Proceedings of the XVI International Winter School on Electronic Properties of Novel Materials”. IWEPNM 2002 2002: , 633, 113-117. Print.

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Misra, S., et al.Atomic Scale Imaging and Spectroscopy of a CuO2 Plane at the Surface of the High-Tc Superconductor Bi2Sr2Ca2CuO8+3”. Physical Review Letters 2002. Print.
Misra, S., et al.Formation of Andreev Bound State at the Step Edges of Bi2Sr2CaCu2O8 Surface”. Physical Review B 2002. Print.
Hornbaker, D. J., et al.Mapping the One-Dimensional Electronic States of Nanotube Peapod Structures”. Science 2002: , 295, 828-831. Print.

Cover Story

Kane, C. L., et al.Theory of Scanning Tunneling Spectroscopy of Fullerene Peapods”. Physical Review B 2002. Print.
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