@article { WOS:000711685600005,
title = {Acoustic-Phonon-Mediated Superconductivity in Rhombohedral Trilayer Graphene},
journal = {Phys. Rev. Lett.},
volume = {127},
number = {18},
year = {2021},
month = {OCT 29},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {Motivated by the observation of two distinct superconducting phases in the moireless ABC-stacked rhombohedral trilayer graphene, we investigate the electron-acoustic-phonon coupling as a possible pairing mechanism. We predict the existence of superconductivity with the highest T-c similar to 3 K near the Van Hove singularity. Away from the Van Hove singularity, T-c remains finite in a wide range of doping. In our model, the s-wave spin-singlet and f-wave spin-triplet pairings yield the same T-c, while other pairing states have negligible T-c. Our theory provides a simple explanation for the two distinct superconducting phases in the experiment and suggests that superconductivity and other interaction-driven phases (e.g., ferromagnetism) can have different origins.},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.127.187001},
author = {Chou, Yang-Zhi and Wu, Fengcheng and Sau, Jay D. and Das Sarma, Sankar}
}
@article { WOS:000722573400002,
title = {Band manipulation and spin texture in interacting moire helical edges},
journal = {Phys. Rev. B},
volume = {104},
number = {20},
year = {2021},
month = {NOV 23},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We develop a theory for manipulating the effective band structure of interacting helical edge states realized on the boundary of two-dimensional time-reversal symmetric topological insulators. For a sufficiently strong interaction, an interacting edge band gap develops, spontaneously breaking time-reversal symmetry on the edge. The resulting spin texture, as well as the energy of the time-reversal breaking gaps, can be tuned by an external moire potential (i.e., a superlattice potential). Remarkably, we establish that by tuning the strength and period of the potential, the interacting gaps can be fully suppressed and interacting Dirac points reemerge. In addition, nearly flat bands can be created by the moire potential with a sufficiently long period. Our theory provides an unprecedented way to enhance the coherence length of interacting helical edges by suppressing the interacting gap. The implications of this finding for ongoing experiments on helical edge states is discussed.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.104.L201113},
author = {Chou, Yang-Zhi and Cano, Jennifer and Pixley, J. H.}
}
@article { WOS:000678812000001,
title = {Charge density wave and finite-temperature transport in minimally twisted bilayer graphene},
journal = {Phys. Rev. B},
volume = {104},
number = {4},
year = {2021},
month = {JUL 28},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We study phenomena driven by electron-electron interactions in the minimally twisted bilayer graphene (mTBLG) with a perpendicular electric field. The low-energy degrees of freedom in mTBLG are governed by a network of one-dimensional domain-wall states, described by two channels of one-dimensional linearly dispersing spin-1/2 fermions. We show that the interaction can realize a spin-gapped interchannel charge density wave (CDW) state at low temperatures, forming a {\textquoteleft}{\textquoteleft}Coulomb drag{{\textquoteright}{\textquoteright}} between the channels and leaving only one charge conducting mode. For sufficiently high temperatures, power-law-in-temperature resistivity emerges from the charge Umklapp scatterings within a domain wall. Remarkably, the presence of the CDW states can strengthen the charge Umklapp scattering and induce a resistivity minimum at an intermediate temperature corresponding to the CDW correlation energy. We further discuss the conditions that resistivity of the network is dominated by the domain walls. In particular, the power-law-in-temperature resistivity results can apply to other systems that manifest topological domain-wall structures.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.104.045146},
author = {Chou, Yang-Zhi and Wu, Fengcheng and Sau, Jay D.}
}
@article { WOS:000720123400004,
title = {Correlation-Induced Triplet Pairing Superconductivity in Graphene-Based Moire {\textquoteleft} Systems},
journal = {Phys. Rev. Lett.},
volume = {127},
number = {21},
year = {2021},
month = {NOV 15},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {Motivated by the possible non-spin-singlet superconductivity in the magic-angle twisted trilayer graphene experiment, we investigate the triplet-pairing superconductivity arising from a correlationinduced spin-fermion model of Dirac fermions with spin, valley, and sublattice degrees of freedom. We find that the f-wave pairing is favored due to the valley-sublattice structure, and the superconducting state is time-reversal symmetric, fully gapped, and nontopological. With a small in-plane magnetic field, the superconducting state becomes partially polarized, and the transition temperature can be slightly enhanced. Our results apply qualitatively to Dirac fermions for the triplet-pairing superconductivity in graphene-based moire systems, which is fundamentally distinct from triplet superconductivity in 3He and ferromagnetic superconductors.},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.127.217001},
author = {Chou, Yang-Zhi and Wu, Fengcheng and Sau, Jay D. and Das Sarma, Sankar}
}
@article { WOS:000664572100002,
title = {Coulomb drag in topological wires separated by an air gap},
journal = {Nat. Electron.},
volume = {4},
number = {8},
year = {2021},
month = {AUG},
pages = {573-578},
publisher = {NATURE PORTFOLIO},
type = {Article},
abstract = {Measurements of one-dimensional Coulomb drag between adjacent edge states of quantum spin Hall insulators that are separated by an air gap suggest that quantum spin Hall effects could be used to suppress the impact of Coulomb interactions on the performance of future nanocircuits. Strong electron-electron interactions between adjacent nanoscale wires can lead to one-dimensional Coulomb drag, where current in one wire induces a voltage in the second wire via Coulomb interactions. This effect creates challenges for the development of nanoelectronic devices. Quantum spin Hall (QSH) insulators are a promising platform for the development of low-power electronic devices due to their topological protection of edge states from non-magnetic disorder. However, although Coulomb drag in QSH edges has been considered theoretically, experimental explorations of the effect remain limited. Here, we show that one-dimensional Coulomb drag can be observed between adjacent QSH edges that are separated by an air gap. The pair of one-dimensional helical edge states is created in split H-bar devices in inverted InAs/GaSb quantum wells. Near the Dirac point, negative drag signals dominate at low temperatures and exhibit a non-monotonic temperature dependence, suggesting that distinct drag mechanisms compete and cancel out at higher temperatures. The results suggest that QSH effects could be used to suppress the impact of Coulomb interactions on the performance of future nanocircuits.},
issn = {2520-1131},
doi = {10.1038/s41928-021-00603-y},
author = {Du, Lingjie and Zheng, Jianmin and Chou, Yang-Zhi and Zhang, Jie and Wu, Xingjun and Sullivan, Gerard and Ikhlassi, Amal and Du, Rui-Rui}
}
@article {chou_marginally_2021,
title = {Marginally localized edges of time-reversal symmetric topological superconductors},
journal = {Phys. Rev. B},
volume = {103},
number = {7},
year = {2021},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {feb},
abstract = {We demonstrate that the one-dimensional helical Majorana edges of two-dimensional time-reversal symmetric topological superconductors (class DIII) can become gapless and insulating by a combination of random edge velocity and interaction. Such a gapless insulating edge breaks time-reversal symmetry inhomogeneously, and the local symmetry broken regions can be regarded as static mass potentials or dynamical Ising spins. In both limits, we find that such gapless insulating Majorana edges are generically exponentially localized and trap Majorana zero modes. Interestingly, for a statistically time-reversal symmetric edge (symmetry is broken locally, but the symmetry breaking order parameter is zero on average), the low-energy theory can be mapped to a Dyson model at zero energy, manifesting a diverging density of states and exhibiting marginal localization (i.e., a diverging localization length). Although the ballistic edge state transport is absent, the localized Majorana zero modes reflect the nontrivial topology in the bulk. Experimental signatures are also discussed.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.103.075120},
author = {Chou, Yang-Zhi and Nandkishore, Rahul M.}
}
@article { ISI:000507863600003,
title = {Anomalous localization at the boundary of an interacting topological insulator},
journal = {Phys. Rev. B},
volume = {101},
number = {3},
year = {2020},
month = {JAN 17},
pages = {035131},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {The boundary of a topological insulator (TI) hosts an anomaly restricting its possible phases: e.g., three-dimensional (3D) strong and weak TIs maintain surface conductivity at any disorder if symmetry is preserved on average at least when electron interactions on the surface are weak. However, the interplay of strong interactions and disorder with the boundary anomaly has not yet been theoretically addressed. Here we study this combination for the edge of a two-dimensional TI and the surface of a 3D weak TI, showing how it can lead to an {\textquoteleft}{\textquoteleft}Anomalous Many Body Localized{{\textquoteright}{\textquoteright}} (AMBL) phase that preserves the anomaly. We discuss how the anomalous Kramers parity switching with pi flux arises in the bosonized theory of the localized helical state. The anomaly can be probed in localized boundaries by electrostatically sensing nonlinear hopping transport with e/2 shot noise. Our AMBL construction in 3D weak TIs fails for 3D strong TIs, which suggests that their anomaly restrictions are distinguished by strong interactions.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.101.035131},
author = {Kimchi, Itamar and Chou, Yang-Zhi and Nandkishore, Rahul M. and Radzihovsky, Leo}
}
@article { ISI:000562933100003,
title = {Finite-temperature spectroscopy of dirty helical Luttinger liquids},
journal = {Phys. Rev. B},
volume = {102},
number = {8},
year = {2020},
month = {AUG 27},
pages = {085152},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We develop a theory of finite-temperature momentum-resolved tunneling spectroscopy (MRTS) for disordered, interacting, two-dimensional, topological-insulator edges. The MRTS complements conventional electrical transport measurement in characterizing the properties of the helical Luttinger liquid edges. Using the standard bosonization technique, we study low-energy spectral function and the MRTS tunneling current, providing a detailed description controlled by disorder, interaction, and temperature, taking into account Rashba spin-orbit coupling, interedge interaction, and distinct edge velocities. Our theory provides a systematic description of the spectroscopic signals in the MRTS measurement we hope will stimulate future experimental studies on the two-dimensional time-reversal invariant topological insulator.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.102.085152},
author = {Hsieh, Tzu-Chi and Chou, Yang-Zhi and Radzihovsky, Leo}
}
@article {chou_hofstadter_2020,
title = {Hofstadter butterfly and {Floquet} topological insulators in minimally twisted bilayer graphene},
journal = {Phys. Rev. Res.},
volume = {2},
number = {3},
year = {2020},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {aug},
abstract = {We theoretically study the Hofstadter butterfly of a triangular network model in minimally twisted bilayer graphene. The band structure manifests periodicity in energy, mimicking that of Floquet systems. The butterfly diagrams provide fingerprints of the model parameters and reveal the hidden band topology. In a strong magnetic field, we establish that minimally twisted bilayer graphene realizes low-energy Floquet topological insulators (FTIs) carrying zero Chern number, while hosting chiral edge states in bulk gaps. We identify the FTIs by analyzing the nontrivial spectral flow in the Hofstadter butterfly, and by explicitly computing the chiral edge states. Our theory paves the way for an effective practical realization of FTIs in equilibrium solid-state systems.},
doi = {10.1103/PhysRevResearch.2.033271},
author = {Chou, Yang-Zhi and Wu, Fengcheng and Das Sarma, Sankar}
}
@article { ISI:000575114800001,
title = {Magic-angle semimetals},
journal = {npj Quantum Mater.},
volume = {5},
number = {1},
year = {2020},
month = {OCT 6},
pages = {71},
publisher = {NATURE RESEARCH},
type = {Article},
abstract = {Breakthroughs in two-dimensional van der Waals heterostructures have revealed that twisting creates a moire pattern that quenches the kinetic energy of electrons, allowing for exotic many-body states. We show that cold atomic, trapped ion, and metamaterial systems can emulate the effects of a twist in many models from one to three dimensions. Further, we demonstrate at larger angles (and argue at smaller angles) that by considering incommensurate effects, the magic-angle effect becomes a single-particle quantum phase transition (including in a model for twisted bilayer graphene in the chiral limit). We call these models {\textquoteleft}{\textquoteleft}magic-angle semimetals{{\textquoteright}{\textquoteright}}. Each contains nodes in the band structure and an incommensurate modulation. At magic-angle criticality, we report a nonanalytic density of states, flat bands, multifractal wave functions that Anderson delocalize in momentum space, and an essentially divergent effective interaction scale. As a particular example, we discuss how to observe this effect in an ultracold Fermi gas.},
doi = {10.1038/s41535-020-00271-9},
author = {Fu, Yixing and Konig, Elio J. and Wilson, Justin H. and Chou, Yang-Zhi and Pixley, Jedediah H.}
}
@article {chou_magic-angle_2020,
title = {Magic-angle semimetals with chiral symmetry},
journal = {Phys. Rev. B},
volume = {101},
number = {23},
year = {2020},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {jun},
abstract = {We construct and solve a two-dimensional, chirally symmetric model of Dirac cones subjected to a quasiperiodic modulation. In real space, this is realized with a quasiperiodic hopping term. This hopping model, as we show, at the Dirac node energy has a rich phase diagram with a semimetal-to-metal phase transition at intermediate amplitude of the quasiperiodic modulation, and a transition to a phase with a diverging density of states (DOS) and subdiffusive transport when the quasiperiodic hopping is strongest. We further demonstrate that the semimetal-to-metal phase transition can be characterized by the multifractal structure of eigenstates in momentum space and can be considered as a unique {\textquotedblleft}unfreezing{\textquotedblright} transition. This unfreezing transition in momentum space generates flat bands with a dramatically renormalized bandwidth in the metallic phase similar to the phenomena of the band structure of twisted bilayer graphene at the magic angle. We characterize the nature of this transition numerically as well as analytically in terms of the formation of a band of topological zero modes. For pure quasiperiodic hopping, we provide strong numerical evidence that the low-energy DOS develops a divergence and the eigenstates exhibit Chalker (quantum-critical) scaling despite the model not being random. At particular commensurate limits the model realizes higher-order topological insulating phases. We discuss how these systems can be realized in experiments on ultracold atoms and metamaterials.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.101.235121},
author = {Chou, Yang-Zhi and Fu, Yixing and Wilson, Justin H. and Konig, E. J. and Pixley, J. H.}
}
@article { ISI:000517213700002,
title = {Nonmonotonic plasmon dispersion in strongly interacting Coulomb Luttinger liquids},
journal = {Phys. Rev. B},
volume = {101},
number = {7},
year = {2020},
month = {FEB 27},
pages = {075430},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We demonstrate that the plasmon in one-dimensional Coulomb interacting electron fluids can develop a finite-momentum maxon-roton-like nonmonotonic energy-momentum dispersion. Such an unusual nonmonotonicity arises from the strongly interacting 1/r Coulomb potential going beyond the conventional band linearization approximation used in the standard bosonization theories of Luttinger liquids. We provide details for the nonmonotonic plasmon dispersion using both bosonization and random-phase approximation theories. We also calculate the specific heat including the nonmonotonicity and discuss possibilities for observing the nonmonotonic plasmon dispersion in various physical systems, including semiconductor quantum wires, carbon nanotubes, and the twisted bilayer graphene at subdegree twist angles, which naturally realize one-dimensional domain-wall states. We provide results for several different models of long-range interaction showing that the nonomonotonic charge collective mode dispersion is a generic phenomenon in one-dimensional strongly interacting electron systems.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.101.075430},
author = {Chou, Yang-Zhi and Das Sarma, Sankar}
}
@article {ISI:000485761800002,
title = {Superconductor versus insulator in twisted bilayer graphene},
journal = {Phys. Rev. B},
volume = {100},
number = {11},
year = {2019},
month = {SEP 13},
pages = {115128},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We present a simple model that we believe captures the key aspects of the competition between superconducting and insulating states in twisted bilayer graphene. Within this model, the superconducting phase is primary, and arises at generic fillings, but is interrupted by the insulator at commensurate fillings. Importantly, the insulator forms because of electron-electron interactions, but the model is agnostic as to the superconducting pairing mechanism, which need not originate with electron-electron interactions. The model is composed of a collection of crossed one-dimensional quantum wires whose intersections form a superlattice. At each superlattice point, we place a locally superconducting puddle which can exchange Cooper pairs with the quantum wires. We analyze this model assuming weak wire-puddle and wire-wire couplings. We show that for a range of repulsive intrawire interactions, the system is superconducting at {\textquoteleft}{\textquoteleft}generic{{\textquoteright}{\textquoteright}} incommensurate fillings, with the superconductivity being {\textquoteleft}{\textquoteleft}interrupted{{\textquoteright}{\textquoteright}} by an insulating phase at commensurate fillings. We further show that the gapped insulating states at commensurate fillings give way to gapless states upon application of external Zeeman fields. These features are consistent with experimental observations in magic-angle twisted bilayer graphenes despite the distinct microscopic details. We further study the full phase diagram of this model and discover that it contains several distinct correlated insulating states, which we characterize herein.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.100.115128},
author = {Chou, Yang-Zhi and Lin, Yu-Ping and S. Das Sarma and Nandkishore, Rahul M.}
}
@article {ISI:000402467200001,
title = {Single-particle excitations in disordered Weyl fluids},
journal = {PHYSICAL REVIEW B},
volume = {95},
number = {23},
year = {2017},
month = {JUN 1},
pages = {235101},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We theoretically study the single-particle Green function of a three-dimensional disordered Weyl semimetal using a combination of techniques. These include analytic T-matrix and renormalization group methods with complementary regimes of validity and an exact numerical approach based on the kernel polynomial technique. We show that at any nonzero disorder, Weyl excitations are not ballistic: They instead have a nonzero linewidth that for weak short-range disorder arises from nonperturbative resonant impurity scattering. Perturbative approaches find a quantum critical point between a semimetal and a metal at a finite disorder strength, but this transition is avoided due to nonperturbative effects. At moderate disorder strength and intermediate energies the avoided quantum critical point renormalizes the scaling of single-particle properties. In this regime we compute numerically the anomalous dimension of the fermion field and find eta = 0.13 +/- 0.04, which agrees well with a renormalization group analysis (eta = 0.125). Our predictions can be directly tested by ARPES and STM measurements in samples dominated by neutral impurities.}, \%\%Address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},
issn = {2469-9950},
doi = {10.1103/PhysRevB.95.235101},
author = {Pixley, J. H. and Chou, Yang-Zhi and Goswami, Pallab and Huse, David A. and Nandkishore, Rahul and Radzihovsky, Leo and S. Das Sarma}
}