Strongly Enhanced Tunneling at Total Charge Neutrality in Double-Bilayer Graphene-
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 Heterostructures

Burg, G. William; Prasad, Nitin; Kim, Kyounghwan; Taniguchi, Takashi; Watanabe, Kenji; MacDonald, Allan H.; Register, Leonard F.; Tutuc, Emanuel

doi:10.1103/physrevlett.120.177702

Cited by 133 publications

(108 citation statements)

References 34 publications

(41 reference statements)

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“…Such systems rely on high external magnetic fields. A recent experiment studying double-bilayer graphene systems has, however, been able to detect the enhanced zero-bias tunneling conductance signature of indirect exciton condensation without any magnetic field, by controlling the electron and hole populations through gate voltages [53]. This is an indication of the possible existence of an exciton condensate, and shows promise for finding a magnetic-field free exciton condensate.…”

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confidence: 99%

Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

et al. 2019

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Electrons and holes residing on the opposing sides of an insulating barrier and experiencing an attractive Coulomb interaction can spontaneously form a coherent state known as an indirect exciton condensate. We study a trilayer system where the barrier is an antiferromagnetic insulator. The electrons and holes here additionally interact via interfacial coupling to the antiferromagnetic magnons. We show that by employing magnetically uncompensated interfaces, we can design the magnon-mediated interaction to be attractive or repulsive by varying the thickness of the antiferromagnetic insulator by a single atomic layer. We derive an analytical expression for the critical temperature T c of the indirect exciton condensation. Within our model, anisotropy is found to be crucial for achieving a finite T c , which increases with the strength of the exchange interaction in the antiferromagnetic bulk. For realistic material parameters, we estimate T c to be around 7 K, the same order of magnitude as the current experimentally achievable exciton condensation where the attraction is solely due to the Coulomb interaction. The magnon-mediated interaction is expected to cooperate with the Coulomb interaction for condensation of indirect excitons, thereby providing a means to significantly increase the exciton condensation temperature range.Introduction.-Interactions between fermions result in exotic states of matter. Superconductivity is a prime example, where the negatively charged electrons can have an overall attractive coupling mediated by individual couplings to the vibrations, known as phonons, of the positively charged lattice. In addition to charge, the electron also has a spin degree of freedom. The electron spin can interact with localized magnetic moments through an exchange interaction exciting the magnetic moment by transfer of angular momentum. These excitations are quasiparticles known as magnons. Theoretical predictions of electron-magnon interactions have shown that these can also induce effects such as superconductivity [1][2][3][4][5][6][7][8][9][10].Research interest in antiferromagnetic materials is surging [11,12]. This enthusiasm is due to the promising properties of antiferromagnets such as high resonance frequencies in the THz regime and a vanishing net magnetic moment. Much of this research focuses on interactions involving magnons or spin waves at magnetic interfaces in hybrid structures. Examples of this are spin pumping [13-19], spin transfer [15, 20-22], and spin Hall magnetoresistance [23-28] at normal metal interfaces, and magnon-mediated superconductivity [9,10]. Recently, an experiment has also demonstrated spin transport in an antiferromagnetic insulator over distances up to 80 µm [29]. Moreover, antiferromagnetic materials are also of interest since it is believed that high-temperature superconductivity in cuprates is intricately linked to magnetic fluctuations near an antiferromagnetic Mott insulating phase [30,31]. Thus it is crucial to achieve a good understanding of antiferromagnetic magn...

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Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

et al. 2019

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“…QSH effect is also predicted in graphene interacting with single crystal WS 2 or WSe 2 . Experimentally, such heterostructures show promising features with a substantial enhancement in the spin–orbit coupling strength in graphene …”

Section: Creating Quantum Spin Hall States In Graphenementioning

confidence: 75%

Quantum Spin Hall Materials

Cao

Chen

2019

Adv Quantum Tech

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The quantum spin Hall (QSH) effect describes the state of matter in certain 2D electron systems, in which an insulating bulk state arises together with helical states at the edge of the sample. In stark contrast to its closest kin, the integer quantum Hall state, the QSH state exists only in time‐reversal symmetric system (e.g., in non‐magnetic materials and without the application of external magnetic field). This article reviews the development of the understanding and construction of the QSH states after their first theoretical proposal, with an emphasis on the materials perspective. Certain semiconductor quantum wells and 2D materials with strong spin–orbit coupling have been found to support QSH states.

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“…In order to reduce the electron–hole recombination rate it was suggested to use a system where electrons and holes are spatially separated. Examples of this are bilayer quantum well (QW) systems, topological EIs, double 2D electron gases in a strong magnetic field, two parallel, independently gated graphene monolayers separated by a finite insulating barrier, and very recently two bilayer graphene electron systems separated by hexagonal BN or WSe 2 …”

Section: Introductionmentioning

confidence: 99%

Quantum Transport Properties of an Exciton Insulator/Superconductor Hybrid Junction

2018

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A theoretical study of electronic transport in a hybrid junction consisting of an excitonic insulator sandwiched between a normal and a superconducting electrode is presented. The normal region is described as a two‐band semi‐metal and the superconducting lead as a two‐band superconductor. In the excitonic insulator region, the coupling between carriers in the two bands leads to an excitonic condensate and a gap Γ in the quasi‐particle spectrum. Four different scattering processes at both interfaces are identified: Two types of normal reflection, intra‐ and inter‐band; and two different Andreev reflections, one retro‐reflective within the same band and one specular reflective between the two bands. The differential conductance of the structure is calculated and the existence of a minimum at voltages of the order of the excitonic gap is shown. The findings are useful toward the detection of the excitonic condensate and provide a plausible explanation for recent transport experiments on HgTe quantum wells and InAs/GaSb bilayer systems.

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Strongly Enhanced Tunneling at Total Charge Neutrality in Double-Bilayer Graphene- WSe2 Heterostructures

Cited by 133 publications

References 34 publications

Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

Quantum Spin Hall Materials

Quantum Transport Properties of an Exciton Insulator/Superconductor Hybrid Junction

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