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Coexisting Charge Density Wave and Superconducting Order in Quantizing Magnetic Fields
Authors:
Ron Q. Nguyen,
Peiyu Qin,
Hai-Tian Wu,
Sparsh Mishra,
Tobias Wolf,
Joseph Roll,
Erin Morissette,
Naiyuan J. Zhang,
Sarah Alkidim,
Kenji Watanabe,
Takashi Taniguchi,
Aaron W. Hui,
Dima E. Feldman,
Allan MacDonald,
J. I. A. Li
Abstract:
Charge density wave (CDW) and superconductivity are both common in strongly interacting electron systems. While CDW order is ubiquitous in both quantum Hall systems and unconventional superconductors, superconductivity is generally suppressed by the strong magnetic fields required for Landau quantization. Here we investigate the intertwined CDW and superconducting phases of rhombohedral hexalayer…
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Charge density wave (CDW) and superconductivity are both common in strongly interacting electron systems. While CDW order is ubiquitous in both quantum Hall systems and unconventional superconductors, superconductivity is generally suppressed by the strong magnetic fields required for Landau quantization. Here we investigate the intertwined CDW and superconducting phases of rhombohedral hexalayer graphene (R6G) in a large displacement field, which generates tunable flat band edges, and a strong magnetic field, which generates a manifold of nearly degenerate Landau levels. We find a series of integer quantum Hall effects with Hall conductance quantum numbers that deviate from nearby integer filling factors, an observation that can be explained only by CDW order that mixes many Landau levels. We also find a nearby superconducting phase stabilized by perpendicular magnetic fields and persists deep within the quantum Hall regime. This intertwinement provides new insight into superconductivity in R6G at zero magnetic field.
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Submitted 13 August, 2026; v1 submitted 6 July, 2026;
originally announced July 2026.
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Creating a three dimensional intrinsic electric dipole on rotated CrI$_3$ bilayers
Authors:
Shiva P. Poudel,
Juan M. Marmolejo-Tejada,
Joseph E. Roll,
Martín A. Mosquera,
Salvador Barraza-Lopez
Abstract:
Two-dimensional (2D) materials are being explored as a novel multiferroic platform. One of the most studied magnetoelectric multiferroic 2D materials are antiferromagnetically-coupled (AFM) CrI$_3$ bilayers. Neglecting magnetism, those bilayers possess a crystalline point of inversion, which is only removed by the antiparallel spin configuration among its two constituent monolayers. The resultant…
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Two-dimensional (2D) materials are being explored as a novel multiferroic platform. One of the most studied magnetoelectric multiferroic 2D materials are antiferromagnetically-coupled (AFM) CrI$_3$ bilayers. Neglecting magnetism, those bilayers possess a crystalline point of inversion, which is only removed by the antiparallel spin configuration among its two constituent monolayers. The resultant intrinsic electric dipole on those bilayers has a magnitude no larger than 0.04 pC/m, it points out-of-plane, and it reverts direction when the--Ising-like--cromium spins are flipped (toward opposite layers {\em versus} away from opposite layers). The combined presence of antiferromagnetism and a weak intrinsic electric dipole makes this material a two-dimensional magnetoelectric multiferroic. Here, we remove the crystalline center of inversion of the bilayer by a relative $60^{\circ}$ rotation of its constituent monolayers. This process {\em enhances} the out-of-plane intrinsic electric dipole tenfold with respect to its magnitude in the non-rotated AFM bilayer and also creates an even stronger and switchable in-plane intrinsic electric dipole. The ability to create a three-dimensional electric dipole is important, because it enhances the magnetoelectric coupling on this experimentally accessible 2D material, which is explicitly calculated here as well.
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Submitted 1 May, 2023;
originally announced May 2023.
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Slippery paraelectric transition metal dichalcogenide bilayers
Authors:
Juan M. Marmolejo-Tejada,
Joseph E. Roll,
Shiva Prasad Poudel,
Salvador Barraza-Lopez,
Martin A. Mosquera
Abstract:
Traditional ferroelectrics undergo thermally-induced phase transitions whereby their structural symmetry increases. The associated higher-symmetry structure is dubbed {\em paraelectric}. Ferroelectric transition metal dichalcogenide bilayers have been recently shown to become paraelectric, but not much has been said of the atomistic configuration of such a phase. As discovered through numerical ca…
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Traditional ferroelectrics undergo thermally-induced phase transitions whereby their structural symmetry increases. The associated higher-symmetry structure is dubbed {\em paraelectric}. Ferroelectric transition metal dichalcogenide bilayers have been recently shown to become paraelectric, but not much has been said of the atomistic configuration of such a phase. As discovered through numerical calculations that include molecular dynamics here, their paraelectricity can only be ascribed to a time average of ferroelectric phases with opposing intrinsic polarizations, whose switching requires macroscopically large areas to slip in unison.
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Submitted 28 September, 2022;
originally announced September 2022.
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Elasticity of 2D ferroelectrics across their paraelectric phase transformation
Authors:
Joseph E. Roll,
John M. Davis,
John W. Villanova,
Salvador Barraza-Lopez
Abstract:
The mechanical behavior of two-dimensional (2D) materials across 2D phase changes is unknown, and the finite temperature ($T$) elasticity of paradigmatic SnSe monolayers -- ferroelectric 2D materials turning paraelectric as their unit cell (u.c.) turns from a rectangle onto a square -- is described here in a progressive manner. To begin with, their zero$-T$ {\em elastic energy landscape} gives way…
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The mechanical behavior of two-dimensional (2D) materials across 2D phase changes is unknown, and the finite temperature ($T$) elasticity of paradigmatic SnSe monolayers -- ferroelectric 2D materials turning paraelectric as their unit cell (u.c.) turns from a rectangle onto a square -- is described here in a progressive manner. To begin with, their zero$-T$ {\em elastic energy landscape} gives way to (Boltzmann-like) averages from which the elastic behavior is determined. These estimates are complemented with results from the strain-fluctuation method, which employs the energy landscape or {\em ab initio} molecular dynamics (MD) data. Both approaches capture the coalescence of elastic moduli $\langle C_{11}(T)\rangle=\langle C_{22}(T)\rangle$ due to the structural transformation. The broad evolution and sudden changes of elastic parameters $\langle C_{11}(T)\rangle$, $\langle C_{22}(T)\rangle$, and $\langle C_{12}(T)\rangle$ of these atomically-thin phase-change membranes establishes a heretofore overlooked connection among 2D materials and soft matter.
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Submitted 15 March, 2022;
originally announced March 2022.
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Magnetic Topological Semimetal Phase with Electronic Correlation Enhancement in SmSbTe
Authors:
Krishna Pandey,
Debashis Mondal,
John William Villanova,
Joseph Roll,
Rabindra Basnet,
Aaron Wegner,
Gokul Acharya,
Md Rafique Un Nabi,
Barun Ghosh,
Jun Fujii,
Jian Wang,
Bo Da,
Amit Agarwal,
Ivana Vobornik,
Antonio Politano,
Salvador Barraza-Lopez,
Jin Hu
Abstract:
The ZrSiS family of compounds hosts various exotic quantum phenomena due to the presence of both topological nonsymmorphic Dirac fermions and nodal-line fermions. In this material family, the LnSbTe (Ln= lanthanide) compounds are particularly interesting owing to the intrinsic magnetism from magnetic Ln which leads to new properties and quantum states. In this work, the authors focus on the previo…
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The ZrSiS family of compounds hosts various exotic quantum phenomena due to the presence of both topological nonsymmorphic Dirac fermions and nodal-line fermions. In this material family, the LnSbTe (Ln= lanthanide) compounds are particularly interesting owing to the intrinsic magnetism from magnetic Ln which leads to new properties and quantum states. In this work, the authors focus on the previously unexplored compound SmSbTe. The studies reveal a rare combination of a few functional properties in this material, including antiferromagnetism with possible magnetic frustration, electron correlation enhancement, and Dirac nodal-line fermions. These properties enable SmSbTe as a unique platform to explore exotic quantum phenomena and advanced functionalities arising from the interplay between magnetism, topology, and electronic correlations.
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Submitted 24 August, 2021;
originally announced August 2021.