Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F60: Correlated States IFocus Recordings Available
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Chair: Andrey Baydin, Rice University Room: Hyatt Regency Hotel -DuSable C |
Tuesday, March 15, 2022 8:00AM - 8:36AM |
F60.00001: Quantum anomalous Hall and magnetic insulating states in semiconductor moiré material Invited Speaker: Shengwei Jiang Electron correlation and topology are two central threads of modern condensed matter physics. Semiconductor moiré materials provide a highly tunable platform for studies of electron correlation. Here we report the observation of the electric-field-induced transition from a Mott insulator to a quantum anomalous Hall state and correlated magnetic insulating states in AB-stacked MoTe2/WSe2 moiré heterobilayers. An out-of-plane electric field controls bandwidth, charge transfer gap, and thus the band topology by intertwining moiré bands centered at different high symmetry stacking sites. At half band filling, we observe a series of correlated and topological electronic states, including Mott insulator, quantum anomalous Hall, and magnetic insulator. Our study paves the path for the discovery of a wealth of emergent phenomena arising from the combined influence of strong correlation and topology in semiconductor moiré materials. |
Tuesday, March 15, 2022 8:36AM - 8:48AM |
F60.00002: Imaging gate-tunable Tomonaga-Luttinger liquids in 1H-MoSe2 mirror twin boundaries Tiancong Zhu, Wei Ruan, Yanqi Wang, Hsin-zon Tsai, Shuopei Wang, Canxun Zhang, Tianye Wang, Franklin Liou, Kenji Watanabe, Takashi Taniguchi, Jeffrey B Neaton, Alex Weber-Bargioni, Alex K Zettl, Zi Q. Qiu, Guangyu Zhang, feng wang, Joel E Moore, Michael F Crommie Naturally-occurring grain boundaries in single-layer semiconducting transition metal dichalcogenides provide 1D conducting channels that have been proposed to host Tomonaga-Luttinger liquids due to electron-electron interactions, but charge density wave physics has also been suggested to explain their behavior. Clear identification of the electronic ground state of this system has been hampered by an inability to electrostatically gate these interface states and thereby tune their charge carrier concentration. We present a scanning tunneling microscopy/spectroscopy (STM/STS) study of gate-tunable mirror twin boundaries (MTBs) in single-layer 1H-MoSe2 devices. Gating enables STM spectroscopy to be performed for different MTB electron densities, thus allowing precise characterization of electron-electron interaction parameters. Visualization of MTB electronic structure under these conditions allows unambiguous identification of collective density wave excitations having two distinct velocities, in quantitative agreement with the spin-charge separation predicted by finite-length Tomonaga-Luttinger-liquid theory. |
Tuesday, March 15, 2022 8:48AM - 9:00AM |
F60.00003: Many-body exciton and inter-valley correlations in heavily electron-doped WSe2 monolayers Scott A Crooker, Mateusz M Goryca, Jing Li, Xiaodong Xu, Junho Choi In monolayer transition-metal dichalcogenide semiconductors, many-body correlations can manifest in optical spectra when photoexcited electron-hole pairs (excitons) are introduced into a 2D Fermi sea of mobile carriers. At low background electron and hole densities, the formation of negatively and positively charged excitons (X-, X+) is well documented. However, in WSe2 monolayers an additional strong absorption resonance, often called X-' , emerges at higher electron doping. Its origin is not understood. Here we investigate the nature of the X-' state, via polarized absorption spectroscopy of electrostatically-gated WSe2 monolayers in high magnetic fields to 60 T. Field-induced filling and emptying of the lowest optically-active Landau level in the K' valley leads to repeated quenching of the corresponding optical absorption. Surprisingly, however, these quenchings are accompanied by changes in the absorption to higher-lying Landau levels in both the K' and K valleys, which are unoccupied. These results cannot be reconciled within a single particle picture, and demonstrate the many-body nature and inter-valley correlations of the X-' quasiparticle state. |
Tuesday, March 15, 2022 9:00AM - 9:12AM |
F60.00004: Electron-Lattice Coupling in 2D Transition Metal Dihalides MX2 and Trihalides MX3 Alexandru Bogdan Georgescu, Andrew J Millis, James M Rondinelli The range of phenomena allowed in a correlated material is determined by an interplay between the lattice structure and electronic physics, with the roles of the two often the topic of debate. |
Tuesday, March 15, 2022 9:12AM - 9:24AM |
F60.00005: Confined monolayer Ag as a large gap 2D semiconductor and its quasiparticle interactions with high-density Dirac electrons Woojoo Lee, Yuanxi Wang, Hyunsue Kim, Mengke Liu, Timothy N Nunley, Bin Fang, Rinu Maniyara, Chengye Dong, Joshua A Robinson, Vincent H Crespi, Xiaoqin (Elaine) Li, Allan H MacDonald, Chih-Kang Shih 2D materials have been spotlighted due to their intriguing quantum phenomena distinctive from their bulk counterparts as shown in graphene, transition metal dichalcogenides (TMDs), or other 2D families. On top of that, epitaxially synthesized wafer-scale 2D metals, composed of elemental atoms, are recently attracting attention not only for their future applications but also for exotic quantum effects such as superconductivity [1]. It was theoretically predicted that, unlike its conductive bulk form, the monolayer In and Ag have a gapped electronic structure. Here, we utilize time- and angle-resolved photoemission spectroscopy (trARPES) to reveal the unoccupied electronic structure of monolayer Ag and verify its gapped feature. The gap size was measured to be ~ 1eV and, along with valence band dispersion, it showed a good agreement with GW corrected DFT calculations. In addition, interestingly, we observed a strong mass enhancement of the Γ point conduction band, a factor of 2.6 larger than the theoretical prediction. We attribute this massive renormalization of the conduction band dispersion to the high-density Dirac electrons (~ 4 × 1013/cm2) of the capping bilayer graphene. |
Tuesday, March 15, 2022 9:24AM - 9:36AM |
F60.00006: Charged bosons made of fermions in bilayer structures near metallic surfaces Igor V Bondarev, David W Snoke In 1996, V.I.Yudson proposed the existence of stable four-carrier complexes in bilayer semiconductors, which may be called "quaternions". If a bilayer semiconductor structure is placed parallel to a nearby metal layer, then under optical pumping an interlayer exciton can be created, which picks up two free same-layer electrons (or two holes). Due to image charge below the metal surface, much of the repulsive interaction in such a complex is canceled out, to make a stable charged boson state of four fermions. Such a quaternion complex is recently observed in PL spectroscopy experiments on doped bilayer TMD structures placed near the Nb surface at a distance controlled by extra hBN separation layers[1]. To explain these experiments, we develop the theory for a variant of the Yudson geometry, which is structurally a trion in one layer bound to a free like-charge carrier in the parallel layer. The calculations we discuss are consistent with experimental observations. A Bose-Einstein condensate of such quaternions would be a Schafroth superconductor ─ a collective multiparticle superfluid state of doubly charged bosons, a state not requiring Cooper pairing, to open up the door to a new kind of unconventional high-T superconductivity. – [1] Z.Sun, et al., Nano Lett. 21, 7669 (2021). |
Tuesday, March 15, 2022 9:36AM - 9:48AM |
F60.00007: Charged Bosonic Excitonic State in Bilayer Structures with Strong Metallic Screening Qiaochu Wan, Sun Zheng, Igor V Bondarev, David W Snoke, Jonathan C Beaumariage, Hassan A Alnatah, Nicholas M Hougland, Jessica Chisholm, Qingrui Cao, Kenji Watanabe, Takashi Taniguchi, Benjamin M Hunt Two-dimensional monolayers of transition metal dichalcogenides (TMDs) have already shown the existence of many higher-order excitonic bound states such as trions and biexcitons. Stacking multiple TMD layers allows even more complex and novel excitonic states. |
Tuesday, March 15, 2022 9:48AM - 10:00AM |
F60.00008: Quantum phases in 1T-TaS2: from bulk to atomically-thin layers and van der Waals heterostructures. Samuel Mañas-Valero Quantum materials exhibiting magnetic frustration are connected to diverse phenomena, including high Tc superconductivity, topological order, and quantum spin liquids (QSLs). A QSL is a quantum phase (QP) related to a quantum-entangled fluid-like state of matter. A relevant example is provided by 1T-TaS2, which shows a multifaceted electronic and magnetic scenario due to the existence of several charge density waves (CDW) configurations, including quantum hidden phases, superconductivity and even quantum spin liquid phases, that are highly dependent on the out-of-plane stacking of the CDW. |
Tuesday, March 15, 2022 10:00AM - 10:12AM |
F60.00009: Exciton supersolid of spatially indirect exciton in bilayer semiconductor devices. Sara Conti, David Neilson, Andrea Perali, Francois M Peeters We predict a supersolid phase of spatially indirect excitons[1]. The electrons and holes are confined in separate layers of a bilayer semiconductor heterostructure. The separation between layers and the electron and hole densities are used as parameters to tune the strength of the exciton-exciton dipolar-like repulsive interactions. |
Tuesday, March 15, 2022 10:12AM - 10:24AM Withdrawn |
F60.00010: Effect on electron-hole superfluidity of band flattening from twisting of semiconductor bilayers David Neilson, Sara Conti, Andrey Chaves, Francois M Peeters, Milorad Milošević Superfluid condensation of electron-hole pairs has been predicted and subsequently demonstrated to occur at small layer separations in bilayer semiconductor heterostructures [1-2]. The strength of the spatially separated electron-hole pairing is increased when the dispersion of the single electron and hole energy bands is made flatter [3]. It has been shown that twisting two layers of Transition Metal Dichalcogenides or two layers of Black Phosphorus can significantly flatten the single-particle energy bands[4-5]. We systematically calculate realistic multibands of the electrons and holes as a function of twisting angle, so as to follow the change in pairing strength with band flattening. In this way we can investigate the effect of band flattening from twisting on electron-hole superfluid properties. |
Tuesday, March 15, 2022 10:24AM - 10:36AM |
F60.00011: Electronic characterization of the 1T-TaSe2/1H-TaSe2 bilayer heterostructure Miguel M Ugeda, Wen Wan, Paul L Dreher, Rishav Harsh, Fernando de Juan Single layers of transition metal dichalcogenide materials (TMDs) provide an ideal platform to explore collective phenomena such as magnetism driven by strong electronic correlations. Here we report the electronic characterization of the low-lying electronic structure of the 1T-TaSe2/1H-TaSe2 bilayer heterostructure around the Fermi level (EF) by means of high-resolution scanning tunneling spectroscopy at 300 mK. Our STS results show the clear presence of a two-peak structure separated by ~ 1meV and symmetric with respect to the Fermi level. The energy location of the resonances is found to vary with the application of a perpendicular magnetic and show two distinct regimes; a linear regime for high fields compatible with a Zeeman splitting and an intriguing non-linear regime for fields < 1 T. Our experimental observations along with specific calculations for this system enable us to paint a clear picture of the heavy fermion physics at play in this system. |
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