Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session W39: 2D Materials: Charge Density Waves, Skyrmions, and Electronic Structure |
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Sponsoring Units: DMP Chair: Salvador Barraza-Lopez, University of Arkansas; Yang Liu Room: Room 231 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W39.00001: Temperature dependent electronic structure of Cr1/4NbSe2 thin films revealed by angle-resolved photoemission spectroscopy Satoshi Hamao, Bruno K Saika, Xiang Huang, Yuki Majima, Hideki Matsuoka, Miho Kitamura, Masato Sakano, Takuya Nomoto, Motoaki Hirayama, Koji Horiba, Hiroshi Kumigashira, Ryotaro Arita, Yoshihiro Iwasa, Masaki Nakano, Kyoko Ishizaka Intercalation of 3d transition metal atoms in transition metal dichalcogenides is known to produce magnetic phases with varied spin structures. Particularly, 3d-intercalated Nb and Ta disulfides were widely studied in the past, in which itinerant electrons of the parent compounds are thought to mediate the exchange between magnetic atoms via the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction. In accordance with the magnetic atom and host layer, RKKY interactions may lead to a variety of magnetic phases, such as ferromagnetic, antiferromagnetic, helimagnetic, etc. CrxNbSe2 is an example of different magnetic phases appearing according to the composition ratio between intercalants and host layer [1]. Recently, we have employed molecular-beam epitaxy to fabricate high-quality CrxNbSe2 epitaxial thin films and clarified the topological electronic structure realized in ferromagnetic x = 1/3 via angle-resolved photoemission spectroscopy (ARPES) [2]. In this work, we further investigate the nonmagnetic Cr1/4NbSe2 and discuss the peculiar temperature dependent electronic structure associated with the anomalous transport property. |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W39.00002: Role of Apical Ions in the CDW Phases of AV3Sb5 Kagome Metals Turan Birol, Fan Yang, Rafael M Fernandes, Ethan T Ritz Charge density wave (CDW) instabilities of AV3Sb5 Kagome metals can be understood to emerge from a single Kagome plane, but the low energy CDW phases also involve an out-of-plane modulation of the crystal structure. This raises the question if other ions, such as the apical Sb's, have any role in determining the structural energy landscape. In this talk, using first principles calculations, we show that the apical Sb ions are essential in determining the energy scale of the CDW phases. We also discuss the possible connections of this observations with the nature of the superconducting order parameter in these systems. |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W39.00003: Tunable Magnetism in 1T-CrTe2 Due to Competing Charge and Spin Density Waves Ahmed Elrashidy, Jia-An Yan
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Thursday, March 9, 2023 3:36PM - 3:48PM |
W39.00004: In-operando Magneto-Raman spectroscopy of 2D materials: graphene and 2M-WS2 Son T Le, Tehseen Adel, Maria F Munoz, Piumi I Samarawickrama, Joseph McBride, John Ackerman, Brian Leonard, Jifa Tian, Angela R Hight Walker We highlight the measurement capabilities of our custom-built magneto-Raman spectrometer with simultaneous electrical measurement, focusing on two different devices. The first is a gated graphene hall bar. We obtain Raman spectra of graphene as a function of gate voltage and applied magnetic field at 1.6 K, in the quantum Hall regime. The second device is made from a novel 2D material, 2M-WS2, with exotic topological superconducting phase below 8 K. We study the effect of superconductivity on Raman active phonons, by varying the temperature and magnetic field. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W39.00005: Evidences for the exciton gas phase and its condensation in monolayer 1T-ZrTe2 Chunjing Jia, Thomas Devereaux, Jonathan A Sobota, Patrick S Kirchmann, Sung-Kwan Mo, Zhi-Xun Shen, Shujie Tang Here we report a distinct correlated phase beyond the 2×2 CDW ground state emerging in epitaxially grown monolayer 1T-ZrTe2 and its investigation by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). The results show novel band- and energy-dependent folding behavior in a two-step process, evidenced by an exciton gas phase prior to its condensation into the final CDW state. The excellent agreement between experiments and theoretical predictions on the recovery of the pristine band structure by carrier-density-dependent suppression of the CDW state further corroborates the monolayer 1T-ZrTe2 as an EI. Our findings provide a versatile two-dimensional platform that allows tuning of the excitonic effect. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W39.00006: Lattice distortions in the gyrotropic semimetal 1T-TiSe2 Kwangrae Kim, Hyunwoo J Kim, BJ Kim 1T-TiSe2 exhibits a circular photogalvanic effect, which implies the absence of any mirror planes, inversion centers, and roto-inversion axes. It is believed that a formation of a chiral charge density wave order underlies this effect. However, no corresponding lattice distortions have been found to date, leading to apparent violation of the Neumann's principle, which states that the symmetry of any physical property must include the symmetry elements of the point group of the lattice. A necessary condition to realize a chiral lattice is the condensation of phonon modes at both L and M points in the Brillouin zone. In this talk, we will discuss on our measurements of the phonon modes using Raman spectroscopy and inelastic x-ray scattering. Our results show that while there is no condensation of the M phonon mode, breaking of the three-fold roto-inversion is implied by the lifting of degeneracy of Eg phonon modes. We analyze possible lattice structures consistent with these observations. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W39.00007: Doping-induced nematic charge density wave in 1T-TiSe2. Daniel Muñoz-Segovia, Jörn W Venderbos, Adolfo G Grushin, Fernando de Juan The ground state of pristine 1T-TiSe2 is known to be a commensurate 2x2x2 charge density wave, although its origin is still debated between the strong electron-phonon coupling and the excitonic insulator mechanism. While the generally accepted charge density wave respects the threefold symmetry of the lattice, some experiments display signatures of the breaking of this symmetry. We propose that these seemingly contradictory observations can be rationalized by a nematic charge density wave state induced by electron doping, which arises due to the competition between two order parameters. This scenario is supported by our microscopic mean-field calculations of an effective tight-binding model for monolayer 1T-TiSe2. Finally, we discuss the implications of our prediction in transport experiments. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W39.00008: Dynamic stability and magnetism of David star charge density waves in transition metal dichalcogenide systems Jan Phillips, Adolfo O Fumega, Victor Pardo Monolayer group V transition metal dichalcogenides in their 1T phase have recently emerged as a platform the investigate rich phases of matter resulting from strong electron correlations. The magnetism of these systems interplays with different ordered phases, such as charge density waves (CDW). In particular, the so-called David star CDW phase (with a √13×√13 reconstruction) that might arise in these systems leads to the emergence of a spin 1/2 per David star, which has been discussed in the framework of spin liquids. In this talk, we present ab initio calculations based on the density functional theory of different V-, Nb-, and Ta-based chalcogenides. We study the band structure, density of states, and phonon spectra of various of these compounds in the √13×√13 cell, obtaining information about their electronic structure and the possible charge-density-wave q-vectors that may be responsible for the appearing instabilities, if these exist. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W39.00009: Symmetry of real and imaginary charge density waves in AV3Sb5 Kagome metals Ethan T Ritz, Rafael M Fernandes, Turan Birol The AV3Sb5 (A=K, Rb, Cs) family of Kagome metals exhibit charge ordered phases in addition to superconducting and topological properties.This charge ordering behavior may involve both bond distortions ( "real" charge density waves, or rCDW) and loop currents, which break time reversal (TR) symmetry ("imaginary" charge density waves, or iCDW). Establishing whether there is spontaneous TR symmetry breaking in these systems is crucial to understand their rich phase diagrams. In particular, TR symmetry enforces constraints on observable bulk properties, such as the magneto-optical Kerr effect (MOKE) and the piezomagnetoelectric effect. Importantly, these quantities behave differently for distinct types of loop-current configurations, which provides a route to identify which, if any, loop-current pattern is realized. Using group and representation theoretical approaches, we classify the various symmetry-allowed phases of the AV3Sb5 family in which both rCDW and iCDW order parameters condense. We then compare the properties of the response tensors in each allowed phase by using their magnetic space groups, and propose experiments to help determine the symmetries of the charge-ordered state in this material. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W39.00010: Isotropic strain effects on twisted bilayer graphene near the magic angle Dinesh K Yadav, Chuankun Liu, Jasper Bradford, Kenji Watanabe, Takashi Taniguchi, Vikram V Deshpande In recent years, the magic angle of graphene has caused many researchers to focus on twisted bilayer graphene at the magic angle and the various ground states it manifests including superconductivity, ferromagnetism, topological states, etc. However, graphene is also attractive for its extremely high mechanical strength and endurance and it may be asked how these states respond to high levels of mechanical strain. Indeed, it is thought that built-in strain during sample fabrication may explain some sample-to-sample variation that exists in the literature [1]. By fabricating samples on flexible substrates and applying displacement to them out of plane isotropically, we are able to apply isotropic strains up to several percent, which we calibrate by directly measuring the shift of alignment marks on the substate and by recording the response of single layer graphene Landau levels to such strain. Applying this technique to twisted bilayer graphene samples away from the magic angle, we are able to tune the Hofstadter butterfly of the system with strain. Finally, studying samples closer to the magic-angle, in preliminary data, we find that strain tunes a correlated non-magnetic state at moire miniband filling factor equal to one (quarter filling) to a ferromagnetic state, detected via a gate-tunable anomalous Hall effect. Thus, we expect our strain technique to play an important role in tuning the superlattice and resultant ground states of twisted bilayer graphene. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W39.00011: Chromium substitution suppresses the charge density wave in ScV6Sn6 Charles Young, William R Meier, Shirin Mozaffari, Richa Madhogaria, David G Mandrus The diverse HfFe6Ge6-type compounds exhibit interesting magnetic and electronic properties arising from their transition metal kagome layers. For example, the vanadium kagome layers in ScV6Sn6 help support a charge density wave (CDW) below 92 K. [1] I grew and characterized single crystals of Sc(V1-xCrx)6Sn6 to investigate the impact of band filling on CDW formation. Temperature dependent physical properties reveal that chromium substitution suppresses the CDW. I will discuss the how this observation sheds light on the factors which govern CDW formation in kagome metals. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W39.00012: Magneto-Skyrmion excitations of bilayer electron-hole fluids Bo Zou, Allan H MacDonald The exciton condensate of bilayer electron-hole fluids has been a topic of both experimental and theoretical interest in recent years. In this talk we will discuss the influence of strong perpendicular magnetic fields on bilayer electron-hole fluids. In the limit of very strong fields exciton condensation occurs for both electron-hole and electron-electron fluids. We show that although condensate states are more persistent in the electron-hole case, they are interrupted by incompressible quantum Hall states when the magnetic field is strong and the densities of both electrons and holes are close to integer Landau level filling factors. Non-zero angular momentum condensates can be stabilized when the filling factors of electrons and holes differ. At strong fields the ground states of charged electron-fluids can be unstable to the formation of states with lattices of magneto-Skyrmions, charged textures with strong hole polarization in the core of condensate vortices. We will discuss strategies to observe magneto-Skyrmion lattices experimentally. |
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