Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B56: Graphene: Electron-Electron InteractionsRecordings Available
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Sponsoring Units: DCMP Chair: Talip Serkan Kasırga Room: Hyatt Regency Hotel -Burnham |
Monday, March 14, 2022 11:30AM - 11:42AM |
B56.00001: Magnetism and Superconductivity in Crystalline Few-Layer Graphene Haoxin Zhou, Tian Xie, Yu Saito, Liam A Cohen, Areg Ghazaryan, Tobias Holder, William Huynh, Caitlin L Patterson, Fangyuan Yang, James Ehrets, Eric M Spanton, Takashi Taniguchi, Kenji Watanabe, Erez Berg, Maksym Serbyn, Andrea Young Bernal bilayer and rhombohedral trilayer graphene are two crystalline graphene allotropes. Their energy band structures share similar aspects -- both feature van Hove singularities at the band edges that can be enhanced by an electric field. Tunning the Fermi surface close to the van Hove singularities tends to induce instability and therefore novel electronic phenomena. Combining quantum capacitance measurement and electronic transport measurement, we observed a series of gate-tuned phase transitions associated with spontaneous spin- and valley-symmetry breaking in both the bilayer and trilayer systems. More surprisingly, superconductivity was observed in rhombohedral trilayer graphene near some of the phase boundaries and in Bernal bilayer graphene when an in-plane magnetic field is applied. Although the pairing mechanism remains puzzling, we believe our observation introduces significant new constraints to the theory of superconductivity in graphene systems. |
Monday, March 14, 2022 11:42AM - 11:54AM |
B56.00002: Competing orders and theory of fractioanl metal in graphene-based layered materials Bitan Roy Graphene-based layered materials accommodate nodal quasiparticles that (a) feature continuous SU(2) chiral symmetries stemming from the valley or isospin and real spin degrees of freedom, for example, each of which leads to two-fold band degeneracy and (b) can develop (spontaneously or externally) Dirac masses leading to uniform and isotropic spectral gap. Irrespective of the band curvature of such chiral quasiparticle dispersion, I will show that it is always conceivable to construct a right number of mutually commuting masses that systematically lift the band degeneracy. I then show how such generic picture can be germane to recently observed half and quarter metal in rhobmohedral trilayer graphene in the presence of external electric displacement field. Finally, I will also discuss the possible superconducting states originating from such fractional metal. |
Monday, March 14, 2022 11:54AM - 12:06PM |
B56.00003: Renormalization group study of superconductivity and intervalley coherence in the rhombohedral trilayer graphene Dachuan Lu, Taige Wang, Shubhayu Chatterjee, Michael P Zaletel, Yizhuang You Recent experiments on rhombohedral trilayer graphene (RTG) observe the superconductivity and isospin symmetry breaking. In this work, we study the fate of the fermion interactions which originates from the microscopic model of this RTG system using the renormalization group (RG) method. We build the hotspot model based on the fermi surface nesting and the proximity to the van Hove singularities. We derived the renormalization group equations for the momentum-dependent interaction vertices, and we investigated the effect of Hund's coupling and the Berry curvature in the RG flow. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B56.00004: Tunable charge transfer in graphene on chromium trihalides Chun-Chih Tseng, Tiancheng Song, Jaehyun Suh, Zhong Lin, Kenji Watanabe, Takashi Taniguchi, Jiun-Haw Chu, David H Cobden, Xiaodong Xu, Matthew A Yankowitz The proximity effect in van der Waals (vdW) heterostructures has been extensively investigated as a controllable method to engineer new materials properties. Interfacing graphene with vdW materials featuring ferromagnetic ordering and strong spin-orbit coupling has been a longstanding goal, owing to predictions of emergent gapped topological states. Here, we investigate heterostructures of monolayer graphene resting on various atomically-thin CrX3 layered magnets (X=I/Br). We find that charge transfer is ubiquitous in these systems owing to a large work function mismatch between the graphene and CrX3. In graphene on CrI3, transport is strongly hysteretic as the gate voltage is swept back and forth. The hysteresis vanishes upon doping the system into the CrI3 band gap, suggesting that it arises due to a kinetic barrier for transferring charge between graphene and CrI3. The hysteretic behavior is concomitant with a highly nonlinear relationship between the gate voltage and the charge doping in the graphene, leading to very extended quantum Hall plateaus. Curiously, however, we do not observe any detectible signatures of magnetic exchange coupling in graphene despite achieving a clean interface with the magnetic CrX3 substrate. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B56.00005: Correlation-driven electron-hole asymmetry in graphene field effect devices Nicholas G Dale, Ryo Mori, Iqbal B Utama, Jonathan D Denlinger, Conrad Stansbury, Claudia G Fatuzzo, Sihan Zhao, Kyunghoon Lee, Takashi Taniguchi, Kenji Watanabe, Christopher Jozwiak, Aaron Bostwick, Roland Koch, Eli Rotenberg, feng wang, Alessandra Lanzara Electron-hole asymmetry is a fundamental property in solids that can determine the nature of quantum phase transitions and the regime of operation for devices. The observation of electron-hole asymmetry in graphene and recently in twisted graphene and moir\'{e} heterostructures has spurred interest into whether it stems from single particle effects or from correlations, which are core to the emergence of intriguing phases in moir\'{e} systems. Here, we report an effective way to access electron-hole asymmetry in 2D materials by directly measuring the quasiparticle self-energy in graphene/Boron Nitride field effect devices. As the chemical potential moves from the hole to the electron doped side, we see an increased strength of electronic correlations manifested by an increase in the band velocity and inverse quasiparticle lifetime. These results suggest that electronic correlations intrinsically drive the electron-hole asymmetry in graphene and by leveraging this asymmetry can provide alternative avenues to generate exotic phases in twisted moir\'{e} heterostructures. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B56.00006: Coexistence of extended and point-like van Hove singularity in heavily n-doped graphene Asish K Kundu, Ze-Bin Wu, Zengyi Du, Abhay N Pasupathy, Kazuhiro Fujita, Ilya K Drozdov Tuning the Fermi level to a van Hove singularity (VHS) can lead to new quantum phases such as superconductivity, charge, or spin density waves due to the instability of the Fermi surface emerging from the divergence of the density of states. Here, we present an angle-resolved photoemission spectroscopy study of Yb-intercalated graphene on a 4H-SiC(0001) substate doped to the VHS. We observe different topologies of the two VHS below (point-like) and above (extended) the Dirac point of graphene. The appearance of an extended VHS suggests a renormalization of the electronic structure due to the enhanced many-body interactions in the system. Strong hybridization of Yb states with the π bands of graphene is observed that open up an energy gap of ∼ 300 meV in the graphene Dirac states. Our results also show that the majority of the intercalated Yb atoms stay in the Yb2+ charge state. The mixing of states of intercalated atoms with the graphene states ensures the possibility of realizing spin-polarized Dirac states when doped with the magnetic atoms. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B56.00007: Anomalous Weak Localisation Phase in Ultra-Clean van der Waals Heterostructures David Perkins, Frederico Sousa, Aires Ferreira Over the past two decades, two-dimensional (2D) van der Waals (vdW) materials have been the subject of numerous theoretical and experimental quantum transport investigations. In this talk we present a non-perturbative analysis of quantum corrections to the DC conductivity in 2D Dirac materials with symmetry-breaking spin-orbit coupling (SOC). We find that the commonly reported weak localisation to weak anti-localisation (WL-to-WAL) transition that is driven by increasing the strength of SOC is reversed in ultra-clean graphene heterostructures (i.e. WAL-to-WL). This counter-intuitive result can be traced back to the strong non-perturbative coupling between the pseudospin and spin degrees of freedom induced by SOC, which gaps out the delocalised modes of the Cooperon for large SOC strengths. Our results suggest that the nature of localisation in spin-orbit coupled 2D vdW materials is richer than first thought, highlighting the importance of non-perturbative methods in quantum interference studies of ultra-clean vdW heterostructures. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B56.00008: Topological Superconductivity in open boundary condition graphene Jonas Hauck, Carsten Honerkamp, Dante M Kennes Recently, van-Hove doped graphene was achieved for the first time, thus bringing us closer to realize topological superconductivity in this material. The behavior of the order parameter at the boundaries is especially interesting, as there majorana fermions can exist in a zeeman field. Thus, it is of importance to understand the behavior of the topological superconductor at the boundary, which was already studied on a mean field level with attractive interactions as input. Here, we go beyond this by using the recently developed realspace truncated unity functional renomalization group (RS-TUfRG) and the simpler random phase approximation (RPA) to obtain a more realistic effective interaction in one dimensional graphene slabs. On the basis of this effective interactions we perform a self consistent Bogoliubov-de-Gennes approach to obtain the pairing gap. We then discuss the interplay between the boundaries and the pairing interaction and the possible influences which arise due to the open boundaries on the level of the BdG decoupling of the effective interaction. We also highlight the differences of the effective interaction generated by the two methods and discuss the importance of the inclusion of the selfenergy. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B56.00009: Ultrafast carrier cooling in bilayer graphene with intercalated hydrogen atoms Sachin Sharma, Edward Sanchez, Rachael Myers-Ward2, Matthew DeJarld, Kurt D Gaskill, Paola Barbara, Stephen B Cronin, Ioannis Chatzakis We report on energy relaxation dynamics in epitaxially grown quasi-free-standing bilayer graphene on SiC substrate utilizing THz pump-probe spectroscopy. Hydrogen atom intercalation (HI) between the graphene and substrate is introduced to study graphene-substrate coupling on the energy relaxation process. Recently, interlayer energy transfer mechanisms are observed through carrier relaxation time measurements. We investigate a distinct current-heating mechanism to establish the role of HI on the carrier energy relaxation. Increased relaxation times for H intercalated substrates has been attributed to reduced coupling between the graphene and the substrate. In our samples, control of the density of partial intercalation of H atoms is carried out during the growth process; we will report on the energy flow rate for fully and partially intercalated graphene. We record the energy relaxation via THz spectroscopy post photoexcitation of graphene. Moreover, changes in THz conductivity have been measured. Experimental data do not reflect remarkable variations in THz conductivity as a function of excitation wavelength between 1.7um – 4.3um. These measurements were performed using quasi-free-bilayer graphene on SiC. The role of intercalation of hydrogen is undergoing further investigation. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B56.00010: Plasmon-induced magnetization in the edges of higher Chern insulators Prathyush P Poduval, Thomas L Schmidt, Eddwi H Hasdeo This work theoretically discusses the collective behavior (plasmons) of chiral edge modes in higher Chern (hC) insulators, which have large Chern numbers. In the bulk, hC insulators have a band gap and quantized Hall conductivity according to the Chern number, C. In the edge, it has C number of chiral modes. Similar to edge plasmons in normal metals, oscillating chiral modes' self-generated potential can produce a circularly polarized electric field. The electric field then drives the electron in a circular fashion inducing an orbital magnetic moment, known as the inverse Faraday effect. This orbital motion will split spin up and spin down states allowing the spintronics application from edge plasmon. According to previous formalism, the magnetization is proportional to square of electric field and inversely proportional to charge density. In hC plasmons, the self-generated electric field will increase with the number of chiral edge channels and bulk density can be very small thus, we can expect a large enhancement of the induced magnetization. Moreover, the hc plasmons dispersion is largely linear in contrast to √q behavior of 2D edge plasmons and tunable by dielectric constant and band gap. The results will allow interesting opto-electronic applications using hC materials. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B56.00011: Cyclotron resonance in the hydrodynamic regime of bi-layer graphene Joseph R Cruise, Alexander Seidel, Erik A Henriksen, Giovanni Vignale We calculate the thermo-electric coefficients and extract resonant frequencies for bi-layer graphene in the hydrodynamic regime. In clean systems where interactions are dominated by electron-electron collisions, mild magnetic fields can induce collective cyclotron motion in the charge carrying electrons and holes, with a resonant frequency different from the usual eB/m as a result of electron-hole collisions. We contrast this with single layer graphene, and argue that the hydrodynamic regime in the bilayer case exhibits a broader window where the cyclotron resonance can be accessed by light absorption experiments at room temperature. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B56.00012: Theoretical study of viscosity in monolayer and bilayer graphene Indra Yudhistira, Ramal Afrose, Shaffique Adam The advancements in technology in recent years have allowed for the experimental realisation of ultraclean monolayer and bilayer graphene samples where impurity or phonon scattering are no longer the dominant scattering mechanism. The strong electron-electron interaction in these ultraclean samples results in the emergence of hydrodynamic electron behaviour where electron transport is governed by an electronic Navier-Stokes equation analogous to classical fluids. In this theoretical study, we carry out a theoretical calculation of dynamic viscosity in monolayer and bilayer graphene from a microscopic theory. We find a non-monotonic temperature dependence of the dynamic viscosity in both monolayer and bilayer graphene that approaches a universal limit at high temperature and strong electron-electron interaction. We show that our results agrees very well with available experimental data. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B56.00013: Electron-hole drag viscosity and magnetotransport in semimetals Eddwi H Hasdeo, Edvin G Idrisov, Thomas L Schmidt In clean two-dimensional materials exposed at intermediate temperatures, interparticle collision dominates over momentum-relaxing collisions such from impurities and phonons. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B56.00014: Vortex dynamics and nonlocal phases in hydrodynamic and ballistic AC transport Gitansh Kataria, Adbhut Gupta, Jean J Heremans, Mani Chandra, Ravishankar Sundararaman Transport in conductors is typically dominated by momentum-relaxing (MR) collisions of electrons with the lattice or defects. However, clean systems hosting two-dimensional electron systems allow for the suppression of MR scattering so that the dominant effect is now the collision of electrons either with other electrons (hydrodynamic regime) or with device boundaries (ballistic regime). Unlike MR scattering, (normal) electron-electron and electron-boundary collisions conserve the total momentum of the electrons in the bulk leading to the observation of fluid-like phenomena such as current vortices and negative nonlocal resistance under a DC bias. We investigate AC transport in these regimes and showcase the striking vortex dynamics that occur in hydrodynamic and ballistic transport. The nonlocal current-voltage and voltage-voltage phases allow for an unambiguous discrimination between diffusive, hydrodynamic and ballistic transport. |
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