Indra Yudhistira
CA2DM Publications:
2024 |
Peng, Liangtao; Yudhistira, Indra; Vignale, Giovanni; Adam, Shaffique Theoretical determination of the effect of a screening gate on plasmon-induced superconductivity in twisted bilayer graphene Journal Article PHYSICAL REVIEW B, 109 (4), 2024, ISSN: 2469-9950. @article{ISI:001173887400003, title = {Theoretical determination of the effect of a screening gate on plasmon-induced superconductivity in twisted bilayer graphene}, author = {Liangtao Peng and Indra Yudhistira and Giovanni Vignale and Shaffique Adam}, doi = {10.1103/PhysRevB.109.045404}, times_cited = {0}, issn = {2469-9950}, year = {2024}, date = {2024-01-05}, journal = {PHYSICAL REVIEW B}, volume = {109}, number = {4}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {The microscopic pairing mechanism for superconductivity in magic-angle twisted bilayer graphene remains an open question. Recent experimental studies seem to rule out a purely electronic mechanism due to the insensitivity of the critical superconducting temperature to either a highly doped screening layer or the proximity to a metallic screening gate. In this theoretical work, we explore the role of external screening layers on the superconducting properties of twisted bilayer graphene within a purely electronic mechanism. Consistent with the experimental observations, we find that the critical temperature is unaffected by screening unless the screening layer is closer than 3 nm from the superconductor. Thus, the available transport data are not in contradiction with a plasmon-mediated mechanism. We also investigate other properties of this plasmon-mediated superconductivity, including signatures in the tunneling density of states as probed in spectroscopy experiments.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The microscopic pairing mechanism for superconductivity in magic-angle twisted bilayer graphene remains an open question. Recent experimental studies seem to rule out a purely electronic mechanism due to the insensitivity of the critical superconducting temperature to either a highly doped screening layer or the proximity to a metallic screening gate. In this theoretical work, we explore the role of external screening layers on the superconducting properties of twisted bilayer graphene within a purely electronic mechanism. Consistent with the experimental observations, we find that the critical temperature is unaffected by screening unless the screening layer is closer than 3 nm from the superconductor. Thus, the available transport data are not in contradiction with a plasmon-mediated mechanism. We also investigate other properties of this plasmon-mediated superconductivity, including signatures in the tunneling density of states as probed in spectroscopy experiments. |
2022 |
Tan, Cheng; Ho, Derek Y H; Wang, Lei; Li, Jia I A; Yudhistira, Indra; Rhodes, Daniel A; Taniguchi, Takashi; Watanabe, Kenji; Shepard, Kenneth; McEuen, Paul L; Dean, Cory R; Adam, Shaffique; Hone, James Dissipation-enabled hydrodynamic conductivity in a tunable bandgap semiconductor Journal Article SCIENCE ADVANCES, 8 (15), 2022, ISSN: 2375-2548. @article{ISI:000786201300005, title = {Dissipation-enabled hydrodynamic conductivity in a tunable bandgap semiconductor}, author = {Cheng Tan and Derek Y H Ho and Lei Wang and Jia I A Li and Indra Yudhistira and Daniel A Rhodes and Takashi Taniguchi and Kenji Watanabe and Kenneth Shepard and Paul L McEuen and Cory R Dean and Shaffique Adam and James Hone}, doi = {10.1126/sciadv.abi8481}, times_cited = {0}, issn = {2375-2548}, year = {2022}, date = {2022-04-01}, journal = {SCIENCE ADVANCES}, volume = {8}, number = {15}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {Electronic transport in the regime where carrier-carrier collisions are the dominant scattering mechanism has taken on new relevance with the advent of ultraclean two-dimensional materials. Here, we present a combined theoretical and experimental study of ambipolar hydrodynamic transport in bilayer graphene demonstrating that the conductivity is given by the sum of two Drude-like terms that describe relative motion between electrons and holes, and the collective motion of the electron-hole plasma. As predicted, the measured conductivity of gapless, charge-neutral bilayer graphene is sample- and temperature-independent over a wide range. Away from neutrality, the electron-hole conductivity collapses to a single curve, and a set of just four fitting parameters provides quantitative agreement between theory and experiment at all densities, temperatures, and gaps measured. This work validates recent theories for dissipation-enabled hydrodynamic conductivity and creates a link between semiconductor physics and the emerging field of viscous electronics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electronic transport in the regime where carrier-carrier collisions are the dominant scattering mechanism has taken on new relevance with the advent of ultraclean two-dimensional materials. Here, we present a combined theoretical and experimental study of ambipolar hydrodynamic transport in bilayer graphene demonstrating that the conductivity is given by the sum of two Drude-like terms that describe relative motion between electrons and holes, and the collective motion of the electron-hole plasma. As predicted, the measured conductivity of gapless, charge-neutral bilayer graphene is sample- and temperature-independent over a wide range. Away from neutrality, the electron-hole conductivity collapses to a single curve, and a set of just four fitting parameters provides quantitative agreement between theory and experiment at all densities, temperatures, and gaps measured. This work validates recent theories for dissipation-enabled hydrodynamic conductivity and creates a link between semiconductor physics and the emerging field of viscous electronics. |
2021 |
Sharma, Girish; Yudhistira, Indra; Chakraborty, Nilotpal; Ho, Derek Y H; Ezzi, Al M M; Fuhrer, Michael S; Vignale, Giovanni; Adam, Shaffique Carrier transport theory for twisted bilayer graphene in the metallic regime Journal Article NATURE COMMUNICATIONS, 12 (1), 2021. @article{ISI:000702528800007, title = {Carrier transport theory for twisted bilayer graphene in the metallic regime}, author = {Girish Sharma and Indra Yudhistira and Nilotpal Chakraborty and Derek Y H Ho and Al M M Ezzi and Michael S Fuhrer and Giovanni Vignale and Shaffique Adam}, doi = {10.1038/s41467-021-25864-1}, times_cited = {0}, year = {2021}, date = {2021-09-30}, journal = {NATURE COMMUNICATIONS}, volume = {12}, number = {1}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {The mechanisms responsible for the strongly correlated insulating and superconducting phases in twisted bilayer graphene are still debated. The authors provide a theory for phonon-dominated transport that explains several experimental observations, and contrast it with the Planckian dissipation mechanism.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The mechanisms responsible for the strongly correlated insulating and superconducting phases in twisted bilayer graphene are still debated. The authors provide a theory for phonon-dominated transport that explains several experimental observations, and contrast it with the Planckian dissipation mechanism. |
2020 |
Zarenia, Mohammad; Yudishtira, Indra; Adam, Shaffique; Vignale, Giovanni Enhanced hydrodynamic transport in near magic angle twisted bilayer graphene Journal Article PHYSICAL REVIEW B, 101 (4), 2020, ISSN: 2469-9950. @article{ISI:000507864100003, title = {Enhanced hydrodynamic transport in near magic angle twisted bilayer graphene}, author = {Mohammad Zarenia and Indra Yudishtira and Shaffique Adam and Giovanni Vignale}, doi = {10.1103/PhysRevB.101.045421}, times_cited = {3}, issn = {2469-9950}, year = {2020}, date = {2020-01-17}, journal = {PHYSICAL REVIEW B}, volume = {101}, number = {4}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Using the semiclassical quantum Boltzmann theory and employing the Dirac model with twist angle-dependent Fermi velocity, we obtain results for the electrical resistivity, the electronic thermal resistivity, the Seebeck coefficient, and the Wiedemann-Franz ratio in near magic angle twisted bilayer graphene, as functions of doping density (around the charge-neutrality point) and modified Fermi velocity (v) over tilde. The (v) over tilde dependence of the relevant scattering mechanisms, i.e., electron-hole Coulomb, long-range impurities, and acoustic gauge phonons, is considered in detail. We find a range of twist angles and temperatures, where the combined effect of momentum-nonconserving collisions (long-range impurities and phonons) is minimal, opening a window for the observation of strong hydrodynamic transport. Several experimental signatures are identified, such as a sharp dependence of the electric resistivity on doping density and a large enhancement of the Wiedemann-Franz ratio and the Seebeck coefficient.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Using the semiclassical quantum Boltzmann theory and employing the Dirac model with twist angle-dependent Fermi velocity, we obtain results for the electrical resistivity, the electronic thermal resistivity, the Seebeck coefficient, and the Wiedemann-Franz ratio in near magic angle twisted bilayer graphene, as functions of doping density (around the charge-neutrality point) and modified Fermi velocity (v) over tilde. The (v) over tilde dependence of the relevant scattering mechanisms, i.e., electron-hole Coulomb, long-range impurities, and acoustic gauge phonons, is considered in detail. We find a range of twist angles and temperatures, where the combined effect of momentum-nonconserving collisions (long-range impurities and phonons) is minimal, opening a window for the observation of strong hydrodynamic transport. Several experimental signatures are identified, such as a sharp dependence of the electric resistivity on doping density and a large enhancement of the Wiedemann-Franz ratio and the Seebeck coefficient. |
2019 |
Chu, Leiqiang; Yudhistira, Indra; Schmidt, Hennrik; Wu, Tsz Chun; Adam, Shaffique; Eda, Goki Phase coherent transport in bilayer and trilayer MoS2 Journal Article PHYSICAL REVIEW B, 100 (12), 2019, ISSN: 2469-9950. @article{ISI:000485193300009, title = {Phase coherent transport in bilayer and trilayer MoS_{2}}, author = {Leiqiang Chu and Indra Yudhistira and Hennrik Schmidt and Tsz Chun Wu and Shaffique Adam and Goki Eda}, doi = {10.1103/PhysRevB.100.125410}, times_cited = {0}, issn = {2469-9950}, year = {2019}, date = {2019-09-09}, journal = {PHYSICAL REVIEW B}, volume = {100}, number = {12}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Bilayer MoS2 is a centrosymmetric semiconductor with degenerate spin states in the six valleys at the corners of the Brillouin zone. It has been proposed that breaking of this inversion symmetry by an out-of-plane electric field breaks this degeneracy, allowing for spin and valley lifetimes to be manipulated electrically in bilayer MoS2 with an electric field. In this work, we report phase coherent transport properties of double-gated mono-, bi-, and trilayer MoS2. We observe a similar crossover from weak localization to weak antilocalization, from which we extract the spin relaxation time as a function of both electric field and temperature. We find that the spin relaxation time is inversely proportional to momentum relaxation time, indicating that the D' yakonov-Perel mechanism is dominant in all devices despite the centrosymmetry of the bilayer device. Further, we found no evidence of electric-field-induced changes in spin-orbit coupling strength. This suggests that the interlayer coupling is sufficiently weak and that electron-doped dichalcogenide multilayers behave electrically as decoupled monolayers.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Bilayer MoS2 is a centrosymmetric semiconductor with degenerate spin states in the six valleys at the corners of the Brillouin zone. It has been proposed that breaking of this inversion symmetry by an out-of-plane electric field breaks this degeneracy, allowing for spin and valley lifetimes to be manipulated electrically in bilayer MoS2 with an electric field. In this work, we report phase coherent transport properties of double-gated mono-, bi-, and trilayer MoS2. We observe a similar crossover from weak localization to weak antilocalization, from which we extract the spin relaxation time as a function of both electric field and temperature. We find that the spin relaxation time is inversely proportional to momentum relaxation time, indicating that the D' yakonov-Perel mechanism is dominant in all devices despite the centrosymmetry of the bilayer device. Further, we found no evidence of electric-field-induced changes in spin-orbit coupling strength. This suggests that the interlayer coupling is sufficiently weak and that electron-doped dichalcogenide multilayers behave electrically as decoupled monolayers. |
Rosen, Ilan T; Yudhistira, Indra; Sharma, Girish; Salehi, Maryam; Kastner, M A; Oh, Seongshik; Adam, Shaffique; Goldhaber-Gordon, David Absence of strong localization at low conductivity in the topological surface state of low-disorder Sb2Te3 Journal Article PHYSICAL REVIEW B, 99 (20), 2019, ISSN: 2469-9950. @article{ISI:000466609900001, title = {Absence of strong localization at low conductivity in the topological surface state of low-disorder Sb_{2}Te_{3}}, author = {Ilan T Rosen and Indra Yudhistira and Girish Sharma and Maryam Salehi and M A Kastner and Seongshik Oh and Shaffique Adam and David Goldhaber-Gordon}, doi = {10.1103/PhysRevB.99.201101}, times_cited = {0}, issn = {2469-9950}, year = {2019}, date = {2019-05-02}, journal = {PHYSICAL REVIEW B}, volume = {99}, number = {20}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We present low-temperature transport measurements of a gate-tunable thin-film topological insulator system that features high mobility and low carrier density. Upon gate tuning to a regime around the charge neutrality point, we infer an absence of strong localization even at conductivities well below e(2)/h, where two-dimensional electron systems should conventionally scale to an insulating state. Oddly, in this regime the localization coherence peak lacks conventional temperature broadening, though its tails do change dramatically with temperature. Using a model with electron-impurity scattering, we extract values for the disorder potential and the hybridization of the top and bottom surface states.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present low-temperature transport measurements of a gate-tunable thin-film topological insulator system that features high mobility and low carrier density. Upon gate tuning to a regime around the charge neutrality point, we infer an absence of strong localization even at conductivities well below e(2)/h, where two-dimensional electron systems should conventionally scale to an insulating state. Oddly, in this regime the localization coherence peak lacks conventional temperature broadening, though its tails do change dramatically with temperature. Using a model with electron-impurity scattering, we extract values for the disorder potential and the hybridization of the top and bottom surface states. |
Yudhistira, Indra; Chakraborty, Nilotpal; Sharma, Girish; Ho, Derek Y H; Laksono, Evan; Sushkov, Oleg P; Vignale, Giovanni; Adam, Shaffique Gauge-phonon dominated resistivity in twisted bilayer graphene near magic angle Journal Article PHYSICAL REVIEW B, 99 (14), 2019, ISSN: 2469-9950. @article{ISI:000465159300001, title = {Gauge-phonon dominated resistivity in twisted bilayer graphene near magic angle}, author = {Indra Yudhistira and Nilotpal Chakraborty and Girish Sharma and Derek Y H Ho and Evan Laksono and Oleg P Sushkov and Giovanni Vignale and Shaffique Adam}, doi = {10.1103/PhysRevB.99.140302}, times_cited = {0}, issn = {2469-9950}, year = {2019}, date = {2019-04-17}, journal = {PHYSICAL REVIEW B}, volume = {99}, number = {14}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Recent experiments on twisted bilayer graphene (tBG) close to magic angle show that a small relative rotation in a van der Waals heterostructure greatly alters its electronic properties. We consider various scattering mechanisms and show that the carrier transport in tBG is dominated by a combination of charged impurities and acoustic gauge phonons. Charged impurities still dominate at low temperature and densities because of the inability of Dirac fermions to screen long-range Coulomb potentials at charge neutrality; however, the gauge phonons dominate for most of the experimental regime because, although they couple to current, they do not induce charge and are therefore unscreened by the large density of states close to magic angle. We show that the resistivity has a strong monotonically decreasing carrier density dependence at low temperature due to charged impurity scattering, and weak density dependence at high temperature due to gauge phonons. Away from charge neutrality, the resistivity increases with temperature, while it does the opposite close to the Dirac point. A nonmonotonic temperature dependence observed only at low temperature and carrier density is a signature of our theory that can be tested in experimentally available samples.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Recent experiments on twisted bilayer graphene (tBG) close to magic angle show that a small relative rotation in a van der Waals heterostructure greatly alters its electronic properties. We consider various scattering mechanisms and show that the carrier transport in tBG is dominated by a combination of charged impurities and acoustic gauge phonons. Charged impurities still dominate at low temperature and densities because of the inability of Dirac fermions to screen long-range Coulomb potentials at charge neutrality; however, the gauge phonons dominate for most of the experimental regime because, although they couple to current, they do not induce charge and are therefore unscreened by the large density of states close to magic angle. We show that the resistivity has a strong monotonically decreasing carrier density dependence at low temperature due to charged impurity scattering, and weak density dependence at high temperature due to gauge phonons. Away from charge neutrality, the resistivity increases with temperature, while it does the opposite close to the Dirac point. A nonmonotonic temperature dependence observed only at low temperature and carrier density is a signature of our theory that can be tested in experimentally available samples. |
Woo, Sung Oh; Yudhistira, Indra; Hemmatiyan, Shayan; Morrison, Tyler D; Rathnayaka, K D D; Naugle, Donald G Transport properties of bilayer graphene decorated by K adatoms in the framework of Thomas-Fermi screening Journal Article PHYSICAL REVIEW B, 99 (8), 2019, ISSN: 2469-9950. @article{ISI:000458368400005, title = {Transport properties of bilayer graphene decorated by K adatoms in the framework of Thomas-Fermi screening}, author = {Sung Oh Woo and Indra Yudhistira and Shayan Hemmatiyan and Tyler D Morrison and K D D Rathnayaka and Donald G Naugle}, doi = {10.1103/PhysRevB.99.085416}, times_cited = {0}, issn = {2469-9950}, year = {2019}, date = {2019-02-12}, journal = {PHYSICAL REVIEW B}, volume = {99}, number = {8}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We report the transport properties of bilayer graphene (BLG) due to the increase of Coulomb potential fluctuations and the decrease of K adatom concentration (n(K)) induced by diffusion and cluster formation of the K adatom as a function of temperature (20-300 K) and time at room temperature (RT). Upon K adatom deposition on BLG at T = 20 K, conductivity decreased due to the emergence of Coulomb scatterers, and the dependence of conductivity transformed from linear (sigma similar to n(alpha), alpha similar to 1) to superlinear (alpha similar to 1.5). As the inhomogeneity of the Coulomb potential on BLG increased by cluster formation of K adatoms, the magnitude of the conductivity increased, and the dependence of conductivity on charge carrier density (curvature) shifted towards linear behavior. We fit the experimental data with Boltzmann transport theory to show that the changes in the transport properties of BLG in the presence of charged impurities originate from two factors, n(K) and the Thomas-Fermi screening vector (q(TF)), which are both affected by cluster formation of K adatoms on BLG and the subsequent increase of Coulomb potential inhomogeneity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report the transport properties of bilayer graphene (BLG) due to the increase of Coulomb potential fluctuations and the decrease of K adatom concentration (n(K)) induced by diffusion and cluster formation of the K adatom as a function of temperature (20-300 K) and time at room temperature (RT). Upon K adatom deposition on BLG at T = 20 K, conductivity decreased due to the emergence of Coulomb scatterers, and the dependence of conductivity transformed from linear (sigma similar to n(alpha), alpha similar to 1) to superlinear (alpha similar to 1.5). As the inhomogeneity of the Coulomb potential on BLG increased by cluster formation of K adatoms, the magnitude of the conductivity increased, and the dependence of conductivity on charge carrier density (curvature) shifted towards linear behavior. We fit the experimental data with Boltzmann transport theory to show that the changes in the transport properties of BLG in the presence of charged impurities originate from two factors, n(K) and the Thomas-Fermi screening vector (q(TF)), which are both affected by cluster formation of K adatoms on BLG and the subsequent increase of Coulomb potential inhomogeneity. |
2018 |
Ho, Derek Y H; Yudhistira, Indra; Hu, Ben Yu-Kuang; Adam, Shaffique Theory of Coulomb drag in spatially inhomogeneous 2D materials Journal Article COMMUNICATIONS PHYSICS, 1 , 2018, ISSN: 2399-3650. @article{ISI:000442026300001, title = {Theory of Coulomb drag in spatially inhomogeneous 2D materials}, author = {Derek Y H Ho and Indra Yudhistira and Ben Yu-Kuang Hu and Shaffique Adam}, doi = {10.1038/s42005-018-0039-y}, times_cited = {0}, issn = {2399-3650}, year = {2018}, date = {2018-07-27}, journal = {COMMUNICATIONS PHYSICS}, volume = {1}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Coulomb drag is a favored experimental probe of Coulomb interactions between layers of 2D materials. In reality, these layers display spatial charge density fluctuations known as puddles due to various imperfections. A theoretical formalism for incorporating density inhomogeneity into calculations has however not been developed, making the understanding of experiments difficult. Here, we remedy this by formulating an effective medium theory of drag that applies in all 2D materials. We show that a number of striking features at zero magnetic field in graphene drag experiment which have not been explained by existing literature emerge naturally within this theory. Applying the theory to a phenomenological model of exciton condensation, we show that the expected divergence in drag resistivity is replaced by a peak that diminishes with increasing puddle strength. Given that puddles are ubiquitous in 2D materials, this work will be useful for a wide range of future studies.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Coulomb drag is a favored experimental probe of Coulomb interactions between layers of 2D materials. In reality, these layers display spatial charge density fluctuations known as puddles due to various imperfections. A theoretical formalism for incorporating density inhomogeneity into calculations has however not been developed, making the understanding of experiments difficult. Here, we remedy this by formulating an effective medium theory of drag that applies in all 2D materials. We show that a number of striking features at zero magnetic field in graphene drag experiment which have not been explained by existing literature emerge naturally within this theory. Applying the theory to a phenomenological model of exciton condensation, we show that the expected divergence in drag resistivity is replaced by a peak that diminishes with increasing puddle strength. Given that puddles are ubiquitous in 2D materials, this work will be useful for a wide range of future studies. |
Liu, Yanpeng; Yudhistira, Indra; Yang, Ming; Laksono, Evan; Luo, Yong Zheng; Chen, Jianyi; Lu, Junpeng; Feng, Yuan Ping; Adam, Shaffique; Loh, Kian Ping Phonon-Mediated Colossal Magnetoresistance in Graphene/Black Phosphorus Heterostructures Journal Article NANO LETTERS, 18 (6), pp. 3377-3383, 2018, ISSN: 1530-6984. @article{ISI:000435524300009, title = {Phonon-Mediated Colossal Magnetoresistance in Graphene/Black Phosphorus Heterostructures}, author = {Yanpeng Liu and Indra Yudhistira and Ming Yang and Evan Laksono and Yong Zheng Luo and Jianyi Chen and Junpeng Lu and Yuan Ping Feng and Shaffique Adam and Kian Ping Loh}, doi = {10.1021/acs.nanolett.8b00155}, times_cited = {0}, issn = {1530-6984}, year = {2018}, date = {2018-06-01}, journal = {NANO LETTERS}, volume = {18}, number = {6}, pages = {3377-3383}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {There is a huge demand for magnetoresistance (MR) sensors with high sensitivity, low energy consumption, and room temperature operation. It is well-known that spatial charge inhomogeneity due to impurities or defects introduces mobility fluctuations in monolayer graphene and gives rise to MR in the presence of an externally applied magnetic field. However, to realize a MR sensor based on this effect is hampered by the difficulty in controlling the spatial distribution of impurities and the weak magnetoresistance effect at the monolayer regime. Here, we fabricate a highly stable monolayer graphene-on-black phosphorus (G/BP) heterostructure device that exhibits a giant MR of 775% at 9 T magnetic field and 300 K, exceeding by far the MR effects from devices made from either monolayer graphene or few-layer BP alone. The positive MR of the G/BP device decreases when the temperature is lowered, indicating a phonon-mediated process in addition to scattering by charge impurities. Moreover, a nonlocal MR of >10 000% is achieved for the G/BP device at room temperature due to an enhanced flavor Hall effect induced by the BP channel. Our results show that electron-phonon coupling between 2D material and a suitable substrate can be exploited to create giant MR effects in Dirac semimetals.}, keywords = {}, pubstate = {published}, tppubtype = {article} } There is a huge demand for magnetoresistance (MR) sensors with high sensitivity, low energy consumption, and room temperature operation. It is well-known that spatial charge inhomogeneity due to impurities or defects introduces mobility fluctuations in monolayer graphene and gives rise to MR in the presence of an externally applied magnetic field. However, to realize a MR sensor based on this effect is hampered by the difficulty in controlling the spatial distribution of impurities and the weak magnetoresistance effect at the monolayer regime. Here, we fabricate a highly stable monolayer graphene-on-black phosphorus (G/BP) heterostructure device that exhibits a giant MR of 775% at 9 T magnetic field and 300 K, exceeding by far the MR effects from devices made from either monolayer graphene or few-layer BP alone. The positive MR of the G/BP device decreases when the temperature is lowered, indicating a phonon-mediated process in addition to scattering by charge impurities. Moreover, a nonlocal MR of >10 000% is achieved for the G/BP device at room temperature due to an enhanced flavor Hall effect induced by the BP channel. Our results show that electron-phonon coupling between 2D material and a suitable substrate can be exploited to create giant MR effects in Dirac semimetals. |
Ho, Derek Y H; Yudhistira, Indra; Chakraborty, Nilotpal; Adam, Shaffique Theoretical determination of hydrodynamic window in monolayer and bilayer graphene from scattering rates Journal Article PHYSICAL REVIEW B, 97 (12), 2018, ISSN: 2469-9950. @article{ISI:000428011700002, title = {Theoretical determination of hydrodynamic window in monolayer and bilayer graphene from scattering rates}, author = {Derek Y H Ho and Indra Yudhistira and Nilotpal Chakraborty and Shaffique Adam}, doi = {10.1103/PhysRevB.97.121404}, times_cited = {0}, issn = {2469-9950}, year = {2018}, date = {2018-03-22}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {12}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Electrons behave like a classical fluid with a momentum distribution function that varies slowly in space and time when the quantum-mechanical carrier-carrier scattering dominates over all other scattering processes. Recent experiments in monolayer and bilayer graphene have reported signatures of such hydrodynamic electron behavior in ultraclean devices. In this theoretical work, starting from a microscopic treatment of electron-electron, electron-phonon, and electron-impurity interactions within the random phase approximation, we demonstrate that monolayer and bilayer graphene both host two different hydrodynamic regimes. We predict that the hydrodynamic window in bilayer graphene is stronger than in monolayer graphene, and has a characteristic "v shape" as opposed to a "lung shape." Finally, we collapse experimental data onto a universal disorder-limited theory, demonstrating that the observed violation of the Wiedemann-Franz law in monolayers occurs in a regime dominated by impurity-induced electron-hole puddles.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electrons behave like a classical fluid with a momentum distribution function that varies slowly in space and time when the quantum-mechanical carrier-carrier scattering dominates over all other scattering processes. Recent experiments in monolayer and bilayer graphene have reported signatures of such hydrodynamic electron behavior in ultraclean devices. In this theoretical work, starting from a microscopic treatment of electron-electron, electron-phonon, and electron-impurity interactions within the random phase approximation, we demonstrate that monolayer and bilayer graphene both host two different hydrodynamic regimes. We predict that the hydrodynamic window in bilayer graphene is stronger than in monolayer graphene, and has a characteristic "v shape" as opposed to a "lung shape." Finally, we collapse experimental data onto a universal disorder-limited theory, demonstrating that the observed violation of the Wiedemann-Franz law in monolayers occurs in a regime dominated by impurity-induced electron-hole puddles. |
2017 |
Edmonds, Mark T; Collins, James L; Hellerstedt, Jack; Yudhistira, Indra; Gomes, Lidia C; Rodrigues, Joao N B; Adam, Shaffique; Fuhrer, Michael S Spatial charge inhomogeneity and defect states in topological Dirac semimetal thin films of Na3Bi Journal Article SCIENCE ADVANCES, 3 (12), 2017, ISSN: 2375-2548. @article{ISI:000426690900012, title = {Spatial charge inhomogeneity and defect states in topological Dirac semimetal thin films of Na_{3}Bi}, author = {Mark T Edmonds and James L Collins and Jack Hellerstedt and Indra Yudhistira and Lidia C Gomes and Joao N B Rodrigues and Shaffique Adam and Michael S Fuhrer}, doi = {10.1126/sciadv.aao6661}, times_cited = {0}, issn = {2375-2548}, year = {2017}, date = {2017-12-01}, journal = {SCIENCE ADVANCES}, volume = {3}, number = {12}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {Topological Dirac semimetals (TDSs) are three-dimensional analogs of graphene, with carriers behaving like mass-less Dirac fermions in three dimensions. In graphene, substrate disorder drives fluctuations in Fermi energy, necessitating construction of heterostructures of graphene and hexagonal boron nitride (h-BN) to minimize the fluctuations. Three-dimensional TDSs obviate the substrate and should show reduced E-F fluctuations due to better metallic screening and higher dielectric constants. We map the potential fluctuations in TDS Na3Bi using a scanning tunneling microscope. The rms potential fluctuations are significantly smaller than the thermal energy room temperature (Delta E-F,E-rms = 4 to 6 meV = 40 to 70 K) and comparable to the highest-quality graphene on h-BN. Surface Na vacancies produce a novel resonance close to the Dirac point with surprisingly large spatial extent and provide a unique way to tune the surface density of states in a TDS thin-film material. Sparse defect clusters show bound states whose occupation may be changed by applying a bias to the scanning tunneling microscope tip, offering an opportunity to study a quantum dot connected to a TDS reservoir.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Topological Dirac semimetals (TDSs) are three-dimensional analogs of graphene, with carriers behaving like mass-less Dirac fermions in three dimensions. In graphene, substrate disorder drives fluctuations in Fermi energy, necessitating construction of heterostructures of graphene and hexagonal boron nitride (h-BN) to minimize the fluctuations. Three-dimensional TDSs obviate the substrate and should show reduced E-F fluctuations due to better metallic screening and higher dielectric constants. We map the potential fluctuations in TDS Na3Bi using a scanning tunneling microscope. The rms potential fluctuations are significantly smaller than the thermal energy room temperature (Delta E-F,E-rms = 4 to 6 meV = 40 to 70 K) and comparable to the highest-quality graphene on h-BN. Surface Na vacancies produce a novel resonance close to the Dirac point with surprisingly large spatial extent and provide a unique way to tune the surface density of states in a TDS thin-film material. Sparse defect clusters show bound states whose occupation may be changed by applying a bias to the scanning tunneling microscope tip, offering an opportunity to study a quantum dot connected to a TDS reservoir. |
Hellerstedt, Jack; Yudhistira, Indra; Edmonds, Mark T; Liu, Chang; Collins, James; Adam, Shaffique; Fuhrer, Michael S Electrostatic modulation of the electronic properties of Dirac semimetal Na3Bi thin films Journal Article PHYSICAL REVIEW MATERIALS, 1 (5), 2017, ISSN: 2475-9953. @article{ISI:000416590800004, title = {Electrostatic modulation of the electronic properties of Dirac semimetal Na_{3}Bi thin films}, author = {Jack Hellerstedt and Indra Yudhistira and Mark T Edmonds and Chang Liu and James Collins and Shaffique Adam and Michael S Fuhrer}, doi = {10.1103/PhysRevMaterials.1.054203}, times_cited = {0}, issn = {2475-9953}, year = {2017}, date = {2017-10-30}, journal = {PHYSICAL REVIEW MATERIALS}, volume = {1}, number = {5}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Large-area thin films of topological Dirac semimetal Na3Bi are grown on amorphous SiO2:Si substrates to realize a field-effect transistor with the doped Si acting as a back gate. As-grown films show charge carrier mobilities exceeding 7 000 cm(2)/V s and carrier densities below 3 x 10(18) cm(-3), comparable to the best thin-film Na3Bi. An ambipolar field effect and minimum conductivity are observed, characteristic of Dirac electronic systems. The results are quantitatively understood within a model of disorder-induced charge inhomogeneity in topological Dirac semimetals. The hole mobility is significantly larger than the electron mobility in Na3Bi which we ascribe to the inverted band structure. When present, these holes dominate the transport properties.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Large-area thin films of topological Dirac semimetal Na3Bi are grown on amorphous SiO2:Si substrates to realize a field-effect transistor with the doped Si acting as a back gate. As-grown films show charge carrier mobilities exceeding 7 000 cm(2)/V s and carrier densities below 3 x 10(18) cm(-3), comparable to the best thin-film Na3Bi. An ambipolar field effect and minimum conductivity are observed, characteristic of Dirac electronic systems. The results are quantitatively understood within a model of disorder-induced charge inhomogeneity in topological Dirac semimetals. The hole mobility is significantly larger than the electron mobility in Na3Bi which we ascribe to the inverted band structure. When present, these holes dominate the transport properties. |
Datta, Subhadeep; Cai, Yongqing; Yudhistira, Indra; Zeng, Zebing; Zhang, Yong-Wei; Zhang, Han; Adam, Shaffique; Wu, Jishan; Loh, Kian Ping Tuning magnetoresistance in molybdenum disulphide and graphene using a molecular spin transition Journal Article NATURE COMMUNICATIONS, 8 , 2017, ISSN: 2041-1723. @article{ISI:000411526700022, title = {Tuning magnetoresistance in molybdenum disulphide and graphene using a molecular spin transition}, author = {Subhadeep Datta and Yongqing Cai and Indra Yudhistira and Zebing Zeng and Yong-Wei Zhang and Han Zhang and Shaffique Adam and Jishan Wu and Kian Ping Loh}, doi = {10.1038/s41467-017-00727-w}, times_cited = {2}, issn = {2041-1723}, year = {2017}, date = {2017-09-22}, journal = {NATURE COMMUNICATIONS}, volume = {8}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Coupling spins of molecular magnets to two-dimensional (2D) materials provides a framework to manipulate the magneto-conductance of 2D materials. However, with most molecules, the spin coupling is usually weak and devices fabricated from these require operation at low temperatures, which prevents practical applications. Here, we demonstrate field-effect transistors based on the coupling of a magnetic molecule quinoidal dithienyl perylenequinodimethane (QDTP) to 2D materials. Uniquely, QDTP switches from a spin-singlet state at low temperature to a spin-triplet state above 370 K, and the spin transition can be electrically transduced by both graphene and molybdenum disulphide. Graphene-QDTP shows hole-doping and a large positive magnetoresistance (similar to 50%), while molybdenum disulphide-QDTP demonstrates electron-doping and a switch to large negative magnetoresistance (similar to 100%) above the magnetic transition. Our work shows the promise of spin detection at high temperature by coupling 2D materials and molecular magnets.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Coupling spins of molecular magnets to two-dimensional (2D) materials provides a framework to manipulate the magneto-conductance of 2D materials. However, with most molecules, the spin coupling is usually weak and devices fabricated from these require operation at low temperatures, which prevents practical applications. Here, we demonstrate field-effect transistors based on the coupling of a magnetic molecule quinoidal dithienyl perylenequinodimethane (QDTP) to 2D materials. Uniquely, QDTP switches from a spin-singlet state at low temperature to a spin-triplet state above 370 K, and the spin transition can be electrically transduced by both graphene and molybdenum disulphide. Graphene-QDTP shows hole-doping and a large positive magnetoresistance (similar to 50%), while molybdenum disulphide-QDTP demonstrates electron-doping and a switch to large negative magnetoresistance (similar to 100%) above the magnetic transition. Our work shows the promise of spin detection at high temperature by coupling 2D materials and molecular magnets. |
2015 |
Yudhistira, Indra; Adam, Shaffique Theory for electron transport in graphene Journal Article SYNTHETIC METALS, 210 , pp. 2-8, 2015, ISSN: 0379-6779. @article{ISI:000367770200002, title = {Theory for electron transport in graphene}, author = {Indra Yudhistira and Shaffique Adam}, doi = {10.1016/j.synthmet.2015.07.027}, times_cited = {0}, issn = {0379-6779}, year = {2015}, date = {2015-12-01}, journal = {SYNTHETIC METALS}, volume = {210}, pages = {2-8}, publisher = {ELSEVIER SCIENCE SA}, address = {PO BOX 564, 1001 LAUSANNE, SWITZERLAND}, abstract = {In this pedagogical article, we address a surprising result in the graphene transport literature, namely, measurements of the classical transport indicate that charged impurities dominate the electron scattering, while quantum transport measurements suggest that mechanical deformations that break time-reversal symmetry within a valley dominate the scattering. But surely it is the same impurities that are at play for both the phase-incoherent and phase-coherent components to the electron transport. By selectively reviewing the relevant theories for the classical and quantum transport and a careful examination of available experimental data, we show that the uncertainty in the quantum transport data makes it consistent with both with ripple-scattering being completely negligible, but also with the unphysical case of ripple scattering contributing only to quantum transport but not the classical transport. We therefore conclude that the experimental uncertainty in the available quantum transport data is too large to make any definitive statements about the relevant transport mechanisms in graphene. (C) 2015 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this pedagogical article, we address a surprising result in the graphene transport literature, namely, measurements of the classical transport indicate that charged impurities dominate the electron scattering, while quantum transport measurements suggest that mechanical deformations that break time-reversal symmetry within a valley dominate the scattering. But surely it is the same impurities that are at play for both the phase-incoherent and phase-coherent components to the electron transport. By selectively reviewing the relevant theories for the classical and quantum transport and a careful examination of available experimental data, we show that the uncertainty in the quantum transport data makes it consistent with both with ripple-scattering being completely negligible, but also with the unphysical case of ripple scattering contributing only to quantum transport but not the classical transport. We therefore conclude that the experimental uncertainty in the available quantum transport data is too large to make any definitive statements about the relevant transport mechanisms in graphene. (C) 2015 Elsevier B.V. All rights reserved. |