Deshdeep Sahdev - Academia.edu (original) (raw)

Papers by Deshdeep Sahdev

Physical review, Dec 15, 1984

A range of solutions to Einstein's equations in 1+d +D dimensions is presented for a variety of p... more A range of solutions to Einstein's equations in 1+d +D dimensions is presented for a variety of perfect-Quid energy-momentum tensors. The techniques used to obtain these solutions are explained at some length. Solutions with D dimensions eventually collapsing and d expanding are singled put and studied in detail. It is explained how the higher-dimensional universe passes into a (1+8)dimensional Friedmann-Robertson-Walker phase. The modifications in the thermal history of the universe are traced. It is found that this altered scenario offers a resolution to the horizon problem.

Bulletin of the American Physical Society, Mar 3, 2020

Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering d... more Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering due to defects and phonons. These processes can become sufficiently weak in two-dimensional materials, giving rise to either ballistic or hydrodynamic transport, depending on the strength of electron-electron scattering. We show that the ballistic regime is a quantum critical point (QCP) on the regime boundary separating Ohmic and hydrodynamic transport. The QCP corresponds to a free conformal field theory (CFT) with a dynamical scaling exponent z = 1. Its nontrivial aspects emerge in device geometries with shear, wherein the regime has an intrinsic universal dissipation, a nonlocal current-voltage relation, and exhibits the critical scaling of the underlying CFT. The Fermi surface has electron-hole pockets across all angular scales and the current flow has vortices at all spatial scales. We image the fluctuations in high-definition and animate their emergence as experimental parameters are tuned to the QCP a. The vortices clearly demonstrate that Pauli exclusion alone can produce collective effects, with low-frequency AC transport mediated by vortex dynamics b. The scale-invariant spatial structure is much richer than that of an interaction-dominated hydrodynamic regime, which only has a single vortex at the device scale. Our findings provide a theoretical framework for both interaction-free and interaction-dominated non-Ohmic transport in two-dimensional materials, as seen in several contemporary experiments.

arXiv: Mesoscale and Nanoscale Physics, 2018

Electron transport can transition from Ohmic to hydrodynamic when electron-electron scattering do... more Electron transport can transition from Ohmic to hydrodynamic when electron-electron scattering dominates, as shown in several recent experiments in systems such as Graphene. We show that microwave-frequency AC sources can excite hydrodynamic behavior involving vigorous vortex generation and reconnection, far more easily than the DC sources used so far. We identify the change of sign in a nonlocal current - voltage phase as a robust probe of the transition to the electronic hydrodynamic regime.

Physical Review D, 1994

Scalar waves in a wormhole geometry

Physica D: Nonlinear Phenomena, 1996

We study the Gödel universe through worldlines associated with motion at constant speed and const... more We study the Gödel universe through worldlines associated with motion at constant speed and constant acceleration orthogonal to the instantaneous velocity (WSAs). We show that these worldlines can be used to access every region — both spatial and temporal — of the space-time. We capture the insights they accord in a series of sketches, which extend significantly the Hawking and Ellis picture of the Gödel universe.

AIP Advances, 2021

Temperature-dependent magnetic and a.c. susceptibility measurements were done on single phase pol... more Temperature-dependent magnetic and a.c. susceptibility measurements were done on single phase polycrystalline LaMn1-yCoyO3 (y = 0.1, 0.4) samples. The field cooled and zero field cooled magnetic measurements performed indicate the presence of spin glass state which is established using a.c. susceptibility measurements. The a.c. susceptibility data analyzed using Arrhenius and Vogel–Fulcher (VF) law reveal the presence of canonical spin glass.

Electron transport in clean 2D systems with weak electron-phonon (e-ph) coupling can transition f... more Electron transport in clean 2D systems with weak electron-phonon (e-ph) coupling can transition from an Ohmic to a ballistic or a hydrodynamic regime. The ballistic regime occurs when electronelectron (e-e) scattering is weak whereas the hydrodynamic regime arises when this scattering is strong. Despite this difference, we find that vortices and a negative nonlocal resistance believed to be quintessentially hydrodynamic are equally characteristic of the ballistic regime. These nonOhmic regimes cannot be distinguished in DC transport without changing experimental conditions. Further, as our kinetic calculations show, the hydrodynamic regime in DC transport is highly fragile and is wiped out by even sparse disorder and e-ph scattering. We show that microwave-frequency AC sources by contrast readily excite hydrodynamic modes with current vortices that are robust to disorder and e-ph scattering. Indeed, current reversals in the non-Ohmic regimes occur via repeated vortex generation and ...

arXiv: Mesoscale and Nanoscale Physics, 2019

Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering d... more Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering due to defects and phonons. These processes can become sufficiently weak in two-dimensional materials, giving rise to either ballistic or hydrodynamic transport, depending on the strength of electron-electron scattering. We show that the ballistic regime is a quantum critical point (QCP) on the regime boundary separating Ohmic and hydrodynamic transport. The QCP corresponds to a \emph{free} conformal field theory (CFT) with a dynamical scaling exponent z=1z = 1z=1. Its nontrivial aspects emerge in device geometries with shear, wherein the regime has an intrinsic universal dissipation, a nonlocal current-voltage relation, and exhibits the critical scaling of the underlying CFT. The Fermi surface has electron-hole pockets across all angular scales and the current flow has \emph{vortices} at all spatial scales. We image the fluctuations in high-definition and animate their emergence as experimen...

A radio frequency Quadrupole Mass Analyser (QMA) separates ions of different charge-tomass ratio ... more A radio frequency Quadrupole Mass Analyser (QMA) separates ions of different charge-tomass ratio by exploiting the phenomenon of parametric resonance for charged particles moving through an AC quadrupole field. We have studied the standard configurations of QMAs in detail with extensive simulations, and have accurately calculated the non-linear corrections to the quadrupole field. We have also found a novel configuration of electrodes which has much better field linearity due to simultaneous cancellation of several higher moments, and this should enable us to push the current limit on resolution set by non-linear resonances. We have almost completed the fabrication of a conventional QMA from scratch, including a quadrupole of 4 cylindrical electrodes, an Electron Impact (EI) ion source for producing a collimated beam of ions from a gas sample, a Faraday Cup detector arrangement with associated low-noise electronics, and the vacuum chambers to house the entire arrangement. We will pr...

Physical Review B

Electron transport in clean 2D systems with weak electron-phonon (e-ph) coupling can transition f... more Electron transport in clean 2D systems with weak electron-phonon (e-ph) coupling can transition from an Ohmic to a ballistic or a hydrodynamic regime. The ballistic regime occurs when electronelectron (e-e) scattering is weak whereas the hydrodynamic regime arises when this scattering is strong. Despite this difference, we find that vortices and a negative nonlocal resistance believed to be quintessentially hydrodynamic are equally characteristic of the ballistic regime. These non-Ohmic regimes cannot be distinguished in DC transport without changing experimental conditions. Further, as our kinetic calculations show, the hydrodynamic regime in DC transport is highly fragile and is wiped out by even sparse disorder and e-ph scattering. We show that microwave-frequency AC sources by contrast readily excite hydrodynamic modes with current vortices that are robust to disorder and e-ph scattering. Indeed, current reversals in the non-Ohmic regimes occur via repeated vortex generation and mergers through reconnections, as in classical 2D fluids. Crucially, AC sources give rise to strong correlations across the entire device that unambiguously distinguish all regimes. These correlations in the form of nonlocal current-voltage and voltage-voltage phases directly check for the presence of a nonlocal current-voltage relation signifying the onset of non-Ohmic behavior as well as also for the dominance of bulk interactions, needed to confirm the presence of a hydrodynamic regime. We use these probes to demarcate all regimes in an experimentally realizable graphene device and find that the ballistic regime has a much larger extent in parameter space than the hydrodynamic regime.

Thesis Case Western Reserve University 1979 Source Dissertation Abstracts International Volume 40 07 Section B Page 3230, 1979

ABSTRACT We define charge conjugation asymmetries for quark-anti-quark and quark-quark processes,... more ABSTRACT We define charge conjugation asymmetries for quark-anti-quark and quark-quark processes, which lead to asymmetries for a host of hadronic reactions. The underlying asymmetry is free of infrared divergences and has QED analogs which can be used for purposes of comparison. The convoluted asymmetry is insensitive to the precise form of the parton distribution functions and thus provides us with a direct probe of the world of quarks and gluons. The experimental issues involved with picking out the asymmetry are also discussed.

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We study the G\"odel universe through worldlines associated with motion at constant speed an... more We study the G\"odel universe through worldlines associated with motion at constant speed and constant acceleration orthogonal to the instantaneous velocity (WSAs). We show that these worldlines can be used to access every region -- both spatial and temporal -- of the space-time. We capture the insights they accord in a series of sketches, which extend significantly the Hawking and

Phys Rev D, 1979

We augment a previous discussion of the production of pairs of gauge bosons with a study of the r... more We augment a previous discussion of the production of pairs of gauge bosons with a study of the reactions pp and p¯p-->WZ0X or WgammaX. As before, these depend upon trilinear boson couplings and the high-energy behavior is controlled by gauge cancellations. In particular, the (hard) photon production is sensitive to the magnetic-moment parameter kappa for the W. We also discuss the related neutrino reactions, nue-->WZ0 or Wgamma, which may be of interest in very-high-energy cosmic-ray physics.

We investigate vacuum solutions of Einstein's equation for a universe with an S^1 topology of... more We investigate vacuum solutions of Einstein's equation for a universe with an S^1 topology of time. Such a universe behaves like a time-machine and has geodesics which coincide with closed time-like curves (CTCs). A system evolving along a CTC experiences the Loschmidt velocity reversion and undergoes a recurrence commensurate with the universal period. We indicate why this universe is free

We study the G\"odel universe through worldlines associated with motion at constant speed an... more We study the G\"odel universe through worldlines associated with motion at constant speed and constant acceleration orthogonal to the instantaneous velocity (WSAs). We show that these worldlines can be used to access every region -- both spatial and temporal -- of the space-time. We capture the insights they accord in a series of sketches, which extend significantly the Hawking and

Physical Review Letters, 1979

... RW Brown and KO Mikaelian, Phys. ... MWG giJ j Qi + 1 2) 2 +u2+ 2sM W2 + - 1)(Q + 1 t -u wher... more ... RW Brown and KO Mikaelian, Phys. ... MWG giJ j Qi + 1 2) 2 +u2+ 2sM W2 + - 1)(Q + 1 t -u where s= (k +k2)2, t (p -k )2, and u (p -k2)2, with s + t + u =Mw2, gi; = cosOc for qi?j, -= and sT, and gij = sin0c for qii?j =siu and dco Qi I el is the charge of the quark qj; we have set Qj =Qi +1 ...

Physical review, Dec 15, 1984

A range of solutions to Einstein's equations in 1+d +D dimensions is presented for a variety of p... more A range of solutions to Einstein's equations in 1+d +D dimensions is presented for a variety of perfect-Quid energy-momentum tensors. The techniques used to obtain these solutions are explained at some length. Solutions with D dimensions eventually collapsing and d expanding are singled put and studied in detail. It is explained how the higher-dimensional universe passes into a (1+8)dimensional Friedmann-Robertson-Walker phase. The modifications in the thermal history of the universe are traced. It is found that this altered scenario offers a resolution to the horizon problem.

Bulletin of the American Physical Society, Mar 3, 2020

Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering d... more Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering due to defects and phonons. These processes can become sufficiently weak in two-dimensional materials, giving rise to either ballistic or hydrodynamic transport, depending on the strength of electron-electron scattering. We show that the ballistic regime is a quantum critical point (QCP) on the regime boundary separating Ohmic and hydrodynamic transport. The QCP corresponds to a free conformal field theory (CFT) with a dynamical scaling exponent z = 1. Its nontrivial aspects emerge in device geometries with shear, wherein the regime has an intrinsic universal dissipation, a nonlocal current-voltage relation, and exhibits the critical scaling of the underlying CFT. The Fermi surface has electron-hole pockets across all angular scales and the current flow has vortices at all spatial scales. We image the fluctuations in high-definition and animate their emergence as experimental parameters are tuned to the QCP a. The vortices clearly demonstrate that Pauli exclusion alone can produce collective effects, with low-frequency AC transport mediated by vortex dynamics b. The scale-invariant spatial structure is much richer than that of an interaction-dominated hydrodynamic regime, which only has a single vortex at the device scale. Our findings provide a theoretical framework for both interaction-free and interaction-dominated non-Ohmic transport in two-dimensional materials, as seen in several contemporary experiments.

arXiv: Mesoscale and Nanoscale Physics, 2018

Electron transport can transition from Ohmic to hydrodynamic when electron-electron scattering do... more Electron transport can transition from Ohmic to hydrodynamic when electron-electron scattering dominates, as shown in several recent experiments in systems such as Graphene. We show that microwave-frequency AC sources can excite hydrodynamic behavior involving vigorous vortex generation and reconnection, far more easily than the DC sources used so far. We identify the change of sign in a nonlocal current - voltage phase as a robust probe of the transition to the electronic hydrodynamic regime.

Physical Review D, 1994

Scalar waves in a wormhole geometry

Physica D: Nonlinear Phenomena, 1996

We study the Gödel universe through worldlines associated with motion at constant speed and const... more We study the Gödel universe through worldlines associated with motion at constant speed and constant acceleration orthogonal to the instantaneous velocity (WSAs). We show that these worldlines can be used to access every region — both spatial and temporal — of the space-time. We capture the insights they accord in a series of sketches, which extend significantly the Hawking and Ellis picture of the Gödel universe.

AIP Advances, 2021

Temperature-dependent magnetic and a.c. susceptibility measurements were done on single phase pol... more Temperature-dependent magnetic and a.c. susceptibility measurements were done on single phase polycrystalline LaMn1-yCoyO3 (y = 0.1, 0.4) samples. The field cooled and zero field cooled magnetic measurements performed indicate the presence of spin glass state which is established using a.c. susceptibility measurements. The a.c. susceptibility data analyzed using Arrhenius and Vogel–Fulcher (VF) law reveal the presence of canonical spin glass.

Electron transport in clean 2D systems with weak electron-phonon (e-ph) coupling can transition f... more Electron transport in clean 2D systems with weak electron-phonon (e-ph) coupling can transition from an Ohmic to a ballistic or a hydrodynamic regime. The ballistic regime occurs when electronelectron (e-e) scattering is weak whereas the hydrodynamic regime arises when this scattering is strong. Despite this difference, we find that vortices and a negative nonlocal resistance believed to be quintessentially hydrodynamic are equally characteristic of the ballistic regime. These nonOhmic regimes cannot be distinguished in DC transport without changing experimental conditions. Further, as our kinetic calculations show, the hydrodynamic regime in DC transport is highly fragile and is wiped out by even sparse disorder and e-ph scattering. We show that microwave-frequency AC sources by contrast readily excite hydrodynamic modes with current vortices that are robust to disorder and e-ph scattering. Indeed, current reversals in the non-Ohmic regimes occur via repeated vortex generation and ...

arXiv: Mesoscale and Nanoscale Physics, 2019

Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering d... more Electronic transport in Fermi liquids is usually Ohmic, because of momentum-relaxing scattering due to defects and phonons. These processes can become sufficiently weak in two-dimensional materials, giving rise to either ballistic or hydrodynamic transport, depending on the strength of electron-electron scattering. We show that the ballistic regime is a quantum critical point (QCP) on the regime boundary separating Ohmic and hydrodynamic transport. The QCP corresponds to a \emph{free} conformal field theory (CFT) with a dynamical scaling exponent z=1z = 1z=1. Its nontrivial aspects emerge in device geometries with shear, wherein the regime has an intrinsic universal dissipation, a nonlocal current-voltage relation, and exhibits the critical scaling of the underlying CFT. The Fermi surface has electron-hole pockets across all angular scales and the current flow has \emph{vortices} at all spatial scales. We image the fluctuations in high-definition and animate their emergence as experimen...

A radio frequency Quadrupole Mass Analyser (QMA) separates ions of different charge-tomass ratio ... more A radio frequency Quadrupole Mass Analyser (QMA) separates ions of different charge-tomass ratio by exploiting the phenomenon of parametric resonance for charged particles moving through an AC quadrupole field. We have studied the standard configurations of QMAs in detail with extensive simulations, and have accurately calculated the non-linear corrections to the quadrupole field. We have also found a novel configuration of electrodes which has much better field linearity due to simultaneous cancellation of several higher moments, and this should enable us to push the current limit on resolution set by non-linear resonances. We have almost completed the fabrication of a conventional QMA from scratch, including a quadrupole of 4 cylindrical electrodes, an Electron Impact (EI) ion source for producing a collimated beam of ions from a gas sample, a Faraday Cup detector arrangement with associated low-noise electronics, and the vacuum chambers to house the entire arrangement. We will pr...

Physical Review B

Electron transport in clean 2D systems with weak electron-phonon (e-ph) coupling can transition f... more Electron transport in clean 2D systems with weak electron-phonon (e-ph) coupling can transition from an Ohmic to a ballistic or a hydrodynamic regime. The ballistic regime occurs when electronelectron (e-e) scattering is weak whereas the hydrodynamic regime arises when this scattering is strong. Despite this difference, we find that vortices and a negative nonlocal resistance believed to be quintessentially hydrodynamic are equally characteristic of the ballistic regime. These non-Ohmic regimes cannot be distinguished in DC transport without changing experimental conditions. Further, as our kinetic calculations show, the hydrodynamic regime in DC transport is highly fragile and is wiped out by even sparse disorder and e-ph scattering. We show that microwave-frequency AC sources by contrast readily excite hydrodynamic modes with current vortices that are robust to disorder and e-ph scattering. Indeed, current reversals in the non-Ohmic regimes occur via repeated vortex generation and mergers through reconnections, as in classical 2D fluids. Crucially, AC sources give rise to strong correlations across the entire device that unambiguously distinguish all regimes. These correlations in the form of nonlocal current-voltage and voltage-voltage phases directly check for the presence of a nonlocal current-voltage relation signifying the onset of non-Ohmic behavior as well as also for the dominance of bulk interactions, needed to confirm the presence of a hydrodynamic regime. We use these probes to demarcate all regimes in an experimentally realizable graphene device and find that the ballistic regime has a much larger extent in parameter space than the hydrodynamic regime.

Thesis Case Western Reserve University 1979 Source Dissertation Abstracts International Volume 40 07 Section B Page 3230, 1979

ABSTRACT We define charge conjugation asymmetries for quark-anti-quark and quark-quark processes,... more ABSTRACT We define charge conjugation asymmetries for quark-anti-quark and quark-quark processes, which lead to asymmetries for a host of hadronic reactions. The underlying asymmetry is free of infrared divergences and has QED analogs which can be used for purposes of comparison. The convoluted asymmetry is insensitive to the precise form of the parton distribution functions and thus provides us with a direct probe of the world of quarks and gluons. The experimental issues involved with picking out the asymmetry are also discussed.

[

We study the G\"odel universe through worldlines associated with motion at constant speed an... more We study the G\"odel universe through worldlines associated with motion at constant speed and constant acceleration orthogonal to the instantaneous velocity (WSAs). We show that these worldlines can be used to access every region -- both spatial and temporal -- of the space-time. We capture the insights they accord in a series of sketches, which extend significantly the Hawking and

Phys Rev D, 1979

We augment a previous discussion of the production of pairs of gauge bosons with a study of the r... more We augment a previous discussion of the production of pairs of gauge bosons with a study of the reactions pp and p¯p-->WZ0X or WgammaX. As before, these depend upon trilinear boson couplings and the high-energy behavior is controlled by gauge cancellations. In particular, the (hard) photon production is sensitive to the magnetic-moment parameter kappa for the W. We also discuss the related neutrino reactions, nue-->WZ0 or Wgamma, which may be of interest in very-high-energy cosmic-ray physics.

We investigate vacuum solutions of Einstein's equation for a universe with an S^1 topology of... more We investigate vacuum solutions of Einstein's equation for a universe with an S^1 topology of time. Such a universe behaves like a time-machine and has geodesics which coincide with closed time-like curves (CTCs). A system evolving along a CTC experiences the Loschmidt velocity reversion and undergoes a recurrence commensurate with the universal period. We indicate why this universe is free

We study the G\"odel universe through worldlines associated with motion at constant speed an... more We study the G\"odel universe through worldlines associated with motion at constant speed and constant acceleration orthogonal to the instantaneous velocity (WSAs). We show that these worldlines can be used to access every region -- both spatial and temporal -- of the space-time. We capture the insights they accord in a series of sketches, which extend significantly the Hawking and

Physical Review Letters, 1979

... RW Brown and KO Mikaelian, Phys. ... MWG giJ j Qi + 1 2) 2 +u2+ 2sM W2 + - 1)(Q + 1 t -u wher... more ... RW Brown and KO Mikaelian, Phys. ... MWG giJ j Qi + 1 2) 2 +u2+ 2sM W2 + - 1)(Q + 1 t -u where s= (k +k2)2, t (p -k )2, and u (p -k2)2, with s + t + u =Mw2, gi; = cosOc for qi?j, -= and sT, and gij = sin0c for qii?j =siu and dco Qi I el is the charge of the quark qj; we have set Qj =Qi +1 ...