H. Stoof - Profile on Academia.edu (original) (raw)
Papers by H. Stoof
Physical Review B, 2016
We study the electromagnetic properties of Weyl semimetals with strong interactions. Aiming for a... more We study the electromagnetic properties of Weyl semimetals with strong interactions. Aiming for a large-N expansion, we induce strong interactions by coupling a Weyl fermion with a tunable coupling constant g f to a quantum critical system with a large number of order O(N) fermionic and bosonic degrees of freedom. The critical fluctuations are described by a conformal field theory containing also fermionic composite operators with scaling dimension ∆. Employing the methods of the holographic correspondence, we then derive the effective theory of the Weyl fermions in the presence of external electric and magnetic fields in the large-N limit. In particular, we determine their frequency and momentum-dependent anomalous magnetic moment. We also determine the conductivity of the Weyl semimetal including the vertex corrections consistent with the Ward identity. Finally, we connect our construction to the case of Coulomb interactions in Weyl semimetals by tuning the parameters ∆ → 5/2 and g 2 f → e/ √ c 0.
Submitted to: New J. Phys
Lecture Notes in Physics, 2011
We present a theory for the low-temperature properties of a resonantly interacting Fermi mixture ... more We present a theory for the low-temperature properties of a resonantly interacting Fermi mixture in a trap, that goes beyond the local-density approximation. The theory corresponds essentially to a Landau-Ginzburg-like approach that includes self-energy effects to account for the strong interactions at unitarity. We show diagrammatically how these self-energy effects arise from fluctuations in the superfluid order parameter. Gradient terms of the order parameter are included to account for inhomogeneities. This approach incorporates the state-of-the-art knowledge of the homogeneous mixture with a population imbalance exactly and gives good agreement with the experimental density profiles of Shin et al. [Nature 451, 689 (2008)]. This allows us to calculate the universal surface tension of the interface between the equal-density superfluid and the partially polarized normal state of the mixture. We also discuss the possibility of a metastable state to explain the deformation of the superfluid core that is seen in the experiment of Partridge et al.
Hoge-temperatuur supergeleiding in ultrakoude Fermi-gassen
Physical Review Letters, 2004
We show that in an atomic Fermi gas near a Feshbach resonance the crossover between a Bose-Einste... more We show that in an atomic Fermi gas near a Feshbach resonance the crossover between a Bose-Einstein condensate of diatomic molecules and a Bose-Einstein condensate of Cooper pairs occurs at positive detuning, i.e., when the molecular energy level lies in the two-atom continuum. We determine the crossover temperature as a function of the applied magnetic field and find excellent agreement with the experiment of Regal et al. [Phys. Rev. Lett. 92, 040403 (2004)] that has recently observed this crossover temperature.
Physical Review B, 2001
We apply the theory of elasticity to study the effects of skyrmion mass on lattice dynamics in qu... more We apply the theory of elasticity to study the effects of skyrmion mass on lattice dynamics in quantum Hall systems. We find that massive Skyrme lattices behave like a Wigner crystal in the presence of a uniform perpendicular magnetic field. We make a comparison with the microscopic Hartree-Fock results to characterize the mass of quantum Hall skyrmions at ν = 1 and investigate how the low temperature phase of Skyrme lattices may be affected by the skyrmion mass.
Degeneracy effects on the relaxation and recombination of adsorbed doubly polarized atomic hydrogen
Physical Review B, 1994
... A gas of doubly spin-polarized hydrogen atoms ad-sorbed on superfluid helium with a binding e... more ... A gas of doubly spin-polarized hydrogen atoms ad-sorbed on superfluid helium with a binding energy of about one kelvin would be ... In particular, we can obtain the intrinsic two-body rate without degeneracy effects by using l i & =l p, p' & and tak-ing the limit p,p'J, O for pAp'. ...
Reply to “Comment on ‘Feshbach resonances in an optical lattice’ ”
Physical Review A, 2006
We show that the Comment by Diener and Ho [Phys. Rev. A 73, 017601 (2006)] is based on the misund... more We show that the Comment by Diener and Ho [Phys. Rev. A 73, 017601 (2006)] is based on the misunderstanding that the Hamiltonian used by Dickerscheid to describe Feshbach resonances in an optical lattice is a microscopic Hamiltonian as opposed to an effective Hamiltonian.
Journal of High Energy Physics, 2013
We continue our recently proposed holographic description of single-particle correlation function... more We continue our recently proposed holographic description of single-particle correlation functions for four-dimensional chiral fermions with Lifshitz scaling at zero chemical potential, paying particular attention to the dynamical exponent z = 2. We present new results for the spectral densities and dispersion relations at non-zero momenta and temperature. In contrast to the relativistic case with z = 1, we find the existence of a quantum phase transition from a non-Fermi liquid into a Fermi liquid in which two Fermi surfaces spontaneously form, even at zero chemical potential. Our findings show that the boundary system behaves like an undoped Weyl semimetal.
Journal of High Energy Physics, 2012
We study correlation functions of elementary fermions in strongly interacting field theories usin... more We study correlation functions of elementary fermions in strongly interacting field theories using the AdS/CFT correspondence. This correspondence generically associates bulk fields to composite operators in field theory. We modify the holographic prescription in order to obtain correlators that correspond to fermonic single-particle excitations by introducing a dynamical fermionic source localized on a UV brane in a holographic background. We work out the conditions when these correlators obey the zeroth frequency sum-rule satisfied by angle-resolved photo-emission spectroscopy (ARPES) and are thus directly relevant to the AdS/CMT correspondence. To illustrate our techniques, we study field theories at zero chemical potential with an arbitrary dynamical exponent z, i.e., the Lifshitz invariant conformal field theories, including the usual relativistic case z = 1.
Physical Review Letters, 2006
The real-space densities of a polarized strongly interacting two-component Fermi gas of 6 Li atom... more The real-space densities of a polarized strongly interacting two-component Fermi gas of 6 Li atoms reveal two low-temperature regimes, both with a fully paired core. At the lowest temperatures, the unpolarized core deforms with increasing polarization. Sharp boundaries between the core and the excess unpaired atoms are consistent with a phase separation driven by a first-order phase transition. In contrast, at higher temperatures the core does not deform but remains unpolarized up to a critical polarization. The boundaries are not sharp in this case, indicating a partially polarized shell between the core and the unpaired atoms. The temperature dependence is consistent with a tricritical point in the phase diagram.
Physical Review Letters, 2002
We study experimentally the transverse monopole mode of an elongated rubidium condensate. Because... more We study experimentally the transverse monopole mode of an elongated rubidium condensate. Because of the scaling invariance of the nonlinear Schrödinger (Gross-Pitaevskii) equation, the oscillation is monochromatic and sinusoidal at short times, even under strong excitation. For ultralow temperatures, the quality factor Q v 0 ͞g 0 can exceed 2000, where v 0 and g 0 are the mode angular frequency and damping rate. This value is much larger than any previously reported for other eigenmodes of a condensate. We also present the temperature variation of v 0 and g 0 .
Physical Review Letters, 2007
We present a general approach for describing trapped Fermi gases, when the cloud shape is distort... more We present a general approach for describing trapped Fermi gases, when the cloud shape is distorted with respect to the trap shape. Our approach provides a consistent way to explore physics beyond the local density approximation, if this is necessary due to the distortion. We illustrate this by analyzing in detail experimentally observed distortions in a trapped imbalanced Fermi mixture. In particular, we demonstrate in that case dramatic deviations from ellipsoidal cloud shapes arising from the competition between surface and bulk energies.
Physical Review Letters, 1997
At Landau level filling factors near n 1, quantum Hall ferromagnets form a Skyrme crystal state w... more At Landau level filling factors near n 1, quantum Hall ferromagnets form a Skyrme crystal state with quasi-long-range translational and noncollinear magnetic order. We develop an effective low energy theory which explains the presence of magnetic excitations in these systems at energies below the Larmor gap (D) and that predicts a dramatic enhancement of the nuclear spin relaxation rate by a factor of 10 3. The effective theory predicts a rich set of quantum and classical phase transitions. Based in part on accurate time-dependent Hartree-Fock calculations of the ordered state collective excitation spectrum, we discuss aspects of the T-n-D Skyrme crystal phase diagram. [S0031-9007(97)03424-8]
Physical Review Letters, 1989
DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:
Physical Review Letters, 2002
We variationally determine the dynamics of bright soliton trains composed of harmonically trapped... more We variationally determine the dynamics of bright soliton trains composed of harmonically trapped Bose-Einstein condensates with attractive interatomic interactions. In particular, we obtain the interaction potential between two solitons. We also discuss the formation of soliton trains due to the quantum mechanical phase fluctuations of a one-dimensional condensate.
Physical Review B, 2016
We study the electromagnetic properties of Weyl semimetals with strong interactions. Aiming for a... more We study the electromagnetic properties of Weyl semimetals with strong interactions. Aiming for a large-N expansion, we induce strong interactions by coupling a Weyl fermion with a tunable coupling constant g f to a quantum critical system with a large number of order O(N) fermionic and bosonic degrees of freedom. The critical fluctuations are described by a conformal field theory containing also fermionic composite operators with scaling dimension ∆. Employing the methods of the holographic correspondence, we then derive the effective theory of the Weyl fermions in the presence of external electric and magnetic fields in the large-N limit. In particular, we determine their frequency and momentum-dependent anomalous magnetic moment. We also determine the conductivity of the Weyl semimetal including the vertex corrections consistent with the Ward identity. Finally, we connect our construction to the case of Coulomb interactions in Weyl semimetals by tuning the parameters ∆ → 5/2 and g 2 f → e/ √ c 0.
Submitted to: New J. Phys
Lecture Notes in Physics, 2011
We present a theory for the low-temperature properties of a resonantly interacting Fermi mixture ... more We present a theory for the low-temperature properties of a resonantly interacting Fermi mixture in a trap, that goes beyond the local-density approximation. The theory corresponds essentially to a Landau-Ginzburg-like approach that includes self-energy effects to account for the strong interactions at unitarity. We show diagrammatically how these self-energy effects arise from fluctuations in the superfluid order parameter. Gradient terms of the order parameter are included to account for inhomogeneities. This approach incorporates the state-of-the-art knowledge of the homogeneous mixture with a population imbalance exactly and gives good agreement with the experimental density profiles of Shin et al. [Nature 451, 689 (2008)]. This allows us to calculate the universal surface tension of the interface between the equal-density superfluid and the partially polarized normal state of the mixture. We also discuss the possibility of a metastable state to explain the deformation of the superfluid core that is seen in the experiment of Partridge et al.
Hoge-temperatuur supergeleiding in ultrakoude Fermi-gassen
Physical Review Letters, 2004
We show that in an atomic Fermi gas near a Feshbach resonance the crossover between a Bose-Einste... more We show that in an atomic Fermi gas near a Feshbach resonance the crossover between a Bose-Einstein condensate of diatomic molecules and a Bose-Einstein condensate of Cooper pairs occurs at positive detuning, i.e., when the molecular energy level lies in the two-atom continuum. We determine the crossover temperature as a function of the applied magnetic field and find excellent agreement with the experiment of Regal et al. [Phys. Rev. Lett. 92, 040403 (2004)] that has recently observed this crossover temperature.
Physical Review B, 2001
We apply the theory of elasticity to study the effects of skyrmion mass on lattice dynamics in qu... more We apply the theory of elasticity to study the effects of skyrmion mass on lattice dynamics in quantum Hall systems. We find that massive Skyrme lattices behave like a Wigner crystal in the presence of a uniform perpendicular magnetic field. We make a comparison with the microscopic Hartree-Fock results to characterize the mass of quantum Hall skyrmions at ν = 1 and investigate how the low temperature phase of Skyrme lattices may be affected by the skyrmion mass.
Degeneracy effects on the relaxation and recombination of adsorbed doubly polarized atomic hydrogen
Physical Review B, 1994
... A gas of doubly spin-polarized hydrogen atoms ad-sorbed on superfluid helium with a binding e... more ... A gas of doubly spin-polarized hydrogen atoms ad-sorbed on superfluid helium with a binding energy of about one kelvin would be ... In particular, we can obtain the intrinsic two-body rate without degeneracy effects by using l i & =l p, p' & and tak-ing the limit p,p'J, O for pAp'. ...
Reply to “Comment on ‘Feshbach resonances in an optical lattice’ ”
Physical Review A, 2006
We show that the Comment by Diener and Ho [Phys. Rev. A 73, 017601 (2006)] is based on the misund... more We show that the Comment by Diener and Ho [Phys. Rev. A 73, 017601 (2006)] is based on the misunderstanding that the Hamiltonian used by Dickerscheid to describe Feshbach resonances in an optical lattice is a microscopic Hamiltonian as opposed to an effective Hamiltonian.
Journal of High Energy Physics, 2013
We continue our recently proposed holographic description of single-particle correlation function... more We continue our recently proposed holographic description of single-particle correlation functions for four-dimensional chiral fermions with Lifshitz scaling at zero chemical potential, paying particular attention to the dynamical exponent z = 2. We present new results for the spectral densities and dispersion relations at non-zero momenta and temperature. In contrast to the relativistic case with z = 1, we find the existence of a quantum phase transition from a non-Fermi liquid into a Fermi liquid in which two Fermi surfaces spontaneously form, even at zero chemical potential. Our findings show that the boundary system behaves like an undoped Weyl semimetal.
Journal of High Energy Physics, 2012
We study correlation functions of elementary fermions in strongly interacting field theories usin... more We study correlation functions of elementary fermions in strongly interacting field theories using the AdS/CFT correspondence. This correspondence generically associates bulk fields to composite operators in field theory. We modify the holographic prescription in order to obtain correlators that correspond to fermonic single-particle excitations by introducing a dynamical fermionic source localized on a UV brane in a holographic background. We work out the conditions when these correlators obey the zeroth frequency sum-rule satisfied by angle-resolved photo-emission spectroscopy (ARPES) and are thus directly relevant to the AdS/CMT correspondence. To illustrate our techniques, we study field theories at zero chemical potential with an arbitrary dynamical exponent z, i.e., the Lifshitz invariant conformal field theories, including the usual relativistic case z = 1.
Physical Review Letters, 2006
The real-space densities of a polarized strongly interacting two-component Fermi gas of 6 Li atom... more The real-space densities of a polarized strongly interacting two-component Fermi gas of 6 Li atoms reveal two low-temperature regimes, both with a fully paired core. At the lowest temperatures, the unpolarized core deforms with increasing polarization. Sharp boundaries between the core and the excess unpaired atoms are consistent with a phase separation driven by a first-order phase transition. In contrast, at higher temperatures the core does not deform but remains unpolarized up to a critical polarization. The boundaries are not sharp in this case, indicating a partially polarized shell between the core and the unpaired atoms. The temperature dependence is consistent with a tricritical point in the phase diagram.
Physical Review Letters, 2002
We study experimentally the transverse monopole mode of an elongated rubidium condensate. Because... more We study experimentally the transverse monopole mode of an elongated rubidium condensate. Because of the scaling invariance of the nonlinear Schrödinger (Gross-Pitaevskii) equation, the oscillation is monochromatic and sinusoidal at short times, even under strong excitation. For ultralow temperatures, the quality factor Q v 0 ͞g 0 can exceed 2000, where v 0 and g 0 are the mode angular frequency and damping rate. This value is much larger than any previously reported for other eigenmodes of a condensate. We also present the temperature variation of v 0 and g 0 .
Physical Review Letters, 2007
We present a general approach for describing trapped Fermi gases, when the cloud shape is distort... more We present a general approach for describing trapped Fermi gases, when the cloud shape is distorted with respect to the trap shape. Our approach provides a consistent way to explore physics beyond the local density approximation, if this is necessary due to the distortion. We illustrate this by analyzing in detail experimentally observed distortions in a trapped imbalanced Fermi mixture. In particular, we demonstrate in that case dramatic deviations from ellipsoidal cloud shapes arising from the competition between surface and bulk energies.
Physical Review Letters, 1997
At Landau level filling factors near n 1, quantum Hall ferromagnets form a Skyrme crystal state w... more At Landau level filling factors near n 1, quantum Hall ferromagnets form a Skyrme crystal state with quasi-long-range translational and noncollinear magnetic order. We develop an effective low energy theory which explains the presence of magnetic excitations in these systems at energies below the Larmor gap (D) and that predicts a dramatic enhancement of the nuclear spin relaxation rate by a factor of 10 3. The effective theory predicts a rich set of quantum and classical phase transitions. Based in part on accurate time-dependent Hartree-Fock calculations of the ordered state collective excitation spectrum, we discuss aspects of the T-n-D Skyrme crystal phase diagram. [S0031-9007(97)03424-8]
Physical Review Letters, 1989
DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:
Physical Review Letters, 2002
We variationally determine the dynamics of bright soliton trains composed of harmonically trapped... more We variationally determine the dynamics of bright soliton trains composed of harmonically trapped Bose-Einstein condensates with attractive interatomic interactions. In particular, we obtain the interaction potential between two solitons. We also discuss the formation of soliton trains due to the quantum mechanical phase fluctuations of a one-dimensional condensate.