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Guo J, Ghosh P, Hill D, Chen Y, Stingaciu L, Zolnierczuk P, Ullrich CA, Singh DK. Persistent dynamic magnetic state in artificial honeycomb spin ice. Nat Commun 2023; 14:5212. [PMID: 37626129 PMCID: PMC10457338 DOI: 10.1038/s41467-023-41003-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Accepted: 08/18/2023] [Indexed: 08/27/2023] Open
Abstract
Topological magnetic charges, arising due to the non-vanishing magnetic flux on spin ice vertices, serve as the origin of magnetic monopoles that traverse the underlying lattice effortlessly. Unlike spin ice materials of atomic origin, the dynamic state in artificial honeycomb spin ice is conventionally described in terms of finite size domain wall kinetics that require magnetic field or current application. Contrary to this common understanding, here we show that a thermally tunable artificial permalloy honeycomb lattice exhibits a perpetual dynamic state due to self-propelled magnetic charge defect relaxation in the absence of any external tuning agent. Quantitative investigation of magnetic charge defect dynamics using neutron spin echo spectroscopy reveals sub-ns relaxation times that are comparable to the relaxation of monopoles in bulk spin ices. Most importantly, the kinetic process remains unabated at low temperature where thermal fluctuation is negligible. This suggests that dynamic phenomena in honeycomb spin ice are mediated by quasi-particle type entities, also confirmed by dynamic Monte-Carlo simulations that replicate the kinetic behavior. Our research unveils a macroscopic magnetic particle that shares many known traits of quantum particles, namely magnetic monopole and magnon.
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Affiliation(s)
- J Guo
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, USA
| | - P Ghosh
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, USA
| | - D Hill
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, USA
| | - Y Chen
- Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, China
| | - L Stingaciu
- Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - P Zolnierczuk
- Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - C A Ullrich
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, USA.
| | - D K Singh
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, USA.
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Perez F, Baboux F, Ullrich CA, D'Amico I, Vignale G, Karczewski G, Wojtowicz T. Spin-Orbit Twisted Spin Waves: Group Velocity Control. Phys Rev Lett 2016; 117:137204. [PMID: 27715118 DOI: 10.1103/physrevlett.117.137204] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Indexed: 06/06/2023]
Abstract
We present a theoretical and experimental study of the interplay between spin-orbit coupling (SOC), Coulomb interaction, and motion of conduction electrons in a magnetized two-dimensional electron gas. Via a transformation of the many-body Hamiltonian we introduce the concept of spin-orbit twisted spin waves, whose energy dispersions and damping rates are obtained by a simple wave-vector shift of the spin waves without SOC. These theoretical predictions are validated by Raman scattering measurements. With optical gating of the density, we vary the strength of the SOC to alter the group velocity of the spin wave. The findings presented here differ from that of spin systems subject to the Dzyaloshinskii-Moriya interaction. Our results pave the way for novel applications in spin-wave routing devices and for the realization of lenses for spin waves.
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Affiliation(s)
- F Perez
- Institut des Nanosciences de Paris, CNRS/Université Paris VI, Paris 75005, France
| | - F Baboux
- Institut des Nanosciences de Paris, CNRS/Université Paris VI, Paris 75005, France
- Laboratoire de Photonique et de Nanostructures, LPN/CNRS, 91460 Marcoussis, France
| | - C A Ullrich
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
| | - I D'Amico
- Department of Physics, University of York, York YO10 5DD, United Kingdom
| | - G Vignale
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
| | - G Karczewski
- Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - T Wojtowicz
- Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
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Baboux F, Perez F, Ullrich CA, D’Amico I, Gómez J, Bernard M. Anisotropic spin-orbit induced splitting of intersubband spin plasmons. EPJ Web of Conferences 2013. [DOI: 10.1051/epjconf/20134018002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Baboux F, Perez F, Ullrich CA, D'Amico I, Gómez J, Bernard M. Giant collective spin-orbit field in a quantum well: fine structure of spin plasmons. Phys Rev Lett 2012; 109:166401. [PMID: 23215097 DOI: 10.1103/physrevlett.109.166401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Indexed: 06/01/2023]
Abstract
We employ inelastic light scattering with magnetic fields to study intersubband spin plasmons in a quantum well. We demonstrate the existence of a giant collective spin-orbit (SO) field that splits the spin-plasmon spectrum into a triplet. The effect is remarkable as each individual electron would be expected to precess in its own momentum-dependent SO field, leading to D'yakonov-Perel' dephasing. Instead, many-body effects lead to a striking organization of the SO fields at the collective level. The macroscopic spin moment is quantized by a uniform collective SO field, five times higher than the individual SO field. We provide a momentum-space cartography of this field.
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Affiliation(s)
- F Baboux
- Institut des Nanosciences de Paris, CNRS/Université Paris VI, Paris 75005, France.
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Kyrychenko FV, Ullrich CA. Transport and optical conductivity in dilute magnetic semiconductors. J Phys Condens Matter 2009; 21:084202. [PMID: 21817354 DOI: 10.1088/0953-8984/21/8/084202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A theory of transport in spin and charge disordered media is developed, with a particular emphasis on dilute magnetic semiconductors. The approach is based on the equation of motion for the current-current response function and considers both spin and charge disorder and electron-electron interaction on an equal footing. The formalism is applied to the specific case of Ga(1-x)Mn(x)As. Within the single parabolic band approximation it is shown that both spin (p-d exchange) and charge (Coulomb) scattering contributions to the resistivity are of the same order of magnitude and should be treated simultaneously. Positional correlations of charged impurities are shown to significantly increase the Coulomb scattering. In the magnetically ordered phase, the suppression of localized spin fluctuations leads to a sizable reduction of spin scattering, which may contribute to the experimentally observed drop in resistivity below the critical temperature. The developed model allows for a comprehensive treatment of electron-electron interaction, screening and correlation effects by means of time-dependent density-functional theory. It is shown that collective modes and a dynamical treatment of electron-electron interaction are essential for an accurate description of the infrared absorption spectrum.
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Affiliation(s)
- F V Kyrychenko
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
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Affiliation(s)
- C. A. Ullrich
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211
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Vieira D, Capelle K, Ullrich CA. Physical signatures of discontinuities of the time-dependent exchange–correlation potential. Phys Chem Chem Phys 2009; 11:4647-54. [DOI: 10.1039/b902613d] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Wijewardane HO, Ullrich CA. Real-time electron dynamics with exact-exchange time-dependent density-functional theory. Phys Rev Lett 2008; 100:056404. [PMID: 18352401 DOI: 10.1103/physrevlett.100.056404] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2007] [Indexed: 05/26/2023]
Abstract
The exact exchange potential in time-dependent density-functional theory is defined as an orbital functional through the time-dependent optimized effective potential (TDOEP) method. We numerically solve the TDOEP integral equation for the real-time nonlinear intersubband electron dynamics in a semiconductor quantum well with two occupied subbands. It is found that memory effects become significant in the vicinity of intersubband resonances.
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Affiliation(s)
- H O Wijewardane
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
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Orestes E, Capelle K, da Silva ABF, Ullrich CA. Generator coordinate method in time-dependent density-functional theory: Memory made simple. J Chem Phys 2007; 127:124101. [PMID: 17902887 DOI: 10.1063/1.2768368] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The generator coordinate (GC) method is a variational approach to the quantum many-body problem in which interacting many-body wave functions are constructed as superpositions of (generally nonorthogonal) eigenstates of auxiliary Hamiltonians containing a deformation parameter. This paper presents a time-dependent extension of the GC method as a new approach to improve existing approximations of the exchange-correlation (XC) potential in time-dependent density-functional theory (TDDFT). The time-dependent GC method is shown to be a conceptually and computationally simple tool to build memory effects into any existing adiabatic XC potential. As an illustration, the method is applied to driven parametric oscillations of two interacting electrons in a harmonic potential (Hooke's atom). It is demonstrated that a proper choice of time-dependent generator coordinates in conjunction with the adiabatic local-density approximation reproduces the exact linear and nonlinear two-electron dynamics quite accurately, including features associated with double excitations that cannot be captured by TDDFT in the adiabatic approximation.
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Affiliation(s)
- E Orestes
- Departamento de Química e Física Molecular, Instituto de Química de São Carlos, Universidade de São Paulo, Caixa Postal 780, São Carlos, São Paulo 13560-970, Brazil
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Ullrich CA. Time-dependent density-functional theory beyond the adiabatic approximation: Insights from a two-electron model system. J Chem Phys 2006; 125:234108. [PMID: 17190548 DOI: 10.1063/1.2406069] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Most applications of time-dependent density-functional theory (TDDFT) use the adiabatic local-density approximation (ALDA) for the dynamical exchange-correlation potential V(xc)(r,t). An exact (i.e., nonadiabatic) extension of the ground-state LDA into the dynamical regime leads to a V(xc)(r,t) with a memory, which causes the electron dynamics to become dissipative. To illustrate and explain this nonadiabatic behavior, this paper studies the dynamics of two interacting electrons on a two-dimensional quantum strip of finite size, comparing TDDFT within and beyond the ALDA with numerical solutions of the two-electron time-dependent Schrodinger equation. It is shown explicitly how dissipation arises through multiple particle-hole excitations, and how the nonadiabatic extension of the ALDA fails for finite systems but becomes correct in the thermodynamic limit.
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Affiliation(s)
- C A Ullrich
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
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Abstract
In time-dependent density-functional theory, exchange and correlation (xc) beyond the adiabatic approximation can be described by viscoelastic stresses in the electron liquid. In the time domain, the resulting velocity-dependent xc vector potential has a memory containing short- and long-range components, leading to decoherence and energy relaxation. We solve the associated time-dependent Kohn-Sham equations, including the dependence on densities and currents at previous times, for the case of charge-density oscillations in a quantum well. We illustrate xc memory effects, clarify the dissipation mechanism, and extract intersubband relaxation rates for weak and strong excitations.
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Affiliation(s)
- H O Wijewardane
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
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Abstract
Time-dependent density-functional theory in the adiabatic approximation has been very successful for calculating excitation energies in molecular systems. This paper studies nonadiabatic effects for excitation energies, using the current-density functional of Vignale and Kohn [Phys. Rev. Lett. 77, 2037 (1996)]. We derive a general analytic expression for nonadiabatic corrections to excitation energies of finite systems and calculate singlet s-->s and s-->p excitations of closed-shell atoms. The approach works well for s-->s excitations, giving a small improvement over the adiabatic local-density approximation, but tends to overcorrect s-->p excitations. We find that the observed problems with the nonadiabatic correction have two main sources: (1) the currents associated with the s-->p excitations are highly nonuniform and, in particular, change direction between atomic shells, (2) the so-called exchange-correlation kernels of the homogeneous electron gas, f(xc) (L) and f(xc) (T), are incompletely known, in particular in the high-density atomic core regions.
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Affiliation(s)
- C A Ullrich
- Department of Physics, University of Missouri-Rolla, Rolla, Missouri 65409, USA.
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Abstract
This paper clarifies the topology of the mapping between the v and n spaces in fermionic systems. Density manifolds corresponding to degeneracies g=1 and g>1 are shown to have the same mathematical measure: Every density near a g-ensemble-v-representable (g-VR) n(r) is also g-VR (except "boundary densities" of lower measure). The role of symmetry and the connection between T=0 and T=0(+) are discussed. A lattice model and the Be series are used as illustrations.
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Affiliation(s)
- C A Ullrich
- Department of Physics, University of Missouri-Rolla, 65409, USA
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Abstract
An electron density distribution n(r) which can be represented by that of a single-determinant ground state of noninteracting electrons in an external potential v(r) is called pure-state v-representable (P-VR). Most physical electronic systems are P-VR. Systems which require a weighted sum of several such determinants to represent their density are called ensemble v-representable (E-VR). This paper develops formal Kohn-Sham equations for E-VR physical systems, using the appropriate coupling constant integration. It also derives local density- and generalized gradient approximations, and conditions and corrections specific to ensembles.
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Affiliation(s)
- C A Ullrich
- iQUEST, University of California, Santa Barbara, 93106, USA
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Abstract
Intersubband (ISB) plasmons in remotely doped wide quantum wells acquire a linewidth even at zero temperature and in-plane wave vector q(parallel) = 0 by a combination of intrinsic (electron-electron interaction) and extrinsic effects (impurities and interface roughness). We present a quantitatively accurate theory of the linewidth that treats both effects on equal footing and from first principles by a combination of time-dependent density-functional theory with the memory function formalism. Comparison with recent optical absorption experiments shows that the ISB plasmon linewidth has a significant contribution from electron-electron interaction, and is only weakly related to the mobility.
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Affiliation(s)
- C A Ullrich
- iQUEST, University of California, Santa Barbara, California 93106, USA
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Ullrich CA, Domps A, Calvayrac F, Suraud E, Reinhard PG. Electron response of metallic clusters to strong laser pulses and energetic ion collisions. ACTA ACUST UNITED AC 1997. [DOI: 10.1007/s004600050207] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Ullrich CA, Gross EKU. Density Functional Theory of Normal and Superconducting Electron Liquids: Explicit Functionals via the Gradient Expansion. ACTA ACUST UNITED AC 1996. [DOI: 10.1071/ph960103] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The basic idea of density functional theory is to map an interacting many-particle system on an effective non-interacting system in such a way that the ground-state densities of the two systems are identical. The non-interacting particles move in an effective local potential which is a functional of the density. The central task of density functional theory is to find good approximations for the density dependence of this local single-particle potential. An overview of recent advances in the construction of this potential (beyond the local-density approximation) will be given along with successful applications in quantum chemistry and solid state theory. We then turn to the extension of density functional theory to superconductors and first discuss the Hohenberg-Kohn-Sham-type existence theorems. In the superconducting analogue of the the normal-state Kohn-Sham formalism, a local single-particle potential is needed which now depends on two densities, the ordinary density n(r) and the anomalous density △(r,r/). As a first step towards the construction of such a potential, a gradient expansion technique for superconductors is presented and applied to calculate an approximation of the non-interacting kinetic energy functional Ts[n, △]. We also obtain a Thomas-Fermi-type variational equation for superconductors.
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