Theoretical analysis of neutron scattering results for quasi-two dimensional ferromagnets

Sarkar, Subhajit; Paul, Samir K.; Chaudhury, Ranjan

doi:10.1140/epjb/e2012-30200-6

Cited by 5 publications

(18 citation statements)

References 52 publications

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“…The application of the BKT inspired phenomenological treatment reproduces the central peak as well for the first system; however, the dynamical structure factor becomes negative in a large regime of the -space and hence exhibits unphysical behaviour [17]. This signals the failure and limitation of the semiclassical treatment involving BKT (see Figure 1) and calls for a fully fledged quantum treatment [17]. In the second system, the results from BKTlike phenomenology for the experimental observations from inelastic neutron scattering experiment involving staggered spin field and the RG calculational results available for the very weak XY-anisotropy limit disagree quantitatively by a large factor (about 4) [12].…”

Section: Methodsmentioning

confidence: 90%

Section: Methodsmentioning

confidence: 97%

“…The presence of such a term in fact indicates a very strong possibility for the existence of topological excitations in the system and furthermore the numerical magnitude of this term (always an integer) represents the "winding number" for such configurations. The approach we adopted is the following [12,17,[22][23][24][25][26].…”

Section: Methodsmentioning

confidence: 99%

“…The next important step in this direction would be to identify signature of vortex dynamics (a) in the theoretical calculation for the dynamical structure factor (q, ) corresponding to our quantum spin models and (b) in the observed data from inelastic neutron scattering experiment corresponding to the appropriate materials. We have made a theoretical study analyzing available results from inelastic neutron scattering experiment performed on a quasi-twodimensional spin-1/2 ferromagnetic material K 2 CuF 4 and spin-1/2 antiferromagnetic material La 2 CuO 4 [12,17].…”

Section: Phenomenology Based Analysismentioning

confidence: 99%

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Topological Excitations in Quantum Spin Systems

Chaudhury

Paul

2013

Advances in Condensed Matter Physics

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The origin and significance of topological excitations in quantum spin models in low dimensions are presented in detail. Besides a general review, our own work in this area is described in great depth. Apart from theoretical analysis of the existence and properties of spin vortices and antivortices, the possible experimental consequences and signatures are also highlighted. In particular, the distinguishing features between the even and odd charged topological excitations are brought out through a detailed analysis of the topological term in the quantum action. Moreover, an interesting symmetry property is predicted between the excitations from a ferromagnetic model and an antiferromagnetic model. Through a novel approach of ours, a bridge is established between field theoretical formalism and the well-known statistical mechanical treatment of Berezinskii-Kosterlitz-Thouless (BKT) transition involving these topological excitations. Furthermore, a detailed phenomenological analysis of the experimentally observed static and dynamic magnetic properties of the layered magnetic materials, possessing XY anisotropy in the in-plane spin-spin couplings, is undertaken to test the theoretical predictions regarding the behaviour of these excitations. The importance and the crucial role of quantum spin fluctuations in these studies are also brought out very clearly by our analysis.

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Section: Methodsmentioning

confidence: 90%

Section: Methodsmentioning

confidence: 97%

Section: Methodsmentioning

confidence: 99%

Section: Phenomenology Based Analysismentioning

confidence: 99%

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Topological Excitations in Quantum Spin Systems

Chaudhury

Paul

2013

Advances in Condensed Matter Physics

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“…The generation of the geometric phase (GP) is a witness of a singular point in the energy spectrum that arises in all non-trivial geometric evolutions. In this respect, the connection of the geometric phase with quantum phase transition (QPT) has been explored very recently [29][30][31][32]. The geometric phase can be used as a tool to probe QPT in many body systems.…”

Section: Motivation Of This Research Papermentioning

confidence: 99%

Quantum criticality of geometric phase in coupled optical cavity arrays under linear quench

Sarkar

2014

Physica B: Condensed Matter

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The atoms trapped in microcavities and interacting through the exchange of virtual photons can be modeled as an anisotropic Heisenberg spin-1/2 lattice. We study the dynamics of the geometric phase of this system under the linear quenching process of laser field detuning which shows the XX criticality of the geometric phase in presence of single Rabi frequency oscillation.We also study the quantum criticality for different quenching rate in the presence of single or two Rabi frequencies oscillation in the system.

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Semi-phenomenological analysis of neutron scattering results for quasi-two dimensional quantum anti-ferromagnet

Sarkar

Chaudhury

Paul

2017

Journal of Magnetism and Magnetic Materials

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The available results from the inelastic neutron scattering experiment performed on the quasi-two dimensional spin 1 2 anti-ferromagnetic material La2CuO4 have been analysed theoretically. The formalism of ours is based on a semi-classical like treatment involving a model of an ideal gas of mobile vortices and anti-vortices built on the background of the Néel state, using the bipartite classical spin configuration corresponding to an XY-anisotropic Heisenberg anti-ferromagnet on a square lattice. The results for the integrated intensities for our spin 1 2 model corresponding to different temperatures, show occurrence of vigorous unphysical oscillations, when convoluted with a realistic spectral window function. These results indicate failure of the conventional semi-classical theoretical model of ideal vortex/anti-vortex gas arising in the Berezinskii-Kosterlitz-Thouless theory for the low spin magnetic systems. A full fledged quantum mechanical formalism and calculations seem crucial for the understanding of topological excitations in such low spin systems. Furthermore, a severe disagreement is found to occur at finite values of energy transfer between the integrated intensities obtained theoretically from the conventional formalism and those obtained experimentally. This further suggests strongly that the full quantum treatment should also incorporate the interaction between the fragile-magnons and the topological excitations. This is quite plausible in view of the recent work establishing such a process in XXZ quantum ferromagnet on 2D lattice. The high spin XXZ quasi-two dimensional antiferromagnet like M nP S3 however follows the conventional theory quite well. Keywords: Spin dynamics, Topological spin excitations, Berezinskii-Kosterlitz-Thouless transition, Spin 1/2 easy plane Anti-ferromagnet.Highlights:• Inadequacies in the conventional meron gas phenomenology in explaining the spin dynamics corresponding to layered low-spin anti-ferromagnets.• Requirement of a full fledged quantum mechanical formalism for the understanding of spin dynamics induced by both topological and conventional excitations.• Necessity of a proper understanding of the interaction between the conventional and topological excitations at the quantum level.

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Theoretical analysis of neutron scattering results for quasi-two dimensional ferromagnets

Cited by 5 publications

References 52 publications

Topological Excitations in Quantum Spin Systems

Topological Excitations in Quantum Spin Systems

Quantum criticality of geometric phase in coupled optical cavity arrays under linear quench

Semi-phenomenological analysis of neutron scattering results for quasi-two dimensional quantum anti-ferromagnet

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