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z=1 and z=2 quantum criticality in one dimension

Vendredi 14 septembre 2018 11:00 - Duree : 1 heure
Lieu : ILL 4, Seminar Room (no 163), 71 avenue des Martyrs - Grenoble

Orateur : Andrey ZHELUDEV (Laboratory for Solid State Physics - ETH Zurich -Switzerland)

Magnetic materials have always been the models of choice for studying critical phenomena. One dimensional spin systems in particular host a number of very interesting and fundamentally important quantum critical states. The latter can in many cases be understood through a mapping of the spin Hamiltonian on that of interacting Fermions. This correspondence enables exact theoretical predictions not only fro the critical exponents, but also for scaling functions of both thermodynamic properties and correlations. Moreover, these exponents and scaling functions turn out to be partially or even completely universal, in that they are independent of any microscopic details of the underlying spin Hamiltonian. This, in turn, allows for a quantitative comparison of experimental results to exact theory without almost any knowledge about the material under study !

Theoretically, the problem of interaction Fermions in one dimension is an old one and has been fully resolved over two decades ago. Nevertheless, many of these predictions could not be properly verified experimentally. It has only become possible quite recently, thanks to breakthroughs in the synthesis of new materials, new high resolution neutron spectroscopy techniques and new numerical methods. In my talk I will describe several examples of such recent studies in quantum spin chains and ladders. One (somewhat older) study addresses the so-called attractive Tomonaga-Lutinger spin liquid (a quantum critical state of attractive Fermions that has a dynamical exponent z=1) [1,2]. More recent experiments have to do with "zero-scale-factor" universality at a quantum phase transition with the dynamical exponent z=2 [3,4]. In all cases we used neutron spectroscopy to directly measure the scaling of temporal correlation functions for a direct comparison with exact analytical results.

[1] Schmidiger et al., Phys. Rev. B 91, 020406(R) (2015)

[2] Jeong et al., Phys. Rev. Lett. 117, 106402 (2016)

[3] Blosser et al., Phys Rev B 96, 134406 (2017)

[4] Blosser et al., arXiv:1806.10392 (2018)

Contact : dubouloz@ill.fr

Discipline évènement : (Physique)
Entité organisatrice : (ILL)
Nature évènement : (Séminaire)
Evènement répétitif : (General ILL Seminar - College 4)
Site de l'évènement : Polygone scientifique

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