<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><span style="background-color: rgb(255, 255, 255);" class="">Дорогие коллеги,</span><br class=""><div class=""><span class="" style="background-color: rgb(255, 255, 255);"><br class="">Международная лаборатория физики конденсированного состояния НИУ ВШЭ приглашает на доклады М. Житомирского.<br class=""></span></div><div class=""><span class="" style="background-color: rgb(255, 255, 255);"><br class=""></span></div><div class=""><span class="" style="background-color: rgb(255, 255, 255);"><br class=""></span></div><div class=""><span class="" style="background-color: rgb(255, 255, 255);">В четверг 8 ноября в 11:00</span><br class="" style="background-color: rgb(255, 255, 255);"><span class="" style="background-color: rgb(255, 255, 255);">ИФП им. П.Л.Капицы РАН, ул. Косыгина, д.2</span><br class="" style="background-color: rgb(255, 255, 255);"><br class="" style="background-color: rgb(255, 255, 255);"><span class="" style="background-color: rgb(255, 255, 255);">М.Е.Житомирский (CEA, Гренобль)</span><br class="" style="background-color: rgb(255, 255, 255);"><br class="" style="background-color: rgb(255, 255, 255);"><span class="" style="font-family: Tahoma; font-size: 13.333333015441895px; background-color: rgb(255, 255, 255);">Multi-k states in frustrated spinel and kagome antiferromagnets</span></div><div class=""><font face="Tahoma" size="2" class=""><br class=""></font></div><div class=""><div class="" style="font-family: Tahoma; font-size: 13.333333015441895px;">Competing exchange interactions may produce various non-collinear spin structures. Still majority of such magnetic states are coplanar with non coplanar states presented by only a few known examples. <span class="" style="font-size: 9pt;">We investigate the multi-</span><span class="" style="font-size: 9pt;">k </span><span class="" style="font-size: 9pt;">magnetic structures with commensurate propagation wave vectors that can appear in spinel and kagome materials. </span></div><div class="" style="font-family: Tahoma; font-size: 13.333333015441895px;"><span class="" style="font-size: 9pt;">For the isotropic Heisenberg Hamiltonian we find that the triple-</span><span class="" style="font-size: 9pt;">k </span><span class="" style="font-size: 9pt;">configurations are the most stable states in zero field for both systems. With increasing magnetic field they universally transform into the double-</span><span class="" style="font-size: 9pt;">k </span><span class="" style="font-size: 9pt;">magnetic structures. We also study the effect of magnetic anisotropies on the equilibrium spin configurations and in particular demonstrate that the splitting of the transition in GeNi</span><span class="" style="font-size: 6pt; vertical-align: -1pt;">2</span><span class="" style="font-size: 9pt;">O</span><span class="" style="font-size: 6pt; vertical-align: -1pt;">4 </span><span class="" style="font-size: 9pt;">is naturally explained by the local easy-plane anisotropy.</span></div><div class=""><span class="" style="font-size: 9pt;"><br class=""></span></div><br class="" style="background-color: rgb(255, 255, 255);"><span class="" style="background-color: rgb(255, 255, 255);">---------------------------------------------------------------------------------------</span><br class="" style="background-color: rgb(255, 255, 255);"><span class="" style="background-color: rgb(255, 255, 255);">Во вторник 13 ноября в 11:00</span><br class="" style="background-color: rgb(255, 255, 255);"><span class="" style="background-color: rgb(255, 255, 255);">Ст.Басманная д.21/4, стр.5, ауд. Б-813 (8 этаж)</span><br class="" style="background-color: rgb(255, 255, 255);"><br class="" style="background-color: rgb(255, 255, 255);"><span class="" style="background-color: rgb(255, 255, 255);">М.Е.Житомирский (CEA, Гренобль)</span><br class="" style="background-color: rgb(255, 255, 255);"><br class="" style="background-color: rgb(255, 255, 255);"><div class="" style="background-color: rgb(255, 255, 255);"><div class="">Interacting quasiparticles in quantum magnets: spin-wave decay and magnon pairing</div><div class=""><br class=""></div><div class="">Quantum solids, liquids, and magnets typically exhibit collective excitations - phonons, magnons and so on.</div><div class="">These involve motion of many constituent particles, yet act like individual weakly interacting entities —</div><div class="">quasiparticles. Recently, two new phenomena have been predicted in the field of Quantum Magnetism, where </div><div class="">residual quasiparticle interactions play a paramount role. The first example is spontaneous magnon decay, </div><div class="">which occurs at zero temperature and is inherent to noncollinear magnetic structures and spin liquids. </div><div class="">The second effect corresponds to formation of bound magnon pairs in spin systems with competing ferro- and </div><div class="">antiferromagnetic interactions. Their subsequent condensation in an applied magnetic field produces novel </div><div class="">spin nematic states. I shall present an overview of main theoretical approaches to both phenomena and also </div><div class="">discuss possible experimental observations of such effects.</div></div><br class="" style="background-color: rgb(255, 255, 255);"><font class="" size="3" style="background-color: rgb(255, 255, 255);"><span class="" style="font-family: "Helvetica Neue", Arial, sans-serif; font-variant-ligatures: normal; orphans: 2; widows: 2;">При необходимости заказа пропуска в НИУ ВШЭ обращайтесь к Ирине Аванесовой, </span><span class="s3" style="border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgba(0, 122, 197, 0.298039); color: rgb(0, 122, 197); cursor: pointer; background-image: none; font-family: "Helvetica Neue", Arial, sans-serif; font-variant-ligatures: normal; orphans: 2; widows: 2;"><font color="#000000" class=""><a href="https://e.mail.ru/compose/?mailto=mailto%3aiavanesova@hse.ru" class="link external" target="_blank" style="text-decoration: none; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgba(0, 122, 197, 0.298039); cursor: pointer; background-image: none;">iavanesova@hse.ru</a></font></span></font></div></body></html>