شماره راهنما :
1082 دكتري
پديد آورنده :
قرباني، الهه
عنوان :
سيماي فاز كوانتمي مدل هايزنبرگ كژديس بر روي شبكه‌هاي مثلثي و لانه‌زنبوري
محل تحصيل :
اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك
صفحه شمار :
هفت، ۱۱۰ص.: مصور، جدول، نمودار
استاد راهنما :
فرهاد شهبازي
توصيفگر ها :
مدل هايزنبرگ , ناكامي كوانتمي مغناطيسي , مايع اسپيني , نظم جفتي , نظم پيچشي
استاد داور :
ممتحن داخلي: پيمان صاحب سرا; ممتحن خارجي: عبداله لنگري، حشمت اله ياوري
تاريخ ورود اطلاعات :
1396/08/15
كد ايرانداك :
ID1082 دكتري
چكيده انگليسي :
AbstractLow dimensional quantum spin systems display intriguing ground state properties whi may have important consequences for the existence of fractionalized excitationsor the emergence of high temperature superconductivity In this thesis we consider thematerial in two dimensions whi they can be good candidates of existence spin liq uid phases Among various materials that show promising low temperature behaviors the family of organic arge transfer salts ET 2 X with the anisotropic triangularla ice InCu2 3 V1 3 O3 Bi3 Mn4 O12 NO3 BMNO and Cu3 Ni2 SbO6 with the honey comb la ice represent a very important candidate for hosting spin liquid properties So we study these compounds with two di erent te niques 1 antum variational Monte Carlo for transfer salts and 2 Modi ed spin wave forother compounds that they are mentioned above 1 By using variational wave functions and quantum Monte Carlo te niques we inves tigate the complete phase diagram of the Heisenberg model on the anisotropic triangu lar la ice where two out of three bonds have superex ange couplings J and the thirdone has instead J is model interpolates between the square la ice and the isotropictriangular one for J J 1 and between the isotropic triangular la ice and a set ofdecoupled ains for J J 1 We consider all the fully symmetric spin liquids thatcan be constructed with the fermionic projective symmetry group classi cation Zhouand Wen arXiv cond mat 0210662 and we compare them with the spiral magnetic or ders that can be accommodated on nite clusters Our results show that for J J 1 the phase diagram is dominated by magnetic orderings even though a spin liquid statemay be possible in a small parameter window i e 0 7 J J 0 8 In contrast forJ J 1 a large spin liquid region appears close to the limit of decoupled ains i e for J J 0 6 while magnetically ordered phases with spiral order are stabilized closeto the isotropic point 2 Using modi ed spin wave MSW method we study the J1 J2 Heisenberg modelwith rst and second neighbor antiferromagnetic ex ange interactions For symmet ric S 1 2 model with the same couplings for all the equivalent neighbors we ndthree phase in terms of frustration parameter J2 J1 1 a commensurate collinear ordering with staggered magnetization Neel I state for 0 0 0 207 2 a mag netically gapped disordered state for 0 207 0 396 preserving all the symmetries of the Hamiltonian and la ice hence by de nition is a quantum spin liquid QSL stateand 3 a commensurate collinear ordering in whi two out of three nearest neighbormagnetizations are antiparallel and the remaining pair are parallel Neel II state for0 396 1 0 We also explore the phase diagram of distorted J1 J2 model with S 1 2 Distortion is introduced as an inequality of one nearest neighbor couplingwith the other two is yields a ri er phase diagram by the appearance of a newgapped QSL a gapless QSL and also a valence bond crystal VBC phase in addition tothe previously three phases found for undistorted model Keywords Heisenberg Model Frustrated antum Magnets Spin Liquied DimerizedOrder Spiral Order
استاد راهنما :
فرهاد شهبازي
استاد داور :
ممتحن داخلي: پيمان صاحب سرا; ممتحن خارجي: عبداله لنگري، حشمت اله ياوري
