Motivated by the unusual temperature dependence of the specific heat in MnSi, comprising a combination of a sharp first-order feature accompanied by a broad hump, we study the extended Heisenberg model with competing exchange $J$ and anisotropic Dzyaloshinskii-Moriya $D$ interactions in a broad range of ratio $D/J$. Utilizing classical Monte Carlo simulations we find an evolution of the temperature dependence of the specific heat and magnetic susceptibility with variation of $D/J$. Combined with an analysis of the Bragg intensity patterns, we clearly demonstrate that the observed puzzling hump in the specific heat of MnSi originates from smearing out of the virtual ferromagnetic second order phase transition by helical fluctuations, which manifest themselves in the transient multiple spiral state. These fluctuations finally condense into the helical ordered phase via a first order phase transition as is indicated by the specific heat peak. Thus the model demonstrates a crossover from a second-order to a first-order transition with increasing $D/J$. Upon further increasing $D/J$ another crossover from a first-order to a second-order transition takes place in the system. Moreover, the results of the calculations clearly indicate that these competing interactions are the primary factor responsible for the appearance of first order phase transitions in helical magnets with the Dzyaloshinskii-Moriya (DM) interaction.
Monte Carlo study of magnetoresistance in a chiral soliton lattice
单轴手征磁体在垂直于螺旋轴的磁场中可以形成一种特殊的非共线自旋结构，称为手征孤子晶格。利用蒙特卡罗模拟方法，研究了一维Kondo晶格模型中包含经典局域自旋间Dzyaloshinskiii-Moriya相互作用的手征孤子晶格的磁性和电输运性质.结果表明，该模型在零磁场下呈现螺旋自旋结构，随着外磁场的增大，该结构转变为手征孤立子晶格，最终转变为受迫铁磁态。在手征孤子晶格态中，我们发现低温下负磁阻与孤子数目成正比，这证实了手征孤子对电子的自旋散射。我们还讨论了温度和磁场的自旋结构因子和电阻率的依赖关系，在与实验比较CrNb $_{3}$ S $_{6}$。
Spin Liquid Landscapes in the Kagome Lattice: A Variational Monte Carlo Study of the Chiral Heisenberg Model and Experimental Signatures
Korea Advanced Institute of Science and Technology（韩国科学技术院）；University of Notre Dame（圣母大学）；HUN-REN Wigner Research Centre for Physics（匈牙利研究与创新网络维格纳物理研究中心）
Monte-Carlo study of the semimetal-insulator phase transition in monolayer graphene with realistic inter-electron interaction potential
我们报告的结果的第一原理的数值研究的手征（亚晶格）对称性的自发破缺悬浮单层石墨烯由于静电相互作用，其中考虑到屏蔽的库仑电位的$σ$ -轨道上的电子。与之前未屏蔽势的数值模拟结果相比，我们发现悬浮石墨烯处于导电相，具有未破缺的手征对称性。这一发现与曼彻斯特小组\cite{Elias et al, 2011}最近的实验结果一致。此外，通过人为增加相互作用强度，我们证明，悬浮石墨烯是非常接近的相变与自发手征对称性破缺，这表明手性和非微扰效应的波动可能仍然是相当重要的。
