Impact of thermal fluctuations on transport in antiferromagnetic semimetals

作     者：Youngseok Kim Moon Jip Park David G. Cahill Matthew J. Gilbert 

作者机构：Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Urbana Illinois 61801 USA Micro and Nanotechnology Laboratory University of Illinois 208 N. Wright Street Urbana Illinois 61801 USA Department of Physics University of Illinois at Urbana-Champaign Urbana Illinois 61801 USA Department of Materials Science and Engineering and Materials Research Laboratory University of Illinois Urbana Illinois 61801 USA Department of Electrical Engineering Stanford University Stanford California 94305 USA 

出 版 物：《Physical Review B》 (Phys. Rev. B)

年 卷 期：2018年第98卷第2期

页      面：024409-024409页

核心收录：

基　　金：National Science Foundation, NSF National Science Foundation, NSF, (DMR-1720633, DMR-1720633) 

主　　题：Antiferromagnetism Dirac fermions Magnetoresistance Metal-insulator transition Dirac semimetal Green's function methods Landau-Lifschitz-Gilbert equation 

摘      要：Recent demonstrations on manipulating antiferromagnetic (AF) order have triggered a growing interest in antiferromagnetic metal, and potential high-density spintronic applications demand further improvements in the anisotropic magnetoresistance (AMR). The antiferromagnetic semimetals (AFS) are newly discovered materials that possess massless Dirac fermions that are protected by the crystalline symmetries. In this material, a reorientation of the AF order may break the underlying symmetries and induce a finite energy gap. As such, the possible phase transition from the semimetallic to insulating phase gives us a choice for a wide range of resistance, ensuring a large AMR. To further understand the robustness of the phase transition, we study thermal fluctuations of the AF order in AFS at a finite temperature. For macroscopic samples, we find that the thermal fluctuations effectively decrease the magnitude of the AF order by renormalizing the effective Hamiltonian. Our finding suggests that the insulating phase exhibits a gap narrowing at elevated temperatures, which leads to a substantial decrease in AMR. We also examine spatially correlated thermal fluctuations for microscopic samples by solving the microscopic Landau-Lifshitz-Gilbert equation, finding a quantitative difference in the gap narrowing effect from that of the macroscopic sample. For both cases, the semimetallic phase shows a minimal change in its transmission spectrum, illustrating the robustness of the symmetry-protected states in AFS. Our finding may serve as a guideline for estimating and maximizing AMR of the AFS samples at elevated temperatures.