Matsuura Masato, Sasaki Takahiko, Iguchi Satoshi, Gati Elena, Müller Jens, Stockert Oliver, Piovano Andrea, Böhm Martin, Park Jitae T, Biswas Sananda, Winter Stephen M, Valentí Roser, Nakao Akiko, Lang Michael
Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), Tokai, Ibaraki 319-1106, Japan.
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Phys Rev Lett. 2019 Jul 12;123(2):027601. doi: 10.1103/PhysRevLett.123.027601.
Inelastic neutron scattering measurements on the molecular dimer-Mott insulator κ-(BEDT-TTF){2}Cu[N(CN){2}]Cl reveal a phonon anomaly in a wide temperature range. Starting from T_{ins}∼50-60 K where the charge gap opens, the low-lying optical phonon modes become overdamped upon cooling towards the antiferromagnetic ordering temperature T_{N}=27 K, where also a ferroelectric ordering at T_{FE}≈T_{N} occurs. Conversely, the phonon damping becomes small again when spins and charges are ordered below T_{N}, while no change of the lattice symmetry is observed across T_{N} in neutron diffraction measurements. We assign the phonon anomalies to structural fluctuations coupled to charge and spin degrees of freedom in the BEDT-TTF molecules.
对分子二聚体-莫特绝缘体κ-(BEDT-TTF)₂Cu[N(CN)₂]Cl进行的非弹性中子散射测量揭示了在很宽温度范围内的声子异常。从电荷能隙打开的T_ins∼50 - 60 K开始，低能光学声子模式在冷却至反铁磁有序温度T_N = 27 K时变得过阻尼，在T_FE≈T_N处还发生铁电有序。相反，当自旋和电荷在T_N以下有序排列时，声子阻尼又再次变小，而在中子衍射测量中未观察到晶格对称性在T_N处发生变化。我们将声子异常归因于与BEDT-TTF分子中的电荷和自旋自由度耦合的结构涨落。
