Magnetic fluctuations and specific heat in Na(x)CoO2 near a Lifshitz transition.
Magnetic fluctuations and specific heat in Na(x)CoO2 near a Lifshitz transition.
复制标题
DOI：
10.1103/physrevlett.114.066403
复制
发表时间：
2014-09
影响因子：
8.6
通讯作者：
S. Slizovskiy;A. Chubukov;J. Betouras
中科院分区：
文献类型：
--
作者：
S. Slizovskiy;A. Chubukov;J. Betouras
我们分析了Na（x）CoO（2）中比热C（T）的温度和掺杂依赖性。该材料在x=x（c）=0.62处发生Lifshitz型拓扑转变，在该转变中，除了已有的具有大k（F）的空穴袋外，在Γ点处还出现了新的电子费米袋。数据表明，在x=x（c）附近，随着x从下往上接近x（c），C（T）/T的温度依赖性在低T时变强，在x≥x（c）时，C（T）/T的温度依赖性反转并改变符号。我们认为，这种行为可以在自旋涨落理论定量解释。结果表明，当新口袋形成时，x（c）附近的磁涨落在k（F）附近的动量处增强，其动力学在x≤x（c）和x>x（c）之间变化.我们证明了这解释了C（T）/T的温度依赖性。我们发现，在较大的x（x>0.65）的系统进入磁量子临界区，其中C（T）/T大致标度为logT。当x增加到x ≥ 0.75的磁不稳定性时，这种行为逐渐延伸到较低的T。
We analyze the temperature and doping dependence of the specific heat C(T) in Na(x)CoO(2). This material was conjectured to undergo a Lifshitz-type topological transition at x=x(c)=0.62, in which a new electron Fermi pocket emerges at the Γ point, in addition to the existing hole pocket with large k(F). The data show that near x=x(c), the temperature dependence of C(T)/T at low T gets stronger as x approaches x(c) from below and then reverses the trend and changes sign at x≥x(c). We argue that this behavior can be quantitatively explained within the spin-fluctuation theory. We show that magnetic fluctuations are enhanced near x(c) at momenta around k(F), and their dynamics changes between x≤x(c) and x>x(c), when the new pocket forms. We demonstrate that this explains the temperature dependence of C(T)/T. We show that at larger x (x>0.65) the system enters a magnetic quantum critical regime where C(T)/T roughly scales as logT. This behavior extends to progressively lower T as x increases towards a magnetic instability at x≈0.75.