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arXiv 0808.0616cond-mat.str-el
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量子临界金属磁体中的维度交叉

Dimensional crossover in quantum critical metallic magnets

Markus Garst, Lars Fritz, Achim Rosch, Matthias Vojta

摘要:

近磁性金属通常具有层状晶格结构,由耦合平面组成。在这种情况下,物理性质将显示,在降低温度或能量时,从二维(2d)到三维(3d)行为的维度交叉,这在量子临界附近特别有趣。在这里,我们研究这种交叉在热力学中使用适当的推广Landau-Ginzburg-Wilson方法的临界行为,结合重整化群技术。我们专注于两个实验相关的情况下:从二维到三维反铁磁体的交叉,从二维铁磁体到三维反铁磁体的交叉。我们讨论了相边界和交叉线的位置,并确定了重要热力学量的交叉函数。由于朴素标度不适用于上临界尺寸和以上,两个交叉尺度出现,可以分别与经典和量子涨落的单独维度交叉相关联。特别是,我们发现一个中间政权与新的幂律量子波动仍然有一个2D和经典波动已经有一个3D字符。对于铁磁-反铁磁交叉,2D和3D制度之间的动力学指数的不匹配导致一个更丰富的交叉结构,一个有趣的2D非临界制度夹在两个临界制度。对于所有的情况下,我们发现,热膨胀和压缩性是特别敏感的探头的尺寸交叉。最后,我们将我们的结果与量子临界重费米子金属CeCu(6-x)Au(x),YbRh(2)Si(2)和CeCoIn(5)的实验相关联。

英文摘要:

Nearly magnetic metals often have layered lattice structures, consisting of coupled planes. In such a situation, physical properties will display, upon decreasing temperature or energy, a dimensional crossover from two-dimensional (2d) to three-dimensional (3d) behavior, which is particularly interesting near quantum criticality. Here we study this crossover in thermodynamics using a suitably generalized Landau-Ginzburg-Wilson approach to the critical behavior, combined with renormalization group techniques. We focus on two experimentally relevant cases: the crossover from a 2d to a 3d antiferromagnet, and the crossover from a 2d ferromagnet to a 3d antiferromagnet. We discuss the location of phase boundary and crossover lines and determine the crossover functions for important thermodynamic quantities. As naive scaling does not apply at and above the upper critical dimension, two crossover scales arise which can be associated with separate dimensional crossovers of classical and quantum fluctuations, respectively. In particular, we find an intermediate regime with novel power laws where the quantum fluctuations still have a 2d and the classical fluctuations already have a 3d character. For the ferromagnet-to-antiferromagnet crossover, the mismatch of the dynamical exponents between the 2d and 3d regimes leads to an even richer crossover structure, with an interesting 2d non-critical regime sandwiched between two critical regimes. For all cases, we find that thermal expansion and compressibility are particularly sensitive probes of the dimensional crossover. Finally, we relate our results to experiments on the quantum critical heavy-fermion metals CeCu(6-x)Au(x), YbRh(2)Si(2) and CeCoIn(5).

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