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arXiv 1204.5409cond-mat.str-elcond-mat.stat-mech
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玻色-玻璃/超流转变的量子临界标度:理论与模型量子磁体的实验

Quantum critical scaling at a Bose-glass/superfluid transition: theory and experiment on a model quantum magnet

Rong Yu, Corneliu F. Miclea, Franziska Weickert, Roman Movshovich, Armando Paduan-Filho, Vivien S. Zapf, Tommaso Roscilde

摘要:

本文研究了在磁场作用下,掺Br(Br-DTN)或稀释的NiCl_(2·4)SC(NH_2)_2(dichloro-tetrakis-thiourea-Nickel,DTN)中从磁性玻色玻璃到磁性玻色-爱因斯坦凝聚的量子相变.对Br-DTN模型哈密顿量的量子相变进行的量子蒙特卡罗模拟,以及对场地稀释DTN的模拟,与量子临界点处的常规标度一致,并且临界指数z验证了预测z=d;此外,发现相关长度指数为nu = 0.75(10),序参量指数为beta = 0.95(10)。我们研究了低温热力学在量子临界场的Br-DTN的数值和实验,并提取的磁化强度和比热的幂律行为。我们的结果的指数的幂律,以及以前的结果的标度的临界温度的磁有序与所施加的磁场,是不兼容的传统的交叉标度分析提出的Fisher等人,[Phys. Rev. B 40,546(1989)],但它们都可以在一个危险的不相关算子存在的现象学的假设中得到调和。

英文摘要:

In this paper we investigate the quantum phase transition from magnetic Bose glass to magnetic Bose-Einstein condensation induced by a magnetic field in NiCl2.4SC(NH2)2 (dichloro-tetrakis-thiourea-Nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z=d; moreover the correlation length exponent is found to be nu = 0.75(10) and the order parameter exponent to be beta = 0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher et al., [Phys. Rev. B 40, 546 (1989)], but they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator.

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