Park Tuson, Ronning F, Yuan H Q, Salamon M B, Movshovich R, Sarrao J L, Thompson J D
Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Nature. 2006 Mar 2;440(7080):65-8. doi: 10.1038/nature04571.
With only a few exceptions that are well understood, conventional superconductivity does not coexist with long-range magnetic order (for example, ref. 1). Unconventional superconductivity, on the other hand, develops near a phase boundary separating magnetically ordered and magnetically disordered phases. A maximum in the superconducting transition temperature T(c) develops where this boundary extrapolates to zero Kelvin, suggesting that fluctuations associated with this magnetic quantum-critical point are essential for unconventional superconductivity. Invariably, though, unconventional superconductivity masks the magnetic phase boundary when T < T(c), preventing proof of a magnetic quantum-critical point. Here we report specific-heat measurements of the pressure-tuned unconventional superconductor CeRhIn5 in which we find a line of quantum-phase transitions induced inside the superconducting state by an applied magnetic field. This quantum-critical line separates a phase of coexisting antiferromagnetism and superconductivity from a purely unconventional superconducting phase, and terminates at a quantum tetracritical point where the magnetic field completely suppresses superconductivity. The T --> 0 K magnetic field-pressure phase diagram of CeRhIn5 is well described with a theoretical model developed to explain field-induced magnetism in the high-T(c) copper oxides, but in which a clear delineation of quantum-phase boundaries has not been possible. These experiments establish a common relationship among hidden magnetism, quantum criticality and unconventional superconductivity in copper oxides and heavy-electron systems such as CeRhIn5.
除了少数已被充分理解的例外情况，传统超导性并不与长程磁有序共存（例如参考文献1）。另一方面，非常规超导性是在磁有序相和磁无序相之间的相边界附近发展起来的。当这个边界外推到零开尔文时，超导转变温度T(c)会出现一个最大值，这表明与这个磁量子临界点相关的涨落对于非常规超导性至关重要。然而，当T < T(c)时，非常规超导性总是会掩盖磁相边界，从而无法证明磁量子临界点的存在。在这里，我们报告了对压力调谐的非常规超导体CeRhIn5的比热测量结果，我们发现在施加磁场的情况下，超导态内部会诱导出一系列量子相变。这条量子临界线将共存的反铁磁性和超导性相从纯非常规超导相中分离出来，并在一个量子四临界点处终止，在该点磁场完全抑制了超导性。CeRhIn5的T → 0 K磁场 - 压力相图可以用一个为解释高温超导铜氧化物中的场致磁性而发展的理论模型很好地描述，但在该模型中，量子相边界一直无法清晰界定。这些实验在铜氧化物和诸如CeRhIn5这样的重电子系统中的隐藏磁性、量子临界性和非常规超导性之间建立了一种共同关系。
